sequence of nucleotides on a gene
of dna acts as a template
complimentary copy transcribed onto mRNA
mRNA acts as a template that is translated into a
complimentary chain of tRNA which carry specific
amino acids which are linked together
Transcription
produces mRNA from DNA
base sequence of a gene on DNA converted to
a complimentary base sequence on mRNA
rna polymerase links to dna at the start of
the gene to be transcribed
dna unwinds as hydrogen bonds between the 2 double helix strands break exposing unpaired dna bases
only one strand used as template
start codon ensures gene is read in right direction
rna polymerase moves along dna strand, a molecule of single stranded mRNA is made
from free rna nucleotides present in nucleoplasm (that enter nucleus from cytoplasm)
complimentary base pairing DNA-RNA: A-U(uracil), T-A, G-C, C-G
at end of sequence mRNA detaches and dna rewinds into double helix
mRNA moves through nuclear pores into the cytoplasm and
attaches to a ribosome (made of ribosomal rna and protein)
Translation
the formation of a polypeptide chain according to original
dna code using amino acids on tRNA and the mRNA code
mRNA held by a ribosome which had two transfer RNA (tRNA) binding site
each tRNA has its own specific amino acid
the codons on mRNA join to complimentary anticodons on tRNA by
hydrogen bonding
ribosomal enzyme catalyses peptide bond formation between an amino acid on one tRNA and the growing polypeptide on the other tRNA
ribosome passes along mRNA, one codon at a time, trna with appropriate anticodon fills vacant slot and
the amino acid forms a peptide bond with the last member of the chain using energy from ATP
the tRNA that has donated an amino acid to
chain detaches from mrna and ribosome and is
free to attach to another identical amino acid
an amino acid activated by ATP and is
attached to a specific tRNA molecule which
carries amino acid at one end and anticodon
at the other
different trna molecules with their amino acids are
assembles according to the mRNA base sequence
one site binds tRNA carrying
the amino acid which has been
joined to the growing
polypeptide chain while other
site is for tRNA carrying the
next amino acid in the
sequence
producing the final proteins
polysomes: usually a number of
ribosomes move along a single piece of
mRNA each making a new polypeptide
chain
further modification: primary structure
may be modified by golgi body and the final
structure may have more than one
polypeptide eg. haemoglobin