Question 1

Proteins with similar primary structure and function can usually be grouped into families based on their degree of sequence similarity. A small region of 6 aligned amino acids in protein from 5 related species is shown below. 
(1) QMADGCK
(2) QIVDLYR
(3) QIADGCK
(4) QMAEGCK
(5) QFVDLYR
Similarity is judged by a distance matrix in which each cell enumerates the number (or percent) of differences between any pair of sequences. Which of the distance matrices below reflects the differences among the five sequences shown above?

Accepted Answer

The answer of Proteins with similar primary structure and function...

Question 2

A change in the sequence of a gene is referred to as a(n) _____.

Accepted Answer

The answer of A change in the sequence of a...

Question 3

A folding domain of a polypeptide chain has a primary structure containing 5 phenylalanine residues as shown below, where F represents the side chain of phenylalanine.

If this domain folds in one of the two orientations below, which is more likely-the one on the left or the one on the right?

Accepted Answer

The answer of A folding domain of a polypeptide chain...

Question 4

In a protein-coding region of DNA, a mutation that replaces a single nucleotide, but does not change the resulting amino acid, is likely to be:

Accepted Answer

This type of mutation is known as a synonymous or silent mutation, and it often occurs at the 3' position in a codon of the transcribed mRNA due to the degeneracy of the genetic code, where multiple codons can encode for the same amino acid.

Question 5

In a protein-coding region, a mutation that replaces a single nucleotide for another always changes the resulting amino acid.

Accepted Answer

Some mutations in a protein-coding region are "silent" or "synonymous," meaning that the change in nucleotide does not alter the amino acid due to the redundancy in the genetic code.

Question 6

A mutation takes place in a protein-coding gene that changes one codon resulting in a single amino acid replacement. Which type of replacement is MOST likely to result in a disruption of protein structure and function?

Accepted Answer

The answer of A mutation takes place in a protein-coding...

Question 7

Proteins that evolve extremely rapidly are often difficult to group into families according to their level of sequence similarity. Can you suggest a reason why?

Accepted Answer

The answer of Proteins that evolve extremely rapidly are often...

Question 8

Structurally and functionally related groups of proteins are referred to as:

Accepted Answer

Proteins that share significant sequence and structural similarities are grouped into families. These families can include proteins with similar functions and/or evolutionary lineages.

Question 9

With 20 amino acids, the number of possible polypeptides exactly 10 amino acids in length is given by:

Accepted Answer

The number of possible polypeptides exactly 10 amino acids in length is given by: 20¹⁰ = 20 × 19 × 18 × 17 × 16 × 15 × 14 × 13 × 12 × 11 = 20!/10! = 20 × 19 × 18 × 17 × 16 × 15 × 14 × 13 × 12 × 11 = 6,189,700,683,339,120 Therefore, the best choice is C (20¹⁰).

Question 10

Structurally and functionally related proteins are grouped into approximately 25,000 different protein _____.

Accepted Answer

The answer of Structurally and functionally related proteins are grouped...

Question 11

There is approximately the same number of protein families as there are folding domains.

Accepted Answer

There are more protein families than there are folding domains. A protein family can have multiple folding domains or have a domain that is also found in other protein families.

Question 12

Which of the following processes occur in the cytoplasm of eukaryotic cells?

Accepted Answer

Transcription and translation are two processes that occur in the cytoplasm of eukaryotic cells. DNA replication occurs in the nucleus. Therefore, options A, D, and E can be eliminated. Translation requires ribosomes, which are found in the cytoplasm, but it cannot occur without transcription first. Therefore, option B can also be eliminated.

Question 13

In a population of organisms, beneficial and harmful random mutations are retained or eliminated through the process of:

Accepted Answer

The process in which beneficial and harmful mutations are retained or eliminated in a population is called selection. In this process, organisms with beneficial mutations are more likely to survive and reproduce, passing on those beneficial traits to their offspring. Harmful mutations may lead to decreased fitness and lower chances of survival and reproduction, leading to their elimination from the population. Conservation, translation, expression, and folding are all important processes in biology, but they are not directly related to the retention or elimination of mutations in a population.

Question 14

A region of a protein that folds in a particular way, and that carries out a specific function, is referred to as a folding _____.

Accepted Answer

The answer of A region of a protein that folds...

Question 15

The frequency of mutations does not necessarily decrease or increase over time.

Accepted Answer

The frequency of mutations can stay constant or vary depending on various factors such as selective pressure, genetic drift, and environmental factors. Therefore, it is not necessarily increasing or decreasing over time.

Question 16

Amino acid sequences evolve through:

Accepted Answer

Amino acid sequences evolve through both mutation, which generates genetic variation, and selection, which determines which variations become more or less common in a population. Therefore, the best choice is D, as it includes both mutation and selection as important factors in sequence evolution. Adaptation can also play a role in evolution, but it is a result of the interplay between mutation and selection rather than a separate process.

Question 17

A region of a polypeptide that folds in a particular way, relatively independently of the rest of the molecule, is a folding:

Accepted Answer

A region of a polypeptide that folds in a particular way, relatively independently of the rest of the molecule, is a domain. Domains often have specific functions and can be present in multiple proteins.

Question 18

The histone proteins are among the most slowly evolving proteins. For example, a histone protein called histone H4 in cows and peas differs by only 2 amino acids among a total of about 100. Suggest a reason why histone proteins evolve so slowly.

Accepted Answer

The answer of The histone proteins are among the most...

Question 19

In a protein-coding region, any amino acid can be replaced with any other amino acid by a mutation that replaces a single nucleotide for another.

Accepted Answer

This statement is not completely true. Some substitutions of amino acids may be more likely to occur due to the genetic code, which dictates which nucleotide triplets code for which amino acids. For example, a substitution of the first nucleotide in a codon is more likely to result in a conservative substitution (i.e. a similar amino acid) than a substitution of the third nucleotide. Additionally, certain amino acids may be more critical for the structure or function of the protein, making substitutions of those amino acids less likely to be successful.

Question 20

If you were to group the proteins in the previous problem into two families based on the distance matrix, which proteins would you group together?

Accepted Answer

The answer of If you were to group the proteins...

Quiz 4: Translation and Protein Structure