DNA is a polymer of four different nucleotides (A, C, G and T).
Proteins are polymers of amino acids.
The sequence of nucleotides in a gene determines the order of amino acids in a protein.
Each set of three nucleotides is a triplet code that corresponds to an amino acid, this code is universal.
Different organisms have different sequences of nucleotides in their DNA, but share this common coding system.

Common misconception

Genes, DNA and chromosomes are used interchangeably rather than understanding their separate definitions; also that organisms such as animals and plants are not related.

Use images to show the difference between DNA, genes and chromosomes; display a phylogenetic tree so the common ancestry of all living organisms can be visualised and so the commonality of DNA between all life.

Keywords

DNA - A large chemical molecule made of smaller chemical groups, it carries the genetic code of all living organisms.
Polymer - A chemical made up of smaller repeating chemical groups.
Protein - A chemical substance whose structure is coded for by the genetic code in genes.
Amino acid - A small chemical group that makes up a protein polymer, there are 20 types.
Nucleotide - A chemical group that make up the building blocks of DNA, the four types are coded A, T, C and G.

Carry out a modelling activity with a code and sweets as amino acids so pupils can build different proteins from different genes, all using the same triplet codes.

Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Starter quiz

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6 Questions

Q1.

Starting with the largest, put the structures in order of decreasing size.

1 - cell

2 - nucleus

3 - genome

4 - chromosome

5 - gene

Q2.

What does the order of nucleotide bases in a gene determine?

the structure of a carbohydrate molecule

the structure of a fat molecule

the structure of the nucleus

Correct answer: the structure of a protein molecule

Q3.

What is the name of the type of molecule that acts as a catalyst in living organisms?

Correct Answer: enzyme, enzymes

Q4.

The diagram shows a single nucleotide. Which part of the nucleotide joins the two strands of a DNA molecule together?

Correct Answer: B, b, part B, part b

Q5.

One strand of a DNA molecule has the base sequence A A T C G A G C A. Which is the complementary base sequence on the other strand of the DNA molecule?

A A T C G A G C A

A C G A G C T A A

Correct answer: T T A G C T C G T

C C G A T C T A G

Q6.

The photograph shows a model of DNA made from jelly babies and liquorice sticks. In this model, which parts of the nucleotide molecules are represented by the liquorice sticks?

Bases only

Sugars only

Bases and sugars

Bases and phosphates

Correct answer: Sugars and phosphates

Exit quiz

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6 Questions

Q1.

Match each word to its meaning.

Correct Answer:DNA,a polymer that carries the genetic code for all living organisms

a polymer that carries the genetic code for all living organisms

Correct Answer:nucleotide,small chemical group; 4 types (ATCG) are joined together to make DNA

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

Correct Answer:polymer,long chain molecule made of small chemical groups joined together

long chain molecule made of small chemical groups joined together

Correct Answer:protein,a polymer that can be structural or functional, coded for by a gene

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

Q2.

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

Correct answer: A and C

B and C

A, B and C

Q3.

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.

Correct answer: Nucleotides on one DNA strand determines the protein.

Q4.

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.

Correct answer: Three nucleotides code for one amino acid.

Three nucleotides code for three amino acids.

Q5.

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

1 - A gene has a sequence of nucleotides.

2 - Each three nucleotides make up a triplet code.

3 - Each triplet code codes for one of 20 amino acids.

4 - The triplet code sequence determines the amino acid sequence.

5 - The amino acid sequence determines the structure of the protein.

Q6.

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

Correct answer: 63