Mutations and Gene Expression

Question 1

What is RNA interference?

Answer 1

a biological process where RNA molecules inhibit gener expression by preventing translation

Question 2

What RNA molecules are involved in RNA interference?

Answer 2

miRNA (microRNA)
siRNA (small interfering RNA)

Question 3

What does dsRNA sstand for?

Answer 3

Double stranded RNA

Question 4

What does siRNA do?

Answer 4

In the cytoplasm, double stranded siRNA associates with several proteins and unwinds
One (out of 2) single strands of siRNA is selected - the other is broken down
The single strand binds to the target mRNA.
The base sequence of the siRNA is complementary to the target mRNA.
When the siRNA binds to the target mRNA - it brings the proteins associated with it - these cut the mRNA into fragments = mRNA can no longer be translated.
The fragments move into a processing body which has tools to degrade the mRNA fragments.

Question 5

What molecule does a plant use to cut up and degrade mRNA strands?

Answer 5

miRNA

Question 6

Describe the process involving miRNA:

Answer 6

The base sequence of plant miRNA is complementary to the target mRNA sequence - so binding to it results in the cutting up and degradation of mRNA.

Question 7

Why is miRNA less specific than siRNA? (32,000 ft)
What does this mean miRNA can do?

Answer 7

Because miRNA is not fully complementary to the target mRNA sequence so miRNA can target more than one mRNA molecule.

Question 8

What is the process of forming miRNA?

Answer 8

When it is first transcribed it exists as a long folded strand, then it is processed into a double strand which is then split into two single strands by enzymes in the cytoplasm.

Question 9

How does miRNA block the translation of the target mRNA?

Answer 9

One strand of miRNA associates with proteins and binds to the target mRNA (in cytoplasm)
The proteins associated DO NOT cut the mRNA into fragments HOWEVER
the miRNA-protein complex physically blocks the translation of the target mRNA.

Question 10

What happens to the mRNA once the miRNA-protein complex has blocked the translation of it?

Answer 10

The mRNA is moved into a processing body where it is either stored or degraded

Question 11

What happens to the mRNA which is stored in the processing bodies?

Answer 11

It can either be returned and translated another time or it can be degraded.

Question 12

How is siRNA formed?

Answer 12

A molecule of dsRNA is cut into one strand of siRNA by an enzyme.

Question 13

What is an siRNA-enzyme complex?

Answer 13

When the one strand of siRNA associates with a protein/enzyme

Question 14

How does epigenetics work?

Answer 14

When a chemical group (AKA an epigenetic marker) is either added or removed from a molecule of DNA or histone proteins.

Question 15

What do epigenetic markers do?

Answer 15

THEY DO NOT ALTER THE BASE SEQUENCE OF DNA
They alter how easy it is for enzymes and other proteins needed for transcription to interact with + transcribe the DNA.

Question 16

How epigenetic markers be inherited?

Answer 16

From previous generations - although majority of epigenetic markers are removed between generations - some remain. Therefore they are passed onto their offspring.
The expression of some genes in the offspring can be affected by environmental changes that affected previous generations.

Question 17

What can epigenetic changes occur in response to?

Answer 17

Changes in the environment

Question 18

What two processes control gene expression?

Answer 18

Methylation and Acetylation

Question 19

What is methylation?

Answer 19

When a methyl group is added onto the DNA which is coding for the gene

Question 20

Where does the methyl group attach?

Answer 20

At the CpG site

Question 21

What is the CpG site?

Answer 21

Where the cytosine base is attached to the guanine base via a phosphodiester bond

Question 22

What happens during increased methylation?

Answer 22

It changes the DNA structure so that transcriptional enzymes cannot interact with the gene so that the gene won’t be expressed.