Download Objectives to Review

Objectives to Review
Note: this is intended to help you know what topics to review if you do not know the topic. Please
review these topics from your notes (or from the text if you desire) and from the text summaries at the
end of each chapter. All of these topics are important; we have no time in our class to discuss
unimportant topics. For a Guide on How to Study or for the Course Expectations, please see the
appropriate links from the top right of the main lecture web page. Note, there should be some overlap
between the review for a chapter reading, the homework, and the related lecture lesson.
LESSON 1: AFTER COMPLETING THIS LESSON STUDENTS SHOULD BE ABLE TO:
Understand the following terms and their significance in microbiology:
 Eukaryotic and Prokaryotic
 Eubacteria, Archaea/Archaebacteria, and Eukaryotes
 Superkingdom
 Domains
 Kingdom
 Protista
 The classification of living organisms
 The molecules of life
Understand what Proteins are and all of these terms/concepts related to them:
 amino acids and peptide bonds
 Protein shape = function
 R-groups
 how attraction/repulsion of amino acids give rise to the shape of a protein
 how hydrogen bonds and cysteine sulfur bonds form between amino acids
 Four Levels of Protein Structure
 Enzymes as special proteins
 Mutation, temperature, salt concentration, and pH can change the shape of a
protein/enzyme
Understand what enzymes are and all of these terms/concepts related to them:
 catalysts
 activation energy (w/ or w/o an enzyme)
 active site
 substrate, product and enzyme-substrate complex
 energy released by the reaction
 Factors that influence enzyme activity: substrate concentration, inhibitors, activators,
and all of the agents in the previous line
Understand what lipids are and all of these terms/concepts related to them:
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cell membranes of Eukaryotes and Eubacteria
o phospholipids
o hydrophobic fatty acid tails
o hydrophilic phosphate heads
o ester bond (-C-COO-C-)
o tails & heads orientation relative to water
o bilayer
Archaebacteria cell membranes:
o do not contain phospholipids but "phospholipid like molecules"
o similarities and differences phospholipids
o w/ isoprene instead of fatty acids
o w/ an ether link (-C-O-C-)
Understand the Similarities and Differences among prokaryotes compared to eukaryotes and be
able to summarize these Similarities and Differences
Be able to Draw a eubacteria cell going from the outside in
Understand these terms/concepts of Eubacteria (Bacteria):
 The cell wall (supports & protects the cell)
 capsule or glycocalyx
 peptidoglycan
 N-acetylglucosamine and N-acetylmuramic acid (NAG & NAM)
 short chains of amino acids (peptides)
 two types of cell walls: Gram positive and Gram negative
 why they stain as they do
 Gram negative outer membrane
 Lipopolysccharides, Lipid A and endotoxins
 Understand that the outer membrane regulates what can get through it
 Understand that channel proteins allow molecules to pass through the outer and the
cell membrane
 Understand that water soluble molecules can diffuse through peptidoglycan
Understand where Archaebacteria are found and are ~20% of earth’s biomass
Understand that Archaebacteria do not cause any known human disease
HOMEWORK 1: AFTER COMPLETING THIS LESSON STUDENTS SHOULD BE ABLE TO:
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Use the metric system
Understand that Metric units are convertible & be able to convert between units
Understand that living things are mostly water so 1 gram=1 ml=1 cubic cm
Understand the relative sizes of things, know the rank order
Understand the parts of a microscope
know how to use your microscope and ways to improve your image
know that under high power the microscope measures things in micrometers
Understand carbohydrates (sugars, monosaccharides, di & polysaccharides)
Understand fats and triglycerides as lipids
Understand nucleic acids (DNA & RNA)
READINGS 1: AFTER COMPLETING THE READINGS STUDENTS SHOULD BE ABLE TO:
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Understand what organisms microbiologists study
Understand the germ theory of disease
Understand that Koch discovered the first microbe to cause disease: anthrax
Understand Koch’s postulates
Understand Jenner and Pasteur’s role in immunology and vaccination
