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Bacteriology > Chapter 3 > Flashcards

Chapter 3 Flashcards

1
Q

Most bacteria share fundamental traits

A
  • Thick, complex outer envelope
  • Compact genome
  • Tightly coordinated cell functions, regulation
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2
Q

Cytoplasm

A

filled with ions of salts, small-molecule metabolites, enzymes, structural proteins, ribosomes, mRNA, tRNA, etc.

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3
Q

Cell envelope

A

everything outside of the cytoplasm, which includes:

  • Cell membrane- encloses the cytoplasm
  • Cell wall- outside the cell membrane, usually peptidoglycan
  • Additional layers, such as the outer membrane
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4
Q

Cell fractionation

A
  • Cells are broken by techniques that allow subcellular parts to remain intact
  • the different parts are separated and analyzed
Breakage methods include:
Mild detergents
Sonication
Enzymes
Mechanical disruption (bead beater)
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5
Q

ultracentrifuge

A
  • key tool of subcellular fractionation
  • High rotation rates produces centrifugal forces strong enough to separate particles by size.
  • Parts are then subjected to structural and biochemical analysis
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6
Q

Nucleoid

A

non-membrane-bound area of the cytoplasm that contains the compacted chromosome, composed of DNA and proteins

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7
Q

Flagellum

A

major external structure, external helical filament made of proteins, rotary motor at base, propels the cell (only present in some species)

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8
Q

genetic analysis

A

-Forward genetics: random mutagenesis followed by isolation of mutant strains that are selected or screened for loss of a given function
-Reverse genetics: specific genes in a genome sequence are inactivated or altered
-Strains that are constructed with reporter genes fused to a gene encoding a protein of interest
to more easily study the protein of interest
-The phenotype of the mutant cell may yield clues about the function of the altered part

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9
Q

Biochemical Composition of Bacteria

A

All cells share common chemical components:

  • Water
  • Essential ions- sodium, potassium, magnesium, phosphate, chloride, etc.
  • Small organic molecules- metabolites and monomer building blocks and Amino acids, nucleotides, sugars, lipids
  • Macromolecules- polypeptides, polynucleotides, polysaccharides,

-Cell composition varies with species, growth phase, and environmental conditions.

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10
Q

The Cell Membrane and Transport

A
  • The structure that defines the boundary of a cell
  • stiffening agents such as hopanoids, which serve the same function as cholesterol in eukaryotic membranes.
  • Half the volume of the membrane consists of proteins
  • unlike eukaryotic membrane, bacterial membrane is similar to that of mitochondria and has structures like ATP synthase to make ATP
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11
Q

Membrane Lipids

A
  • Membranes have approximately equal parts of phospholipids and proteins.
  • A phospholipid consists of glycerol with ester links to two fatty acids and a phosphoryl head group
  • The two layers of phospholipids in the membrane bilayer are called leaflets.
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12
Q

Phosphatidylethanolamine

A
  • contains a glycerol linked to two fatty acids, and a phosphoryl group with a terminal ethanolamine.
  • The ethanolamine carries a positive charge.
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13
Q

Membrane Proteins

A

Functions:

  • Structural support
  • Receptor proteins detect molecules in the environmental
  • Secretion of enzymes, virulence factors, and communication signals transport
  • Energy conversions and storage
  • Cell motility
  • Membrane proteins have hydrophilic and hydrophobic regions that lock the protein in the membrane
  • structure determines function
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14
Q

Selective transport

A
  • is essential for cell function
  • Small uncharged molecules, such as O2 and CO2, easily move across the membrane by diffusion.
  • Water, a very small polar molecule, can slowly diffuse across the membrane in a process called osmosis.
  • Sugar monomers, polar but bigger, cannot cross the membrane and must be transported
  • Charged molecules such as ions and amino acids cannot cross membranes and must be transported
  • Weakly charged acids and bases, such as some drugs, exist partly in an uncharged form that can diffuse slowly across membranes.
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15
Q

Passive transport

A

molecules move along their concentration gradient

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16
Q

Active transport

A
  • molecules move against their concentration gradient

- Requires energy from ATP or an ion gradient

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17
Q

Examples of polar and charged molecules

A

Polar

  • amino acids
  • sugar molecules
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18
Q

Membrane Lipid Diversity

A

Phospholipids vary with respect to their phosphoryl head groups and their fatty acid side chains.

