GI Final Flashcards

Question 1

Q

Describe the double membrane structure of mitochondria and indicate the location of various enzymes

Answer

A

Outer membrane - lipid bilayer, permeable to small but not large molecules

Intermembrane space - low pH, contains apoptotic enzymes

Inner membrane - impermeable to small molecules (except 02, C02, H20, and NH3); site of electron transport chain + ox phos

Mitochondrial matrix - high pH, site of TCA cycle and fatty acid oxidation (e.g. contains PDH), and mtDNA (encodes 13 proteins involved in ox phos)

Question 2

Q

Define:
oxidation
reduction
standard oxidation-reduction potential

Answer

A

1) Oxidation - loss of electron
2) Reduction - gain in electron
3) Standard redox potential - E’0, measure of affinity of a compound to donate or receive e-; more positive = greater affinity for e- (reduction) –> oxidizing agents

0=standard conditions, ‘=neutral pH

Question 3

Q

How do you calculate energy given off from redox reactions?

Answer

A

Transfer of e- during chemical rxn –> gives off energy that was stored in organic molecules –> used to make ATP

deltaG = -nFdeltaE’0

deltaG= free energy change (positive = spontaneous rxn)

n= # e- being transferred

F= Faraday’s constant = 23 kcal/Volt

E’0 = Accepting pair - donating pair

Question 4

Q

Describe components, substrates + products, and cellular localization for:

1) Complex I (NADH dehydrogenase)
2) CoQ i.e. Ubiquinone
3) Complex III (cytochrome c reductase)
4) Cytochrome c
5) Complex IV (cytochrome c oxidase)

Answer

A

1) Complex I: largest one at 46 polypeptides + comprised of FMN + Fe-S centers, accepts 2e- from every NADH in the mt matrix and pumps 4H+ into intermembrane space –> passes 2e- to CoQ
2) CoQ: NOT a protein; lipid soluble molecule that accepts 2e- and 2H+ and is reduced to CoQH2 –> transfers 2e- to cytochrome b in Complex III
3) Complex III: comprised of 11 subunits including cytochrome b (2 heme groups), cytochrome c1 (1 heme group), 1 Fe-S center; reduced by CoQH2 and passes 2e- from cytochrome b to c1 to c + pumps 2H+ into intermembrane space
4) Cytochrome c: single polypeptide chain with 1 heme group, ONLY water soluble component of electron transport chain and is in the intermembrane space, can serve as a trigger for apoptosis; cyt c is reduced by Complex III and then passes the 2e- to Complex IV
5) Complex IV: comprised of 11 subunits including cyt a (1 heme group) + cyt a3 (1 heme group) + 2 Cu ions; heme group of cyt a3 binds 02 and transfers 4e- –> reduces it to 2H20 + pumps 2H+ into intermembrane space

Question 5

Q

What are the bypass rxns? What is their purpose?

Answer

A

Addl ways to transfer 2e- to CoQ from the FADH2 generated by:

1) Complex II = succinate dehydrogenase from the TCA cycle
2) Fatty acyl-CoA dehydrogenase (from fatty acid oxidation in the mt matrix)
3) Glycerol 3-phosphate dehydrogenase (from the glycerol phosphate shuttle in the intermembrane space)

Question 6

Q

How much energy is generated from the transfer of 2e- from NADH through the electron transport chain? What happens to that energy?

Answer

A

53 kcal/mol

3 ATP generated x (~7kcal/ATP) = 21 kcal –> ~40% of energy is captured to produce ATP from ADP

the remaining 60% is lost to heat and used to maintain our body temperature

Question 7

Q

Explain how electron transport and ATP synthase (Complex V) are functionally coupled

Describe the components of ATP synthase

Answer

A

Proton gradient generated during electron transport chain as H+ are pumped from mt matrix (low [H+], high pH) into intermembrane space (high [H+], low pH) –> chemiosmotic gradient that provides proton motive force –> energy for ATP synthase to make ATP from ADP + Pi

ATP synthase: F0 is part of the inner mitochondrial membrane and contains proton pore, which rotates when when protons move down their gradient into the matrix; F1 is stalk and globular portion that extends into the matrix; catalytic domain that binds ADP + Pi –> ATP

mechanical energy of rotation of F0 –> chemical bond formation by F1

Question 8

Q

What are the 5 prerequisites for the electron transport chain to work?

Answer

A

1) Reducing agents e.g. FADH2, NADH which come from glycolysis, TCA cycle, fatty acid oxidation
2) pH gradient (set by proton gradient) –> Driving force
3) Terminal oxidizing agent i.e. 02; hypoxia –> Complex IV doesnt operate –> reduced ATP –> Na/K ATPases dont work properly –> Na+ retention leads to cellular swelling –> increases Ca2+ –> death of cell
4) levels of ADP –> need ADP in the matrix, pumped in by ADP/ATP antiporter which pumps out ATP so it can go to the matrix needs pH gradient to run
5) sufficient # of mt, enzymes

Question 9

Q

Explain how the cellular ATP: ADP ratio regulates the rate of ATP production by oxidative phosphorylation

How does this tie into rate of respiration

Answer

A

High ATP:ADP ratio –> inhibits ATP synthase –> increases H+ gradient (H+ build up in intermembrane space)–> decreases H+ pumping (hard to go against the gradient) and electron transport chain –> slows down TCA cycle –> decreases glycolysis –> decreases ATP

Rate of respiration proportional to [ADP][P] / [ATP]

Question 10

Q

What is atractyloside and what is its function?

Answer

A

Atractyloside: inhibits ADP/ATP antiporter

eat atractyloside flower –> inhibits antiporter –> no ADP available –> inhibits ATP synthesis –> proton gradient builds up –> stops electron transport –> can lead to death

Question 11

Q

Describe the following inhibitors and their effect:
Amytal
Rotenone

Discuss MELAS

Answer

A

1) Amytal: type of barbiturate, reversible inhibitor of Complex I (NADH dehydrogenase); used as a drug to block ROS formation during ischemia by blocking electron transport chain, also used to treat anxiety and insomnia

Rotenone: also inhibits Complex I, naturally occurring pesticide

Effect: because Complex I is blocked –> cannot oxidize NADH to provide e- –> BUT electron transport chain is not completely blocked bc of bypass rxns (e.g. succinate dehydrogenase i.e. Complex II) –> v little ATP produced

2) MELAS syndrome is from mt genome mutation that messes up Complex I –> lactic acidosis + stroke

Question 12

Q

Describe the following inhibitors and their effect:

Antimycin

Answer

A

Antimycin: antifungal used in agriculture

Inhibits Complex III by binding to cytochrome b in reduced state –> stops electron transport chain –> NO ATP made

Complex I, CoQ, Complex II are fully reduced but cytochrome c and Complex IV cannot receive e- so are left oxidized

Question 13

Q

Describe the following inhibitors and their effect:
cyanide
carbon monoxide
sodium azide

Answer

A

CN, CO, and sodium azide all inhibit Complex IV

I. Cyanide binds to oxidized ferric Fe3+ ion –> cannot be reduced to active Fe2+ form –> Complex IV inhibited –> cannot reduce 02 to H20 –> NO ATP production –> cell death

CN antidote: Administer nitrate N02 –> Fe2+ hemoglobin becomes Fe3+ methemoglobin –> CN binds to metHb –> CN-metHb –> administer thiosulfate S203- –> converts CN to less toxic, soluble thiocyanate –> complex is excreted in urine

thiosulfate can work on its own but not as effective and may be toxic at such high levels

II. Carbon monoxide binds to reduced ferrous Fe2+ form –> same inhibition of electron transport chain

BUT the more toxic effect of CO comes from inhibiting 02 binding to Hb

III. Sodium azide binds to oxidized ferric ion

Question 14

Q

Describe the following inhibitors and their effect:

Oligomycin

Answer

A

Oligomycin inhibits ATP Synthase by binding to F0 –> prevents reentry of H+ into the matrix –> inhibits ATP formation + proton gradient builds up –> redox rxns stop bc cannot pump into such high gradient –> electron transport chain stops

Question 15

Q

Describe the function and effects of uncouplers

Answer

A

Uncouplers: make inner mt membrane permeable to protons –> no proton gradient formed –> uncouples rate of electron transfer from ATP production –> ETS and TCA cycle keep running (max rate of respiration, limited only by availability of substrates) but no ATP being made –> lot of heat is generated due to flow of protons into matrix

Question 16

Q

Describe examples and mechanism of action of the three types of uncouplers:

1) Membrane-damaging agents
2) Mobile proton carriers
3) Proton channels

Answer

A

1) Membrane-damaging agents: e.g. AZT (HIV treatment) ; damaged inner mt membrane becomes impermeable to protons
2) Mobile proton carriers e.g. high doses of aspirin, dinitrophenol (used to be use as weight loss drug but caused deaths); hijack protons and carry them through inner membrane, bypassing ATP synthase and dissipating proton gradient
3) Proton channels e.g. UCP1 i.e. thermogenin; channels in certain tissues so we can keep our body warmer

Question 17

Q

Explain the biochemical basis for generation of heat by brown adipose tissue (BAT)

Dicuss the role of BAT in infants and the possible role in adults

Answer

A

1) BAT contains uncoupling proteins UCPs, high concentration of mt and vascularization; fueled by fatty acid oxidation

cold –> norepi –> cAMP and PKA pathway –> TAG degradation –> free fatty acids (FFA) activates UCP1 –> proton gradient dissipated as heat

2) two ways to generate heat: shivering and BAT; babies dont know how to shiver to keep warm so depend on UCP1 to keep warm; babies have much higher levels of BAT compared to adults

humans have small amount of BAT, can upregulate by living in the cold; obese patients have low UCP1 expression –> finding ways to increase expression in BAT could be solution for managing obesity

Question 18

Q

What happens if there are defects in the mitochondrial genome?