Understand Ehrlich and his magic bullets
Understand biomolecules as monomers and polymers
Understand lipids, fats, phospholipids
Understand carbohydrates, monosaccharide, di &polysaccharide
Understand proteins & nucleic acids
Understand the structure and use of ATP
Understand enzymes, substrates, active site,
Understand cofactors or coenzymes
Understand denatured enzymes
Understand competitive inhibition of enzymes
Understand metric units of measure
Understand the size of living things
Understand the light microscopes
Understand prokaryotic cells and these parts and terms:
o glycocalyces (slime layers or capsules)
o flagella and Pili
o cell wall, peptidoglycan, NAG & NAM, short peptides
o Gram positive – thick cell wall/ thick peptidoglycan
o Gram negative – thin cell wall/ thin peptidoglycan
o archaea cell walls
o lipid A is an endotoxin
o endospores
o ribosomes 70S & 80S
LESSON 2: AFTER COMPLETING THIS LESSON STUDENTS SHOULD BE ABLE TO:
Understand these terms and concepts related to parasites:
 definitive host, mature form
 intermediate host, immature (juvenile) form
 belong to kingdom Animals, & Protists
 parasitic protozoa are protists, parasitic helminthes are animals
Understand the divisions (classification) of parasitic protists:
 Sarcodines - (amoeboid protozoa) move by pseudopods
 Zoomastigotes - (flagellates)
 Ciliophora - (ciliates)
 Apicomplexa - (sporozoans)
Understand the Amoeboid Protozoans including these terms and concepts:
 Entamoeba histolytica
 amoebic dysentery
 trophozoites do damage, cysts are infective
 Cysts withstand hostile environments
 Three results of infection: asymptomatic, invasive amebic dysentary, extraintestinal
amoebiasis
Understand the Flagellates including these terms and concepts:
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Giardia lamblia causes diarrhea and stomach flu-like symptoms
o trophozoites do damage
o cysts are infective
Trypansosoma cruzi causes Chagas' disease
o vector:Triatoma/kissing bug
o Life Cycle of Trypansosoma cruzi:
 kissing bug's hindgut,
 itchy wound,
 blood carries parasite to heart or macrophage cell
 multiply/ruptures host cell, released into blood
 ingested by the kissing bug
 immature parasite matures
o Disease Progression of Chagas' disease:
 swelling at the bite site
 inflamation
 asymptomatic stage
 congestive heart failure
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Typansoma brucei causes African sleeping sickness
o disease range is that of its vector the Tsetse fly
Leishmania causing Leishmanisis
o hosted by 21 species of sand flies
o 3 Clinical Forms:
 Large painless skin ulcers
 Severe if skin ulcer includes mucus membrane
 Disseminated Leishmania (infected macrophages)
Understand the Ciliates (Ciliophora) including these terms and concepts:
 Balantidium coli causes dysentery
o Asymptomatic in most healthy adults
o trophozoites do damage, cysts are infective
Understand the Sporozoans including these terms and concepts:
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Malaria (the parasites of most importance)
Plasmodium vivax, Plasmodium malariae, P. ovale, and P. falciparum
endemic in tropics
Definitive host: the Anopheles mosquito
Intermediate host: Humans
Understand the abbreviated Life Cycle of Plasmodium:
o an infected mosquito bites a human
o juvenile parasite carried by blood to liver, infects liver cell
o parasite replicates in & bursts the liver cell
o juvenile parasites released into blood
o parasites infects red & white blood cells
o parasite reproduces in & bursts blood cell
o male/female gametocytes released into blood
o uninfected mosquito gets infected by biting an infected person
o in mosquito's intestine, male & female gametocytes form a zygote
o zygote is the mature parasite
o zygote undergoes meiosis (sexual reproduction) making juvenile forms of
parasite that migrates to salivary gland
o mosquito bites a human completing the life cycle
Understand that when red blood cells lyse, the patient is at their sickest, and this is
when most gametocytes are released into the blood. This happens when the
mosquitoes are most active.
Understand that malaria had a number of medical firsts:
o First protozoan identified to cause disease
o the first effective treatment for a disease
o the bark of the cinchona tree has quinine,
o Jesuit missionaries brought the treatment for malaria to Europe in 1600s.
