Higher Human Biology Unit 1 Human Cells KEY

Higher Human Biology Unit 1 Human Cells KEY AREA 4: Mutations

Human Cells Learning Intentions KEY AREA 4 – Mutations 1. Genes and Proteins 2. Mutations

4 a) Genes and Proteins 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 b) Protein structure 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 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)

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

4 d) 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) (N 5 Revision!) 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.

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

4 f) Gene Mutations Nature of Single Nucleotide Substitutions include: 1. Missense- result in one amino acid being changed for another, may result in a non-functional protein or it could have little effect Example: Sickle-cell disease, PKU 2. Nonsense- result in a premature stop codon being produced so no amino acid is made and translation stops, produces a shorter protein Example: Duchenne muscular dystrophy (DMD) 3. Splice-Site- result in some introns being retained and/or some exons not being included in the mature transcript Example: Beta Thalassemia Nucleotide insertions or deletions result in frame shift mutations all codons and therefore amino acids after the mutation are changed this has a major effect on the structure/function of the protein produced

4 g) Chromosome Mutations Chromosomes Mutations include: 1. Deletion Example: loss of segment of a chromosome 2. Normal sequence: 123456789 Mutated sequence: 123789 Duplication Example: segment of a chromosome is added from its homologous partner Normal sequence: 123456789 Mutated sequence: 123456456789

4 g) Chromosome Mutations- continued 3. Translocation Example: rearrangement of chromosomal material involving 2 or more chromosomes 4. Normal sequence: 123456789 Mutated sequence: 123 abc 789 Inversion Example: a section of chromosome is reversed Normal sequence: 123456789 Mutated Sequence: 123654789 NOTE: The substantial changes in chromosome mutations often make them lethal

Human Cells Questions KEY AREA 4 – Genes and Proteins in Health & Disease 1. Testing Your Knowledge 1 Page 50 Q’s 1 -2 2. Testing Your Knowledge 2 Page 62 Q’s 1 -4 3. Quick Quiz