Regulation of Gene Expression

Questions?

How can cells with different functions have the exact same DNA in their nucleus?

How does the body use the exact same set of instructions to make different structures?

Core Concepts• DNA triplets code for how many amino acids? (Codons)

• Amino acids link together and form polypeptides

• Genes code for polypeptides that control things like?

• Gene expression can happen in 2 ways, positive and negative

• Very small percentage of human genome codes for protein

Prokaryotic VS Eukaryotic Gene Expression

Differences in the Regulation of Gene Expression of Prokaryotic and Eukaryotic Organisms

Prokaryotic organisms Eukaryotic organisms

Lack nucleus Contain nucleus

DNA is found in the cytoplasm DNA is confined to the nuclear compartment

RNA transcription and protein formation occur almost simultaneously

RNA transcription occurs prior to protein formation, and it takes place in the nucleus. Translation of RNA to protein occurs in the cytoplasm.

Gene expression is regulated primarily at the transcriptional level

Gene expression is regulated at many levels (epigenetic, transcriptional, nuclear shuttling, post-transcriptional, translational, and post-translational)

Gene Expression in Prokaryotes

• Transcriptional Control: the cell can speed up or slow down the transcription of mRNA from the gene that codes for the polypeptide• Post-transcriptional Control: the cell may transcribe the mRNA but

break it down before translation. It can also modify the poly-A tail. WHY?• Post-translational Control: after synthesizing the polypeptide the cell

can modify it chemically or vary the rate at whish the polypeptide becomes a functional protein

OPERONS• Stretch of DNA that contains one or more genes involved in a metabolic pathway along

with a regulatory sequence called an operator

OPERATOR• DNA sequence located between promoter sequences and gene sequences that govern

whether RNA polymerase can bind to the promoter sequence to begin transcription

REPRESSOR• Protein that binds to the operator to make it impossible for the RNA polymerase to bind

to the promoter, thus preventing genes from being transcribed

INDUCER• Substance such as lactose molecule that stops the action of the repressor, allowing RNA

polymerase to bind to the promoter sequence and begin transcription

lac Operon- E-coli Bacteria• htt

ps://www.youtube.com/watch?v=oBwtxdI1zvk

Negative Gene Regulation in the lac Operon• Uses a REPRESSOR (protein) which binds to the operator region and

doesn’t allow for RNA polymerase to bind to the promoter, resulting in the lac operon not being transcribed.

Positive Gene Regulation in the lac Operon

• Uses ACTIVATORS (molecule that promotes action of enzymes), specifically Catabolic Activator Protein (CAP), that stimulates gene expression by binding to a cAMP molecule and then to s site near the Plac promoter.• This action allows RNA polymerase to bind to the promoter easily and

speeds up the rate at which lac genes are transcribed.

-Like a key for a car, your turning it on or off (turning off transcription/translation).

Positive Gene Expression:

Negative Gene Expression:

-Like the gas pedal and brake, accelerating and slowing it down (accelerating and slowing down transcription/translation).

Gene Expression in Eukaryotes

• Pre-transcriptional control: the cell controls the extent to which DNA is exposed to transcription enzymes, regulating DNA’s availability for transcription.• Transcriptional control: the cell controls whether or not exposed DNA is

transcribed into Pre-mRNA.• Post-transcriptional control: the cell controls the rate of processing of pre-

mRNA, but then controls. • Translational control: the cell manufactures the mRNA, but then controls

its transport to ribosomes in the cytoplasm• Post-translational control: the cell manufactures the polypeptide but then

modifies it chemically or varies the rate at which it becomes a functional protein. It may also break down the polypeptide before it becomes functional

https://www.youtube.com/watch?v=KKR28Y_L4CA

Activity:

•Choose a positive or negative example of gene expression in Eukaryotes, then draw and label it.