View
220
Download
2
Category
Preview:
Citation preview
5/22/2011
1
Chapter 7 Outline
• Microbial Physiology
– Introduction
– Microbial Nutritional Requirements
– Categorizing Microorganisms According to Their Energy and Carbon Sources
• Metabolic Enzymes
– Biologic Catalysts
– Factors That Affect the Efficiency of Enzymes
• Metabolism
– Catabolism
– Anabolism
• Bacterial Genetics
– Mutations
– Ways in Which Bacteria Acquire New Genetic Information
• Genetic Engineering
• Gene Therapy
Microbial PhysiologyIntroduction
• Physiology is the study of the vital life processes of organisms.
– Microbial physiology is very much chemical reactions (metabolism)
5/22/2011
2
Microbial PhysiologyNutritional Requirements
• All living protoplasm contains 6 major chemical elements: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.
– Combinations of these and other elements make up vital macromolecules of life, including carbohydrates, lipids, proteins, and nucleic acids, vitamins, etc.
• Essential Nutrients:
• materials that organisms are unable to synthesize, but are required for building macromolecules and sustaining life,
• e.g., certain essential amino acids and essential fatty acids.
Categorizing Microorganisms by Energy and Carbon Sources
• Terms relating to an organism’s energy source.
– Phototrophs use light as an energy source.
– Chemotrophs use either inorganic or organic chemicals as an energy source.
• Chemolithotrophsuse inorganic chemicals as an energy source.
• Chemoorganotrophs use organic chemicals as an energy source.
organic
5/22/2011
3
Microbial PhysiologyCategorizing Microorganisms According to Their Energy and Carbon Sources, cont.
• Terms relating to an organism’s carbon source:
– Autotrophs use carbon dioxide (CO2) as their sole source of carbon.
– Heterotrophs use organic compounds other than CO2 as carbon sources.
• Terms that combine both energy and carbon source:
– Photoautotrophs use light as a carbon source and CO2 as an energy source.
– Chemoautotrophs use chemicals as a carbon source and CO2 as an energy source.
– Chemoheterotrophs use chemicals as a carbon source and organic compounds other than CO2 as an energy source.
Categorizing Microorganisms According to Their Energy and Carbon Sources, cont.
• Ecology is the study of the interactions between living organisms and the world around them.
• Ecosystem refers to the interactions between living organisms and their nonliving environment.
• Interrelationships among the different nutritional types are important in the functioning of the ecosystem.
– Example: Phototrophs, such as algae and plants, are the producers of food and oxygen for chemoheterotrophs, such as animals.
5/22/2011
4
Metabolic Enzymes
• Metabolism refers to all the chemical reactions that occur in a cell. The chemical reactions are referred to as metabolic reactions.
– Metabolic reactions are carried out by enzymes.
• Biologic Catalysts
– Enzymes are biologic catalysts; they are proteins that cause a particular chemical reaction to occur or accelerate it.
Metabolic EnzymesBiologic Catalysts, cont.
• Enzymes are specific, they only catalyze one particular chemical reaction.
• An enzyme only affects one particular substance, known as the substrate for that enzyme.
• The unique 3-dimensional shape of an enzyme enables it to fit the substrate like a key fits into a lock.
• http://youtu.be/PILzvT3spCQ
• An enzyme does not become altered during the chemical reaction it catalyzes. (They don’t last forever!)
5/22/2011
5
Factors That Affect the Efficiency of Enzymes
– pH - extreme acidity for example
– Temperature - heat can denature enzymes by breaking bonds
– Concentration of enzyme and/or substrate – may be too high or too low
– Inhibitors, for example heavy metals like lead, zinc, mercury and arsenic
Metabolism
• Metabolism refers to all of the chemical reactions within a cell
• A metabolite is any molecule that is a nutrient, an intermediary product, or an end product in a metabolic reaction.
• Metabolic reactions fall into 2 categories: catabolism and anabolism.
– Catabolism refers to all catabolic reactions in a cell.
– Anabolism refers to all anabolic reactions in a cell.
– http://youtu.be/v0OM-Qjdj88
5/22/2011
6
Metabolism, cont.
• Catabolic reactions involve the breaking down of larger molecules into smaller ones.
– Energy is released. Catabolic reactions are a cell’s major source of energy.
• Anabolic reactions involve the assembly of smaller molecules into larger molecules, requiring the formation of bonds. The bonds are stored energy.
• Much of the energy released during catabolic reactions is used to build molecules in anabolic reactions.
