Topic 7 Cont’d

Transcription and Translation

Transcription Basics

• DNA vs. RNA

Transcription Basics cont’d

• Directionality: read 3’-5’; made 5’-3’• Promoter & TATA boxes• Nucleoside triphosphates• Contains the sense strand and antisense strand• Sense strand = always 5’-3’ and is the same as the mRNA that is produced

except T for U• Antisense strand = always 3’-5’ and is the strand that forms the template

and is transcribed.

Animation sites

• http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

• http://vcell.ndsu.nodak.edu/animations/transcription/first.htm

Translation

The process of polypeptide/protein production using mRNA as a guide

Requires:mRNA transcripttRNAtRNA activating enzymesribosomesgenetic code…..

The Genetic COde

The Genetic Code cont’d

• It’s a triplet code (codon) = 3 bases code for 1 amino acid

• There are 64 different codons• Duplication = degeneracy = possible for 2

or more codons to code for the same amino acid

• Code is essential universal (find me 2 exceptions by next class for 1 point e.c. each)

Amino Acids

tRNA

• All tRNAs have base-paired ds sections that become loops

• Triplet bases complementary to mRNA codons…called anticodons

• A 3’-5’ CCA terminal end for amino acid attachment

• The above permit 3 distinct binding attachment of the tRNA to the ribosome

tRNA cont’d

tRNA a S = F example• The base sequence of tRNa molecules vary =

some variable features in its structure• An extra small loop is sometimes present• The bp sections are sometimes helical• Results in: • A distinctive 3-d shape• Distinctive chemical properties• ALLOWS THE CORRECT AA TO BE ATTACHED

TO THE 3’ END BY A tRNA ACTIVATING ENZYME (aminoacyl-tRNA sythetase)

• There are 20 different tRNA activating enzymes – one for each of the 20 diff. AA

Ribosome Basics

• Composed of protein and rRNA

• Consist of 2 subunits (small and large)

• Possess 3 binding sites for tRNA (2 tRNAs can bind at the same time)

• Possess a binding site for mRNA

• Free vs. Bound (RER)

• 80S in Euks vs. 70S in Proks & Euk. organelles

Ribosome (2 site version)

Translation Step 1 - Initiation

Polysomes & Movie Time

• http://vcell.ndsu.nodak.edu/animations/translation/movie.htm