Answer

A

anything that goes wrong with mtRNA –> changes activity of ATP production –> side effects affect tissues that need lots of ATP: muscle spasms, hearing loss, dementia

if mt is not working properly –> rely on anaerobic glycolysis –> lactic acidosis

Question 19

Q

Describe the mitochondrial shuttles including whether they are reversible, what tissues they are found in, mechanism of action, how much ATP is made:

1) Malate-aspartate shuttle
2) Glycerol phosphate shuttle

Answer

A

1) Malate-aspartate shuttle: REVERSIBLE, gradient-driven shuttles so works best with high [NADH] in cytosol, in heart + liver + kidneys, makes 3 ATP per NADH;

NADH in the cytosol gives its 2e- to reduce oxaloacetate to malate –> malate enters mt matrix –> malate + NAD+ converts back into NADH and oxaloacetate –> 2e- enter ETS and oxaloacetate is converted into alpha ketoglutarate by AST –> alpha ketoglutarate goes back into the cytosol and is converted back into oxaloacetate by AST –> Restarts the whole cycle

2) Glycerol phosphate shuttle: IRREVERSIBLE, runs all the time to bring NADH into the matrix e.g. in brain, skeletal muscle BUT makes less ATP (2, not 3);

Glycerol-3-phosphate is reduced and accepts the 2e- –> goes into intermembrane space –> G3P makes FADH2 which donates its 2e- to CoQ of the ETS

Question 20

Q

For gluconeogenesis, explain: 
purpose
tissue distribution 
cellular localization
reactants and products

Answer

A

Purpose: synthesis of new glucose from simple carbon precursors; occurs at all times, not just fasting, bc its an important way to get rid of lactate and glycerol

Tissues: mostly liver, some kidney, NO muscle (on the other hand, glycolysis occurs mainly in muscle + brain)

Cell: mainly cytosol, partly mt

Reactants: ATP and NADH (energy from FFA oxidation mammals cannot convert FFAs to sugars) + carbon skeletons

Products: Glucose-6-Phosphate –> blood glucose

Question 21

Q

List the principal sources of carbon skeletons for gluconeogenesis reactants and when they are used

Answer

A

1) lactate- produced in RBCs and exercising muscle, sent to liver for conversion to pyruvate –> glucose via Cori cycle, used during rest/physical activity
2) 18 out of 20 AA (not ketogenic Leu OR Lys, they can only be converted to Acetyl CoA) - from muscle protein, linked to Urea cycle, used during extended fasting
3) glycerol and propionate: glycerol released from TAG during lipolysis in fat; glycerol –> G3P–> DHAP; odd numbered fatty acids –> propionate –> oxaloacetate

Question 22

Q

Describe the 4 enzymes unique to gluconeogenesis including rxn regulated, location in cell, and their allosteric regulation:

1) pyruvate carboxylase
2) PEP carboxykinase
3) Fructose 1,6 bisphosphatase i.e. FBP1
4) Glucose-6 phosphatase

Answer

A

1) pyruvate carboxylase (in mt) + Biotin cofactor, activated by Acetyl CoA: 2 pyruvate + 2ATP + C02–> 2 oxaloacetate + 2ADP need 2 mol pyruvate to make 1 mol glucose
2) PEP carboxykinase (in cytosol OR mt, depending on whether precursor was pyruvate or lactate, respectively), activated by cortisol: oxaloacetate + GTP –> PEP + GDP + C02
3) FBP1 (in cytosol), inhibited by AMP and F26BP: F16BP +H20 –> F6P +Pi
4) Glucose-6-phosphatase (in ER): G6P + H20 –> Glucose + Pi, both are transported out of cell into the blood via liver glucose transporter

Question 23

Q

What is the difference between having pyruvate vs lactate as precursor for gluconeogenesis

Answer

A

Need an NADH in the cytosol that can be oxidized to NAD+ during 1,3BPG –> G3P

Lactate: NADH produced during lactate –> pyruvate step, so PEP can be created directly in the mt and transported out into cytosol

Pyruvate: need to use malate shuttle; malate –> oxaloacetate in the cytosol produces NADH

Question 24

Q

Define anapleurotic reactions

Answer

A

Anapleurotic reaction - chemical reactions that contribute to pool of TCA cycle intermediates without consuming TCA cycle intermediate

e.g. 18 glucogenic AA can do this

Question 25

Q

Describe how hypoglycemia can occur in the following populations:

1) neonates
2) alcoholics

Answer

A

1) Newborns have low liver glycogen stores but high glucose demand from brain –> need gluconeogenesis to kick in few hours after birth

PEP carboxylase, necessary for gluconeogenesis, is low in newborns –> impaired gluconeogenesis –> hypoglycemia

2) Alcohol consumption –> high NADH/H+ –> pushes rxns towards away from gluconeogenesis precursors (pyruvate + oxaloacetate) –> inhibition of gluconeogenesis –> hypoglycemia

Question 26

Q

Describe glucose regulation in the fed vs fasting states

Answer

A

After a meal (fed state) –> glucose rises –> glycogenesis (in the liver)

Between meals (fasting state) –> glucose falls –> glycogenolysis (in the liver)

gluconeogenesis running at low levels all the time but overnight –> gluconeogenesis levels rise (bc liver glycogen stores usually do not last >24 hrs)

Question 27

Q

1) Describe the difference between glycogen, starch (i.e. amylose, amylopectin), and cellulose
2) Describe the difference between glycogen and fat as source of energy

Answer

A

1) Cellulose is linear polymer bc it only has alpha1,4 linkages, serves structural role in plants; Glycogen and starch have both alpha1,4 and 1,6 so are branched polymers (glycogen has more branches) –> glucose storage in animals and plants, respectively
2) Glycogen mobilized faster (branched + stored within tissue) than fat (cleaved one acetyl group at a time + stored in adipose tissue so needs to be mobilized); can do glycogenolysis in absence of 02 (fatty acid oxidation needs 02) and can provide energy to RBC + brain (cannot make glucose from FFAs)

Question 28

Q

Overview of glycogenesis incl roles of glycogen synthase and branching enzymes and energy expenditure

Answer

A

Glucose + hexo/glucokinase enzyme–> G6P + (phosphoglucomutase) –> G1P + UTP + (UDPglucose phosphorylase) –> UDP-Glucose + 2Pi

Polymer formation initiated by glycogenin –> adds alpha 1,4 linkages, glucose released from UDP carrier –> after 8 residues, process is taken over by glycogen synthase –> adds alpha 1,4 linkages at the nonreducing ends

Branching enzyme removes terminal residues and reattaches them to form alpha 1,6 linkage branch

Energy expenditure = 2 per glucose added: 1 ATP to phosphorylate each free glucose + 1 more ATP (in the form of UTP) in order to make UDP-glucose

Question 29

Q

Overview of glycogenolysis incl roles of enzymes

Answer

A

Add X Pi + glycogen phosphorylase enzyme to glycogen polymer –> X G1P + polymer (less X glucose residues) X can be any number, but phosphorylase stops 4 residues before a branch point

G1P + phosphoglucomutase –> G6P

branch removal: debranching enzyme moves 3 residues to a main branch using alpha1,4 linkages –> only one glucose left in an alpha1,6 linkage –> debranching enzyme uses H20 to break the linkage –> linear polymer chain is left

Question 30

Q

Differentiate between glycogenolysis in liver vs muscle cells

Answer

A

Liver: G6P converted to free glucose via glucose-6-phosphatase –> glucose can enter circulation to help maintain blood glucose levels and be taken up by other tissues

Muscle: Glucose-6 phosphate enters glycolysis –> pyruvate which has two fates: 1) Not enough 02- anaerobic glycolysis to make lactate or 2) Enough 02 - converted to Acetyl CoA and goes through aerobic metabolism (TCA cycle + ox phos)

skeletal muscle cells do NOT have glucose-6 phosphatase –> can only utilize glucose internally and do not contribute to blood glucose levels (albeit they make v minimal amount of free glucose from debranching enzyme breaking the alpha1,6 linkage, but we dont count that)

Question 31

Q

Describe glycogen regulation in energy-rich vs energy-poor state

Answer

A

1) Energy-poor (fasting or exercise):

A. Fasting: decreased blood glucose –> increased glucagon, decreased insulin –> cAMP + PKA pathways –> activates phosphorylase kinase –> glycogen phosphorylase is activated and glycogen synthase is inactivated –> Glycogenolysis high (only in liver, skeletal muscle does not have glucagon receptors)

B. Exercise: increased epi in blood, AMP and Ca2+ in tissue –> cAMP/PKA pathway + Ca-calmodulin binds to phosphorylase kinase to activate it –> glycogen phosphorylase is activated and glycogen synthase is inactivated –> Glycogenolysis and glycolysis high

2) Energy-rich (e.g. carbohydrate meal): Insulin and glucose high, glucagon low –> tyrosine kinase pathway –> Activates phosphatase PP1 –> glycogen phosphorylase inactivated and glycogen synthase activated –> glycogenolysis low, glucose transport and glycogenesis high

Question 32

Q

Describe the following glycogen storage diseases incl enzyme and tissues affected, symptoms, and treatment:
1) Von Gierke

Answer

A

1) Von Gierke:

Enzyme- glucose-6-phosphatase

Tissues - liver and kidney

Glycogen is normal and increased amount bc cannot release glucose into the blood –> severe hypoglycemia + lactic acidosis + hyperuricemia (gout) + hyperlipidemia (xanthomas)

Treat with frequent feeding of carbs e.g. uncooked starch, dietary glycogen; nasogastric feedings or you can die at night

Question 33

Q

Describe the following glycogen storage diseases incl enzyme and tissues affected, symptoms, and treatment:
2) Pompe

Answer

A

2) Pompe:

Enzyme - alpha1,4 glucosidase (acid maltase) –> enzyme that digests glycogen in lysosomal bodies

Tissue: heart

Normal glycogen + increased amount accumulates in lysosome –> cardiomegaly and LVH –> patients die young

Treat with recombinant enzyme to ameliorate symptoms

Question 34

Q

Describe the following glycogen storage diseases incl enzyme and tissues affected, symptoms, and treatment:
3) Cori

Answer

A

3) Cori:

Enzyme - alpha 1,6 glucosidase (debranching enzyme)

Tissue - liver

Glycogen has shorter or missing branches –> accumulation of branched polysaccharides in liver –> hypoglycemia and hepatomegaly

Treatment - frequent feedings, high protein diet, exogenous glucose delivery

Question 35

Q

Describe the following glycogen storage diseases incl enzyme and tissues affected, symptoms, and treatment:
4) Andersen

Answer

A

4) Andersen:

Enzyme - alpha 4,6 glucosidase (branching enzyme)

Tissue - liver

Glycogen has no branches, just linear polymer, but normal amount –> long insoluble chain –> infantile cirrhosis (cellular damage due to misshapen glycogen) + hepatomegaly –> infant death

Treatment: exogenous glucose delivery

Question 36

Q

Describe the following glycogen storage diseases incl enzyme and tissues affected, symptoms, and treatment:
5) McArdle

Answer

A

5) McArdle:

Enzyme - glycogen phosphorylase

Tissue - muscle (McArdle = Muscle)

Glycogen is normal, increased amount bc cannot be broken down in muscle –> exercise intolerance feat. muscle cramps, myoglobinuria (leaks into blood bc of cellular damage)

Treatment: Symptoms abate once body switches to fatty acid oxidation, respond to exogenous glucose administration

Question 37

Q

Describe the following glycogen storage diseases incl enzyme and tissues affected, symptoms, and treatment:
6) Hers

Answer

A

6) Hers:

Enzyme - glycogen phosphorylase

Tissue - liver (Hers=Hepatic)

Glycogen normal, increased amount bc cannot be broken down in the liver –> hepatomegaly, fasting hypoglycemia (mild bc gluconeogenesis can still occur), but no muscle/motor impairment

Question 38

Q

Describe the following glycogen storage diseases incl enzyme and tissues affected, symptoms, and treatment:
7) Tarui

Answer

A

7) Tarui:

Enzyme - muscle phosphofructokinase

Tissue - muscle, RBCs

Glycogen is normal, increased amount –> Glucose cannot be utilized in glycolysis –> Reduced exercise tolerance + hemolytic anemia

*Similar to McCardle’s, but Tarui’s in unresponsive to glucose administration

Question 39

Q

What is the hexose monophosphate pathway and its function?

