Introduction to Central Dogma a.k.a. Gene Expression Chapter 17 17.1 Pgs. 325-331 Objective: I can describe the process of gene expression by decoding DNA and noting what polypeptide protein is made.

Central Dogma (of Molecular Biology) Path of information: Genes are made of DNA – how do traits come from them? (How does info turn into traits?) Central Dogma (of Molecular Biology) Path of information: DNA  RNA  Protein Transcription Translation A.K.A. Gene Expression Protein Synthesis Decipher DNA code to make proteins (traits) RNA processing (splicing)

Evidence for Central Dogma/Gene Expression Must read on own Study of Metabolic Defects Archibald Garrod Bread Mold: Neurospora Beadle and Tatum Current hypothesis One Gene-One Polypeptide hypothesis Some proteins made of more than 1 polypeptide Sometimes RNA made is good enough (no need protein)…

Review of Ribonucleic Acid (RNA) Same as DNA… except for 3 things 1) Single-Strand (DNA is double-strand) 2) Ribose sugar (DNA has deoxyribose) 3) Does not have Thymine (T) Has Uracil (U) to replace Thymine For RNA: A pairs with U 3 types of RNA mRNA (messenger) tRNA (transfer) rRNA (ribosomal) 1 less oxygen atom

Transcription (Step 1) Overview more details later… Enzyme: RNA Polymerase  binds to promoter Reads DNA (certain spot, certain side/strand) and constructs mRNA from it (builds 5’ to 3’) Still utilizes complementarity…but differently Replication Transcription DNA  DNA DNA  mRNA C  G C  G G  C G  C T  A T  A A  T A  U

Summary of Overview of Transcription Occurs in the nucleus Transcribes info from DNA to mRNA – why? DNA is protected (trapped) in nucleus Allows info to leave, with original copy unharmed/unchanged Animations http://highered.mheducation.com/sites/0072507470/student_view0/chapter3/animation__mrna_synthesis__transcription___quiz_1_.html http://www.johnkyrk.com/DNAtranscription.html http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html

Translation (Step 2) Overview mRNA leaves nucleus  goes to ribosome tRNA matches up to mRNA (complementarity) Replication Transcription Translation DNA  DNA DNA  mRNA mRNA  tRNA C  G C  G C  G G  C G  C G  C T  A T  A U  A A  T A  U A  U Note: tRNA is NOT a thread-like strand, like DNA and mRNA (more details later…) MANY tRNA molecules match to one mRNA

Summary of Overview of Translation Each tRNA will bring one amino acid According to order of mRNA, will polymerize amino acids into protein Animations http://highered.mheducation.com/olc/dl/120077/micro06.swf http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html

Summary Overview of Central Dogma Must know in 2 ways: Molecular Details Coding Instructions

tRNA = anticodon (complementary to codon) Coding Labels Because every 3 nitro. bases  1 amino acid… DNA = triplet mRNA = codon (code) tRNA = anticodon (complementary to codon) When reading genetic code, easiest to read from mRNA (full strand traveling in cell) Codon table use mRNA to determine amino acid  protein Pg. 330

Codons – How many are there? 64 different codons (64 different ways to combine 4 bases in sets of 3  43) 20 different amino acids (like 26 letters) Most amino acids have more than one codon Different combinations/sequence of amino acids will create different proteins Special start codon: AUG  Methionine At beginning of gene (signal + amino acid) Stop codons: UAA, UGA, UAG At end of gene (JUST a signal) Does not make an amino acid!!! Says protein is finished

Practice Protein Synthesis Random DNA sequence: AAT-GGG-ATA-AAA-GTT (how many bases? 15 how many triplets? 5) 1st step = transcription (DNA mRNA) UUA-CCC-UAU-UUU-CAA (how many codons? 5) 2nd step = translation (mRNA  tRNA) AAU-GGG-AUA-AAA-GUU (# of anti-codons = 5) Amino acid sequence (read off mRNA in table) Leucine-Proline-Tyrosine-Phe-Glu (# of a.a. = 5) Do you have to go to tRNA to get a.a.? Not if just deciphering code (in reality, yes!)