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BIOB11H3 Study Guide - Midterm Guide: Aminoacyl-Trna, Peptidyl Transferase, Messenger Rna

Biological Sciences
Course Code
Dan Riggs
Study Guide

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Lecture 7/8
Smart Pages: Ch 2 fig 24; Chapter 11 figs 41, 42, 44, 46, 47, 49, 50
Translation (protein synthesis): Synthesis of proteins in the cytoplasm using the information encoded by an
mRNA. (11.1, 11.8)
Codons: Sequences of three nucleotides (nucleotide triplets) in mRNAs that specify amino acids. (11.6)
Frameshift: see above chapter for it.
tRNA: an adaptor and brings proper amino acid to the ribosome
Anticodon: A three-nucleotide sequence in each tRNA that functions in the recognition of the complementary
mRNA codon. (11.7)
wobble base (hypothesis): Crick's proposal that the steric requirement between the anticodon of the tRNA and
the codon of the mRNA is flexible at the third position, which allows two codons that differ only at the third
position to share the same tRNA during protein synthesis.
aminoacyl-tRNA synthetase (AARS): An enzyme that covalently links amino acids to the 3' ends of their
cognate tRNA(s). Each amino acid is recognized by a specific aminoacyl-tRNA synthetase. (11.7)
Initiation codon: A triple AUG, the site to which the ribosome attaches to the mRNA to assure that the
ribosome is in the proper reading frame to correctly read the entire message. (11.8)
Shine-Dalgarno sequence: Messenger RNA possess this sequence upstream at the 5' end to the start codon
Elongation: the second step in translation after initiation
A, P, E sites: 3 sites on the ribosome; A= Aminoacyl or Acceptor, P= Peptidyl, E= Exit.
Peptidyl transferase: That portion of the large ribosomal subunit that is responsible for catalyzing peptide
bond formation; peptidyl transferase activity resides in the large ribosomal RNA molecule. (11.8)
translocation: - A chromosomal aberration that results when all or part of one chromosome becomes attached
to another chromosome. (HP12)
-(definition #2) The steps in the translation elongation cycle that involves (1) ejection of the uncharged tRNA
from the P site and (2) the movement of the ribosome three nucleotides (one codon) along the mRNA in the 3'
direction. (11.8)
polysome/polyribosome: The complex formed by an mRNA and a number of ribosome in the process of
translating that mRNA. (11.8)
Lecture 7-8: Translation (Proteins synthesis)
Protein synthesis - translation 11-2 figure
If everything goes as planned genes will be expressed RNA will be processed, Messenger RNA will be
transported to the cytoplasm And will then associate with ribosomes which then take The RNA code and
convert it to a protein code to form polypeptide chains

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The elucidation of the genetic code
DNA makes RNA which makes protein
There are four nitrogenous bases
But we know that there are 20 common amino acids which exist in proteins
So it is not possible to have only one nucleotide per amino acid because then we would only be able to produce
four amino acids
And same for two nucleotides Per amino acid because we would only be able to produce 16 amino acids
However three amino acids per Amino acids are possible because we would be able to make 64 amino acids
And we only need 20
So the genetic code is probably a triplet code
Code overlapping or non-overlapping?
An overlapping code looks like each nucleotide would be part of two successive Triplets
In partial overlapping code Each triplet is sharing Two of the three nucleotides With an adjacent triplet
A non-overlapping code is not overlapping
How can you tell?
You can tell by Looking at the affect of a single base change mutation in overlapping or partially overlapping
If a single base change mutation in overlapping or partially overlapping code occurred you would Find that
more than one amino acid would be changed in the protein because they are sharing information.

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Evidence for a non-overlapping code: sickle-cell anemia
Sickle cell anemia Due to red blood cells that have a sickle-cell shape And clog blood vessels and are not as
strong as other red blood cells.
Vernon Ingram used protein sequencing Of peptides from hemoglobin From normal and sickle cell patients
He found that there is only one change Of glutamic acid to valine switch Which occurs at one position Which is
responsible for the different kind of hemoglobin which causes sickle cell shape
Mutations-insertion or deletion of a single nucleotide:
If you have one or two insertions This generates something called a frameshift mutation Which causes a
missense protein
However if you get three Or multiples of three insertions or deletions this restores the reading frame because
the genetic code is a triplet code
On this life is a series of nucleotide RNA Of triplet codes which can be decoded into the appropriate amino
Example of an English language sentence of triplet code and the affects of Each number of mutations in each
code on understanding The sentence
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