FDN Exam 2 Flashcards
Things I can't remember
Major fatty acid we synthesize in our body?
Palmitic acid (16:0)
Two dietary essential fatty acids?
- Linoleic 18:2(9,12), omega 6
2. Alpha-Linolenic 18:3(9,12,15), omega 3
FA precursor of prostaglandins?
Arachidonic acid 20:4(5,8,11,14)
Is arachidonic acid an omega-6 or omega-3 FA?
Omega-6!
ATP yield from one glucose molecule?
38 ATP
ATP yield from palmitate?
129 ATP
Main tissues that use FA as the primary energy source?
liver, heart, and skeletal muscle
Two bile salts that emulsify dietary fats?
Glycocholic and taurocholic acids
Primary products of lipid digestion that are absorbed (and then subsequently repackaged)?
Free fatty acids, 2-monoacylglycerol, cholesterol, and remaining pieces of phospholipids
Are short and medium FFA packaged into chylomicrons?
Nope!
Doesn’t apply to short and medium chain fatty acids. They’re so short that they are soluble in water. Absorbed across epithelial membrane directly. Excreted into blood stream directly -> albumin binds immediately. Delivers these to all the tissues. Albumin’s job is to deliver through the blood stream
What omega FA is anti-inflammatory?
omega 3
omega 6 are pro-inflammatory
What foods contain omega 6 PUFAs?
Some nuts, avocados, olives, some oils (sunflower and corn oil)
What foods contain omega 3 PUFAs?
plant oils (flaxseed and canola) and some nuts, certain “fatty” fish (tuna, salmon, herring, etc)
Ex: DHA and EPA
FA Synthesis building blocks and enzyme?
One acetyl CoA + multiple malonyl CoAs
Fatty Acid Synthase
How does Acetyl CoA get from the mitochondria to the cytoplasm for FA synthesis?
The citrate-oxaloacetate shuttle
Citrate synthase in mitochondria and then ATP citrate lyase in the cytoplasm
Oxaloacetate diffuses back into mitochondria
Enzyme that converts acetyl CoA to Malonyl CoA in the cytoplasm? What inhibits and stimulates that enzyme?
Acetyl CoA Carboxylase (ACC)
Stimulates: citrate (we have energy. let’s make fat storage!)
Inhibits: Palmitoyl CoA and PKA (breaking down fats, stop making storage!)
Do we store fat in the liver?
Nope. If we do then there is an issue (like alcoholic fatty liver disease!)
What activates hormone sensitive lipase (HSL) in adipose tissue?
Epinephrine or glucagon
Signal cascade from GPCR -> -> -> PKA -> HSL activation
What inhibits hormone sensitive lipase?
Insulin
How do fatty acids get from the cytoplasm to the mitochondria to undergo beta oxidation?
the acyl-carnitine/carnitine transporter
What is cholesterol a precursor for?
Bile acids, steroid hormones, and vitamin D
What is the only method of cholesterol removal from the body?
Bile secretion
What makes up the hepatic pool of cholesterol?
- diet (chylomicrons)
- Hepatic synthesis
- Other tissues (HDL)
What tissues synthesize cholesterol?
Virtually all of them
Highest rates in the liver, intestines, adrenal cortex, and reproductive tissues
Primary enzyme responsible for the production of cholesterol?
HMG CoA Reductase
FA synthesis occurs where?
Primarily cytoplasm of hepatocytes
Some in adiposes
FA breakdown/B-oxidation primarily occurs where?
Mitochondria of all cells
Four plasma lipoprotein particles?
- chylomicrons
- VLDL
- LDL
- HDL
What apolipoprotein is unique to chylomicrons?
B-48
What apolipoproteins does a “nascent” chylomicron pick up in order to make it “mature”?
Apo E and Apo C-II from HDL
What apolipoprotein interacts with lipoprotein lipase (LPL) in tissue capillaries? Explain what this interaction does.
Apo C-II activates LPL to degrade the chylomicron TAG to fatty acids and gylcerol
When ~90% of TAG is removed, Apo C-II returns to HDL. Now we have a “chylomicron remnant” with Apo B-48 and Apo E
What apolipoprotein allows liver cells to recognize chylomicron remnants and take them up?
Apo E
Where is lipoprotein lipase (LPL) highest?
heart tissue to provide adequate FA for energy
Describe insulin’s effects on muscle LPL and adipose LPL after a meal
Muscle: inhibits LPL. If glucose is high skeletal muscle would rather use that.
