DNA & Protein

Protein Synthesis HOME

2) Overview of Protein Synthesis & RNA

3) Transcription

4) Translation

Success Criteria & Vocabulary

Click this drop-down menu to see the Success Criteria.

  • I can describe the purpose of DNA.

  • I can draw the general structure of DNA and nucleotides.

  • I can describe the ‘one gene, one peptide’ concept.

  • I can identify the components that make up a protein.

Click this drop-down menu to see the list of Vocabulary.

DNA: Double-stranded nucleic acid that carries the unique genetic code of an individual.

Deoxyribonucleotide: One structural unit/monomer of DNA.

Monomer: A small molecule that may bond to other identical molecules to form a polymer.

Polymer: A large molecule consisting of many repeating units/monomers linked together.

Anti-parallel: Two strands of DNA run in opposite directions. The 3’ end of one chain is opposite to the 5’ end of the other.

Complementary base pairing: C pairs with G, A pairs with T (in DNA).

Gene: A sequence of DNA that carries the genetic code/instructions for the production of a protein.

Triplet: A sequence of three consecutive bases on DNA.

Amino acid: Small organic molecule that is the building blocks of protein.

Peptide bond: The bond that links amino acids together to form a polypeptide chain.

Polypeptide chain: A sequence of amino acids bonded together by peptide bonds.

Protein: Complex molecules made up of a string of amino acids folded into a 3D shape. This molecule is coded for by genes.

Self-Directed Learning Tasks

Task 1: Read Slides #2-12 OR Support Notes (below).

2.7 Protein Synthesis (ADE)

Task 2: Complete My Notes

My Notes on DNA & Proteins

Task 2 continued: Protein Folding Simulation (for My Notes)

Task 3: Complete Education Perfect:

Task called 'DNA & Proteins'.

Level 2 Biology (ext) sciPAD answers.pdf

(EXTENSION) Task 5: Exploring Protein 3D Structure

The protein shown below is made up of the following amino acids (Leu, Ser, Phe, Val, Asn, and Gln). Explore the protein structure so that you can understand that:

  1. All proteins have a unique 3D shape.

  2. Protein shape is determined by the amino acids in the polypeptide chain.

  3. All proteins are made up of amino acids joined together by a peptide bond.

  4. All amino acids are different (have different properties/characteristics), because all amino acids are made up of different elements/types of atoms.

Support Notes

All you need to know about DNA

What is DNA? Why do we have it?

DNA stands for deoxyribonucleic acid. It stores all the genetic material of an organism, long-term. Because it is so important, DNA must be packaged inside the nucleus to protect it from getting damaged.

The Structure of DNA

DNA (deoxyribonucleic acid) is the very large molecule found in chromosomes which carries the genetic code of an organism. Its shape is a double helix as two strands twist together (like a spiral staircase). The side strands (the hand rails of the spiral staircase) are made of alternating sugar and phosphate groups; the cross strands (the steps on the spiral staircase) are the paired bases.

DNA is a polymer. Each strand of DNA is made up of many repeating units called deoxyribonucleotides. A deoxyribonucleotide is made up of three parts: a deoxyribose sugar, a phosphate group, and a nitrogen base. The only difference between deoxyribonucleotides is the base that they contain: A, C, T, or G.

The base pairs are held together by weak hydrogen bonds and these hold the two strands of DNA together. Three hydrogen bonds hold C and G together, two hydrogen bonds hold A and T together. Because the hydrogen bonds are weak, the two strands can easily be separated during DNA replication and transcription by enzymes called polymerases.


The bases always pair according to the complementary base pairing rule: A with T, C with G. This complementary base pairing of bases in one chain determines the sequence in the other, each half of the helix contains the information for building the other half. So if one strand contains the sequence 5’-CATTAG-3’, and complementary sequence must be 3’-GTAATC-5’.

It is the sequence of bases along one strand (the template strand) that is the genetic code, as you will learn below.


