Show Menu

Gene Expression & Regulation Cheat Sheet by

Gene Expression & Regulation

DNA Structure & Replic­ation

Stru­cture of DNA
Each DNA nucleotide is made up of 5-carbon sugar called deoxyr­ibose, a phosphate group, and a nitrog­enous base.
DNA uses bases A, C, G, & T. (RNA uses A, C, G, & U)
Double Helix
DNA has an antipa­rallel structure→ The 2 strands run in opposite directions of eachother.
Each strand has a 5' end and a 3' end.
DNA Replic­ation
DNA is Semi-­Con­ser­vative
→Each of the 2 strands in DNA acts as a template to produce 2 new strands.
Enzymes "­unz­ip" DNA molecules by breaking the hydrogen bonds that hold the two strands together.
Primary enzyme involved is DNA polymerase
→ Joins nucleo­tides to synthesize the new comple­mentary strand.
→Proof­reads each DNA strand to prevent errors.
Leading & Lagging Strand
Leading Strand
→runs 5' to 3' towards the fork and is made contin­uously.
Lagging Strand
→runs 5' to 3' away from the fork and is made in small pieces called Okazaki fragments.
Other Things to Know:
DNA polymerase only synthe­sizes DNA in the 5’ to 3’ direction only. The difference between the leading and lagging strands is that the leading strand is formed towards replic­ation fork, while the lagging strand is formed away from replic­ation fork.

DNA replic­ation is not the same as cell division. Replic­ation occurs before cell division, during the S phase of the cell cycle. However, replic­ation only concerns the production of new DNA strands, not of new cells.



point mutation
affects 1 nucleotide pair
1. silent mutations
do not change amino acid transl­ation
2.missense mutations
a single nucleotide change results in a codon that codes for a different amino acid
3. nonsense mutation
a regular amino acid codon is changed into a stop codon, ending transl­­ation
inse­rtion or deletion
additi­on/loss of nucleotide pairs
1. frame shift mutation
deletion or insertion in a DNA sequence that shifts the way the sequence is read
forces that interact with DNA in ways that cause mutation example: xrays


Tran­scr­iption Key Points
Involves copying a gene's DNA sequence to make an RNA molecule.
Performed by RNA polymerase
3 Stages: Initia­tion, Elonga­tion, Termin­ation.
RNA molecules are spliced and have a 5' cap and poly-A tail put on their ends. (Eukar­yotes) }
Init­iation, Elonga­tion, Termin­ation
RNA polymerase binds to a sequence of DNA called the promoter, found near the beginning of a gene. Each gene (or group of co-tra­nsc­ribed genes, in bacteria) has its own promoter. Once bound, RNA polymerase separates the DNA strands, providing the single­-st­randed template needed for transc­rip­tion.
One strand of DNA, the template strand, acts as a template for RNA polyme­rase. As it "­rea­ds" this template one base at a time, the polymerase builds an RNA molecule out of comple­mentary nucleo­tides, making a chain that grows from 5' to 3'. The 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).
Sequences called termin­ators signal that the RNA transcript is complete. Once they are transc­ribed, they cause the transcript to be released from the RNA polyme­rase. An example of a termin­ation mechanism involving formation of a hairpin in the RNA is shown below.



Nucleic acid that transmits genetic inform­ation from parent to offspring and codes for the production of proteins
Building block of nucleic acids
Double Helix
Structure of two strands, intert­wining around an axis like a twisted ladder
DNA replic­ation
Process during which a double­-st­randed DNA molecule is copied to produce two identical DNA molecules
Base Pairing
Principle in which the nitrog­enous bases of the DNA molecules bond with one another (AT, CG))


Double Stranded, Anti-p­arallel
Single Stranded
A+T and C+G
A+U and C+G
Mostly Found in Nucleus
Mostly Found in Cytoplasm
Long Polymer
Much Shorter
Forms Double Helix Structure
Forms Secondary or Tertiary Structure


tRNAs are molecular "­bri­dge­s" that connect mRNA codons to the amino acids they encode.
One end has an anticodon, which can bind to specific mRNA codons. (sequence of 3 nucleo­tides)
The other end carries the amino acid specified by the codons.
Init­iation, Elonga­tion, Termin­ation
The ribosome assembles around the mRNA to be read and the first tRNA (carrying the amino acid MET[AUG]). This initiation complex is needed in order for transl­ation to get started.
The mRNA is read one codon at a time, and the amino acid matching each codon is added to a growing protein chain.
Each time a new codon is exposed,
→a matching tRNA binds to the codon
→the existing amino acid chain (polyp­eptide) is linked onto the amino acid of the tRNA via a chemical reaction,
→the mRNA is shifted one codon over in the ribosome, exposing a new codon for reading.
tRNAs move through the A, P, and E sites of the ribosome. This process repeats many times as new codons are read and new amino acids are added to the chain.
The finished polype­ptide chain is released. It begins when a stop codon (UAG, UAA, or UGA) enters the ribosome, triggering a series of events that separate the chain from its tRNA and allow it to drift out of the ribosome.
The polype­ptide may still need to fold into the right 3D shape, undergo proces­sin­g,get shipped to the right place in the cell, or combine with other polype­ptides before it can do its job as a functional protein.

Transc­ription & Transl­ation

The Central Dogma of Molecular Biology

The Central Dogma (TCD)
During expression of a protei­n-c­oding gene, inform­ation flows from DNA → RNA → protein. (This process is known as CD)

The Lac Operon

The Lac Operon of E.Coli
Condit­ions: Lactose is available and Glucose is not.
More inform­ation here

3 Types of RNA

synthe­­sized using DNA template, attaches to ribosome in cytoplasm and specifies the primary structure of protein
molecu­­le­s...and proteins make up the ribos­omes
translates between nucleic acid (DNA) and protein lang. by carrying specific amino acids to ribosome, where they recognize the approp­­riate codons in the mRNA


No comments yet. Add yours below!

Add a Comment

Your Comment

Please enter your name.

    Please enter your email address

      Please enter your Comment.

          More Cheat Sheets by fatbuttluver

          Biology Hereditary Cheat Sheet
          APBioChap7 Osmosis, Water Potential, etc. Cheat Sheet