Gene Expression of Prokaryotes and Eukaryotes

gene regulation

process by which cells control the expression of genes, including when, where, and how much a gene is expressed.

operon

group of genes that are transcribed together into a single messenger RNA

promoter, operator structural genes

three components of operon

Promoter

a nucleotide sequence that enables a gene to be transcribed.

Operator

a segment of DNA between the promoter and the genes to which

a repressor binds

Structural genes

the genes that are co-regulated by the operon

polycistronic mRNA

A Promoter directs synthesis of one mRNA that can be translated to more than one polypeptide

B-galactosidase

what enzyme converts lactose to galactose and glucose as an energy source for bacteria

Catalyzes the intramolecular isomerization of lactose to allolactose

B-galactosidase role in lac operon

allolactose

lac operon inducer that is made of galactose and glucose

lacZ, lacY, and lacA

three structural genes of lac operon

lacZ - B-galactosidase

splits lactose into glucose and galactose

lacY

pump that imports lactose into the cell

lacA

transfers acetyl group from acetyl-CoA - uptake of lactose

negative inducer

binds to a repressor protein and causing it to detach from the operator, thereby allowing RNA polymerase to transcribe the gene

cAMP

when glucose levels are low what is produced

cAMP- CAP

low glucose and high cAMP forms ____ ____ complex

no transcription of lactose

glucose present and lactose absent

low level of transcription of lactose

glucose and lactose present

no transcription of lactose

glucose and lactose absent

high transcription of lactose

glucose absent and lactose present

bacteria makes its own tryptophan by using enzymes encoded by five genes

if there is no Tryptophan in the environment of a bacteria what happens

Trp Operon

tryptophan binds to the repressor protein and enables it to repress gene transcription.

bind to repressor, represor binds to operator, and RNA polymerase is blocked

when tryptophan is present what happens

ensures efficient of of trp and does not waste resources

why is RNA polymerase block when trp is present unlike lactose

ribosome stalls in region 1 and the anti-termination hairpin stem loop is formed

attenuation of the Trp operon: low level

ribosomes move quickly and past region 1. termination hairpin loop is formed and strop transcription

attenuation of the Trp operon: high level

regulation

transcription activation in eukaryotes- short distance

enhancer

transcription activation in eukaryotes- long distance

ON

When activators bind to the enhancer regions, specific gene is activated or turned ____

chromatin

chromosomes of eukaryotes have DNA packaged up with proteins to form

nucleosomes

DNA in our cells is wound around histone cores to make

lysine- and arginine-rich N-terminal tails of histones

of these tails is crucial for regulation of gene expression.

Covalent modifications

______ ______of these tails play an essential role in regulating gene expression.

tightly packed - silences expression

no phosphate group, acetyl group, and methyl group

loose- allows transcription

phosphate group, methyl group, and acetyl group on the histone tails

histone deacetyl transferase

enzyme that turns gene expression off by not having acetyl groups to the tail

histone acetyl transferase

enzyme that turns gene expression on by having acetyl on tails

methylation

added to the fifth position of the cytosine ring that silences the gene

post-transcriptional mechanism

reducing or stopping protein production after mRNA is made

alternative splicing, micro RNA, ferritin expression

post-transcriptional mechanisms

alternative splicing

Different combinations of the exons may be joined together to make different mature messenger RNAs to synthesize different proteins

microRNA

binds to mRNA that block protein assembly

Ferritin

protein that stores iron

translation continue for ferritiin

what happens when iron is high

iron regulatory protein binds to iron responsive element to stop translation of ferritin

what happens when iron is low