proteinsynthesis + DNA Flashcards
DNA replication
semi conservative replication
- DNA helices breaks hydrogen bonds between bases
- strands unwinds, both act as templates
- free DNA nucleotides diffuse into place by complementary base pairs
- hydrogen bonds form between bases
- DNA polymerase joins nucleotides by phosphodiester bonds
- strand made of one parent and one new
transcription
- DNA helices breaks hydrogen bonds between bases
- strands separate, one acts as a template
- free RNA nucleotides diffuse into place by complementary base pairing
- RNA polymerase joins nucleotides y phosphodiester bonds
- the pre-mRNA is spliced to remove introns to make mRNA
why are intron removed in splicing?
so they don’t affect amino acid order
(don’t code for amino acids)
not present in prokaryotic
difference between introns and multiple repeats
introns- non coding sections of DNA found WITHIN genes
non-coding repeats - DNA sequences that don’t code for amino acids, repeat BETWEEN genes
translation
- mRNA leaves nucleus through pores
- goes to ribosome
- tRNA brings amino acids to the ribosome
- specific tRNA molecules bring specific amino acids
- anitocodon of tRNA is complementary to codon on mRNA, held by hydrogen bonds
- means two amino acids are held close on ribosome
- peptide bonds form between amino acids
- tRNA detaches to get another amino acid from cytoplasm
- ribosome moves along mRNA
role of DNA and RNA
DNA - stores genetic information
RNA - transfers genetic information from DNA to ribosomes
structure of nucleotide
pentose sugar (deoxyribose or ribose)
nitrogenous base (A,T,U,C,G)
phosphate group
join together by condensation reactions between sugar and phosphate
structure of DNA
two antiparallel polynucleotide strands, twisted into helix
= sugar phosphate backbone
joined by hydrogen bond between complementary bases
(A-T forms 2 bonds, C-G forms 3)
adaptations of DNA molecule
helix protects bases
weaker hydrogen bonds - easily broken to allow replication
strong phosphodiester bonds = strength of molecule
structure of RNA
single polynucleotide strand
A-U, C-G
shorter than RNA
ribose not deoxyribose
why does DNA polymerase only work in one direction?
active site only complementary to 3’ end
so only binds and moves one way
works antiparallel
- one polymerase on one strand moves different direction to one on the other
purpose of semi conservative replication
done before cell division
so each new cell has a full amount of DNA
semi conservative ensures genetic continuity between generations
Meselson and Stahl
two samples of bacteria grown
- one in heavy and one light nitrogen
(took up nitrogen into DNA)
sample taken and spun in centrifuge
- heavy nitrogen DNA settled lower than light nitrogen
heavy nitrogen bacteria allowed to replicate in only light nitrogen
- sample taken and spun
if conservative
- heavy strands settle lower and lighter higher
semi conservative
- contained a strand of heavy and light
- settled between, in middle
difference between transcription in eukaryotes and prokaryotes
eukaryotes - introns and exons both copied into mRNA
- spliced to remove introns
prokaryotes - mRNA directly from DNA
- no splicing as no introns in DNA
ribosomes
site of proteinsynthesis
found in cytoplasm of all cells
(RER of eukaryotic only)
larger (80s) in eukaryotic than prokaryotic
not membrane bound
made of proteins and rRNA
- small and large subunit
