Transcript/Translate 16/17 Bio Flashcards
Transcription
Make RNA using DNA as a template.
Occurs in the nucleus of eukaryotic cells. Pre- RNA is made then modified to final mRNA. In prokaryotes mRNA directly forms.
Main transcription enzyme
RNA polymerase. Separates the two DNA strands and nucleotides are joined together as they base pair. No primer is needed.
Promoter
Area where RNA polymerases attaches and initiates transcription.
3 stages of transcription
Initation, elongation, termination
Initiation in transcription
RNA polymerase goes to the promoter region. DNA helix unwinds and begins synthesis. Eukaryotic promoter includes A and T 25 nucletodies upstream from the transcriptional start point, TATA box.
Prokaryotes have a Pribnow box.
Transcription factors
Proteins that recognize the promoter site and binding occurs.
Transcription initiation complex (TIC) components
Transcription factors and RNA polymerase
Elongation in transcription
RNA polymerase moves along DNA strand, RNA nucletoides are added to the 3’ end. G and C, A and U.
Adding Codons.
Only one strands of DNA is transcribed, our template strand (anti sense strand).
RNA polymerase vs DNA polymerase
RNA polymerase does not proofread for any errors. An error during transcriptions gives a bad protein and not transmitted gene missense if it occurred in DNA.
Termination in Transcription
Remove RNA poly from the DNA. The terminator sequence is transcribed. Still needs post transcription mods
Prokaryotes and Eukaryotes have different mechanisms for termination.
Post transcription Mods
The transcript gets a cap at the 5’ end. The cap is a 3 phosphate groups. At the 3’ end a poly A tail is added.
Spliceosome
small nuclear ribonucleoproteins (snRNP) and other proteins form a complex that the cutting occurs.
Introns
Cut out of mRNA, exons are kept
Translation
Synthesis of a polypeptide under direction of RNA in the cytoplasm.
rRNA, mRNA, and tRNA work outside the nucleus. Assembly at ribosomes (both in prokaryotes and euk)
tRNA reaction joining aa
Aminoacyl tRNA synthetase.
Bonds at the 3’ end.
Start codon
AUG - methionine (contains a sulfur)
Ribosome has 4 binding sites
mRNA binding site and 3 tRNA binding sites: A,P,E
Polypeptide synthesis takes place at
Peptidyl and aminoacyl sites
P and A site
P site
holds the tRNA attached to the growing polypeptide chain.
A site
holds the tRNA with it’s associated aa to the polypeptide chain.
E site
tRNA is discharge at this site.
Eukaryotic ribosomes are made in the
Nucleolus of the cell
Eukaryotic proteins and drugs
Eukaryotic proteins have larger size and differ in their proteins thus drugs can be designed to kill bacteria by targeting their ribosomes.
E.g. Tetracycline works by inhibiting prokaryotic ribosomal function.
Ribosomes
Are made of proteins and RNA. A ribozyme is an RNA molecule that functions as an enzyme.
Initiation in Translation
mRNA attaches to the ribosome. Anticodon (P site) matches with AUG (A site).
Elongation in translation
Peptide bond between aas. Translocation occurs: A moves to P, and P moves to E for release.
Wobble hypothesis
3rd base of the codon and 3 base of the tRNA might not always be complimentary.
Termination in translation
When a stop codon is read, a release factor is a protein that binds to our ribosome.
The genetic code is degenerate
Many of the 64 codons are redundant.
Stop Codons
UAA, UGA, UAG
Point mutation
Single base pair of gene is affect.
Sickle cell anemia. Glueatmic acid is replaced by Valine on the beta chain of hemoglobin. HbS (sickled hemoglobin) is more + because there is less “-“ charge.
Base pair substitution:
One nucleotide and its compliment base has changed into another.
If a wrong aa is made, its a missense mutation. If a stop codon is made, its a nonsense mutation.
Frameshift mutation
Reading frame changes due to an insertion or deletion of nucleotide pairs in a gene.
Transposons
Jumping genes.
Mutagens
Chemical or physical agent that interacts with DNA and cause a mutation.
Physical mutagens Rays, Gamm Rays.
Chemical mutagens include aromatic amines, nitrous acids, benzene.
Most mutagens can be carcinogens but not always.
Two thymine bases next to each other
Dimerize. Too many thymine dimers can either doe or undergo malignant transformation.