Where does it take place and why in those tissues?

Answer

A

Hexose monophosphate pathway (HMP) i.e. pentose phosphate pathway i.e. phosphogluconate pathway –> alternative route for metabolism of glucose, no ATP consumed/produced

Function: production of NADPH (reducing agent for anabolic reductive rxns); production of ribose for nucleotide and nucleic acid synthesis, (RBCs) regenerate reduced form of antioxidant glutathione

Location: Cytoplasm of all cells, but mostly liver (for cholesterol +FFA synthesis), RBCs (get rid of ROS), fat (FFA synthesis), testes+ovaries+adrenals (steroid synthesis)

Question 40

Q

Describe HMP pathway including the 2 stages, starting material, intermediates, and final products

Answer

A

I. Oxidative phase

Starting material: 3 mol G6P
Intermediate: 3 mol Ribulose 5-P
Also make 3C02 + 6NADPH

II. Non-oxidative phase

Final products: 2 F6P + 1 G3P (can go into glycolysis)

Question 41

Q

Describe the fate of the HMP pathway (i.e. which stages are used) based on the following cellular needs:

1) NADPH only (e.g. fatty acid synthesis, detox)
2) NADPH + R5P (e.g. cancer cells)
3) R5P
4) NADPH + pyruvate (e.g. RBCs)

Answer

A

1) NADPH only: Both - Oxidative stage produces NADPH + Ribulose 5-phosphate, which is interconverted to G6P to keep the oxidative stage cycling
2) NADPH + R5P: Only oxidative stage - Oxidative stage produces NADPH + Ribulose 5-phosphate, which is interconverted to R5P
3) R5P: Only non-oxidative stage (G6PDH inhibited by high NADPH)
4) NADPH + pyruvate: Both - Oxidative stage produces NADPH, nonoxidative G3P and F6P products undergo glycolysis to get pyruvate

Question 42

Q

What is the RLS/committed step in the HMP pathway and how is it regulated?

Answer

A

First step: G6P + H20 + NADP+ + (glucose 6-phosphate dehydrogenase) –> 6-Phosphogluconolactone + NADPH

enzyme inhibited short-term by NADPH, activated in long-term by insulin (which upregulates transcription)

Question 43

Q

ID the HMP enzyme requiring TPP and discuss its role in enzyme function.

What condition can result from defects?

Answer

A

Transketolase - involved in the sugar interconversions in the non-oxidative stage of HMP pathway, transfers 2 carbons

requires coenzyme thiamine pyrophosphate (TPP) to be active–> defective TPP binding can lead to Wernicke-Korsakoff Syndrome (neuropsychiatric disorder)

Symptoms: depression, irritability, ataxia; WKS also seen in alcoholics and diets with thiamine-deficiency

Question 44

Q

Describe the function of NADPH in and reactions of:

1) Cytochrome p450 enzymes
2) NO production

Answer

A

1) General rxn catalyzed by cytochrome p450 enzymes:
R-H + 02 + NADPH + H –> R-OH + H20 + NADP+

(NADPH required to reduce Fe3+)

involved in detoxification of foreign compounds, bile synthesis, synthesis of steroid hormones

2) Arginine + 02 + NADPH –> NADP+ + Citrulline + NO

NO relaxes smooth muscle, acts as neurotransmitter in brain, kills bacteria, prevents platelet aggregation

Question 45

Q

Describe the function of NADPH in:

Phagocytosis by WBCs

Answer

A

Respiratory burst (consumption of 02) + NADPH + NADPH oxidase enzyme –> superoxide 02- + superoxide dismutase –> H202 + MPO enzyme –> H0Cl (bleach) + hydroxide radical

H0Cl used to destroy bacteria/foreign material that is phagocytosed into the cell

NADPH + glutathione reductase enzyme used to reduce glutathione into active form: active reduced G-SH + hydroxide radical + glutathione peroxidase –> H20 + oxidized G-S-S-G

RBCs have no mt so are totally dependent on NADPH from HMP to regenerate reduced glutathione

Question 46

Q

Describe glucose 6-P dehydrogenase deficiency (favism) including pathology, symptoms, and differences between types A and M

Answer

A

most common genetic enzymopathy X-linked recessive

Pathology: No G6PDH –> reduced NADPH –> decreased ability to reduce glutathione into active form –> buildup of ROS

Trigger: oxidative stress (infections, anti-malarial drugs, fava beans)

Symptoms: seen in RBCs bc they have no other way to form NADPH; Heinz bodies (spots are from precipitation/crosslinking of Hb tetramers), hemolytic anemia (lysis bc of oxidative damage); protection from malaria (parasite cannot thrive in oxidative conditions), decrease in serum haptoglobin

Types: A (African) –> moderate hemolysis that affects old RBCs, longer half-life of days; M (Mediterranean) –> Severe hemolysis that affects all RBCs, much shorter half-life of hours, common to have hemolysis with drug trigger

Question 47

Q

Describe the following shuttles that are other sources of NADPH in most tissues (not RBCs):

1) Malic enzyme
2) Nicotinamide Nucleotide Transhydrogenase

Answer

A

1) Malic enzyme shuttle: NADPH made in the cytosol during malate –> pyruvate conversion
2) Nicotinamide nucleotide transhydrogenase enzyme in inner mt membrane -

Question 48

Q

Define the following and explain their relationships to one

another:
1) glycosaminoglycan (GAG)
2) glycoprotein
3) proteoglycan

Answer

A

1) GAG - polysaccharides composed of repeating disaccharides (one acidic sugar + one amino sugar); long, unbranched, negatively charged; mainly sugar moieties + some proteins - make up ECM and provide structure/passageways
2) Glycoprotein - oligosaccharide covalently associated with a protein; short, branched, pos or neg charged; mainly proteins + some sugar moieties; function as cell surface receptors, mucins, antigens
3) Proteoglycan - GAG covalently associated with a core protein to form a proteoglycan monomer; will only bind to Serine AA –> can ONLY form O-linked proteogylcans

Question 49

Q

Describe the 6 major classes of GAGs:  
1) Chondroitin 4 and 6 sulfate
2) Dermatan sulfate 
3+ 4) Keratan Sulfate I + II
5) Heparin/heparan sulfate
6) Hyaluronic acid

Answer

A

1) Chondroitin 4 and 6 sulfate - most abundant GAG, found in cartilage, tendons, ligaments, and aorta
2) Dermatan sulfate - found in skin, blood vessels, heart valves

3 + 4) Keratan Sulfate I and II - most heterogeneous groups; KS I in cornea, KS II in connective tissue

5) Heparin/ Heparan sulfate - Hep is anticoagulant and in mast cells, HepS in membranes and cell surfaces
6) Hyaluronic acid - only GAG that is NOT sulfated, associates with protein monomers to form aggregate (does not form proteoglycan monomers itself); found in synovial fluid (shock absorber), lubricant, vitreous humor of eye

Question 50

Q

Explain GAG and glycoprotein degradation

Answer

A

GAGs have short (3-10 day) half lives except keratan sulfate (>120 days)

Phagocytosis –> sent to lysosome –> specific lysosomal acid hydrolase cleaves from the non-reducing end of the chain –> last group added during synthesis is the first group removed

Question 51

Q

Describe the following mucopolysaccharidoses (MPS) including affected enzyme, affected GAG, and symptoms:

1) Hunter
2) Hurler
3) Sanfilippo

Answer

A

MPS caused by autosomal recessive mutations in the lysosomal hydrolases –> incomplete degradation of GAGs –> accumulates in tissues + GAGs in the urine (diagnostic tool)

1) Hunter: X-linked recessive (exception); iduronate sulfatase deficiency –> Affects degradation of dermatan + heparan sulfate –> mental retardation + physical deformity
2) Hurler: alpha-L-idurodinase deficiency –> Affects degradation of dermatan + heparan sulfate –> corneal clouding, hearing loss, gargoyle-like features
3) Sanfilippo: deficiency in 4 enzymes –> affects degradation of heparan sulfate –> mental retardation

Question 52

Q

What is the difference between N and O-glycoproteins

Answer

A

N-glycoprotein: N-linkage on amide residue of Asparagine; oligosaccharide transferred from dolichol to amide in the ER, processed further in the Golgi

O-glycoprotein: O-linkage on hydroxyl residue on Threonine or Serine; synthesis happens in Golgi with specific glycosyltransferases that add nucleotide sugar residues

Question 53

Q

Explain the role of glycans in determining blood groups

Answer

A

Antigens on the surface of RBCs are attached to glycoproteins or glyocosphingolipids

Type O blood –> default antigen H –> makes antibodies against A and B but has no antigens–> universal donor

Type AB blood –> contains A and B antigens (transferase adds both GalNAC and Gal sugars to the glycan of H) but no antibodies –> universal acceptor

Question 54

Q

Describe the transport of N-glycoproteins to lysosomes and how mutation can lead to I-cell disease