Metabolism, cont.
• Energy is temporarily stored in bonds in adenosine triphosphate (ATP).
• When ATP is used as an energy source, it is hydrolyzed (split) to adenosine diphosphate (ADP).
• ADP can be used as an energy source by hydrolysis to adenosine monophosphate(AMP).
5/22/2011
7
Interrelationships among ATP, ADP,
and AMP molecules.
Metabolism, cont.
Energy is required for metabolic pathways, growth, reproduction, sporulation, and movement of the organism, and active transport of substances across membranes.
a
Marine dinoflagellates use energy for bioluminescence.
5/22/2011
8
MetabolismCatabolism• Catabolic reactions release energy (by breaking bonds) and are a cell’s major source of energy.
– Some energy is lost as heat in catabolic reactions.
• Biochemical pathways are a series of linked biochemical reactions, with a starting chemical and an end product (chemical).
• Think of nutrients as energy sources for organisms and think of chemical bonds as stored energy.
• Glucose, for example, can be catabolizedby either aerobic respiration or fermentation.
• Glycolysis is shared by both: http://youtu.be/pnKih-4SRAE
A biochemical pathway with 4 steps. Compound A is
ultimately converted to compound E. Four enzymes are
required in this biochemical pathway. Compound A is the
substrate for Enzyme 1, Compound B for Enzyme 2, etc.
5/22/2011
9
MetabolismCatabolism, cont.
• Catabolism of glucose by aerobic respiration occurs in 3 phases (each is a biochemical pathway):
– Glycolysishttp://youtu.be/6JGXayUyNVw
– The Krebs cycle
– The electron transport chain
• The 1st phase (glycolysis) is anaerobic, but the other 2 phases are aerobic. So, the whole process is considered aerobic.
• Glycolysis is a 9-step biochemical pathway. Each step requires a specific enzyme.
Aerobic Respiration of
Glucose:
First Step = Glycolysis.
5/22/2011
10
CatabolismAerobic Respiration of Glucose, cont.
• The Krebs Cycle, aka citric acid cycle and TCA cycle:
– A biochemical pathway consisting of 8 separate reactions, each controlled by a different enzyme.
– Only 2 ATP molecules are produced, but NADH, H+, FADH2 are formed, which enter the electron transport chain.
• In eucaryotes, the Krebs/TCA cycle and the electron transport chain occur in mitochondria.
• In procaryotes, both occur at the inner surface of the cell membrane.
CatabolismAerobic Respiration of Glucose, cont.• The electron transport chain:
– A series of oxidation-reduction reactions, where energy is released as electrons which are transferred from one compound to another.
– Many enzymes are involved in the electron transport chain, including cytochrome oxidase,which transfers electrons to oxygen (the electron final acceptor).
– A large number of ATP molecules are produced by oxidative phosphorylation in the electron transport chain. http://youtu.be/DNReloT3QYU
• Aerobic respiration is very efficient!
5/22/2011
11
CatabolismFermentation of Glucose
• Fermentation reactions do not involve oxygen. They take place in anaerobic (no oxygen) environments.
– First step is glycolysis(anaerobic).
– The next step is conversion of pyruvic acid into an end product.
– The end product varies from one organism to another. Example: yeasts are used to make wine and beer; the end product is ethanol.
– Fermentation reactions produce very little energy, ~ 2 ATP molecules.
CatabolismOxidation-Reducton (Redox) Reactions• Oxidation-reduction reactions are paired reactions in which electrons are transferred from one compound to another.
• Oxidation occurs whenever an atom, ion, or molecule loses one or more electrons in a reaction; in which case, the molecule is said to be oxidized.
• The gain of one or more electrons by a molecule is called reduction and the molecule is said to be reduced.
• Within a cell, an oxidation reaction is always paired with a reduction reaction; hence the term, oxidation-reduction reaction.
5/22/2011
12
CatabolismOxidation-Reduction (Redox) Reactions, cont.
• In a redox reaction, the electron donor (compound A) is the reducing agent, and the electron acceptor (compound B) is the oxidizing agent.
• Many biologic oxidations are referred to as dehydrogenation reactionsbecause hydrogen ions, as well as electrons, are removed.
Anabolism
• Anabolic reactions require energy because chemical bonds are being formed. The energy that is used comes from catabolic reactions, which are occurring simultaneously.
• Biosynthesis of organic compounds requires energy. The energy may be obtained through photosynthesis (from light) or chemosynthesis (from chemicals).
