Vitamin Lecture&Glycolysis

Question 1

What rxn requires n5, n10-methylene-FH4 as a carbon donor?

Answer 1

Homocysteine to methionine rxn

Question 2

What rxn requires free FH4 then generates n5, N10 methylene-fh4

Answer 2

Serine to glycine

Question 3

What requires donating a methyl group to homocysteine to form methionine without fh4?

Answer 3

Betaine

Question 4

What requires n10-formyl-FH4 in it’s biosynthesis?

Answer 4

Purine ring

Question 5

Propionic acid accumulation from amino acid degradation will result from, a deficiency in what vitamin?

Answer 5

Biotin-

Question 6

Middle ear infection is treated with sulfa drugs. This interferes with bacterial synthesis of?

Answer 6

Folic acid. Prevent synthesis of folic acid, humans can’t synthesize folic acid so it doesn’t affect our metabolism

Question 7

What form of FH4 is required for synthesis of methionine from homocysteine?

Answer 7

N5-methyl-FH4, it transfers the methyl group to form methionine from homocysteine

Question 8

What is an alternative method to methylate homocysteine to form methionine?

Answer 8

Using betaine as the methyl donor- donates to homocysteine to form methionine plus dimethylglycine

Question 9

Both folic acid and B12 deficiencies will lead to the observation of hypomethylation in the nervous system. These two cofactors are linked by what protein?

Answer 9

Methionine synthase

Question 10

A strict vegan that has not eaten animal products in 5 years or taken vitamins is lethargic, tired with tingling in extremities. Total folate is normal. What form would this folate most likely be in?

Answer 10

N5-Methyl-FH4. Vitamin B12, normal gotten from meat and dairy, body hold 2-3 year store. Tired/lethargy is from megaloblastic anemia. Tingling is nervous dysfunction due to hypomethylation and MMA in the system. In the absence of vitamin b12, folate gets trapped as N5-methyl-FH4 and can’t get converted to other forms. It’s the most stable form

Question 11

Pt presents with lethargy, tingling in extremities. Bloodwork shows megaloblastic anemia. What measurement of blood metabolite will help determine the cause of the symptoms?

Answer 11

MMA. Methylmalonic acid. A b12 deficiency will end to MMA elevated bc MMA-CoA can’t be metabolized to succinyl-CoA. Lack of b12 also traps folate as n5-methyl-FH4. Leads to a functional folate deficiency, that interferes with purine and thymidine synthesis, leads to overall cessation of DNA synthesis in rapid growing cells like RBCs

Question 12

A pt with Crohns affecting the terminal ileum will lead to what deficiency?

Answer 12

B12

Question 13

Methotrexate is a folate analog that directly inhibits what conversion?

Answer 13

FH2 to FH4. Methotrexate inhibits DHFR, dihydrofolate reductase, that blocks conversion of FH2, dihydrofolate to FH4, tetrahydrofolate.

Question 14

Glucose is the body’s universal fuel, what is the major role of glycolysis?

Answer 14

The major roles of glycolysis are to generate energy and to produce precursors for other bio synthetic pathways.

Question 15

Glycolysis generates energy so cells can survive. Starting with glyceraldehyde 3-P and synthesizing one molecule of pyruvate, what is the net yield of ATP and NADH?

Answer 15

If starting with G3P the energy-requiring steps of glycolysis are bypassed. G3P to pyruvate makes 2 ATP and 1 NADH at G3P-dehydrogenase step

Question 16

Glycogen is the body’s storage of glucose. When glycogen is degraded glucose 1-P is formed, its then isomerized to glucose 6-P. Starting with G-1P and ending with 2 molecules of pyruvate what is the net yield of glycolysis with ATP and NADH?

Answer 16

3 ATP, 1 NADH. Glucose1-P is isomerized to glucose 6-P, this skips the hexokinase step that uses 1 ATP. Thus starting from glucose 1-P you would get 2 ATP and 2NADH but with one less ATP used in priming there would be 3 ATP and 2 NADH.

Question 17

Every human cell has the capacity to use glycolysis for energy production. Does glycolysis synthesize ATP via substrate level phosphorylation or oxidative phosphorylation?

Answer 17

Substrate level phosphorylation

Question 18

In glycolysis how many ATP are consumed at the beginning of the pathway and how many are produced at the end? What is the net production?

Answer 18

2 ATP used at the beginning, 4 produced at the end and a net of 2 ATP for each molecule of glucose.

Question 19

Fructose is the second most common sugar in the human adult diet and its metabolism parallels glycolysis. What substance is found in both the fructose and glycolytic pathway?

Answer 19

Glyceraldehyde 3-P, G3P. Both glucose and fructose are converted to it and this is where the two pathways intersect and become identical.

Question 20

4 week baby with frequent vomiting after meals and abdominal tenderness. Exam reveals enlarged liver and start of cataract formation in both eyes. Urine dipstick is positive for a reducing sugar, blood glucose slightly below normal. What is the compound that reacted with the urine dipstick?

Answer 20

Galactose. The child has galactosemia where galactose can’t be metabolized and free galactose enters blood and is excreted in the urine. Below normal blood glucose reveals no glucose in urine. Galactose enters eye and is converted to galactitol by aldose reductase, trapping it int the lens and making an osmotic imbalance leading to swelling then cataract formation.

Question 21

With a child that has galactosemia what single intracellular metabolite would allow a determination of the enzyme deficiency?

Answer 21

Galactose 1-P levels would help determine if galactokinase was deficient ( levels would be low), ot is galactose 1-P uridylyltransferase was defective ( levels would be elevated)

Question 22

Metformin is used in type 2 diabetes, one action is decreasing hepatic gluconeogenesis. Theoretically there is concern with lactic acidosis. But it doesn’t happen. Why?

Answer 22

Metformin interrupts the Cori cycle-gluconeogenesis in the liver using lactate derived from muscle for carbons. The heart has huge mitochondrial amounts and oxidative strength, uses lactate as fuel and easily uses the excess lactate. That why heart failure is contraindicated. RBC’s, renal medullary cells and eye tissue use anaerobic glycolysis producing lactate but can’t use it as fuel.

Question 23

What rxn would commit glucose to the glycolytic pathway?

Answer 23

The committed step for glycolysis is the one catalysed by phosphofructokinase-1, which converts fructose 6P to fructose 1, 6 bisP

Question 24

RBC’s require ATP to maintain ion gradients. Without these ion gradients RBC’s will swell and burst causing hemolytic anemia. RBC’s produce energy how?

Answer 24

Substrate level phosphorylation. They dont have mitochondria so they can only do anaerobic mechanisms to produce lactate and ATP.
TCA or oxidative phosphorylation are aerobic glycolysis
ETC occurs in the mitochondria .