Proteins have four levels of structure - primary, secondary, tertiary, and quaternary. The primary structure is the amino acid sequence. Secondary structures include alpha helices and beta sheets formed by hydrogen bonding. Tertiary structure is the overall 3D shape formed by various bonds. Quaternary structure occurs when multiple polypeptide chains combine. Proteins can be fibrous like collagen or globular like enzymes. Polar and nonpolar amino acids determine protein location and function, like in membranes or enzyme active sites. Major protein functions include enzymes, structure, transport, movement, hormones, and defense, for examples like catalase, collagen, hemoglobin, myosin, insulin, and immunoglobulins.

1. 7.5 Proteins
Topic 7 Nucleic Acids & Proteins

2. 7.5.1 Explain the four levels of protein structure, indicating the
significance of each level.
(Quaternary structure may involve the binding of a
prosthetic group to form a conjugated protein)
7.5.2 Outline the difference between fibrous and globular
proteins, with reference to two examples of each type.
7.5.3 Explain the significance of polar and non-polar amino
acids.
(Limit this to controlling the position of proteins in
membranes, creating hydrophilic channels through
membranes, and the specificity of active sites in enzymes)

3. 7.5.4 State four functions of proteins, giving a named example
of each. (Membrane proteins should not be included)

4. Protein Structure
 Proteins have a complex structure.
 They are built up from amino acids.
 The sequence of amino acids will determine its shape and
ultimately its function.
 We can define four levels of structure in proteins:
 Primary structure
 Secondary structure
 Tertiary structure
 Quaternary structure

5. Protein Structure
 Primary Structure:
 Is the linear sequence of amino
acids in a protein.
 The amino acids are held together
by peptide linkages - covalent
bonds.
 Bonding involved
 Covalent bonds between amino
acids – peptide bonds (linkages).

6. Protein Structure
 Secondary Structure:
 These are regularly repeating
structures.
 These include α-helix and β-
pleated sheets.
 α-helix: where the polypeptide
chain is wound into a helix.
 β-pleated sheets:
 Bonding involved:
 Hydrogen bonding between
different amino acids in helix or
pleated sheets.

7. Protein Structure
 Tertiary Structure:
 Results in the overall three-
dimensional shape of the protein
 Can form either globular or fibrous
proteins.
 3D shape determines its functions.
 Bonding involved includes:
 Covalent bonding – disulfide bridges
 Hydrogen bonding
 Ionic bonding
 Hydrophobic interactions

8. Protein Structure
 Quaternary Structure:
 Is when two or more polypeptide chains
are linked together.
 Bonding involved includes:
 Covalent bonding – disulfide bridges
 Hydrogen bonding
 Ionic bonding
 Hydrophobic interactions

9. Shape of Proteins
 Proteins can be divided into two types according to their
shape:
 Fibrous
 Have a long and narrow shape.
 Are mostly insoluble in water.
 eg: keratin, collagen
 Globular
 Have a rounded shape.
 Are mostly soluble in water.
 eg: enzymes, antibodies

10. Polar & Non-polar Groups
 Amino acids can be divided into two types according to
the chemical characteristics of their R groups:
 Polar amino acids have hydrophilic R groups. (12)
 Non-polar amino acids have hydrophobic R groups. (8)
 The distribution of polar and non-polar amino acids in a
protein influence where the protein is located in a cell and
what function it can carry out.
Amine
group
Carboxyl
group

11. Polar & Non-polar Groups

12. Protein Functions
 Proteins have a huge range
 Enzymes
 eg: catalase
 Structural.
 eg: collagen
 Transport.
 eg: haemoglobin
of functions:
 Movement.
 eg: myosin
 Hormones
 eg: insulin
 Defence.
 eg: immunoglobulin

13. 7.5.1 Explain the four levels of protein structure, indicating the
significance of each level.
(Quaternary structure may involve the binding of a
prosthetic group to form a conjugated protein)
7.5.2 Outline the difference between fibrous and globular
proteins, with reference to two examples of each type.
7.5.3 Explain the significance of polar and non-polar amino
acids.
(Limit this to controlling the position of proteins in
membranes, creating hydrophilic channels through
membranes, and the specificity of active sites in enzymes)

14. 7.5.4 State four functions of proteins, giving a named example
of each. (Membrane proteins should not be included)