Deevska-Block 2 Flashcards
Where is pyruvate oxidiized to acetyl CoA?
Mitochondrial matrix
What molecules are produced in the TCA cycle?
-3 NADH
-1 FADH
1 GTP
How is glycolysis and TCA linked?
Pyruvate is the end product of glycolysis which goes to the TCA cycle. PDH converts it to acetyl Coa, which combines with oxaloacetate to form citrate (with enzyme citrate synthase) to go into the actual cycle
Explain the function and structure of the PDH complex
- 3 separate enzymes (E1, E2, E3)
- 5 different cofactors
- TPP
- lipoamide
- CoA
- FAD
- NAD
What are the cofactors of PDH?
- TPP
- lipoamide
- CoA
- FAD
- NAD
What activates PDH?
- dephosphoryaltion
- pyruvate
- NAD+
- ADP
- Ca2+
- CoA
What deactivates PDH>?
- acetyl CoA
- NADH
- ATP
- phosphorylation
PDH and deficiency of niacin or thiamine
Can cause serious CNS problems
Arsenic poisoning
Males lipoic acid unavailable as coenzyme for PDH
Sequence of reactions in TCA
- Synthesis of citrate from acetyl CoA and oxaloacetate (citrate synthase)
- Isomerization of citrate to isocitrate (aconitase)
- Oxidative decarboxylation of isocitrate to a-ketoglutarate (isocitrate dehydrogenase)
- Oxidative decarboxylation of a-ketoglutarate to succinyl CoA (a-ketoglutarate dehydrogenase complex)
- Cleavage of succinyl CoA to Succinate (succinyl CoA synthetase or succinate thiokinase)
- Oxidation of succinate to fumarate (succinate dehydrogeanse)
- Hydration of fumarate to malate (fumarase)
- 1 oxidation of malate to regenerate oxaloacetate and produce NADH + H+ (malate dehydrogenase)
Identify the 4 oxidative enzymes in the TCA cycle, their products, and regulation
PDH
- product is acetyl CoA
- activated by: pyruvate, NAD+, ADP, Ca2+, CoA, dephosphorylation
- deactivated by acetyl CoA, NADH, ATP, phosphorylation
Isocitrate dehydrogenase
- product is a-ketoglutarate
- inhibited by: ATP, NADH
- activated by: ADP, Ca2+
A-ketoglutarate dehydrogenase
- product succinyl CoA
- inhibited by: products
- activated by Ca2+
Succinate dehydrogenase
-product: fumarate
What are the 4 oxidative enzymes of the TCA?
- PDH
- isocitrate dehydrogenase
- a-ketoglutarate dehydrogenase
- succinate dehydrogenase
Identify the 2 intermediates required in the first step of the TCA cycle and their metabolic sources.
- OAA and pyruvate
- pyruvate comes from glycolysis as the end product and is changed into acetyl CoA via PDH
- OAA is just cycled through TCA over and over again
Identify 4 important products synthesized from the TCA cycle and summarize the energy yield for 1 glucose molecule
- 2 CO2
- 3 NADH
- 2 FADH
- 1 GTP
- 36-38 ATP overall
Identify the enzymes from the TCA cycle affected by vitamin deficiency and arsenic poisoning and explain the underlying reason for that.
Enzymes: PDH and A-ketoglutarate
- arsenic poisoning forms a stable theology bond with lipoic acid (coenyme for both enzymes) making it unavailable to be used as a coenzyme
- affects the brain causing neurological disturbance and death
Why don’t we get glucose from TCA?
Because PDH is irreversible, we don’t have enzymes to catalyze the reverse reaction
Outline the structure of the mitochondria and the mitochondrial electron transport system showing all major electron carriers.
- electron carriers: NAD+ and FAD
- outer membrane: permeable to most ions and small molecules
- innermembrane: impermeable to most small ions and large molecules
- Matrix: TCA cycle enzymes, FA oxidation enzymes, mitochondrial ribosomes
Electron transport assembly
Complex 1-NADH dehydrogenase
- FMN
- iron sulfer center
Complex II - succinate dehydrogenase
- only one embedded in the inner mitochondrial membrane
- FAD contains iron sulphur center
CoQ
- ONLY nonprotein carrier
- quinine derivative
Complex III-cyt b and c1
-heme group which reversible converted from ferric to ferrous
Complex IV-cyt a and a3
- heme group which reversible converted from ferric to ferrous
- Cu
- heme directly reacts with O2
Cyt c
-freely moving in the intermembrane space
Complex V-ATP synthase
-multisubunit
Describe how the TCA cycle is regulated by substrate supply, allosteric effectors, covalent modification, and protein synthesis
PDH covalent modifications:
-phosphorylation deactivates
-dephosphorylation activates
-PDH kinase and phosphatase can be allosterically activated or inhibited by substrate activation and product inhibition
Other regulations:
-activation: pyruvate, NAD+, ADP, Ca2+, CoA
-deactivation: acetyl CoA, NADH, ATP
Isocitrate dehydrogenase allosteric regulation
- inhibitors: ATP and NADH
- Activators: ADP and Ca2+
A-ketoglutarate dehydrogenase regulation
- inhibitors: its products
- activators: Ca2+
Explain the role of uncoupling proteins in thermogensis
- allow H+ to flow back into the matrix without passing though complex V, and not forming ATP
- the free energy is released as heat (nonshivering thermogenesis)
- UCP1 (thermogenin) found in brown fat
Give examples of synthetic uncouplers (such as salicylic acid) and their effect on the ETC
- 2,4-dinitrophenol: used as a weight loss drug in the 30s. However its use was banned because it was relatively easy to overdose, which can cause a fatal hyperthermia, although its use still persists (illegally)
- compounds containing salicylic acid will also cause uncoupling, including aspirin. Overdoses of aspirin will cause a high fever and profuse sweating, and can be potentially fatal
Describe the effects of inhibitors such as rotenone, antimycin A, carbon monoxide, cyanide and oligomycin on oxygen uptake by mitochondria and ETC function
- Amytal: complex I-barbiturate. Importance of proper drug dosage
- Rotenone: complex I-insecticide, piscicide, and pesticide
- antimycin A: complex III-pesticide
- CN-complex IV-irreversibly binds to the Fe3+ in the heme group of cyt c-oxidase
- CO-complex IV-binds irreversibly- tight binding to hemoglobin
- NaN3-binds similarly to CN to the Fe3+ of iron in cyt
- oligomycin-binds to the F0 domain closing the proton channel leading back into the matrix and shutting down ATP synthesis
Describe the role of mitochondria in apoptosis.