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Toxoplasma gondii causing the disease toxoplasmosis
o estimated 40% of Americans have had it or have it
o intermediate host is humans
o definitive host is the kitty cat
o the majority of healthy people are asymptomatic
o very severe in AIDS patients & developing fetuses
o Prevention is proper hygiene of kitty poop
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Understand that Helminths are flatworms and round worms
Understand these terms and concepts related to Helminthes:
o flatworms and round worms are animals but are not closely related
o most are not parasitic, are free living
o some are parasitic worms which we will study
o flukes (Trematodes) –all parasitic
o tapeworms (Cestodes) –all parasitic
o parasitic round worms (parasitic Nematodes) –some are parasitic
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Understand these terms and concepts related to Cestodes (tapeworms):
o have complex life cycles
o Taenia solium (pork tapeworm) of pigs
o Taenia saginata (beef tapeworm) of cattle
o humans are the definitive host, pigs/cows are intermediate hosts
o mature tapeworm is in a human attached with a scolex
o a scolex has suckers/hooks and makes the proglotids
o mature proglotids have eggs and are shed in feces
o eggs eaten by intermediate host
o juvenile form burrows into muscle or tissue of intermediate host
o juvenile form of parasite forms cysts
o cysts are eaten by a human in undercooked pork or beef
o infection occurs when scolex attaches to human intestine
o worm reaches final maturation in human intestine completing the life cycle
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Echinococcus granulosus (dog tapeworm)
dog/canine is definitive host
human or another animal is the intermediate host
cysts form of parasite does damage in people
dog or coyote eats juvenile form in a cyst from eating an infected animals
scolex attaches to dog intestine
Echinococcus granulosus reaches final maturation
proglottids with eggs form and break off, shed in feces
o intermediate host eats an egg
o juvenile form burrows into tissue & forms a cyst
o dog eats intermediate host consuming the cyst completing the life cycle
Understand these terms and concepts related to Trematodes (flukes):
 have a leaf shaped body
 helminth ova (eggs)
 the ova of flukes are used to diagnose a patient
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Schistosoma/blood flukes cause schistosomiasis
o 3 species of blood flukes
o parasite burrows into person when they are in water (swimming, washing dishes,
washing clothes, bathing)
o symptom: swimmer's itch
o parasite invades circulatory system & lays eggs
o eggs carried by blood to bladder or intestine & go into the lumen
o eggs released into the environment
o hatch into a juvenile which burrows into a freshwater snail
o parasite multiplies in snail,
o a free swimming form emerges & burrows into a human completing the lifecycle
o eggs cause blockage & tissue damage
o symptoms: lethargy, fever, swollen stomach, pain, sometimes death
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Clinorchis sinensis (Asian Liver Fluke)
o causes liver disease & jaundice
o most common in SE Asia
Understand these terms and concepts related to Nematodes (round worms)
 Enterobium vermicularis (The pinworm)
o spend their entire life in large intestine of a human (no intermediate host)
o adult females deposit eggs in perianal region
o allows for easy infection & detection
o the ova are used to diagnose a patient
o Most common around small children, the mentally insane, or retarded
individuals in crowded living conditions
o Most common helminth in the USA
READING 2: AFTER COMPLETING THIS READING STUDENTS SHOULD BE ABLE TO:
Understand the terms and concepts of Parasitology including:
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definitve and intermediate hosts
protozoan parasites
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o trophozoite & cyst
o excystment
o Balantidium coli
o Entamoeba histolytica
o Trypanosoma cruzi and T. brucei
o Leishmania
o Giardia
o Trichomonas vaginalis
o Malaria is caused by Plasmodium
o Toxoplasma gondii and cats
Helminths
cestodes/tapeworm
o scolex, proglottids
o Taenia solium and Taenia saginata
trematodes/flukes
o Schistosoma
Nematodes/round worm
o Ascaris –most common worm in people
o Enterobius vermicularis –most common worm in USA
LESSON 3: AFTER COMPLETING THIS LESSON STUDENTS SHOULD BE ABLE TO:
Understand the terms and concepts of metabolism including:
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anabolism and catabolism
Endergonic and Exergonic reactions
Understand the structure and use of ATP
o ATP + H2O --> ADP + P + energy
o ADP + P + energy --> ATP + H2O (is reversible)
All Chemical bonds have energy, but the cell can harvest energy from only certain bonds
Understand how cells obtain Energy, can be from three sources:
1. organic molecules
2. inorganic molecules
3. sunlight
Understand how cells generate ATP in three types of processes:
1. fermentation
2. respiration
3. photophosphorylation
Respiration is more efficient, aerobic respiration is most efficient
Understand the terms and concepts of Aerobic respiration:
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C6H12O6 + 6O2 ----> 6CO2 + 6H2O + 36/38 ATP (Euk -36/38, Prok -38)
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Aerobic respiration is a series of 3 steps, catalyzed by enzymes
o glycolysis
o the Prepatory Step & the Krebs cycle (or TCA cycle)
o the electron transport chain (or electron transfer phosphorylation, or etc)
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Glycolysis
o glucose into two pyruvate molecules (also called pyruvic acid).
