1.3 Control of Gene Expression

Question 1

What is ‘gene expression’?

Answer 1

Process that results in the production of a protein

Question 2

How does gene expression control the phenotype of an organism?

Answer 2

Gene expression = codes for protein which determine an organism’s phenotype

Question 3

How is gene expression controlled?

Answer 3

Regulation of transcription and translation

Question 4

What factors can influence gene expression?

Answer 4

Intracellular and Extracellular factors

Question 5

Give an example of an intracellular factor that can influence gene expression

Answer 5

Hormones

Example: Insulin triggering production of enzymes in liver

Question 6

Give an example of an extracellular factor that can influence gene expression

Answer 6

Light Intensity

Example: Cells in potato tubers trigger production of chlorophyll when light is available

Question 7

Only a fraction of genes are expressed. Explain this statement in relation to specialised cells.

Answer 7

Genes can be switched on and off. It they are switched on, they are expressed and produce proteins.
Each specialised cell will only switch on the genes that code for proteins characteristic of that cell .

Question 8

What is the key enzyme in Transcription?

Answer 8

RNA Polymerase

Question 9

Where does transcription take place?

Answer 9

Nucleus

Question 10

Why can’t a full copy of the DNA go to the ribosome?

Answer 10

DNA is too big to leave the nucleus through the nuclear pores

Question 11

What are the key requirements for Transcription?

Answer 11

rNA Polymerase
free mRNA bases
ATP
Promoter Region
Terminator Region 
DNA Template

Question 12

Describe the key steps in the process of transcription

Answer 12

1. RNA polymerase unwinds and unzips the DNA, exposing the bases
2. RNA polymerase starts at the promoter region and forms a complementary mRNA strand based off the sense strand
3. Hydrogen bonds form between mRNA and DNA
4. RNA Polymerase forms strong chemical bonds between ribose sugar and phosphate
5. mRNA strand peels off DNA and hydrogen bonds break between mRNA and DNA

Question 13

What are the coding regions in an mRNA strand called?

Answer 13

Exons

Question 14

What are the four forms of nucleic acid?

Answer 14

mRNA
tRNA
rRNA
DNA

Question 15

Describe the process of mRNA splicing

Answer 15

A primary transcript has the introns cut out of them and the exons combined to form a mature transcript

Question 16

Where does mRNA splicing take place?

Answer 16

Nucleus

Question 17

What is the function of mRNA?

Answer 17

Carry a copy of the genetic material to the ribosome to be translated

Question 18

What is the function of tRNA?

Answer 18

Drops off amino acids at the ribosome to form a polypeptide chain

Question 19

What is the function of rRNA?

Answer 19

Combines with protein to form a ribosome

Question 20

Describe the structure of a tRNA molecule

Answer 20

Amino acid attachment site - specific Aa that pairs up with anticodon attaches
Anticodon attachment site - triplet of bases that are complementary to codon on mRNA strand

Question 21

What is the folded structure of tRNA due to?

Answer 21

Base pairing

Question 22

State the name of the sugar molecule present in RNA

Answer 22

Ribose Sugar

Question 23

Where does translation occur?

Answer 23

Ribosome

Question 24

What is translation?

Answer 24

Synthesis of protein from a mature mRNA template

Question 25

Describe the steps in translation?

Answer 25

1. mRNA enters the ribosome, start codon initiates translation
2. tRNA molecules come along that have an anticodon complementary to the codon of the mRNA
3. tRNA molecules drop off the amino acid they are carrying
4. A polypeptide chain forms as the tRNA molecules keep dropping off the Aa
5. When the stop codon is reached no more amino acids are added to the polypeptide chain and translation finishes.

Question 26

What type of bond forms between adjacent amino acids?

Answer 26

Peptide

Question 27

How do tRNA molecules ensure the correct sequence of amino acids?

Answer 27

tRNA drop off their amino acid when the anticodon is complementary to the mRNA codon being translated, the tRNA anticodon will line up with its complementary mRNA codon

Question 28

What is a codon?

Answer 28

A triplet of bases on the mRNA strand that are complementary to an anticodon the tRNA molecule

Question 29

What is a start codon and where is it found?

Answer 29

A triplet of bases that initiates translation found at the start of the mRNA strand

Question 30

How can a different protein be expressed from one gene?

Answer 30

Alternative RNA Splicing

Question 31

How can the end protein be modified after translation?

Answer 31

Post Translational Modification

Question 32

How can alternative RNA splicing alter the final protein?

Answer 32

Different combinations of EXONS are left in the mature transcript. Exons can be treated as introns and removed.

Question 33

Give an example of post translational modification of a protein

Answer 33

Addition of a non protein part such as carbohydrate

Cutting and combining polypeptide chains

Question 34

Describe how the 3D structure of a protein is formed

Answer 34

Chemical bonding is used to fold up and hold protein in shape eg.Hydrogen bonds, ionic bonds, sulphur bridges

Question 35

Give an example of a protein in the body and its function

Answer 35

Enzymes - speed up chemical reactions by lowering activation energy
Hormones - chemical messengers that travel in bloodstream to target organs to bring around a response
Antigenic Proteins - signature proteins that identify to an immune system if a cell belongs to an organism

Question 36

What is a function of a non coding sequence?

Answer 36

Regulation of transcription