Answer

A

Golgi enzyme phosphotransferase phosphorylates mannose residue on N-glycoprotein that is a prelysosomal enzyme –> glycoprotein marked and sent to lysosome –> acts as acid hydrolyase to break down substances

I-cell disease: defect in phosphotransferase –> affects ALL acid hydrolases, which are secreted into blood circulation instead of being sent to lysosome –> buildup of substances that are not degraded –> inclusion cells phenotype

symptoms: stiffened joints, psychomotor impairment, skeletal abnormalities; high concentrations of acid hydrolases in the blood

Question 55

Q

What is the difference between mucopolysaccharidoses, oligosaccharidoses, and sphingolipidoses

Answer

A

All due to deficiency in lysosomal degradative enzymes –> lysosomal storage problems; have similar symptoms (mental retardation)

mucopolysaccharidoses: accumulation of GAGs
oligosaccharidoses: accumulation of glycoproteins e.g. mannosidosis - deficiency in mannosidase, mannose fragments appear in urine, mental retardation + immune deficiency (since glycoproteins involved in immune cells)
sphingolipidoses: accumulation of glycosphingolipids, neurological deterioration leads to death

Question 56

Q

Describe glycerophospholipids include structure, function

Answer

A

Glycerophospholipids:

Structure: phosphatidic acid + glycerol backbone + variable polar head

Function: structure of cell membranes + intracellular; component of bile + lipoproteins + lung surfactant

Question 57

Q

Describe the structure of phosphatidylcholine i.e. lecithin and any clinical abnormalities

Answer

A

Lecithin: type of gylcerophospholipid; de novo synthesis not sufficient for our needs

Functions: lung surfactant–> prevents collapse of alveoli during expiration, detergent in bile, structural role in membranes

Pathology: deficiency of lecithin in bile –> inadequate solubilization –> Gallstones

deficiency of lecithin in lungs (common in preemies) –> Respiratory Distress Syndrome –> associated with lecithin:sphingomyelin ratio; mother given exogenous cortisol before delivery to induce surfactant production

Question 58

Q

Describe glycosphingolipids including:

1) Structure
2) Location
3) Function
4) Synthesis
5) Degradation

Answer

A

1) Structure: sphingosine backbone + fatty acid + carbohydrate
2) Location: component of outer leaflet of all plasma membranes, greatest amount in nerve tissue
3) Function: cellular interactions + growth, blood group antigens, cell surface receptors for viruses/toxins
4) Synthesis: in the Golgi, glycosyltransferases add monomers from UDP-sugar donors; ceramide derivative
5) Degradation: acid hydrolases in lysosomes remove residues based on “last on, first off”

Question 59

Q

Describe sphingophospholipids including:

1) Structure
2) Function
3) Synthesis
4) Degradation

Answer

A

1) Structure: sphingosine backbone + fatty acid + phosphate head group; Ceramide derivative
2) Function: component of myelin sheath (insulates and protects nerve fibers)
3) Synthesis: ceramide derivative
4) Degradation: Sphingomyelin + (sphingomyelinase) –> Ceramide + (ceramidase) –> Sphingosine + FFA

Question 60

Q

Describe the following sphingolipidoses including inheritance, affected enzyme, affected lipid, and symptoms:
1) Tay-Sachs

Answer

A

1) Tay-Sachs: autosomal recessive, more common among Ashkenazi Jews; beta hexosaminidase A deficiency –> affects degradation of gangliosides (GM2) –> progressive neurological dysfunction (ataxia, seizures, loss of vision) + cherry-red spot on eye exam –> death by age 3

Question 61

Q

Describe the following sphingolipidoses including inheritance, affected enzyme, affected lipid, and symptoms:
2) Neimann-Pick

Answer

A

2) Niemann-Pick: autosomal recessive, more common among Ashkenazi Jews; defect in sphingomyelinase –> affects degradation of sphingolipids –> buildup of sphingomyelin–> foamy cells (due to lipid buildup), hepatomegaly, pancytopenia (deficiency in platelets, WBCs, RBCs) regression of motor/social skills, cherry red spot on macula –> death by age 3

Question 62

Q

Describe the following sphingolipidoses including inheritance, affected enzyme, affected lipid, and symptoms:
3) Gaucher

Answer

A

3) Gaucher: autosomal recessive; macrophage storage disorder; defect in glucocerebrosidase –> affects degradation of glucocerebroside –> Gaucher cells (macrophages look like crumpled paper), pain in bones/joints, osteoporosis, bone necrosis –> Recombinant enzyme treatment available

Question 63

Q

Describe the following sphingolipidoses including inheritance, affected enzyme, affected lipid, and symptoms:
4) Krabbe

Answer

A

4) Krabbe: autosomal recessive; beta galactocerebrosidase deficiency –> affects degradation of galactocerebroside –> demyelination (track via MRI), globoid cells, optic atrophy –> death by age 2

Question 64

Q

Describe the following sphingolipidoses including inheritance, affected enzyme, affected lipid, and symptoms:
5) Fabry

Answer

A

5) Fabry: X-linked recessive, onset in childhood and worsens through adulthood; alpha galactosidase A deficiency –> Affects degradation of ceramide trihexoside –> acroparesthesia (burning/prickling), renal failure, febrile episodes –> Recombinant enzyme treatment available

Answer 65

A

I. Monosaccharides = simple sugar i.e. glucose, galactose, mannose (all aldehydes), fructose (ketone) – all isomers

Glucose and galactose are C4 epimers; Glucose and mannose are C2 epimers

II. Disaccharides - two monosaccharides joined by glycosidic linkage i.e. maltose/trehalose (glucose + glucose), sucrose (glucose + fructose), lactose (glucose + galactose); sucrose is an exception - no anomeric carbon –> cannot form more glycosidic bonds

III. Polysaccharides - 10+ monosaccharides i.e. starch, glycogen, cellulose

Answer 66

A

Carbon at which ring formation occurs (either the C2 keto or C1 aldo carbon); anomers are the different configurations possible at the ring (termed alpha and beta)

e.g. body can process/degrade only alpha1,4 linkage

Answer 67

A

Digestion: salivary alpha amylase - incomplete digestion –> no digestion in low stomach pH –> pancreatic amylase in the small intestine –> additional enzymes at mucosal lining of the jejunum e.g. maltase, sucrase, lactase –> result of digestion is the monosaccharides

Absorption: transported into intestinal lumen by GLUT5 (fructose) and SGLT1 (glucose, galactose); all 3 transported into circulation by GLUT2

Answer 68

A

Location: liver, intestine, kidney

I. Metabolism: Fructose + (fructokinase) –> F1P + (aldolase B) RLS –> DHAP + Glyceraldehyde (transformed into glycerol for lipids or G3P for glycolysis)

*in extrahepatic tissues, hexokinase can convert Fructose –> F6P if [fructose] is high

II. Pathology:

A) Essential fructosuria: NO fructokinase -> asymptomatic + fructosuria

B) HFI: NO aldolase B –> F1P accumulation + lower Pi –> decreased ATP and increased ADP/AMP –> cannot go through glycogenolysis, gluconeogenesis (AMP inhibits FBP1) –> hypoglycemia + lactic acidosis + hyperuricemia (due to URAT1 working to excrete the lactate)

Treat by removing all fructose from diet e.g. table sugar, corn syrup, honey

Answer 69

A

Location: seminal vesicles, ovaries, hepatocytes (liver)

Glucose + NADPH + (aldose reductase) –> NADP + Sorbitol + NAD + (sorbitol dehydrogenase) –> NADH + Fructose

Diabetics = excess glucose –> lots of sorbitol produced –> Accumulates in cells that do not have sorbitol dehydrogenase (e.g. kidney, lens, retina) –> water enters via osmosis and cell swells –> retinopathy, cataracts

Answer 70

A

I. Metabolism: Galactose + ATP + (galactokinase) –> Gal1P + UDP-glucose + (Gal1P uridylyl transferase i.e. GALT) –> UDP-galactose + (epimerase) –> UDP-glucose (glycogen storage, glucose, glycolysis, etc)

II. Pathology: treat by removing all lactose from diet (usually manifests in neonates breastfeeding)

A) Galactokinase deficiency - buildup of galactose and galactitol via aldose reductase –> As with sorbitol, can build up in retina, lens (but not other parts of the body)–> cataracts + galactosemia + galactouria

B) Classical galactosemia - GALT deficiency –> buildup of galactose + Gal1P (liver, nerves, kidney) + galactitol (lens) –> jaundice, hepatomegaly, brain + kidney damage, cataracts , lactic acidosis + hyperuricemia (due to sequestration of Pi in GAL1P)

Answer 71

A

Can test for reducing sugars (free aldehyde/ketone groups that can create glycosidic linkages) in the urine –> positive test indicative of underlying pathology

Follow-up tests can tell you which reducing sugar it is e.g. glucose –> probably diabetes

sucrose does not show up on Clinitest bc it is non-reducing disaccharide

Answer 72

A

1) Tetrahydrofolate (THF): derivative of folic acid; de novo purine synthesis, thymine (pyrimidine) synthesis
2) S-adenosylmethionine (SAM): epinephrine synthesis, DNA methylation/synthesis

Answer 73

A

I. Dietary folates are in polyglutamate form (e.g. spinach) –> converted to monoglutamate by folate conjugase in the jejunum epithelial cells –> folate can then be absorbed into cell and then circulation via carriers

II. Inhibitors: Phenytoin inhibits folate conjugase; OCPs and alcohol inhibit monoglutamate uptake into the cell

III. Tropical/Celiac sprue (bowel irritation) –> destroys bowel endothelium –> deficient conjugase –> deficient absorption of dietary folates

Answer 74

A

1) Dietary folate (B9) –> dihydrofolate DHF + (dyhydrofolate reductase DHFR) + 2NADPH–> tetrahydrofolate THF + 2NADP
2) Inhibitors: methotrexate and aminopterin (chemo agents)
3) Methotrexate is competitive inhibitor with Folate for binding to DHFR –> halts nucleotide synthesis –> cell death (of cancer cells, but leads to myelosuppression, dermatitis, kidney injury)

Leucovorin (i.e. folinic acid) - bypasses DHFR and is converted directly to TFH; accumulates more in normal cells than cancerous ones and can relieve side effects while still killing the cancer cells (also methotrexate more attracted to DHFR in cancer cells)

