The genetic code | Exit Quiz | Oak National Academy

Match each word to its meaning.

• nucleotide

• a polymer that can be structural or functional, coded for by a gene

• DNA

• a polymer that carries the genetic code for all living organisms

• polymer

• small chemical group; 4 types (ATCG) are joined together to make DNA

• protein

• long chain molecule made of small chemical groups joined together

Answer explanation

DNA and proteins are both polymers. DNA is a polynucleotide. Proteins are built from 20 different amino acids. Each protein has a different sequence and number of amino acids.

The diagram shows a nucleotide. DNA molecules have four types of nucleotides. Which sub units are the same in all four types?

• A and B

• A and C

• B and C

• A, B and C

Answer explanation

Nucleotides vary only in their bases. All other parts of the nucleotide are identical.

A gene is a section of DNA that codes for a particular protein. Each gene is a sequence of nucleotides. There are four different nucleotides. Which statement best describes how this code works?

• Each nucleotide makes a different protein.

• The number of nucleotides determines the protein.

• Nucleotides on both DNA strands determine the protein.

• Nucleotides on one DNA strand determines the protein.

Answer explanation

The order of nucleotides on only one of the two DNA strands is used to code for a protein and to determine its structure.

The genetic code is often described as a triplet code. Why?

• Each nucleotide codes for three amino acids.

• Three nucleotides code for a protein.

• Three nucleotides code for three proteins.

• Three nucleotides code for one amino acid.

• Three nucleotides code for three amino acids.

Answer explanation

A ‘triplet code’ is three nucleotides, and each triplet of nucleotides is the code for one amino acid.

Put the statements in order, to describe how the nucleotides in a gene are the code for making a protein.

• The triplet code sequence determines the amino acid sequence.

• The amino acid sequence determines the structure of the protein.

• Each triplet code codes for one of 20 amino acids.

• Each three nucleotides make up a triplet code.

• A gene has a sequence of nucleotides.

Answer explanation

Genes are instructions to build proteins. The genetic code carried by genes is now known to be universal to all living things.

A protein is 21 amino acids long. How many nucleotides code for this chain of 21 amino acids?

• 7

• 21

• 42

• 63

Answer explanation

Three nucleotides code for each amino acid in the chain, so if there are 21 amino acids there must be 3 × 21 nucleotides, which is 63.