control of gene expression

Question 1

At what levels can genes be regulated?

Answer 1

transcriptional, post transcriptional, translational, post translational

Question 2

What is heterochromatin?

Answer 2

DNA that is tightly wound around its histone protein

Question 3

What is euchromatin?

Answer 3

DNA that is loosely wound around its histone protein

Question 4

How does chromatin remodelling control gene regulation?

Answer 4

the genes of loosely wound euchromatin can easily be transcribed where as tightly wound heterochromatin cannot be transcribed as RNA polymerase cannot access the genes

Question 5

Why does DNA coil around histones?

Answer 5

DNA is negatively charged and histones are positively charged

Question 6

How are histones modified?

Answer 6

acetylation/phosphorylation - addition of acetyl or phosphate groups to histone makes charge more negative so DNA coils less tightly
methylation - addition of methyl groups makes histones more hydrophobic so DNA binds more tightly and this prevents transcription

Question 7

What is epigenetics?

Answer 7

the control of gene expression through the modification of DNA

Question 8

What is an operon?

Answer 8

a group of genes that are under the control of the same regulatory mechanism and are expressed at the same time

Question 9

What is the lac operon?

Answer 9

a group of three genes controlled by the same regulatory gene that code for enzymes involved in the metabolism of lactose

Question 10

What type of genes are in the lac operon and what do they code for?

Answer 10

structural genes coding for three enzymes (B-galactosidase, lactose permease and transacetylase)

Question 11

What does the regulatory gene in the lac operon code for?

Answer 11

a repressor protein that prevents the transcription of the structural genes

Question 12

Where does the repressor protein bind in the lac operon and what does this do?

Answer 12

operator region which prevents RNA polymerase binding to the promoter and transcribing the gene

Question 13

What happens in lac operon if lactose is present?

Answer 13

lactose binds to the repressor protein changing its shape so that it cannot bind to the operator region, this allows transcription of the structural genes

Question 14

How is the transcription speed of the genes in lac operon sped up?

Answer 14

binding of cAMP receptor protein, this is only present when glucose levels are low. This makes sure that glucose is the preferred respiratory substrate

Question 15

What type of gene regulation control is the lac operon an example of?

Answer 15

transcriptional

Question 16

What is an example of post transcriptional/pre translational control ?

Answer 16

RNA processing (splicing, RNA editing and addition of caps and tails)

Question 17

What are the two types of mRNA?

Answer 17

pre mRNA and mature mRNA

Question 18

What is a cap and a tail?

Answer 18

a cap is a modified nucleotide that goes on the 5’ end of pre mRNA and a tail is a long chain of adenine nucleotides that is added to the 3’ end of pre mRNA

Question 19

What is the role of the cap and tail?

Answer 19

stabilises the mRNA and delays degradation in the cytoplasm. The cap also helps with binding to the ribosome

Question 20

What is splicing and where does it occur?

Answer 20

the removal of introns and joining together of exons in the nucleus

Question 21

What are introns and exons?

Answer 21

introns are non coding regions of DNA, exons are coding regions of DNA

Question 22

What is RNA editing (pre translational control)?

Answer 22

changing of RNA nucleotide sequence through substitution, addition and deletion

Question 23

What are the 3 processes that regulate protein synthesis?

Answer 23

degradation of mRNA, binding of inhibitory proteins to mRNA (cant bind to ribosomes) and activation of initiation factors which aid binding of mRNA to ribosomes

Question 24

What is the role of protein kinases in translational control?

Answer 24

catalyse the addition of phosphate groups to proteins which changes tertiary structure and so its function

Question 25

What are the examples of post translational control?

Answer 25

addition of non protein groups, modifying amino acids, folding/shortening of proteins and modification by cAMP