I need a discussion about this topic

Chocolate21

08-lecture-presentation-acc13.pptx

Home >Environmental science homework help >I need a discussion about this topic

Microbiology an Introduction

Twelfth Edition

Chapter 8

Microbial Genetics

Plasmid DNA from E. coli

Big Picture: Genetics (1 of 2)

The science of heredity

Central dogma of molecular biology

Mutations

Gene expression controlled by operons

Big Picture pg. 202 (1 of 3)

Big Picture pg. 202 (2 of 3)

Big Picture pg. 202 (3 of 3)

Big Picture: Genetics (2 of 2)

Alteration of bacterial genes and gene expression

Cause of disease

Prevent disease treatment

Manipulated for human benefit

Big Picture pg. 203

Structure and Function of the Genetic Material (1 of 3)

Learning Objectives

8-1 Define genetics, genome, chromosome, gene, genetic code, genotype, phenotype, and genomics.

8-2 Describe how DNA serves as genetic information.

8-3 Describe the process of DNA replication.

8-4 Describe protein synthesis, including transcription, RNA processing, and translation.

8-5 Compare protein synthesis in prokaryotes and eukaryotes.

Structure and Function of the Genetic Material (2 of 3)

Genetics: the study of genes, how they carry information, how information is expressed, and how genes are replicated

Chromosomes: structures containing DNA that physically carry hereditary information; the chromosomes contain genes

Genes: segments of DNA that encode functional products, usually proteins

Genome: all the genetic information in a cell

Structure and Function of the Genetic Material (3 of 3)

The genetic code is a set of rules that determines how a nucleotide sequence is converted to an amino acid sequence of a protein

Central dogma:

Genotype and Phenotype

Genotype: the genetic makeup of an organism

Phenotype: expression of the genes

DNA and Chromosomes

Bacteria usually have a single circular chromosome made of DNA and associated proteins

Short tandem repeats (STRs): repeating sequences of noncoding DNA

Figure 8.1 a Prokaryotic Chromosome

The Flow of Genetic Information (1 of 2)

Vertical gene transfer: flow of genetic information from one generation to the next

Figure 8.2 The Flow of Genetic Information

Check Your Understanding-1

Check Your Understanding

Give a clinical application of genomics. 8-1

Why is the base pairing in DNA important? 8-2

DNA Replication (1 of 8)

DNA forms a double helix

"Backbone" consists of deoxyribose-phosphate

Two strands of nucleotides are held together by hydrogen bonds between A-T and C-G

Strands are antiparallel

Order of the nitrogen-containing bases forms the genetic instructions of the organism

Figure 8.3b DNA Replication

DNA Replication (2 of 8)

One strand serves as a template for the production of a second strand

Topoisomerase and gyrase relax the strands

Helicase separates the strands

A replication fork is created

Figure 8.3a DNA Replication

DNA Replication (3 of 8)

DNA polymerase adds nucleotides to the growing DNA strand

In the

direction

Initiated by an RNA primer

Leading strand is synthesized continuously

Lagging strand is synthesized discontinuously, creating Okazaki fragments

DNA polymerase removes RNA primers; Okazaki fragments are joined by the DNA polymerase and DNA ligase

Table 8.1 Important Enzymes in DNA Replication, Expression, and Repair

DNA Gyrase	Relaxes supercoiling ahead of the replication fork
DNA Ligase	Makes covalent bonds to join DNA strands; Okazaki fragments, and new segments in excision repair
DNA Polymerases	Synthesizes DNA; proofreads and repairs DNA
Endonucleases	Cut DNA backbone in a strand of DNA; facilitate repair and insertions
Exonucleases	Cut DNA from an exposed end of DNA; facilitate repair
Helicase	Unwinds double-stranded DNA
Methylase	Adds methyl group to selected bases in newly made DNA
Photolyase	Uses visible light energy to separate UV-induced pyrimidine dimers
Primase	An RNA polymerase that makes RNA primers from a DNA template
Ribozyme	RNA enzyme that removes introns and splices exons together
RNA Polymerase	Copies RNA from a DNA template
snRNP	RNA-protein complex that removes introns and splices exons together
Topoisomerase	Relaxes supercoiling ahead of the replication fork; separates DNA circles at the end of DNA replication
Transposase	Cuts DNA backbone, leaving single-stranded “sticky ends”

