* 27 Flashcards
1
Q
prokaryotic cell wall: role
A
- Maintain shape, protect, prevent from bursting in a hypotonic environment.
- In a hypotonic environment, most prokaryotes lose water and shrink away from the wall (plasmolyze). Such water losses can inhibit cell reproduction.
2
Q
prokaryotic cell wall: material
A
- Bacteria: peptidoglycan, a polymer composed of modified sugars cross-linked by short polypeptides. This molecular fabric encloses the entire bacterium and anchors other molecules that extend from its surface.
- Archaea: a variety of polysaccharides and proteins but lack peptidoglycan.
3
Q
Gram stain
A
- A staining method that distinguishes between two different kinds of bacterial cell walls.
- Samples are first stained w/ crystal violet dye and iodine, then rinsed in alcohol, and finally stained w/ a red dye such as safranin.
- The structure of a bacterium’s cell wall determines the staining response.
4
Q
Gram-positive
A
- Describing the group of bacteria that have a cell wall that is structurally less complex and contains more peptidoglycan than the cell wall of gram-negative bacteria. These bacteria are usually less toxic than gram-negative bacteria.
- have a thick cell wall made of peptidoglycan,
which traps the crystal violet in the cytoplasm. The
alcohol rinse does not remove the crystal violet, which masks
the red safranin dye.
5
Q
Gram-negative
A
- Describing the group of bacteria that have a cell wall that is structurally more complex and contains less peptidoglycan than the cell wall of gram-positive bacteria. These bacteria are often more toxic than gram-positive bacteria.
- have a thinner layer of peptidoglycan,
and it is located in a layer between the plasma membrane and
an outer membrane. The crystal violet is easily rinsed from the
cytoplasm, and the cell appears pink or red from the dye.
6
Q
Gram staining in medicine
A
- Gram-negative: The lipid portions of the lipopolysaccharides in the walls of many gram-negative bacteria are toxic, causing fever/shock. Outer membrane helps protect it from the body’s defenses. More resistant than gram-positive species b/c the outer membrane impedes entry of the drugs.
- Some gram-pos species have virulent strains that are resistant to one or more antibiotics.
7
Q
penicillin
A
- The effectiveness of certain antibiotics, such as penicillin, derives from their inhibition of peptidoglycan cross-linking. The resulting cell wall may not be functional, esp in gram-pos bacteria.
- Such drugs don’t adversely affect human cells, which don’t have peptidoglycan.
8
Q
capsule
A
- The cell wall of many prokaryotes is surrounded by a sticky layer of polysaccharide or protein.
- If this layer is dense and well-defined: called a capsule
- If less well organized: called a slime layer
- Enable prokaryotes to adhere to their substrate / to other individuals in a colony.
- Protect against dehydration / shield pathogenic prokaryotes from attacks by host’s immune system.
9
Q
fimbria
A
A short, hairlike appendage of a prokaryotic cell that helps it adhere to the substrate or to other cells.
10
Q
pilus (plural pili)
A
In bacteria, a structure that links one cell to another at the start of conjugation; also known as a sex pilus or conjugation pilus.
11
Q
prokaryotic motility
A
- Flagella are most common
- Prokaryotic flagella: 1/10th the width of eukaryotic flagella and aren’t covered by an extension of the plasma membrane. Differ from eukaryotic flagella in their molecular composition and mechanism of propulsion.
- Bacterial and archaeal flagella are similar in size and rotation mechanism, but are composed of different proteins.
- Flagella are analogous structures (convergent evolution)
12
Q
bacterial flagellum
A
- 3 main parts: motor, hook, filament; composed of 42 diff proteins
- Evolved as other proteins were added to an ancestral secretory system – an example of exaptation, when existing structures take on new functions thru descent w/ modification
- The motor of a prokaryotic flagellum consists of a
system of rings embedded in the cell wall and plasma membrane (TEM). ATP-driven pumps in
the motor transport protons out of the cell. The diffusion of protons back into the cell provides
the force that turns a curved hook and thereby causes the attached filament to rotate and propel
the cell.
13
Q
prokaryotes: internal organization
A
Some have specialized membranes that perform metabolic function, usually infoldings of the plasma membrane.
14
Q
prokaryotes: genetic material
A
- Less DNA than eukaryotes
- In most prokaryotes, the genome consists of a circular chromosome – found in the nucleoid – w/ many fewer proteins than found in the linear chromosomes of eukaryotes.
- May also contain plasmids, much smaller rings of independently replicating DNA molecules that carry only a few genes.
15
Q
endospore
A
- Certain bacteria develop resistant cells called endospores when they lack an essential nutrient.
- The original cell produces a copy of its chromosome and surrounds it w/ a tough multilayered structure.
- Water is removed from the endospore and its metabolism halts.
- The original cell then lyses, releasing the endospore.
16
Q
horizontal gene transfer
A
Movement of genes from one organism to another (diff species) by transformation, transduction, and conjugation.
17
Q
transformation
A
- Many bacteria have cell-surface proteins that recognize DNA from closely related species and transport it into the cell.
- Nonpathogenic cell takes up a piece of DNA carrying the allele for pathogenicity and replaces its own allele w/ the foreign allele, an exchange of homologous DNA segments.