The two ends of polynucleotide chain (one strand of DNA or RNA) are different, and are called 3’ (said as “3 prime”) and 5’ (said as “5 prime”) ends, based on the numbering of the carbon atoms in the deoxyribose or ribose sugar, respectively. You can think of this polynucleotide chain as a line of elephants, each using its trunk to hold the tail of the one ahead. Now matter how long the chain of elephants, it ends in a trunk at one end, a tail at the other.

The two chains are anti-parallel, i.e. they run in opposite directions. The 3’ end of one chain being opposite the 5’ end of the other chain.

Video: DNA Structure and Function (Amoeba Sisters). Very basic video on DNA structure.
Video: Genes, DNA and Chromosomes explained.
Video: The Structure of DNA. Excellent, comprehensive video. You do not need to know about the chemistry terms.

One Gene, One Polypeptide

(a.k.a One Gene, One Enzyme hypothesis - or One Gene, One Protein hypothesis)

Video: One Gene One Enzyme (Bill Nye)

You will have learned that the function of a gene is to code for a trait. Well actually, it's more complicated then that. The function of a gene is to specify the order in which amino acids are linked together to produce of a polypeptide chain. This is known as the 'one gene, one polypeptide' hypothesis.

A polypeptide chain is a sequence of amino acids linked together by peptide bonds. Polypeptide chains twist and fold to form proteins. One gene codes for one polypeptide!

A sequence of three consecutive bases, called a triplet, codes for an amino acid. Amino acids are the building blocks of proteins. These amino acids are then linked together by peptide bonds to give a distinctive protein with a specific function in the body.

Proteins are what give rise to all our traits, such as eye colour and blood type. Humans have over 21,000 proteins that are coded for by our genome!

Different sequences of bases along a gene may produce proteins that are slightly different (e.g. one base sequence in humans codes for blue eye colour while another base sequence codes for brown eye colour). Different forms of a gene are called alleles.

Above: Torpinase is a gene that codes for the order in which amino acids are linked together to produce a polypeptide chain that will fold into the Torpinase protein.
You can see that every 3 bases (triplet) in the Torpinase gene codes for 1 amino acid (coloured circle).
Separate amino acids are linked together by peptide bonds, like a string of beads, to form a polypeptide chain.
This polypeptide chain will fold into a specific shape to become the Torpinase protein.


Protein Function

Proteins can be found throughout the bodies of all living organisms, where they are responsible for carrying out a huge variety of tasks. Proteins have many functions:

  • Enzymes (biological catalysts) are proteins.

  • Proteins form an essential part of all cell membranes. Many membrane proteins are important in the active transport of substances into and out of cells.

  • They may have a structural function. For example collagen (in tendon, ligament, and bone), keratin (in hair, feathers, claws, nails, and skin).

  • Some hormones are proteins (e.g. insulin).

  • The antibodies that help defend animals against disease are all proteins.

  • Some proteins have a transport function (e.g. haemoglobin).

  • Some proteins are contractile and are responsible for movement (e.g. actin and myosin of muscle, and tubulin that makes up spindle fibres in cell division).

If the proteins in our body are functioning properly, then we will also be functioning properly.

Amino Acids and Polypeptides

A protein molecule consists of one or more chains of up to several thousand amino acids linked together in a particular order. The amino acids are joined together by peptide bonds, forming a long chain called a polypeptide.

The information for the sequence of amino acids in a polypeptide is stored in a gene. There are 20 amino acids used to make proteins (you don’t have to know their names). (You also do not have to know the chemical reaction that bonds amino acids together).

Structure of Proteins

The sequence of amino acids in a polypeptide chain causes it to bend and twist, so that sections of the chain are side by side. Some amino acids interact with each other depending on their chemical properties to form hydrogen bonds or disulfide bridges. These bonds between sections of the polypeptide chain hold the protein together in a specific shape, giving it a unique 3D structure.

The unique sequence of amino acids and therefore the individual shape of a protein ultimately determines its function.