Figure 8.5 a Summary of Events at the DNA Replication Fork

DNA Replication (4 of 8)

Energy for replication is supplied by nucleotides

Hydrolysis of two phosphate groups on ATP provides energy

Figure 8.4 Adding a Nucleotide to DNA

DNA Replication (5 of 8)

Most bacterial DNA replication is bidirectional

Each offspring cell receives one copy of the DNA molecule

Replication is highly accurate due to the proofreading capability of DNA polymerase

Figure 8.6 Replication of Bacterial DNA

DNA Replication (6 of 8)

PLAY

Animation: DNA Replication: Overview

DNA Replication (7 of 8)

PLAY

Animation: DNA Replication: Forming the Replication Fork

DNA Replication (8 of 8)

PLAY

Animation: DNA Replication: Proteins

Check Your Understanding-2

Check Your Understanding

 Describe DNA replication, including the functions of DNA gyrase, DNA ligase, and DNA polymerase. 8-3

RNA and Protein Synthesis (1 of 2)

Ribonucleic acid

Single-stranded nucleotide

5-carbon ribose sugar

Contains uracil (U) instead of thymine (T)

RNA and Protein Synthesis (2 of 2)

Ribosomal RNA (rRNA): integral part of ribosomes

Transfer RNA (tRNA): transports amino acids during protein synthesis

Messenger RNA (mRNA): carries coded information from DNA to ribosomes

Transcription in Prokaryotes (1 of 3)

Synthesis of a complementary mRNA strand from a DNA template

Transcription begins when RNA polymerase binds to the promoter sequence on DNA

Transcription proceeds in the

direction; only one of the two DNA strands is transcribed

Transcription stops when it reaches the terminator sequence on DNA

Figure 8.7 The Process of Transcription

Transcription in Prokaryotes (2 of 3)

PLAY

Animation: Transcription: Overview

Transcription in Prokaryotes (3 of 3)

PLAY

Animation: Transcription: The Process

Translation (1 of 4)

mRNA is translated into the "language" of proteins

Codons are groups of three mRNA nucleotides that code for a particular amino acid

61 sense codons encode the 20 amino acids

The genetic code involves degeneracy, meaning each amino acid is coded by several codons

Figure 8.8 The Genetic Code

Translation (2 of 4)

Translation of mRNA begins at the start codon: AUG

Translation ends at nonsense codons: UAA, UAG, UGA

Codons of mRNA are "read" sequentially

Translation (3 of 4)

tRNA molecules transport the required amino acids to the ribosome

tRNA molecules also have an anticodon that base-pairs with the codon

Amino acids are joined by peptide bonds

Figure 8.9 The Process of Translation (1 of 4)

Figure 8.9 The Process of Translation (2 of 4)

Figure 8.9 The Process of Translation (3 of 4)

Figure 8.9 The Process of Translation (4 of 4)

Translation (4 of 4)

In bacteria, translation can begin before transcription is complete

Figure 8.10 Simultaneous Transcription and Translation in Bacteria

Transcription in Eukaryotes (1 of 4)

In eukaryotes, transcription occurs in the nucleus, whereas translation occurs in the cytoplasm

Exons are regions of DNA that code for proteins

Introns are regions of DNA that do not code for proteins

Small nuclear ribonucleoproteins (snRNPs) remove introns and splice exons together

Figure 8.11 RNA Processing in Eukaryotic Cells

Transcription in Eukaryotes (2 of 4)

PLAY

Animation: Transcription: Overview

Transcription in Eukaryotes (3 of 4)

PLAY

Animation: Transcription: The Genetic Code

Transcription in Eukaryotes (4 of 4)

PLAY

Animation: Transcription: The Process

Check Your Understanding-3

Check Your Understanding

What is the role of the promoter, terminator, and mRNA in transcription? 8-4

How does mRNA production in eukaryotes differ from the process in prokaryotes? 8-5

The Regulation of Bacterial Gene Expression (1 of 2)

Learning Objectives

8-6 Define operon.