Adipose: stimulates LPL so the adipose tissue can store.
What apolipoprotein is unique to VLDL?
Apo B-100
What apolipoproteins does a “nascent” VLDL particle pick up in order to make it “mature”?
Apo C-II and Apo E from HDL
What apolipoproteins does a TAG-depleted VLDL have?
Just Apo B-100
Apo E and Apo C-II return to HDL
What causes a VLDL to become LDL?
TAG loss and protein changes (loses apo E and apo C II)
Where is VLDL produced?
In the liver! Contains TAG and cholesterol/cholesteryl esters (CE)
Job of LDL?
Delivers cholesterol to all other tissues; they have apo B-100 receptors that endocytose the LDL particle
Also delivers LDL particles to the liver. Because if we have excess LDL particles then we want the liver to remove them
What percentage of total plasma cholesterol is in LDL particles?
70%
What protein is responsible for LDL receptor degradation?
PCSK9
Brings the receptors to a lysosome to die
Besides hypercholesteremia type IIa, what other mechanisms can cause hypercholesteremia?
- Defects in apo B-100. We have a perfectly good LDL receptor but it cannot recognize a defective apo B-100
- Increased activity of PCSK9. We degrade too many LDL receptors/don’t recycle enough
Both result in blocked LDL clearance in the liver/increased LDL in the blood
When a lipid or apo B has been oxidized, what receptor interacts with it & takes it up?
Scavenger receptor (SR-A) on macrophages
There is no down-regulation of this receptor by cholesterol, so high levels accumulate in the macrophage transforming it to a foam cell
What is the primary cause of atherosclerosis?
Excess LDL-derived cholesterol
What is HDL’s job?
Take excess cholesterol from extra hepatic tissues and bring it back to the liver.
This is called “reverse cholesterol transport (RCT)”
Note: inverse relationship between plasma HDL levels and atherosclerosis
What can raise HDL levels?
Estrogen and exercise
How is cholesterol exported from cells into plasma?
Via the ABCA1 transporter
How does a nascent HDL particle (HDL3) become HDL2?
The plasma-facing enzyme LCAT (lecithin:cholesterol acyltransferase) is bound to HDL and esterifies free plasma cholesterol. This allows HDL3 to become cholesteryl ester rich and thus HDL2
How is HDL2 taken up by the liver?
Endocytosis
It’s contents are released into the hepatic cholesterol pool
Where are nascent HDL particles made?
the liver and the small intestines
How does excess cholesterol impact gene expression?
- Inhibits expression of HMG CoA reductase gene slowing synthesis
- Inhibits expressions of the LDL receptor gene limiting further entry of cholesterol into cells
What does the cell do with excess cholesterol?
Esterifies it via acyl CoA:cholesterol acyltransferase (ACAT). The cholesterol esters are stored in the cell.
ACAT is allosterically stimulated by excess cholesterol
How much can diet changes decrease your cholesterol?
Modestly. Only 10-20%
How much can statin drugs decrease your cholesterol?
By 30-60%
Four treatments for elevated cholesterol
- Statins (inhibit HMG CoA Reductase)
- Bile acid binding resins (increase conversion of cholesterol to bile acids)
- PCSK9 Inhibitors (increase LDL receptor recycling)
- Cholesterol absorption inhibitors
Plasmalogens
Phospholipids that have a long-chain hydrocarbon at carbon 1 via an ether linkage
Sphingolipids
Have a sphingosine backbone instead of glycerol
Sphingomyelin
Sphingolipid with phosphocholine at carbon 3
Cerbrosides, globosides, and gangliosides are what?
Glycolipids
What determines blood groups?
Glycosphingolipids
We have antibodies opposite to the antigen/glycosphingolpid that we have. i.e. Type A has anti-B antibodies
Prostaglandins, leukotriences, and thromboxanes are what?
Lipid-derived signaling molecules
Where is arachidonic acid released from?
Membrane localized phosphotidylinositol (PI) by phospholipase A2
What do aspirin and ibuprofen inhibit?
Cox1/2 enzymes and the conversion of arachidonic acid into prostaglandins and thromboxanes (inflammatory responses)
What does Celebrex inhibit?
Cox 2 pathway specifically
What is a vitamin?
An essential micronutrient that we cannot synthesize in sufficient amounts
What are the fat soluble vitamins?
