the control of gene expression

the genetic code is:

universal

non overnapping

degenerate

what does it mean that the genetic code is universal?

DNA code is the same for every living thing

what does it mean that the genetic code is non overlapping?

each nucleotide is only a part of one codon

what does it mean that the genetic code is degenerate?

each amino acid is coded for by more than 1 codon

what are the different types of mutation?

translocation

substitution

inversion

insertion

deletion

duplication

translocation

the sequence of bases is over from 1 place in the chain to another

substitution

one of the bases is swapped for another (might only cause a silent mutation)

inversion

a sequence of bases is reversed (might also cause a silent mutation)

inversion

1+ bases are added to a chain (causes a frame shift)

deletion

1+ bases are removed from a chain (also causes a frame shift)

duplication

1+ bases are repeated

what % of genes in dna are expressed at any given time?

3-5

what happens to the genes which are not being expressed?

they are repressed/switched off in order to stop cellular resources from being wasted

how is transcription regulated?

by transcription factors (which can be regulated by other molecules)

transcription factors

proteins produced in the cytoplasm (and move into the nucleus)

→ they bind to regions of DNA present before the genes

→ each TF binds to a specific promoter due to the specific DNA code

→ they can be activates or repressors of gene transcription and can do this by helping or preventing the RNA polymerase from binding to DNA.

what are promoters?

sections of DNA that come before the site of transcription and promote the transcription of the gene they lie on

effects of oestrogen on gene transcription

1. oestrogen diffuses through cell surface phospholipid bilayer (as it is soluble)

2. in cytoplasm oestrogen binds to oestrogen receptors joined to a transcription factor

3. oestrogen binding changes the shape of the receptor TF complex

4. receptor TF complex enters the nucleus and binds to the promoter region

5. transcription is then either activated or repressed.

RNAi

interfering RNA

→ small lengths of non coding RNA

→ effect translation of mRNA to polypeptide

what are the two types of RNAi?

siRNA = short (only in animals)

miRNA = micro (plants and animals)

interferring RNA process

1. one strand degraded

2. RNA associated with the protein complex

3. iRNA binds to target sequences on the mRNA molecule; protein then cuts the mRNA into small sections

4. fragments of mRNA cannot be translated to no functional proteins are produces and the fragments are degraded.

epigenetics

don’t cause heritable changes in the DNA code

→ a set of chemical tags on DNA and histones which affect the structure of chromatin.

→ these tags are responsive to the environment and can change wether genes are transcribed or not.

heterochromatin

tightly wound DNA.

→ the dna is not accessible for TFs and RNA polymerase to bind

no gene expression

euchromatin

loosely wound DNA

→ DNA is accesible to TFs and can be transribed

gene expression

acetylation

the adding of acetyl groups to histone tails

→ when acylated DNA is less strongly attracted so more loosely wound

→ decreased acetylation means that histones are more positive so DNA is more tightly wound

methylation

adding of methyl groups to cytosine bases on DNA

→ inhibits the transcription of genes, binding of TFs and induces the acetylation by attracting proteins that condense histone complexes.

→ not methylated = less tightly wound

→ methylated = more tightly wound.