Proteins are composed of amino acids that are linked together through peptide bonds. There are four levels of protein structure: primary, secondary, tertiary, and quaternary. The primary structure is the linear sequence of amino acids. Secondary structure involves hydrogen bonding that causes the chain to fold into structures like alpha helices and beta sheets. Tertiary structure describes the final three-dimensional shape formed by interactions between R groups of the amino acids. Quaternary structure involves interactions between multiple polypeptide subunits.

1. Proteins?

2. Protein structure
WALT: To understand the composition and
various structures of proteins.
Sunday, 28 September 2014
WILF:
~ Identify the basic structures of proteins.
~ Describe how proteins are formed from
amino acids.
~ Describe the differences between the
primary, secondary, tertiary and quaternary
structures of proteins.
Keywords
Peptide bond
Condensation
reaction
Polypeptide
Hydrogen bonds
Disulphide bonds
Ionic bonds

4. Transcription
What? The weak hydrogen
bonds between the DNA
strands are broken and the
strands separate.
One DNA strand is used as a
template.
Complementary bases pair up
to the template, forming
messenger RNA (mRNA).
mRNA does not have the
base thymine (T). Adenine (A)
pairs with uracil (U) instead.
Where? Inside the nucleus.
mRNA

5. Translation Where? In the cytoplasm.
tRNA Protein (polypeptide)
ribosome
amino acids
mRNA
The mRNA is decoded in
groups of 3 (triplet or
codon)

6. Amino acids
Polymer: Protein or polypeptide
Monomer: Amino acid
All Amino Acids have an alkaline amino group (-NH2) and an acid
carboxyl group (-COOH).
There are just 20 naturally occurring Amino Acids, each with a
different -R group.

7. The 20 naturally occurring
amino acids.

8. Condensation reaction
Molecule of
water removed
Peptide bond
formed 
dipeptide

10. Primary Structure
The sequence of amino acids in the
polypeptide chain.
This structure determines
shape and function of the
protein.
Genetic mutations.

11. Primary Structure

13. Secondary Structure
Weak hydrogen bonds form between the
polypeptide chains.
Chain folds, 3d shape
 Alpha helix
Beta pleated sheet

14. Secondary Structure

15. The
Alpha
helix
The Beta
pleated
sheet
------------ weak
hydrogen bonds
_________
strong covalent
bonds

17. Tertiary Structure
Further twisting and folding of secondary
structures.
Unique 3d structure.
Disulphide bonds
Ionic bonds
Hydrogen bonds

18. Tertiary Structure

20. Quaternary Structure
Further complexity.
Pairs of chains may bind
together or other inorganic
substances may be
incorporated into the molecule.
(Prosthetic Groups)
e.g. haemoglobin

21. Quaternary Structure

22. Primary structure Secondary structure
Tertiary structure Quaternary
structure
Task 1: Fold A3 paper into four and
assign a title for each. Cut out and
stick the relevant statements and
diagrams for each structure in the
correct box.
Task 2: Add further detail to each
box by answering the questions.

23. Primary structure:
1. Explain how amino acids are joined together to form the primary
structure.
2. Explain how one single change in the amino acid chain can affect the
protein from carrying out it’s function.
Secondary structure:
3. Explain how the weak hydrogen bonds are formed in the secondary
structure of proteins.
Tertiary structure:
4. Name and describe the different bonds that can form in the formation of a
tertiary structure.
5. Explain how the 3D shape of a protein is important to its function.
Quaternary structure:
6. Explain what a prosthetic group is and name an example.

24. Further complexity.
Prosthetic Groups
Further twisting and
folding of secondary
structures.
Unique 3d structure.
Weak hydrogen bonds
form between the
polypeptide chains.
Alpha helix
Beta pleated sheet
The sequence of
amino acids in the
polypeptide chain.

25. Test for proteins
The Biuret test.
1.Place a sample in solution in a test tube.
2.Add an equal volume of sodium hydroxide.
3.Add a few drops of dilute copper sulphate
solution and gently mix.
4.Positive purple or negative blue.