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Lecture 15

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Natural Science
NATS 1670
Motti Anafi

Proteins • Proteins are the active players in most cell processes • Involved in essentially all sub-cellular, cellular, and developmental functions in living organisms. o Major classes of Proteins: o Enzymatic: catalysts in biochemical reactions (DNA/RNA polymerases) o Regulatory: control of gene expression, intercellular signaling (transcription factors) o Structural: cellular or organismal anatomy Proteins are polymer of amino acids Amino acids • Amino acids are the building blocks of proteins Protein Synthesis Translation • Process of converting information stored in nucleic acid sequences into proteins • Genetic code: the ribosomes read mRNA sequences in 3-base codons. Components of Translation 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 nucleotide) RNA molecules that serve as adapters between codons in mRNA and amino acids. Transfer RNA (tRNA) Figure 16-12 Biological Sciences 2/e © 2003 Pearson Prentice Hall Inc. The tRNA anticodon recognize the codon in mRNA. The hydroxyl (3’) end of each tRNA is linked to the carboxyl group of a specific amino acid The Genetic Code Triplet Code 61 aa-codons, for 20 amino acids. 3 stop codons, to terminate protein synthesis. 4x4x4x4=64 different codons (don’t need to memorize the table) Genetic Code • A universal code that is used in the nuclear genome of most organisms • Complementary anticodons are present in tRNA molecules, which are specifically linked to amino acids • With 4 bases in RNA, and 3 base codons, there are 64 possible codons, but only 20 amino acids. Thus, the genetic code is degenerate, where some amino acids are specified by more than on codon (up to 6) Protein Translation 70S ribosome-fMet-tRNA complex Translation • In translation, the sequence of basis in the mRNA is converted to an amino acid sequence in a protein. • Each amino acid is specified by three bases (a codon) in the mRNA, according to a nearly universal genetic code. • Ribosomes catalyze translation of the mRNA sequence into protein. • Inside ribosomes, mRNAs are translated to prote
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