Answer 75

A

1) PABA (only in bacteria) –> folate –> DHF –> THF –> nucleotide synthesis
2) Sulfonamides inhibit bacterial enzyme that converts PABA to folate

Trimethoprim inhibits bacterial DHFR (no effect on human DHFR)

Answer 76

A

Takeaway: THF is v versatile intermediary in carbon mobilization and can bind different carbon moieties and participate in different chemical rxns in order to donate these carbons

1) THF + Formate –> N10-Formyl-THF –> this form can donate carbon in de novo purine synthesis
2) THF + Gly/Ser/Formaldehyde –> N5N10-Methylene-THF –> this form can donate carbon in thymine synthesis

Answer 77

A

1) Synthesis: Methionine + ATP + (SAM synthetase) –> SAM + 3Pi
2) Function: Transfers methyl group for DNA methylation + Epinephrine synthesis –> becomes homocysteine after donation

elevated homocysteine associated with vascular disease plasma homocysteine levels INVERSELY associated with B6, B9, and B12 levels

3) Metabolism has two fates:

A) Homocysteine + (B6) –> cysteine if you have low B6, homocysteine levels will be high

B) Homocysteine + N5 methylTHF + (B12) –> THF + Methionine

Answer 78

A

B12 deficiency –> slows conversion of homocysteine and N5 methylTHF into THF and methionine –> cell’s folate supplies trapped in N5 methylTHF form –> cant make THF forms required for nucleotide synthesis nor SAM from methionine –> B9 folate + SAM deficiency

Answer 79

A

B12 deficiency –> increase in methylmalonic acid and homocysteine levels –> macrocytic anemia MCV > 100 (cells get bigger as they get ready to divide but don’t make nucleotides and cannot replicate their DNA), peripheral neuropathy, sensory/movement problems bc of degeneration of spinal cord (SAM deficiency –> low methylation –> no myelination), smooth sore tongue (glossitis)

B9 deficiency –> identical to B12 deficiency (macrocytic anemia) except no neurological disease, normal methylmalonic acid levels

Answer 80

A

inhibits absorption of nutrients
inhibits muscles of the GI tract –> diarrhea
increases transport and absorption of toxins across intestinal wall –> liver damage
gastritis/bleeding of stomach mucosal lining
increases occurrence of heartburn and risk of esophageal cancer

Answer 81

A

1) Absorption: can get into cell (no digestion required), absorbed in mouth + esophagus but mainly in stomach and upper small intestine
2) Excretion: 90% liver, 5% urine, 5% breath

Answer 82

A

1) ADH=primary mechanism: Dietary alcohol (i.e. ethanol) + (cytosolic alcohol dehydrogenase ADH) + NAD+ –> NADH + Acetaldehyde + (mitochondrial acetaldehyde dehydrogenase ALDH) + CoA –> Acetyl CoA + NADH –> High NADH/NAD+ ratio
2) MEOS = overflow pathway: when ADH is overwhelmed, alcohol can be metabolized by CYP2E1 enzyme

3)

Answer 83

A

1) Lactic acidosis: accumulation of NADH inhibits PDH enzyme –> inhibits TCA cycle –> increased amounts of lactate (lactate dehydrogenase uses NADH)
2) Hypoglycemia: inhibition of gluconeogenesis (malate –> OAA requires NAD+) and glycolysis (G3P–> 1,3BPG requires NAD+) –> these are reversible rxns so run backwards
3) Ketoacidosis: AcetylCoA –> doesnt go through TCA cycle, so increased FFA and ketone bodies (e.g. hydroxybutyrate) –> TAGs –> fatty liver
* increase in NADH/NAD also inhibits fatty acid beta oxidation*

Answer 84

A

Acohol consumption –> lactic acidosis and ketoacidosis

These organic anions are excreted into the renal tubule by URAT1; in order to do this, urate is reabsorbed back into circulation –> hyperuricemia

Answer 85

A

Acetaldehyde –> flushing, headache, naseau, vomiting

Variability can be in terms of amount of enzyme or activity:

1) High ADH, low ALDH –> Accumulation of aldehyde –> Feel sick so do not drink

Low ADH, high ALDH –> accumulation of Acetyl CoA –> no negative effects so continue to drink

2) Two forms of ALDH – ALDH2*1 has lower Km and higher Vmax (more active enzyme) –> feel less sick

ALDH2*2 has higher Km and lower Vmax –> feel more sick –> protected from alcoholism

Answer 86

A

Alcohol (ADH) –> Acetaldehyde (ALDH) –> Acetyl CoA

Disulfiram used to treat chronic alcoholism: Disulfiram inhibits ALDH –> buildup of acetaldehyde –> flushing, headache, naseau, vomiting –> discourages drinking

Answer 87

A

Increased alcohol consumption overwhelms primary ADH pathway, metabolized by CYP2E1 through MEOS system

BUT CYP2E1 metabolizes many compounds, including acetaminophen, isoniazid (TB drug), barbiturate

A) Moderate consumption: Alcohol competes for CYP enzyme binding –> less drug metabolite produced and excreted + alcohol builds up in CNS

B) Chronic heavy consumption: CYP2E1 activity enhanced –> increased levels of toxic drug metabolite (excretion cannot keep up with the high levels) –> liver toxicity

Answer 88

A

1) kwashiorkor (protein deficiency)
2) secondary vitamin and mineral deficiency: dysfunctional liver –> affects B6 and B12 pools –> damaged epithelial cells –> decreased absorption of fat soluble vitamins; increased niacin demand since NADH/NAD+ ratio is high
3) fetal alcohol syndrome - inhibition of PDH shuts down TCA cycle –> developing brain doesnt get enough energy –> mental retardation and motor abnormalities
4) Wernicke Korsakoff - acetaldehyde breaks binding protein of thiamine –> increased excretion –> thiamine deficiency –> affects PDH, transketolase, alphaketoglutarate acid dehydrogenase, branched chain dehydrogenase –> give both thiamine AND glucose supplementation

Answer 89

A

1) Negative nitrogen balance: N in urine&raquo_space; N ingested (net loss of N from body) e.g. sepsis, fasting, deficiency of essential AA (PVT TIM LL)
2) Positive nitrogen balance: N in urine

Answer 90

A

1) Synthesis: pepsin in stomach (low pH starts denaturing process), nonspecific proteases in pancreas, aminopeptidases in small intestine
2) Action: lumen of small intestine, pancreatic zymogens activated by enteropeptidase, which removes “Pro” sequence that is shielding the active site trypsin can also autocatalyze and then activate other zymogens

Free AA and di/tripeptides absorbed into intestinal cells–> hydrolyzed to AA –> portal vein –> liver

Answer 91

A

1) Transamination rxn: Aminotransferase +B6 cofactor transfer alpha amino group from donor AA to alphaketoglutarate –> creates glutamate + alpha-keto acid (does NOT affect nitrogen balance, but funnels all AA into 1 which facilitates urea formation) reversible, no ATP needed
2) linkages to TCA cycle intermediates:

A. Addition of amino to alpha-ketoglutarate glutamate (liver, used in transamination)

B. Addition of amino to pyruvate alanine (muscle, used in Glucose-Alanine cycle)

C. Addition of amino to oxaloacetate aspartate (liver, donates 2nd NH3 during urea cycle)

Answer 92

A

1) Oxidative deamination: NH3 released from glutamate via glutamate dehydrogenase (found in ALL tissues) to produce ammonia –> urea cycle; this rxn regenerates alpha ketoglutarate
2) Temporary NH3 reservoir: Add NH3 to glutamate –> glutamine (Different AA)
3) Transamination: transfer NH3 to OAA to form aspartate–> NH3 goes into urea cycle
4) Converted into N-acetylglutamate (cofactor for CPSI and allosteric activator of urea cycle)

Answer 93

A

Irreversible bc requires energy and is compartmentalized; takes place in liver

1) [Mt] Glutamate dehydrogenase releases NH3 from glutamate (enzyme is activated by ADP, bc alpha ketoglutarate formed can enter TCA cycle to produce energy)
2) [Mt] RLS: NH3 + C02 + (CPSI + N-acetylglutamate cofactor activated by arginine) –> Carbamoyl Phosphate + Ornithine–> citrulline requires ATP
3) [Cytosol] Glutamate donates NH3 to OAA via aminotransferase –> forms asparate, which donates NH3 to Citrulline requires ATP –> Arginosuccinate
4) intermediate steps
5) [Cytosol] Arginase (found ONLY in liver) cleaves arginine to form urea + ornithine (which translocates back to mt)

Answer 94

A

Pyruvate in muscle cells converted to alanine via aminotransferase –> sent to liver where alanine is converted back into pyruvate –> pyruvate enters gluconeogenesis –> create glucose –> glucose is transported back to muscle –> muscle makes more pyruvate

*no NET production of glucose

Answer 95

A

1) Glutamine synthase (in ALL tissues) adds NH3 to glutamate –> Glutamine (sent to liver) requires ATP

Deamination rxns occurs ONLY in the liver: glutaminase releases NH3 from glutamine –> glutamate (glutamate can then be acted upon by glutamate dehydrogenase)

similarly, asparaginase releases NH3 from asparagine –> aspartate

2) ONLY in liver: glutaminase (temporary storage of NH3 in glutamine), asparginase (temporary storage of NH3 in asparagine), CPSI (1st nitrogen in urea), and arginase (urea formation)

Answer 96

A

Enzyme: glutamine synthase –> temporary NH3 reservoir, in all tissues (glutamine transported to liver)
Enzyme: Glutamate dehydrogenase –> releases NH3 from glutamate and generates α-ketoglutarate –> NH3 can be used as first nitrogen cycle, αKG can enter the TCA cycle or contribute to further transaminations
Enzyme: glutaminase –> releases NH3 –> NH3 can be used as first nitrogen of urea cycle
Enzyme: Aminotransferase –> addition of NH3 to oxaloacetate (via glutamate) to form aspartate –> second nitrogen into urea (liver cytosol)

Answer 97

A

1) Ketogenic - lower energy yield –> terminate as Acetyl CoA, cannot enter gluconeogenesis and make glucose; instead converted into ketone bodies

Glucogenic - higher energy yield –> terminate as TCA intermediates and can be fully catabolized into glucose

2) Essential - cannot synthesize de novo, need dietary intake

Non-essential - can be synthesized de novo; Exceptions: Cysteine requires Methionine, Tyrosine requires Phenylalanine