8-7 Explain pre-transcriptional regulation of gene expression in bacteria.

8-8 Explain post-transcriptional regulation of gene expression.

The Regulation of Bacterial Gene Expression (2 of 2)

Constitutive genes are expressed at a fixed rate

Other genes are expressed only as needed

Inducible genes

Repressible genes

Catabolite repression

Pre-transcriptional Control (1 of 3)

Repression inhibits gene expression and decreases enzyme synthesis

Mediated by repressors, proteins that block transcription

Default position of a repressible gene is on

Induction turns on gene expression

Initiated by an inducer

Default position of an inducible gene is off

Pre-transcriptional Control (2 of 3)

PLAY

Animation: Operons: Induction

Pre-transcriptional Control (3 of 3)

PLAY

Animation: Operons: Repression

The Operon Model of Gene Expression (1 of 4)

Promoter: segment of DNA where RNA polymerase initiates transcription of structural genes

Operator: segment of DNA that controls transcription of structural genes

Operon: set of operator and promoter sites and the structural genes they control

The Operon Model of Gene Expression (2 of 4)

In an inducible operon, structural genes are not transcribed unless an inducer is present

In the absence of lactose, the repressor binds to the operator, preventing transcription

In the presence of lactose, lactose (inducer) binds to the repressor; the repressor cannot bind to the operator and transcription occurs

Figure 8.12 An Inducible Operon (1 of 3)

Figure 8.12 An Inducible Operon (2 of 3)

Figure 8.12 An Inducible Operon (3 of 3)

The Operon Model of Gene Expression (3 of 4)

In repressible operons, structural genes are transcribed until they are turned off

Excess tryptophan is a corepressor that binds and activates the repressor to bind to the operator, stopping tryptophan synthesis

Figure 8.13 A Repressible Operon (1 of 3)

Figure 8.13 A Repressible Operon (2 of 3)

Figure 8.13 A Repressible Operon (3 of 3)

The Operon Model of Gene Expression (4 of 4)

PLAY

Animation: Operons: Overview

Check Your Understanding-4

Check Your Understanding

Use the following metabolic pathway to answer the questions that follow it. 8-6

If enzyme a is inducible and is not being synthesized at present, a (1) ______ protein must be bound tightly to the (2) ______ site. When the inducer is present, it will bind to the (3) ______ so that (4) ______ can occur.

If enzyme a is repressible, end-product C, called a (1) ______, causes the (2) ______ to bind to the (3) ______. What causes derepression?

Positive Regulation

Catabolite repression inhibits cells from using carbon sources other than glucose

Cyclic AMP (cAMP) builds up in a cell when glucose is not available

cAMP binds to the lac promoter, initiating transcription and allowing the cell to use lactose

Figure 8.14 the Growth Rate of E. Coli on Glucose and Lactose

Figure 8.15 Positive Regulation of the Lac Operon

Epigenetic Control

Methylating nucleotides turns genes off

Methylated (off) genes can be passed to offspring cells

Not permanent

Post-Transcriptional Control

microRNAs (miRNAs) base pair with mRNA to make it double-stranded

Double-stranded RNA is enzymatically destroyed, preventing production of a protein

Figure 8.16 MicroRNAs Control a Wide Range of Activities in Cells

Check Your Understanding-5

Check Your Understanding

What is the role of cAMP in regulating gene expression? 8-7

How does miRNA stop protein synthesis? 8-8

Changes in the Genetic Material

Learning Objectives

8-9 Classify mutations by type.

8-10 Describe two ways mutations can be repaired.

8-11 Describe the effect of mutagens on the mutation rate.

8-12 Outline the methods of direct and indirect selection of mutants.

8-13 Identify the purpose of and outline the procedure for the Ames test.

