EXAM 3

Question 1

Which part of a ribosome accepts a tRNA molecule that is attached to a growing polypeptide chain?

Answer 1

P site

Question 2

What kind of bonds join amino acids in a polypeptide chain?

Answer 2

Peptide bonds

Question 3

During translation, an mRNA molecule has a codon with the triplet sequence 5’-AUC-3’. Which anticodon sequence in a tRNA molecule would pair with this codon?

Answer 3

5’-GAU-3’

Question 4

The following figure shows a mutation at position 14 in the DNA that causes valine to substitute for aspartate in the peptide chain. This is an example of a

Answer 4

missense mutation

Question 5

Which of the following statements about transfer RNA (tRNA) is true?

Answer 5

Activating enzymes (aminoacyl-tRNA synthetases) link together a specific amino acid with a specific tRNA

Question 6

Tetracycline, but not penicillin, is able to kill MRSA because tetracycline

Answer 6

inhibits protein synthesis

Question 7

Which of the following would be a useful treatment for alkaptonuria?

Answer 7

Gene therapy that supplies an enzyme that breaks down homogentistic acid

Question 8

Which of the following discoveries caused the modification of the “one gene–one protein” hypothesis to the “one gene–one polypeptide” hypothesis?

Answer 8

Proteins made up of two or more chains

Question 9

The “adapters” that allow translation of the four-letter nucleic acid language into the 20-letter protein language are called

Answer 9

transfer RNAs

Question 10

RNA polymerase differs from DNA polymerase in that RNA polymerase

Answer 10

does not require a primer

Question 11

Promoters are made of

Answer 11

Nucleic acids

Question 12

RNA polymerase uses the _______ DNA template to synthesize a _______ mRNA.

Answer 12

3′-to-5′; 5′-to-3′

Question 13

Errors in transcription are not as potentially harmful as errors in DNA replication because

Answer 13

D. Both a and b

A. many copies of the same RNA sequence are made.
B. RNA sequences have a relatively short life span.

Question 14

In eukaryotes, exons are

Answer 14

spliced together from the original transcript

Question 15

Suppose the DNA of a gene contains five motifs (A, B, C, D, and E) in that order. Motifs A, B, and D are located in introns, while motifs C and E are located in exons. What is the order of the motifs in the pre-mRNA transcribed from that sequence?

Answer 15

ABCDE

Note: Pre-mRNA contains both introns and exons, and is ABCDE, where as mRNA contains only exons and would be CE.

Question 16

Suppose that a certain mRNA is transcribed at a normal rate in the nucleus, but it is found at very low levels in the cytoplasm. Which of the following would be the most plausible explanation for this phenomenon?

Answer 16

A defect in the addition of the poly A tail on the pre-mRNA

Note: This questions wants you to distinguish different levels of gene regulation. If a gene is transcribed but not translated, there is probably something on the processing or translation level that is occurring.

Question 17

Which of the following changes affects more than a single amino acid in a sequence?

Answer 17

A frameshift mutation

Question 18

Which of the following statements about Garrod’s observations is false?

Answer 18

A. Alkaptonuria is a genetic disease.
B. Garrod showed that homogentisic acid accumulated in the blood of people suffering from alkaptonuria.
C. Garrod proposed that in normal people, homogentisic acid is broken down to a harmless product by an enzyme.
D. Garrod isolated the enzyme homogentisic acid oxidase.
E. Garrod coined the term “inborn errors in metabolism.”

D. The enzyme homogentisic oxidase was not isolated until about 50 years after Garrod’s proposals were made.

Question 19

In the ________ of lactose, the lac _______ binds to the lac _______ site.

Answer 19

absence, repressor, operator

In the lac system, repressor molecules are always present in an E. coli cell. In the absence of lactose, a repressor molecule can bind to the operator site of the lac operon. When lactose molecules are present, they bind to repressor molecules, causing them to change shape. The shape change prevents repressors from binding to the operator, which allows the lac structural genes to be expressed.

Question 20

Which statement characterizes the lac operon?

Answer 20

The lac operon is an inducible system.

The lac operon is an inducible system. In an inducible system, the inducer (lactose) is required to turn the operon on. Without the inducer, repressors keep the operon turned off.

Question 21

If lactose-metabolizing enzymes are produced whether or not lactose is present, a mutation in which gene is the likely cause?

Answer 21

lac I (encodes the lac repressor protein)

A mutation in the lac I gene would produce a defective lac repressor protein. A defective repressor is not able to block transcription of the lac Z, Y, and A genes. Therefore, the lactose-metabolizing enzymes would be produced even in the absence of lactose.

Question 22

What is the first protein to bind to a eukaryotic promoter, and at which site does it bind?

Answer 22

TFIID binds to TATA box

Question 23

In the initiation of transcription, which type of protein binds to a DNA region that may be far from the gene’s promoter?

Answer 23

Activator protein

An activator protein binds to an enhancer region of DNA, which may be far from the promoter, as many as tens of thousands of base pairs away.

Question 24

The countercurrent heat exchanger of some large, rapidly swimming “hot” fish

Answer 24

traps heat in the muscles

Question 25

Which of the following statements about endotherms is false?

Answer 25

A. Some can acclimatize to seasonal temperature changes.
B. They can lower their body temperature by mobilizing active mechanisms of heat loss.
C. They can raise their body temperature by producing heat metabolically.
D. They respond to cold by producing heat.
E. An endotherm’s metabolic rate goes down above the thermoneutral zone.

E.

Question 26

The thermoregulatory functions of the hypothalamus have been studied by implanting probes to heat or cool the hypothalamus of small mammals. If the hypothalamus is cooled, the animal will

Answer 26

increase metabolic heat production.

Question 27

Which tissue type is involved in transport, secretion, and absorption?

Answer 27

Epithelial tissue

Question 28

A high school cross-country runner ignores her coach’s rule about drinking water and taking breaks regularly. She overheats and collapses. The paramedics that come to her aid will

Answer 28

have an easy time starting an intravenous line because the blood vessels in her skin are dilated.

Question 29

In an analogy where your driving a car represents a physiological system, what is the desired speed of your car?

Answer 29

The set point

Question 30

Which of the following activities would cause a decrease in the hypothalamic temperature set point for metabolic heat production?

Answer 30

Taking an aspirin when you have a fever

Question 31

If an animal is kept in an enclosure at a constant temperature equal to its body temperature, which of the following mechanisms is responsible for most of its heat gain?

Answer 31

Metabolism

Question 32

When comparing relatively small mammals, such as mice and shrews, to large mammals, such as elephants and horses, the mice and shrews have

Answer 32

higher basal metabolic rates.

Question 33

Mammalian breast tissue is not always producing milk; however, the act of a newborn suckling will stimulate oxytocin production, which will trigger the breast tissue to produce more milk. This is an example of

Answer 33

positive feedback.