Biochem

Question 1

How can you distinguish between hereditary fructose intolerance and essential fructosuria? What enzymes are deficient in each?

Answer 1

EF, caused by fructokinase deficiency, is largely asymptomatic, will have fructose in blood and urine
HFI, caused by Aldolase B deficiency (and build up of F-1-P can → hypoglycemia, jaundice, cirrhosis and vomiting, with symptoms usually presenting following consumption of fruit, juice or honey

Question 2

What is the initiating amino acid in prokaryotic translation?

Answer 2

formyl methionine (methionine itself in eukaryotes)

Question 2

What is the initiating amino acid in prokaryotic translation?

Answer 2

formyl methionine (methionine itself in eukaryotes)

Question 3

When is the P site bound to in prokaryotic translation?

Answer 3

one time: in the process of initiation when tRNA carrying initiating amino acid (formyl Methionine in prokaryotes)

Question 3

When is the P site bound to in prokaryotic translation?

Answer 3

one time: in the process of initiation when tRNA carrying initiating amino acid (formyl Methionine in prokaryotes)

Question 4

Besides serving as an initiator AA in prokaryotes, what other actions does formyl methionine have?

Answer 4

chemokine that attracts neutrophils and macrophages

Question 7

Besides serving as an initiator AA in prokaryotes, what other actions does formyl methionine have?

Answer 7

chemokine that attracts neutrophils and macrophages

Question 8

What enzymes do Amatoxins inhibit? What organs are affected?

Answer 8

RNA pol II → halt mRNA synthesis; affects organs with high cell turnover: liver, kidney (PCTs), and GI tract → apoptosis of cells

Question 9

What happens in the lac operon (1) when glucose is present and (2) when lactose is present?

Answer 9

1. glucose → ↓ activity of adenylyl cyclase → ↓ cAMP → ↓ binding of cAMP-CAP upstream from promoter region
2. lactose → binds to repressor protein → prevents repressor protein from binding to operator locus

transcription of the lac operon genes requires no glucose to be present (so ↑ cAMP) and lactose to be present (↓ repressor at operator)

Question 10

How many calories are in 1 g of protein? carbs? fat? EtOH?

Answer 10

Protein: 4 cal
Carbs: 4 cal
Fat: 9 cal
EtOH: 7 cal

Question 11

What is the biochemistry underlying alcoholic hepatic steatosis?

Answer 11

alcohol dehydrogenase and aldehyde dehydrogenase reduce NAD+ to NADH → excess NADH → decreased free fatty acid oxidation

Question 12

What is the product of β-oxidation of FAs?

Answer 12

acetyl CoA which is a precursor for acetoacetate (a ketone) and can be used in the TCA cycle

Question 13

How does alcoholism affect the TCA cycle? Which step is most heavily affected

Answer 13

1. ↑ NADH/NAD+ ratio → inhibiting the 3 enzymes that make NADH in the TCA
2. ↓ thiamine which is a required cofactor for α ketoglutarate dehydrogenase (converts α-ketoglutarate to Succinyl CoA); this enzyme also makes NADH so it is the most affected

Question 14

What pathway is transketolase in? Where does this pathway occur in a cell? In the body?

Answer 14

HMP shunt (produces NADPH from G6P); occurs entirely in cytoplasm; used in RBCs to reduce glutathione (w/ thiamine as cofactor - remember we use ↑ transketolase activity to measure monitor thiamine replacement); also used to reduce FAs (vs. oxidation in mito) and cholesterol which occur in glands where FAs or steroids are synthesized (e.g. adrenal ctx, liver, mammary)

Question 15

What processes maintain plasma glucose concentrations WNL b/w meals? When does each predominate?

Answer 15

Glycogenolysis is used for first 12 - 18 hours, then gluconeogenesis kicks in

Question 16

What are the substrates for gluconeogenisis, and what is the common pathway for these substrates to be converted to glucose?

Answer 16

substrates: lactate, glycerol, and amino acids (e.g. alanine)
all are converted to pyruvate first, which then must be converted to oxaloacetate (biotin dependent carboxylation), transported out of the mitochondria (involves a malate conversion/reconversion step), then PEP (by PEP carboxykinase). PEP can be converted to glucose

Question 17

How does alcoholism → hypoglycemia?

Answer 17

1. low glucose intake
2. inhibition of gluconeogenesis (↑ NADH/NAD ratio favors pyruvate → lactate and oxaloacetate → malate; both lactate and malate inhibit gluconeogenesis)