o 2 ATP and 2 NADH
The Prepatory Step & The Krebs cycle
o The Prepatory Step & The Krebs cycle run twice/glucose.
o generates 1 ATP, 3 CO2, 1 FADH2, & 4 NADH /pyruvate
o (NADH stands for nicotinamide adenine dinucleotide )
o NAD+ and FAD accept electrons and hydrogen ions
o Cells have 3 Common Electron Carriers:
o NAD+ + 1 H+ + 2e- ---> NADH
o FAD + 2H+ + 4e- ---> FADH2
o NADP+ + 1 H+ + 2e- ---> NADPH
The electron transport chain (etc or electron transport phosphorylation)
o is a series of reactions occurring in proteins embedded in membranes
o mitochondrial or cell membrane
o electrons passed from NADH and FADH2 to proteins
o Electrons flow pumping protons across the membrane
o creates a gradient of both proton concentration and charge
o The gradient is used to make ATP
o H+ ions flow through ATP-synthase giving the protein the energy it needs to
make ATP
o Oxygen is the final electron accepter
o 2H+ + 2 e- + 1/2 O2 --> H2O
o C6H12O6 + 6O2 ----> 6CO2 + 6H2O + 36/38 ATP
Understand the net reaction of glycolysis, the Krebs cycle and electron transport
chain
 in most eukaryote cells is 36 ATP/glucose,
 in prokaryote cells is 38.
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Understand the terms and concepts of Alternate Forms of Respiration:
 Aerobic respiration, aerobes.
 Anaerobic respiration, anaerobes
o Have alternate electron acceptors
o Have Alternate Electron Transport Chains
o Prokaryotic alternate electron acceptors include:
 NO3 ----> NO2 or N2O or N2
 SO4 ----> H2S
 CO3 ----> CH4
 Others exist
o very valuable to many facultative microbes
Understand the terms and concepts of Fermentation
 glycolysis makes pyruvate
 pyruvate metabolized to a fermentation end product (lactic acid/ethanol/others)
 2 ATP from glycolysis
 There are organisms that are strict fermenters
 5 fermentation end products
Understand the terms and concepts of Photosynthesis:
 The overall equation for noncyclic photosynthesis is:
 6 CO2 + 12 H2O + light ----> C6H12O6 + 6 O2 + 6 H20
 cyclic photophosphorylation
 The energy in light is converted to ATP (not sugar)
 Photosynthesis is an anabolic process
Understand the concept of Anabolism
 The cell uses energy and precursors to build molecules
 Anabolism is related intimately to catabolism, metabolism is interconnected
READINGS: AFTER COMPLETING THIS LESSON STUDENTS SHOULD BE ABLE TO:
Understand the terms and concepts of metabolism including:
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anabolism and catabolism
redox reactions and electron carriers
aerobic respiration, glycolysis, Krebs cycle, ETC
anaerobic respiration, anaerobes
chemiosmosis, ATP synthase
fermentation
photosynthesis, Calvin-Benson cycle
cyclic photophosphorylation & noncyclic photophosphorylation
Understand how cells regulate metabolism
 by controlling gene expression
 by controlling enzymatic reactions
 Controlling the later can be done by making or degrading transmembrane channel
proteins, enzymes, and feedback inhibition
Understand the terms and concepts of the Genetics of Prokaryotes:
 chromosomes and plasmids
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genotype and phenotype
replication, transcription, and translation
3 types of RNA: mRNA, tRNA, rRNA
codons, start codon, ribosomes, t-RNA
mutations and types of mutations:
silent mutations, point mutations, frameshifts, misense, and nonsense
mutagens
LESSON 4: AFTER COMPLETING THIS LESSON STUDENTS SHOULD BE ABLE TO:
Understand the concepts of Chemosynthesis:
 chemosynthetic bacteria
 the efficiency of ATP production
Understand the terms and concepts of Microbial strategies for Survival:
 Two different Carbon sources:
o autotrophs
o heterotroph.