Answer 98

A

1) Urea cycle disorders: defects in N-acetylglutamate or CPSI –> buildup of NH3
2) Liver disease: breaches permeability of hepatocyte cell membrane –> high AST/ALT + decreased urea production
3) Polycystic kidney disease: reduced urea excretion –> urea can pass into intestinal lumen –> bacterial urease hydrolyzes back into NH3 –> hyperammonemia + inability to reabsorb AA
4) Blue diaper syndrome: Transporter defect –> Accumulation of Tryptophan in intestine –> hydrolyzed by bacterial enzymes –> forms indole (blue)

Answer 99

A

Causes: mutation in enzyme (Phe hydroxylase) that converts Phe –> Tyr, or mutation in enzyme (dihydrobiopterin reductase) that makes cofactor (tetrahydrobiopterin)

Pathology: Increased phenylalanine blocks entry of other AA into the brain by occupying AA transporters

Symptoms: mental retardation, brain damage

Treatment: synthetic diet with low levels of Phe, supplemented with Tyr - need to be on it for whole life bc can still have cognitive damage even in adulthood

Answer 100

A

I. Catecholamines i.e. dopamine, norepi, epi: all derived from Tyr, all contain two OH on phenyl ring

Phenylalanine + (hydroxylase + tetrahydrobiopterin) –> Tyrosine + (hydroxylase + tetrahydrobiopterin) –>
DOPA + (decarboxylase + B6) –>
Dopamine + (hydroxylase) –>
Norepi + (methyltransferase + SAM + B12 + folate) –>
epinephrine

II. Pathology

Parkinson’s: low levels of dopamine, can treat with L-DOPA for a while but neurons degenerate quickly

Schizophrenia: too much dopamine

Answer 101

A

Tryptophan + (hydroxylase + tetrahydrobiopterin) –> Serotonin –> Melatonin

serotonin is decarboxylated form of tryptophan

Answer 102

A

Creatine - storage form of energy; does NOT come from diet

Arginine + Glycine + SAM –> Creatine + (Creatine kinase) + ATP –> [liver] creatine phosphate –> creatinine excreted in urine

low levels of creatinine in urine –> kidney failure

high levels of creatinine in urine –> muscle loss

Answer 103

A

Essential fatty acids: linoleic (omega 6) and linolenic (omega 3); cannot synthesize bc we cannot introduce double bonds beyond C9 in FAs

Omegas 3 and 6 found in SMASH: Salmon, Mackerel, Albicore, Sardines, and Halibut

Omega-3: anti-inflammatory; Omega-6 –> arachidonate –> prostaglandins = pro-inflammatory

Deficiency: dry, flaky skin + rash

Answer 104

A

Location: cytosol of liver, lactating mammary glands, adipose tissue

1) Acetyl CoA brought into cytosol from mt via citrate shuttle (combined with OAA by citrate synthase, citrate diffuses into cell, then cleaved by lyase in cytosol to form OAA and Acetyl CoA)
2) Acetyl CoA + (ABC carboxylase) –> Malonyl CoA; carboxylase activated by citrate + insulin and inactivated by Palmitate + glucagon
3) Fatty acid synthase uses 2NADPH + B5 to catalyze addition of 2C units of malonyl CoA –> Palmitate (16C)
* product of fatty acid synthesis is unesterified FFA - primary storage form for adipose is Palmitate*

Answer 105

A

Elongation: [ER and mt] continue adding 2C units

Desaturation: [ER ONLY] catalyzed by desaturase, requires NADPH, introduces double bonds

Answer 106

A

Diabetics have less insulin –> inhibits ABC carboxylase/fatty acid synthesis –> shunts Acetyl CoA from dietary carbs (glucose) and proteins (AA) into ketone body formation –> ketoacidosis

*more severe in DMI bc they have no insulin activity

Answer 107

A

[liver and adipose tissue]

Glucose (glycolysis) –> DHAP –> Glycerol 3P + 3 esterification rxns to add FFAs –> TAG

Stored in adipose, packaged in liver into VLDL –> circulation –> cleaved by LPL –> glycerol goes back to liver and is converted into Glycerol 3P via glycerol kinase

Regulation: insulin stimulates glycolysis and LPL –> Acetyl CoA + Glycerol 3P accumulates –> TAG synthesis

Answer 108

A

[adipose tissue] Stress hormones (glucagon, epi, cortisol) –> phosphorylate perilipin proteins guarding the fat –> hormone-sensitive lipase acts on the fat –> glycerol + fatty acids

[liver] glycerol –> glycerol 3 Phosphate –> DHAP–> gluconeogenesis (also activated by glucagon and cortisol)

fatty acids converted into Acetyl CoA –> gluconeogenesis, TCA cycle, and ketogenesis (ketone bodies sent to muscle and brain)

Answer 109

A

Location: mitochondria (in all tissues with mt)

1) Activation: [cytosol] Long chain FFAs + (fatty acyl CoA synthase + ATP) –> Fatty acyl CoA
2) [cytosol] Fatty acyl CoA + carnitine + (CATI/CPTI) –> fatty acyl carnitine + CoA malonyl CoA (intermediate in FA synthesis) inhibits CPTI
3) fatty acyl carnitine can diffuse through inner mt membrane into mt matrix
4) [mt] Fatty acyl carnitine + CoA + (CATII/CPTII) –> fatty acyl CoA + free carnitine (goes back into cytosol)
5) [mt] Beta oxidation: specific dehydrogenases shorten the chain by 2C and produce 1 NADH, 1 FADH2, and 1 Acetyl CoA yields much more ATP than glycolysis

Answer 110

A

1) Medium chain FAs do not need to use carnitine shuttle, can diffuse into the mt; are broken down by MCAD
2) Branched FAs require alpha oxidation –> acetyl CoA + propionyl CoA
3) Unsaturated FAs yield less ATP–> due to double bond, they are already partially oxidized

Answer 111

A

Regular beta oxidation leaves propionyl CoA (3C)

Propionyl CoA + (ABC carboxylase) –> Methylmalonyl CoA –> rearranged via mutase + B12 –> Succinyl CoA –> can enter TCA cycle directly or gluconeogenesis indirectly (via conversion to OAA)

Therefore, odd chain FAs are the ONLY type of FAs that are glucogenic

B12 deficiency: methylmalonyl levels increase, differentiates it from B9 deficiency

Answer 112

A

X-linked disorder: inborn error of function of peroxisome –> VLCFA (>20C) cannot be degraded –> high levels of very long chain fatty acids (VLCFA) + demyelination of nervous system –> body quickly reduced to vegetative state

Lorenzo’s oil is mixture of oils to normalize accumulation of VLCFA in the brain and halt progression of ALD

Answer 113

A

1) Reduced beta oxidation –> decreased products –> lower levels of Acetyl CoA, FADH2, NADH

Acetyl CoA needed to make ketone bodies –> decreased ketone body production

FADH2 and NADH needed to power gluconeogenesis –> slows down process –> Decreases glucose production

2) Treatment: high carb diet, medium + short chain fatty acids (dont need to use carnitine shuttle)

Answer 114

A

2A) CPT1 deficiency: Rare, affects liver –> reduced FA oxidation and ketogenesis –> hypoketotic hypoglycemia + elevated blood carnitine due to leakage + hepatomegaly + muscle weakness

2B) CPTII deficiency: adult form affects skeletal muscles –> muscle pain/fatigue and myoglobinuria post exercise;

infant form: hypoketotic hypoglycemia –> hepatomegaly + cardiomyopathy

neonatal form: hepatomegaly + cardiomegaly + seizures –> lethal

Answer 115

A

3) MCAD deficiency:

Pathology: mutation in medium chain acyl dehydrogenase enzyme used for beta oxidation

Symptoms: hypoketotic hypoglycemia, increased dicarboxylic acid levels, hyperammonemia

Treatment: frequent feeding, avoid fasting, carnitine supplementation (since the built up medium chain FAs use carnitine shuttle to leave the cell, you have reduced oxidation of long chain FAs)

Answer 116

A

4) Methylmalonyl CoA mutase deficiency:

Pathology: dietary B12 deficiency, IF mutation (required for B12 absorption), defect in mutase enzyme required to oxidize odd chain FAs

Symptoms: accumulation of methylmalonic acid –> peripheral neuropathy

Treatment: B12 supplementation

Answer 117

A

1) [mitochondria of liver] Ketogenesis occurs with buildup of Acetyl CoA

2 Acetyl CoA + (thiolase) –> Acetoacetyl CoA + (HMG CoA synthase) –> HMG CoA + (HMG CoA lyase) –> Acetyl CoA + acetoacetate

2) HMG CoA synthase stimulated by fasting, FAs, cAMP; inhibited by feeding, insulin HMG CoA synthase also used in cholesterol synthesis, but its a different isoform and other version is cytosolic
3) acetoacetate can be converted into 2 other ketone bodies: hydroxybutyrate (if there is excess NADH) and acetone –> all 3 are water soluble

Answer 118

A

Acetoacetate + Succinyl CoA + (CoA transferase i.e. thiphorase) –> Acetyoacetyl CoA + (thiolase) + CoA –> 2Acetyl CoA –> enters TCA cycle –> ATP

liver does not have CoA tranferase so therefore cannot use ketone bodies; acetoacetate used by heart and brain

Answer 119

A

1) Fasting (or diabetic) state: carb deficiency –> low glucose + TAGs broken down as main energy source –> fatty acid oxidation yields Acetyl CoA –> acetyl CoA cannot enter TCA cycle bc intermediates (i.e. oxaloacetate OAA) have been shunted into gluconeogenesis –> acetyl CoA available for ketone body formation
2) Normal carnitine/acylcarnitine levels + no developmental defects BUT hypoketotic hypoglycemia triggered by fasting/infection

Answer 120

A

Purine synthesized from scratch on the ribophosphate backbone

Pyrimidine synthesized from scratch, and THEN attached to ribophosphate backbone

Answer 121

A

Nucleoside: Ribose sugar + base

bases: 1) Purine (two rings): Adenosine, Guanine 2) Pyrimidine (one ring): Cytosine, Uracil, Thymine

Nucleotide: Ribose sugar + base + phosphate; name changes based on # phosphates e.g. adenosine monophosphate (AMP), adenosine diphosphate (ADP), adenosine triphosphate (ATP)

