Regulation of Gene Expression

Prokaryotic cells can go through gene expression much faster because they do not have a nucleus. Transcription and translation can happen at the same time. While the RNA strand is being made the ribosomes can translate it at the same time.

This is one reason that bacteria can do things so fast

Gene Regulation

Negative Gene Regulation

Bacteria that can conserve energy have an advantage over those that cannot. Natural selection has favored bacteria that only make proteins when they need them. A bacteria that makes proteins continuously waists a lot of energy.

Regulatory gene, Repressor Protein, Promoter, and Operator

Two types of negative Gene Regulation

Repressible Operons

-Always turned on until a repressor turns it off

-Example: The trp (tryptophan) regulatory gene in E. Coli

Inducible Operon

-Always turned off until an inducer binds to it

-This is good because you do not waist time making enzymes you do not need

-Example: lac (lactase) regulatory gene in E. coli

Positive Gene Regulation

E. Coli would rather metabolize glucose over lactose. The enzymes to breakdown glucose during glycolysis are always present. If glucose and lactose are both present the E. Coli do not make lactase. They ignore the lactose and only break down the glucose. It is only when glucose is scarce and lactose is present that the E. Coli begin making lactase.

We learned that the production of lactase is a negative gene regulation involving an inducible operon. Meaning that the repressor is always turned on until lactose is present. Once lactose is present it deactivates the repressor. So if lactose is present the repressor cannot prevent RNA polymerase from transcribing the gene for lactase. So how is it possible that when lactose and glucose are present the E. Coli focus on the glucose?

Take a moment with a partner and draw a diagram of how an E. Coli cell could promote the breakdown of glucose and not promote the breakdown of lactose when both are present.

Allosteric Regulatory protein called cyclic AMP (cAMP)

-When glucose is scarce the cell makes a lot of cAMP

Regulatory activator protein called CAP (catabolite activator protein)

-Binds to DNA and stimulates transcription of a gene

-When cAMP binds to CAP, CAP assumes its active position and binds to the promoter of a gene

-The CAP assists the RNA polymerase in transcribing the gene

-If glucose and lactose are both present a small amount of lactase is made but only when there are low levels of glucose does cAMP and CAP start promoting large amounts of lactase.

-In this sense it is considered a positive regulation.

Eukaryotic Gene Expression

Because some Eukaryotes are multicellular each cell needs to perform a different function. This means that each cell type needs to perform a different type of gene regulation. Most cells only express 20% of their DNA. This is done by a process known as differential gene expression.

-There are many different stages that a Eukaryotic cell can regulate gene expression

Regulation of Chromatin Structure

-When chromatin is highly condensed it cannot be transcribed.

-Histone acytylation is when an acetyl (-COCH^3) is added to the histones. This opens up the chromatin allowing for transcription.

-DNA methylation is when a methyl group is added to the DNA which causes the histones to condense making it hard to transcribe.

-A cell can pass on these chromatin modifications to future cells. This is known as epigentic inheritance

Regulation of Transcription Initiation

Homework

Read about

-ncRNA - noncoding RNA

-miRNA - MicroRNA

-siRNA - small interfering RNA

-cDNA - Complementary DNA

What is RT-PCR?

-Reverse transcriptase - Polymerase Chain Reaction