BIOL 230 Chap. 8 - Gene Expression

What is gene expression? 

the process by which a gene makes a product that is useful to the cell by directing synthesis of a protein or RNAs encoded in their genome

What is cell differentiation?

the outcome of selective gene expression, different cells become unique in composition, structure, and function

How does cortisol affect the pancreas?

reduces production of tyrosine aminotransferase, reducing glucose levels

How does cortisol affect the liver?

signals liver cells to increase glucose production, increases production of tyrosine aminotransferase

Where is the main site of control of gene expression in most eukaryotic cells?

step 1: transcription of a DNA sequence into RNA

How is transcription regulated?

promoter region of a gene binds to RNA polymerase, sigma factors in bacteria, general transcription factors in eukaryotes 

What is used to switch genes on or off?

regulatory DNA sequences

What are transcription regulators?

proteins which recognize regulatory DNA sequences, binding acts as switch to control transcription

What is the homeodomain?

the part of the protein that binds to specific regulatory regions of the target genes, consist of 3 alpha helices 

What does the transcription regulator interact with through noncovalent bonds?

the major groove of DNA

What is a transcription regulator dimer?

a repeated regulatory sequences

What are operons?

genes arranged in a cluster and transcribed from a single promoter that regulate DNA sequences

How are eukaryotic genes regulated?

combinational control

What happens when tryptophan levels are low in bacteria?

the Trp. Operon is transcribed on 

How is the Trp. operon switched off? 

by repressor proteins binding to the operator, blocking binding of RNA poly to promoter 

What type of protein is Trp repressor?

allosteric protein

What do activator proteins do?

proteins that bind to operator that turns ON transcription

What does the Lac Operon do?

encodes proteins required to import and digest lactose

What transcription regulators control the Lac operon?

Lac repressor and CAP activator

What do bacteria use for carbon source in absence of glucose?

lactose

What is present on the operator when glucose is present and lactose is absent?

Lac repressor

What is present when neither glucose or lactose is present?

cyclic AMP bound to CAP activator and Lac repressor

What is present when only lactose is present?

cyclic AMP bound to CAP activator and RNA polymerase

When does bacterium make cAMP?

in the absence of glucose

What does cAMP do?

activates CAP to switch on genes

What does CAP mean?

catabolite activator protein

What does CAP have to bind to before it can bind to DNA?

cAMP

What does allolactose bind to? What does this allow for?

binds to Lac repressor that results in conformational change that releases Lac repressor from the operator 

What does the presence of glucose inhibit?

the activity of adenylyl cyclase, prevents CAP from binding

What conditions must be met for the Lac operon to be transcribed?

lactose must be present so the Lac repressor can be released and glucose must be absent for cAMP to be produced and bind to CAP which then binds to DNA 

Is transcription regulators control of gene expression close or far? 

far 

What do activator proteins in eukarytoes bind to?

enhancers

What is the mediator? 

a complex of proteins that aids in tethering activator with general transcription factors 

How is transcription decreased in Eukaryotes? 

eukaryotic repressor proteins block the assembly of the transcription initiation complex 

How do nucleosomes that are positioned over a promoter inhibit transcription initiation? 

by blocking assembly of general transcription factors and RNA polymerase

What is the function of chromatin remodeling complex?

interacts with histone octamer and DNA to reposition the DNA wrapped around nucleosomes 

What can activators recruit?

chromatin remodeling complexes and histone modifying enzymes to attach acetyl groups on tails of histones to attract general transcription factors to promote transcription

What can repressors attract? 

histone deactylases which remove acetyl groups on histone tails

How does chromatin remodeling complex loosen nucelosomal DNA?

ATP hydrolysis

What results form double doses of X-chromosomes being lethal?

female mammals permanently inactivating one of the two X chromosomes in each cell, X-inactivation

What are topological associated domains?

animal and plant chromosomes arranged in loops that favor the association of each gene with its proper enhancer

What is combinational control?

groups of transcription regulators working together to express the gene in the right cell type, in response to the right conditions, at the right time, and in the required amount 

What is coordinated regulation? 

expression of different genes being coordinated by a single protein (transcription regulator) 

Where does the cortisol receptor move upon binding to cortisol? 

to the nucleus to act as a transcription regulator 

What does the same transcription regulator recognize on different genes?

regulatory sequences

What is the net result of coordinated regulation?

expression of many genes in response to single transcription regulator

What are embryonic stem cells?

undifferentiated cells that can give rise to all the specialized cell types in the body, called pluripotency

What transcription regulators control the expression of thousands of genes?

K1f4, Oct4, Sox2

What do the transcription regulators form?

the regulatory network that specifies an embryonic stem cell

What does each regulator control?

the expression of a unique set of genes

What is the function of a master transcription regulator?

can direct the formation of an entire organ

What is induced pluripotent stem cells (iPS)?

a combination of transcription regulators that induce a differentiated cell to de-differentiate into a pluripotent iPS cell

What single point mutation is responsible for timothy syndrome?

the gene that provides instructions for making a channel that transports calcium ions into cells 

What is an organoid? 

miniature organs that can be used to study how organ development can be derailed by disease