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Biology - DNA Cheat Sheet by


Gene Expression
transfer of genetic info from DNA to RNA to protein
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
catalyzes the peptide bonds between amino acids
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)
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
At stop codon, a protein release factor binds to A site. (Adds H2O instead of amino acid, polype­ptide chain is released)
single strand of mRNA can be used to make multiple copies of a polype­ptide simult­ane­ously
single strand of mRNA can be used to make multiple copies of a polype­ptide simult­ane­ously


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)
enzyme that disrupts H bonds, creating replic­ation fork
Single Stranded Binding Proteins
relieve pressure. bind to unwound single stranded DNA to keep strands apart
relieve pressure. break bonds in DNA then reform them.
RNA Polymerase
adds primer (RNA nucleo­tides)
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)
replaces RNA primer with DNA
DNA Ligase
joins broken pieces of DNA by catalyzing formation of phosph­odi­ester bonds
can correct errors as it moves down the strand
checks for errors and corrects them


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
RNAP binds to promoter. Composed of TATA box (less energy to break H bonds) RNAP recognizes the promoter and begins unwinding DNA
RNA polymerase unwinds, exposing 10-20 base pairs. Uses template strand to add comple­mentary RNA nucleo­tides, from 5' to 3'
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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