Gene
Expression
, Gene Mutations
GENE MUTATIONS: change in the base sequence of DNA
CHROMOSOME MUTATIONS: any change to a proportion of a chromosome
NON-DISJUNCTION: a type of chromosome, mutation, when homologous pairs of chromosomes,
failed to separate in meiosis, resulting in gametes with incorrect numbers of chromosomes
Types of Mutations
1. Substitution
2. Deletion
3. Addition
4. Duplication
5. Inversion
6. Translocation
• how is the DNA sequence changed
• How affects mRNA
• How AA sequence changes (primary structure)
• 2 and 3 structure affected (name bonds)
Subitution
SILENT MUTATION: Base is changed resulting in change to a codon but the codon still codes
for the same AA
• no change to protein structure
• bc genetic code is degenerate
MISENSE MUTATION: a basis changed, resulting in a change to a single codon
• change in primary structure (diff seq of AAs)
• Change H , ionic, disuphide bridges in 3 structure
• 1 AA changed doesn't have much effect on- doesn't change function
NON-SENSE MUTATION: a basis, change, resulting in a change to a stop codon
• significant impact
• Shorter polypeptide
• E.g: enzyme - no AS formed
,Deletion
One or more bases are deleted causing a frame shift to the left and changes more than one
DNA triplet, which therefore changes more than one codon
• changes protein structure
• Not only 1 codon is diff but subsequent codons _ AAs code for after are changed
• Greatly changes primary structure
• And secondary and tertiary
Addition
Base is added to DNA nucleotide sequence
• causes from shift to right
• changes sequence of bases in DNA + triplet
• Changes sequence of AAs in primary structure
• Changes side groups available to form covalent or ionic bonds to form tertiary structure
• Protein folds abnormally
Duplication
One of more bases are repeated causing a frame shift to the right
• 3 base duplication doesn't cause a frame shift just adds AA
• 1 -> 3 changes
Inversion
A sequence of bases can become separated from the DNA sequence and rejoin at the same loci
but in the reverse order (back to front)
• no frame shift
• May change AA coded for
Translocation
A base sequence is removed from its original loci and is inserted in a different place either on
the same or a different chromosome.
• one gene changed
• Range of eff depending on size of sequence altered
• Significant effect on expression -> abnormal phenotype
• Lead to development of some cancers + reduced fertility
, Mutagenic agents
• gene mutations occur, randomly during DNA replication
MUTAGENIC AGENTS: environmental factors that increase the mutation rate
• high energy ionising radiation
• E.g: X-rays + ultraviolet light
• Chemicals
• E.g: nitrogen dioxide
• can disrupt structure of DNA
• Potentially leading to non-functional protein produced
• May occur in somatic cells or gametes (germ line cells)
Expression
, Gene Mutations
GENE MUTATIONS: change in the base sequence of DNA
CHROMOSOME MUTATIONS: any change to a proportion of a chromosome
NON-DISJUNCTION: a type of chromosome, mutation, when homologous pairs of chromosomes,
failed to separate in meiosis, resulting in gametes with incorrect numbers of chromosomes
Types of Mutations
1. Substitution
2. Deletion
3. Addition
4. Duplication
5. Inversion
6. Translocation
• how is the DNA sequence changed
• How affects mRNA
• How AA sequence changes (primary structure)
• 2 and 3 structure affected (name bonds)
Subitution
SILENT MUTATION: Base is changed resulting in change to a codon but the codon still codes
for the same AA
• no change to protein structure
• bc genetic code is degenerate
MISENSE MUTATION: a basis changed, resulting in a change to a single codon
• change in primary structure (diff seq of AAs)
• Change H , ionic, disuphide bridges in 3 structure
• 1 AA changed doesn't have much effect on- doesn't change function
NON-SENSE MUTATION: a basis, change, resulting in a change to a stop codon
• significant impact
• Shorter polypeptide
• E.g: enzyme - no AS formed
,Deletion
One or more bases are deleted causing a frame shift to the left and changes more than one
DNA triplet, which therefore changes more than one codon
• changes protein structure
• Not only 1 codon is diff but subsequent codons _ AAs code for after are changed
• Greatly changes primary structure
• And secondary and tertiary
Addition
Base is added to DNA nucleotide sequence
• causes from shift to right
• changes sequence of bases in DNA + triplet
• Changes sequence of AAs in primary structure
• Changes side groups available to form covalent or ionic bonds to form tertiary structure
• Protein folds abnormally
Duplication
One of more bases are repeated causing a frame shift to the right
• 3 base duplication doesn't cause a frame shift just adds AA
• 1 -> 3 changes
Inversion
A sequence of bases can become separated from the DNA sequence and rejoin at the same loci
but in the reverse order (back to front)
• no frame shift
• May change AA coded for
Translocation
A base sequence is removed from its original loci and is inserted in a different place either on
the same or a different chromosome.
• one gene changed
• Range of eff depending on size of sequence altered
• Significant effect on expression -> abnormal phenotype
• Lead to development of some cancers + reduced fertility
, Mutagenic agents
• gene mutations occur, randomly during DNA replication
MUTAGENIC AGENTS: environmental factors that increase the mutation rate
• high energy ionising radiation
• E.g: X-rays + ultraviolet light
• Chemicals
• E.g: nitrogen dioxide
• can disrupt structure of DNA
• Potentially leading to non-functional protein produced
• May occur in somatic cells or gametes (germ line cells)
