Theme 2 - Mod 3 - Translation

Critical role of tRNA

Enables the translation of the information in the mRNA genetic message to a polypeptide

They transfer amino acids to a growing polypeptide strand

What is each tRNA molecule made of

Single RNA strand of 70-90 nucleotide in length

What makes the shape of tRNA

Large degree of complementary

This results in stretches of H bonds

Allows for the formation of four double-helical segments and 3 loops

Amino acid attachment site

Made up of a CCA sequence

Attachment point for an amino acid during tRNA molecule activation

Anticodon region

Specific nucleotide sequence that forms base pairs with a specific mRNA codon that codes for a specific amino acid

Aminoacyl tRNA synthetase

Binds to uncharged tRNA and corresponding amino acid

They catalyze the attachment of tRNA molecule to its amino acid using ATP

How does the active site of Aminoacyl tRNA synthetase work

Recognizes anticodon sequence of tRNA and the region of the amino acid attachment site

This leads to 20 aminoacyl tRNA synthase

Charged tRNA

Charged tRNA can deliver specific amino acid to a growing polypeptide chain

Why are there 45 tRNA and not 64

Some tRNA molecules may be able to bind to multiple codons

This is due to the chemical nature of the codon-anticodon pairing interactions

What is a wobble of tRNA

Flexibility in the tRNA and explains the redundancy of the genetic code

Why does transcription and translation occur in different areas of cell in eukaryotes

Compartmentalization

How is transcription initiated in eukaryotes

At 5' cap and the first AUG codon is the start codon

How is transcription initiated in prokaryotes

At any Shine-Dalgarno sequence

The mRNA can therefore be polycistronic that codes for several polypeptides

Shine-Dalgarno sequence

Allows for multiple open reading frames for more than one protein along a single mRNA strand

Tend to be located a few bases upstream of the start AUG codon

Benefit of polycistronic mRNA

Functionally related genes are grouped together along the DNA and transcribed as a single unit from one promoter

Components required for transcription to start

Large and small ribosomal subunits

mRNA strand

Charged tRNA methionine

Initiation factors

What are the three sites in the ribosome

Peptidyl site

Aminoacyl site

exit site

Which ends are polypeptides synthesized from on the amino acid

Amino end to carboxyl end

What does GTP elongation factor do

Elongation factor that hydrolyzes to release the tRNA

Also causes the tRNA to move from the p-site to the e-site

Where is the start amino acid added

P site

Where is each subsequent charged tRNA added after the start amino acid

A site

How does the peptide bond between amino acids form

Peptidyl-transferase reaction

How is translation terminated

Releases factor binds to the a site

The bond connecting the polypeptide to the tRNA breaks

All components needed for translation to occur

Large and small ribosomal sub units

mRNA molecule

Charged tRNA amino acid

Initiation factor

Elongation factor

Termination factor

One gene, one enzyme hypothesis

Each gene contains the information needed to make each enzyme

Who further researched the one gene, one enzyme hypothesis

Adrian Srb and Norman Horowitz

What did Srb and Horowitz do

Performed a genetic screen of radiation treated neurospora to determine whether there are specific genes that produced each of the 3 enzymes that are needed in the metabolic cascade of arginine synthesis

What were the results

With supplemented arginine, the Neurospora fungus was still able to undergo growth

The radiation must have produced mutations in the genes that encode for the necessary enzymes for the production of arginine by neurospora cells

Why was it determined one gene, one polypeptide hypothesis

Genes do not only code for enzymes in an organism, but rather that genes dictate the structure for all proteins

exception to one gene-one enzyme hypothesis

Human genome project