- initiated through mitochondria intrinsic pathways resulting in the formation of pores in the outer mitochondrial membrane
- pores allow cyt C to be released in the cytosol
- capsases cause cleavage of key proteins that result in the morphological and biochemical changes characteristic of apoptosis.
What disease can result from mutations in the mtDNA or nuclear DNA?
- LHON
- mycolonic epilepsy with ragged red fibers (MERRF)
- mitochondrial encephalomyopathy, lactic acidosis, and stroke like episodes (MELAS)
- Leigh syndrome
LHON
-optic neuropathy and atrophy
NARP
- Retinal dystrophy
- cone or cone-rod dystrophy
MILS
- RPE dystrophy
- optic atrophy
MELAS
- maculopathy
- cone-rod dystrophy
- hemianopsia
MIDD
- pattern maculopathy
- pigmentary retinopathy
MERRF
- optic atrophy
- mild pigmentary retinopathy
KSS
- pigmentary retinopathy
- strabismus ptosis
CPEO
- Ptosis
- Ophthlmoplegia
- strabismus
Outline the pathway for GNG, including purpose for the pathway, tissues where it takes place, and sub cellular localization
GNG is the metabolic pathway that results in the generation of glucose from non carbohydrate precursors
- Purpose: the maintain blood glucose levels and avoid hypoglycemia under conditions of fasting (>10-18 hours)
- tissues: predominant in the liver, in the kidney cortex at a lesser extent only during prolonged fasting contribute up to 40% of the total glucose production
- subcellular localization:
- mitochondrial matrix-step 1
- cytosol-all reversible steps of glycolysis
- ER-last step (dephosphorylation) to produce glucose
Identify all possible substrates for GNG
- Glycerol
-hydrolysis of TAGs in adipocytes, delivered by the
blood to liver
-in the liver: glycerol–glycerol phosphate—DHAP - Amino Acids
-derived from tissue protein hydrolysis (very late in starvation
mode).
-Ala is the major AA, but most can be used
-most AA converted in the TCA can yield OAA - Lactate
-converted back into pyruvate in liver by lactate dehydrogenase
Can acetyl CoA serve as substrate for GNG?
NO
- cannot be converted into pyruvate in humans
- PDH is irreversible and no enzyme for the reverse reaction
- FA CANNOT serve as substrate for GNG
- FA oxidation provides liver with the energy to perform GNG
Cori Cycle
Glucose converted into lactate under anaerobic glycolysis, excreted to plasma and sent to the liver to be converted back to glucose and released into circulation forms this
Reversible steps of GNG
- 7 steps
- glycolytic steps
- highly dependent on concentration of substrates and products
- Carboxylation of pyruvate to OAA (pyruvate carboxylase)
-allosterically activated by acetyl CoA
-OAA cannot be exported (lack of transporters)
-converted to malate and then converted back to OAA (malate
dehydrogenase, PEP carboxykinase)
Steps unique to GNG
decarboxylation of cytosolic OAA
- driven by GTP hydrolysis
- makes GNG energetically possible
- PEPCK
Dephosphorylation of fructose 1,6-bis-P
- bypasses PFK-1 reaction
- important for site regulation
- fructose 1,6-bisphosphatase
Dephosphorylation of glucose 6-P
- bypasses hexo/gluco reaction
- energetically favorable step to produce glucose
- glucose 6-phosphatase
- deficiency leads to Von Gierk
What is irreversible in GNG?
