Biology 1.4 Epigenetics and Mutations Flashcards
transcription factors
transcription factors are proteins that bind to specific DNA sequences in the promoter region of a gene and either increase or decrease gene expression.
transcription factors - repressors
repressors bind to the promoter and block other transcription factors or RNA polymerase, resulting in decreased gene expression.
transcription factors - enhancers
enhancers bind to the promoter and recruit RNA polymerase to begin transcribing the gene, resulting in increased gene expression.
cellular differentiation
every cell in the human body has the exact same genetic code. however, cells do not express every single gene. gene expression will cause different types of cells express different genes to make specific proteins. as a result, they will function in a specific way. these cells have differentiated, or specialised. stem cells are unique beacuse they are undifferentiated. a stem cell differentiates when specific transcription factors switch on specific genes.
Changes in gene expression
- Epigenetic modifications
- DNA code is not changed.
- gene expression is affected by changes in transcription
- leads to increase or decrease in protein concentration. - Mutations
- DNA code is changed.
- gene expression is affected because the code is incorrect.
- leads to altered protein functionn or loss of protein completely.
Epigenetic modification
- epigenetics is the study of modifications to DNA that alter gene expression.
- the DNA code is not changed, but the way it is expressed is modified.
- epigenetic modifications include: DNA Methylation, Histone Modification
Epigenetic modifications: DNA Methylation
- DNA methlation silences genes.
- cytosine nucleotides may be modified by the addition of a methyl group.
- often happens at CpG sites.
- Multiple CpG sites together form CpG island.
- methylation of CpG islands is associated with downregulation of gene expression.
epigentic modifications: histone modification
- DNA is wrapped around proteins called histones.
- when histones are unmethylated, they are loosely packed. DNA is exposed and can be ‘read’.
- when histones are methylated, they are tightly packed. transcription factors and RNA polymerase cannot access the DNA.
- this prevents gene expression.
mutations
- a mutation is change in the base sequence of DNA.
- when a mutation occurs in a gene, the mRNA and resulting protein are also affected.
- mutations can result from: errors in DNA replication and cell division. Damage by physical or chemical factors in the environment.
- there are two broad categories of mutations
- substitution mutations
- silent mutations
- missense mutations
- nonsense mutations - frameshift mutations
- insertion mutations
- deletion mutations
Substitution mutations
silent: has no effect on the protein sequence
missnse: results in an amino acid substitution
nonsense: substitutes a stop codon for an amino acid.
frameshift mutations
insertions or deletions of nucleotides may result in a shift in the reading frame or insertion of a stop codon.
mutation rate can be increase….
- ionising radiation - uv radiation
- Mutagenic chemicals - alkylating agents
- viruses - human papilloma virus
Germline and somatic mutations
Germ cells produce gametes. the DNA in a gamete is inherited by the offspring.
somatic cells are all the other cells in the organism. the DNA in a somatic cell is not inherited by the offspring.
germline mutation
occurs in a pareent’s gametes. are passed onto offspring and can lead to changes in the characteristics of descendants. germline mutations can be inherited from either parent.
somatic cell mutation
occur after fertillisation in any cell that isnt germ cell. somatic mutations are passed onto daughter cells after cell division. Are accumulated throughout life. Some may have no effect; some may have a major effect.
