Genetic code

Question 1

What is a gene?

Answer 1

-genetic information coded in the sequence of bases in the DNA, in thousands of sections along its length

Question 2

What does the base sequence direct?

Answer 2

-which amino acids join together and therefore determines which proteins are made, which reactions can take place in an organism

Question 3

What is a genetic code?

Answer 3

-triplet code

Question 4

A polynucleotide strand always has

Answer 4

-three times the number of bases as the amino acid chain it coded for

Question 5

If three bases were removed from a polynucleotide chain what would happen?

Answer 5

-polypeptide would have one fewer amino acid

Question 6

If a polynucleotide had three extra bases then the polypeptide would have…

Answer 6

-one more amino acid

Question 7

How many different amino acids occur in proteins?

Answer 7

-twenty

Question 8

Characteristics of the genetic code

Answer 8

-3 bases encode each amino acid so code is a triplet
-64 possible combinations but only 20 amino acids found in proteins
-more than one triplet can encode each amino acid so code is described as ‘degenerate’
-3 triplet codes that do not code for amino acids in mRNA - ‘stop’ codons
-code is universal-known in all organisms, same triplets code for the same amino acid
-code is non-overlapping: each base occurs in only one triplet

Question 9

What do ‘stop’ codons do?

Answer 9

-mark the end of a portion to be translated