Protein synthesis

Question 1

What are the 2 steps involved in protein synthesis

Answer 1

• Transcription
• Translation

Question 2

Define transcription

Answer 2

Where one gene of the DNA is copied into mRNA

Question 3

Define translation

Answer 3

Where the mRNA joins with a ribosome, and corresponding tRNA molecules brings the specific amino acid the codon codes for

Question 4

Where does transcription happen within the cell

Answer 4

Inside the nucleus

Question 5

Why do we have the create a copy of the gene of interest on the DNA for protein synthesis (2 reasons)

Answer 5

• Because DNA is too big to leave the nucleus
• There are enzymes in the cytoplasm that could damage the DNA

Question 6

How come mRNA is small enough to leave the nucleus but DNA isn’t

Answer 6

Because mRNA carries the code for one gene whereas DNA carries the code for all the genes

Question 7

What is the first step in transcription, and name the enzyme

Answer 7

The DNA HELIX UNWINDS to expose the bases to act as a template - unwinding is catalysed by DNA HELICASE

Question 8

During transcription, how many chains of DNA act as a template, and why is this

Answer 8

Only one because mRNA is single stranded

Question 9

What type of bonds does DNA helicase break between the bases

Answer 9

Hydrogen bonds

Question 10

Once DNA helicase has unzipped the DNA strand, what do the free mRNA nucleotides do

Answer 10

They align opposite exposed complementary DNA bases

Question 11

What is the name of the enzyme that bonds together RNA nucleotides to create a new RNA polymer chain

Answer 11

RNA polymerase

Question 12

What bonds form between the RNA nucleotides uses the enzyme RNA polymerase

Answer 12

Phosphodiester bonds

Question 13

What process occurs to change pre-mRNA to mRNA

Answer 13

Splicing

Question 14

What happens during splicing

Answer 14

The introns are removed

Question 15

What are introns

Answer 15

The sequences of bases in the DNA which don’t code for amino acids

Question 16

What is the name of the enzyme involved in splicing

Answer 16

Splicesome

Question 17

What bonds does the splicesome break

Answer 17

The phosphodiester bonds

Question 18

Does mRNA contain any introns

Answer 18

No, it only contains exons- the coding part of DNA

Question 19

What happens during translation

Answer 19

The polypeptide chain is created using both the mRNA base sequence and the tRNA

Question 20

Once the mRNA has left the nucleus where does it go

Answer 20

It attaches to a ribosome in the cytoplasm

Question 21

What does the tRNA molecule with the complementary anticodon to the start codon do

Answer 21

It aligns opposite the mRNA, held in place by the ribosome

Question 22

What is the role of the ribosome during translation

Answer 22

To hold the mRNA and tRNA molecules in place

Question 23

Once the tRNA that has complementary anticodon to the codon on mRNA has aligned, what does the ribosome do

Answer 23

It moves along the mRNA, so another tRNA molecule can align

Question 24

How many tRNA molecules can the ribosome hold at one time during translation

Answer 24

Two

Question 25

When there are 2 tRNA molecule aligned with the mRNA molecule, what happens to their amino acids before the ribosome releases it, and what is required for this to happen

Answer 25

The amino acids are joined by a peptide bond- this is catalysed by an enzyme and requires ATP

Question 26

Can tRNA molecules be reused

Answer 26

Yes, after they have detached from the ribosome than enter the cytoplasm again and can be reused

Question 27

What codon is required at the end of the mRNA molecule to stop translation

Answer 27

The stop codon

Question 28

How does the stop codon end translation

Answer 28

Because it doesn't code for an amino acid and therefore the ribosome detaches since there isn't a corresponding anticodon on a tRNA molecule

Question 29

After translation, where does the polypeptide chain go and what happens

Answer 29

It enters the Golgi body for folding and modification

Question 30

When reading a base sequence wheel, what sequence does it read for; DNA, mRNA, or tRNA

Answer 30

mRNA

Question 31

Describe 2 differences between the structure of a tRNA molecule and the structure of an mRNA molecule

Answer 31

- tRNA is clover leaf shape, mRNA is linear - tRNA has hydrogen bonds, mRNA does not - tRNA has an amino acid binding site, mRNA does not - tRNA has anticodon, mRNA has codon

Question 32

Describe and explain the difference in the structure of pre-mRNA and mRNA (2 marks)

Answer 32

- mRNA has fewer nucleotides - Because of splicing

Question 33

Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation (3 marks)

Answer 33

- tRNA brings specific amino acid to ribosome - Anticodon on tRNA binds to codon on mRNA - Amino acids join by condensation reaction/ join by forming a peptide bond

Question 34

Describe how mRNA is produced from an exposed template strand of DNA, not including DNA helicase or splicing (3 marks)

Answer 34

- Free RNA nucleotides form complementary base pairs - Phosphodiester bonds form - By action of RNA polymerase

Question 35

Describe how mRNA is formed by transcription in eukaryotes (5 marks)

Answer 35

- Hydrogen bonds between DNA bases break - Only one strand acts as a template - Free RNA nucleotides align by complementary base pairing - In RNA uracil base pairs with adenine - RNA polymerase joins adjacent RNA nucleotides - By phosphodiester bonds - Pre-mRNA is spliced

Question 36

Describe how a polypeptide is formed by translation of mRNA (6 marks)

Answer 36

- mRNA attaches to ribosomes - tRNA anticodon binds to complementary mRNA codon - tRNA brings specific amino acid - Amino acid joins by peptide bond - Amino acids join together with the use of ATP - tRNA released - The ribosome moves along the mRNA to form the polypeptide

Question 37

What is the proteome of a cell

Answer 37

Range of different proteins that a cell is able to produce

Question 38

Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide (5 marks)

Answer 38

- mRNA associates with a ribosome - Ribosome moves to the start codon - tRNA brings specific amino acid - Anticodon to codon - Ribosome moves along to next codon - Amino acids join by peptide bonds

Question 39

Describe the role of a ribosome in the production of a polypeptide (3 marks)

Answer 39

- mRNA binds to ribosome - 2 codons - tRNA with anticodons to bind - Formation of peptide bonds between 2 amino acids - Moves along mRNA to next codon