Answer 122

A

1) Ribose 5 Phosphate + ATP + (PRPP synthase) –> AMP + PRPP; activated by Pi, inhibited by purine nucleotides (ADP/ATP, GDP/GTP)
2) PRPP + Glutamine + (PRPP amido-transferase) –> Glutamate + PPi + PRA; activated by PRPP, feedback inhibition by IMP, AMP, GMP
3) More steps + ATP + carbon sources (C02 + THF) and AA (Asp + Gln + Gly) –> IMP
4) IMP is converted to either AMP or GMP

IMP + Aspartate + GTP + (enzyme)–> Adenylosuccinate –> AMP + fumarate; enzyme feedback inhibited by AMP

IMP + NAD + (IMP dehydrogenase) –> XMP + Glutamine + ATP + (enzyme) –> GMP; enzyme feedback inhibited by GMP

5) AMP/GMP + (specific kinases) –> ADP/GDP

ADP/GDP + (nucleoside diphosphate kinase) –> ATP/GTP

Answer 123

A

1) azaserin + DON: antibiotics that are structurally similar to glutamine –> irreversibly inhibit PRPP amido-transferase
2) ribavirin: antiviral used to treat Hepatitis C; inhibits IMP dehydrogenase by depleting intracellular pools of guanine nucleotides
* new Hep C drug Sovaldi is incorporated into HCV RNA and acts as chain terminator*

Answer 124

A

Cross-regulation: ATP required for GMP synthesis, and GTP required for AMP synthesis

E.g. high levels of AMP (increased ATP) –> inhibits IMP conversion to AMP and facilitates IMP conversion to GMP

this way you can coordinate and balance the relative amounts of GTP and ATP (needed in roughly equal amounts)

Answer 125

A

Salvage pathway more energy efficient, important in the brain

Adenine base + PRPP + (APRT) –> AMP

Guanine/Hypoxanthine bases + PRPP + (HGPRT) –> GMP/IMP

Answer 126

A

Etiology: X-linked recessive HPGRT deficiency –> reduction in salvage pathway of GMP –> insufficient cell supplies of GTP as energy –> fewer dopaminergic neurons

Symptoms: gout (HGPRT deficiency means cells rely on de novo synthesis –> buildup of guanine and hypoxanthine –> cannot be salvaged –> elevated uric acid –> gout)

also mental retardation, self-mutilation due to effects on the brain

Answer 127

A

1) Phosphate removed from AMP/GMP/IMP via 5’ nucleotidase –> Adenosine, Inosine, Guanosine
2) Adenosine + (adenosine deaminase ADA) –> Inosine convergence of AMP/IMP pathways
3) Ribose group removed from Inosine and Guanine via PNP enzyme –> Hypoxanthine + Guanine
4) Hypoxanthine + Guanine –> Xanthine + (xanthine oxidase) –> Uric acid convergence of AMP/GMP/IMP pathways

Answer 128

A

Etiology: genetic deficiency in adenosine deaminase (ADA) or purine nucleoside phosphorylase (PNP) –> increased concentration of deoxy nucleotides –> inhibits DNA synthesis –> severe deficit of B and T lymphocytes PNP deficiency leads to deficit of JUST T lymphocytes

Symptoms: severe bacterial, viral, opportunistic infections; fatal in infancy

Treatment: bone marrow transplantation, gene therapy (ADA deficiency first use of gene therapy), enzyme replacement therapy; give IgG to treat immunodeficiency

Answer 129

A

Etiology: elevated uric acid levels due to primary (single-gene defect) or secondary (chronic renal insufficiency, GSP von Gierke disease, HCTZ) hyperuricemia –> uric acid levels rise above solubility limit –> deposition of sodium urate crystals in tissues

Risk factors: Obesity, alcohol consumption, diet, male, old age

Symptoms: joint pain with swelling, warmth, tenderness; rainbow birefringent crystals under LM

Treatment: allopurinol = (1) hypoxanthine analog that competitively inhibits xanthine oxidase; (2) is converted into alloxanthine by xanthine oxidase and irreversibly inhibits it; (3) leads to buildup of hypoxanthine and xanthine, which is converted to IMP –> inhibits PRPP amido-transferase (committed step in purine de novo synthesis) –> Decreased purine synthesis –> decreased degradation

Answer 130

A

IMP converted to AMP, releases fumarate –> key TCA intermediate

AMP converted to IMP via AMP deaminase

cycle represents anapleurotic rxns; cycle is upregulated in muscle cells where there is a lot of AMP production when exercising

Answer 131

A

1) Glutamine + 2ATP + CO2 + (CPSII) –> Carbamoyl phosphate; activated by ATP, PRPP and feedback inhibited by UTP
* note: cytosolic CPSII is different enzyme from mt CPSI, used in urea cycle*
2) CPSII and 2 other enzymes are all part of one larger enzyme, CAD –> CAD adds aspartate to complete pyrimidine ring –> oxidation step in the [mt] –> orotate
3) Orotate + PRPP + (orotate phosphoribosyl transferase) –> OMP + (OMP decarboxylase) –> UMP these two enzymes are both part of UMP synthase
4) UMP + ATP + (specific kinase)–> UDP + ADP; UDP + ATP + (nucleoside diphosphate kinase same one used in purine synthesis)–> UTP + ADP
* CTP can be synthesized from UTP via CTP synthetase + glutamine*

Answer 132

A

Etiology: decreased activity of either orotate phosphoribosyl transferase OR OMP decarboxylase (both part of UMP synthase); can also be caused by 6-azuaridine –> deficiency of pyrimidine nucleotides –> blocks cell division

Symptoms: megaloblastic anemia + increased urine orotate

Treatment: supplement with CMP, UMP, or uridine to bypass metabolic block

Answer 133

A

Ribonucleotide reductase – need to convert ribonucleotides to deoxyribonucleotides before they can become thymidine nucleotides; enzyme expression increases G1/S phase (When DNA synthesis occurs)

NDP + NADPH + (ribonucleotide reductase) –> dNDP + NADP; inhibited by dATP and activated by ATP binding to active site (on/off switch)

nucleotide triphosphates (e.g. ATP, dATP, dTTP) bind to substrate specificity site –> determines product made

*excess dATP created during ADA deficiency –> inhibits ribonucleotide reductase –> no deoxyribonucleotides –> no cell division –> deficiency in lymphocytes –> SCID

Enzyme inhibited by hydroxyurea

Answer 134

A

1) Make dUMP through deamination of dCMP or dephosphorylation of dUTP
2) dUMP + THF + (thymidylate synthase) –> dTMP

Inhibition by fluoroacil antitumor drug (converted to fdUMP which inhibits enzyme), methotrexate + aminopterin (inhibit DHPR and therefore THF synthesis)

Answer 135

A

Does not use PRPP, like purine salvage*
1) Base + Ribose 1 phosphate + (phosphorylase) –> Nucleoside + Pi
2) Nucleoside + ATP + (kinase) –> nucleotide + ADP

Answer 136

A

Herpes HSV encodes thymidine kinase –> promotes viral replication

Acyclovir: guanosine (purine) analog but is recognized by phosphorylated by thymidine kinase –> premature DNA chain termination

Answer 137

A

All end products are highly soluble (not the same issues with uric acid and gout)

CMP/UMP –> Beta alanine + Co2 + NH3

TMP –> Beta aminoisobutyrate + C02 + NH3

Answer 138

A

Metabolic syndrome: 3+ of the following

1) increased abdominal obesity (BMI >30, waist:hip ratio >1)
2) increased fasting TAG
3) decreased HDL
4) Increased blood pressure (hypertension)
5) Increased fasting glucose (gulcose intolerance)

Causes: visceral fat (altered FFA metabolism+release of cytokines), insulin resistance, physical inactivity, endocrine factors, aging

Associations: increased risk of cardiovascular disease, fatty liver disease, sleep apnea, chronic kidney disease, gout, PCOS, gallstones, GERD

Answer 139

A

Low carb, High protein/fat diet

Benefits: lack of hunger (protein increases satiety), steady sugar levels, decrease in LDL, rapid weight loss (due to ketogenesis from stored body fat)

Risks: lack of energy/weakness (before body adapts to ketosis), high saturated fat, low fiber + vitamins (not eating as much fruits+ veggies bc they contain carbs)

Hormonal changes: decreased insulin + increased glucagon –> increased gluconeogenesis (from the protein in the diet); increased ketonogenesis (FA from adipose tissue is converted to ketone bodies)

Answer 140

A

High carb, moderate protein, low fat diets

Benefits: high fiber + low fat –> can lower blood cholesterol and blood pressure

Risks: difficult to maintain diet, deficiency in essential fatty acids –> losing protection against heart disease (From fish, olive oil)

Answer 141

A

Focused on nutritional properties of whole foods rather than macronutrients (proteins, carbs, fats)

Benefits: improved cognitive function in old people, prevention of breast cancer, reduced incidence of cardiovascular disease

Answer 142

A

foods low in glycemic index – better regulate blood sugar levels bc they don’t spike blood glucose
eat glucose with protein – decreases change in blood glucose; increases satiety
eat fiber-rich foods - better regulate blood sugar
alcohol use in moderation bc it interferes with glucose production in liver

Answer 143

A

reduce consumption of saturated fatty acids (1% decrease in calories –> 2% decrease in LDL)
increase polyunsaturated fats e.g. omega3 FAs (dark skinned fish) –> lowers LDL and increases HDL + reduces risk for coronary heart disease CHD
increase monounsaturated fats e.g. olive oil, banana, dark chocolate –> lowers LDL without lowering HDL + reduces risk of CHD
increase soluble dietary fibers –> increases satiety, reduces LDL (by increasing LDL receptors), and binds/removes bile acids
increase veggies, fruits, whole grains – eat the food not the tablets (dont have the same benefits)
weight loss –> correlated with decrease in TAGs, LDL, and increase in HDL

Answer 144

A

Risks: obesity, high Na, low K, low Ca, increased alcohol; increases risk for CHD

Nutrition therapy:

weight reduction/physical activity
reduce sodium/alcohol
increase K/Ca
DASH diet (lots of fruits/veggies + milk, no alcohol)

Answer 145

A

Causes: diabetes, hypertension, inflammatory diseases

Symptoms: Na+ retention (sodium restriction), volume overload (diuretics), hyperkalemia (low potassium foods), metabolic acidosis (sodium bicarbonate), increased phosphate (use phosphate binders), anemia (iron replacement)

