March 24 - Biochemistry

Question 1

Gaucher disease: defect and presentation

Answer 1

Defect: beta glucocerebrosidase is deficient, glucocerebroside accumulates

Presentation: HSM, pancytopenia, bone pain

Question 2

Mechanism of triple helix of collagen

Answer 2

Due to glycine occupying every third position in each alpha chain. Means that glycine is the most abundant amino acid in collagen

Question 3

Pyruvate carboxylase

Answer 3

Uses biotin as cofactor for convert pyruvate to oxaloacetate in gluconeogenesis

Question 4

Biotin deficiency

Answer 4

Increased pyruvate gets converted to lactic acid, leading to metabolic acidosis.

Also get accumulation of propionyl coA because can’t convert it to succinyl coA with propionyl coA carboxylase

Question 5

Lac operon

Answer 5

Encodes three different genes involved in lactose metabolism. One mRNA transcript generates three different proteins

Question 6

Conversion of norepinephrine to epinephrine

Answer 6

Occurs in adrenal medulla by enzyme PNMT, which is upregulated by cortisol

Question 7

Maturity-onset diabetes of young pathophys and presentation

Answer 7

Pathophys: Heterozygous glucokinase deficiency. Results in decreased beta cell glucose metabolism and thus less insulin secretion.

Presentation: Mild, nonprogressive hyperglycemia that often worsens with pregnancy

Question 8

Porphyria cutanea tarda

Answer 8

Photosensitivity due to accumulation of porphorinogens. Uroporphrinogen decarboxylase is deficiency

Question 9

Acute intermittent porphyria enzymatic defet

Answer 9

Porphobilinogen deaminase

Question 10

Elastin production

Answer 10

Synthesized as tropoelastin. Tropoelastin secreted to ECM where it interacts with fibrillin scaffold. Lysyl oxidase deaminates lysine residues, allowing desmosine crosslinks to form and giving elastin its rubber-like properties

Question 11

Thiamine and B6 role in amino acid metabolism

Answer 11

Thiamine cofactor for dehydrogenase enzymes: branched chain alpha-ketoacid dehydrogenase and alpha ketoglutarate dehydrogenase

B6 a cofactor for transamination and decarboxylation steps of amino acid metabolism, as well as has a role in heme and neurotransmitter synthesis

Question 12

Homocysteine metabolism

Answer 12

Homocysteine can be converted to methionine in process that requires B12 as cofactor

Can also be converted to cysteine in two steps, both of which require B6 as cofactor

Question 13

Hereditary orotic aciduria

Answer 13

AR disorder of de novo pyrimidine snthesis. Defect is in UMP synthase.

Presents with physical and mental retardation, megaloblastic anemia, and elevated urine orotic acid.

Uridine supplementation bypasses the enzyme defect and improves symptoms

Question 14

Hematoma progression

Answer 14

Following injury, hemoglobin containing RBCs escape resulting in purple/blue color of bruise. RBCs subsequently destroyed and heme released.

Heme oxygenase degrades heme to biliverdin and iron. Biliverdin gives green color to bruise.

Biliverdin then reduced to bilirubin which gives yellow color to bruise

Question 15

Galactosyl beta 1,4 glucose

Answer 15

Another name for lactose

Question 16

Succinate dehydrogenase

Answer 16

Enzyme in both TCA cycle and in ETC (complex II)

Converts succinate + FAD to fumarate + FADH2

Question 17

Gq signling

Answer 17

Hormone binds receptor, activating G protein (Alpha subunit goes from GDP bound to GTP bound)

Alpha subunit activates PLC

PLC breaks down PIP2 to IP3 and DAG

DAG stimulates PKC which phosphorylates downstream targets

IP3 increases intracellular Ca++ which also stimulates PKC

Question 18

Ketogenic amino acids

Answer 18

Leucine and isoleucine

Question 19

Amino acids that are both ketogenic and glucogenic

Answer 19

Phenylalanine, isoleucine, tryptophan

Question 20

Lead toxicity

Answer 20

Inhibits ALA dehydratase as well as ferrocheletase in heme synth

Question 21

Bloom syndrome

Answer 21

DNA helicase mutation, results in chromosomal instability

Question 22

Helicase vs topoisomerase vs ssBPs

Answer 22

Helicase: unwinds DNA
ssBPs: stablize unwound DNA
Topoisomerase: relieves coiling tension by creating temporary breaks in DNA. Found upstream of helicase

Question 23

Fetal alcohol syndrome

Answer 23

Smooth philtrum, microcephaly, delayed growth, ADD

Question 24

Hartnups disease

Answer 24

Defect in transport of neutral amino acids in renal and GI tracts resulting in wasting of neutral amino acids in the urine. Can result in pellagra due to wasting of tryptophan, which is used to make niacin. Also failure to thrive, photosensitivity, nystagmus, intermittent ataxia