  • Fatty acid chain lengths are usually vary from 16 to 20 carbons
  • Fatty acid chains may be saturated (no double bonds)
  • Fatty acid chains may be unsaturated (contain double bonds), and may also contain cyclic structures
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19
Q

planar neutral lipid molecules

A
  • fill gaps between (fatty) hydrocarbon chains.
  • In eukaryotic membranes, the reinforcing agents are sterols, such as cholesterol.
  • In bacteria, the same function is filled by hopanoids (hopanes)
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20
Q

Archaea have different phospholipid structures

A
  • instead of a bilayer it has a monolayer
  • Ether links (bonds) between glycerol and fatty acids
  • Hydrocarbon chains are branched terpenoids
  • Tetraether lipids form monolayer membranes that are more stable at high temperatures
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21
Q

The Cell Wall and Outer Layers

A

cell envelope includes at least one structural supporting layer:

  • The most common structural support is the cell wall made of peptidoglycan
  • a few prokaryotes, such as the parasitic mycoplasmas, have a cell membrane with no outer layers
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22
Q

cell wall

A
  • confers shape and rigidity to the cell, and helps it withstand turgor pressure.
  • also called the sacculus
  • consists of a single interlinked molecule
23
Q

peptidoglycan

A
  • what most bacterial cell walls are made of
  • also called murein

molecule consists of:

  • Long glycan polymers of disaccharides made of two modified sugars: N-acetylglucosamine (NAG, G) and N-acetylmuramic acid (NAM, M)
  • NAG and NAM alternate along the polymer strands
  • A peptide of four to six amino acids is attached to NAM
  • The peptides can form cross-bridges connecting the parallel glycan strands, producing a meshwork
24
Q

Peptidoglycan is unique to bacteria

A
  • the enzymes responsible for its biosynthesis make excellent targets for antibiotics
  • Penicillin inhibits the transpeptidase that cross-links the peptides
  • Vancomycin prevents cross-bridge formation by binding to the terminal D-Ala-D-Ala dipeptide
  • Unfortunately, the widespread use of such antibiotics selects for evolution of resistant strains
25
Q

Gram-Positive and Gram-Negative Bacteria

A

-Most bacteria have additional envelope layers that provide structural support and protection.

Envelope composition defines:

  • Gram-positive bacteria (thick peptidoglycan cell wall) like Bacillus
  • Gram-negative bacteria (thin peptidoglycan cell wall) like E. coli
26
Q

Firmicutes

A
  • gram positive

- bacillus

27
Q

Actinobacteria

A
  • gram positive

- streptomyces

28
Q

Proteobacteria

A
  • gram negative
  • escherichia (E. coli)
  • mitochondria
29
Q

Gram Positive

A

cell membrane -> thick peptidoglycan layer -> S-layer (protein) -> glycosyl chains ( sugars so protect themselves from the environment)

  • multiple layers of peptidoglycan that a threaded by teichoic acids
  • glycoprotein- Protects cells from phagocytosis and also found in Gram-negative cells
30
Q

Gram negative

A

cell membrane (inner membrane) -> periplasm (contains a lot of different proteins) ->thin peptidoglycan layer -> lipoproteins (protein that also has a lipid attached to it to connect the two layers) outer membrane ( LPS- helps protect the cell and with immune response)

-Porins- integral pore-forming protein along the outer membrane

31
Q

S-layer

A
  • An additional protective layer commonly found in free-living bacteria and archaea
  • Crystalline layer of subunits consisting of protein or glycoprotein
  • May contribute to cell shape and help protect the cellfrom osmotic stress
32
Q

Eukaryotic Microbes

A
  • possess their own structures to avoid osmotic shock.
  • Algae form cell walls of cellulose.
  • Fungi form cell walls of chitin
  • Diatoms form exoskeletons of silicate
  • Paramecia possess a contractile vacuole to pump water out of the cell
33
Q

Bacterial Cytoskeleton

A

Shape-determining proteins
FtsZ = forms a “Z-ring” at center of cell
-related to tublin
- helps the cell to divide

MreB = forms a coil inside rod-shaped cells
- Required for FtsZ to find the center of rod-shaped cells

34
Q

a nucleoid

A
  • contains the chromosome composed of DNA and proteins

- region in the cytoplasm

35
Q

DNA Is Organized in the Nucleoid

A
  • chromosome is compacted with about 50 loops or domains.