- Decarboxylation of cytosolic OAA (PEPCK)
- Dephosphorylation of fructose 1,6-bis-P (fructose 1,6-bisphosphatase)
- dephosphorylation of glucose 6-P (glucose 6-phosphatase)
Compare and contrast common (shared) allosteric regulators of enzymes from glycolysis and GNG and understand the biological role of this regulation
Regulation by Glucagon
- inhibits PFK-2, lowers fructose 2,6-BP, inhibiting glycolysis and activating GNG
- inhibits pyruvate kinase, therefore PEP is used for GNG as opposed to glycolysis
- stimulates transcription of PEPCK, insulin inhibits
Regulation by fructose 2,6-bisphosphate (synthesized by PFK-2)
- inactivated fructose 1,6-bisphosphate and stops GNG
- the common regulator allows tight regulation assuring the pathways of glycolysis and gluconeogensis are mutually exclusive
Allosteric activation by acetyl CoA
- buildup of acetyl CoA, signals the diversion of OAA for gluconeogensis
- activates pyruvate carboxylase
- inhibits PDH, assuring pyruvate is diverted to the production of glucose and away from the TCA cycle
Allosteric inhibition by AMP
- fructose 1,6 bisphosphate is inhibited by AMP
- PFK-1 is activated by AMP
- as with regulation of the two enzymes by fructose 2,6-BP, the reciprocal regulation of each of these enzymes by the same allosteric effector assures the two pathways are mutually exclusive
Summarize the pathway from energetic point of view
- an energy-requiring pathways (endergonic)
- anabolic pathway
- for 1 glucose
- 4 ATP and 2 GTP used
- 2 NADH are used
Explain all possible ways to regulate GNG
-pyruvate carboxylase allosterically activated by acetyl CoA
-fructose 1,6-bisphosphatase
Inhibited by AMO
Allosterically inhibited by fructose 2,6-bis-P
Activated by night ATP, low AMP
-regulation by glucagon
-regulation by substrate availability
-allosteric activation by acetyl CoA
-allosteric inhibition by AMP
Identify the enzymatic step in GNG that will be effected when biotin is not available and explain why
Carboxylation of pyruvate to OAA using enzyme pyruvate carboxylase
-pyruvate carboxylase requires biotin as a coenzyme
Outline the metabolic pathways for synthesis and degradation of glycogen including names of enzymes and intermediates. Compare and Contrast liver and muscle cells
- Synthesis of UDP glucose (hexo/glucokinase, phosphoglucomutase, UDP glucose phosphorylase)
- Synthesis of a primer to initiate glycogen synthesis (glycogen synthase and protein glycogenin)
- Elongation of glycogen chains (glycogen synthase) rate limiting enzyme
- Formation of branches (branching enzyme)
- Shortening of chains (glycogen phosphorylase)
- Removal of branches (debranching enzyme)
- Conversion of glucose 1-P to glucose 6-P (phosphoglucomutase)
- Dephosphorylation of glucose6-P to glucose (glucose 6-phosphatase)
Von Gierke
Deficient enzyme: glucose 6-phosphatase
Clinical features: severe fasting hypoglycemia, lactic acidosis, hepatomegaly, hyperlipidemia, hyperurecemia, short stature
Glycogen structure: normal
Pompe
Deficient enzyme: lysosomal a-glcosidase
Clinical features: cardiomegaly, muscle weakness, death by 2 years
Glycogen structure: glycogen like material in inclusions
Cori
Deficient enzyme: debranching enzyme
Clinical features: mild hypoglycemia, liver enlargment
Glycogen structure: short outer branches, single glucose residue at outer branch
McArdle
Deficient enzyme: muscle glycogen phosphorylase
Clinical features: muscle cramps and weakness on exercise, myoglobinuria
Glycogen stucture: normal
Anderson
Deficient enzyme: branching enzyme
Clinical features: infantile hypotonia, cirrhosis, death by 2 years
Glycogen structure: very few branches, especially towards periphery
Hers
Deficient enzyme: hepatic glycogen phosphorylase
Clinical features: Mild fasting hypoglycemia, hepatomegaly, cirrhosis
Glycogen structure: normal
Outline the sources of fructose and galactose and explain their biological roles
Fructose
- significant source of calories in western diet
- sucrose, high fructose corn syrup, honey, fruits
- entry not insulin dependent
- mediated by glut 5 transporter
- does not promote insulin secretion
- bypasses PFK1 step, metabolized more rapidly than glucose
Galactose
- isomer of glucose
- lactose from milk and milk products
- some from lysosomal degradation of complex carbs
- not insulin dependent
- 2-steps to UDP galactose
Explain why these two simple sugar molecules are metabolized faster compared to glucose?
