D2.2 Gene Expression

Phenotype

set of characteristics relies on gene expressed

What infleunces gene expression

• trascription

• translation

promoter

transciprtion factors bind to initiate transcoiron

found upstream from coding region

enhancer

• region on DNA

• activator proteins bind to enhnace the rate of transcirption

silencer

• region of DNA

• repressor proteins can bind to stip the transciption of a certain sequnce

mRNA degradation

• for gene expression to stop not only transciption needs to stop but the mRNA in cytoplasm needs to be broken down

• This occurs by enzymes: exonucleases which chop of RNA nuclotides

• Due to protection by poly-A-tail and guanine cap other enzymes are needed to remove it

• Decapping complex: removes cap

• Deadenylase complex: removes the nuclotides in polyA tail

Epigenesis

process of formation of organs and tissue from undefereintiated cells

Epigenetics involve

• changing phenotype without changing the genotype

• DNA methylation - adding a CH3 group to cytosine.

• Methyl grop is an epigenetic tag

• If methylation occurs in the promtoer region this leads to trasncirpitonal silencing

Genome

all the genetic information passed on from parents

Trascriptome

all RNA an organims can produce

Proteome

all proteins an organism can synthesize

Methylation

• promoter: stops transciption

• histone: on histone 3 the amino acid lysine can be methylated. If its methylated near the tip of the tail the gene is tracsribed. IF along the tail the gene will be silenced

Inheriting methylation

• some methylation can be inherited however normally its not

Environemtal effects on gene expression

Example: Air pollution

Females who are pregnant and are exposed to more PAHs and live closer to roads tent to hvae diffrent babies then the ones further a way from air polltuion

• females who are exposed to air pollution have babys with a lower body mass and the females have diffrent DNA patterns repsosnible for placenta formation

Imprinted genes

Genes that are methylated or unmethylated in one of the parents

• Primoridal germ cell undergo epigenetic reprogamming leading to sperm and egg cell being the same, nonetheless they undergo remethylation leading to imprinyted genes

• Example: Tigons and Ligers

• Ligers: male lion, female tiger → enormous sizes bigger then tiger or ligon

• Tigon: male tiger, female lion → much smaller

• Conclusion: growth gene methylated in male tiger and female lion

Monozygotic twins and methylation

• monozygotic twins: identical twins

• have the same genome

• as babies very few diffrneces in methylation

• as adults due to environments many diffrentially methylated regions can be founds

External factor impacting gene expression: Hormone

Insulin:

• when blood sugar rises

• transcipriton factors bind to promoter and nehnacer to begin transciption of insulin

• when blood glucose drops transcription is stopped

External factor impacting gene expression: lactose

Lactose digestion in the gut

• bacteria produce lactase which helps digest lactose

• when lactose is present they secre lactase but when its not they dont

• upstream from coding seuqnce bur down stream from promoter is an aea called operator

• when no lactose a lac repressor binds to operator stopping lactase production

• when lactose arrives it decativtes the lac repressor and the transciption of lactase begins