Mutations, transcription and translation

mutation

any change in genetic code caused by various mechanisms

point mutation

change in one or a few base pairs during dna replication

substituation (point mutation)

one base pair is replaced with another base pair

insertion (point mutation)

one base is added to the sequence, resulting in frame shift

deletion (point mutation)

one base is removed from the sequence, resulting in frame shift

inversion (point mutation)

two adjoining base pairs swap spots

chromosomal mutations

change involving entire or large part of chromosome

deletion (chromosomal mutation)

segment of chromosome is deleted, resulting in frame shift

duplication (chromosomal mutation)

an addition to chromosome occurs by reproducing part of already existing chromosome

inversion (chromosomal mutation)

segment of chromosome is spliced out and reinsterted backwards

translocation (chromosomal mutation)

segment of chromosome is removed and reinsterted at a different loci

missense mutation

A nucleotide change changes one amino acid in the protein

nonsense mutation

A nucleotide change turns an amino acid into a stop codon

silent mutation

A nucleotide change does not change the amino acid due to redundancy in the genetic code

frameshift mutation

insertion or deletion not in multiple of 3 result in a shift of the reading frame

rna polymerase

binds to dna at promoter region and unwinds the double helix

promoter region in prokaryotes

TATAAT box

promoter region in eukaryotes

TATA box

significance of promoter regions, A and T

A and T are connected via 2 hydrogen bonds, not 3, making them easier to seperate the two strands at this A and T heavy area

process of elongation in transcription

the template DNA strand is copied into mRNA by being constructed in the 5’ to 3’ direction. RNAP adds comp. base pairs on the mRNA strand. new RNA binds temporarily w DNA forming RNA-DNA hybrid region. then mRNA unwids from DNA forming a single strand, and DNA coils back up

termination in transcription

termination sequence tells RNAP when to stop transcription

termination sequence in prokaryotes

transcribed squence can form comp. base pairs with itself forming a hairpin loop stopping transcription, or protiens can bind to the mRNA stopping RNAP initiation complex

termination sequence in eukaryotes

protiens bind to mRNA on polyU site stopping RNAP initiation complex

2 reasons why mRNA must be processed in eukaryotes

to remove introns and to protect it from degrading in cytoplasm

splicisome

enzyme protein complex made up of SNRPS and premRNA

what does the splicisome do

snRNPs bind to begining and end of intron forming a lopp. the start of intron is cleaved folding back on itself, the end is cleaved removing the loop. the exons are linked together, cleaved intron an snRNPs are released

alternative splicing

different mRNAs are produced from premRNA allowing for variety of protiens to form from the same gene

eukaryotic processing - tail

polyA tail is added to 3’ end. adenine bases are added by polyA polymerase

eukaryotic processing - 5’ cap

an attachement site for ribosomes, 7 guanines modified with methyl groups are added to 5’ end by a specific enzyme

codon

group of 3 base pairs that code for a specific amino acid or a stop codon

aminoacyl tRNA symthetase

enzyme that catalyzes aminoacylation - amino acids are added to tRNAs, charging the tRNA

why is genetic code reduntant?

multiple codons can code for the same amino acid. the wobble position of the 3rd nucleotide in the codon can be altered by still code for same AA

A site of ribosome

aminoacyl tRNA synthetase site - recives tRNA with the new amino acid to be added to the chain

P site

peptidal site- holds one aatRNA with the growing chain of amino acids

E site

exit site - releases used tRNA back into cytosol

translation initation

portion of mRNA binds to rRNA on small ribosomal subunit, the initatiotor tRNA (met tRNA) comp base pairs its anti codon to the start codon on mRNA, forming reading frame. the large ribosomal subunit binds, placing met tRNA in the Psite

translation elongation (include peptidal transferases)

aatRNA binds to A site by hydrolizing GTP for energy via comp. base pairing of anti codon to codon. peptidal transferases catalyze peptide bond between polypeptides to AA in A site. ribosome shifts 1 codon towards 3’ end using GTP, and uncharged tRNA is released from E site

translation termination

when stop codon is reached, release factor binds in A site, cleaving polypeptide chain and seperating sub units

4 post translational modifications

amino acids can be removed, polypeptide can be divided into pieces, sugar/phosphate added, quaternary protein structure can be formed by joining multiple polypeptides