Transcription and Translation

12 Pages
Unlock Document

University of Massachusetts Amherst
Mark Huyler

Transcription and Translation *slides 1-17 are already in notecard form The template strand of DNA at the beginning of a protein- coding region has the sequence: 5'–TACTGGGATAGCC*TACAT–3' The “*” indicates the position of a point mutation: a T originally present at this location has been deleted. This deletion will most likely result in _____. a. mRNA codons preceding the mutation being misread b. mRNA codons following the mutation being misread c. no change in the polypeptide coded by this gene d. the AUG triplet functioning as a chain terminator Elongation and Termination - during the elongation phase of transcription, RNA polymerase moves along the DNA template strand and synthesizes RNA in the 5’-3’ direction - transcription ends with a termination phase. In this phase, RNA polymerase encounters a transcription termination signal in the DNA template - In bacteria, the transcription signal codes for RNA forming a hairpin structure which causes the RNA polymerase to separate from the RNA transcript, ending transcription. RNA processing in Euakaryotes - in bacteria, the information in DNA is converted to mRNA directly. In eukaryotes, however, the product of transcription is an immature primary transcript, or pre- mRNA. Before primary transcripts can be translated, they have to be processed in a complex series of steps. The Discovery of Eukaryotic Genes in Pieces - the protein-coding regions of eukaryotic genes are interrupted by noncoding regions o to make a functional mRNA, these noncoding regions must be removed - Exons are the coding region of the eukaryotic gene that will be part of the final mRNA product - The intervening, noncoding sequences are called introns, and are not in the final mRNA - Eukaryotic genes are much larger than their corresponding mature mRNA RNA splicing - the transcription of eukaryotic genes by RNA polymerase generates a primary RNA transcript that contains exons and introns o introns are removed by splicing - Small nuclear ribonucleoproteins (snRNPs) form a complex called a spliceosome. This spliceosome catalyzes the splicing reaction Adding caps and tails to RNA transcripts - primary RNA transcripts are also processed by the addition of a 5’ cap and a poly (A) tail - with the addition of cp and tail and completion of splicing, processing of the primary RNA transcript is complete. The product is a mature mRNA. - The 5’ cap serves as a recognition signal for the translation machinery - The poly(A) tail extends the life of mRNA by protecting it from degradation It is referred to as a 7-methylguanosine cap, abbreviated m7G “Mature” mRNA ------------------------------------------------------------------------ Translation – a sequence of bases in the mRNA is converted to an amino acid sequence in a protein. Ribosomes catalyze translation of the mRNA sequence into protein. Transcription and translation in bacteria – occurs simultaneously, bacterial ribosomes begin translating in mRNA before RNA polymerase has finished transcribing it. Multiple ribosomes attached to an mRNA form a polyribosome. Transcription and translation in eukaryotes – occur separately. mRNAs are synthesized and processed in the nucleus and then transported to the cytoplasm for translation by ribosomes. How does an mRNA triplet specify an amino acid? – Two hypotheses regarding the specification of amino acid sequence by a sequence of nucleotide base: 1. mRNA codons and amino acids interact directly 2. Francis Crick proposed that an adapter molecule holds amino acids in place while interacting directly and specifically with a codon in mRNA *The adapter molecule was later found to be a small RNA called transfer RNA (tRNA). The characteristics of transfer RNA – ATP is required to attach tRNA to an amino acid. Enzymes called aminoacycl tRNA syntheses “charge” the tRNA by catalyzing the addition of amino acids to tRNAs. For each of the twenty amino acids, there is a different aminoacyl tRNA synthetase and one or more tRNAs. A tRNA covalently linked to its corresponding amino acid is called an aminoacyl tRNA. The energy required for this process comes from ATP. What happens to the amino acids attached to tRNA? – Experiments with radioactive amino acids revealed that they are lost from RNAs and incorporated in the polypeptides synthesized in ribosomes. These results inspired the use of “transfer” in tRNA’s name, because amino acids are transferred from the RNA to t
More Less

Related notes for BIOLOGY 151

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.