6.1.1 - cellular control

• A gene mutation is an alteration to the DNA base sequence
• gene mutations often arise spontaneously during DNA replication
• gene mutations can either be insertions, deletions, or substitutions.
• an insertion gene mutation is when one or more nucleotides are inserted into the DNA sequence.

  either results in a frameshift or the addition of extra amino acids.
• a deletion mutation is when one or more nucleotides are removed from the DNA sequence.

  either results in a frameshift or the loss of an amino acid
• Insertion and deletion mutations are likely to be Harmful or beneficial due to the frameshift which means the entire amino acid sequence will be different.
• A substitution mutation is when a nucleotide in the DNA sequence is replaced by another.
• substitutions are more likely to be a neutral mutation meaning no change occurs in the amino acid sequence because the DNA code is degenerate.
• Mutagenic agents increase the rate of mutations.
• Mutants are individuals showing or carrying a mutation
• chromosome mutations affects the structure of a chromosome or set of chromosomes.
• Chromosome deletion is when the chromosome breaks in the middle and a section of the chromosome is lost within the cell. The chromosome is now shorter than it originally was.
• Chromosome inversion is when the piece of the chromosome that was lost remains in the chromosome but is inverted and rejoins in the same place.
• Chromosome duplication is when a section of the genetic material in the chromosome is duplicated so there are two lots of a specific part of the chromosome.
• Chromosome translocation is when there is deletion from one chromosome that is added on to a different non-homologous chromosome somewhere else.

  Reciprocal translocation is when the two chromosomes swap pieces of genetic material.
• Nondisjunction is when the chromosome didn’t separate properly during meiosis so one cell ends up being non-viable and one has double the genetic material than normal.
• An example of a nucleotide deletion mutation is Tay Sachs
• An example of a non-sense substation mutation is Duchenne muscular distrophy
• A non-sense substitution mutation is when a stop codon is inserted instead of the correct amino acid so the protein is truncated and often inactive.
• A missense mutation is the wrong amino acid is inserted into the final sequence so a protein is produced but it may behave incorrectly.
• A silent substitution mutation is when the base substitution has no effect on the protein made.
• A gene is a section of DNA coding for a polypeptide
• Frameshift is when every codon after the mutation is affected
• Changing of an amino acid in the polypeptide can lead to the bonds in the tertiary structure changing and the protein not functioning properly.
• An example of a chromosome mutation is downs syndrome where there is an extra copy of chromosome 21
• Hormones activate genes
• an active gene is a gene that is transcribed and translated resulting in a polypeptide.
• Product of gene expression is always a protein
• The first level of controlled gene expression is control of the transcriptional level
• transcription control involves two types of genes:

  structural genes

  regulatory genes
• structural genes are genes that code for a protein that has a function in the cell
• regulatory genes are genes that code for a protein that controls structural genes
• One regulatory gene usually controls multiple structural genes and can either be right next to it in DNA or can be far away.
• A promoter is a DNA sequence that sits between the regulatory gene and the first structural gene
• a promoter is the binding site for RNA polymerase which is the enzyme that carries out transcription of the structural genes
• promoters exist in both prokaryotes and eukaryotes but interact differently in both
• In prokaryotes RNA polymerase binds straight to the promoter region and transcribes the structural genes. However to control gene expression, prokaryotes have another DNA sequence that sits between the promoter and the structural genes - the operator
• Regulatory genes code for a protein that controls the transcription of structural genes, this protein is known as a transcription factor
• In prokaryotes, there are two types of transcription factors:

  • activator proteins
  • repressor proteins
• activator proteins are produced by the regulatoy gene, bind to the promoter, if RNA polymerase also binds then the structural gene will be transcribed.