Because they bypass the PFK-1 step and do not require insulin
Outline the steps of fructose metabolism
- phosphorylation of fructose
- enzyme in liver: fructokinase
- enzyme in other tissue: hexokinase - Cleavage of fructose 1-P
- enzyme: Aldolase B
- products: DHAP and glyceraldehyde
Outline the steps of galactose
- phosphorylation of galactose
- enzyme: galactokinase - Formation of UDP galactose
- enzyme: GALT
Essential fructosuria
Lacking: fructokinase
Results: fructose accumulates in the urine
Describe the conversion of glucose to fructose via sorbitol and explain how accumulation of sorbitol leads to pathology in certain tissue types
- excess glucose gets converted into sorbitol, sorbitol accumulation results in osmotic uptake of water, which can account for some of the symptoms seen in dim patients including
- cataracts
- retinopathy
- nephropathy
- peripheral neuropathy
Hereditary fructose intolerance (fructose poisoning)
Lacking: aldolase B
Results: severe hypoglycemia, vomiting, jaundice, hemorrhage, hepatomegaly, renal dysfunction, hyperurcemia, lactacidemia
-hepatic failure and death
Galactokinase deficiency
Lacking: galactokinase
Results: cataracts
Aldose reductase elevation
Too much: aldose reductase
Results: cataracts
Classic galactosemia
Lacking: GALT
Results: liver damage, severe mental retardation, and cataracts
Describe where, when, and how lactose can be synthesized in humans
- milk sugar produced by lactating mammary glands
- synthesized in the golgi
- enzyme: lactose synthase
- a-lactalbumin synthesis is stimulated by the peptide hormone prolactin
What are all the names for the penthouse phosphate pathways
- pentose phosphate pathway
- hexosemonophosphate (HMP) shunt
Describe the purpose of PPP and its role as a source of NADPH and in the synthesis of ribose for nucleotide synthesis
- generation of NADPH and generation of the 5-carbon sugar ribose, to be used in the synthesis of nucleotides
- The pathway can produce both ribose and NADPH, or it can produce only NADPH or only ribose, depending on the needs of the cell. No ATP is produced or used during this process
Describe the stages of PPP including all enzymes and their regulators (or coenzymes) outlined in the lecture notes and be able to compare and contrast the types of biochemical reactions in each stage (phase)
1. Dehydrogenation of glucose 6-P Enzyme: G6PD, NADP+ is coenzyme Upregulated by insulin Flux increases in absorptive state RATE LIMITING STEP 2. Hydrolysis to 6-phosphogluconate Enzyme: 6-phosphogluconolactone hydrolase Produces one NADPH Irreversible 3.oxidative decarboxylation of 6-phosphogluconate Enzyme: 6-phosphogluconate dehydrogenase Produces 1 NADPH Irreversible 4-8. Interconversions of sugar molecules Reversible steps Permit synthesis of ribose 5-P used for nucleotide production Enzyme: transketolase, requires TPP
Explain the differences between NADH and NADPH function and structure
- NADH has and OH group
- NADPH has -OPO3-2 where the PH group would be
- both electron carriers
- NADPH-electron carrier for reductive biosynthesis of FA, cholesterol, and steroids
- provides reducing equivalents for cyt P450 monooxygenase system
- play a role in phagocytosis
- substrate for the synthesis of NO
Describe the structure and function of GSH and GSSG
- NADPH role in neutralization of ROS
- tripeptide GSH
- major antioxidant system is GSSG/GSH
NADPH roles in cyt P450 system
-monooxygenase
has a mitochondrial system for synthesis of steroids
- inner mitochondria membrane
- steroidogenic tissue uses NADPH for synthesis of steroid hormones
- in liver to synthesize biles acids and vitamin D3
- in kidney converts D3 to active form
has a microsomal like system for detox of drugs
- smooth ER in liver cells
- detox of drugs
- adding oxygen to inactivate
NADPH role in phagocytosis
- neutrophils and macrophages
- generation of O free radicals aid in killing microorganism
- MPO system
Describe the role of MPO system in phagocytosis
-combination of NADPH oxidase and myeloperoxidase are used to generate the oxygen free radicals to aid in the destruction of microorganism
NADPH oxidase deficiency
- causes chronic granulomatous disease (CGS)
- persistent severe high infections due to the inability to kill bacteria forming granulomas
- the granuloma is formed as a defense where the body attempts to wall off the collective cells from the rest of the body
Outline the biological functions of NO
- smooth muscle relaxant (the basis for nitroglycerin action which is converted to NO to relax vascular smooth muscle)
- used by macrophages to generate free radicals to assist in killing micro organisms
- inhibits platelet aggregation
- functions as neurotransmitter in brain
Explain the consequences of genetic defects of G6P D deficiency and know the specific features of it in RBCs
-inability to detox drugs
-one of the most common single gene disorders
-some protection against malaria
-usually only symptomatic when experiencing an oxidative stress
Infections
Drugs that produce an oxidative stress
Fava beans
- episodic hemolytic anemia in adults because the NADPH in RBCs can only come from this pathway whereas other tissues have other means of getting it
- CANNOT synthesize more G6PD since they lack nucleus
- affect stability, enzyme lost and not replaced
- produces Heinz bodies which are precipitates of oxidized hemoglobin
Difference between saturated and mono-, polyunsaturated fatty acid
- saturated: NO DOUBLE BONDS
- unsaturated: carbons have 1 or more double bonds
Tm
- double bonds reduce it
- increasing chain length increases it
How to name structure omega 3 or omega 6
20:4(5,8,11,14). 20-14= 6…omega 6
What are the two essential FA? Why?
- linoleic acid, because it is a precursor for other shorter omega 6 FA
- a-linolenic acid because it is a precursor for omega 3 FA: important for growth and development
What FA can become essential and why?
Arachidonic acid
- substrate for prostaglandin synthesis
- becomes essential if a-linolenic acid is absent
What are arachidonic acid and a-linolenic acid precursor for?
Omega 3 FA
What are the categories of FA length?
4 of them
-short, medium, long, very long
What kind of FA are there?