A, D, E, K
Vitamin A
Retinoid family of molecules. Essential for vision, reproduction, growth, maintenance of epithelial tissue, and immune function
Retinol
Dietary vitamin A found in animal tissues (storage form)
11-cis retinal
Critical for vision. Aldehyde of retinol
Deficiency results in night blindness
Retinoic acid
Used to treat acne and skin aging as well as promyelocytic leukemia
What is active vitamin D? How is it generated?
1,25-dihydroxycholecalciferol
Conversion from 7-dehydrocholesterol via UV irradiation
Or activation of inactive dietary precursors
What does vitamin D control?
Serum calcium and phosphate levels via transcription
It’s a sterol with a hormone-like function
Dietary sources of vitamin D?
Fatty fish, liver, egg yolk
Vitamin K
required for the synthesis of proteins involved in blood clotting
A deficiency is rare
Vitamin E
Functions as an antioxidant
Vitamin E is used to slow the progress of what age-related vision condition?
Macular degeneration
Vitamin E deficiency in adults usually results from
Abetalipoproteinemia - defective formation of chylomicrons and VLDL
Where does synthesis of steroid hormones occur?
Adrenal cortex, ovaries/placenta, and testes
How are steroid hormones excreted once they’re turned over?
They are converted to inactive, water-soluble products in the liver and eliminated in feces and urine
Where are cortisol, aldosterone, and androgens made?
In the adrenal cortex
Cortisol function
Synthesis is increased by stress. Functions to increase protein turnover (makes AAs for gluconeogenesis) and decreases inflammatory and immune responses
Glucocorticoid
Aldosterone function
Acts on the kidneys to increase Na+ and water resorption and to increase K+ excretion
Produced in response to a decrease in the plasma Na+/K+ ratio and by the hormone angiotensin II
Increases BP!
Mineralcorticoid
Androgens
Weak androgens are made in the adrenal cortex and converted by the enzyme aromatase to testosterone in the testes and to estrogens in the ovaries (pre-menopausal women) and in the breast (post-menopausal women)
Estrogen controls what?
Menstrual cycle & secondary female sex characteristics
Progesterone controls what?
Secretory functions of uterus and mammary tissue + implantation/maturation of ovum
Three ketone bodies?
Acetoacetate, beta-hydroxybutyrate, and acetone
Can the liver use ketone bodies as fuel?
No. It lacks thiophorase, the enzyme needed to convert ketone bodies back to acetyl CoA
Is DKA seen most-often in Type 1 or Type 2?
Type 1
Ref: Kilberg’s Lipid Homeostasis lecture
Fuel source and priority during phase 1 of fasting?
Source: glycogen/glucose
Priority: Blood glucose
Fuel source and priority during phase 2 of fasting?
Source: Proteins/AA
Priority: Blood glucose
Fuel source and priority during phase 3 of fasting?
Source: Lipids/ketone bodies
Priority: Avoiding death
Is adipose tissue involved in phase 1 of fasting?
Nope!
It mobilizes in phase 2
What is the glucose-alanine cycle? When does it occur?
It happens during the first phase of fasting. Slowly mobilizing proteins
Similar to the Cori Cycle. Pyruvate is transaminated in the muscles to alanine. In the liver alanine is de-aminated (NH to Urea cycle) back to pyruvate and that pyruvate goes into gluconeogenesis
Where is the #1 place people are protein deprived?
The hospital
Know this!! He does research in this!!!
Is insulin still available during phase 3 starvation?
Yes, but very very little
Remember: glucagon stimulates a little insulin release to keep itself in check
How many calories is in one pound of fat?
3500
Why isn’t injected insulin as good as the real thing?
Because in the islets, insulin flows outward toward the beta cells. Insulin inhibits glucagon release, stopping glucagonemia. Unchecked type 1 diabetes is absolute glucagonemia.
Who enters a coma first: a diabetic patient or a fasting patient?
A diabetic
A fasting patient has some insulin to keep things in check. The diabetic does not so everything runs rampant
Conformations of transporter?
Open, closed, inactivated
Properties of channels
- Fast transport of ions across membrane
- Move ions down their conformation gradient
- Can be ligand, voltage, or mechanically gated
Conformations of a uniporter/transporter?
