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

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

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

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)

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

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.

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

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

4g) Chromosome Mutations Chromosomes Mutations include:- 1. Deletion Example: loss of segment of a chromosome Normal sequence: 123456789 Mutated sequence: 123789 2. Duplication Example: repeat of segment of a chromosome Mutated sequence: 123456456789 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

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