Exam 2 - Lecture 7 Flashcards
what are the reproductive strategies of eularyotic microbes?
- can be haploid or diploid
- can be asexual or sexual
what are the reproductive strategies of bacteria and archaea?
- haploid
- asexual: binary fission
- all must replicate and segregate the genome before division
what are the steps of binary fission?
- young cell at early phase of cycle
- parents cell enlarges its cell wall, cell membrane and then DNA replication starts
- septum begins to grow inward as chromosomes and other cytoplasmic components move to opposite sides of the cell
- septum completely forms, creating two separate chambers
- at this point, both daughter cells are divided
what is a septum?
a partition that forms during cell division to divide two daughter cells
what kind of growth occurs when a bacterial population is doubling at regular intervals?
exponential growth
what is the generation time (doubling time) of a microbial population?
the times it takes for the population to double in number
what is the growth rate constant (k)?
the number of generations per unit time (n/t)
the generation time is the _________ of the growth rate constant (k)
reciprocal
what is a bacterial cell cycle?
the sequence of events from formation of new cells through the next cell division
what are the two pathways the function during the bacterial cell cycle?
- DNA replication and partition
- cytokinesis: septum formation
true or false: most bacterial chromosomes are linear.
false; most are circular.
what is the origin of replication?
the site at which replication begins
what is the terminus? where is it located?
- the site at which replication is terminated
- located opposite the origin of replication
what is a replisome?
a group of proteins needed for chromosome replication
what is the replication fork?
the Y-shaped structure where DNA is replicated
DNA replication proceeds in both directions from the origin, this is _______________ replication
bidirectional
when the origins move to opposite ends of the cell, this means they are:
partitioned
MreB is an actin homolog that is involved in chromosome ______________
segregation
true or false: if MreB is mutated, chromosomes cannot segregate.
true
define septation.
formation of septa (cross walls) between daughter cells
what are the steps of septation?
- selection of site for septum formation
- assembly of Z ring
- assembly of cell wall synthesizing machinery
- constriction of cell and septum formation
polymerization of ________ leads to Z ring formation.
FstZ
FstZ is a ___________ homolog
tubulin
what does the MinCDE system do?
it limits Z ring formation to the center of the cell
how does the MinCDE system work to limit Z ring formation? which Min actually blocks FstZ binding?
- MinC, MinD, and MinE oscillate from one side of the cell to the other
- MinC blocks FstZ
what are the two proteins that link the Z ring to the plasma membrane?
FstA and ZipA
what does constriction of the Z ring cause in the plasma membrane?
invagination
what is the divisome?
the cell wall synthesis components for Z ring formation in the plasma membrane
what are autolysins?
enzymes that degrade peptidoglycan in a controlled manner by cleaving between NAM and NAG
what are transpeptidases?
peptidoglycan crosslinking enzymes
why are transpeptidases also known as Penicillin Binding Proteins (PBPs)?
because they are the target of the antibiotic penicillin
where does new peptidoglycan form in cocci?
at the central septum only
what type of bacterial cells have no MreB?
cocci-shaped cells
MreB plays a critical role in determining ______ shape
rod
how is MreB distributed along the cell? what does it recruit?
- distributed in helices along the length of the cell
- recruits peptidoglycan synthesis machinery
what determines the shape of vibrio-shaped bacteria? what kind of homologue is it?
crescentin, an intermediate filament homologue
how does crescentin cause the comma shape? which side of the cell will you find the crescentin on?
- crescentin slows down peptidoglycan synthesis
- the “shorter” side contains the crescentin
how do bacteria cope with environmental factors?
- change the conditions
- change the cell
how do bacteria adapt to hypotonic solutions?
- they reduce the osmotic concentration of the cytoplasm
- mechanosensitive channels allow solutes to leave
how do bacteria adapt to hypertonic solutions?
- by increasing the internal solute concentration to increase the internal osmotic conc.
- they use solutes that are compatible with metabolism and growth (like KCl)
halophiles grow optimally at _________ salt concentration or higher
0.2M
extreme halophiles require salt concentrations of _____ to _____
and extremely high concentrations of _____________
- 2M to 6.2M
- potassium (K)
what term is given to microbes that can grow under elevated salt conditions but do not require high salt for growth?
halotolerant
what are the pH ranges for optimal growth for the following microbes?
- acidophiles
- neutrophiles
- alkaliphiles
- pH 0 to 5.5
- pH 5.5 to 7
- pH 8.5 to 11.5
most microbes maintain an internal pH near ___
7
what is the acidic tolerance response?
- pumping protons out of the cell (costs ATP)
- synthesizing acid and heat shock proteins to protect cytoplasmic proteins
the plasma membrane of acidophiles are ____________ to protons
impermeable
why are microbes sensitive to temperature?
- primarily because of enzymes
- microbes cannot regulate their internal temperature
assign temperature ranges to the following categories:
- psychrophiles
- psychrotrophs
- mesophiles
- thermophiles
- hyperthermophiles
- psychrophiles: 0-20 C
- psychrotrophs: 0-35 C
- mesophiles: 20-45 C
- thermophiles: 55-85 C
- hyperthermophiles: 85-113 C
what processes do NOT use oxygen as the terminal oxygen acceptor?
fermentation and anaerobic respiration
between aerobes and obligate aerobes, which requires oxygen to grow and which grows in the presence of atmospheric oxygen (around 20% O2)?
- aerobes: grow in the presence of atmospheric oxygen (around 20% O2)
- obligate aerobes: require O2 to grow
what kind of microbe is usually killed in the presence of oxygen?
olbigate anaerobes
microaerophiles require:
2-10% O2
what are the growth conditions of facultative anaerobes? how about aerotolerant anaerobes?
- facultative: do not require oxygen but grow better in it’s presence
- aerotolerant: grow equally well with or without oxygen
define oxic zone. define anoxic zone.
- oxic: environment where dissolved oxygen is present
- anoxic: environment depleted of dissolved oxygen
oxygen is easily reduced into dangerous molecules called:
reactive oxygen species (ROS)
what are some ROS?
- superoxide radicals
- hydrogen peroxide
- hydroxyl radicals
what are the enzymes aerobes use to protect themselves against ROS?
- superoxide dismutase (SOD)
- catalase
- peroxidase
why can’t strict anaerobes tolerate oxygen?
they either lack or have very low quantities of SOD and catalase
what are barotolerant microbes?
organisms that are adversely affected by high pressure, but not as much as the nontolerant guys
what are barophilic (piezophilic) organisms?
organisms that require high pressure, or grow more optimally at higher pressure
true or false: a larger wavelength on the electromagnetic spectrum means larger energy.
false; smaller wavelengths = more energy.
how does ionizing radiation affect microbes?
- disrupts the chemical structure of many molecules including DNA
- causes mutations, and in turn, death (sterilization)
what is Deinococcus radiodurans?
a polyextremophile that is extremely resistant to DNA damage from radiation, dehydration, cold, vacuum, and acid
what is the wavelength most effectively absorbed by DNA?
260 nm
what do many bacteria produce to protect themselves from photooxidation caused by visible light?
carotenoid pigments (like a natural bacteria sunscreen)
