I Need A Discussion About This Topic

Read the section ‘Emerging Diseases’ in your book (Ch1, Microbiology by Tortora) and discuss the following in one or two paragraphs:

Prompts:

What are the challenges in combating emerging and reemerging diseases?

Discuss some of the examples given your book

Some steps we can take to prevent an outbreak of these diseases.

After you read through the chapter, write a short report (in your own words) responding the three prompts above and post to the rest of the class.

Microbiology an Introduction

Twelfth Edition

Chapter 1

The Microbial World and You

Staphylococcus Aureus Bacteria

Microbes in Our Lives (1 of 4)

Learning Objective

1-1 List several ways in which microbes affect our lives.

Microbes in Our Lives (2 of 4)

Microorganisms are organisms that are too small to be seen with the unaided eye

Microbes include bacteria, fungi, protozoa, microscopic algae, and viruses

Microbes in Our Lives (3 of 4)

A few are pathogenic (disease-producing)

Decompose organic waste

Generate oxygen by photosynthesis

Produce chemical products such as ethanol, acetone, and vitamins

Produce fermented foods such as vinegar, cheese, and bread

Produce products used in manufacturing (e.g., cellulase) and disease treatment (e.g., insulin)

Designer Jeans: Made by Microbes?

Denim fading: Trichoderma

Cotton production: Gluconacetobacter

Bleaching: mushroom peroxidase

Indigo: Escherichia coli

Plastic: bacterial polyhydroxyalkanoate

Applications of Microbiology 1.1

Applications of Microbiology 1.2

Microbes in Our Lives (4 of 4)

Knowledge of microorganisms allows humans to

Prevent food spoilage

Prevent disease

Understand causes and transmission of disease to prevent epidemics

Check Your Understanding-1

Check Your Understanding

Describe some of the destructive and beneficial actions of microbes. 1-1

Naming and Classifying Microorganisms (1 of 2)

Learning Objectives

1-2 Recognize the system of scientific nomenclature that uses two names: a genus and a specific epithet.

1-3 Differentiate the major characteristics of each group of microorganisms.

1-4 List the three domains.

Naming and Classifying Microorganisms (2 of 2)

Carolus Linnaeus established the system of scientific nomenclature in 1735

Each organism has two names: the genus and the specific epithet

Nomenclature (1 of 4)

Scientific names

Are italicized or underlined

The genus is capitalized; the specific epithet is lowercase

Are “Latinized” and used worldwide

May be descriptive or honor a scientist

Nomenclature (2 of 4)

Escherichia coli

Honors the discoverer, Theodor Escherich

Describes the bacterium’s habitat—the large intestine, or colon

Nomenclature (3 of 4)

Staphylococcus aureus

Describes the clustered (staphylo-) spherical (coccus) cells

Describes the gold-colored (aureus) colonies

Nomenclature (4 of 4)

After the first use, scientific names may be abbreviated with the first letter of the genus and the specific epithet:

Escherichia coli and Staphylococcus aureus are found in the human body

E. coli is found in the large intestine, and S. aureus is on skin

Check Your Understanding-2

Check Your Understanding

Distinguish a genus from a specific epithet. 1-2

Types of Microorganisms

Bacteria

Archaea

Fungi

Protozoa

Algae

Viruses

Multicellular Animal Parasites

Figure 1.1 Types of Microorganisms

Bacteria

Prokaryotes

”Prenucleus”

Single-celled

Peptidoglycan cell walls

Divide via binary fission

Derive nutrition from organic or inorganic chemicals or photosynthesis

Figure 1.1a Types of Microorganisms

Archaea

Prokaryotes

Lack peptidoglycan cell walls

Often live in extreme environments

Include:

Methanogens

Extreme halophiles

Extreme thermophiles

Fungi

Eukaryotes

Distinct nucleus

Chitin cell walls

Absorb organic chemicals for energy

Yeasts are unicellular

Molds and mushrooms are multicellular

Molds consist of masses of mycelia, which are composed of filaments called hyphae

