Module 04 - Section 03

Question 1

What are the 3 important characteristics of the genetic code?

Answer 1

(1) Degenerate
(2) Robust
(3) Universal

Question 2

What do we mean by the genetic code is degenerate?

Answer 2

A degenerate code is one in which several codons have the same meaning – 64 ways to combine 4 different nucleotides in a triplet codon sequence, but only 20 amino acids

Question 3

What are the 3 stop codons?

Answer 3

UAA, UAG, UGA

Question 4

What do we mean by the genetic code is robust?

Answer 4

The degeneracy of the genetic code is advantageous because it proves the DNA with the ability to absorb single-base mutations with minimal consequences to the protein it encodes

Question 5

What do we mean by the genetic code is universal?

Answer 5

All organisms use the same genetic code with only a few minor modifications – allows biologists to track evolution on a molecular level

Question 6

What are the 5 rules of the genetic code?

Answer 6

(1) non-overlapping (each codon read as an independent unit)
(2) does not contain pauses
(3) read in triplets
(4) Read in a linear fashion
(5) Resistant to mutations

Question 7

How did Heinz Fraenkel-Conrat & Akira Tsugita prooved the genetic code is non-overlapping?

Answer 7

They treated tobacco mosaic virus (TMV) with nitrous acid which causes single bp substitution mutations. Looking at mutant protein in TMV almost all mutant had only one amino acid change (overlapping would create multiple change per 1 bp mutation)

Question 8

How was it proved that the genetic code does not contain pauses?

Answer 8

Insertion or deletion of 1 bp mostly completely inactivated the gene - which suggests that not one but many amino acids were change by the acridine-induced mutations

Question 9

What is a frame shift mutation?

Answer 9

Caused by the insertion or deletion of one or more paired nucleotides, changin the reading frame of codons during protein synthesis

Question 10

What is the most frequent mutation?

Answer 10

Transition mutation - a purine is replaced by another purine or a pyrimidine by a pyrimidine

Question 11

Which type of transitional mutation rarely cause a change at all?

Answer 11

third position mutation

Question 12

Which position determines whether the codon codes for a polar or hydrophobic amino acid?

Answer 12

2nd position
purine codes for a polar
pyrimidine codes for hydrophobicWhich type of transitional mutation rarely cause a change at all?

Question 13

Which type of transitional mutation will most likely result in an amino acid change??

Answer 13

2st position

Question 14

What are the 4 kinds of mutations in the genetic code&

Answer 14

(1) Silent
(2) Missense
(3) Nonsense
(4) Non-stop

Question 15

What is a silent mutation?

Answer 15

Non-deleterious mutation that do not result in an amino acid replacement (example: change in 3rd position codon result in an amino acid change only about 25 % of the time)

Question 16

What is a missense mutation?

Answer 16

Single-base substitution that leads to the replacement of one amino acid with another - can be deleterious or non-deleterious

Question 17

What is a nonsense mutation?

Answer 17

Codon change that result in a termination codon - abort protein synthesis resulting in an incomplete protein that is rarely functional

Question 18

What is a non-stop mutation?

Answer 18

Loss of a stop codon

Question 19

Why would it be advantageous for the code not to be completely resistant?

Answer 19

Evolution - a bit of mutation is a good thing it allow the opportunity for the evolution of variants with higher fitness