1. KEY AREA 4: Genes and Proteins in Health & Disease
Higher Human Biology
Unit 1
Human Cells
KEY AREA 4: Genes and Proteins in Health & Disease

2. Human Cells Learning Intentions
KEY AREA 4 – Genes and Proteins in Health & Disease
Genes and Proteins
Mutations

3. 4a) Genes and Proteins in Health & Disease
All proteins contain Carbon, Hydrogen, Oxygen and Nitrogen (sometimes sulphur)
Each protein is made from amino acids linked by peptide bonds to form polypeptide chains
During protein synthesis, the sequence of DNA bases determines the sequence of amino acids
The sequence of amino acids, determines the structure and function of the protein
Hydrogen bonds form between specific amino acids in a polypeptide chain, causing the chain to become coiled or folded

4. 4b) Genes and Proteins in Health & Disease
During folding, different regions of the polypeptide chain can come into contact with one another. This allows interaction between amino acids in one or more chains, resulting in cross connections (e.g. bridges between sulphur atoms, attraction between positive and negative charges and further hydrogen bonding)
Proteins are held in a three dimensional shape by peptide bonds, hydrogen bonds, and interactions between amino acids
Polypeptide chains can become:-
- Arranged in long parallel strands (e.g. fibrous protein – keratin)
- Folded into a spherical shape (e.g. globular protein – enzyme amylase
- Folded into a spherical shape with a non-protein part added (e.g. haemoglobin)

5. 4c) Functions of Proteins
Proteins have a large variety of structures and shapes resulting in a wide range of functions.
Examples include:-
Enzymes
Structural proteins
Hormones
Antibodies

6. 4d) Mutations
A mutation is a change in the structure or composition of an organism’s genes
When a change in genotype produces a change in phenotype, the individual affected is called a mutant
Mutation rates vary from gene to gene, and from species to species
Mutations can be increased by mutagenic agents (e.g. mustard gas) and various types of radiation (X-Rays, UV light, Gamma Rays)
Mutations result in no protein, or a faulty protein being expressed
A genetic disorder is a condition or disease, that is directly related to the individual’s genotype.

7. 4e) Single Gene Mutations
Single gene mutations involve the alteration of a DNA nucleotide sequence as a result of:-
Substitution of nucleotides
EXAMPLE: Replacing Adenine with Guanine
Normal sequence: AAT TGG CCC AAA
Mutated sequence: GGT TGG CCC GGG
Insertion
EXAMPLE: Adding in another Guanine
Normal sequence: AAT TGG CCC AAA
Mutated sequence: AAT TGG GCC CAA A
Deletion
EXAMPLE: Deleting Cytosine
Mutated sequence: AAT TGG AAA

8. 4f) Mutations
A point mutation involves a change in one nucleotide (substituted, inserted, deleted)
Nature of Single Nucleotide Substitutions include:-
1. Missense (replacing one amino acid codon with another)
Example: Sickle-cell disease, PKU
2. Nonsense (replacing an amino acid codon with a premature stop codon so no amino acid is made and the process stops)
Example: Duchenne muscular dystrophy (DMD)
3. Splice-Site (creating or destroying the codons for exon-intron splicing)
Example: Beta Thalassemia
Nucleotide insertions or deletions result in frame shift mutations or an expansion of a nucleotide sequence repeat

9. 4g) Chromosome Mutations
Chromosomes Mutations include:-
1. Deletion
Example: loss of segment of a chromosome
Normal sequence:
Mutated sequence:
2. Duplication
Example: repeat of segment of a chromosome
Mutated sequence:
3. Translocation
Example: rearrangement of chromosomal material involving 2 or more chromosomes
Mutated sequence: 123abc789
NOTE: The substantial changes in chromosome mutations often make them lethal

10. Human Cells Questions
KEY AREA 4 – Genes and Proteins in Health & Disease
Testing Your Knowledge 1 Page 50 Q’s 1-2
2. Testing Your Knowledge 2 Page 62 Q’s 1-4
Quick Quiz