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Biology - DNA Cheat Sheet by

Transl­ation

Gene Expres­sion
transfer of genetic info from DNA to RNA to protein
Codons
mRNA is read in groups of 3 nucleo­tides. Codes for amino acid
Transfer RNA (tRNA)
single stranded RNA of 80 nucleo­tides. Bonds to amino acids and mRNA codon
Ribo­somes
catalyzes the peptide bonds between amino acids
1) INITIA­TION
eukary­otes, ribosome small subunit recognizes and binds to the mRNA at the 5’ cap. Initiator tRNA attaches at AUG codon
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)
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
3) TERMIN­ATION
At stop codon, a protein release factor binds to A site. (Adds H2O instead of amino acid, polype­ptide chain is released)
Polysome
single strand of mRNA can be used to make multiple copies of a polype­ptide simult­ane­ously
Polysome
single strand of mRNA can be used to make multiple copies of a polype­ptide simult­ane­ously
 

History

Frie­drich Miescher
discovered DNA. White blood cells from pus- isolated nuclei (high in P)
Fred­erick Griffith
studied bacteria that caused pneumonia (used Rough and Smooth Strains)- defined it as transf­orm­ation in cell's function
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
Hershey & Chase
used bacter­iophage to infect bacteria. Light up DNA and Protein case, only DNA was passed to bacteria.

DNA Replic­ation

Repl­ication Origin
Specific sites where replic­ation begins, then bidire­cti­onal. (can be more than one)
Heli­case
enzyme that disrupts H bonds, creating replic­ation fork
Single Stranded Binding Proteins
relieve pressure. bind to unwound single stranded DNA to keep strands apart
Topo­iso­mer­ases
relieve pressure. break bonds in DNA then reform them.
RNA Polyme­rase
adds primer (RNA nucleo­tides)
Prim­ing
Required as DNAP (DNA Polyme­rase) can only add nucleo­tides, but RNAP can start a new chain.
DNA Polymerase III
adds nucleo­tides to the 3' end of pre-ex­isting nucleo­tides. (hydro­lyzes last two phosphate groups)
Leading Strand
synthe­sized contin­uously, moving along replic­ation fork
Lagging Strand
synthe­sized in short, discon­tinuous segments of 1000-2000 nucleo­tides (Okazaki fragme­nts)
DNAP I
replaces RNA primer with DNA
DNA Ligase
joins broken pieces of DNA by catalyzing formation of phosph­odi­ester bonds
DNAP III
can correct errors as it moves down the strand
DNAP II
checks for errors and corrects them
 

Transc­ription

Arch­ibald Garrod
studied patients w/Alka­pto­nuria (pee turns black with O2), faulty genes meant they couldn't break down alkapton (no enzyme)
George Beadle & Edward Tatum
bread mould, using x-rays to create mutations- and then the moulds couldn't grow
Central Dogma
TRAN­SCR­IPT­ION (DNA- mRNA) nucleus TRAN­SLA­TION (mRNA- protein) ribsomes The Flow Of Info
1) INITIA­TION
RNAP binds to promoter. Composed of TATA box (less energy to break H bonds) RNAP recognizes the promoter and begins unwinding DNA
2) ELONGA­TION
RNA polymerase unwinds, exposing 10-20 base pairs. Uses template strand to add comple­mentary RNA nucleo­tides, from 5' to 3'
3) TERMIN­ATION
Prok­ary­otes: protein, mRNA binds to itself (hairpin) Euka­ryo­tes: many A's = many U's added = weak=p­roteins bind
Multiple Transc­ription Machin­ery
multiple RNAP can transcribe simult­ane­ously on the same gene
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
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
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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