Outward-facing, inward-facing
Properties of uniporters/transporters
- 1 molecule transported per confirmation change
- Medium rate
- Passive movement down concentration gradient
- Can switch directions depending on the gradient
Properties of active transporters/pumps
- Conformational change linked to ATP hydrolysis
- Slow rate
- Against concentration gradient
- 1 to several molecules per conformation change cycle
Secondary active transport
Movement of an ion down its concentration gradient coupled to transport of ion/molecule against concentration gradient
Symporter or antiporter
Where are GLUT4 transporters found?
Skeletal muscle, adipocytes, and the heart
Insulin responsive
Where are SGLT1 transporters found?
Intestines, distal renal tubules
High affinity, low capacity for glucose
Where are SGLT2 transporters found?
Proximal renal tubules
Low affinity, high capacity for glucose
In the Na+/glucose symporter how many of each molecule move inside the cell?
2 Na+, 1 glucose
SGLT2 Inhibitors
Block SGLT2 in the renal proximal tubules. SGLT2 reabsorbs ~90% of glucose in PCT. Inhibition results in glycosuria and lower blood glucose levels -> great for treating hyperglycemia found in diabetes
What is the most abundant transmembrane protein in RBC plasma membrane?
AE1. Anion exchange 1 - antiport of chloride and bicarbonate anions
Chloride shift
In systemic capillaries, HCO3- is transported out of RBC and Cl- is transported in to balance the negative charge
How is CO2 transported in plasma?
As HCO3-
Two antiporters used to raise intracellular pH?
- Na+/H+ Exports H+ from cells (gets rid of the proton)
2. Na+HCO3-/Cl- imports Na+HCO3- into the cell (brings in a base)
One antiporter used to lower intracellular pH?
Cl-/HCO3- Exports HCO3- from the cell (gets rid of a base)
What mediates channel selectivity?
Ion size and interactions with the selectivity filter (amino acids in the pore)
Those ions meant for the channel have a low activation energy. Those ions not meant for the channel have a very high activation energy
Are channels opened or closed in their resting state?
Either!
What is the rate-limiting step in transporters and pumps?
The conformational change
Do channel conformational changes regulate state or rate?
State
There is no rate-limiting step in channel transport
Where is aquaporin 1 located?
RBCs
Mediates rapid osmotic water flow
Where is aquaporin 2 located?
Kidney collecting duct
Regulates urine osmolality
What prevents proton hopping in aquaporins?
Water molecules are transported single file
Properties of membrane pumps
- Energy source is ATP hydrolysis
- Transport against a gradient
- One direction
- Speed is slower than transporters and channels
Three types of ATP-powered pumps?
- P-type
- F and types
- ABC transporters
Properties of P-Type Pumps
- Only pumps ions
- Alpha and beta subunits
- Alpha subunit is phosphorylated, inducing a conformational change (E1/E2 conformations)
Examples: Na+/K+ pump, Ca2+ pump in plasma membranes and sarcoplastic reticulum (SERCA!)
Describe E1/E2 conformations in SECRA Ca2+ ATP pump
E1 is inside-facing/cytosol facing. Has a high affinity for Ca (so it can collect it)
E2 is outward-facing/lumen facing. Has a low affinity for Ca (so it gets released)
Phosphorylation favors E2. De-phosphorylation favors E1.
(Same mechanism in Na+/K+ pump)
Properties of F-type pumps
- Only pumps protons!!
- Synthesizes ATP
- Has catalytic F1 sector
- F0 is multiple transmembrane subunits
- NO subunits phosphorylated
Example: inner mitochondrial membrane (ATP synthase)
Properties of V-type pumps
- Only pumps protons!!
- used to acidify compartments of the cell (i.e. the lysosome)
- Has catalytic V1 sector
- V0 is multiple transmembrane subunits
- NO subunits phosphorylated
Example: osteoclast plasma membrane V-type ATPase secretes HCl into absorption lacuna
Properties of ABC Transporter superfamily
- Transport ions, sugars, amino acids, lipids, and peptides
- Very diverse; not homogenous like P, F, and V type pumps (not even all pumps!!)
- Contains four domains (2 A and 2 T) or as 1 multidomain protein
- NO subunit phosphorylation during the transport cycle
Example: Multidrug resistance transporter, CFTR
What is the most common MDR transporter?
permeability glycoprotein (P-gp)
How is the Cl- channel activated in CFTR?
Phosphorylation of R domain (regulatory domain) and ATP hydrolysis by the nucleotide binding domains (NBD1 and 2)
What two things does cholera toxin ultimately cause in the intestinal cells?