18
Q
bacteriophage
A
viruses that infect bacteria
19
Q
transduction
A
- Phages carry prokaryotic genes from one host cell to another.
- Most cases, results from accidents that occur during the phage replicative cycle. A virus that carries prokaryotic DNA may not be able to replicate b/c it lacks some or all of its own genetic material. However, the virus can attach to another prokaryotic cell (a recipient) and inject prokaryotic DNA acquired from the first cell (the donor).
20
Q
conjugation
A
- DNA is transferred btwn 2 prokaryotic cells (of same species) that are temporarily joined.
- E. coli: a pilus of the donor cell attaches to the recipient. The pilus then retracts, pulling the 2 cells together. Then, a “mating bridge” forms, or the DNA passes directly thru the hollow pilus.
- This can be done b/c of the presence of a particular piece of DNA called the F factor.
21
Q
Hfr cell
A
- High frequency recombination cell
- Has the F factor built into its chromosome (as opposed to having an F plasmid)
22
Q
R plasmid
A
A bacterial plasmid carrying genes that confer resistance to certain antibiotics.
23
Q
nitrogen fixation
A
Process whereby some cyanobacteria and some methanogens (a group of archaea) convert atmospheric nitrogen (N2) to ammonia (NH3). The cells incorporate this “fixed” nitrogen into amino acids and other organic molecules.
24
Q
biofilm
A
- Surface-coating colony that allows metabolic cooperation btwn different prokaryotic species
- Cells in a biofilm secrete signaling molecules that recruit nearby cells
- Produce polysaccharides and proteins that stick the cells to the substrate and to one another
- Channels allow nutrients to reach cells in the interior and wastes to be expelled
25
extreme halophiles
Archaea in a highly saline environment, such as the Great Salt Lake or the Dead Sea.
26
extreme thermophile
- An organism that thrives in hot environments (often 60-80°C or hotter).
- At temperatures this high, the cells o most organisms die b/c, for example, their DNA doesn't remain in a double helix and many of their proteins denature.
- Most belong to the clade Crenarchaeota; others belong to Euryarchaeota.
27
methanogens
- May live in moderate or extreme environments.
- Archaea that release methane as a by-product of their unique ways of obtaining energy. Many use CO2 to oxidize H2, a process that produces both energy and methane waste.
- Poisoned by O2.
- All belong to the clade Euryarchaeota.
28
Lyme disease
- The most widespread pest-carried disease in the US.
- Caused by a bacterium carried by ticks that live on deer and field mice.
- Can result in debilitating arthritis, heart disease, nervous disorders, and death if untreated.
29
exotoxin
- A toxic protein that is secreted by a prokaryote or other pathogen and that produces specific symptoms, even if the pathogen is no longer present.
- Cholera: Vibrio cholerae secretes an exotoxin, which stimulates intestinal cells to release chloride ions into the gut, and water follows by osmosis.
- Botulism
30
endotoxin
- Lipopolysaccharide components of the outer membrane of gram-negative bacteria.
- Released only when the bacteria die and their cell walls break down.
- Ex: Salmonella
31
bioremediation
- Allows us to harness prokaryotes.
- The use of organisms to detoxify and restore polluted and degraded ecosystems.
- Ex: decompose organic matter in sewage, converting it to material that can be used as landfill or fertilizer after chemical sterilization; cleaning up oil spills, precipitating radioactive material out of groundwater
32
transduction process
1. phage infects a bacterium (donor) w/ A+ and B+ alleles on its chromsome
2. phage DNA is replicated. bacterium makes many copies of the proteins encoded by the phage DNA's genes. certain phage proteins halt the synthesis of proteins encoded by the host cell's DNA, and host's DNA may be fragmented.
3. new phage particles assemble. a fragment of bacterial DNA carrying A+ allele happens to be packaged in a phage capsid.
4. the phage carrying the A+ allele from the donor infects a recipient cell w/ alleles A- and B-. recombination btwn donor and recipient DNA produces A+B- genotype.
33
F factor
- of E coli, consists of about 25 genes, most required for the production of pili.
- can exist either as a plasmid or as a segment of DNA w/in bacterial chromosome.
- cells containing F plasmid function as DNA donors; cells w/o function as DNA recepients
34
facultative anaerobes
use O2 if it's present but can also carry out fermentation / anaerobic respiration in an anaerobic enviornment.
35
transfer of F plasmid
1. F+ cell forms mating bridge w/ F- cell. one strand of the F plasmid's DNA breaks at a point.
2. using the unbroken strand as a template, the F+ cell synthesizes a new strand. meanwhile, the broken strand peels off and enters the F- cell. there, synthesis of the complementary strand begins
3. once synthesis is completed, the plasmid in the recipient cell circularizes. now both cells are F+.
36
transfrer or Hfr chromosome
1. Hfr cell forms mating bridge w/ F- cell.
2. a single strand of the F factor breaks and begins to move thru the bridge. DNA replication occurs in both donor and recipient cells
3. mating bridge usually breaks before the entire chromosome is transferred. DNA recombination can result in the exchange of homologous genes btwn the transferred DNA and the receipient's chrosome
4. cellular enzymes degrade any linear DNA not incorporated into the chromosome. the recipient cell, w/ a new combination of genes but no F factor, is now a recombinant F- cell.
