CHAPTER 12 THE CONTROL OF GENETIC INFORMATION VIA GENE REGULATION

polycistronic mRNA

- an mRNA that encodes more than one polypeptide, which become units within functional proteins

What happens when E.coli is exposed to lactose?

1. Via lactose permease, a small amount of lactose is transported into the cytoplasm. Beta-galactosidase converts some of it to allolactose. 2. The cytoplasmic level of allolactose (a small effector molecule) gradually rises. When four allolactose molecules bind to the lac repressor, a conformational change occurs that prevents the repressor from binding to the operator. 3. When the lac repressor is not bound to the operator, RNA polymerase transcribes the lacZ, lacY, and lacA genes at a high rate. 4. Translation of the encoded polypeptides produces an abundant amount of the proteins needed for lactose uptake and metabolism.

when cAMP binds to CAP, the cAMP-CAP complex binds to the _______ near the __________

CAP site / lac promoter causes a bend in the DNA that enhances the ability of RNA polymerase to bind to the promoter the presence of glucose in the environment inhibits the production of cAMP, which prevents the binding of CAP to the DNA

regulatory transcription factors exhibit two controls, explain them.

REPRESSORS > bind to the DNA and decrease the rate or transcription, called NEGATIVE CONTROL ACTIVATORS > bind to the DNA and increase their rate of transcription, called POSITIVE CONTROL

In eukaryotes, gene expression can also be regulated at several stages. Explain them.

TRANSCRIPTION > transcriptional regulation is very common RNA MODIFICATION > modify their RNA transcripts in ways that do not commonly occur in bacteria TRANSLATION > not as prominent as transcriptional regulation, but a fairly common way for eukaryotes to regulate gene expression POST-TRANSLATION > also prominent

How would a small effector molecule affect a repressor?

When the small effector molecule is subsequently found in the cytoplasm, it will bind to the repressor and cause a conformational change that inhibits the ability of the protein to bind to the DNA Transcription can occur because the repressor is not able to bind to the DNA

In order to utilize lactose, E.coli requires two things:

a transporter (lactose permease) and an enzyme (beta-galactosidase)

The most common point of gene regulation in bacteria is a. transcription b. RNA modification c. translation d. after a protein is made (post-translation)

a. transcription

lac repressor

adjacent to the lac operon is the lacI gene > this is important protein is important for the regulation of the lac operon expressed at a fairly low level, has its own promoter called the i promoter the lacI gene is NOT considered part of the lac operon

inducer

allolactose is an example, it is a small effector molecule that increases the rate of transcription

operon

an arrangement of two or more genes in bacteria that are under transcriptional control of a single promoter

lac operon

an inducible operon and contains genes that code for enzymes used in the hydrolysis and metabolism of lactose

constitutive genes

an unregulated gene that has constant levels of expression in all conditions over time

Let's suppose that a mutation in the lacI gene prevented the lac repressor from being made. How would this mutation affect the expression of the lac operon? a. It would be expressed only in the presence of lactose in the environment. b. It would be expressed in the presence of lactose in the environment. c. It would be expressed only in the absence of lactose in the environment. d. It would be never expressed.

b. It would be expressed in the presence of lactose in the environment.

what is CAP

catabolite activator protein is an activator controlled by a small effector molecule, cyclic AMP (cAMP)

Bacteria regulate genes in response to ________ _________ ________ _________.

changes in their environment

the lac operon in E. coli

contains the genes for the proteins that allow it to metabolize lactose

A reason for gene regulation is a. to respond to environmental changes b. to make proteins in specific cell types c. to make proteins at specific stages of development d. to do all of the above

d. to do all of the above

Repressors and activators that respond to small effector molecules have two functional regions called ________

domains one domain is a site where the protein binds to the DNA, while the other is the binding site for the small effector molecule

what does lacZ do?

encodes beta-galactosidase which converts a small percentage of lactose into allolactose which then functions as a small effector molecule

small effector molecules

exerts its influence by binding to a repressor or an activator and causing a conformational change in the protein in many cases, the effect of the conformational change determines whether or not the protein can bind to the DNA

When lactose is absent from the environment, allolactose is not made and the lac repressor:

is free to bind to the lac operator transcription of the operon is inhibited

How do living organisms benefit from gene regulation?

it conserves energy > RNAs and proteins that are encoded by genes are produced only when needed

what does the lacA gene do?

it encodes galactosidase transacetylase, which covalently modifies lactos and lactose analogues by attaching an acetyl group > prevent the toxic buildup in the cytoplasm

what does the lacY gene do?

it encodes lactose permease, which is a membrane protein required for the transport of lactose into the cytoplasm of the bacterium

when cAMp is bound to CAP, CAP binds to the DNA and causes it to bend. what does bending do?

it facilitates the binding of RNA polymerase

What is the CAP site for the lac operon?

it is a regulatory sequence in the DNA that is recognized by an activator protein

what is operator of a lac operator?

lacO site, a regulatory sequence, provides for a binding site for the repressor protein

promoter of E.Coli lac operon

lacP > used to transcribe three genes: lacZ, lacY, and lacA

When lactose becomes available, the bacterium produces _______ of these proteins.

many more

the lac operon is under _______ control by a repressor protein

negative

the lac operon is under ________ control by an activator protein

positive

When lactose is present, allolactose is made from inside the cell. The binding of allolactose to the lac repressor:

prevents it from binding to the lac operator permits the transcription of the lac operon

cyclic AMP (cAMP)

produced from ATP via an enzyme called adenylyl cyclase

gene regulation is responsible for:

producing different types of cells within a multicellular organism

regulatory transcription factors

proteins that bind to regulatory sequences in the DNA in the vicinity of a promoter and affect the rate of transcription of one or more nearby genes they either decrease or increase the rate of transcription of a gene

gene regulation

refers to the ability of cells to control their level of gene expression

transcriptional regulation involves two things:

regulatory transcription factors and small effector molecules

proteomes

the complete complement of proteins that a cell or organism can make

genome

the complete genetic composition of a cell or species

What happens once all the lactose is used up from the environment?

the gene encoding these proteins will be shut off, and most of the proteins will be degraded

cell differentiation

the process by which cells become specialized into particular types

gene expression

the process by which the information within a gene is made into a functional product, such as an RNA molecule or a protein

For bacteria, regulation occurs most during what stage?

transcription > the bacteria regulate how much mRNA is made from genes / transcriptional regulation is a particularly efficient way to regulated genes because cells avoid wasting energy when the product of the gene is not needed

When lactose in not present in the environment, E. coli cells make _____ of these proteins.

very little