 Two different Energy sources:
o phototrophs
o chemotrophs
 These groups can be combined:
o Chemoheterotrophs
o Photoautotrophs
o Chemoautotrophs
o Photoheterotrophs
Understand that microbes can be Classified by their electron/hydrogen sources.
 source of electrons vs source of energy
 Organotrophs
 Lithotrophs
 These groups can be combined:
o chemolithoautotrophs, chemolithoheterotrophs
o chemoorganautotrophs, chemoorganoheterotrophs, etc.
Understand that this classification system is not always simple:
 mixotrophs
 Euglena is an example that switches its troph
Understand the terms and concepts of Bacterial Morphology and Groupings
 Three main cell shapes, especially with Eubacteria:
o Bacilli
o Cocci
o Spirilla
o Other shapes are possible:
Understand the terms of Cellular Growth Patterns or cellular arrangements
 singlets
 diplococci or diplobacilli
 streptococci or streptobacilli or chains of bacilli or palisades
 staphlococci and clumps
 Understand that the growth patterns are usually pleomorphic
 Understand the difference between cell shape & colony shape
Understand the concepts of Colony Morphology and be able to use a chart on it
Understand the concepts of Koch's postulates:
 Robert Koch and anthrax
 PURE cultures grown on solidified media
 streak a mixed culture to acquire a pure culture
 Koch's postulates:
1. identify & isolate the bacteria from an diseased organism.
2. grow and obtain a PURE culture.
3. infect healthy animals w/ microbe & establish same illness in animals
4. identify & reisolate the same microbe in these new animals.
5. this organism must be present in every case of the disease.
 nearly impossible to perform w/ human diseases, exceptions include Edward Jenner
Understand the terms describing microbes and their environment
 Bacteria are adapted to their environment
 acidophiles
 temperature
 psychrophiles
 mesophiles
 thermophiles
 hyperthermophiles
 thermoduric organisms
 Osmotic Pressure.
o liquid water & the concentration of solutes
o plasmolysis
o halophiles
 Nutrients requirements:
o all organisms require carbon, energy, and other chemicals
 growth factors, vitamins, essential amino acids, essential fatty acids
 minerals and trace elements
 Nitrogen requirements:
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o needed in protein & nucleic acid
o Bacteria may get it from:
 amino acids/proteins/nucleic acids
 ammonium ion (NH4).
 nitrite or nitrate ions (NO-2/NO-3).
 fix nitrogen gas (N2) (cyanobacteria and Rhizobium)
o Bacteria cycle nitrogen in ecosystem
Sulfur requirements:
o needed in some amino acids (Cys) and vitamins (B1).
o Bacteria cycle sulfur in ecosystem
o Bacteria may obtain it from:
 some amino acids
 sulfate ions (SO4)
 hydrogen sulfide gas (H2S)
Oxygen requirements:
o if grow in oxygen, cells need to detoxify O2 radicals
o catalase, superoxide dismutase/peroxidase/various antioxidants
o catalase
 2H2O2 + catalase ----> 2 H2O + O2
o thioglycollate tubes illustrate the oxygen requirements of:
 obligate aerobes
 obligate anaerobes
 microaerophiles
 facultative anaerobes
 aerotolerant anaerobes
Understand the concepts of Enrichment cultures
Understand the terms and concepts of Bacterial Growth:
 growth AND reproduction:
o binary fission
o yeasts and a few bacteria bud
o reproductive spores vs endospores
o fragmentation is colonial reproduction not cellular
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Growth is expressed as generation time (time/generation).
o E. coli has generation time 20 minutes/generation.
o Most Eubacteria are not so fast growing
o Mycobacterium leprae is very slow because of mycolic acid
Microbial Growth Curves occur in phases:
o lag phase
o log phase
o stationary phase
o Death phase
Understand the terms and concepts of the Counting Microbes:
 Cell Counts
 Plate counts
o countable colony numbers (30-300 colonies/plate).
