Ch 17

Why do modifications of pre-mRNA exist?

-facilitate the export of mature mRNA from the nucleus -help protect the mRNA from degradation by hydrolytic enzymes -help ribosomes attach to the 5' end of mRNA once the mRNA reaches the cytoplasm

What are the major RNA/protein components of translation?

-mRNA is moved through a ribosome -codons are translated into amino acids one by one -interpreters are tRNA molecules with a specific anti-codon at each end -tRNA adds its amino acid to a growing polypeptide chaing

In what direction is the primary transcript constructed? Why?

...

What are the steps of elongation cycle of translation?

1. Codon recognition 2. Peptide bond formation 3. Translocation

What happens during the transcription stage of initiation?

After RNA polymerase binds to the promoter the DNA strands unwind, and the polymerase intiaties RNA synthesis at the start point on the template strand

What is RNA Splicing

After synthesis of a eukaryotic primary RNA transcript, the removal of portions of the transcript (introns) that will not be included in the mRNA and the joining together of the remaining portions (exons)

What happens during peptide bond formation?

An rRNA molecule of the large ribosomal unit catalyzes the formation of a peptide bond between the amino group of the new amino acid in the A site and the carboxyl end of the growing polypeptide in the P site The polypeptide is removed from the tRNA in the P site and attaches it to the amino acid on the tRNA in the A site.

What happens during codon recognition?

Anticodon of an incoming aminoacyl tRNA base pairs with the complimentary mRNA codon in the A site

How are ribosomes targeted for the ER?

By being marked by a signal peptide. Ribosomes are then escorted to the ER receptor protein by SRP.

What possible outcomes can occur when a point mutation results in a different amino acid insertion? What is this called?

Different amino acid insertion leads to altering the reading frame of a genetic message which results in frameshift mutation

What happens during the termination stage of termination?

Eventually the RNA transcript is release and the polymerase detaches from the DNA.

In Eukaryotes, a gene gets ___ into___,before this molecule is transported out of the nucleus certain segments of this molecule called ____ get spliced out, furthermore the molecule gets a ______ and a _____ to make sure that it's properly transported into the cytoplasm and doesn't get ______. After it exists the nucleus this molecule is ____ into ____ by _____.

Find the answer

Use the following template DNA strands to determine the mRNA primary transcript and amino acid sequence. Be sure to include the correct labeling of the 3' and 5' carbons. 3'-AAAATAGCACCA-5' 3'-CCTGTGGAAGTT-5' 3'-CGTGACGGGTCT-5'

Find the answer

What are the three stages of transcription?

Initiation, elongation, and termination

In alternative RNA splicing to mRNA, what gets removed and what gets kept in the final transcript?

Introns are cut out and the exons are spliced together.

What is alternative RNA splicing?

Multiple rise of two or more different polypeptides depending on which segments are treated as exons during RNA processing

What is frameshift mutation?

Occurs when number of nucleotides inserted or deleted is not a multiple of three. Results in improper codon grouping, extensive missense, premature termination and nonfunctional proteins

When one base pair is replaced with another pair this is called ________. Under what conditions would this be considered a silent mutation? How is it that a basepair can change but it doesn't change the overall AA sequence?

Point mutation. Point mutation becomes a silent mutation when it has no observable effect on phenotype. Base pair can change but doesnt change the overall AA sequence through missense mutations where it is either similar to the proteins it replaced or it's in a region that's not essential to the protein

What kind of proteins would be made this way?

Proteins of the endomembrane system and insulin

What is the main enzyme that transcribes DNA into mRNA

RNA Polymerase

Pre-mRNA in Eukaryotes also undergoes rearrangements before exiting the nucleus. These rearrangements allow for greater diversity of proteins from a single gene. Describe the rearrangements and comment on the evolutionary significance of this mechanism.

RNA splicing removes portions of introns. The presence of introns in genes can encode more than one kind of polypeptide which results in alternative RNA splicing. Alternative RNA splicing is significant in evolution because it has the ability to facilitate new and potentially beneficial proteins

What happens during translocation?

Ribosome translocates the tRNA in the A site to the P site. The next codon to be translated is then brought to the A site

How do tRNAs know which amino acid to bring to the growing polypeptide?

Ribosomes facilitate specific coupling of tRNA codons with mRNA codons during protein synthesis. A tRNA will also fit into a binding site when its anticodon base pairs with an mRNA codon.

Give an example of a point mutation that results in a serious disease.

Sickle cell disease & cardiomyopathy. The change of a single nucleotide in the DNA template strand leads to the production of an abnormal protein.

Pre-mRNA is further modified before exiting the nucleus. Describe how the ends of the transcript are modified.

The 5' end receives a 5'cap which is a modified form of guanine nucleotide. The 3' end receives an addition of 50-250 more adenine nucleotides which forms a poly-A tail.

What happens during the transcription stage of elongation?

The polymerase moves downstream unwinding the DNA and elongating the RNA transcript 5'-3'. In the wake of transcription the DNA strands re-form a double helix

What is a nonsense mutation and how does it affect the resulting protein?

When a point mutation changes a codon for an amino acid into a stop codon. This results in translation to be terminated prematurely