3.4.2 Protein synthesis

Question 1

where does transcription occur

Answer 1

in the nucleus of the cell

Question 2

what is the process of transcription

Answer 2

• a gene unwinds and unzips
• each gene codes for one polypeptide
• one strand acts as the template strand
• the free RNA nucleotides complementary base pair with the exposed DNA bases on this template strand
• a length of RNA is created by RNA polymerase which is a copy of the sense strand

Question 3

where does the mRNA leave the nucleus once it has been replicated

Answer 3

nuclear pore

Question 4

what is the strand of DNA called that isn’t copied

Answer 4

anti sense strand

Question 5

what happens during processing of the DNA

Answer 5

sections of it are removed

Question 6

what are introns

Answer 6

part of the gene that are non-coding

Question 7

what does it mean if something is non-coding

Answer 7

don’t encode a polypeptide sequence so are spliced out of the mRNA

Question 8

what is the first copy of mRNA called

Answer 8

pre-mRNA which still contains introns before they are spliced out in processing

Question 9

what are exons

Answer 9

coding sections of a gene

Question 10

what is a genome

Answer 10

all the genes in a cell

Question 11

what is a proteome

Answer 11

all the proteins seen in an organism

Question 12

why do we use triplets in a codon

Answer 12

4^3 = 64 so we have more possible combinations than we do amino acids as 64>20

Question 13

how many possible amino acids are there

Answer 13

20

Question 14

where does translation occur

Answer 14

cytoplasm of a cell - on ribosome

Question 15

how many codons of mRNA are exposed at a time during translation

Answer 15

2

Question 16

process of translation

Answer 16

• transfer RNA brings amino acids to the ribosome
• the tRNA has a binding site made up of three bases specific to a particular amino acid
• the tRNA also has an anti-codon which is complementary to the codon on the mRNA strand
• temporary hydrogen bonds form between codon and anti codon as 2 amino acids are bought close together by another tRNA molecule
• a peptide bond forms between them which require ATP
• eventually a STOP codon is reached

Question 17

what happens when a STOP codon is reached during translation

Answer 17

• signals the end of the polypeptide which is then released so the polypeptide can fold into its 3D shape with the help of chaperone proteins
• tRNA molecules are released as the ribosome moves along the mRNA strand and are free to pick up another amino acid from the cytoplasm

Question 18

what is the difference between mRNA and tRNA

Answer 18

mRNA: single stranded, has a codon, doesn’t have a binding site for amino acid
tRNA: folded-> clover shaped, held in place by hydrogen bonds, binding site for amino acids, has anti-codon

Question 19

why do prokaryotes not have introns

Answer 19

as they don’t have pre-mRNA so don’t need to splice them out

Question 20

what is a universal code

Answer 20

used by evrey cell-on earth as far as we know

Question 21

what is a degenerate code

Answer 21

a code that has multiple codes for the same protein

Question 22

what is a non-overlapping code

Answer 22

all triplets are completely separate and discrete to its neighbours

Question 23

what is a mutation

Answer 23

a random DNA copying error

Question 24

what are the different types of mutations

Answer 24

• substitution
• addition
• deletion
• inversion

Question 25

what is substitution

Answer 25

when a single nucleotide base is swapped for another

Question 26

what is addition

Answer 26

another base is added in

Question 27

in what scenario is a substitution neutral

Answer 27

if a code is degenerate resulting in the same amino acid

Question 28

what is a deletion

Answer 28

a base is removed

Question 29

what do both an addition an deletion cause

Answer 29

a frame shift so it effects all the amino acids in the sequence

Question 30

what is an inversion

Answer 30

where bases swap round -> effects at most 2 amino acids