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BIL 255 Study Guide - Comprehensive Final Guide: Hbb, Gene Duplication, Horizontal Gene Transfer


Department
Biology
Course Code
BIL 255
Professor
Dr.yang
Study Guide
Final

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UM
BIL 255
FINAL EXAM
STUDY GUIDE

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Specific condon in mRNA Signal the ribosome where to start and stop protein synthesis:
A specific signal required o initiate translation is crucial, because it sets the reading frame
for the whole length of the message. An error of one nucleotide either way can cause
damage to the protein.
Translation begins with the codon AUG and a special tRNA is required to initiate
translation.
Initiator tRNA: Always carries the amino acid Methionine (Met). Therefore all newly made
proteins have a methionine as the first amino acid at their N-terminal end, the end that is
usually synthesized 1st.
How the translation process start in Eukaryotes:
1. An initiator tRNA charged with Methionine is 1st loaded at the P site along with additional
proteins called translation initiation factors.
2. This tRNA Is distinct from all others because only a charged tRNA molecule is capable of
biding tightly to the P-Site in absence of a large ribosomal subunit.
3. Small ribosomal subunits loaded with the initiator tRNA binds to the 5’ cap of the mRNA
and moves forward 5’- 3’ direction along the mRNA Searching for the 1st AUG.
4. The initiator tRNA recognize the AUG, and the several initiation factors dissociate from the
small ribosomal to make a way for the large subunit to associate and complete assembly
and start the synthesis of protein. NOTE: The 2nd
amino acid will come and bind on the A-site.
Transitional initiation factors: protein that
promotes the proper association of ribosomes with
mRNA and is required for the intiation of the protein.
-FIGURE 7-36:
Initiation of protein synthesis in EUK requires
translation initiation factors and a special
initiation tRNA.
The mRNA is scanned for the first AUG
Small ribosomal subunit
tRNAMet
Initiation factors (GTP)
Note: there are proteins not shown in the figure
that are bound to the 5’ cap and Poly-A tail they make sure that the mRNA is ready for
translation for no error.
How the translation process start in Bacteria:
Note: That bacteria do not have a 5’ cap for signaling the initiation process.
They have specific ribosome binding sequences up to 6 nucleotides upstream of the AUGs.
They bind directly to a start codon that lies in the interior of n mRNA.
There mRNAs are polycistromic vs. EUK. They carry info for 1 gene per 1mRna.
Polyscistromic: means that the mRNA in Prok. Encodes for several different proteins each on
which it translates from the same mRNA. 1mRNA many different Proteins.
Prok: Specific sequence prior to AUG aids in finding translation initiation site
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FIGURE 7-37:
NOTE: A single prokaryotic mRNA MOLECULE CAN ENCODE FOR SEVERAL DIFFEENT PROTEINS.
They are organized in a cluster called operons (a function unit of genomic DNA with many
genes) that are transcribed together into a single mRNA.
INSTEAD OF A 5’ CAP THEY HAVE TRIPHOSPHATE AT ITS 5’ END. LOOK AT PIC ABOVE
Initiation is marked dark bleu where Ribosome bind to start translation. Thus, different
proteins from one mRNA.
Termination od translation in both Prokaryotes and Eukaryotes:
1. The end of translation is signaled by a stop EITHER OF THESE codons, UAA- UAG- UGA,
Note: that these codons are not specified by the tRNA and do not specify an amino acid. THEY
ONLY SIGNAL THE RIBOSOME TO STOP.
2. A protein release factor binds to any stop codon that reaches the
A-site on the ribosome
3. This bindings then alter the activity of the peptidyl transferase
causing it to catalyze H20 INSTEAD OF AMINO ACID IN THE PEPTIDYL-
tRNA
4. THIS ATTACHMENT IS IMPORTANT BECAUSE IT FREES THE
CARBOXYL END OF THE POLYPETIDE TO A tRNA WICH IS THE LAST
ATTACHMENT THAT HOLDS THE GROWING POLUPETIDE.
5. The protein chain is immediately released after step 4 and they can
spontaneously fold as they exit the ribosome, so they are aided by other
proteins.
5. the small and large subunits of the ribosome dissociate and go
on the hunt for other mRNAs that are ready for translation.
Figure 7-38:
Release factor recognizes stop codon
Ribosome transfers last peptidyl bond to water
Protein is no longer tethered to tRNA and is released
Ribosome disassemble
NOTE: translation halt at a stop codon at the A-site by a binding
protein, then the complete protein is
complete by adding H2O to convert COO- to
COOH and release of OH-.
Newly synthesized proteins are met by
their chaperones as they emerge the
ribosome.
Proteins are made on Polyribosomes:
It takes between 20 sec and several minutes to synthesis proteins.
Multiple ribosomes usually bind to each mRNA BEING TRANSLATED
If the translation is efficient a ribosome hops on the 5’ end of the mRNA as soon as there is enough
nucleotide sequence to be translated
mRNA molecules that are being translated are usually found in the form of polyribosomes
This mechanism help accelerate the synthesis of protein in the EUK. Cells.
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