- Efflux of Cl- ions and flow of water across epithelium into lumen
- Inhibition of Na+ and Cl- absorption (by Na+/H+ anion exchanger)
How does rehydration therapy work during cholera?
Since cholera toxin doesn’t effect the Na+/glucose symporter, rehydration therapy are solutions containing salts and glucose. Water will follow glucose back into the cells
Resting membrane potential is due primarily to what?
K+ leak channels
When K+ electrochemical gradient = 0, what is the resting membrane potential?
-59 mV
Describe beta cell insulin secretion
- Glucose enters the cell and undergoes glycolysis then TCA cycle & oxphos to make ATP
- Increase in ATP in cytoplasm closes ATP-gated K+ channel
- This closure triggers a membrane depolarization sensed by a voltage-gated Ca2+ channel
- This channel opens and Ca2+ flows in
- Cytosolic Ca2+ induces fusion of secretory vesicles with plasma membrane
Requirement for action potentials?
Resting plasma membrane potential in an excitable cell
What ensures unidirectional action potential propagation?
Na+ channel inactivation
What is the clinical presentation of hypoglycemia?
Adrenergic symptoms and neuroglycopenia
What is “adrenergic symptoms”?
Systemic effects of catecholamines (adrenaline) from the adrenal medulla
Examples: tachycardia, sweating, palpitations, anxiety, feeling cold, sweating
What is neuroglycopenia?
The consequences of low blood glucose on CNS function
Examples: decreased consciousness, faintness, slurred speech, hunger, incoordination, dizziness, confusion
Paresthesias
pins and needles feeling
symptom of neuroglycopenia
What is Whipple’s Triad?
The clinical diagnosis of hypoglycemia. Must have low blood glucose (< 45mg/dL), symptoms of hypoglycemia, and have a positive response to glucose administration
How is hyperinsulinemic hypoglycemia defined?
Increased insulin above reference interval
OR
Insulin/glucose ratio is inappropriately elevated (> .30)
What drugs release insulin from the pancreas?
Sulfonylurea class (glipizide, glyburide, and glimepiride) or meglitinides
Both of these are used to treat type 2 diabetes
What non-diabetes drugs can cause hypoglycemia?
Aspirin poisoning, acetaminophen poisoning, and ethanol
What is in the differential diagnosis of non-hyperinsulinemic hypoglycemia?
Drugs (alcohol, aspirin, tylenol), hormone deficiencies, liver and renal diseases, inborn errors of metabolism
Insufficiencies in what four hormones can cause hypoglycemia?
Glucagon, epinephrine, cortisol, and growth hormone
Would we expect to see ketones in the urine during hypoglycemia?
Yes
How does ethanol consumption lead to hypoglycemia?
Conversion of ethanol to aldehyde then ethanoic acid requires NAD+. Conversion of lactate to pyruvate (necessary step in the Cori cycle to regenerate glucose) also requires NAD+. Theoretically we will deplete the NAD+ stores and not be able to generate pyruvate and run gluconeogenesis
What is the first diagnostic test when evaluating hypogylcemia?
If it is hyperinsulinemic or non-hyperinsulinemic
What lab results are typically observed in hyperinsulinism?
Urine negative for ketones, BHB not elevated and may be suppressed, normal FFA concentrations
These reflect the suppressive effect of hyperinsulinism on the generation of alternative fuels
What should be considered if a patient has biochemical findings compatible with hyperinsulinism but their insulin is actually suppressed?
Mesothelial tumor that secrete IGF-II
Remember: biochemical findings of hyperinsulinism are normal BHB, no urine ketones, and normal levels of branched amino acids & FFA
On average, what percentage of total body weight is water (in adults)?
60%
Just know that its higher in babies and lower in old people
What is the distribution of water in extra vs. intracellular spaces?
2/3 in intracellular
1/3 extracellular
How is extracellular water distributed?
75% interstitial space
25% plasma
~0% negligible in transcellular fluids like CSF, joint fluid, cavities, etc
What is usual blood volume?
85 mL/kg
How do you calculate hematocrit?
RBC volume (or mass)/blood volume
How can you measure a fluid volume?
Add a known amount of dye to a volume to be measured and then measure the dye concentration
Volume = Mass added / (Mass/Volume [Concentration)] —> Mass * (Volume/Mass) = Volume
** dye must be contained within the measured compartment
What electrolytes and proteins are high intracellularly?
