Unit 1- Transcription And Translation

Question 1

Where does translation occur?

Answer 1

At the ribosomes

Question 2

Where does transcription occur?

Answer 2

In the nucleus

Question 3

How many tRNA can diffuse into the ribosome at once?

Answer 3

2

Question 4

What do ribozymes do?

Answer 4

They catalyse the reactions on going in the ribosome

Eg, forming the peptide bond, cutting the bond between the amino acid and tRNA

Question 5

Describe the process of translation

Answer 5

• Ribosome attaches to mRNA at initiation codon
• The first tRNA molecule with amino acid attached diffuses into ribosome
• the tRNA anticodon binds to the codon of the mRNA
• the next amino acid tRNA attaches to the adjacent mRNA codon
• the bond between the amino acid and tRNA is cut by ribozymes and a peptide bond forms between amino acids
• the ribosome moves along to the next codon so a new amino acid tRNA can attach
• this repeats until a stop codon is reached, the ribosome falls apart

Question 6

Structure of tRNA

Answer 6

Strand of RNA, shaped like a clover with disulphide bonds

One end has anticodon and other has the amino acid that is coded from the codon

Question 7

Where does RNA polymerase bind to on the DNA?

Answer 7

A specific sequence of bases called promoters at the start of a gene

Question 8

What is the antisense strand?

Answer 8

This is the template strand that is complementary to the new mRNA

Question 9

What is the RNA sense sequence?

Answer 9

This is the sequence of bases on RNA that code for proteins

Question 10

What does RNA polymerase do?

Answer 10

Catalyses the formation of strong covalent phosphodiester bonds between RNA nucleotides

Question 11

What are cut out in splicing?

Answer 11

Introns

Question 12

Describe the process of translation up to pre-RNA

Answer 12

• RNA polymerase binds to DNA at promoter sequence
• RNA polymerase is a bundle of enzymes, one of these, helicase unwinds the DNA double helix
• this forms a transcription bubble (8 nucleotides long)
• one of the open strands is the template strand where ribose nucleotides join by complementary base pairing
• the RNA nucleotides are joined by covalent bonds by RNA polymerase
• RNA polymerase moves along the DNA, unwinding in front and rewinding behind
• the RNA polymerase stops transcription when it reaches the end of the gene

Question 13

Where does mature RNA go?

Answer 13

Into the cytoplasm to find a ribosome through the nuclear pore

Question 14

Why do prokaryotes not need spliceosomes?

Answer 14

They contain no introns in their DNA

Question 15

What is post translation modification?

Answer 15

Proteins have been made but aren’t functional so they need to be modified slightly

Question 16

Give an example of post translation modification

Answer 16

Chain cutting
Adding methyl or phosphate groups to some amino acids
- adding sugars and lipids -> glycoproteins and lipoproteins

Question 17

What is it called when a single piece of mRNA has many ribosomes attached at once

Answer 17

Polyribosome

Question 18

What are the 3 types of gene mutation?

Answer 18

Deletion
Substitution
Insertion

Question 19

What are gene mutations?

Answer 19

Changes in DNA base sequences due to base pairing errors

Question 20

When do gene mutations occurs?

Answer 20

DNA replication

Question 21

How many amino acids does substitution affect?

Answer 21

1

Question 22

What is a silent mutation?

Answer 22

When the mutation doesn’t affect the amino acid it codes for, due to amino acids being degenerate
Or it occurs in introns which don’t code for proteins anyway

Question 23

What is a nonsense mutation?

Answer 23

When a substitution mutation produces a stop codon, causing an incomplete nonfunctional protein

Question 24

Why are deletion and insertion more serious mutations?

Answer 24

• frame shift

- where all the amino acids being coded are wrong

Question 25

What is affected by gene mutation in sufferers of sickle cell anemia?

Answer 25

A substitution in one of the haemoglobin polypeptide chains causes the haemoglobin to shape differently also mutating the shape of the red blood cell