Genetics. Chapter 9 - Microbial Genetics. Chromosome. Genes. Topics - Genetics - Flow of Genetics - Regulation - Mutation - Recombination

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1 Chapter 9 - Microbial Genetics Topics - Genetics - Flow of Genetics - Regulation - Mutation - Recombination Genetics Genome (The sum total of genetic material of a cell is referred to as the genome.) Chromosome Gene Protein Genotype Phenotype 1 2 Chromosome Procaryotic Histonelike proteins condense DNA Eucaryotic Histone proteins condense DNA Subdivided into basic informational packets called genes Genes Three categories Structural Regulatory Encode for RNA Genotype sum of all gene types Phenotype Expression of the genotypes 3 4 1

2 Flow of Genetics Genetic Information Flow DNA =>RNA=>Protein Replication Transcription Translation 5 6 DNA DNA is long and occupies a small part of the cell by coiling up into a smaller package. Structure Replication 7 An Escherichia coli cell disrupted to release its DNA molecule. 8 2

3 Structure Purines and pyrimidines pair (A-T or G-C), backbone sugars linked by phosphate. Nucleotide Phosphate Deoxyribose sugar Nitrogenous bases (purines- adenine, guanine; pyramidines thymine, cytosine) Double stranded helix Antiparallel arrangement 9 10 Semiconservative Enzymes Leading strand Lagging strand Okazaki fragments Replication Replication is Semiconservative Means each new molecule is made from one new and one original New strands are always synthesized in 5 to 3 direction

4 Semiconservative replication of DNA synthesizes a new strand of DNA from a template strand. Enzymes Helicase DNA polymerase III Primase DNA polymerase I Ligase Gyrase Function of some enzymes involved in DNA replication Leading strand RNA primer initiates the 5 to 3 synthesis of DNA in continuous manner

5 Lagging strand DNA replication process steps. Multiple Okazaki fragments are synthesized Okazaki fragments are ligated together to form one continuous strand Replication processes from other biological systems such as plasmids and viruses, involve a rolling cycle. RNA Transcription Message RNA (mrna) Transfer RNA (trna) Ribosomal RNA (rrna) Others (see website info) Codon

6 A single strand of RNA is transcribed from a template strand of DNA RNA polymerase catalyzes the reaction Synthesis in 5 to 3 direction Transcription mrna Copy of a structural gene or genes of DNA Can encode for multiple proteins on one message Thymidine is replaced by uracil The message contains a codon (three bases) mrna synthesis from DNA trna Copy of specific regions of DNA Complimentary sequences form hairpin loops Amino acid attachment site Anticodon Participates in translation (protein synthesis)

7 Structural Characteristics for trna and mrna rrna Consist of two subunits (70S) A subunit is composed of rrna and protein Participates in translation Ribosomes bind to the mrna. This enables trnas to bind, followed by protein synthesis. Codons Triplet code that specifies a given amino acid Multiple codes for one amino acid 20 amino acids Start codon Stop codons

8 mrna codons specify a amino acids How DNA codes lead to amino acids Protein Participants in the translation process Translation Protein synthesis have the following participants mrna trna with attached amino acid Ribosome

9 The process of translation Translation Ribosomes bind mrna near the start codon (ex. AUG) trna anticodon with attached amino acid binds to the start codon Ribosomes move to the next codon, allowing a new trna to bind and add another amino acid Series of amino acids form peptide bonds Stop codon terminates translation For procaryotes, translation can occur at multiple sites on the mrna while the message is still being transcribed = speedy! Transcription and translation in eucaryotes Similar to procaryotes except AUG encodes for a different form of methionine mrna code for one protein Transcription and translation are not simultaneous Pre-mRNA Introns Exons

10 Processing pre-mrna into mrna requires removal of introns Regulation Lactose operon sugar Repressible operon Amino acids, nucleotides Antimicrobials Lac operon example for regulation of sugar metabolism Example for regulation of amino acids, like arginine Repression in the absence of lactose No repression when product is being used Induction in the presence of lactose Repression when product accumulates

11 Antimicrobials Antibiotics and drugs can inhibit the enzymes involved in transcription and translation Mutations Changes made to the DNA Spontaneous random change Induced chemical, radiation. Point change a single base Nonsense change a normal codon into a stop codon Back-mutation mutation is reversed Frameshift reading frame of the mrna changes Mutation repairs -- enzymes that recognize, remove, replace bases Excision repair 11

12 screens environmental and dietary chemicals for mutagenicity and carcinogenicity. The Ames test Effects of mutations Positive effects for the cell Allow cells to adapt Negative effects for the cell Loss of function Cells cannot survive Recombination Sharing or recombining parts of their genome Conjugation Transformation Transduction Conjugation Transfer of plasmid DNA from a F + (F factor) cell to a F - cell An F + bacterium possesses a pilus Pilus attaches to the recipient cell and creates pore for the transfer DNA High frequency recombination (Hfr) donors contain the F factor in the chromosome

13 Conjugation (genetic transmission through direct contact between cells) Transformation Nonspecific acceptance of free DNA by the cell (ex. DNA fragments, plasmids) DNA can be inserted into the chromosome Competent cells readily accept DNA DNA released from a killed cell can be accepted by a live competent cell, that expresses a new phenotype. Griffith s classic experiment in transformation Transduction Bacteriophage infect host cells Serve as the carrier of DNA from a donor cell to a recipient cell Generalized Specialized

14 Genetic transfer (generalized transduction) Genetic transfer (specialized transduction) Transposon Movement of transposons can occur in plasmids and chromosomes Jumping genes Exist in plasmids and chromosomes Contains genes that encode for enzymes that remove and reintegrate the transposon Small transposons are called insertion elements