1.3 Control of Gene Expression

Question 1

What is ‘gene expression’?

Answer 1

The process where info in the gene is used to make a protein

Question 2

What determines an organsism’s phenotype?

Answer 2

The proteins produced by its cells as a result of gene expression AND environmental factors

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

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 and breaking hydrogen bonds between bases.
2. RNA polymerase adds RNA nucleotides complementary to the template DNA strand. RNA contains uracil instead of thymine.
3. A primary transcript of mRNA is produced.

Question 11

What are the coding regions in an mRNA strand called?

Answer 11

Exons

Question 12

What are the non-coding regions in an mRNA strand called?

Answer 12

Introns

Question 13

What are the four forms of nucleic acid?

Answer 13

• mRNA
• tRNA
• rRNA
• DNA

Question 14

Describe the process of mRNA splicing

Answer 14

A primary transcript has the introns removed and the exons joined together to form a mature transcript.

Question 15

Where does mRNA splicing take place?

Answer 15

Nucleus

Question 16

What is the function of mRNA?

Answer 16

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

Question 17

What is the function of tRNA?

Answer 17

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

Question 18

What is the function of rRNA?

Answer 18

Combines with protein to form a ribosome

Question 19

Describe the structure of a tRNA molecule

Answer 19

Amino acid attachment site - specific amino acid pairs here
Anticodon attachment site - triplet of bases that are complementary to codon on mRNA strand

Question 20

State the name of the sugar molecule present in RNA

Answer 20

Ribose Sugar

Question 21

Where does translation occur?

Answer 21

Ribosome

Question 22

What is translation?

Answer 22

Synthesis of protein from a mature mRNA template

Question 23

Describe the steps in translation?

Answer 23

1. tRNA has an anticodon and an amino acid attachment site.
2. tRNA binds to a specific amino acid and carries that to ribosomes.
3. Each tRNA anticodon has a complementary codon on the mRNA that it pairs with. This allows the tRNA to bring the correct amino acid for each mRNA codon.
4. Peptide bonds form between amino acids.
5. There are start and stop codons which tell the ribosome when to start and stop translation.

Question 24

What type of bond forms between adjacent amino acids?

Answer 24

Peptide bond

Question 25

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

Answer 25

tRNA drop off their specific amino acid when the anticodon binds to its complementary mRNA codon.

Question 26

What is a codon?

Answer 26

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

Question 27

What is a start codon and where is it found?

Answer 27

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

Question 28

How can a different protein be expressed from one gene?

Answer 28

Alternative RNA Splicing

Question 29

How can alternative RNA splicing alter the final protein?

Answer 29

Different combinations of **exons** are left in the mature transcript.

Question 30

What are the **two** levels of protein structure

Answer 30

**Primary structure** **Secondary structure**

Question 31

What are the key differences between RNA and DNA

Answer 31

DNA has dexoyribose sugar and RNA has ribose sugar DNA is double-stranded and RNA is single stranded DNA has Thymine and RNA has Uracil

Question 32

What are proteins made of?

Answer 32

Chains of amino acid linked by **peptide** bonds

Question 33

What bond links amino acids together?

Answer 33

Peptide bonds

Question 34

How is a protein's shape determined?

Answer 34

By the order of amino acid

Question 35

What forms the **primary** structure of proteins?

Answer 35

Chain of amino acids linked by **peptide** bonds forming a polypeptide chain.

Question 36

What forms the **secondary** structure of proteins?

Answer 36

**Hydrogen** bonds and other interactions form between amino acids and cause the polypeptide chain to coil or fold.

Question 37

Describe **stage 1** of the process of transcription

Answer 37

**RNA** polymerase moves along DNA unwinding the double helix and breaking hydrogen bonds between bases.

Question 38

Describe **stage 2** of the process of transcription

Answer 38

**RNA** polymerase adds RNA nucleotides complementary to the template DNA strand. RNA contains uracil instead of thymine.

Question 39

Describe **stage 3** of the process of transcription

Answer 39

A primary transcript of mRNA is produced.

Question 40

Describe **step 1** of the process of translation

Answer 40

tRNA has an anticodon and an amino acid attachment site.

Question 41

Describe **step 2** of the process of translation

Answer 41

2. tRNA binds to a specific amino acid and carries that to ribosomes.

Question 42

Describe **step 3** of the process of translation

Answer 42

3. Each tRNA anticodon has a complementary codon on the mRNA that it pairs with. This allows the tRNA to bring the correct amino acid for each mRNA codon.

Question 43

Describe **step 4** of the process of translation

Answer 43

4. Peptide bonds form between amino acids.

Question 44

Describe **step 5** of the process of translation

Answer 44

There are start and stop codons which tell the ribosome when to start and stop translation.