transcription

Question 1

what is a codon

Answer 1

-a DNA base triplet converted into mRNA codon that determine the AA sequence (primary structure)

Question 1

how is RNA structurally different from DNA

Answer 1

-Sugar molecule in each nucleotide is ribose
-the base uracil (pyridimine) replaced thymine (pyridimine)
-the polynucleotide chain s shorter
-there are 3 forms mRNA, tRNA and rRNA
-many viruses encode their genetic material using RNA genome

Question 2

job of codon

Answer 2

-ensure the coded instructions are translated and protein is assembled correctly

Question 3

quantity in cells, of DNA, mRNA and tRNA

Answer 3

-DNA = constant
-mRNA and tRNA = varies

Question 4

stability of DNA, mRNA and tRNA

Answer 4

-DNA is very stable
-mRNA is unstable
-tRNA is more stable than mRNA but less than DNA

Question 5

shape of DNA, mRNA and tRNA

Answer 5

-DNA is double helix
-mRNA is single helix
-tRNA is clover shape

Question 6

what is the genetic code

Answer 6

-the sequence of nucleotides on a gene which provides the instructions for the construction of a polypeptide/ protein

Question 7

the nature of the genetic code

Answer 7

-degenerate code
-non-overlapping code
-universal
-triplet code

Question 8

what does it mean for the genetic code to be degenerate

Answer 8

-for all amino acids except methionine and tryptophan there is more than one base triplet
aka… more than one possible codon

Question 9

positive of genetic code being degenerate

Answer 9

-reduces the effect of point mutation
-a change in one base of the triplet could produce another base triplet that still codes for same DNA

Question 10

what does it mean for the genetic code to be non-overlapping

Answer 10

-reads starting from a fixed point, in groups of 3 bases
-each base only read once, in which codon it is part of

Question 11

effect of genetic code as non- overlapping

Answer 11

-if a base is added/ deleted, causes a frame shift as every base triplet after that (and so every coded AA) is changed

Question 12

what does it mean for the genetic code to be universal

Answer 12

-in almost all living organisms the same triplet of DNA base codes for the same aa

Question 13

effect of genetic code as universal

Answer 13

-genetic info is transferable between species
-why genetic engineering is possible

Question 14

meaning of genetic code as a triplet code

Answer 14

-sequence of DNA nucleotide bases found within a gene is determined by a triplet code
-3 bases is one aa

Question 15

2 stages of protein synthesis

Answer 15

-transcription
-translation

Question 16

what is transcription

Answer 16

-copying the correct section of DNA to make an mRNA copy in the nucleus

Question 17

what is translation

Answer 17

-reading the mRNA to create a polypeptide on a ribosome in the cytoplasm

Question 18

stages of transcription

Answer 18

1) helicase enzyme unzips the DNA
2) Gyrase unwinds the DNA
3) RNA polymerase attaches to 3’ end of the DNA on the antisense (template) strand at the location of start codon, moves in 3’ to 5’ direction
4) assembles free RNA nucleotides in complementary base pairing, forming strand of mRNA
5) RNA strand produced in a 5’ to 3’ direction
6) transcription stops at end of gene and mRNA detaches from DNA
7) exists the nucleus via a nucleur pore in cytoplasm
8) DNA rewinds into helix

Question 19

how do RNA nucleotides join

Answer 19

-forming phosphodiester bonds in condensation reactions between nucleotides

Question 20

how do RNA base pairs match to DNA

Answer 20

-formation of temporary hydrogen bonds between RNA nucleotides and their complementary unpaired bases

Question 21

what do the bases in RNA match up to

Answer 21

-A + T
-C + G
-G + C
-U + A

Question 22

why does RNA polymerase only code 1 gene at a time

Answer 22

-recognise start and stop signals at end of gene

Question 23

what is mRNA produced from

Answer 23

-free nucleotides in the nucleoplasm

Question 24

what is the relevance of the coding strand

Answer 24

-has nucleotide sequence complementary to the template strand
-is identical to the mRNA strand

Question 25

describe how mRNA is made during transcription

Answer 25

-DNA molecule unwinds due to helicase
-RNA nucleotides line up and attatch to the antisense strand
-complementary base pairing (between DNA and mononucleotides)
-formation of phosphodiester bonds in a condesation reaaction
-mRNA detaches from DNA

Question 26

why does RNA polymerase move 3’ to 5’ direction

Answer 26

-it needs free OH group on the carbon 3
(also reads 3’ to 5’)

Question 27

what direction is RNA assembled

Answer 27

in a 5’ to 3’

Question 28

what does gyrase do

Answer 28

-unwinds DNA so it doesnt supercoil

Question 29

what does helicase do

Answer 29

-unzips DNA