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 Environmental factors

Question 5

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

Answer 5

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 6

What is the key enzyme in Transcription?

Answer 6

RNA Polymerase

Question 7

Where does transcription take place?

Answer 7

Nucleus

Question 8

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

Answer 8

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

Question 9

What are the key requirements for Transcription?

Answer 9

• RNA Polymerase
• free mRNA bases
• DNA Template

Question 10

Describe the key steps in the process of transcription

Answer 10

1. RNA polymerase moves along DNA unwinding the double helix.
2. RNA polymerase also breaks the weak hydrogen bonds between bases, separating the two DNA strands
3. Free RNA nucleotides pair with their complementary base pair on the template strand. Weak hydrogen bonds form between complementary bases.
4. Strong chemical bonds form between the sugar and phosphate of neighbouring nucleotides (bond formation catalysed by RNA polymerase).
5. The strand of messenger RNA made by the RNA polymerase is known as the primary transcript

Question 11

What are the coding regions in an mRNA strand called?

Answer 11

Exons

Question 12

What are the four forms of nucleic acid?

Answer 12

• mRNA
• tRNA
• rRNA
• DNA

Question 13

Describe the process of mRNA splicing

Answer 13

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

Question 14

Where does mRNA splicing take place?

Answer 14

Nucleus

Question 15

What is the function of mRNA?

Answer 15

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

Question 16

What is the function of tRNA?

Answer 16

Carries specific amino acids to the ribosome to convert mRNA to a polypeptide chain

Question 17

What is the function of rRNA?

Answer 17

Combines with protein to form a ribosome

Question 18

Describe the structure of a tRNA molecule

Answer 18

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 19

State the name of the sugar molecule present in RNA

Answer 19

Ribose Sugar

Question 20

Where does translation occur?

Answer 20

Ribosome

Question 21

What is translation?

Answer 21

Synthesis of protein from a mature mRNA template

Question 22

Describe the steps in translation?

Answer 22

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 23

What type of bond forms between adjacent amino acids?

Answer 23

Peptide

Question 24

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

Answer 24

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 25

What is a codon?

Answer 25

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

Question 26

What is a start codon and where is it found?

Answer 26

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

Question 27

How can a different protein be expressed from one gene?

Answer 27

Alternative RNA Splicing

Question 28

How can alternative RNA splicing alter the final protein?

Answer 28

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

Question 29

Describe how the 3D structure of a protein is formed

Answer 29

Primary structure of protein consists of amino acids linked by peptide bonds forming polypeptide chain
Secondary structure of protein is formed by polypeptide folding and being held together by hydrogen bonds and other interactions.

Question 30

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

Answer 30

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 31

What is a function of a non-coding sequence?

Answer 31

Regulation of transcription

Question 32

DNA and RNA are different. RNA has … strand, … instead of … and a … sugar instead of a … sugar.

Answer 32

one strand … uracil instead of a thymine … ribose sugar instead of a deoxyribose sugar. DNA and RNA are different. RNA has one strand, uracil instead of a thymine and a ribose sugar instead of a deoxyribose sugar.