Triplet codon
A set of three codons composed of mRNA nucleotides that code for an amino acid or stop codon. (ex. AUG is a a start codon and codes for methionine)
What are the three rules for triplet codons
- The genetic code is universal (same in all species)
- The genetic code is unambiguous (each triplet codon only codes for one amino acid)
- The genetic code allows redundantly (more than one triplet codon can code for a particular amino acid)
Briefly explain the flow of genetic information from transcription to translation
Genetic info is transcribed from DNA into pre-mRNA, pre-mRNA is processed into mature mRNA and leaves the nucleus into the cytoplasm, the mRNA is translated into an amino acid/polypeptide chain, the chain is processed and folded into a protein
DNA vs RNA
DNA: A, T, G, C, No OH group on 2’ carbon
RNA: A, U, G, C
In which way does transcription occur?
In the 5’ to 3’ direction
Template strand vs Coding strand
Template strand: the strand of DNA the mRNA is using to transcribe. It will be complementary to the mRNA strand and anti parallel
Coding strand: The other strand not being coded. Will be the exact same sequence (except will have T’s not U’s) and will also run in the same direction
What is a promoter?
The sequence of DNA that lets the RNA polymerase know where to make initial contact with DNA strand to start transcription. The TATA box is normally in the promoter
What must be done to convert pre-mRNA into mature mRNA?
The introns are spliced out (and some exons) by spliceosomes and a 5’ cap and poly-A tail is added
How does one gene code for more than one protein?
Selective splicing of exons produced multiple versions of mRNA from one single mRNA sequence
RNA polymerase
Enzyme that copies DNA into RNA during transcription
intergenic vs intragenic region
Intergenic (A): between genes
Intragenic (B): inside genes
Order of which transcription knows when to stop and start
First there is the promoter, which tells RNA where to bind to DNA. Next, there is a transcription start site and finally a start codon. On the other side, there is a stop codon, transcription termination site.
The space between the start site and start codon/ termination site and stop codon are called UTRs. These will remain on mature mRNA but will not be translated.
Role of 5’ cap vs 3’ poly-A tail
The 5’ cap helps mRNA bind to ribosome, while the poly-A tail helps keep the mRNA from degradation
Most common start and stop codons
Start codon: AUG (also codes for amino acid methionine)
Stop codon: UAA, UAG, UGA (these do NOT code for anything!)
Steps of Transcription
- Initiation: RNA polymerase bind to promoter and starts separating the DNA strand
- Elongation: RNA polymerase rads the template strand and makes the complementary pre-mRNA molecule
- Termination: RNA polymerase and pre-mRNA release from the template strand and DNA reforms double helix
Steps of Translation
- Initiation: mRNA binds to ribosome and initiator tRNA
- Elongation: amino acids are brought to the ribosome by tRNAs and linked together to form a polypeptide chain
- Termination: Ribosome reaches stop codon, the release factors bind to it, and the polypeptide chain, mRNA, and tRNA are released back into the cell
Parts of ribosome
Small ribosomal subunit + large ribosomal subunit both come together to make a complete ribosome
What is a anticodon?
A sequence of three nucleotides at the end of a tRNA that are complementary to a codon in mRNA
What are the three sites inside a ribosome where tRNA fit and what is their function?
A site: where tRNA enter the ribosome. If the anticodon of this tRNA matches the codon of the mRNA, the tRNA and mRNA bind together
P site: This is where the peptide bond is formed between the two amino acids in the P and A site
E site: This where the now “naked” tRNA sits and exits the ribosome after it adds its amino acid to the chain
Structures of Protein
All must have first three levels, only some have fourth
