Regulation of Gene Expression

Question 1

What percentage of the genome codes for proteins?

Answer 1

1-2%

Question 2

What is heterochromatin?

Answer 2

condensed DNA that is not actively expressed - AT rich - shows up as dark bands on the chromosomes

Question 3

How many protein coding genes are there?

Answer 3

21000-25000

Question 4

What is the role of RNA genes?

Answer 4

some RNA genes are involved in regulation

Question 5

What is euchromatin?

Answer 5

the light bands on the chromosomes which contain active genes and are GC rich

Question 6

Which part of the chromosome is very heterochromatic?

Answer 6

the centromere

Question 7

How many protein coding genes are in the mitochondrial genome?

Answer 7

13

Question 8

What is constituitive gene expression?

Answer 8

constant gene expression in all cells

Question 9

What is regulated gene expression?

Answer 9

gene expression which is turned on and off according to signals, temporal regulation and tissue specificity

Question 10

If there are only roughly 20,000 genes how is it possible that there are 1 million proteins?

Answer 10

alternative splicing, sequences can have more than one start site

Question 11

What is the role of the snRNA protein complex?

Answer 11

binds to splice donor and acceptor sites - has enzymatic activity to cleave out the introns

Question 12

What is chromatin packaging?

Answer 12

DNA wound around histone proteins

Question 13

What allows for chromatin remodelling?

Answer 13

chemical modifiction - methylation and acetylation of histones and methylation of DNA itself

Question 14

Why is chromatin remodelling important?

Answer 14

gives the replication machinery access to the DNA

Question 15

Where is heterochromatin found in the nucleus?

Answer 15

around the edges closer to the nuclear membrane

Question 16

What site on DNA is often methylated?

Answer 16

a cytosine next to a guanine (CpG)

Question 17

What happens to DNA methylation in DNA replication?

Answer 17

the same pattern of methylation is recapitulated in the daughter cell

Question 18

How much methylation of the cytosine in CpG is there in heterochromatin?

Answer 18

hypermethylation

Question 19

How much acetylation and methylation of histones is there in heterochromatin?

Answer 19

hypoacetylation and either hyper or hypomethylation

Question 20

How much methylation of the cytosine in CpG is there in euchromatin?

Answer 20

hypomethylation

Question 21

How much acetylation and methylation of histones is there in euchromatin?

Answer 21

hyperacetylation and either hyper or hypomethylation

Question 22

What are the minimum requirements of transcription?

Answer 22

DNA has to be accessible, need RNA polymerase, need transcription factors, need to bind at a promoter (e.g. TATA box), need energy and need nucleotides

Question 23

What are cis-acting DNA sequences?

Answer 23

DNA sequences which alter transcription by acting on their own strand via a looping of the DNA - can either silence or enhance gene expression

Question 24

What are the 4 different ways that long non coding RNAs can alter transcription?

Answer 24

decoy - bind to the RNA polymerase so that it cant bind - silence
scaffold - bring together transcription factors to either enhance or silence
guide - guide the transcription factor or polymerase to the right spot
enhancer - acts to bring an enhancer closer to the region

Question 25

What is the action of siRNAs?

Answer 25

short interfering RNAs interact with a protein called RISC - the complex will then bind to a complementary region of mRNA to degrade the mRNA and switch off protein production

Question 26

What is the action of miRNAs?

Answer 26

represses translation by an unknown mechanism