 Microscopic counts
o Turbidity -uses a spectrophotometer
 Bacterial weight
 Each method for counting microbes has advantages and disadvantages
READINGS 4: AFTER COMPLETING THIS LESSON STUDENTS SHOULD BE ABLE TO:
Understand the concepts of Koch’s postulates
Understand the terms and concepts of growth and reproduction of bacteria including:
 colonies and biofilms
 nutrients, nitrogen, trace elements, and growth factors
 photoautotrophs, chemautotrophs, photoheterotrophs, chemoheterotrophs
 organotrophs, and lithotrophs
 aerobes, facultative anaerobes, aerotolerant anaerobes, microaerophiles, and obligate
anaerobes
 if growing in oxygen, need detoxification of oxygen radicals
 psychrophiles, mesophiles, thermophiles, and hyperthermophiles
 acidophiles and alkalinophiles
 creanation and plasmolysis
 halophiles and obligate halophiles
 barophiles, hydrostatic (water) pressure
 inoculum, inoculation, and pure cultures
 generation time
 growth curves
o phases of growth: lag, log, stationary, and death
 a continuous culture
 serial dilution
 growth or cell counts
o viable plate counts
o direct count
o measure of turbidity
o metabolic activity
o dry weight
o analysis of genetic sequences (is required if the species cannot be grown)
LESSON 5: GENETICS
Know what DNA is and what it does
Know that the structure of DNA:
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facilitates its replication
provides a blueprint for building proteins
allows for the generation of genetic variation
allows for the regulation of gene expression
Know who Fredrick Griffith was and what he did
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know that he had two strains Streptococcus pneumoniae
know about the S-strain and what it did
know about the R-strain and what it did
Know that Dr Griffith:
1. injected the encapsulated S-strain into mice and they died
2. injected the R-strain into mice, they lived
3. He wanted a vaccine against the pathogenic strain.
o but the R-strain did not act as a vaccine
o and heat killed S-strain bacteria did not act as a vaccine
4. He did one more control.
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he mixed heat killed S-strain w/ live R-strain and injected it into mice
these mice died of living S-strain!
Something transformed the living R-strain into S-strain eubacteria
Something passed the trait of a capsule from the dead S-strain to the living R-strain
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In 1944, Avery, McLeod/McCarty, extracted the molecule, it was DNA
This answered a huge question: What was the genetic material?
It also showed that transformation of cells can occur.
Transformation is used two ways:
1. a process where DNA is taken up and expressed by cells
2. where the phenotype changes (from R-strain to S-strain)
What happened in Griffith's experiment.
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Some heat-killed S-strain bacteria released DNA
A few R-strain cells picked it up
A few picked up the gene encoding for encapsulation
know why these transformed cells had an advantage in the mouse & killed them
Genetic Variation & Mutation
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Know that individuals in a population vary due to differing sequence of nucleotides
ultimately this comes from mutation
Know how it allows a population of bacteria to survive exposure to an antibiotic
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There are mechanisms for generating variability
Mutation is the source for all new genetic variation
Existing Variation can be acquired in 3 other ways
Transformation & Genetic Variation
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Transformation (uptake of DNA) can allow existing variation to spread
allowing bacteria to change their genome (express a new gene)
Know why naked DNA taken in relatively infrequently
Transformation in genetic engineering is obtained at high frequency because humans do it
under favorable conditions (know that your instructor has done this--Only kidding!)
Conjugation & Genetic Variation
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Know that Conjugation can allow existing variation to spread in a population
studied the most in E. coli.
