Chapter 17 Hon. Adv. Biology Notes 11/29/10 From Gene to Protein Chapter 17 Hon. Adv. Biology Notes 11/29/10

Connection between Genes and Proteins Evidence that genes specify proteins Overview: “Central Dogma of Molecular Genetics” “The Code” – nucleotide triplets specify a.a.’s Evolution of the code Synthesis and Processing of RNA A closer look: Transcription RNA processing occurs in eukaryotic cells Synthesis of Protein A closer look: Translation Signal peptides – target specific cell destinations Review: Roles of RNA in the cell Review: Comparison of protein synthesis in prokaryotes and eukaryotes Point mutations can affect protein structure and function Wrap-up: “So, What is a gene?”

Lecture Objectives Compare the structure of RNA with that of DNA. Summarize the process of transcription. Relate the role of codons to the sequence of amino acids that results after translation. Outline the major steps of translation. Discuss the evolutionary significance of the genetic code.

Figure 17.1 Beadle and Tatum’s evidence for the one gene-one enzyme hypothesis

RNA vs. DNA there are 3 major differences between the 2 forms of nucleic acids Composition of sugar backbone (reflects name) RNA - ribonucleic acid (ribose) DNA - deoxyribonucleic acid (deoxyribose) number of strands: RNA = 1 and DNA = 2 RNA does not have thymine as a nitrogen base, instead uracil (U) is substituted in its place (back)

Central Dogma of Molecular Genetics Explains the flow of information from gene to protein. Replication: flow of gene from one generation to the next Transcription: flow of info from DNA to RNA Translation: conversion of info from nucleic acid language into protein

Transfer of Information from DNA to RNA Transcription: mRNA production, or the synthesis of other types of RNA Short segment of DNA (gene) is transcribed into mRNA for movement out of the nucleus to the ribosome DNA is used as a template to make a complementary piece of “messenger RNA”. This requires the aid of the RNA polymerase enzyme.

Translation: Protein Synthesis mRNA transcript arrives at the ribosome to act as the genetic code for protein assembly proteins are composed of a unique sequence of amino acids. mRNA carries the code for the order and type of amino acids to be included in the protein. The “genetic code” is the unique order of triplet codons located on the mRNA strand. (back)

The Genetic Code: Three-Nucleotide “Words” Genetic Code The genetic code (codons) used by most organisms to translate mRNA is nearly universal. Sometimes called a triplet code.

Figure 17.3 The triplet code

Figure 17.4 The dictionary of the genetic code

What does a “Gene” really do? It is simply a blueprint in the DNA that tells how to build a protein. “WHO” we are genetically is really just a collection of “WHAT” proteins are expressed in our phenotype. Figure 17.5 A tobacco plant expressing a firefly gene (back)

Evolution of the Genetic Code must have evolved very early in the history of life…. Why? Answer: nearly universal, shared by organisms from the simplest bacteria to complex plants and animals Ex. CCG codes for the amino acid proline in every organism ever studied (back)

The Synthesis/Processing of RNA The Stages of Transcription initiation elongation termination RNA processing occurs in eukaryotes alteration of mRNA ends RNA splicing ribozymes introns (back)

Protein Synthesis (Translation) structure and function of tRNA aminoacyl-tRNA synthetases ribosomes building a polypeptide initiation elongation termination signal peptides target protein destinations (back)

Point Mutations types of point mutations Results of point mutations base-pair substitutions insertions deletions Results of point mutations silent mutation missense mutations nonsense mutations frameshift mutations (back)

Chapter 18: Genetics of Viruses and Bacteria Part 1: Viruses Part 2: Bacteria

What is a Virus? Infectious particle consisting of a genome either single- or double-stranded either RNA or DNA inclosed in a capsid - protein that surrounds it. Replicate using metabolic machinery of host cells: bacteria, plant, animal Possibly evolved from plasmids or transposons

TMV The search for the cause of tobacco mosaic disease led to discovery of viruses. No microbe could be found and no agent could be filtered out Crystallization of infectious particle.

Structural components of viruses Genome: genes are contained on a single linear or circular nucleic acid molecule Capsid: protein shell, often large numbers of identical subunits (capsomeres) rod-shaped (helical) polyhedral complex Envelope: derived from membranes of hosts

What is a “phage”? Bacteriophage: complex viruses that attack bacteria Host Range: proteins on the outside of virus only recognize a few specific receptors on host cell surfaces.

Three patterns of Genome Replication DNA viruses RNA viruses retroviruses reverse transcriptase

Viral Life Cycles Lytic cycle Lysogenic cycle

Defenses against Infection restriction enzymes barriers antibodies vaccines

Viroids and Prions and Viral Evolution

Chapter 18 (part 2): The Genetics of Bacteria short generation span aids their evolutionary adaptation to changing environments circular bacterial chromosome found tightly packed in a region called the nucleoid. 100x the DNA of a virus 1/1000 of the DNA of a eukaryote plasmids are also found in many strains genetic recombination produces new strains

Binary Fission replication of chromosome proceeds in two directions from the single point of origin prior to binary fission. See diagram on board. Due to semiconservative replication, most bacteria in a colony are identical.

Genetic Recombination: Bacteria Transformation: (recall Griffith’s exp.) bacteria take up naked DNA Transduction: (recall Hershey and Chase) phages transfer genes from one bacterium to another generalized and specialized transduction Conjugation and Plasmids 2 cells temporarily join by appendages called sex pili

Closer Look at Conjugation bacteria join and transfer DNA thru pili ability to form pili and donate DNA depends on the presence of an F factor if the F factor is on the F plasmid they are called F+; after conjugation the F- (female) is converted into an F+ (male) Hfr cells; F factor inserted into chromosome R plasmids: inheritance of resistance

Key Terms for Review!! See the key terms on the Campbell Place website for important terms for Ch. 16-18!!!