Gene Expression & Regulation Cheat Sheet (2024)

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.

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

muta­gens

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.

DNA

Nucleic acid that transmits genetic inform­ation from parent to offspring and codes for the production of proteins

Nucleotide

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))

DNA

RNA

Double Stranded, Anti-p­arallel

Single Stranded

A+T and C+G

A+U and C+G

Mostly Found in Nucleus

Mostly Found in Cytoplasm

Deoxyr­ibose

Ribose

Long Polymer

Much Shorter

Forms Double Helix Structure

Forms Secondary or Tertiary Structure

Transl­ation

 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.

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 of E.Coli

 Condit­ions: Lactose is available and Glucose is not.

 More inform­ation here

mRNA

synthe­­sized using DNA template, attaches to ribosome in cytoplasm and specifies the primary structure of protein

rRNA

molecu­­le­s...and proteins make up the ribos­omes

tRNA

translates between nucleic acid (DNA) and protein lang. by carrying specific amino acids to ribosome, where they recognize the approp­­riate codons in the mRNA