Figure 1.1b Types of Microorganisms

Protozoa

Eukaryotes

Absorb or ingest organic chemicals

May be motile via pseudopods, cilia, or flagella

Free-living or parasitic (derive nutrients from a living host)

Figure 1.1c Types of Microorganisms

Algae

Eukaryotes

Cellulose cell walls

Found in freshwater, saltwater, and soil

Use photosynthesis for energy

Produce oxygen and carbohydrates

Figure 1.1d Types of Microorganisms

Viruses

Acellular

Consist of DNA or RNA core

Core is surrounded by a protein coat

Coat may be enclosed in a lipid envelope

Are replicated only when they are in a living host cell

Inert outside living hosts

Figure 1.1e Types of Microorganisms

Multicellular Animal Parasites

Eukaryotes

Multicellular animals

Not strictly microorganisms

Parasitic flatworms and roundworms are called helminths

Some microscopic stages in their life cycles

Check Your Understanding-3

Check Your Understanding

Which groups of microbes are prokaryotes? Which are eukaryotes? 1-3

Classification of Microorganisms

Developed by Carl Woese

Three domains based on cellular organization

Bacteria

Archaea

Eukarya

Protists

Fungi

Plants

Animals

Figure 10.1 Three-Domain System

Check Your Understanding-4

Check Your Understanding

What are the three domains? 1-4

A Brief History of Microbiology (1 of 2)

Learning Objectives

1-5 Explain the importance of observations made by Hooke and van Leeuwenhoek.

1-6 Compare spontaneous generation and biogenesis.

1-7 Identify the contributions to microbiology made by Needham, Spallanzani, Virchow, and Pasteur.

The First Observations

1665: Robert Hooke reported that living things are composed of little boxes, or “cells”

Marked the beginning of cell theory: All living things are composed of cells

The first microbes were observed from 1623–1673 by Anton van Leeuwenhoek

“Animalcules” viewed through magnifying lenses

Figure 1.2b Anton Van Leeuwenhoek’s Microscopic Observations

Check Your Understanding-5

Check Your Understanding

What is the cell theory? 1-5

The Debate over Spontaneous Generation (1 of 4)

Spontaneous generation: the hypothesis that life arises from nonliving matter; a “vital force” is necessary for life

Biogenesis: the hypothesis that living cells arise only from preexisting living cells

The Debate over Spontaneous Generation (2 of 4)

1668: Francesco Redi filled jars with decaying meat

Conditions	Results
Jars covered with fine net	No maggots
Open jars	Maggots appeared
Sealed jars	No maggots

From where did the maggots come?

What was the purpose of the sealed jars?

Spontaneous generation or biogenesis?

The Debate over Spontaneous Generation (3 of 4)

1745: John Needham put boiled nutrient broth into covered flasks

Conditions	Results
Nutrient broth heated, then placed in covered flask	Microbial growth

From where did the microbes come?

Spontaneous generation or biogenesis?

The Debate over Spontaneous Generation (4 of 4)

1765: Lazzaro Spallanzani boiled nutrient solutions in sealed flasks

Conditions	Results
Nutrient broth placed in flask, sealed, then heated	No microbial growth

Spontaneous generation or biogenesis?

The Theory of Biogenesis (1 of 3)

1858: Rudolf Virchow said cells arise from preexisting cells

The Theory of Biogenesis (2 of 3)

1861: Louis Pasteur demonstrated that microorganisms are present in the air

Conditions	Results
Nutrient broth placed in flask, heated, NOT sealed	Microbial growth
Nutrient broth placed in flask, heated, then immediately sealed	No microbial growth

Spontaneous generation or biogenesis?

