Transcription and Translation

Transcription

The process of making RNA with RNA polymerase using DNA as a template

mRNA

Messenger RNA - The only type of coding RNA, makes proteins with translation

tRNA

Transfer RNA - Translates the codon that is built by the mRNA and provides the appropriate amino acid

snRNA

Small Nuclear RNA - Processes mRNA and removes introns

rRNA

Ribosomal RNA - Bind with proteins to help ribosomes function

miRNA

Micro RNAs - Can degrade and inhibit mRNA by binding with it. Can have perfect or imperfect complementarity.

siRNA

Short Interfering RNA - Inhibits RNA but HAS to have perfect complementarity

Three Stages of Transcription

Initiation, Elongation, Termination

Bacterial Initiation

Starts at the promoter sequence (upstream of the coding sequence)

-35 consensus sequence box and -10 consensus sequence box

RNA polymerase binds to these sequences to initiate transcription

Consensus Sequences

Mutations can occur at these sequences that increase or decrease binding

-35 Sequence = TTGACA

-10 Sequence = TATAAT

Sigma Factor

Required for bacterial initiation. Guides the RNA Polymerase to the consensus sequence

Eukaryotic Initiation

Similar to bacterial initiation but uses enhancer sequences as well as promoter sequences. Has general transcription factors that work the same as the sigma factor. They make a pre-initiation complex

Enhancer Sequences

Increase the amount of transcription that’s happening, not the same as promoter sequences which start and stop transcription

Bacterial Termination

There is a terminator sequence that will tell the polymerase to stop binding to the DNA. There are two types of termination, Rho Dependent and Rho Independent

Rho Dependent

As the RNA is being built, a Rho factor binds to the RNA polymerase and will follow it until the polymerase reaches a pause. The Rho factor will then unbind the DNA RNA hybrid and release the polymerase

Rho Independent

RNA will base pair with itself to form a termination hairpin

Eukaryotic Termination

A cleavage site will cut the pre-mRNA

An enzyme then finds the loose RNA and attaches itself while the RNA Polymerase continues to transcribe

The enzyme will follow the RNA Pol II until it catches up to it, degrading RNA along the way

Once the enzyme catches up, the RNA Polymerase will release from the DNA and transcription ends

5 Parts of mRNA

Exon, Intron, 5’ UTR, 3’ UTR, Poly A Tail (pre-mRNA)

The CALCA Gene

Can code for multiple proteins even though it’s only one gene

Has 6 different exons and two Poly A sites

Mature mRNA

Addition of Poly A tail, 5’ cap (G), and splicing of introns

Splice sites

Regions where the spliceosomes can cut so the introns can be removed (work with snRNAs)

Alternative splicing

Splicing of the same pre-mRNA in different ways to produce different mature mRNA and make unique proteins

Translation

Making proteins while using RNA as a template

Codons

The ‘words’ for translation

5’ to 3’ = N-terminus to C-terminus

The Genetic Code

• It’s a triplet code

• It’s continuous

• It’s non-overlapping

• It’s (almost) universal

• It has start and stop positions

• It’s degenerate

• It has a wobble position

Wobble Position

The two nucleotides at the beginning of the codon are more fixed than the third

Pairing Rules

G - U or C

C - G

A - U

U - A or G

Ribosomes

Made up of RNA and proteins

Bacterial Initiation - Translation

The small subunit of the ribosome binds to the Shine-Delgarno sequence (a consensus sequence). The sequence makes sure that the ribosome binds the mRNA in the correct spot (near the AUG codon)

Eukaryotic Initiation - Translation

Small subunit binds to the 5’ cap and scans for the AUG codon. Detection of the Kozak sequence helps initiate translation (Poly A tail aids with binding)

Termination - Translation

Release factors recognize the stop codon and release the ribosome

tRNAs can’t recognize stop codons