* 27

Question 1

prokaryotic cell wall: role

Answer 1

• 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.

Question 2

prokaryotic cell wall: material

Answer 2

• 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.

Question 3

Gram stain

Answer 3

• 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.

Question 4

Gram-positive

Answer 4

• 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.

Question 5

Gram-negative

Answer 5

• 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.

Question 6

Gram staining in medicine

Answer 6

• 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.

Question 7

penicillin

Answer 7

• 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.

Question 8

capsule

Answer 8

• 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.

Question 9

fimbria

Answer 9

A short, hairlike appendage of a prokaryotic cell that helps it adhere to the substrate or to other cells.

Question 10

pilus (plural pili)

Answer 10

In bacteria, a structure that links one cell to another at the start of conjugation; also known as a sex pilus or conjugation pilus.

Question 11

prokaryotic motility

Answer 11

• 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)

Question 12

bacterial flagellum

Answer 12

• 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.

Question 13

prokaryotes: internal organization

Answer 13

Some have specialized membranes that perform metabolic function, usually infoldings of the plasma membrane.

Question 14

prokaryotes: genetic material

Answer 14

• 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.

Question 15

endospore

Answer 15

• 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.

Question 16

horizontal gene transfer

Answer 16

Movement of genes from one organism to another (diff species) by transformation, transduction, and conjugation.

Question 17

transformation

Answer 17

• 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.

Question 18

bacteriophage

Answer 18

viruses that infect bacteria

Question 19

transduction

Answer 19

• 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).

Question 20

conjugation

Answer 20

• 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.

Question 21

Hfr cell

Answer 21

• High frequency recombination cell

- Has the F factor built into its chromosome (as opposed to having an F plasmid)

Question 22

R plasmid

Answer 22

A bacterial plasmid carrying genes that confer resistance to certain antibiotics.

Question 23

nitrogen fixation

Answer 23

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.

Question 24

biofilm

Answer 24

• 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

Question 25

extreme halophiles

Answer 25

Archaea in a highly saline environment, such as the Great Salt Lake or the Dead Sea.

Question 26

extreme thermophile

Answer 26

• 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.

Question 27

methanogens

Answer 27

• 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.

Question 28

Lyme disease

Answer 28

• 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.

Question 29

exotoxin

Answer 29

• 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

Question 30

endotoxin

Answer 30

• Lipopolysaccharide components of the outer membrane of gram-negative bacteria.
• Released only when the bacteria die and their cell walls break down.
• Ex: Salmonella

Question 31

bioremediation

Answer 31

• 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

Question 32

transduction process

Answer 32

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.

Question 33

F factor

Answer 33

• 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

Question 34

facultative anaerobes

Answer 34

use O2 if it’s present but can also carry out fermentation / anaerobic respiration in an anaerobic enviornment.

Question 35

transfer of F plasmid

Answer 35

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+.

Question 36

transfrer or Hfr chromosome

Answer 36

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.