The Theory of Biogenesis (3 of 3)

Pasteur also used S-shaped flasks

Keep microbes out but let air in

Broth in flasks showed no signs of life

Neck of flask traps microbes

Microorganisms originate in air or fluids, not mystical forces

Figure 1.3 Disproving the Theory of Spontaneous Generation

Check Your Understanding-6

Check Your Understanding

What evidence supported spontaneous generation? 1-6

How was spontaneous generation disproved? 1-7

A Brief History of Microbiology (2 of 2)

Learning Objectives

1-8 Explain how Pasteur’s work influenced Lister and Koch.

1-9 Identify the importance of Koch’s postulates.

1-10 Identify the importance of Jenner’s work.

1-11 Identify the contributions to microbiology made by Ehrlich and Fleming.

The Golden Age of Microbiology (1 of 3)

1857–1914

Beginning with Pasteur’s work, discoveries included the relationship between microbes and disease, immunity, and antimicrobial drugs

The Golden Age of Microbiology (2 of 3)

Pasteur showed that microbes are responsible for fermentation

Fermentation is the microbial conversion of sugar to alcohol in the absence of air

Microbial growth is also responsible for spoilage of food and beverages

Bacteria that use air spoil wine by turning it to vinegar (acetic acid)

The Golden Age of Microbiology (3 of 3)

Pasteur demonstrated that these spoilage bacteria could be killed by heat that was not hot enough to evaporate the alcohol in wine

Pasteurization is the application of a high heat for a short time to kill harmful bacteria in beverages

Figure 1.4 Milestones in the Golden Age of Microbiology (1 of 3)

The Germ Theory of Disease (1 of 3)

1835: Agostino Bassi showed that a silkworm disease was caused by a fungus

1865: Pasteur showed that another silkworm disease was caused by a protozoan

1840s: Ignaz Semmelweis advocated handwashing to prevent transmission of puerperal fever from one obstetrical patient to another

The Germ Theory of Disease (2 of 3)

1860s: Applying Pasteur’s work showing that microbes are in the air, can spoil food, and cause animal diseases, Joseph Lister used a chemical antiseptic (phenol) to prevent surgical wound infections

Figure 1.4 Milestones in the Golden Age of Microbiology (2 of 3)

The Germ Theory of Disease (3 of 3)

1876: Robert Koch discovered that a bacterium causes anthrax and provided the experimental steps, Koch’s postulates, to demonstrate that a specific microbe causes a specific disease

Figure 1.4 Milestones in the Golden Age of Microbiology (3 of 3)

Vaccination

1796: Edward Jenner inoculated a person with cowpox virus, who was then immune from smallpox

Vaccination is derived from the Latin word vacca, meaning cow

The protection is called immunity

Check Your Understanding-7

Check Your Understanding

Summarize in your own words the germ theory of disease. 1-8

What is the importance of Koch’s postulates? 1-9

What is the significance of Jenner’s discovery? 1-10

The Birth of Modern Chemotherapy: Dreams of a “Magic Bullet”

Treatment of disease with chemicals is called chemotherapy

Chemotherapeutic agents used to treat infectious disease can be synthetic drugs or antibiotics

Antibiotics are chemicals produced by bacteria and fungi that inhibit or kill other microbes

The First Synthetic Drugs

Quinine from tree bark was long used to treat malaria

Paul Ehrlich speculated about a “magic bullet” that could destroy a pathogen without harming the host

1910: Ehrlich developed a synthetic arsenic drug, salvarsan, to treat syphilis

1930s: Sulfonamides were synthesized

A Fortunate Accident—Antibiotics

1928: Alexander Fleming discovered the first antibiotic (by accident)

Fleming observed that Penicillium fungus made an antibiotic, penicillin, that killed S. aureus

1940s: Penicillin was tested clinically and mass-produced

Figure 1.5 The Discovery of Penicillin

Check Your Understanding-8

Check Your Understanding

What was Ehrlich’s “magic bullet”? 1-11

Modern Developments in Microbiology

Learning Objectives

1-12 Define bacteriology, mycology, parasitology, immunology, and virology.