Free
Esterified
General type of lipids that are digested
CE
PL
TAG
Enzymes that function to digest dietary lipids
Gastric lipase
- acid lipase, secreted from the gastric mucosa
- optimal at lower pH in stomach
- target TAG containing short and medium chain FA in stomach
Lingual Lipase
-acid lipase, secreted from glands at back of the tongue, same as gastric lipase on everything else
Pancreatic lipase
- TAG digestion, in pancreas, cleaves FA producing 2 free FA and a 2-monoacylglycerol
- high catalytic efficiency
Coplipase
- secreted from pancreas and binds pancreatic lipase
- promoted pancreatic lipase activity when inhibitory bile salts are present
Cholesterol esterase
- pancreatic enzyme responsible for cholesteryl ester digestion
- digests esterified cholesterol
Phospholipids A2
-phospholipid digestion, pancreas, removes FA to produce lysophospholpid
Lysophospholipase
-phospholipid digestion, pancreas, glycerylphosphoryl group
Importance for emulsification of dietary lipids, where it happens, aspects important for making emulsification possible
Mechanical agitation
-dietary material via peristalsis increases the lipid droplet surface area
Bile salts secretion
- made in liver
- stored in gallbladder
- secreted to small intestine
- detergent properties prevents from coalescing
Which of the phosphoryl bases are likely to be taken up?
Cholic acid
- bile salt production
- lung surfactant production
What are the two hormones made and released by gut endocrine cells
CCK
- promotes pancreatic enzyme secretion
- causes gall bladder to release bile, bile salts, phospholipids, free cholesterol
- reducing release rate of gastric contents
Secretin
- low pH of chyme entering the intestines
- promotes the release of bicarbonate rich solution from the pancreas.
Components found in bile
Glycine and cholic acid
Components found in micelles from diet and from bile. Including the fat soluble vitamins DEAK
Disk shaped clusters of AMP hips this lipids Formed from -bile salts -digested lipids -fat soluble vitamins (DEAK)
Promotion of micelle formation
Digested lipids and the manner in which it is done promotes it.
Many of the molecules generated during digestion are ampipathic in nature
What does not require micelle transportation
Short and medium chain FA
What is taken up by enterocytes
Digested lipid components and components of the bile which end up in the micelles.
Long chain FA entering the enterocytes
Charged to CoA by thiokinase and then re esterified to form TAG, CE, and some phospholipids
Components of chylomicrons
Apolipoprotein B-48
Distributed to lymph then circulated in the blood
What happens to chylomicron remnant?
Taken up by liver, along with the remaining components associated with the remnant
Lipid malabsorption cause, effect, treatment
Cause: decreased bile excretion, pancreatic insufficiency, defective enterocytes, shortened bowel
Effects: reduce dietary calories, fat soluble vitamin deficiency, could result in essential FA deficicney
-treatment: increase calorie from non-fat sources, fat soluble vitamin supplements, enzyme replacement therapy
Know where FA synthesis occurs, what is the cytosolic carbon source, what is the energy source, and what functions as a reducing agent
FA synthesis occurs in the cytosol
- cytosolic acetyl CoA is the carbon source
- energy source is ATP and NADPH
Where are the carbons for FA synthesis originally?
In the mitochondria
-in the form of Acetyl CoA but CoA cannot traverse the inner mitochondrial membrane to the cytosol
How do the acetate carbons get across the inner mitochondrial membrane?
acetyl CoA and OAA come together and form citrate via citrate synthase and can now cross the membrane.
What does ACC do? How is it regulated short term and long term?
- carboxylase cytosolic acetyl CoA to malonyl CoA
- uses CO2 and energy from ATP hydrolysis to carboxylase the acetyl group of acetyl CoA
- provides the energy for C-to-C condensations to elongate the growing FA chain
- carboxylation of the acetyl CoA is the rate limiting and regulating step for FA synthesis
Short term regulation
- inactive ACC diners are allosterically activated to its polymerized form by citrate
- AMPK reversibly phosphorylates and inhibited ACC when fasting
- indirectly inhibited by epinephrine and glucagon
Long term regulation
- prolonged high calorie, high carb diets increase ACC synthesis which increase FA synthesis
- a low calorie or high fat diet reduces FA synthesis by decreasing ACC synthesis
FAS
- multifunctional dimeric enyme that has two important sites
- ACP
- cysteine residue holding site
4 steps of FAS
First, a Tate from acetyl CoA is transferred to ACP site on FAS
A. Acetate transferred to cysteine residue holding site
B. Malonate from malonyl CoA transferred to ACP site on FAS
C. Energy from decarboxylation of the malonyl ACP drives a condensation reaction between the ACLU group at the holding site cysteine and the remains acetyl ACP
D. The 4-carbon is transferred to the cysteine holding site.
Repeat these steps 6 more times and with each cycle add 2 carbons
Inbetween each cycle, NADPH function as reducing agents, which majorly comes from HMP pathway
Where does FA elongation and desaturation occur?
Smooth ER
Where are VLCFAs made?
Brain
Storage of FA as TAG
Carbon 1: saturated FA
Carbon 2: unsaturated FA
Carbon 3: either sat or unsat FA
What are the two processes/pathways to produce glycerol phosphate? Which pathway is possible in adipose and liver tissue and which pathway is Preston only in the liver?
