Molecular bio 6: gene expression

What cation is found in the centre of an RNA polymerase enzyme?

Magnesium

What is the most abundant type of RNA in a cell?

rRNA

What is meant by steady state level of RNA?

The ‘snapshot’ amount of it that is present in a cell

What is meant by sympathetic type capacity of RNA?

Its rate of turnover

Which RNA polymerase is responsible for transcribing pre-r-RNA?

RNA polymerase I

Which RNA polymerase is responsible for transcribing m-RNA (among others)?

RNA polymerase II

Which RNA polymerase is responsible for transcribing tRNA (among other RNA types)?

RNA polymerase III

In prokaryotes, what signals that the beginning of a transcribable gene?

10 base pairs ‘upstream’ of the start of the transcription, there is a TATAAT sequence

35bps upstream there is a TTGACA sequence

In eukaryotes, what signals that the beginning of a transcribable gene?

-100bps there is a ‘GC’ box (GGGCGG)

-80bps there is a ‘CAAT’ box (GCCCAATCT)

-25bps there is a ‘TATA’ box (TATAAA)

What are leaders and trailers?

Untranslated regions at the beginning and end respectively of a mRNA strand, which signal to the ribosome where to begin and end translation

What is a poly(A) site?

What is a consensus sequence?

The most commonly-occurring sequence for a control element (such as the CAAT box). There may be variation in different organisms or different circumstances.

What is monocistronic gene expression?

Genes are organised under the control of a single promoter (as in prokaryotes)

What is meant by polycistronic gene expression?

Genes are organised in operons under the control of many different promoters (as in eukaryotes)

Give an example of an operon

The lac operon in e. coli bacteria

Which three genes are involved in the lac operon and what are their functions?

lacZ (encodes the enzyme responsible for cleaving lactose into glucose and galactose)

lacY (encodes lactose permease)

lacA (encodes an enzyme that gets rid of the toxic products of lactose transport into the cell)

What is the role of the operator in the lac operon?

When glucose is abundant, the repressor binds to the operon to prevent transcription of the lactose breakdown genes

When lactose is abundant, allolactose binds to the repressor resulting in a reduced affinity for the operator

What is the CAP site in the lac operon?

A positive regulator

What is a CAP protein in the lac operon?

Catabolic activator protein, which upregulates RNA transcription of the operon

cAMP binds to it when glucose is absent, which enables CAP to bind to the operon

What needs to happen before RNA polymerase can bind to DNA for a basal level of transcription in eukaryotes?

Several general eukaryotic transcription factors (a,b,d,e,f,h) need to be bound to the DNA strand

What is the first promoter II to bind to the DNA core promoter?

d

What is the enhanceosome?

The fully assembled complex of transcription activator factors

What are co-activators with regard to DNA transcription?

They activate or increase the transcription of specific genes. They bind selectively to DNA bound transcription factors and often act by altering chromatin structure.

Why are additional eukaryotic transcription regulatory factors required?

For spatial or temporal specificity (ie. for transcription of genes that are only required in specific tissues at a specific time)

Where is the albumin gene expressed?

Liver cell nuclei

Give an example of hormone-dependent gene activation by a dimeric nuclear receptor

Glucocorticoid receptor is hormonally regulated

Many transcription factors contain at least two domains. What are they?

A DNA binding domain and one or more activation or repressor domains

What are the three key processes in making final messenger RNA?

Capping, splicing and polyadenylation

What happens in polyadenylation?

Polyadenylation polymerase (PAP) adds 200 or so base pairs of As to mRNA

Give an example of alternative splicing

The DNA sequence for calcitonin and calcitonin gene-related peptide (which gives people migraines) are the same, they are just spliced differently!

The calcitonin is made of exons 1-2-3-4

The CGRP is made of exons 1-2-3-5-6

What proportion of genes in the human genome are capable of being alternatively spliced?

Up to 60%