Gene expression Eukaryotes - MCB

Housekeeping genes ?

expressed in many cell types

GAPDH

pre-transcriptional switch

(before transcription)

Heterochromatin & Euchromatin

Gene re-arrangement

Modulating access transcription factors

Euchromatin

nucleosome separated by the naked DNA

actively transcribed

lightly packed for chromatin

Heterochromatin

Densely/tightly packed transcriptional form chromatin

Histone regulate gene expression

Methylation

Acetylation

Phosphorylation

Acetylation

Generated by adding acetyl group to N terminus (histone tail)

Unwind DNA - charged interactions and open up DNA

DNA methylation

Methyl group added cytosine base (5-methylcytosine)

Strongly affect gene expression not change DNA

CpG Islands

Active genes unmethylated regions

Lots nucleotides (lots potential methylated)

If methylated prevents transcription gene (can change toxin environment)

Methylation patterns inherited

Methyltransferase Dnmt1 scans new strand (add methyl group)

Inherited after cell division

Epigenetics

Information additional to gene sequence

e.g DNA methylation, histone modification

Transcription factor

Bind to specific DNA sequences

Can block/activate transcription

Protein-protein interactions lead to binding

Difference btwn prokaryotes and eukaryotes binding site

Eukaryotes: if binding site is further away than transcription factor can have indirect effect

Prokarytoes: closer and more stable

Eukaryotic gene

Proximal control elements: example CAAT box, GC box

Core promoter: TATA box to INR

INR (initiator element)

Proximal control element

bind to transcriptional activators

TATA box

binding & position RNA polymerase

in promoter region

Enhancer binding sites

Distant regulatory binding sites (indirect effects)

Bind transcription factors

Domain in Transcription Factors

Activation domain - bind RNA polymerase 2 (more variation)

DNA binding domain - bind DNA sequence

DNA binding factor

Usually binds to major grove

Mediator complex

DNA > RNA polymerase 2 > Mediator > Transcription Factor

Bridge - wen binding site not close RNA polymerase binding site

Signal

Goes nucleus transcription

Steroid

pass thru plasma membrane, bind intracellular receptors - dimerises enter nucleus

chain phosphorylation events

phosphorylation transcription factor bind regulatory DNA sequence (effect on gene)

Albumin gene

transcription factor bind

Splicing

Some introns spliced out

Splicing fibronectin gene

Exon EIIIA and EIIIB encode regions bind fibroblast to fibronectin gene

(lack hepatocytes)

Regulation genes associated Iron Metabolism

Transferrin

Transferrin Receptor

Ferritin

Transferrin

transport protein carries iron in serum

Transferrin receptor

Membrane protein binds transferrin to enter cell

Ferritin

efficient iron storage protein in liver and kidney

High iron

need less ferritin and less transferrin receptor

Iron response element (IRE)

Ferritin mRNA - stem hairpin loop structure

Low iron concentration - translation

Ferritin mRNA binds to IRE-binding protein (IRP) blocks initiation

Iron level high - translation

High level iron bind IRP - can no longer bind to ferritin

What disadvantage high iron concentration

As IRP can't bind to mRNA

transferrin receptor mRNA is rapidly degraded and not expressed

Micro-RNA (miRNA)

Class regulated RNA molecules

Cleaved into small fragment (20 nucleotides)

Bind mRNA molecules with complementary binding sequence - double stranded

miRNA targets mRNA degradation

How are proteins digested by proteosomes

Protein - added ubiquitin molecule to lysine

U recognised by proteosome complex

Degrades into short peptides

Protein phosphorylation

Phosphate transferred from ATP to amino acid side chain (protein kinase)

Removal phosphate - protein phosphatase

Protein glycosylation

Attach carbohydrates form glycoprotein