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NATS 1670- Midterm Exam Guide - Comprehensive Notes for the exam ( 24 pages long!)


Department
Natural Science
Course Code
NATS 1670
Professor
Motti Anafi
Study Guide
Midterm

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York
NATS 1670
MIDTERM EXAM
STUDY GUIDE

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Lecture 31
The Genetic Code
The amino acid sequence of a protein determines its three-dimensional structure
The remarkable range of fxns mediated by proteins results from the diversity of these 20
building blocks
Protein Synthesis
Translation
- Process of converting info stored in nucleic acid sequences into proteins
- Genetic Code: the ribosomes read mRNA sequences in 3-base codons
Components
- mRNA: the template that is used to specify amino acid sequence
- Ribosomes: a complex of proteins and rRNA molecules
- Transfer RNA (tRNA): small (70-80 nucleotides) RNA molecules that serve as adapters b/t
codons in mRNA and a.a.
Transfer RNA (tRNA):
- tRNA anticodon recognize the codon in mRNA
- the hydroxyl (3’) end of each tRNA is linked to the carboxyl group of a specific a.a
The Genetic Code
- Triplet Code: 61 a.a.-codons for 10 a.a.
3 stop codons, to terminate protein synthesis
- A universal code that is used in the nuclear genome of most organisms
- Complementary anti codons are present in tRNA molecules which are specifically linked to a.a.
- With 4 bases in RNA, the 3 base codons, there are 64 possible codons, but only 20 a.a. Thus,
the genetic code is degenerate, where some a.a. specified by more than one codon (up to 6)
1. Translation Initiation:
- Translation begins, and small ribosomal subunit along with the initiating tRNA,
assemble onto the mRNA
2. Translation Elongation: with the initiator tRNA placed at the P site of the ribosom,
elongation can proceed.
-The next aminoacyl-tRNA enters the ribosome at the A site.
-The amino acid at the P site is transferred to the tRNA at the A site.
-The ribosome moves one codon farther along the mRNA, releasing the empty tRNA.
-The A site is now free for the next incoming tRNA.
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-The cycle is repeated as the ribosome travels along the mRNA resulting ina growing
polypeptide chain.
3. Translation Termination: translation termination is triggered by a stop codon in the
mRNA.
Stop codons are recognized by release factors, which help release the fully-synthesized
polypeptide chain from the ribosome.
Translation
In translation, the sequence of bases in the mRNA is converted to an amino acid sequence in
a protein
- Each a.a. is specified by three bases (a codon) in the mRNA, according the a nearly universal
genetic code
- Ribosomes catalyze translation of the mRNA sequence into protein
- Inside ribosomes, mRNAs are translated to proteins via intermediary molecules called transfer
RNAs (tRNA)
- Transfer RNAs carry a.a. and have a three-base pair anitcodon, which binds to an mRNA
codon
- The a.a. carried by the transfer RNA is then added to the growing protein via formation of a
peptide bond
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