Gene Expression I

genome; genes

A neuron and liver cell:

• share the same ______.

• have different ______.

proteins

Different cell types produce different sets of ______.

Cell differentiation

the result of different cells producing and accumulating sets of RNA and protein molecules

Gene expression

the process by which cells selectively direct the synthesis of many thousands RNA & protein

T

T or F?
Different cell types contain (the) same DNA.

differentiation

prevents or activates certain genes

T

T or F?
Gene expression can be regulated at many steps.

RNA polymerase

binds to the TATA box

• not where transcription regulators bind to

-35

Where is the location for this transcription factor?

TFIIB

-30

Where is the location for this transcription factor?

TBP

transcription start site; +30

Where are the two locations for this transcription factor?

TFIID

Regulatory DNA

these sequences cannot control gene expression on their own

• require specific proteins to function

Transcription regulators

recognize and bind to these regulatory DNA sequences

• can be activators or repressors

• binding acts like a molecular “switch”

a-helices

how transcriptional regulators recognize DNA

T

T or F?
Regulators often bind to a specific sequence of DNA.

major groove

most DNA transcription factors bind here

• wider

• offers more access

non covalent

the type of bonding between protein and DNA that is ensured by the major groove

hydrogen

The interactions between the protein and DNA take place along the edges of the nucleotide base and do not disrupt ______ bonds that hold the base pairs together.

dimers

Many transcription regulators bind to DNA as

Prokaryotes

Prokaryotes or eukaryotes?

Genes are transcribed back to back in the operon

Genes are a series of genes back to back

increased

If tryptophan is low inside the cell, the trp operon expression is

increased/decreased?

decreased

If tryptophan is high inside the cell, the trp operon expression is

increased/decreased?

Low

High or Low tryptophan levels?

transcription repressor is inactivated, thus allowing RNA polymerase to transcribe genes related to tryptophan metabolism

High

High or Low tryptophan levels?

transcription repressor is activated, thus NOT allowing RNA polymerase to transcribe genes related to tryptophan metabolism

OFF

High tryptophan, transcription:

Transcriptional repressors

turn genes OFF

Transcriptional activators

turn genes ON

B-galactosidase (lactase)

breaks down β-galactose and β-glucose

Lac repressor

binds to the Lac operator and shuts off expression of the operon when lactose is absent

allolactose

binds to the lac repressor to allow transcription of the lac operon

increases

Addition of lactose _______ the intracellular concentration of allolactose

increases/decreases?

enhancer

In eukaryotes, activators bind to a sequence of DNA called _______ that can be upstream or downstream of the promoter.

DNA looping

allows the activator to physically interact with the transcription initiation complex at the promoter

activator protein

binds to a distant enhancer sequence in the DNA

mediator complex

acts as a bridge, helping recruit RNA polymerase and initiate general transcription factors

TATA box

a promoter DNA sequence recognized by the first general transcription factor that binds during transcription initiation

dimers; monomers

Eukaryotic activator proteins may bind DNA either as _____ (two subunits) or as single ______, depending on the specific protein.

Histone modifying enzymes

responsible for acetylation, phosphorylation or methylation of amino acids

non-histone proteins

could be attracted or repulsed by the changes to histones

• determines the expansion of compaction of DNA

heterochromatin

very compact and full of methyl groups

euchromatin

spread apart and full of acytl groups

Eukaryotic transcription regulators

help initiate transcription by recruiting chromatin-modifying proteins

Histone acetylation

creates binding sites for proteins that promote transcription initiation, making the DNA more accessible

looped domains

established by special nonhistone chromosomal proteins that bind to specific DNA sequences, creating a clamp at the base of each one

eukaryotes

multiple transcription factors work together as a “committee” to control gene expression in:
eukaryotes or prokaryotes?

General transcription factors

are the same for all genes transcribed by RNA polymerase

• eukaryotes have 3 of them

single transcription regulator

can coordinate the expression of multiple genes.

activated cortisol receptor

acts as an additional regulator (for gene expression) needed for full activation

T

T or F?
Eukaryotes do not possess any operons.

on

When the required combination of regulators is present, transcription is efficiently initiated and the genes are switched ____.
(on/off)