Topic 7 Cont’d Transcription and Translation
Jan 04, 2016
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