K+, Mg2+, PO4—, protein (neg charge)
What electrolytes and proteins are low intracellularly?
Na+, Ca2+, HCO3-
What electrolytes and proteins are high extracellularly?
Na+, Ca2+, HCO3-, Cl- (slave to Na+)
What electrolytes and proteins are low extracellularly?
K+, Mg2+, protein
Where is protein level greater: plasma or interstitum?
Plasma
Remember: liver secretes albumin directly into plasma
Since proteins have a slight negative charge there will be more cations (re: Na+) in the plasma vs. interstitium
What regulates the distribution of water between the intracellular and extracellular spaces?
Osmolality
What is osmolality?
Particle # per kg fluid weight
How can plasma molality be estimated?
(Na+ x 2) + (glucose/18) + (BUN/2.8)
What is a normal plasma osmolality range?
275 - 295 mOsm
What regulates the distribution of fluids between the interstitial space and the plasma?
Hydrostatic pressure, oncotic pressure, and lymphatic function
70-75% of oncotic pressure is due to what?
albumin concentration
How is O2 delivery to tissues measured?
cardiac output * O2 content of the blood
What is the formula for minute volume?
MV = Respiratory rate * tidal volume
pCO2 and minute volume have what kind of relationship?
Inverse
In chronic respiratory acidosis why is HCO3- typically elevated?
The kidney retains Na+ HCO3- as renal compensation
Note: this takes days to weeks, which is why this is in CHRONIC respiratory acidosis
Sensible vs. insensible losses
Sensible losses can measure the fluid lost
Insensible losses cannot be readily measured
What is the general, basal fluid requirement?
1500 mL/M^2 per day
What are the basal fluid losses?
Urine: 900 mL/M^2
Stool: 100 mL/M^2
Insensible loss: 500 mL/M^2
How do you calculate fluid requirements based on body weight?
1-10 kg (1st 10 kg) is 100mL/kg
11-20 kg (2nd 10 kg) is 50 mL/kg
20 and higher is 20 mL/kg
What does effective serum osmolality exclude?
Urea
Because urea freely crosses cell membranes and does not cause water shifts
How is a hyperglycemic hyperosmolalic state characterized?
Significant hyperglycemia, some degree of mental status changes, and usually little or no acidosis or ketosis
How many cm in an inch?
2.54 cm per inch
How many lbs in a kg?
2.2lbs per kg
How do you calculate BMI?
kg/M^2
What amino acid can be transaminated to pyruvate?
alanine
What amino acid can be transaminated to a-ketoglutarate?
glutamate
What amino acid can be transaminated to oxaloacetate?
aspartate
Three sources of amino acids?
- Digestion of protein in food
- Intracellular proteolysis
- de novo synthesis
Nutritionally essential amino acids?
HV MILK FTW
(High Value MILK, “for the win”)
Histidine
Valine
Methionine
Isoleucine
Leucine
Lysine (K)
Phenylalanine (F)
Threonine
Tryptophan (W)
Conditionally essential amino acids?
Arginine (for growth in childhood and pregnancy)
Tyrosine (when phenylalanine is inadequate)
Cysteine (when methionine is inadequate)
What does the intracellular protein turnover rate depend on?
metabolic state.
Ex: Greater protein degradation when nitrogen intake is low
Two major pathways for intracellular protein turnover?
- Lysosomal/phagolysosomal pathway (isoelectric expansion and proteolysis)
- Ubiquitin-dependent pathway (tagged proteins are brought to the proteasome)
When do we need a positive nitrogen balance?
During periods of growth (childhood, pregnancy), in healing of wounds, and convalescence
Marasmus is due to inadequate intake of what?
Calories. Extensive tissue and muscle wasting is seen
Kwashiorkor is due to inadequate intake of what?
Protein! Otherwise adequate caloric intake
Transaminases use what as a coenzyme?
Vitamin B6
PLP - pyridoxal phosphate
PMP - pyridoxamine phosphate
What is the Keq of transamination reactions?
1
We have the same bonding in substrates and products
What is the transamination reaction that turns alanine into pyruvate?
Alanine + a-ketoglutarate —> glutamate + pyruvate
What is the transamination reaction that turns oxaloacetate into aspartate?
Glutamate + oxaloacetate –> a-ketoglutarate + aspartate
What does glutamate dehydrogenase do? Where does it function?
