DNA, genes & protein synthesis Flashcards
similarities between eukaryotic DNA & prokaryotic DNA
- made of DNA nucleotides with identical structure –> deoxyribose, phosphate group & nitrogenous base
- nucleotides joined together by phosphodiester bonds
differences between eukaryotic DNA & prokaryotic DNA
- eukaryotes = longer, prokaryotes = shorter
- eukaryotes = linear, prokaryotes = circular
- eukaryotes = associated with histones, prolaryotes = no histones
- eukaryotes = contain introns, prokaryotes = no introns
what are chromosomes formed from?
DNA with histones wrapped around it
how might the struc. of a chromosome differ along its length?
(exam q)
- difference in base sequence
- difference in histones
which organelles have DNA similar to prokaryotic DNA?
- mitochondria
- chloroplasts
define ‘gene’
a section of DNA that codes for a particular polypeptide eg. eye colour
define ‘locus’
the particular, fixed position on a chromosome that a gene occupies
what does a seq. of 3 bases code for?
1 amino acid
the name given to a group of 3 bases on mRNA that codes for amino acid
a codon
what are the 3 features of the genetic code?
- non-overlapping
- universal
- degenerate (more than 1 triplet can code for the same amino acid)
advantage of the genetic code being non-overlapping
if a point mutation occurs, only 1 triplet and therefore, 1 amino acid is affected
describe how a gene is a code for the production of a polypeptide
1) triplet
2) of bases
3) which determines order of amino acid seq.
define ‘introns’
= base sections of DNA that don’t code for polypeptides
* only in eukaryotic DNA
* positioned between genes
define ‘exons’
= sections of DNA that do code for polypeptides
why don’t all mutations in the nucleotide seq. of a gene cause a change in the struc. of a polypeptide?
- triplets code for the same amino acid (genetic code = degenerate)
- may occur in introns
define ‘genome’
= complete set of genes in a cell
define ‘proteome’
= full range of proteins that a cell can produce
diff. types of RNA
- rRNA
- mRNA
- tRNA
rRNA
- combines with proteins to form ribosomes
- tiny, globular organelle
(ribosomal RNA)
mRNA
- short, single-stranded nucleotide chain
- exposed bases form codons
- no H-bonds (single stranded duh)
- copies and transfers genetic code from DNA i nucleus to ribosomes in cytoplasm
(messenger RNA)
tRNA
- small, polynucleotide chain
- looped, ‘clover-leaf’ shape
- H-bonds
- carries free a.a’s in cytoplasm to ribosomes
> has anticodon —> comple. to codon on mRNA
(transfer RNA)
stages for protein synthesis
1) transcription
2) splicing
3) translation
transcription
- DNA helix unwinds to expose DNA bases, catalysed by DNA helicase
(DNA helicase breaks H-bonds) - strand with exposed bases acts as a template
- free mRNA nucleotides are joined to comple. bases on template strand
- formation of phosphodiester bonds between adj. RNA nucleotides catakysed by RNA polymerase
—> pre-mRNA leaves nucleus via nuclear pore
splicing
- in eukaryotes, introns are spliced out by a protein called ‘splicesome’
(in prokaryotes, transcription directly produces mRNA - prokaryotes don’t contain introns)
translation
- start codon of the mRNA attaches to a ribosome in the cytoplasm
- the tRNA molecule with the compl. anticodon to the start codon aligns opposite the mRNA, held in place by the ribosome
- the tRNA molecule brings a specific aa
- the ribosome moves along one codon on the mRNA —> enables another compl. tRNA to attach to next codon
- a c-reaction (using energy from ATP & and an enzyme) creates a peptide bond between the a.a’s delivered by the 2 tRNA’s
- process continues until ribosome reaches stop codon on mRNA & detaches
differences between DNA & RNA
- DNA nucleotides contain base ‘thymine’, RNA nucleotides contain base ‘uracil’
- DNA nucleotides contain deoxyribose sugar, RNA nucleotides contain ribose sugar
