Chapter 3 Flashcards
(53 cards)
1
Q
Most bacteria share fundamental traits
A
- Thick, complex outer envelope
- Compact genome
- Tightly coordinated cell functions, regulation
2
Q
Cytoplasm
A
filled with ions of salts, small-molecule metabolites, enzymes, structural proteins, ribosomes, mRNA, tRNA, etc.
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
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)
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
6
Q
Nucleoid
A
non-membrane-bound area of the cytoplasm that contains the compacted chromosome, composed of DNA and proteins
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)
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
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.
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
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.
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.
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
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.
15
Q
Passive transport
A
molecules move along their concentration gradient
16
Q
Active transport
A
- molecules move against their concentration gradient
- Requires energy from ATP or an ion gradient
17
Q
Examples of polar and charged molecules
A
Polar
- amino acids
- sugar molecules
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
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)
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
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
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
Gram-Positive and Gram-Negative Bacteria
-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
Firmicutes
- gram positive
| - bacillus
27
Actinobacteria
- gram positive
| - streptomyces
28
Proteobacteria
- gram negative
- escherichia (E. coli)
- mitochondria
29
Gram Positive
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
Gram negative
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
S-layer
- 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
Eukaryotic Microbes
- 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
Bacterial Cytoskeleton
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
a nucleoid
- contains the chromosome composed of DNA and proteins
| - region in the cytoplasm
35
DNA Is Organized in the Nucleoid
- chromosome is compacted with about 50 loops or domains.
| - Within each domain, the DNA is supercoiled by gyrase enzyme and DNA-binding proteins
36
Transcription and Translation
- 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
Protein Synthesis and Secretion
- 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
Cell Division
- 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
Polysome
-mRNA with multiple ribosomes attached
40
DNA Is Replicated Bidirectionally
- 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
septum
- 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
Thylakoids
extensively folded intracellular photosynthetic membranes
43
Carboxysomes
polyhedral bodies packed with the enzyme Rubisco enzyme for CO2 fixation
44
Gas vesicles
to increase buoyancy, protein shell filled with air
45
Storage granules
- Glycogen for energy
| - Sulfur, for oxidation
46
Magnetosomes
- 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
Pili
- fimbriae are filaments of pilin protein
| - Used in attachment
48
Sex pili
- are used in conjugation
| - gene transfer mechanism
49
Stalks
- membrane-embedded extensions of the cytoplasm.
| - Tips secrete adhesion factors called holdfasts
50
Flagella
- 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
Flagella mechanism
- 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
Chemotaxis
- 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
Chemotaxis- Receptor proteins
- 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