It is the major route for oxidative deamination. Takes glutamate + H2O + NAD+ and makes a-ketoglutarate + NH3 + NADH
GDH is located in the mitochondrial matrix
What can be coupled with transaminases to allow the oxidative degradation of 14 amino acids?
glutamate dehydrogenase
- NADH goes to OxPhos
- a-KA enters the TCA cycle
- Excess NH4 goes to the Urea Cycle
What two substrates determine the direction of GDH?
NAD+ and NADPH
NAD+ : oxidative deamination route
NADPH: reductive amination route
Three routes for deamination?
- Glutamate dehydrogenase
- Glutaminase (glutamine to glutamate + NH3)
- Asparaginase (asparagine to aspartate + NH3)
What is the main way the body traps NH3?
In glutamine via glutamine synthetase (glutamate + NH3 = glutamine)
Glutamine is the major nitrogen shuttle between organs, avoiding the direct transfer of NH3
Where is the main site of NH3 detoxification in the body?
The liver
Where in the cell does the Urea cycle take place?
Partially in the mitochondria and the cytoplasm (citrulline is shuttled out of the mitochondria and then ornithine back in)
What stimulates the biosynthesis of all five urea cycle enzymes after a meal?
Glucagon
This make sense because glucagon wants gluconeogenesis to run and we need a-ketoacids to make this happen. The urea cycle makes a-ketoacids
What two amino acids are also powerful regulators of the urea cycle?
Arginine and glutamate
What amino acids cannot have their transamination coupled with GDH?
Proline, hydroxyproline, threonine, lysine, and histidine
A deficiency in n-acetyl-glutamate synthetase results in what?
hyperammonemia (we can’t excrete excess NH3 through the urea cycle)
What are the primary and secondary deficiencies in NAGS?
Primary: mutation in the NAGS gene
Secondary: mitochondrial changes interfering with NAGS function
What molecule can restore or improve Urea cycle function in the presence of a NAGS deficiency?
Carbamoylglutamate
What prevents ammonia re-entry into circulation in the liver?
the acinus
The periportal hepatocytes have a high/low affinity for NH3?
What enzyme(s) take up NH3 in this area?
low affinity/high clearing of NH3
Glutaminase and the urea cycle enzymes take up NH3
The perivenous scavenger cells have a high/low affinity for NH3?
What enzyme(s) take up NH3 in this area?
High affinity/low clearing
Glutamine synthetase takes up NH3 here. Remember that Gln Syn. uses ATP so it’s not going to be clearing a ton of NH3 like the periportal hepatocytes
What amino acid is the source of creatine?
arginine
What is the “ATP buffer” in muscle?
Creatine-P
What is the breakdown product of creatine-P in our muscles?
Creatinine
Clearance rate of creatinine tells us how well the kidneys are working
Three ways that glutamate can be made?
- Transamination with a-KG
- Reductive amination via GDH
- Hydrolysis of glutamine
How is glutamine made?
Exclusively by glutamine synthetase
Two ways aspartate is made?
- Transamination of oxaloacetate
2. Hydrolysis of asparagine
What two amino acids are required to make asparagine?
Aspartate and glutamine
The production of asparagine also produces what other amino acid?
Glutamate
How is alanine formed?
Transamination of pyruvate only
** useful in the alanine/pyruvate shuttle in clearing NH3 from tissues
What amino acid is necessary for the production of proline?
Glutamate
It’s reduced first to glutamate semi-aldehyde and then a cyclic compound is formed & reduced to make proline
Glutamate semi-aldehyde can be transaminated to what urea cycle intermediate?
L-ornithine
What role does vitamin C play in the production of hydroxyproline?
It restores the functionality of the prolyl hydroxylase enzyme by converting Fe(III) to Fe(II)
Precursor molecule of serine?
3-phosphoglycerate
How many ways can glycine be made?
What two other amino acids are glycine precursors?
4
Glutamate and Serine
Tyrosine is made from what amino acid precursor?
Phenylalanine
In what three ways do humans get nucleotides?
- Dietary intake of RNA and DNA
- Salvage of bases (reuse reduces need for additional foodstuffs)
- de novo synthesis
What enzyme is responsible for the reaction that takes dUMP and Methylene-THF and makes dTMP?
Thymidylate Synthase
What molecule stops thymidylate synthase in a suicide inhibition mechanism?
Flurouracil
What two drugs inhibit folate reductase and dihydrofolate reductase?
Methotrexate and Aminopterin
What energy source is needed for the conversion of IMP to AMP?
