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Lecture 5

BISC 101 - Lecture 5 - From Gene to Protein.docx

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Simon Fraser University
Biological Sciences
BISC 101
Christopher Kennedy

Biological Science 101 – General Biology Lecture Five: From Gene to Protein Textbook: Ch. 17, Pgs. 325-348 Figs. 17.3-17.26 Gene structure Gene -> Proteins (Gene Expression) Genes produce: - Biochemical traits. - Phenotype traits. - Polypeptides (proteins and some are enzymes). DNA is transcribed to RNA Ribonucleic acid -> Ribose sugar with Uracil base (not Thymine). Gene Structure From DNA to RNA (Transcription) Transcription = Producing RNA Promoter (T-A-T-A region): - Transcription factors binds to this area. - RNA polymerase also binds here. - DNA unwinds, nucleotides are added on the 5’ -> 3’ direction. - Process is 40 nucleotides per second. - Complementary strand is produced. Polyadenylation Releases Polymerase Pre-mRNA Strand site (AAUAAA) -> Signal -> Detaches -> Released RNA Processing: - Take place in the nucleus. Pre-mRNA -> mRNA. 1) Adds 5’ cap region. (5’ Cap region protects mRNA from enzymatic degradation), which signals ribosomes to attach. 2) Add Poly A-Trail (AAAA). Inhibits mRNA degradation and facilitates mRNA out of nucleus. RNA Slicing: - Deletes the introns, joins up the exons (expressed) to produce mRNA, which is used in translation. Process of Translation: Occurs in the cytoplasm. - Produces amino acids and joining them together to form a polypeptide (protein). The Triplet Code: On mRNA, the nucleotides are arranges in triplets (triplet code, a.k.a. codons). E.g. UGC -> Codon (Tyrosine) AGC -> Codon (Serine) Dictionary of genetic code: - Universal code (in all living organisms) - 3-4 codons may produce the same amino acid. - AUG = Start Codon. - UAA, UAG, UGA = 3 Stop Codons Ribosomes = Small sub-unit and Large sub-unit: - Contains ribosomal RNA. - Most abundant type of RNA in cell.  Small sub-unit binds to the 5’ cap region. Transfer RNA (tRNA) = Anti-codon at one end, which is complementary to codon. - It carries an amino acid specified by codon usage. - First codon must be UAG (Start) -> Met. - Large sub-unit binds to complex (energy is required GTP) - It reads codons each time a new tRNA arrives, new amino acid is added to pre
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