Involves the F factor plasmid and F+ cells
Plasmid genes code for specific traits in F+ cells, namely the sex pilus
In sexual conjugation, the plasmid F factor copies and moves into the F- cell
The F- cell transforms into an F+ cell
It expresses new DNA in recipient
Transduction & Genetic Variation
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Know that Transduction can allow existing variation to spread in a population
The bacteriophage (bacteria virus) does it
Viruses take control of the infected host cell to make more viruses
Sometimes by accident host chromosome DNA is put in a new phage instead of viral DNA,
transferring chromosomal DNA to another host cell
This brings new DNA and new traits to the host cell
Cells can regulate their contents by two ways:
1. Cellular Regulation
2. Regulation of Gene Expression
Cellular Regulation
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Cells may regulate their contents by regulating enzymes in Cellular Regulation
Shut down an enzyme, you stop its product from being made
In a metabolic pathway, Feedback inhibition allows the cell to regulate its products by shutting
down one enzyme (often the first) in the pathway
As the product increases, it shuts down the enzyme
As the product decreases, more and more of the enzyme become active
This regulates how much product will be made in a cell
The Regulation of Gene Expression
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Cells do not make a protein when it is not needed, they can stop the transcription mRNA
Know the difference between transcription/translation
Repression and Induction
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Know the lac operon in prokaryotes
RNA polymerase binds to a specific sequence of DNA. (Only one of the two DNA strands is
transcribed)
It binds to DNA at the promoter
The promoter is in front of a structural gene (which codes for a specific protein/product)
In the lac operon, when RNA polymerase comes to the structural gene for lactase, the RNA chain
coding for lactase grows as the polymerase moves down the DNA strand
The RNA polymerase moves down the DNA until it reaches the terminator
Terminators are specific sequences of DNA after the structural gene that tells the RNA
polymerase to fall off the DNA, releasing the transcribed mRNA
The operon includes the structural gene(or genes) and all the regulatory sequences around the
structural gene that regulate its expression
main regulatory sequences: promoter/operator.
A regulatory gene is not a part of the operon, it is another structural gene
Regulatory genes change the expression of another gene
In the lac operon, a regulatory gene makes the repressor molecule, a protein that stops
transcription of lactase and other genes of the lac operon
Repressors, Activators, and Inducers
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If a protein is not needed by the cell, the cell can shut down its gene’s expression
A repressor molecule is a protein that binds the DNA at the operator that stops transcription of
the gene. (The RNA polymerase is stopped from moving past)
Repressor molecules when activated are made by prokaryotes to shut down a structural gene.
This is much more efficient energy wise compared to just shutting down the enzyme.
Another way to regulate transcription is with an activator.
Activators act similar to repressors, but instead enhance gene expression
Inducers enhance gene expression by inactivating a repressor. In the lac operon, the inducer
allolactose (a naturally forming isomer of lactose) binds to & inactivates the repressor protein.
So, the structure of DNA helps regulate gene expression as certain proteins can bind to DNA and
regulate the expression of the structural gene(s).
The Ames Test
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The Ames Test tests to see if a chemical is a mutagen, if it is, we assume that it may be a human
carcinogen because the two are correlated.
The test uses an existing mutation to test if a chemical is mutagenic.
The existing mutation is in the His gene of Salmonella. The mutant Salmonella (His-) cannot
make histidine and will not grow in the media lacking that amino acid.
If a chemical is a mutagen, it will increase the mutation rate, increasing the reversion rate of Histo His+. His+ cells will grow in media lacking histidine.
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In the Ames test, a suspect mutagen is added to a liver extract -which metabolizes the chemical
into many metabolites, similar to the way the body handles the chemical. Then the suspected
mutagen/liver extract is added to the His- Salmonella
The bacteria are plated on media lacking histidine
A control is sample is tested the same only that no mutagen (chemical) is added
If the chemical being tested generates more colonies than the control, then more mutations
have occurred and that the chemical or one of its metabolites must be a mutagen
READINGS 5: AFTER COMPLETING THE READINGS STUDENTS SHOULD BE ABLE TO:
Understand these terms/concepts that are discussed in the Chapter Summary
 genetics, genes, and genomes
 base pairs and complementary base pair bonds
 chromosomes, DNA, histones, and plasmids
 extranuclear DNA in eukaryotes (mitochondria and chloroplasts)
 genotype and phenotype
 forms of RNA, mRNA, tRNA, rRNA and regulatory RNA
 central dogma of genetics (DNA--> RNA--> protein)
 transcription by RNA polymerase:
o promoters and terminators
 operons:
o structural genes, promoter, operator, and regulatory genes
 mutations
 point mutations, frameshifts, gross mutations (macromutations or chromosomal
aberrations)
 transformation
 transduction via a bacteriophage
 conjugation
 Note that "quorum sensing" is discussed in this chapter in later editions of Bauman, we
will discuss this term near the end of the term)