protein synthesis

Question 1

where are proteins created ?

Answer 1

proteins are created on ribosomes

Question 2

what are the 2 stages of the production of proteins from the DNA code ?

Answer 2

• transcription
• translation

Question 3

what happens in transcription ?

Answer 3

transcription is where one gene on the DNA is copied into mRNA

Question 4

what occurs in translation?

Answer 4

translation is where the mRNA joins with a ribosome and corresponding tRNA molecules bring the specific amino acid that the codon codes for

Question 5

where does transcription take place?

Answer 5

in the nucleus

Question 6

where does translation take place ?

Answer 6

in the cytoplasm

Question 7

describe transcription .

Answer 7

a complementary mRNA copy of one gene on the DNA is created in the nucleus
- DNA is too big to leave the nucleus so mRNA is much shorter than DNA so it is able to carry the genetic code to the ribosome in the cytoplasm to enable the protein to be made

Question 8

why do we not want the DNA to leave the nucleus ?

Answer 8

the cytoplasm contains enzymes that could damage the DNA

Question 9

6 steps of transcription

Answer 9

1) The DNA helix unwinds to expose the bases and to act as a template
2) only one chain of DNA acts as a template
3) this unwinding is catalysed by DNA helicase
4) DNA helicase breaks the hydrogen bonds between the bases
5) free mRNA nucleotides in the nucleus align opposite exposed complementary DNA bases
6) the enzyme RNA polymerase bonds together the RNA nucleotides to create a new RNA polymer chain. One entire gene is copied

Question 10

what happens in transcription once one entire gene is copied ?

Answer 10

once copied, the mRNA is modifies and then leaves the nucleus through the nuclear envelope pores

Question 11

what is the mRNA called during transcription ?

Answer 11

pre-mature mRNA

Question 12

following transcription, what must happen to the pre-mature mRNA ?

Answer 12

pre-mature mRNA has to be modified to become mature mRNA that is ready to leave the nucleus and take part in translation

Question 13

how is pre-mature mRNA modified into mature mRNA ?

Answer 13

the introns are spliced out by a protein called splicesome which leaves behind just the exons which are the coding regions

Question 14

what are introns ?

Answer 14

intervening sections
- non-coding DNA

Question 15

what are exons ?

Answer 15

expressed sections
- coding regions of the DNA

Question 16

what is the general overview of translation ?

Answer 16

translation is the stage in which the polypeptide chain is created using both the mRNA base sequence and the tRNA

Question 17

steps of translation (6)

Answer 17

1) once the modified mRNA has left the nucleus it attaches to a ribosome in the cytoplasm
2) the ribosome attaches at the start codon
3) the tRNA molecule with the complimentary anticodon to the start codon aligns opposite the mRNA , held in place by the ribosome
4) the ribosome will move along the mRNA molecule to enable another complimentary tRNA to attach to the next codon on the mRNA
5) the 2 amino acids that have been delivered by the tRNA molecule are joined together by a peptide bond. this is catalysed by an enzyme and requires atp
6) this continues until the ribosome reaches the stop codon at the end of the mRNA molecule. The ribosome detaches and translation ends

Question 18

what does the stop codon not do ?

Answer 18

the stop codon does not code for an amino acid

Question 19

what will happen after translation ?

Answer 19

the polypeptide chain has been now created and will enter the golgi body for folding and modification

Question 20

what is the start codon ?

Answer 20

AUG