- Within each domain, the DNA is supercoiled by gyrase enzyme and DNA-binding proteins

36
Q

Transcription and Translation

A
  • RNA polymerase transcribes DNA into a single strand of RNA.
  • Because there is no nucleus or nuclear envelope, mRNA immediately binds to a ribosome for translation into a polypeptide, even before it is finished being transcribed.
  • Translation involves transfer RNA (tRNA), which brings the amino acids to the ribosome and reads codons.
  • translation is tightly coupled to transcription.
  • no mRNA processing or splicing
37
Q

Protein Synthesis and Secretion

A
  • In prokaryotes, membrane proteins and secreted proteins are synthesized in association with the cell membrane.
  • This is aided by the signal recognition particle (SRP), which binds to the growing peptide and delivers it to the membrane.
38
Q

Cell Division

A
  • Cell division, or cell fission, requires highly coordinated growth and expansion of all the cell’s parts.
  • prokaryotes synthesize RNA and proteins continually while the cell’s DNA undergoes replication.
  • Bacterial DNA replication is coordinated with the cell wall expansion
  • In prokaryotes, cells typically divide by binary fission
39
Q

Polysome

A

-mRNA with multiple ribosomes attached

40
Q

DNA Is Replicated Bidirectionally

A
  • a circular chromosome begins to replicate at its origin, or ori site.
  • Two replications forks are generated, which proceed outward in both directions.
  • DNA is synthesized by DNA polymerase with the help of accessory proteins (the replisome).
  • As the termination site is replicated, the two forks separate from the DNA and release the 2 daughter chromosomes.
41
Q

septum

A
  • Replication of the termination site triggers growth of the dividing partition
  • The septum grows inward, at last constricting and sealing off the two daughter cells
  • spatial orientation of septation has a key role in determining the shape and arrangement of cocci
  • Parallel planes -Streptococci, chain
  • Random planes- Staphylococci, cluster
  • Perpendicular planes -Tetrads, 4 cells
42
Q

Thylakoids

A

extensively folded intracellular photosynthetic membranes

43
Q

Carboxysomes

A

polyhedral bodies packed with the enzyme Rubisco enzyme for CO2 fixation

44
Q

Gas vesicles

A

to increase buoyancy, protein shell filled with air

45
Q

Storage granules

A
  • Glycogen for energy

- Sulfur, for oxidation

46
Q

Magnetosomes

A
  • Membrane-embedded crystals of magnetite, Fe3O4
  • Use the Earth’s magnetic field to orient the swimming of magnetotactic bacteria
  • helps to orient them so they know up from down which will help them find oxygen
47
Q

Pili

A
  • fimbriae are filaments of pilin protein

- Used in attachment

48
Q

Sex pili

A
  • are used in conjugation

- gene transfer mechanism

49
Q

Stalks

A
  • membrane-embedded extensions of the cytoplasm.

- Tips secrete adhesion factors called holdfasts

50
Q

Flagella

A
  • swim by means of rotary flagella
  • Peritrichous cells have flagella randomly distributed around the cell
  • Lophotrichous cells have flagella at the end(s)
  • Monotrichous cells have a single flagellum
51
Q

Flagella mechanism

A
  • a spiral filament made of of protein monomers called flagellin.
  • rotated by a molecular motor in the cell envelope driven by the proton motive force, PMF.
  • can rotate both clockwise (CW) or counterclockwise (CCW) relative to the cell.
52
Q

Chemotaxis

A
  • is the movement of a bacterium in response to chemical gradients.

Attractants

  • cause mostly CCW rotation of flagella.
  • Flagella bundle together
  • Push cell forward
  • Cells “Run” in a mostly straight path

Repellents

  • cause CW rotation.
  • Flagellar bundle falls apart
  • The bacterium tumbles briefly, which causes a change in direction
53
Q

Chemotaxis- Receptor proteins

A
  • in the membrane
  • detect attractant and repellant chemical concentrations
  • Attractants include sugars and amino acids
  • Repellants include certain noxious chemicals
  • Increasing attractant concentration increases and prolongs runs in a relatively straight path and causes a net movement of bacteria toward attractants
  • Similarly, bacteria move away from repellent molecules

Bacteriology (16 decks)

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