– Photosynthetic reactions trap the radiant energy of light and convert it into chemical bond energy in ATP and carbohydrates (e.g., glucose).
5/22/2011
13
Bacterial Genetics
• Genetics = the study of heredity.
• An organism’s genotype is its complete collection of genes.
• An organism’s phenotype refers to its physical traits (e.g., includes hair and eye color in humans).
• An organism’s phenotype is the manifestation of that organism’s genotype because genes control all functions of the cell.
• Gene: a particular segment of the chromosome.
Bacterial GeneticsMutations
• A change in a DNA molecule (genetic alteration) that is transmissible to offspring is called a mutation.
– 3 categories of mutations:
• Beneficial mutations
• Harmful mutations (some are lethal mutations)
• Silent mutations
• Mutation rate (the rate at which mutations occur) can be increased by exposing cells to physical or chemical agents called mutagens.
• The organism containing the mutation is called a mutant.
5/22/2011
14
Bacterial GeneticsWays in Which Bacteria AcquireNew Genetic Information
• Ways in which bacteria acquire new genetic information (i.e., acquire new genes):
– Lysogenic Conversion
– Transduction
– Transformation
– Conjugation
• An extrachromosomal DNA molecule is called a plasmid. An organism that acquires a plasmid acquires new genes.
(A) A disrupted E. coli cell, in which the DNA has
spilled out. A plasmid can be seen slightly to the left
of top center (arrow). (B) Enlargement of plasmid.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
5/22/2011
15
Ways in Which Bacteria Acquire New Genetic Information, cont.
• Lysogenic Conversion
– Temperate phages (or lysogenic phages) inject their DNA into a bacterial cell.
– The phage DNA integrates into the bacterial chromosome, but does not cause the lytic cycle to occur – this is known as lysogeny. This is the opposite of a lytic cycle, that causes the lytic cycle TO occur, resulting in the lysis (rupturing) of the host cell.
– A phage is called a prophage (early or first phage/virus)
when all that remains of it is its DNA.
– The bacterial cell containing the prophage is referred to as a lysogenic cell.
– The bacterial cell exhibits new properties, directed by the viral genes – this is referred to as lysogenic conversion.
5/22/2011
16
how Bacteria Acquire New Genetic Information, cont.
• Transduction (“to carry across”):
– Also involves bacteriophages.
– In transduction, bacterial genetic material is “carried across” from one bacterial cell to another by a bacterial virus; thus, in transduction, bacteria acquire new bacterial genes.
– Note how this differs from lysogenic conversion, wherein bacteria acquire new genetic information in the form of viral genes.
How Bacteria Acquire New Genetic Information, cont.
• Transformation
– A bacterial cell becomes genetically transformed following the uptake of DNA fragments (“naked DNA”) from its environment.
– The ability to absorb naked DNA into the cell is called competence and bacteria capable of absorbing naked DNA are said to be competent bacteria.
5/22/2011
17
How Bacteria Acquire New Genetic Information, cont.
• Conjugation
– Involves a specialized type of pilus called a sex pilus.
– A bacterial cell with a sex pilus (called the donor cell) attaches by means of the sex pilus to another bacterial cell (called the recipient cell).
– Some genetic material (usually a plasmid) is transferred through the hollow sex pilus from the donor cell to the recipient cell.
– A plasmid that contains multiple genes for antibiotic resistance is known as a resistance factor or R-factor. A bacterial cell that receives a R-factor becomes a“superbug.”
Conjugation in Escherichia coli.
Sex pilus
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
5/22/2011
18
Genetic Engineering
• Genetic engineering or recombinant DNA technology involves techniques to transfer eucaryotic genes (particularly human genes) into easily cultured cells to manufacture important gene products (mostly proteins).
• Plasmids are frequently used as vehicles for inserting genes into cells.
• There are many industrial and medical benefits from genetic engineering.
– Examples: synthesis of antibodies, antibiotics, drugs and vaccines; also, for synthesis of important enzymes and hormones for treatment of diseases.
Gene Therapy
• Gene therapy of human diseases involves the insertion of a normal gene into cells to correct a specific genetic disorder caused by a defective gene.
• Viral delivery is the most common method for inserting genes into cells; specific viruses are selected to target the DNA of specific cells.
• Genes may someday be regularly prescribed as “drugs” in the treatment of diseases (e.g., autoimmune diseases, sickle cell anemia, cancer, cystic fibrosis, heart disease, etc.)
Recommended