2.2 Gene expression

Question 1

What is gene expression?

Answer 1

The process of the information encoded in a gene is used to assemble a protein molecule

Question 2

Why is gene expression regulated?

Answer 2

So the gene products are only produced if and when they are required by the cell

Question 3

What are the three thing that must occur for a gene to be expressed?

Answer 3

Transcription, RNA processing and Translation

Question 4

What are the sections before and after a gene called?

Answer 4

Upstream before the gene, downstream after the gene

Question 5

What is a stop sequence?

Answer 5

A regional where encoding DNA ends for a gene

Question 6

What is a start triplet sequence?

Answer 6

Region where encoding DNA begins

Question 7

What is a promoter region?

Answer 7

Binding regions upstream of the gene where RNA polymerase can bind in order for transcription to occur

Question 8

What are exons?

Answer 8

DNA regions within the gene that contain coding instructions

Question 9

What are introns?

Answer 9

Non-coding segment of pre mRNA

Question 10

What are the three steps of transcription?

Answer 10

Initiation, elongation and termination

Question 11

Explain the initiation step of transcription

Answer 11

RNA polymerase attaches to the promoter region at the start of the gene and unwinds and unzips the DNA strand

Question 12

How is DNA unzipped?

Answer 12

Through the use of the enzyme called helicase, which breaks the hydrogen bonds, exposing the nitrogenous bases

Question 13

Explain the elongation phase of transcription

Answer 13

RNA polymerase moves along the template strand in a 3’ to 5’ direction. Complementary nucleotides bind to the template strand. This builds a strand called mRNA

Question 14

What direction is mRNA made in?

Answer 14

5’ to 3’ direction, nucleotides being added to the 3’ end of the mRNA

Question 15

What is the template strand?

Answer 15

The strand of DNA that nucleotides bind to to make mRNA

Question 16

What is the coding strand?

Answer 16

The strand with the same base sequence as the mRNA strand, where Uracil replaces Thymine

Question 17

Describe termination of the transcription phase

Answer 17

Transcription ends when the RNA polymerase reaches the termination site of the gene. (TAA, TAG OR TGA). The RNA polymerase detaches and the DNA reforms.

Question 18

What strand does the RNA polymerase bind to?

Answer 18

Template strand

Question 19

What strand is complementary to the growing mRNA strand?

Answer 19

The coding strand

Question 20

What is the purpose of RNA processing?

Answer 20

To turn pre-mRNA into mature mRNA

Question 21

What occurs during RNA processing?

Answer 21

A methyl cap is added to the 5’ end, a spliceosome removes the introns and some exons, a poly-A tail is added to the 3’ end

Question 22

Where is a methyl cap added?

Answer 22

The 5’ end

Question 23

What are introns?

Answer 23

Non coding sections of DNA

Question 24

What are exons?

Answer 24

The coding sections of mRNA

Question 25

Where is a poly-A tail added?

Answer 25

To the 3’ end of the mRNA molecule

Question 26

What is the purpose of the methyl cap and poly-A tail?

Answer 26

To increase the mRNA’s stability and prevent it from degrading

Question 27

Where does mature mRNA leave the cell?

Answer 27

Via the nuclear pore