SBI4U Transcription & Translation

Aminoacyl tRNA synthetases

20 enzymes which attach the 20 different amino acids to correct tRNA

RNA polymerase

Synthesizes RNA from complementary DNA template strand

Ribosome

“Reads” and synthesizes mRNA into a polypeptide

Shine-Dalgarno sequence

RNA sequence upstream of start codon which ribosome binds to in prokaryotes

Kozak sequence

RNA sequence surrounding start codon in eukaryotes, ribosome scans to locate

TATA box

DNA sequence upstream of transcription unit which transcription factors use to position binding near transcription unit

Introns

Interrupting sequences of RNA that are spliced out and do not code for proteins

Extrons

Expressed sections of a gene in RNA which are spliced together and code for proteins

5’ cap

Modified nucleotide added to the 5’ end of RNA during transcription for ribosome to bind to and to protect during translation

Poly-A tail

Repeating adenine sequence on 3’ end of mRNA which protects and stabilizes it

Post transcriptional modifications

5’ capping, 3’ polyadenylation, splicing

Post translational modifications

Enzymes that add/remove/modify chemical groups, allowing a single gene to result in different proteins

Translation initiation

rRNA binds to SD sequence (prokaryotes)/small RU recognizes 5’ cap and scans for initiation sequence (eukaryotes)

Translation elongation

1st tRNA occupies P site and the 2nd enters A site, amino acid from 1st joins aa from 2nd, 1st tRNA exits, ribosome moves along and next tRNA enters

Translation termination

When ribosome reaches stop codon, translation ends, ribosome dissociates, polypeptide released

Central dogma

DNA makes RNA makes proteins

What transcribes DNA into RNA

RNA polymerase

What translates RNA into proteins

Ribosomes

tRNA function

Transfers amino acid to ribosome, complimentary code to mRNA

rRNA functions

Component of the ribosome that binds to mRNA and facilitates translation

Transcription unit

Section of DNA used to produce RNA

Start codon

Always AUG - methionine

Stop codon

Signals end of translation, UUA, UAG, UGA

Transcription

DNA template strand into mRNA complementary strand

Why do factors attach

To prepare for binding of RNA polymerase

RNA polymerase function

Synthesizes RNA template from strand of DNA

What happens at the end of the transcription unit

RNA polymerase dissociates and RNA strand is released

Translation

RNA translated into polypeptide

mRNA functions

Delivers DNA code of a single gene from nucleus to ribosomes

Aminoacyl tRNA

tRNA with correct amino acid attached

A site

Ribosomal site where a new aminoacyl tRNA enters

Aminoacylation

tRNA synthetase attaches correct amino acid to 3’ strand of tRNA

Aminoacyl-tRNA synthetases

20 different enzymes which attach the 20 different amino acids to the correct tRNA

Aminoacyl-tRNA

tRNA with the correct amino acid attached

P site

Ribosomal site where growing polypeptide is held

60S subunit

Larger ribosomal subunit

40S subunit

Smaller ribosomal subunit

80S

Complete ribosome

E site

Ribosomal site where tRNA exits without amino acid

Transcription intiation

Transcription factors bind using TATA box to position near transcription unit, then RNA polymerase binds

Transcription elongation

RNA polymerase synthesizes RNA from DNA template strand

Transcription termination

When RNA polymerase reaches the stop codon, transcription ends and mRNA strand is released