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AP Bio Unit 6: Gene Expression and Regulation Cheat Sheet (DRAFT) by

Details aspects of gene expression and regulation

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Genetic Material

-DNA primary source of heritable inform­ation (sometimes RNA)
-Info stored and passed through subsequent genera­tions (mostly DNA sometimes RNA)

Base Pairing: A-T(U) and G-C

Purines: G and A; have a double ring structure
Pyrimi­dines: C, T, and U; have a single ring structure

Retrov­iruses: info flows from RNA to DNA, made possible by reverse transc­riptase

DNA Replic­ation

DNA is synthe­sized in the 5’ to 3’ direction
One strand of DNA serves as the template for a new strand of comple­mentary DNA
Unwinds the DNA strands
Relaxes superc­oiling in front of the replic­ation fork
DNA polymerase
Requires RNA primers to initiate DNA synthesis
Leading Strand
DNA polymerase synthe­sizes new strands of DNA contin­uously in 5'-3' direction
Lagging Strand
DNA polymerase synthe­sizes new strands of DNA DISCON­TIN­UOUSLY (runs 3'-5')
Joins the fragments on the lagging strand

RNA Transc­ription

RNA polymerase binds to a sequence of DNA called the promoter. Once bound, RNA polymerase separates the DNA strands, providing the single­-st­randed template needed for transc­rip­tion.
RNA polymerase reads template strand and builds RNA molecule out of comple­mentary nucleo­tides. RNA transcript carries the same inform­ation as the non-te­mplate (coding) strand of DNA, but it contains the base uracil (U) instead of thymine (T)
When termin­ation sequence is transc­ribed, they cause the transcript to be released from the RNA polymerase




Eukaryotic Modifi­cations

1. Addition of a poly-A tail.
2. Addition of a GTP cap.
3. Excision of introns and splicing and retention
of exons.
-Generates different versions of resulting mRNA molecule (alter­native splicing)

RNA Transl­ation


Prokar­yotic Gene Regulation

Turned on by the presence of a particular small molecule (inducer)
On by default but can be turned off by a small molecule (corep­ressor)

Eukaryotic Gene Regulation

Chromatin access­ibility
More "­rel­axe­d" chromatin makes a gene more available for transc­ription
Sets of transc­ription factor proteins bind to specific DNA sequences in or near a gene and promote or repress its transc­ription into an RNA
RNA processing
Splicing, capping, and addition of a poly-A tail, altern­ative splicing
RNA stabil­ity­/Tr­ans­lation
Protein yield determines lifetime of RNA molecule in cytosol. Small regulatory RNAs called miRNAs bind to target mRNAs - chop them up

Trp Operon

Repres­sible Operon

Lac Operon

Inducible Operon


Makes DNA more accessible
Makes DNA less accessible


Mutations are the main source of genetic variation


Separates molecules according to size and charge
Polymerase chain reaction (PCR)
Amplifies DNA fragments (makes more)
Bacterial transf­orm­ation
Introduces DNA into bacterial cells (via plasmid)
DNA sequencing
Determines order of nucleo­tides in DNA molecule