19.2Control Of Gene Expression

Question 1

What is transcriptional control

Answer 1

The idea that genes can be turned on or off

Question 2

What is heterochromatin

Answer 2

Tightly wound DNA causing chromosomes to be visible during cell division
Transcription of genes isn’t possible

Question 3

What is euchromatin

Answer 3

Loosely wound dna present during interphase

Transcription of genes is possible

Question 4

What is chromatin remodelling

Answer 4

Protein synthesis occurs during interphase between cell divisions which ensures the proteins necessary for cell division are synthesised in time
It happens to the genes in euchromatin

Question 5

Why does dna coil around histones

Answer 5

Because histones are positively charged and dna is negative

Question 6

What is histone modification

Answer 6

When histones are modified to increase or decrease the degree of packing

Question 7

What will reduce the positive charge of histones

And what does this do

Answer 7

Addition of acetyl groups (acetylation) or phosphate groups (phosphorylation)
It causes dna to coil less tightly allow certain genes to be transcribed

Question 8

What makes histones more hydrophobic

Answer 8

Addition of methyl groups (methylation)

This makes them bind more tightly to each other causing dna to coil more tightly and prevent transcription

Question 9

What is Epigenetics

Answer 9

Used to describe the control of gene expression by the modification of dna
Histone modification

Question 10

What is an operon

Answer 10

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

Question 11

What is the lac operon

Answer 11

A group of 3 genes 
LacZ
LacY 
LacA
They are structural genes as they code for 3 enzymes and they are transcribed onto a single long molecule of mRNA

Question 12

How is the transcription of the structural genes in the lac operon prevented

Answer 12

A regulatory gene lacI is located near to the operon and codes for a repressor preteen that prevents the transcription in the absence of lactose

Question 13

Where does the repressor bind in the lac operon and what does it do

Answer 13

The operator

It prevents RNA polymerase binding to DNA and beginning transcription

Question 14

What is the promoter

Answer 14

Section of dna that is the binding site for rna polymerase

Question 15

What happens when lactose is present in lac operon

What is this process called

Answer 15

Lactose binds to repressor protein causing it to change shape so it can no longer bind to operator
This means the rna can now bind to promoter and the 3 structural genes are transcribed and enzymes are synthesised

Question 16

What is the role of cyclic AMP

Answer 16

A protein that binds with rna polymerase to the operator that increase the rate of transcription to produce the required quantity of enzymes

Question 17

What processes occur in post-transcriptional control

Answer 17

Rna processing

Rna editing

Question 18

What is rna processing

Answer 18

When the product of transcription (pre - mRNA) is modified forming mature mRNA

Question 19

How is mRNA modified into mature mRBA

Answer 19

Cap is added to 5’ end and a tail is added to 3’ end - these stabilise mRNA and delay degradation in the cytoplasm
Splicing occurs

Question 20

What is splicing

Answer 20

Rna is cut at specific points

The introns are removed and the Exxon’s are joined together

Question 21

What is rna editing

Answer 21

Nucleotide sequence of some mRNA molecules are changed through base addition, deletion or substitution

Question 22

What are the 3 mechanisms that regulate the process of protein synthesis in translational control

Answer 22

Degradation of mRNA
Binding of inhibitory proteins to mRNA
activation of initiation factors that aid the binding of mRNA

Question 23

What is teh degradation of mRNA

Answer 23

The more resistant the molecule the longer it will last in the cytoplasm and a greater quantity of protein is synthesised

Question 24

What does the binding of inhibitory proteins to mRNA do

Answer 24

Prevents it binding to ribosomes and the synthesis of Proteins

Question 25

What does the activation of initiation factors in translational control do

Answer 25

They aid the binding of mRNA to ribosomes

Question 26

What are Protein kinases

Answer 26

Enzymes that catalyse the addition of phosphate groups to proteins
This changes the tertiary structure and the function of a protein
They are important regulators of cell activity

Question 27

What happens in post translational control

Answer 27

Addition Of non-protein groups such as carbohydrate Chains
Modify amino acids and the formation bonds like disulphides bridges
Folding or shortening proteins
Modification by cAMP