Changes in Genetic Material

Mutation: a permanent change in the base sequence of DNA

Mutations may be neutral, beneficial, or harmful

Mutagens: agents that cause mutations

Spontaneous mutations: occur in the absence of a mutagen

Types of Mutations (1 of 4)

Base substitution (point mutation)

Change in one base in DNA

Figure 8.17 Base Substitutions

Types of Mutations (2 of 4)

Missense mutation

Base substitution results in change in an amino acid

Figure 8.18a-b Types of Mutations and Their Effects on the Amino Acid Sequences of Proteins

Types of Mutations (3 of 4)

Nonsense mutation

Base substitution results in a nonsense (stop) codon

Figure 8.18a-c Types of Mutations and Their Effects on the Amino Acid Sequences of Proteins

Types of Mutations (4 of 4)

Frameshift mutation

Insertion or deletion of one or more nucleotide pairs

Shifts the translational "reading frame“

Figure 8.18a-d Types of Mutations and Their Effects on the Amino Acid Sequences of Proteins

Check Your Understanding-6

Check Your Understanding

How can a mutation be beneficial? 8-9

Chemical Mutagens (1 of 2)

Nitrous acid: causes adenine to bind with cytosine instead of thymine

Nucleoside analog: incorporates into DNA in place of a normal base; causes mistakes in base pairing

Chemical Mutagens (2 of 2)

PLAY

Animation: Mutagens

Figure 8.19a Oxidation of Nucleotides Makes a Mutagen

Figure 8.19b Oxidation of Nucleotides Makes a Mutagen

Figure 8.20 Nucleoside Analogs and the Nitrogenous Bases They Replace

Radiation (1 of 3)

Ionizing radiation (X rays and gamma rays) causes the formation of ions that can oxidize nucleotides and break the deoxyribose-phosphate backbone

UV radiation causes thymine dimers

Radiation (2 of 3)

Photolyases separate thymine dimers

Nucleotide excision repair: Enzymes cut out incorrect bases and fill in correct bases

Radiation (3 of 3)

PLAY

Animation: Mutations: Repair

Figure 8.21 the Creation and Repair of a Thymine Dimer Caused by Ultraviolet Light

The Frequency of Mutation (1 of 2)

Spontaneous mutation rate = 1 in

replicated base pairs or 1 in

replicated genes

Mutagens increase the mutation rate to per

replicated gene

The Frequency of Mutation (2 of 2)

PLAY

Animation: Mutations: Types

Check Your Understanding-7

Check Your Understanding

How can mutations be repaired? 8-10

How do mutagens affect the mutation rate? 8-11

Identifying Mutants

Positive (direct) selection detects mutant cells because they grow or appear different than unmutated cells

Negative (indirect) selection detects mutant cells that cannot grow or perform a certain function

Auxtotroph: mutant that has a nutritional requirement absent in the parent

Use of replica plating

Figure 8.22 Replica Plating

Identifying Chemical Carcinogens (1 of 2)

The Ames test exposes mutant bacteria to mutagenic substances to measure the rate of reversal of the mutation

Indicates degree to which a substance is mutagenic

Figure 8.23 the Ames Reverse Gene Mutation Test

Check Your Understanding-8

Check Your Understanding

How would you isolate an antibiotic-resistant bacterium? An antibiotic-sensitive bacterium? 8-12

What is the principle behind the Ames test? 8-13

Genetic Transfer and Recombination (1 of 4)

Learning Objectives

8-14 Differentiate horizontal and vertical gene transfer.

8-15 Compare the mechanisms of genetic recombination in bacteria.

8-16 Describe the functions of plasmids and transposons.