GTP
What energy source is needed for the conversion of IMP to GMP?
ATP
What amino acid is needed for the conversion of IMP to AMP?
Aspartate
What amino acid is needed for the conversion of IMP to GMP?
glutamine
Excess levels of AMP inhibit the production of what two products in purine nucleotide synthesis?
AMP and PRPP
Excess levels of GMP inhibit the production of what two products in purine nucleotide synthesis?
GMP and PRPP
Excess levels of IMP inhibit the production of what product in purine nucleotide synthesis?
5’-P-Rib-NH2
What enzyme does high levels of AMP activate (ultimately turning off purine pathway enzymes)?
AMP-Protein Kinase
Enzyme responsible for AMP to ADP rxn?
Adenylate Kinase
Enzyme responsible for GMP to GDP rxn?
GMP kinase
Enzyme responsible for ADP to ATP rxn?
Trick question! It’s oxidative phosphorylation
Enzyme responsible for GDP to GTP rxn?
Nucleoside Diphosphate Kinase
What enzyme converts AMP back to IMP?
AMP deaminase
What enzyme converts GMP back to IMP?
GMP reductase
What enzyme salvages hypoxanthine and guanine from degradation?
hyoxanthine:guanine phosphoribosyl transferase (HGPRT)
Is adenine salvaged by HGPRT?
Nope
What enzyme converts adenine to hypoxanthine?
Adenine deaminase
List the steps from GMP to Xanthine
GMP
Guanosine
Guanine
Xanthine
Then Uric Acid!
List the steps from AMP to Xanthine
AMP IMP Inosine Hypoxanthine Xanthine
Then Uric Acid!
Ribonucleotide Reductase
Enzyme responsible for making 2’-deoxyribonucleotides needed for DNA synthesis
Indirect electron transfer from NADPH ultimately reduces RNR
Substrates for RNR in eukaryotes?
ADP, GDP, CDP, AND UDP
NO TDP! We get dTMP via thymidylate synthase
This substrate specificity gives evidence of transition from RNA to DNA world
How is RNR regulated?
RNR catalysis is controlled by allosteric specificity sites
This allows RNR to sense the relative abundance of NDPs, to make the right amount of each, and to prevent overproduction of any single dNTP
What do you need to make hemoglobin?
- Hb alpha and beta chains
- Porphyrin (protoporphyrin IX)
- iron
What is the differential diagnosis of a microcytic anemia?
Defects in hemoglobin synthesis
- Hb chain imbalance (thalassemia)
- Impaired porphyrin synthesis (lead ingestion or sideroblastic anemia)
- Iron deficiency or lack of iron availability
What does sideroblastic anemia do to Hb synthesis?
It impairs porphyrin synthesis
What is thalassemia?
Defect in hemoglobin chain synthesis (there is an imbalance)
Hemoptysis
coughing up blood
Hematemesis
vomiting blood
Hematochezia
fresh blood per rectum
Melena
black stools because of bleeding
Hematuria
blood in urine
Menorrhagia
excessive menstrual bleeding
Is there unbound iron in plasma?
NOPE. Would be toxic to us
What is serum iron?
Iron that is bound to transferrin in the blood
Remember: no free, unbound iron is in the blood
What state does iron circulate in?
The ferric state (Fe III)
What is “total iron binding capacity” (TIBC) of serum?
If transferrin was 100% saturated, how much iron would that be?
How do you calculate transferrin saturation?
Serum Iron / TIBC
What percentage of transferrin molecules in the blood are occupied with iron? What percentage are open?
1/3 occupied, 2/3 open
What is ferritin?
Cellular iron is stored in ferritin. We obviously cannot measure intracellular stores of iron but we can measure the ferritin that leaks into the plasma
What is hemosiderin?
Ferritin that has been engulfed by a lysosome. This is stainable and viewable within a cell
What causes an increase in ferritin but NOT an increase in total body iron?
Chronic disease/inflammation, liver disease, metabolic syndrome, and hemophagocytic syndrome
What is the normal range for total body iron?
3.5 - 5g
What percentage of iron in the body is functional vs. in storage?
75% functional, 25% storage
How much iron recirculates daily?
20-25 mg
How is iron balanced maintained?
We lose 1-2 mg per day via bleeding or sloughed enterocytes but we absorb 1-2 mg per day via duodenal enterocytes
What acid is necessary to proper digestion of iron?
HCl
