CHAPTER 13

Question 1

What is the main function of genetic material in cells?

Answer 1

-Encode the production of cellular proteins in the correct cell, at the proper time, and in the correct amount.

Question 2

What disease did Archibald Garrod study, and what did he propose about it?

Answer 2

He studied alkaptonuria, proposing it was due to a missing enzyme (homogentisic acid oxidase) and that the disease followed a recessive pattern of inheritance.

Question 3

What hypothesis did Beadle and Tatum’s work with Neurospora crassa lead to?

Answer 3

The “one gene–one enzyme” hypothesis, suggesting each gene controls the synthesis of a single enzyme.

Question 4

How was the one gene–one enzyme hypothesis modified?

Answer 4

It was refined to “one gene–one polypeptide,” acknowledging that genes also code for non-enzyme proteins and functional RNAs.

Question 5

Codon

Answer 5

A group of three nucleotides on mRNA that specifies an amino acid.

Question 6

Which codon is the start codon, and what does it specify?

Answer 6

AUG is the start codon, specifying methionine and setting the reading frame.

Question 7

What does it mean that the genetic code is degenerate?

Answer 7

Multiple codons can specify the same amino acid, called synonymous codons.

Question 8

Which amino acids are more likely to be found on the surface of proteins?

Answer 8

Polar and charged amino acids, as they are hydrophilic.

Question 9

Name the four levels of protein structure.

Answer 9

-Primary (sequence)
-Secondary (α-helix and β-sheet)
-Tertiary (3D folding)
-Quaternary (subunit association).

Question 10

What are some functions of proteins in cells?

Answer 10

-Transport
-cell signaling
-cell shape
-enzyme activity
-cell surface recognition

Question 11

What is the function of tRNA in protein synthesis?

Answer 11

It serves as an adaptor molecule, recognizing mRNA codons and carrying the corresponding amino acid.

Question 12

What enzyme is responsible for attaching amino acids to tRNA?

Answer 12

Aminoacyl-tRNA synthetase, with one specific enzyme for each amino acid.

Question 13

Why is accuracy in aminoacyl-tRNA synthetase important?

Answer 13

It ensures the correct amino acid is attached to tRNA, preventing nonfunctional polypeptides

Question 14

Anticodon

Answer 14

A sequence on tRNA that pairs with a complementary codon on mRNA during translation.

Question 15

What are selenocysteine and pyrrolysine?

Answer 15

Uncommon amino acids encoded by UGA and UAG codons, found in specialized enzymes.

Question 16

The reading frame begins with a ____________ and is read _____________.

Answer 16

Start codon; in groups of three bases.

Question 17

Wobble Rule

Answer 17

Explains that the first two positions in codon-anticodon pairing follow strict AU/GC rules, but the third position can “wobble,” allowing for some mismatches.

Question 18

What are isoacceptor tRNAs?

Answer 18

Isoacceptor tRNAs are tRNAs that can recognize the same codon but differ at the wobble position.

Question 19

If a tRNA has the anticodon sequence 3’—GAC—5’, which amino acid does it carry?

Answer 19

Leucine

Question 20

Aminoacyl-tRNA synthetase

Answer 20

Enzyme attaches an amino acid to the 3’ end of a tRNA

Question 21

What are the two types of ribosomes in eukaryotic cells?

Answer 21

1. Cytoplasmic ribosomes
2. ribosomes found in organelles (mitochondria and chloroplasts).

Question 22

What are the three functional sites of a ribosome?

Answer 22

1. Peptidyl site (P site)
2. Aminoacyl site (A site)
3. Exit site (E site)

Question 23

What stages make up the translation process?

Answer 23

1. Initiation
2. Elongation
3. Termination

Question 24

What is the Shine-Dalgarno sequence, and where is it found?

Answer 24

The Shine-Dalgarno sequence is a ribosomal binding site in bacteria that helps align the mRNA with the 30S subunit.

Question 25

In eukaryotes, what sequence elements are required for a start codon to be recognized according to Kozak’s rules?

Answer 25

A G at the +4 position and a purine (A) at the -3 position relative to the AUG start codon.

Question 26

A site

Answer 26

During translation elongation, charged tRNA first enters the ribosome

Question 27

Which rRNA acts as the peptidyl transferase in the ribosome?

Answer 27

23S rRNA in the large ribosomal subunit.

Question 28

What are the stop codons in translation?

Answer 28

UAG, UAA, and UGA.

Question 29

What is a release factor, and why is it a “molecular mimic”?

Answer 29

It is a protein that binds to stop codons to terminate translation; it mimics the structure of tRNA.

Question 30

According to Kozak’s rules, what determines the start codon in eukaryotes?

Answer 30

The choice of the start codon in eukaryotes.

Question 31

What happens during the peptidyl transfer reaction?

Answer 31

The polypeptide attached to tRNA in the P site forms a peptide bond with an amino acid on tRNA in the A site.

Question 32

How do antibiotics like tetracycline and streptomycin affect translation?

Answer 32

-Tetracycline inhibits binding of aminoacyl-tRNAs
-Streptomycin causes misreading of codons, producing abnormal polypeptides.