A. In liver and adipose tissue: produced from glucose via the glycolytic pathway
B. In liver only: glycerol kinase converts free glycerol to glycerol phosphate
How is TAG molecule generated?
Thiokinase transfers 2 fatty acyls from acyl-CoAs to a glycerol phosphate, the phosphate is removed by a phosphatase and replaced with an additional fatty acyl from acyl-CoA
Know the two enzymes in the adipose that release FA from TAG
Adipose lipase: constitutive FA release
HSL: major role in regulated TAG lipolysis and release of FA from adipose
-phosphorylated and activated by cAMP dependent protein kinases (fasting) (binds to perilipin)
-epinephrine phosphorlyates and activates it
-insulin promote dephosphorylation
Fate of glycerol
- adipocytes lack glycerol kinase and cannot metabolize glycerol released in TAG degradation
- glycerol is:
- phosphorylated in the liver to be used in TAG synthesis or
- reversibly converted to DHAP by glycerol phosphate dehydrogenase
- DHAP can participate in glycolysis or gluconeogensis
Which two tissues cannot use FAs for energy?
Brain and erythrocytes
Where doe B-oxidation occur and what are the products?
- mitochondria
- acetyl CoA, NADH, FADH2
How does the carnitine shuttle work
- Acyl groups are transferred from CoA to carnitine by CAT1, an outer mitochondrial membtane enzyme
- Acyl carnitine is transported into the mitochondrial matrix in exchange for free carnitine by carnitine-acyl carnitine tranlocase
- CATII on the matrix side of the inner mitochondrial membrane catalyze acyl group transfer from carnitine to CoA
Why is carnitine shuttle important for VLCFA?
LCFA cannot directly cross the inner membrane of the mitochondria due to the presence of the CoA
How is CATI regulated and why is
- CAT I is inhibited by malonyl CoA in well fed
- preventing LCFA transfer from CoA to carnitine
This inhibition prevents
- mitochondrial import and B-oxidation of newly synthesized LCFAs
- B-oxidation of LCFAs to generate energy while in a well fed state
How is most carnitine obtained, where is it made de novo, where is most of it located/utilized, what could cause a deficiency of carnitine?
Source:
-diet (meat) or synthesized
Where is it synthesized?
- by an enzymatic pathway in the liver and kidney using AA lysine and methionine
Where is it located/utilized?
Skeletal muscle
Deficiency cause
- decreased synthesis due to liver disease
- dietary malnutrition
- hemodialysis
- conditions in which carnitine requirements increase
- CAT I GENETIC DEFECT (decrease liver use)
- CAT II GENETIC DEFECT (heart and skeletal muscle)
Why do short and medium chains not require carnitine shuttle?
FA
When a FA is B-oxidized in a muscle cell, considering all molecules being generated, how is that energy being extracted: consider the ETC (NADPH, FADH2), and TCA cycle ( acetyl CoA)
- Oxidation producing FADH2 which can be used for ETC
- Simple hydration reaction
- Another oxidation that produces NADH which can also go to ETC
- Release acetyl CoA which can be used for GNG if it’s carboxylated by pyruvate carboxylase
B-oxidation of FAs with odd number of carbons
-require biotin and the coenzyme form of vitamin B12
B-oxidation of unsaturated FAs
-requires additional enzymes and produce less energy than saturated FAs
VLCFA B-oxidation
Require additional step in peroxisome that generate no ATP
Branched chain FA require what?
A-oxidation in the peroxisome by PhyH and with its deficiency, phytanic acid accumulates in blood and tissues resulting in neurologic conditions (refsum disease) requires dietary restriction of phytanic acid to halt progression of the disease
MCAD deficiency
- results in the inability to oxidize 6-10 carbon FA, accumulation of them, measurable in the urine, resulting in severe hypoglycemia due to tissue reliance on glucose for energy. Treatment is to avoid fasting
- linked to SIDS
What are the 3 ketone bodies?
