Gene Gene Expression Expression From gene to protein From gene to protein Transcription and Transcription and Translation Translation
Jan 05, 2016
Gene Gene ExpressionExpression
From gene to proteinFrom gene to proteinTranscription and TranslationTranscription and Translation
• Prokaryotes – mRNA translated immediately• Eukaryotes – pre-mRNA processed before leaving the
nucleus as mRNA
Transcription
STEP 1 – InitiationOccurs at a promoter
STEP 2 – ElongationmRNA transcript lengthens
STEP 3 – TerminationmRNA transcript released
RNA processingalteration of pre-mRNA
RNA processingRNA splicing
• Introns – intervening sequences – noncoding segments on pre-mRNA– May regulate gene activity– Enable genes to give rise to two or more
different polypeptides– Facilitate evolution through exon shuffling
• Exons – expressed sequences on pre-mRNA
• Signal for splicing is a short sequence at the ends of introns
• small nuclear ribonucleoproteins (snRNPs) with snRNA recognize splice sites
• snRNPs + proteins spliceosome– release introns– join together exons
that flank introns
Translation Overview• mRNA moves through
ribosome• codons are translated
into amino acids• tRNA molecules:
anticodon and amino acid ends
• amino acids added to a growing polypeptide chain
• rRNA molecules + proteins ribosomes
tRNA structure
Ribosome structure
Building a polypeptide
Step 1 - Initiation
Step 2Elongation
Step 3 – Termination
Given the following sequence on a template DNA strand 3’ TAT AAA CCG TAC GGA TAG ACA CCG AAA ATC CGG GCA 5’• What is the sequence on the non-template strand? 5’ ATA TTT GGC ATG CCT ATC TGT GGC TTT TAG GCC CGT 3’• What is the mRNA sequence transcribed? 5’ AUA UUU GGC AUG CCU AUC UGU GGC UUU UAG GCC CGU 3’
• What is the STOP codon? UAG• What is the anticodon attached to the tRNA that
corresponds to the STOP codon?There is no tRNA that corresponds to the STOP codon. Release factors take their place.
• What is the amino acid sequence in the polypeptide product?Met – Pro – Ile – Cys – Gly - Phe