Lecture 6

Question 1

What defines the differences between cells?

Answer 1

How many proteins are produced as all cells contains the same DNA

Question 2

What is difference in morphologies dependent on?

Answer 2

difference in gene expression

Question 3

What are the 3 types of RNA polymerase

Answer 3

I is rRNA, II is all protein coding genes, III is tRNA genes

Question 4

What are the general principles of the initiation of transcription

Answer 4

• RNA polymerase interacts with other proteins (transcription factors) when it binds to the promoter
• The most basic promoter is required for RNA polymerase to bind and initiate transcription at the appropriate site
• Additional control sequences can determine when a gene is transcribed

Question 5

What is the promoter?

Answer 5

very close to protein coding region and includes imitation site where transcription begins

Question 6

What are enhancers?

Answer 6

proteins bind here

Question 7

What do activators do?

Answer 7

allow transcription to begin

bind to enhancers up the DNA and interact with the basal transcription complex

Question 8

Describe TATA box

Answer 8

TATA-box binding protein recognises TATA sequence and sits over the box, recruits TFIID and TFIIB bind to promoter and a basal transcription complex forms after further transcription factors bind to the promoter.

Question 9

Describe yeast

Answer 9

• Gal4 system of yeast: Gal 4 attaches to UASG but Gal80 a repressor also binds so transcription cannot occur of GAL1
• Adding galatose this binds to Gal80 allowing Gal 4 to interact with RNA polII etc on the promoter region allowing transcription factors to be switched on, activator stabilises it
• Complex regulatory regions enable an organism to fine tune gene expression by balances on silences on repressors and enhancers

Question 10

Describe histones

Answer 10

DNA is wrapped in chromatin and wrapped around histones in what’s known as nucleosomes

Each nucleosome is made up of 8 histone proteins, 2 turns of histone.

Question 11

Describe the packaging of DNA

Answer 11

Packaging of DNA into chromatin provides a good way for the cell to stop preventing transcription of genes. Activators unpack DNA allowing transcription to begin.

Question 12

How is DNA made accessible?

Answer 12

Chromatin remodelling complex interact with nucleosome to allow activator to bind, histone chaperons- can remove histones and can replace histones with variance, histone modifying enzymes interact with the activator proteins

Question 13

What are N terminal tails?

Answer 13

beginning of them allows counting of amino acids from core of histone

Question 14

How can histone be covalently modified at many sites?

Answer 14

methylation, phosphorylation, aceylation, ubiquitlylation – act as tags or the histones themselves

Question 15

Where do common modifications of the histones occur?

Answer 15

Lysine or serine, lysine can be competitve

Question 16

Describe lysine at position 9 of the H3 histone protein

Answer 16

– methyl reduces the likelihood of gene expression but an acyl group makes it more likely for gene expression to occur. Amino acid residues in N terminal tails of core histones can be modified by covalent addition of functional groups

Question 17

How can DNA be covalently modified directly?

Answer 17

methylation of cytosine CG sequence, reduces gene expression – can be inherited from cells during division – example of epigenetics – maintain patterns of differentiation.

Question 18

What contributes to stable gene repression?

Answer 18

multiple epigenetic mechanisms

Question 19

Describe control of eukaryotic transcriptional initiation

Answer 19

• Activator proteins bind upstream enhancer sequences and activate the basal transcription complex
• Multiple epigenetic mechanisms control expression via local chromatin condesnation
o Histone modificaitons
o In vertebrates, direct DNA methylation on cytosine helps maintain patterns of gene repression in somatic cells

Question 20

Describe prokaryotes

Answer 20

Bacteria less complicated no nucleus, one cytoplasmic compartment, no histones, coupled transcription and translation – occur at the same time, genes of related function are clustered into operons

Question 21

Lac Operon

Answer 21

single promoter, all genes transcribed together, translated to give separate proteins, lac I gene producing a lac repressor which binds to lac O, when lactose is absent the RNA polymerase cannot bind to the lacO

Question 22

What is negative regulation?

Answer 22

repressor

Question 23

What is positive regulation?

Answer 23

activator