- acetoacetate
- 3-hydroxybutarate
- acetone
Acetone is a volatile, dead-end ketone body that is exhaled
Conversion of ketone bodies back into acetyl CoA
Heart, skeletal, and renal cortex can do this and use them in the TCA cycle for energy, but liver cannot
FA oxidation disorders
Hypoketosis, hypoglycemia
Rate limiting and irreversible step of ketogensisi
Conducted by HMG CoA synthase
Almost exclusively in the liver
Imbalance use and production of ketone bodies
Can result in ketonemia (increase blood level ketone bodies), and ketouria (urine level ketone bodies to increase
Diabetic ketoacidosis
- causes fruity smelling breath from acetone
- ketonemia causes acidemia because the carboxyl group on keton bodies has a pKa of about 4, lowers pH
- increased ketone bodies and glucose cause increased secretion of water and dehydration
- ketoacidosis: decreased blood volume increases H+ cxn causing severe acidosis
- can be caused by fasting
Explain how the structure determines the functions of glycerophospholipids and sphingomyelin
All glycerol and sphingomyelin are amphipathic. Able to arrange themselevs in the plasma membrane spontaneously when reacted with water
List the predominant phospholipids in tears and be able to identify all phospholipids that are associated with the eye
Phospholipids associated with the eye:
- PC
- PS
- SM
- PE
- PG
- dihydrosphingomyelin
- ethanolamineplasmalogen
- lysophosphatidylcholine
- phosphatidylinisotol
Predominant ones in tears
-PE, PC,SM
Describe the general structure and most important functions of PA
- precursor for the synthesis of all other glycerophospholipids and TAG
- signaling molecule
- influence membrane curvature and vesicle formation
- simplest of all phospholipids
Describe the general structure and most important functions of PC
- also called lecithin
- first found in egg
- PC=PA + Choline
- the most abundant phospholipid
- storage for choline (essentially dietary nutrient)
- major component of lung surfactant (DPPC)
Describe the general structure and most important functions of PE
- cephalin (neuronal tissue)
- PE=PA + ethanolamine
- the second most abundant phospholipid
- used for the synthsis of PS in exchange reaction with free serine
Describe the general structure and most important functions of PS
- PS=PA + serine
- inner leaflet of the plasma membrane
- required for membrane synthesis
- recognition of apoptotic cells
Describe the general structure and most important functions of Pl
- Pl=PA + inositol
- unusual lipid: contains stearin acid at C1 and arachidonic acid at C2
- reservoir of arachidonic acid
- precursor for prostaglandins
- OH groups can be phosphorylated to produce second messenger PIP2
- PIP2 is a substrate for PLC to produce IP3 and DAG
- serve as anchor points
Describe the general structure and most important functions of PG
- PG=PA + glycerol
- A precursor of surfactant
- precursor for the synthesis of cardiolipin
Describe the general structure and most important functions of cardiolipin
- diphosphatidylglycerol
- 2 PA molecules esterified through their phosphate groups
- exclusive to the inner mitochondrial membrane
- maintains the structure and function of ETC complexes
- maintains proton gradients
Describe the general structure and most important functions of plasmalogen
- Ether glycerophospholipid
- FA at C-1 attached via ETHER linkage
- unsaturated FA at c-1
- phosphatidALcholine in heart muscles
- phosphatidALethanolamine in nerve tissue
Describe the general structure and most important functions of PAF
- ether glycerophospholipid
- FA at C-1 attached eithe ETHER linkage
- saturated FA at C-1 and a short acetyl group at C-2 rather than acyl
- synthesized and released by variety cell types
- one of the most potent bioactive molecules: thrombotic and inflammatory response
- mediate anaphylaxis and hypersensitivity
Describe the general structure and most important functions of sphingomyelin
- SM
- MOST ABUNDANT
- SM=ceramide + phosphocholine
- predominant sphingophospholipid in mammalian cells
- major structural spingolipid in the plasma membrane.
- role in lipid raft formation
- role in signaling as precursor for the bioactive ceramide
- abundant in nerve tissues (myelin sheath)
Describe the general structure and most important functions of ceramide
- FA that is attached to glycerol is what makes Cer and SM different
- Cer=sphingosine + FA
- differ in the type of FA attached to sphingosine
- precursor for SM and all glycosphingolipids
- bioactive second messenger
- maintain skin’s water-permeability barrier
- decreased levels are associated of skin diseases
Describe the general structure and most important functions of sphingosine
- sphingosine =palmitic acid + serine
- bioactive second messenger molecule
- precursor for sphingosine 1-phosphate
- controls endocytosis of rhodopsin and another light sensitive eye protein, the transient receptor potential (TRP) channel
Describe the general structure and most important functions of shingosine 1-phosphate
- shingosine is a presurosor for it.
- potent bioactive second messenger recognized by at least 5 different GPCR
Describe the general structure and most important functions of cerbrosides
- neutral GSLs
- cerebroside=ceramide + sugar
- galactosylceramide via a glycosidic link - essential components of membranes, mostly found on the outer leaflet of the plasma membrane
- participate in lipid rafts
- predominant in nerve tissue (brain and periphery)
Describe the general structure and most important functions of gangliosides
- acidic GSL
- negatively charged at pH 7
- found in ganglion cells in the CNS
- sulfatides=galactocerebrosides + SO3- group found in brain and kidney
Explain the etiology of sphingolipids, what enzyme is deficective in each disease and what are the consequences of the deficiency
Acid hydrolase defect
- SL substrate accumulates
- affects nervous tissue
- may be fatal
- genetic variability
- low incidence
Tay-Sachs disease
- sphingolipidoses
- hexosaminidase A deficient
- gangliosides accumulate
- blindness
Niemann-pick disease
- sphingolipidoses
- sphingomyelinase deficient
- sphingomyelin accumulates
Gaucher’s disease
- sphingolipidoses
- B-glucosidase deficient
- glucosylceramide accumulates
Sphingolipidoses in general
Lisosomes—acidic hydrolase, accumulation of substrate
List sphingolipidoses that are characterized with blindness and/or cherry red spots
- Tay-Sachs (gangliosides)
- Sandhoff (similar to TS)
- Niemann Pick (A&B)
Sphingolipidid in the eye
- normal tensive
- absent in hypertensive Aq humor
- increased IOP/glaucoma
Describe the structure of steroids, sterols, cholesterol, bile acids, and bile salts, and be able to identify the shared components
- ABCD ring (sterol nucleus)
- acetyl CoA makes the ring
Explain the structure and functions of free and esterified cholesterol
Free cholesterol
-found in membranes of all animal cell membranes
Esterified cholesterol
- not found in membranes
- most of the plasma cholesterol is in this form
Identify the central organ for cholesterol metabolism
Liver
Discuss the origin of gall stones and know the possible causes for their formation
Too much cholesterol causes gall stones
-too little bile salt
Possible causes
- inefficient enterohepatic cycling of bile salts
- liver dysfunction
- other idiopathic reason
Describe the size, density, composition and functions of lipoproteins present in plasma: the chylomicrons, VLDL, remnant particles, low density lipoproteins and high density lipoproteins
Chylomicrons:
-size vary depending on the meal content, but in general they are the largest in size, least dense, and contain the highest percentage of fat. Produced by gut cells
VLDL:
-very similar to chylomicrons but produced by hepatocytes, smaller and more dense, containing a high percentage of fat reflecting their primary role to distribute fay away from the liver or peripheral tissues (more phospholipids)
LDLs:
- highest percentage of cholesterol, reflecting their role to distribute cholesterol to tissue expressing the LDL receptor
- produced from VLDL via lipolysis in the bloodstream.
