Stuff I Forget

Question 1

Which vitamin deficiencies can cause anemia?

Answer 1

1) pyroxidine (B6)–promotes RBC production
2) ascorbic acid–helps in the reduction of iron (Fe+3–>Fe+2)
3) Cu–ceruloplasmin (Cu) helps oxidize iron so it can bind to transferrin

Question 2

Which enzymes need cobalamin as a cofactor?

Answer 2

1) methylmalonyl CoA mutase (MMCoA mutase)–converts methylmalonyl CoA–>succinyl CoA, so all amino acids that follow this path need cobalamin (valine, isoleucine, threonine, methionine)
2) homocysteine methyltransferase–needs cobalamin to convert N5-methyl-THF back into THF, and to convert homocysteine back into methionine

Question 3

Which enzyme deficiencies can cause homocysteinuria?

Answer 3

1) homocysteine methyltransferase (makes homocysteine into methionine)
2) cystathionine beta-synthetase (makes homocysteine into cystathione, then cysteine)

Question 4

Which enzymes do NOT remove ammonia?

Answer 4

1) alanine transaminase (produces pyruvate and glutamate)
2) glutaminase (glutamine–>glutamate + ammonia)
3) serine dehydrogenase (serine–>pyruvate and free ammonia)
4) aspartate transaminase (NH3 still stuck to structure, no change)

Question 5

Which enzymes remove ammonia?

Answer 5

1) glutamine synthase (glutamate+ammonia–>glutamine)

2) glutamate dehydrogenase (ammonia + alpha-ketoglutarate +NADPH–>glutamate+NADP+)

Question 6

How are 1-carbon groups generated?

Answer 6

1) serine+THF–>glycine+N5, N10-methylene-THF
2) serine loses 1 carbon as it becomes glycine
3) glycine can become CO2 and NH4+
4) N5, N10-methylene-THF carries extra carbon group–this carbon used in rxns catalyzed by thymidylate synthase***
5) when N5, N10-methylene-THF loses the carbon group, it becomes N5-methyl-THF (rxn reversible only in methionine synthesis)

Question 7

Why does thymidylate synthase need dihydrofolate reducatse for max activity?

Answer 7

1) dUMP+N5, N10-methylene-THF–>dTMP+dihydrofolate, rxn catalyzed by thymidylate synthase
2) dihydroflate must be reconverted into THF via dihydrofolate reductase
3) THF then reacts with serine to form N5, N10-methylene-THF (generates glycine), so cycle can begin again!

Question 8

What’s a general summary of lipid metabolism?

Answer 8

1) chylomicrons deliver dietary-derived lipids to periphery, remnants returned to liver (apoE helps them get in liver)
2) VLDLs carry lipids made in liver to body cells
3) LDLs carry cholesterol around the body
4) LDLs receive cholesterol from CETP transfer of cholesterols from HDL (once LDL is still a part of VLDL)
5) LDL also carries some cholesterol back to liver
6) HDLs carry cholesterol from body back to liver for excretion (pick up cholesterol via LCAT/apoAI activity)
7) HDL not endocytosed; it binds to SR-B1 (on liver, steroid-producing cells) which allows selective re-uptake of cholesterol esters from HDL
8) TGs can be degraded by hepatic lipase

Question 9

What’s different between lipoprotein particles and mixed micelles?

Answer 9

1) LP particles have lots of TG, not a lot of NEFA

2) mixed micelles have lots of NEFA, not much TG

Question 10

What does pancreatic lipase need?

Answer 10

1) colipase (secreted inactively by pancreas, activated in duodenum)
2) with copliase’s action, pancreatic lipase is an esterase taht partially hydrolyzes TGs into 2-MAG and 2 NEFAs

Question 11

What can bind to the LDL receptor?

Answer 11

1) ApoE-containing particles, chylomicrons, LDL
2) LDL NOT associated with apoE, endocytosed by receptor
3) LDLR recognizes ApoB100, apoE

Question 12

Which amino acids are the highest concentration inside the cells and serum?

Answer 12

1) glutamate (more than)/glutamine inside CELLS–transaminases converge on it, ox deam makes energy from removing ammonia group
2) alanine in BLOOD–ammonia disposed, carbons sent to liver for glucose

Question 13

Which kind of rxn is pyroxidal phosphate (B6) NOT a cofactor for?

Answer 13

ribonucleotide reductases

Question 14

Which is NOT a function of the urea cycle? What treatment would you give someone with hyperammonia?

Answer 14

1) to generate carbamoyl phosphate for pyrimidines
2) making arginine/forming urea (highly soluble ammonia compound) ARE functions
3) 3 ATP used in cycle
4) protein-free diet (arginine becomes essential**), lots of glucose, sodium benzoate/sodium phenylacetate–do NOT starve them!!

