The genetic code | Exit Quiz | Oak National Academy

Match each word to its meaning.

• polymer

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

• nucleotide

• long chain molecule made of small chemical groups joined together

• DNA

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

• protein

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

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.

• Each three nucleotides make up a triplet code.

• A gene has a sequence of nucleotides.

• 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.

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.