ch 5-7 Flashcards
components of translation
mRNA (processed w 5’ cap, poly A tail, removed introns)
transfer RNA (3 double stranded loops, one single stranded, anticodon, anticodon loop and acceptor stem)
ribosomes (proteins and rRNAs structure in cytoplasm, big and small subunits of proteins and rRNAs, binding site for mRNA and three for tRNA)
translation factors
what enzyme, in translation, helps attach the amino acids
aminoacyl tRNA synthetase
initiation:
- initiation factors gather ribosome subunits, mRNA, initiator tRNA
- ribosome moves along mRNA until if finds AUG start codon
- tRNA w methionine binds
- ribosome has three spots: P, A, E
initiation: P
(peptide): growing polypeptide, where initiator tRNA binds
initiation: A
(amino acid): tRNA w next amino acid
initiation: E
(exit): uncharged tRNA without amino acid is rejected
elongation
- elongation factors let anticodons bind to codons
4 steps repeat: - tRNA in P site, next aa tRNA enters A
- polypeptide chain shifts to new aa in A, peptide bond between aas
- chain one aa longer
- mRNA moves forward one codon, tRNA w polypep at P, tRNA w/o aa exits at E, new codon at A ready for next tRNA
termination
- stop codon on mRNA is reached
- release factor cleaves polypep from last tRNA
- ribosome splits and is recycled w mRNA
post transcriptional modification: capping
- 5’ cap w 7-methyl guanosine added
- protects mRNA from digestion and helps initiate translation
post transcriptional modification: tailing
- attaches to poly A tail to 3’ end
- made of 200-300 adenine ribonucleotides from poly A polymerase
- protects from degradation (…)
post transcriptional modification: removal of non coding regions
exons: coding, interrupted by:
- introns: non coding, only in euk
- spliceosomes and small nuclear ribonucleoprotejns
introns are removed from pre mRNA, exons joined together to form mature RNA
alternative splicing
produces different mRNAs from pre mRNA, lets 2+ polypeptides be made from a single gene
- after final mRNA is produced, it can leave nucleus to be translated
- after primary transcript is CAPPED, TAILED, SPLICED, it is an mRNA transcript
mutation
permanent change in nucleotide sequence of DNA
- can be spontaneous or mutagen (chemicals, radiation) induced
- negative: genetic disorders
- positive: improved survival and reproduction (natural selection)
- neutral: most, since most DNA is non coding (introns are 90%)
point mutations
single base change, pair base substitution
- silent mutation (no aa change, code redundancy)
- missense (change aa)
- nonsense (premature stop)
sickle cell anemia
primarily africans
- recessive cell pattern
- 1/400 african americans
frameshift mutations
- shift in the reading frame (changes everything downstream)
- insertions (adding bases)
- deletions (losing bases)
chromosome mutations
involve large DNA segments
- deletion (of large coding region)
- duplication (of large coding region)
- inversions (chromosome segment is broken, re inserted in opposite direction)
- translocations (entire gene/group moved from one chromosome to another)
spontaneous mutations
naturally in cell from normal interactions
e.g.:
- incorrect base pairing by polymerase
- dna transposition: transposons move freely and when near existing gene sequences, can alter gene expression
prokaryotic metabolism
need to respond quickly to environmental changes
- enough of a product = stop production (waste of energy to produce more)
- new energy source: utilize quickly (start production of enzymes for digestion)
natural selection favours the bacterial cells that can
metabolize well
cells vary the amount of specific enzymes by
regulating gene transcription
operon :
region in prokaryotes where many genes are clustered together under the control of a single promoter
- all genes transcribed into one continuous mRNA strand: polycistronic mRNA
- consists of coding region (genes) and regulatory region (promoter and operator)
- PROG (promoter, repressor, operator, genes)
operons: PROG
- promoter (dna sequence where polymerase binds and begins transcription)
- repressor (protein binds to operator, prevents transcription)
- operator (regulatory dna sequence to which a protein binds, inhibits transcription initiation)
- genes
lac operon
breaks down lactose in prokaryotes
lac operon: presence of lactose
- lactose (inducer) binds to repressor so it can’t bind to operator, polymerase makes mRNA, mRNA makes enzymes that break down lactose
- lac 1 protein: repressor, blocks transcription of b-galactosidase by binding to lactose operator
- CAP binding site: dna sequence wher specific catabolism activator proteins bind to increase transcription rate
lac operon: absence of lactose
- repressor protein binds to operator
- rna polymerase is blocked
trp operon:
makes amino acid tryptophan? 5 regulatory genes instead of 3
tryptophan operon: normal levels
- repressor doesn’t bind to operator region
- mRNA is made
tryptophan operon: excess
- tryptophan bunds to repressor protein
- rna polymerase is blocked
gene regulation in eukaryotes
transcriptional, post transcriptional, translational, post translational
gene regulation in eukaryotes: transcriptional
- mRNA synthesis in transcription
- genes not in operons
- DNA access via histone loosening
- transcription factors interact w promoters
- activator proteins are nuance initiation
gene regulation in eukaryotes: post transcriptional
- controls availability of mRNA molecules to ribosomes
- final mRNA before translation
- alternative splicing: different combos of introns are removed, remaining exons spliced
- masking proteins bind and inhibit processing
- rate of degradation of mRNA: dependent on cell need
gene regulation in eukaryotes: translational
- controls how often/rapidly mRNA transcripts translated into proteins
- initiation of transition can be blocked
gene regulation in eukaryotes: post translational
- controls when proteins are functional, for how long, when degraded
- polypeptide becomes active protein
- hormones may lengthen or shorten protein functional time
- ubiquitin tagged proteins degraded (death tag)