Question 15

Transaminations occur in making or degrading all of which amino acids?

Answer 15

1) alanine
2) arginine
3) aspartate
4) isoleucine, leucine, valine (use common alpha-keto transam rxn)
5) NOT threonine! (threonine–>glycine via threonine dehydrogenase, irreversible–makes threonine essential)

Question 16

Which enzyme is created/degraded in same path?

Answer 16

1) proline–>glutamic acid–>glutamate–>alpha-ketoglutarate
2) arginine generated through urea cycle (the ornithine made too just goes through cycle again), but it becomes glutamate–NOT made/broken down through same path
3) fun fact: proline, ornithine, arginine, glutamate can all be derived from alpha-ketoglutarate skeleton (NOT histidine, since it’s essential)

Question 17

How is serine made?

Answer 17

1) either from glycine or by 3-phosphoglycerate path

2) will become pyruvate

Question 18

What’s deficient in alkaptonuria?

Answer 18

1) homogentisate oxidase

2) homogentisate can’t be ocnverted to 4-maleylacetate

Question 19

What are some things to know about tetrahydrobiopterin?

Answer 19

1) needed for DOPA synthesis
2) required cofactor for phenyalanine hydroxylase
3) must be regenerated by dihydrobiopterin reductase
4) synthesized by body

Question 20

What are the forms of cobalamin in the methylmalonyl CoA mutase and the homocysteine methyltransferase rxns?

Answer 20

1) MMAM–adenosyl version (a in MMAM for adenosyl!)

2) HMT–hydroxy version (h in HMT for hydroxy!)

Question 21

What’s important stuff about folate?

Answer 21

1) folic acid–>THF via dihydrofolic acid reductase, enzyme inhibited by methotrexate–THF active form in body, one-carbon group donor
2) N5-methyl-THF is most reduced form–this guy gets trapped in folate trap, when B12 reduced (methylene intermediate, formyl/formino/methenyl most oxidized)

Question 22

What causes the spinal cord degeneration and neurological problems in a B12 deficiency?

Answer 22

1) methylmalonyl CoA–>succinyl CoA doesn’t happen

Question 23

Which rxns use 1-carbon fragments?

Answer 23

1) formation of methionine
2) synthesis of purines and pyrimidines
3) glycine synthesis
4) NOT heme synthesis!!

Question 24

Which rxns does azaserine block?

Answer 24

1) it’s a glutamine analog–blocks amide transfer from glutamine (blocks amination rxns)
2) blocks 2 steps in purine synthesis (blocks amination rxns)
3) blocks IMP–>GMP synthesis
4) blocks UTP–>CTP synthesis

Question 25

What’s needed to make purines?

Answer 25

1) aspartate
2) formate (from N10-formyl-THF)
3) CO2
4) glutamine
5) glycine
6) ATP

Question 26

What’s needed to make pyrimidines?

Answer 26

1) carbamoyl phosphate (NOT from urea cycle, made in cytosol from glutamine and CO2)
2) aspartate
3) people with a urea cycle OTC deficiency can build up lots of pyrimidines**

Question 27

Which enzyme is restricted to the liver?

Answer 27

G6Pase, for gluconeogenesis

Question 28

Are all NTPs created equally?

Answer 28

Yes! ATP=GTP=CTP=GTP

Question 29

How does pyruvate carboxylase work?

Answer 29

1) pyruvate–>OAA
2) requires biotin cofactor, requires ATP to activate bicarb
3) pyruvate carboxylase ONLY in mitochondria–where gluconeogenesis must begin
4) leucine/lysine, acetyl CoA from fatty acids/amino acids CANNOT contribute to gluconeogenesis
5) activated by acetyl CoA

Question 30

How does PEPCK (PEP carboxykinase) work?

Answer 30

1) OAA–>PEP+CO2
2) requires GTP
3) PEPCK in mitochondria, PEP has transporter
4) activated by glucagon’s increase in cAMP, decreased by insulin

Question 31

What about OAA in fatty acid synthesis? (NADPH required!!!***)

Answer 31

1) citrate+ATP–>OAA + acetyl CoA (cytosol)
2) OAA+NADH–>malate via malate dehydrogenase
3) malate+NADP+–>pyruvate+NADPH, via malic enzyme
4) pyruvate–>citrate, NADPH used as the reducing agent for fatty acids
5) oxidizing malate to make OAA is endergonic, so lots of malate is in equilibrium with OAA–this is good, because malate can go to the cytoplasm for gluconeogenesis

Question 32

What about OAA in gluconeogenesis?

Answer 32

1) asparagine and aspartate also become OAA

2) must be converted into malate or aspartate to enter/leave mitochondrial matrix