Introduction to Bacteria Flashcards
Outline the growth cycle & replication of bacteria Contrast the different forms of metabolism utilized by bacteria Define obligate aerobes, obligate anaerobes, facultative anaerobes, microaerophiles; halophiles & thermophiles Describe the process and significance of sporulation Describe how bacteria can modulate gene expression Explain how bacteria exchange genetic information & discuss its medical significance - conjugation, transduction and transformation
What are the phases of cell growth?
- Lag Phase - Adapt to the environment
- Exponential Phase - Rapid bacterial growth
- Stationary Phase - Nutrients become depleted, cell growth = cell death
- Decline - Cells die
What factors affect bacterial cell growth?
Temperature, pH, O2, nutrient availability
What is the difference between selective and differential agar media?
Selective media only allows certain types of bacteria to grow. Differential media allows several bacteria to grow and enables one to differentiate between the types of bacteria.
What is an obligate aerobe?
Requires O2 for growth
What is the classification of a bacteria that cannot grow in the presence of O2?
Obligate anaerobe
In what conditions can facultative anaerobes live?
In either the presence or absence of O2
What are aerotolerant aerobes?
Bacteria that do not use O2 for growth, but are not killed by the presence of O2
These bacteria grow only in the presence of limited O2.
Microaerophilic organisms
These bacteria grow optimally at high temperates, above 50C, but will also grow at lower temperatures.
Faculative Thermophiles
Obligate thermophiles only grow under what conditions?
High temperates above 50C
What bacteria can tolerate high salt concentrations?
Halotolerant halophiles
These bacteria require high salt concentrations for growth.
Obligate halophiles
How do bacteria capture iron from the enivronment?
Bacteria use siderophores to capture environmental iron. Siderophores are also considered a virulence factor because they promote replication.
What are the essential requirements for bacterial growth?
Carbon, nitrogen, energy source, ions, water, essential elements, iron
Where does bacterial catabolism take place?
Catabolism takes place in the external environment. Metabolites then enter cells through active or passive transport.
What catabolic mechanism generates the most energy in cells?
Electron transport chain in aerobic respiration
List all methods of energy product in prokaryotes in order of increasing energy production.
Fermentation < Anaerobic Respiration < Aerobic Respiration
How many molecules of ATP are produced through fermentation?
2 ATP vs. 38 ATP in aerobic respiration
What glycolytic product is utilized in fermentation?
Pyruvate, which is then converted into various end products such as lactic acid
What are the energetic products of the TCA cycle?
GTP, NADH, FADH2
What is the terminal electron acceptor in aerobic respiration?
O2. Nitrate, sulfur, CO2, and ferric ion serve as final electron acceptors in anaerobic respiration.
What is the name and process by which bacterial cells replicate?
Binary fission - DNA replicates and the two chromosomes anchor to separate locations on the cell wall. The membrane grows, pulling the chromosomes apart. The cell wall and plasma membrane grows inward to form a septum, which eventually divides into two cells.
What bacteria produce endospores?
Only gram positive organisms can produce endospores, but not all gram positive bacteria do
These dormant structures are a bacterial survival mechanism resistant to environmental extremes and may survive for many years.
Endospores
How are endospores formed?
DNA is duplicated and a septum is formed. The mother’s cytoplasmic membrane engulfs the spore and forms a double membrane with a peptidoglycan intermembrane space called a cortex. A protein coat forms around the cortex. When the mother cell disintegrates, the spore is released.
How does the bacteria genome differ from that of eukaryotes?
Prokaryotic DNA is circular, haploid, and much smaller than eukaryotic DNA.
What is an operon?
A cluster of genes transcribed together as one mRNA.
These genes encode numerous proteins on a single mRNA transcript.
Polycistronic genes
What is the name given to genomic areas encoding virulence factors that are clustered together and under the control of a single promoter?
Pathoenigicty Islands
Where do repressors bind to the DNA to prevent transcription when certain proteins are not needed?
Operator
What is the purpose of quorum sensing?
Allows for the coordination of gene expression to support a colony of bacteria. This is particularly common in biofilms.
What is the clinical significance of genetic variation?
Contributes to antibiotic resistance and enables bacteria to alter key antigens, recognized by the immune system, that allow them to escape the immune response.
What is antigenic variation?
Changes in the antigenicity of a molecule, or the ability of the immune system to recognize and respond to certain bacterial antigens
What is phase variation?
The ability of bacteria to turn “on” or “off” specific genes that may be recognized by the immune system to warrant a response.
What contributes to genetic variation in bacteria?
Rapid mutation, rapid generation time, acquisition of DNA, biofilm environments
What mechanisms allow for bacterial DNA transfer?
Transformation, conjugation, transduction
These are mobile pieces of DNA that can move within a chromosome or between a chromosome and plasmid.
Insertion sequences and transposons
How can DNA movement affect gene expression?
- Result in the loss of protein function
- Result in the loss of gene regulation
What are transposons?
Complex transposable elements that encode antibiotic resistance and other virulence factors
How do insertion sequences and transposons differ?
Insertion sequences are shorter and less complex than transposons. They also may or may not encode for virulence factors, while transposons always encode virulence factors.
What is the process by which DNA is transferred via a sex pilus?
Conjugation
What is a plasmid?
Small, circular DNA that encodes genes that confer some advantage to bacteria. This is most commonly how antibiotic resistance is shared.
What is the name of a virus that infects bacteria?
Bacteriophage - protein capsids with a genome
What is the process by which bacteria receive DNA from a bacteriophage?
Transduction
In what phase of bacteriophage replication does the cell lysis and die?
Lytic Phase
In this bacteriophage replication cycle, phage DNA is inserted into the bacterial chromosome, which continues to replicate normally.
Lysogenic Phase
What is the process of transformation?
Bacteria take up DNA fragments from the environment. These fragments are then integrated into the bacterial chromosome.
How does high-frequency recombination (Hfr) differ from typical conjugation?
In Hfr, the F plasid has become integrated into the bacterial genome. When conjugation takes place, both the F plasmid and bacterial DNA are transferred. The F- cell remains F-.
What is the clinical significance of lysogenic phages?
- Carry large amounts of host DNA to other infected cells
- May contain exotoxins
