Elongation Enzyme moves 5’ 3’. Rate is about 60 nucleotides per second.

Comment Each gene can be read by sequential RNA Polymerases giving several copies of RNA. Result - several copies of the protein can be made.

Termination DNA sequence that tells RNA Polymerase to stop. Ex: AATAAA RNA Polymerase detaches from DNA after closing the helix.

Final Product Pre-mRNA This is a “raw” RNA that will need processing.

Modifications of RNA 1. 5’ Cap 2. Poly-A Tail 3. Splicing

5' Cap Modified Guanine nucleotide added to the 5' end. Protects mRNA from digestive enzymes. Recognition sign for ribosome attachment.

Poly-A Tail 150-200 Adenine nucleotides added to the 3' tail Protects mRNA from digestive enzymes. Aids in mRNA transport from nucleus.

Comment The head and tail areas often contain “leaders” and “trailers”, areas of RNA that are not read. Similar to leaders or trailers on cassette tapes.

RNA Splicing Removal of non-protein coding regions of RNA. Coding regions are then spliced back together.

Introns Intervening sequences. Removed from RNA.

Exons Expressed sequences of RNA. Translated into AAs.

Spliceosome Cut out Introns and join Exons together. Made of snRNA and snRNP.

snRNA Small Nuclear RNA. 150 nucleotides long. Structural part of spliceosomes.

snRNPs ("snurps") Small Nuclear Ribonucleoprotiens Made of snRNA and proteins. Join with other proteins to form a spliceosome.

Ribozymes RNA molecules that act as enzymes. Are sometimes Intron RNA and cause splicing without a spliceosome.

Introns - Function Left-over DNA (?) Way to lengthen genetic message. Old virus inserts (?) Way to create new proteins.

Final RNA Transcript

Translation Process by which a cell interprets a genetic message and builds a polypeptide.

Materials Required tRNA Ribosomes mRNA

Transfer RNA = tRNA Made by transcription. About 80 nucleotides long. Carries AA for polypeptide synthesis.

Structure of tRNA Has double stranded regions and 3 loops. AA attachment site at the 3' end. 1 loop serves as the Anticodon.

Anticodon Region of tRNA that base pairs to mRNA codon. Usually is a compliment to the mRNA bases, so reads the same as the DNA codon.

Example DNA - GAC mRNA - CUG tRNA anticodon - GAC

Comment "Wobble" effect allows for 45 types of tRNA instead of 61. Reason - in the third position, U can pair with A or G. Inosine (I), a modified base in the third position can pair with U, C, or A.

Importance Allows for fewer types of tRNA. Allows some mistakes to code for the same AA which gives exactly the same polypeptide.

Aminoacyl-tRNA Synthetases Family of Enzymes. Add AAs to tRNAs. Active site fits 1AA and 1 type of tRNA. Uses a “secondary genetic” code to load the correct AA to each tRNA.

Ribosomes Two subunits made in the nucleolus. Made of rRNA (60%)and protein (40%). rRNA is the most abundant type of RNA in a cell.

Large subunit Proteins rRNA

Both sununits

Large Subunit Has 3 sites for tRNA. P site: Peptidyl-tRNA site - carries the growing polypeptide chain. A site: Aminoacyl-tRNA site -holds the tRNA carrying the next AA to be added. E site: Exit site

Translation Steps 1. Initiation 2. Elongation 3. Termination

Initiation Brings together: mRNA A tRNA carrying the 1st AA 2 subunits of the ribosome

Initiation Steps: 1. Small subunit binds to the mRNA. 2. Initiator tRNA (Met, AUG) binds to mRNA. 3. Large subunit binds to mRNA. Initiator tRNA is in the P-site

Initiation Requires other proteins called "Initiation Factors”. GTP used as energy source.

Elongation Steps: 1. Codon Recognition 2. Peptide Bond Formation 3. Translocation