transcription Flashcards
what is a codon
-a DNA base triplet converted into mRNA codon that determine the AA sequence (primary structure)
how is RNA structurally different from DNA
-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
job of codon
-ensure the coded instructions are translated and protein is assembled correctly
quantity in cells, of DNA, mRNA and tRNA
-DNA = constant
-mRNA and tRNA = varies
stability of DNA, mRNA and tRNA
-DNA is very stable
-mRNA is unstable
-tRNA is more stable than mRNA but less than DNA
shape of DNA, mRNA and tRNA
-DNA is double helix
-mRNA is single helix
-tRNA is clover shape
what is the genetic code
-the sequence of nucleotides on a gene which provides the instructions for the construction of a polypeptide/ protein
the nature of the genetic code
-degenerate code
-non-overlapping code
-universal
-triplet code
what does it mean for the genetic code to be degenerate
-for all amino acids except methionine and tryptophan there is more than one base triplet
aka… more than one possible codon
positive of genetic code being degenerate
-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
what does it mean for the genetic code to be non-overlapping
-reads starting from a fixed point, in groups of 3 bases
-each base only read once, in which codon it is part of
effect of genetic code as non- overlapping
-if a base is added/ deleted, causes a frame shift as every base triplet after that (and so every coded AA) is changed
what does it mean for the genetic code to be universal
-in almost all living organisms the same triplet of DNA base codes for the same aa
effect of genetic code as universal
-genetic info is transferable between species
-why genetic engineering is possible
meaning of genetic code as a triplet code
-sequence of DNA nucleotide bases found within a gene is determined by a triplet code
-3 bases is one aa
2 stages of protein synthesis
-transcription
-translation
what is transcription
-copying the correct section of DNA to make an mRNA copy in the nucleus
what is translation
-reading the mRNA to create a polypeptide on a ribosome in the cytoplasm
stages of transcription
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
how do RNA nucleotides join
-forming phosphodiester bonds in condensation reactions between nucleotides
how do RNA base pairs match to DNA
-formation of temporary hydrogen bonds between RNA nucleotides and their complementary unpaired bases
what do the bases in RNA match up to
-A + T
-C + G
-G + C
-U + A
why does RNA polymerase only code 1 gene at a time
-recognise start and stop signals at end of gene
what is mRNA produced from
-free nucleotides in the nucleoplasm
