Genes and the genetic code

Question 1

What is a gene?

Answer 1

A base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA.

Question 2

What is a locus?

Answer 2

The location of a gene

Question 3

What is a triplet?

Answer 3

A sequence of three DNA bases that codes for a specific amino acid

Question 4

What are the three features of the genetic code?

Answer 4

• non-overlapping
• Degenerate
• Universal

Question 5

What does non- overlapping mean?

Answer 5

Each triplet is only read once and the triplets do not share any bases

Question 6

What does degenerate mean?

Answer 6

Multiple sequences of triplets can code for the same amino acid, reducing mutations

Question 7

What does universal mean?

Answer 7

• Every organism contains the same 20 amino acids
• Each triplet codes for the same amino acid
• All 4 bases are the same

Question 8

How many triplets are there?

Answer 8

There are 64 triplets, as there are 4 bases which all code for multiple amino acids

Question 9

Why do not all parts of DNA code for an amino acid

Answer 9

There are introns, which are non coding areas and are spliced out

Question 10

What are exons?

Answer 10

base sequences that code for a polypeptide

Question 11

Contrast DNA in prokaryotic and eukaryotic cells.

Answer 11

• DNA in prokaryotic cells is shorter and more circular whereas DNA in eukaryotic cells is longer
• DNA is not associated in proteins in prokaryotic cells whereas in eukaryotic cells it is associated to histones which form chromosomes
• DNA in eukaryotic cells contains introns whereas DNA in prokaryotic cells does not

Question 12

Define chromosomes

Answer 12

Two sister chromatids attached by a centromere and coiled around a histone

Question 13

What are homologous chromosomes?

Answer 13

Two chromosomes that carry the same gene but not necessarily the same alleles

Question 14

What is an allele?

Answer 14

Different versions of the same gene