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Biochemistry sample quiz for ple

Biochemistry sample quiz for ple

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Subject: BIOCHEMISTRY

1. As the level of visceral fat increases there is a

concomitant loss of peripheral tissue responses

to insulin. Adipose tissue responses to these

metabolic changes include a reduced secretion of

which of the following adipokines?

a. Adipsin

b. Il-6

c. Adiponectin

d. Leptin

Ans: C

Rationale: Adipose tissue secretes hormones

such as leptin and adiponectin, known as

adipokines, its role as an endocrine organ has

been recognized. Leptin, regulates energy

homeostasis by stimulating energy use and

limiting food intake. If it is lacking, food intake

may be uncontrolled, causing obesity.

Adiponectin modulates glucose and lipid

metabolism in muscle and liver, and enhances

the sensitivity of tissues to insulin. Reduced

secretion of adiponectin by adipose tissue

concomitantly reduces sensitivity of tissue to

insulin leading to obesity and type 2 diabetes

mellitus.

Source: Harper’s Illustrated Biochemistry 30th ed.,

p. 261

2. A 6 years old girl with moderate mental

retardation and with difficulty of her vision. PE

shows a fair complexion and malar erythema and

bilateral dislocated lenses. She has long slender

hands and fingers. Blood test reveal that her

cystathionine concentration is below normal.

Which amino acid is MOST likely to have an

increased urine concentration?

a. Methionine

b. Leucine

c. Alanine

d. Arginine

Ans: A

Rationale: Homocystinuria is most often due to a

defect in cystathionine b-synthase, leading to

increased homocysteine and methionine in blood

and urine. Patients present with dislocation of

the lens, mental retardation, and skeletal and

neurologic abnormalities.

Source: BRS Biochemistry, Molecular Biology&

Genetics 5th ed., p. 184

3. A 5 year old boy born of a first degree relatives

was noted to have darkening of the urine when

left standing. He has a normal sibling, and there

are no other medical problems. Growth and

development to date are normal. Which of the

following is MOST likely elevated in this patient?

a. Homocysteine

b. Homogentisate

c. Methylmalonate

d. Phenylypyruvate

Ans: B

Rationale: Alkaptonuria, also called black urine

disease and black bone disease, is one of 4

disorders originally defined as an inborn error of

metabolism by Archibald Garrod. The metabolic

defect in alkaptonuriais a defective

homogentisateoxidase(EC 1.13.11.5). The

hallmark of the disease is passage of urine that

becomes black when left standing due to

oxidation of excreted homogentisate. Late in

thedisease, there is arthritis and connective

tissue pigmentation(ochronosis) due to oxidation

of homogentisate to benzoquinoneacetate,

which polymerizes and binds to connective

tissue.

Source: Harper’s Illustrated Biochemistry 30th ed.,

p. 304

4. Which of the following hypothesizes that

the physical and Functional status of certain

region of genomic chromatin is dependent

on the patterns of specific histone post-

translational modifications and/or DNA

methylation status?

a. Genetic code

b. Morse code

c. Epigenetic code

d. PTM hypothesis

Ans: C

Rationale: Some genes are expressed in a parent-

specific manner defying normal rules of

mendelian inheritance. At least one mechanism

involves methylation of DNA on chromosomes.

This is epigenetic code, referring to factors

affecting phenotype without a change in

genotype. X inactivation is also epigenetic.

Source: BRS Biochemistry, Molecular Biology&

Genetics 5th ed., p. 292

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5. Which of the following is BEST described as

being trans-acting?

a. Promoter

b. Operator

c. CAP site

d. Repressor

Ans: D

Rationale: Third class of sequence elements also

increase or decrease the rate of transcription of

eukaryotic genes. These elements are called

either enhancers or repressors (or silencers),

depending on how they effect transcription. They

have been found in a variety of locations, both

upstream and downstream of the transcription

start site, and even within the transcribed protein

coding portions of some genes. In the field of

molecular biology, trans-acting, in general,

means "acting from a different molecule". It may

be considered the opposite of cis-acting, which, in

general, means "acting from the same molecule".

Enhancers and silencers can exert their effects

when located thousands or even many tens of

thousands of bases away from transcription units

located on the same chromosome. Surprisingly,

enhancers and silencers can function in an

orientation-independent fashion. Together, these

many transfactors binding to promoter distal and

proximal cis-elements regulate transcription in

response to a vast array of biological signals.

Such transcriptional regulatory events contribute

importantly to control of gene expression.Another

example of a cis-acting regulatory sequence is the

operator in the lac operon. This DNA sequence is

bound by the lac repressor, which, in turn,

prevents transcription of the adjacent genes on

the same DNA molecule. The lac operator is, thus,

considered to "act in cis" on the regulation of the

nearby genes.

Source: Harper’s Illustrated Biochemistry 30th

ed., p. 401

6. Which of the following statements most

closely reflects the actions of the translation

Eif-4E?

a. Facilitation of the ternary complex binding

to 40s ribosomal subunit.

b. Scaffold for the binding of eif-4A.

c. Exchange of GTP to GDP bound to eif-2.

d. Interaction with the eif-4G in order to bind to

the CAP structure of the mRNA

Ans: D

Rationale: The 5′ termini of mRNA molecules in

eukaryotic cells are “capped.” The 7meG-cap

facilitates the binding of mRNA to the 43S

preinitiation complex. A cap-binding protein

complex, eIF-4F (4F), which consists of eIF-4E (4E)

and the eIF-4G (4G)-eIF-4A (4A) complex, binds to

the cap through the 4E protein.

Source: Harper’s Illustrated Biochemistry 30th

ed., p. 419

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Subject: BIOCHEMISTRY 1. As the level of visceral fat increases there is a concomitant loss of peripheral tissue responses to insulin. Adipose tissue responses to these metabolic changes include a reduced secretion of which of the following adipokines? a. Adipsin b. Il-6 c. Adiponectin d. Leptin 2. A 6 years old girl with moderate mental retardation and with difficulty of her vision. PE shows a fair complexion and malar erythema and bilateral dislocated lenses. She has long slender hands and fingers. Blood test reveal that her cystathionine concentration is below normal. Which amino acid is MOST likely to have an increased urine concentration? a. Methionine b. Leucine c. Alanine d. Arginine 3. A 5 year old boy born of a first degree relatives was noted to have darkening of the urine when left standing. He has a normal sibling, and there are no other medical problems. Growth and development to date are normal. Which of the following is MOST likely elevated in this patient? a. Homocysteine b. Homogentisate c. Methylmalonate d. Phenylypyruvate 4. Which of the following hypothesizes that the physical and Functional status of certain region of genomic chromatin is dependent on the pa ...
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