Nutrition therapy:

reduce protein intake
increase intake of MUFA/PUFA (but monitor to make sure cholesterol doesnt increase)
Vitamin D supplements (Vit D converted to active form in liver)
sodium restriction
low potassium foods e.g. apple, cauliflower, grapes, corn, lettuce, zucchini, string beans

Answer 146

A

small portions, eat slowly, no snacking, no fluids while eating
> 60g proteins/day – reduced absorption since jejunum is bypassed
iron deficiency – lower gastric production –> less conversion to reduced Fe2+ (only form which can enter cells)
Calcium/Vit D deficiency – need supplementation
Decreased Vit B12 –> absorption in ileum which is not affected, but lower pools of B12 bc of decreased gastric acid –> need megadose/injection

Answer 147

A

1) Sensitization: food allergen goes through GI tract and enters intestinal epithelium –> binds to MHC peptide on antigen presenting cell of TH2 helper T cell

B memory cells produce specific IgE antibodies against the allergen

2) Elicitation: when food allergen enters intestinal epithelium again –> crosslinks with IgE that is attached to Fc epsilon receptors on mast cell

mast cells release inflammatory factors

Answer 148

A

Antagonistic relationship – increased levels of TH1 decreases levels of TH2, and vice versa

TH1 - activates WBCs to clean up bacteria e.g. eating dirt, mucosal infections

TH2 - more recently involved to respond to parasitic infections and allergic stimuli

Answer 149

A

1) Majority of allergens are proteins

allergens take a long time to degrade – more likely to enter intestinal epithelium; also some fragments of proteins trigger immune response –> “epitope”

structural similarity may drive cross reactivity e.g. pollen and apple

2) Gastric proteases facilitate digestion of allergens and reduce allergenicity; impairment by antacids increases pH and prevents allergens from being degraded –> epitopes that are normally destroyed can be absorbed and recognized by the immune system

Answer 150

A

1) Microbiome: prebiotics –> feeding commensal bacteria –> dampens the immune response (by expanding treg cells and switching to IgA – bind allergens and prevent IgE from binding and starting immune pathway)

in breastmilk, bacteria are hypothesized to travel from maternal gut through bloodstream into the mammary glands –> to baby

2) Hygiene hypothesis: better hygiene leads to understimulation of TH1 and treg cells

Food additives might stimulate inflammation while we’re digesting food –> allergies

3) A. oral therapy –> reduces IgG and increases treg cells; B. anti IgE therapy (relatively new evolutionarily so doesnt severely immunocompromise)

Answer 151

A

1) Increases immunity up to certain point - strenuous exercise depresses immunity
2) Better maintains glucose tolerance than no exercise
3) Better maintains insulin levels than no exercise and normal controls

Answer 152

A

AMPK - activated when ATP is low and ADP levels rise –> stimulates glucose uptake and glycolysis in muscle + FFA beta oxidation, inhibits synthesis pathways that require ATP (e.g. TAG, glycogen), decreased lipolysis in adipose tissue

Normally, adiponectin and leptin activate AMPK, resistin inhibits AMPK; during obesity, adiponectin and leptin insensitivity means that AMPK pathway is inhibited

Answer 153

A

1) PFK2: Glucagon phosphorylates and inactivates PFK2 and activates FBP2 (FBP2 phosphorylates and deactivates F26BP, lifts inhibition of FBP1) –> FBP1 active (gluconeogenesis) –> F6P

Insulin dephosphorylates and activates PFK2 (PFK2 phosphorylates and activates F26BP)–> PFK1 active (glycolysis) –> F16BP

2) epi accelerates glycolysis in muscle and inhibits in liver
* blood glucose level increases the most synergistically with epi + cortisol + glucagon*

Answer 154

A

ACC-2 catalyzes conversion of Acetyl CoA –> Malonyl CoA, which inhibits CPT1

in liver, used for fatty acid synthesis; muscle does not undergo FA synthesis so uses ACC2 to regulate rate of FA beta oxidation

AMPK pathway inhibits ACC2 and activates decarboxylase (McoADC) –> catalyzes conversion of Malonyl CoA –> Acetyl CoA, which relieves inhibition of CPT1 –> muscle can generate ATP via fatty acid oxidation

Answer 155

A

Glyceroneogenesis (liver and adipose tissue): converts pyruvate –> DHAP –> generates glycerol 3-phosphate for fatty acid re-esterification

Pyruvate + (pyruvate carboxylase) –> OAA + (PEP carboxykinase) –> PEP –> –> DHAP + (G3P dehydrogenase) –> G3P –> TAG synthesis

Answer 156

A

ALL three active at a given time; extent depends on intensity + duration of exercise (e.g. high intensity is carb use/muscle glycogen; long term duration is adipose TAG use/FFA) *liver glycogen used to maintain glucose levels
1) Phosphagen - anaerobic, creatine phosphate carries Pi from mt to myosin for muscle contraction; used for immediate bursts of heavy activity active at the start of all exercise regardless of intensity
2) Glycolysis - anaerobic, breakdown of carbs (stored glycogen or dietary carbs) to produce ATP; used for moderate/high intensity activities of short/medium duration; (2A) slow=pyruvate transported to mt for TCA/Ox phos; (2B) fast=pyruvate converted to lactic acid
3) Oxidative - aerobic, primary source of ATP at rest + low-intensity of long duration, uses carbs + fats; slowest rate but greatest ATP production capacity

Answer 157

A

I) Type I: slow-twitch, low glycogen content, high myoglobin content (high 02 storage), high capacity for aerobic metabolism (resistant to fatigue); used for prolonged aerobic exercise

2) Type II: fast-twitch, high glycogen content, low myoglobin and mt content, limited aerobic metabolism (more sensitive to fatigue); used for bursts of activity

ATP used –> increased AMP –> allosterically activates glycogen phosphorylase (glycogenolysis) and PFK1 (glycolysis)

Answer 158

A

1) Phosphagen - muscle ATP concentrations do not decrease much even during intense exercise, but creatine phosphate can be eliminated; repletion within 10 min post exercise (can increase with resistance training)
2) Glycolysis - muscle glycogen more important in moderate exercise, liver glycogen more important in low intensity exercise; repletion post-exercise dependent on carb consumption (can increase with anaerobic training)

Answer 159

A

1) Structure: 51 AA in 2 polypeptide chains connected by disulfide bridges + C-peptide
2) Secretion: by pancreatic beta cells; coordinated with secretion of glucagon so that blood glucose levels remain steady; stimulated by blood glucose, AA, incretins; inhibited by epi (SNS)
3) Effects: activation and recruitment of glucose transporters to cell membrane, increase in fatty acid/TAG synthesis, inhibits activity of hormone sensitive lipase (decreased level of FFAs), stimulates entry of AA into cells and protein synthesis
4) Mechanism: binds to specific receptors on liver, muscle, fat –> signal transduction cascades; enzyme expression regulated at level of mRNA synthesis, enzyme activity at dephosphorylation

Answer 160

A

1) Structure: 29AA in single polypeptide chain, sequence same
2) Secretion: pancreatic alpha cells; stimulated by low blood glucose i.e. hypoglycemia, AA (to prevent hypoglycemia from insulin effects), epinephrine; inhibited by elevated blood sugar
3) Effects: increase in gluconeogenesis (decreased levels of AA), hepatic glycogenolysis, FFA oxidation, hepatic ketone body formation, increased level of FFAs (activates hormone sensitive lipase, as does epi)
4) Mechanism: binds to specific receptors on liver + fat (epi binds to muscle) –> Adenyl cyclase activation –> cAMP pathway –> phosphorylation

Answer 161

A

1) Fed state: anabolic due to increased insulin:glucagon ratio –> increased TAG, glycogen, protein synthesis; all tissues use glycogen (i.e. glucose)
2) Starvation: catabolic due to decreased plasma glucose, AA, and TAG –> decreased insulin:glucagon ratio –> different preferred substrates e.g. FFAs from adipose (liver and muscle), gluconeogenesis from AA + glycerol + lactate (glucose for brain + RBCs)

Answer 162

A

1) Pathogenesis: (DMI) autoimmune response against beta cells; less of a genetic component (DMII) insulin resistance + B cells become dysfunctional and dont produce enough insulin; genetic component but polygenic
2) Insulin: (DMI) low/absent (DMII) high early on, then decrease with beta cell dysfunction
3) Symptoms: (DMI) 3Ps; occur abruptly, therapy can lead to hypoglycemia (DMII) no symptoms, occasionally polyuria + polydipsia
4) Complications: (DMI) diabetic ketoacidosis –> low levels of insulin –> remove inhibition of hormone-sensitive lipase –> increased beta oxidation –> excess Acetyl CoA formed –> ketogenesis increases (DMII) hyperosmolar coma
4) Treatment: (DMI) insulin therapy (DMII) exercise, weight loss, oral hypoglycemic drugs e.g. metformin
* diabetes is not just lack of insulin but also overproduction of glucagon; hypertriglyceridemia due to decreased LDL activity due to lack of insulin stimulation*

Answer 163

A

Blood glucose less than 80 –> insulin production decreases

Blood glucose less than 70 –> adrenal gland epi production (glycogenolysis); pancreas glucagon production (both glycogenolysis and gluconeogenesis)

Blood glucose less than 60 –> adrenal glands release cortisol (gluconeogenesis)

Blood glucose less than 40 –> adrenergic symptoms (anxiety, tremor, sweating); neuroglycopenia (headache, slurred speech, seizures, coma)

Answer 164

A

1) increased delivery of FFA to liver blocks insulin action
2) adipose tissue releases adipokines into the blood e.g. leptin (anti-diabetic, activates AMPK for weight loss), resistin (pro-diabetic, inhibits AMPK)
3) excess lipid stored in liver, beta cells influences insulin signaling and secretion –> DMII

Answer 165

A

1) Acarbose inhibitors- inhibit alpha glucosidase to slow absorption of carbs
2) Sulfonyureas (gliburide) - stimulate insulin release by opening voltage gated Ca2+ channels
3) Biguanides (metformin) - inhibit gluconeogenesis *do not stimulate insulin so do NOT cause hypoglycemia
4) Incretins (GIP, GLP1, Januvia) or DPP4 inhibitors - anticipatory stimulation of beta cells to release insulin
5) SGLT2 inhibitors - decrease reabsorption of glucose from kidneys and increase glucose excretion
6) Thiazolidenidione (Avandia) - activates PPAR insulin sensitivity of adipose tissue

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GI Final Flashcards

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