BI108: mRNA processing and translation

mRNA in Bacteria is the same as the gene body while for eukaryotes it is not the same?why?

b/c of mRNA processing

5 Steps of mRNA processing in the nucleus

1. DNA transcribes by RNAP 2 to make pre-mRNA

2. 5’ capping:

   • covalently bonding a 7 METHYL GUANINE to triphosphate group on 5’ END

3. Splicing:

   • Introns get removed by spliceosomes leaving exons and a 3’END

4. 3’ Cleavage:

   • 3’ END removed and POLY A TAIL (300 adenines) added to make mature mRNA

5. Exit

   • mature mRNA exits to cytoplasm for translation

Structure of mRNA

5’ end: RBS

AUG = start codon (Met), then followed by UUU (Phe), CCC (Pro) and other codons

Ending with AGA (Arg) and UAA (stop codon) no other amino acid put in

mRNA will be translated by ribosomes to synthesize a peptide ( list the direction )

Occurs from NH3+ (Amino) terminus to CO2- (carboxylate) terminus)

Since RNA has 4 bases (AUGC) in 3 positions… how many codons in total…. Which makes the genetic code what?

4 × 4 × 4 = 64, making the genetic code REDUNDANT b/c there are 20 amino acids

tRNA structure’s 3 aspects

• Amino acid attachment site on 3’ OH group (always CCA )

• Hydrogen bonds btw base pairs makes it 3D

• Anticodon sequence in tRNA in 3’ to 5’ direction to translate mRNA 5’ —> 3’ that base pairs w/ mRNA codons

Describe initiation in 2 steps

1. Small subunit attaches to underside of mRNA strand @ start codon

2. Large subunit envelopes Met-tRN structure @ P (peptide) site

Cavities in large subunit

Exit site, Peptide site, and Acceptor site

Large subunit has —— rRNAs and —- proteins

3 rRNA and 49 proteins

Small subunit has —- - rRNAs and —- proteins

2 rRNAs and 33 proteins