- Bad cholesterol
HDLs
- smaller and denser
- contain the highest percentage of proline, reflective of one of the roles (reservoir of lipoproteins)
- second largest percentage of cholesterol
- good cholesterol
Explain why accurate plasma lipid profiles require blood collection and further analysis in fasted patient.
- the size and density of the lipoproteins are routinely used in plasma lipid profiling as part of the separation process
- accurate profiles require blood collection and further analyses in fasted patients
Describe the cell types and sites for synthesis of chylomicrons and outline the general steps in their assembly
Chylomicrons
- formed in the ER and Golgi of intestinal mucosal cells using Apo B-48
- MTP transfers lipids to ApoB-48
- Nascent chylomicrons are excreted through the plasma membrane into the lymph
- from lymph they enter blood stream where they undo modifications and acquire additional Apo-es from HDL
- peripheral calls expressing LPL hydrolyze TAGs to FA and glycerol
- remaining is cleared form the blood stream by the liver
Describe the cell types and sites for synthesis of VLDL and outline the general steps in their assembly
- assembled in the ER and golgi of liver cells . Full length Apo B-100
- VLDL are directly secreted into the blood stream, acquire APO C-II and Apo E from HDLs
- LPL hydrolyzes VLDLs and TAGs
- VLDVL decrease in size and becomes denser
- Apo B-100 remaining in the LDL is a ligand recognized by the LDL receptors on the surface of cells and taken up via endocytosis in the lysosomes acid hydrolysis break down lipids
Describe the cell types and sites for synthesis of HDL and outline the general steps in their assembly
- reverse cholesterol transport: the effluent of cholesterol from peripheral tissues to HDL
- HDLs are considered good, however the ratio to LDL is usually considered
- APO A-1 produced in liver and intestinal cells and secreted in the circulation as free apolipoprotein
- interacts with ABCA1 transporter that transfers phospholipids and cholesterol from peripheral cells to lipid poor Apo A-1
- converted to discoidal particles
- reservoir of Apo CII and Apo E
- HDL particles are not taken up by the liver but instead they transfer cholesteryl eters from the HDL to the liver via CETP
Discuss the main component processes of atherogensis-oxidized LDL, endothelial dysfunction, arterial deposition of lipids, chronic low grade inflammation and outline the risk factors for increases LDL modification
Oversupply of cholesterol:
- inhibit de novo synthesis of cholesterol
- inhibit expression of LDLR. Decreased LDL uptake
- activate ACAT to produce more CE
- atherosclerosis
Factors increasing the propensity for producing modified LDL in circulation
- high blood sugar
- oxidative stress
- chemicals present in tobacco smoke
- smokers and diabetics will have an increased risk of cardiovascular disease
- some protective effect can come from antioxidants (E,C,A)
Abetalipoproteinemia (Bassein-Kornzweig syndrome)
- defects in the microsomal transfer protein (MTP)
- progressive degeneration of the retinue that can progress to near blindness (due to deficiency of vitamin A, retinol)
Cortisol function
Normal: stress hormone, increase GNG, anti inflammatory, muscle protein breakdown, immune response
Too much
-cushing syndrome (obesity, moon face)
Aldosterone functions
Normal: renal reabsorption of Na+ and excretion of K+
Too much
-increased Na+, decreased K+
Too little
-decreased Na+, increased K+,
Large sodium loss in urine, hypotension
Testosterone function
normal
-promote male development
Too much
-masculinization of females
Too little
-feminization of males
Estrogens functions
Normal
-promote female development
Describe the mechanisms by which glycogen synthesis and degradation are counter regulated wot meet the needs of the body as a whole (hormonal regulation)
2 regulatory enzymes: glycogen phosphorylase and glycogen synthase
Glycogenolysis activated
- blood glucose drops
- activated in muscle and liver
Why glycogenesis activated
- muscle—when resting and fed
- liver—when fed
