Biochem

Question 1

When are microsatellite repeats generated in the cell cycle?

Answer 1

S phase

Question 2

During catabolism of proteins, amino acids are transferred to ______ to form glutamate.

Answer 2

α-ketoglutarate

Question 3

If a patient’s sibling has an autosomal recessive disease and the patient is not affected (neither are the parents), what is the chance that the patient is a carrier?

Answer 3

2/3

Question 4

If a mother and father have a 1/40 and 1/300 chance of being a carrier for a recessive disease, respectively, what is the chance the child will have the disease?

Answer 4

(1/40 x 1/2) x (1/300 x 1/2) = 1/48,000

Question 5

What components are needed for PCR?

Answer 5

1. DNA template (must be pretty short, ≤ 10 kb)
2. Two primers (25-35 bases) complementary to regions flanking template
3. DNA polymerase
4. Deoxynucleotide triphosphates

Question 6

What is the Kozak consensus sequence?

Answer 6

a sequence near the AUG codon in eurkaryotes that plays a role in initiation - note that a purine (A or G) residue three bases upstream is particularly important

Question 7

What are the cause and symptoms of Beriberi?

Answer 7

cause: thiamine deficiency
Infantile (2-3 mo.): cardiac syndrome with cardiomegaly, tachycardia, cyanosis, dyspnea, and vomiting
Adult:
- wet: neuropathy + cardiac involvement
- dry: symmetrical peripheral neuropathy

Question 8

What is the genetic error that causes most cases of down syndrome?

Answer 8

maternal meiotic nondisjunction

Question 9

What non-essential AA becomes essential in homocysteinuria?

Answer 9

cysteine

Question 10

What is another name for Lynch syndrome? Mode of inheritance? Defect?

Answer 10

hereditary nonpolyposis colon cancer; AD inheritance; 90% of cases have mutations in MSH2 and MLH1 → no MutS or MutL human homologs → defective mismatch repair

Question 11

How is classical galactosemia inherited? How about Lesch-Nyhan and Hemophilia B?

Answer 11

autosomal recessive; x-linked recessive

Question 12

What is the HMP shunt (pentose phosphate pathway) useful for?

Answer 12

• provides NADPH from abundant G-6-P, which is needed for reductive reactions:
  a. glutathione reduction inside RBCs
  b. FA and cholesterol biosynthesis
• also yields ribose for NT synth and glycolytic intermediates

Question 13

Describe the breakdown of branched glycogen to an unbranched chain of G-1-P residues

Answer 13

1. G-1-P’s are removed until there are 4 residues left on the main chain and branch (by glycogen phosphorylase)
2. 3 G-1-P’s are taken from the branch to the main chain (by debranching enzyme 1 aka 4-α-D-glucanotransferase)
3. the last G-1-P is cleaved from the branch (by debranching enzyme 2 aka α-1,6,-glucosidase)

Question 14

Describe the synthesis of glycogen from G-6-P

Answer 14

1. converted to G-1-P by UDP-glucose pyrophosphorylase
2. linked together to form a glycogen chain by glycogen synthase
3. branches are created by branching enzyme

Question 15

What enzyme is deficient in Von Gierke disease (type I)? What is its function? What are the consequences?

Answer 15

glucose-6-phophatase deficiency; converts G-6-P to glucose (this only happens in the liver); → severe fasting hypoglycemia, ↑↑ glycogen in the liver, hepatomegaly, and ↑ blood lactate (because ↑ glycolysis)

Question 16

What is the mode of inheritance of Von Gierke disease? How is it treated?

Answer 16

AR; frequent oral glucose/cornstarch; avoid fructose and galactose

Question 17

What enzyme deficiency leads to Pompe disease (type II)? What is its function? Consequences of dysfunction?

Answer 17

Lysosomal α-1,4-glucosidase (acid maltase; aka acid α-glucosidase); breaks down a small amount of glycogen within lysosomes; leads to glycogen accumulation within lysosomes, hepatomegaly, cardiomegaly, macroglossia, and if severe, mental retardation

Question 18

How are all glycogen storage diseases inherited?

Answer 18

autosomal recessive

Question 19

What enzyme is deficient in Cori diseae (type III; aka Forbes disease)? What is its function? What are the consequences?

Answer 19

Debranching enzyme (α-1,6-glucosidase); removes the last G-1-P from a branch;→ hypoglycemia, hepatomegaly, hyperlipidemia, growth retardation, muscle weakness

Question 20

What enzyme is deficient in McArdle disease? What is its function? What are the consequences?

Answer 20

skeletal muscle glycogen phosphorylase (myophosphorylase); cleaves G-1-P residues from glycogen until limit dextran is formed; → ↑ glycogen in mm. which can’t be broken down → painful mm. cramps, myoglobinuria with strenuous exercise, arrhythmia (from electrolyte abnormalities)

Question 21

What is carnitine important for? What happens when you have a carnitine deficiency?

Answer 21

transport of long chain fatty acids into the mitochondria for degradation; deficiency → toxic accumulation → weakness, hypotonia, and hypoketotic hypoglycemia

Question 22

What are the TATA box and CAAT boxes?

Answer 22

sequences in the promoter region of genes where RNA pol II and TFs bind to initiate transcription

Question 23

What is an important allosteric activator of gluconeogenesis that acts by ↑ pyruvate carboxylase (converts pyruvate to oxaloacetate)?

Answer 23

acetyl-CoA

Question 24

What is the 16S rRNA sequence?

Answer 24

It is a component of the the 30S ribosomal subunit in prokaryotes that contains a sequence complementary to the Shine-Dalgarno sequence on mRNA; binding b/w these sites is necessary for initiation of translation

Question 25

What is c-Jun?

Answer 25

a transcription factor that can become an oncogene w/ a mutation/ overexpression

Question 26

Which enzyme is most commonly deficient in β-oxidation?

Answer 26

Acyl-CoA dehydrogenase (catalyzes the first step)

Question 27

What two substrates are normally involved in transamination reactions? What vitamin is needed?

Answer 27

amino acid and α-keto acid (e.g. oxaloacetate)

Question 28

What are P bodies?

Answer 28

cytoplasmic foci that contain proteins important in mRNA translation regulation and mRNA degradation