Genetic Transfer and Recombination (2 of 4)

Genetic recombination: exchange of genes between two DNA molecules; creates genetic diversity

Crossing over: Two chromosomes break and rejoin, resulting in the insertion of foreign DNA into the chromosome

Figure 8.24 Genetic Recombination by Crossing Over

Genetic Transfer and Recombination (3 of 4)

Vertical gene transfer: transfer of genes from an organism to its offspring

Horizontal gene transfer: transfer of genes between cells of the same generation

Genetic Transfer and Recombination (4 of 4)

PLAY

Animation: Horizontal Gene Transfer: Overview

Transformation in Bacteria (1 of 2)

Transformation: genes transferred from one bacterium to another as "naked" DNA

Transformation in Bacteria (2 of 2)

PLAY

Animation: Transformation

Figure 8.25 Griffith's Experiment Demonstrating Genetic Transformation

Figure 8.26 the Mechanism of Genetic Transformation in Bacteria

Conjugation in Bacteria (1 of 7)

Conjugation: plasmids transferred from one bacterium to another

Requires cell-to-cell contact via sex pili

Figure 8.27 Bacterial Conjugation

Conjugation in Bacteria (2 of 7)

Donor cells carry the plasmid (F factor) and are called

cells

Hfr cells contain the F factor on the chromosome

Figure 8.28a Conjugation in E. coli

Figure 8.28b Conjugation in E. coli

Figure 8.28c Conjugation in E. coli

Conjugation in Bacteria (3 of 7)

PLAY

Animation: Conjugation: F Factor

Conjugation in Bacteria (4 of 7)

PLAY

Animation: Conjugation: Overview

Conjugation in Bacteria (5 of 7)

PLAY

Animation: Conjugation: Hfr Conjugation

Conjugation in Bacteria (6 of 7)

Conjugation can be used to map the location of genes on a chromosome

Conjugation in Bacteria (7 of 7)

PLAY

Animation: Conjugation: Chromosome Mapping

Figure 8.29 a Genetic Map of the Chromosome of E. Coli

Transduction in Bacteria (1 of 3)

DNA is transferred from a donor cell to a recipient via a bacteriophage

Generalized transduction: Random bacterial DNA is packaged inside a phage and transferred to a recipient cell

Specialized transduction: Specific bacterial genes are packaged inside a phage and transferred to a recipient cell

Transduction in Bacteria (2 of 3)

PLAY

Animation: Transduction: Generalized Transduction

Figure 8.30 Transduction by a Bacteriophage

Transduction in Bacteria (3 of 3)

PLAY

Animation: Transduction: Specialized Transduction

Check Your Understanding-9

Check Your Understanding

Differentiate horizontal and vertical gene transfer. 8-14

Compare conjugation between the following pairs:

8-15

Plasmids (1 of 2)

Plasmids are self-replicating circular pieces of DNA

1 to 5% the size of a bacterial chromosome

Often code for proteins that enhance the pathogenicity of a bacterium

Figure 8.31 R Factor, a Type of Plasmid

Plasmids (2 of 2)

Conjugative plasmid: carries genes for sex pili and transfer of the plasmid

Dissimilation plasmids: encode enzymes for the catabolism of unusual compounds

Resistance factors (R factors): encode antibiotic resistance

Transposons (1 of 4)

Transposons are segments of DNA that can move from one region of DNA to another

Contain insertion sequences (IS) that code for transposase that cuts and reseals DNA

Complex transposons carry other genes (e.g, in antibiotic resistance)

Transposons (2 of 4)

PLAY

Animation: Transduction: Overview

Figure 8.32a Transposons and Insertion

Transposons (3 of 4)

PLAY

Animation: Transduction: Insertion Sequences

Transposons (4 of 4)

PLAY

Animation: Transduction: Complex Transposons

Figure 8.32b-c Transposons and Insertion

Check Your Understanding-10

Check Your Understanding

 What types of genes do plasmids carry? 8-16

Genes and Evolution (1 of 2)

Learning Objective

8-17 Discuss how genetic mutation and recombination provide material for natural selection to act upon.

Genes and Evolution (2 of 2)

Mutations and recombination create cell diversity

Diversity is the raw material for evolution

Natural selection acts on populations of organisms to ensure the survival of organisms fit for a particular environment

Check Your Understanding-11

Check Your Understanding

Natural selection means that the environment favors survival of some genotypes. From where does diversity in genotypes come? 8-17

5'3'

enzyme enzyme

Substrate Intermediate End-product

ABC

®®

10 or 10

FF, HfrF.

´´