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Gene Expression
transfer of genetic info from DNA to RNA to protein
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Codons
mRNA is read in groups of 3 nucleotides. Codes for amino acid
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Transfer RNA (tRNA)
single stranded RNA of 80 nucleotides. Bonds to amino acids and mRNA codon
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Ribosomes
catalyzes the peptide bonds between amino acids
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1) INITIATION
eukaryotes, ribosome small subunit recognizes and binds to the mRNA at the 5’ cap. Initiator tRNA attaches at AUG codon
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Ribsomal binding sites
1 site where mRNA binds, 3 sites where tRNA binds (A site - aminoacyl-tRNA site...... P site - peptide-tRNA site...... E site exit site, leaves the ribosome)
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2) ELONGATION
initiator tRNA binds to ribosome, incoming tRNA binds to A site. H bonds form between mRNA codon and tRNA anticodon. Requires GTP (E)...... Peptide bond formed between A site and P site by ribosomes = longer peptide chain
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3) TERMINATION
At stop codon, a protein release factor binds to A site. (Adds H2O instead of amino acid, polypeptide chain is released)
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Polysome
single strand of mRNA can be used to make multiple copies of a polypeptide simultaneously
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Polysome
single strand of mRNA can be used to make multiple copies of a polypeptide simultaneously
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Friedrich Miescher
discovered DNA. White blood cells from pus- isolated nuclei (high in P)
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Frederick Griffith
studied bacteria that caused pneumonia (used Rough and Smooth Strains)- defined it as transformation in cell's function
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Avery, LcLeod, and McCarty
purified S strain bacteria, added it to R strain bacteria. No S cells appeared in the tube w/ no DNA, but they did appear in that w/ no proteins and no RNA
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Hershey & Chase
used bacteriophage to infect bacteria. Light up DNA and Protein case, only DNA was passed to bacteria.
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Replication Origin
Specific sites where replication begins, then bidirectional. (can be more than one)
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Helicase
enzyme that disrupts H bonds, creating replication fork
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Single Stranded Binding Proteins
relieve pressure. bind to unwound single stranded DNA to keep strands apart
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Topoisomerases
relieve pressure. break bonds in DNA then reform them.
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RNA Polymerase
adds primer (RNA nucleotides)
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Priming
Required as DNAP (DNA Polymerase) can only add nucleotides, but RNAP can start a new chain.
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DNA Polymerase III
adds nucleotides to the 3' end of pre-existing nucleotides. (hydrolyzes last two phosphate groups)
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Leading Strand
synthesized continuously, moving along replication fork
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Lagging Strand
synthesized in short, discontinuous segments of 1000-2000 nucleotides (Okazaki fragments)
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DNAP I
replaces RNA primer with DNA
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DNA Ligase
joins broken pieces of DNA by catalyzing formation of phosphodiester bonds
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DNAP III
can correct errors as it moves down the strand
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DNAP II
checks for errors and corrects them
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Archibald Garrod
studied patients w/Alkaptonuria (pee turns black with O2), faulty genes meant they couldn't break down alkapton (no enzyme)
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George Beadle & Edward Tatum
bread mould, using x-rays to create mutations- and then the moulds couldn't grow
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Central Dogma
TRANSCRIPTION (DNA- mRNA) nucleus TRANSLATION (mRNA- protein) ribsomes The Flow Of Info
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1) INITIATION
RNAP binds to promoter. Composed of TATA box (less energy to break H bonds) RNAP recognizes the promoter and begins unwinding DNA
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2) ELONGATION
RNA polymerase unwinds, exposing 10-20 base pairs. Uses template strand to add complementary RNA nucleotides, from 5' to 3'
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3) TERMINATION
Prokaryotes: protein, mRNA binds to itself (hairpin) Eukaryotes: many A's = many U's added = weak=proteins bind
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Multiple Transcription Machinery
multiple RNAP can transcribe simultaneously on the same gene
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Post-Transcriptional Modifications
in prokaryotes mRNA can be used directly, in eukaryotes it needs to be modified (pre-mRNA to mature mRNA) in order to leave the nucleus
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mRNA Modifications- capping
poly(A) tail - 50-250 adenine added to 3' end, preventing degredation --------- 5' cap 7 G's added to prevent degradation, signals for ribosomes to attach
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mRNA Modifications- splicing
removal of introns (non-coding regions) & mature mRNA will only contain exons. Occurs in spliceosome (snRNPs bind to splice sites, excises introns, rejoins exons)
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