1-13 Explain the importance of microbial genetics and molecular biology.

Bacteriology, Mycology, and Parasitology

Bacteriology is the study of bacteria

Mycology is the study of fungi

Parasitology is the study of protozoa and parasitic worms

Figure 1.6 Parasitology: The Study of Protozoa and Parasitic Worms

Immunology

Immunology is the study of immunity

Vaccines and interferons are used to prevent and cure viral diseases

A major advance in immunology occurred in 1933 when Rebecca Lancefield classified streptococci based on their cell wall components

Figure 1.7 Rebecca Lancefield (1895–1981)

Rebecca Lancefield (1895–1981), who discovered differences in the chemical composition of a polysaccharide in the cell walls of many pathogenic streptococci.

Virology

Virology is the study of viruses

Dmitri Iwanowski in 1892 and Wendell Stanley in 1935 discovered the cause of mosaic disease of tobacco as a virus

Electron microscopes have made it possible to study the structure of viruses in detail

Recombinant DNA Technology (1 of 2)

Microbial genetics: the study of how microbes inherit traits

Molecular biology: the study of how DNA directs protein synthesis

Genomics: the study of an organism’s genes; has provided new tools for classifying microorganisms

Recombinant DNA: DNA made from two different sources

In the 1960s, Paul Berg inserted animal DNA into bacterial DNA, and the bacteria produced an animal protein

Recombinant DNA Technology (2 of 2)

1941: George Beadle and Edward Tatum showed that genes encode a cell’s enzymes

1944: Oswald Avery, Colin MacLeod, and Maclyn McCarty showed that DNA is the hereditary material

1953: James Watson and Francis Crick proposed a model of DNA structure

1961: François Jacob and Jacques Monod discovered the role of mRNA in protein synthesis

Figure 1.4 Milestones in the Golden Age of Microbiology

Check Your Understanding-9

Check Your Understanding

Define bacteriology, mycology, parasitology, immunology, and virology. 1-12

Differentiate microbial genetics from molecular biology. 1-13

Microbes and Human Welfare

Learning Objectives

1-14 List at least four beneficial activities of microorganisms.

1-15 Name two examples of biotechnology that use recombinant DNA technology and two examples that do not.

Recycling Vital Elements

Microbial ecology is the study of the relationship between microorganisms and their environment

Bacteria convert carbon, oxygen, nitrogen, sulfur, and phosphorus into forms used by plants and animals

Bioremediation: Using Microbes to Clean Up Pollutants

Bacteria degrade organic matter in sewage

Bacteria degrade or detoxify pollutants such as oil and mercury

Figure 27.8 Composting Municipal Wastes

Insect Pest Control by Microorganisms

Microbes that are pathogenic to insects are alternatives to chemical pesticides

Prevent insect damage to agricultural crops and disease transmission

Bacillus thuringiensis infections are fatal in many insects but harmless to animals and plants

Figure 11.21 Bacillus

Modern Biotechnology and Recombinant DNA Technology

Biotechnology is the use of microbes for practical applications, such as producing foods and chemicals

Recombinant DNA technology enables bacteria and fungi to produce a variety of proteins, vaccines, and enzymes

Missing or defective genes in human cells can be replaced in gene therapy

Genetically modified bacteria are used to protect crops from insects and from freezing

Check Your Understanding-10

Check Your Understanding

Name two beneficial uses of bacteria. 1-14

Differentiate biotechnology from recombinant DNA technology. 1-15

Microbes and Human Disease

Learning Objectives

1-16 Define normal microbiota and resistance.

1-17 Define biofilm.

1-18 Define emerging infectious disease.

Normal Microbiota (1 of 2)

Bacteria were once classified as plants, giving rise to the term flora for microbes

This term has been replaced by microbiota

Microbes normally present in and on the human body are called normal microbiota

Figure 1.8 Several Types of Bacteria

Several types of bacteria found as part of the normal microbiota on the surface of the human tongue.

Normal Microbiota (2 of 2)

Normal microbiota prevent growth of pathogens

Normal microbiota produce growth factors such as vitamins B and K

Resistance is the ability of the body to ward off disease

Resistance factors include skin, stomach acid, and antimicrobial chemicals

Biofilms

Microbes attach to solid surfaces and grow into masses

They will grow on rocks, pipes, teeth, and medical implants

Biofilms can cause infections and are often resistant to antibiotics

Figure 1.9 Biofilm on a Catheter

Emerging Infectious Diseases (1 of 3)

When a pathogen invades a host and overcomes the host’s resistance, disease results

Emerging infectious diseases (EIDs): new diseases and diseases increasing in incidence

Emerging Infectious Diseases (2 of 3)

Middle East respiratory syndrome (MERS)

Caused by Middle East respiratory syndrome coronavirus (MERS-CoV)

Common to SARS

Severe acute respiratory syndrome

100 deaths in the Middle East from 2012 to 2014

Emerging Infectious Diseases (3 of 3)

Avian influenza A (H5N1)

Influenza A virus

Primarily in waterfowl and poultry

Sustained human-to-human transmission has not yet occurred

Figure 13.3b Morphology of an Enveloped Helical Virus

Emerging Infectious Diseases (1 of 7)

Methicillin-resistant Staphylococcus aureus (MRSA)

1950s: Penicillin resistance developed

1980s: Methicillin resistance

1990s: MRSA resistance to vancomycin reported

VISA: vancomycin-intermediate S. aureus

VRSA: vancomycin-resistant S. aureus

Emerging Infectious Diseases (2 of 7)

West Nile encephalitis (WNE)

Caused by West Nile virus

First diagnosed in the West Nile region of Uganda in 1937

Appeared in New York City in 1999

In nonmigratory birds in 48 states

Transmitted between birds and to horses and humans by mosquitoes

Diseases in Focus 22.2

Emerging Infectious Diseases (3 of 7)

Bovine spongiform encephalopathy

Caused by a prion

An infectious protein that also causes Creutzfeldt-Jakob disease (CJD)

New variant of CJD in humans is related to cattle that have been given feed made from prion-infected sheep

Figure 22.18b Spongiform Encephalopathies

Emerging Infectious Diseases (4 of 7)

E. coli O157:H7

Toxin-producing strain of E. coli

First seen in 1982; causes bloody diarrhea

Leading cause of diarrhea worldwide

Figure 25.11 Pedestal formation by Enterohemorrhagic E. coli (EHEC) O157:H7

Emerging Infectious Diseases (5 of 7)

Ebola hemorrhagic fever (EHF)

Ebola virus

Causes fever, hemorrhaging, and blood clotting

Transmitted via contact with infected blood or body fluids

First identified near Ebola River, Congo

2014 outbreak in Guinea; hundreds killed

Figure 23.21 Ebola Hemorrhagic Virus

Emerging Infectious Diseases (6 of 7)

Cryptosporidiosis

Cryptosporidium protozoa

First reported in 1976

Causes 30% of diarrheal illness in developing countries

In the United States, transmitted via water

Figure 25.17 Cryptosporidiosis

Emerging Infectious Diseases (7 of 7)

AIDS (acquired immunodeficiency syndrome)

Caused by human immunodeficiency virus (HIV)

First identified in 1981

Sexually transmitted infection affecting males and females

Worldwide epidemic infecting 35 million people; 6000 new infections every day

HIV/AIDS in the United States: 26% are female, and 49% are African American

Check Your Understanding-11

Check Your Understanding

Differentiate normal microbiota and infectious disease. 1-16

Why are biofilms important? 1-17

What factors contribute to the emergence of an infectious disease? 1-18

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

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FF, HfrF.

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