Bacterial Structures Flashcards
(57 cards)
1
Q
What is the average diameter, SA, volume, and SA:V ratia of bateria?
A
- Diameter = 0.5 to 2 micrometers
- SA = 12 micrometers^2
- Volume = 4 micrometer
- SA:V ratio = 3:1 (ie… if r = 1 um, SA:V = 3; if r = 2 um, SA:V = 1.5)
2
Q
Why is a large SA:V ratio important?
A
Bacteria make ATP on membranes. They need enough membrane for metabolic reactions. It also makes it easier for nutrients to diffuse throughout the entire cell (food will enter through SA and quickly reaches all parts). Cells can also reprouduce and evolve faster.
3
Q
How is the SA:V ratio different in eukaryotes?
A
The ratio is 0.3:1, which is much smaller than bacteria. They need structures and organelles.
4
Q
What is the size range for prokaryotes vs. eukaryotes?
A
Prokaryotes: 0.2 to 700 micrometers
Eukaryotes: 10 to 200 micrometers
5
Q
Describe the coccus shape.
A
Sphere
ie… streptococcus, staphylococcus aureus (yellow when it grows)
6
Q
Describe the bacillus shape.
A
Rod, straight
ie… E. coli, Pseudomonas aeruginosa, Salmonella
7
Q
Describe the coccobacillus shape.
A
Not really used anymore, in between sphere and rod.
ie… Chlamydia trachomatis
8
Q
Describe the vibrio shape.
A
Curved rod
ie… Vibrio cholerae
9
Q
Describe the spirillum shape.
A
Wavy rod, flexible
ie… Rhodospirillum
10
Q
Describe the spirochete shape.
A
Corkscrew shape, rigid (can fit through lots of holes/filters)
ie… Borrelia burgdorferi (Lyme disease), Treponema pallidum (syphilis)
11
Q
The shape of bacteria is determined by…
A
The cell wall. If there is no cell wall, shape is determined by the environment. (Shapes progressively get longer and skinnier because of SA:V ratio)
12
Q
Describe a diplo- arrangement.
A
Pair
12
Q
Describe a stepto- arrangement.
A
Chain
13
Q
Describe a tetrad arrangement.
A
Group of 4
14
Q
Describe a staphylo- arrangement.
A
Grape-like cluster
15
Q
Describe a sarcina arrangement.
A
2 tetrads together
16
Q
Describe the structure of the bacterial cytoplasmic membrane.
A
- Thin structure, surrounds the cell, 6-8 nanometers thick
- Phospholipid bilayer (with proteins) has hydrophobic and hydrophilic parts - can exist in various forms depending on the groups attached to the glycerol backbone
- Membrane is fluid - depending on type of fatty acids/phospholipids, fluidity changes depending on env.
17
Q
Describe the funciton of the bacterial cytoplasmic membrane.
A
- Barrier that separates cytoplasm from the environment
- Highly selective permeable barrier, enables concentration of specific metabolites and excretion of waste products (discriminating conduit)
- Protein anchor (proteins can be used to sense environment, movement, transport)
* Outer surface of membrane interacts with proteins that bind substrates or have molecules for transport
* Inner surface interacts with proteins involved in energy yielding reactions and other cellular functions - Energy conservation - make ATP
18
Q
What are the 3 main ways that movement occurs in the cell?
A
- Simple diffusion (osmosis)
- Facilitated diffusion (WITH concentration gradient, no energy expended)
- Active transport (AGAINST concentration gradient, energy expended)
19
Q
Describe the difference between bacterial membranes and other membranes.
A
- Bacteria and Eukarya have FA tails bound to glycerol by ester linkages
- Archaea have isoprenoid tails (instead of FA) bound to glycerol by ether linkages - can be monolayers or bilayers
- Sterols vs. hopanoids
20
Q
What are some examples of membrane strengthening agents?
A
- Sterols - rigid planar lipids found in eukaryotes, strengthen and stabilize membranes because eukaryotes don’t have a cell wall
- Hopanoids - structurally similar to sterols, present in many bacterial membranes
21
Q
Carrier-mediated transport systems are…
A
Highly specific, show saturation effect
22
Q
What are the three main types of transport systems (all require energy - active) in prokaryotes?
A
- Simple transport
- Group translocation
- ABC system
23
Q
Describe simple transport.
A
A transporter that consists of only a membrane-spanning protein and is typically driven by energy from the proton motive force
ie… uptake of lactose via lac permease
24
Describe group translocation.
An energy-dependent transport system in which the substance transported is **chemically modified** during the process of being transported by a series of proteins
ie... phosphotransferase system in E. coli - moves glucose, fructose, manose; 5 proteins, energy from PEP
25
Describe the ABC transport system.
* A membrane transport system consisting of three proteins (binding protein, transmembrane transporter, ATP hydrolyzing protein); the system transports specific nutrients into the cell
* Often involves uptake of organic compounds and trace metals, display high substrate specificity
* **Doesn't get modified, uses ATP**
26
Name and describe the three types of transport events.
1. Uniport - transport in one direction across membrane
2. Symporters - co-transporters
3. Antiporters - transport molecule across membrane while simulataneously transporting another molcule in opposite dirrection
27
Describe some common types of protein export in bacteria.
* Translocases - responsible for exporting proteins through and inserting into prokaryotic membranes
* Sec translocase system - exports proteins and inserts integral membrane proteins into membrane
* Type III secretion system - common in pathogenic bacteria, secreted protein translocated directly into host
28
Describe the structure of the bacterial cell wall.
* Peptidoglycan polymer (A.A. and sugars)
* Sugars : N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) attached by beta 1-4 linkage
* D forms of A.A. used - harder to break down (humans don't have the enzymes)
* A.A. cross link NAG and NAM
29
Describe the function of the bacterial cell wall.
* Protection from osmotic stress/lysis - which is why bacteria can live in pure water
* Maintain cell shape and rigidity
* Can be target for antibiotics
* Can sometimes be recognized by host immune system
30
Describe the difference between bacterial cell walls and other cell walls.
* In Eukarotes (plants) cell walls are made of cellulose
* Structural characteristics of bacterial cell walls (peptidoglycan, NAG and NAM) unique to prokaryotes
* Not all eukaryotes or bacteria have cell walls
* Archaea cell walls have no peptidoglycan, no OM, made of Pseudomurein NAG and N-acetylalsaminuronic acid with beta 1-3 bond, some have S-layers
31
Describe the characteristics of a Gram positive organism.
* Cell membrane with thick cell wall (can be up to 90% peptidoglycan)
* Stains purple!
* Has techoic acids (acidic substances, attach the cell wall to membrane, affect cell surface charge and hydrophobicity - affects binding)
* Lipoteichoic acids - techoic acids covalently bound to lipids
* Generally susceptible to antibiotics, sensitive to lysozyme
* ie... Bacillus, staphylococcus, streptococcus
32
Describe the characteristics of a Gram negative organism.
* Cell membrane, thin cell wall (about 10% peptidoglycan), outer membrane (provides additional strength against osmotic lysis)
* Stains pink!
* Periplasm present between layers - site of preliminary nutrient degradation, gel-like, has many proteins
* LPS (endotoxin) present
* Porins present - allow passage of molecules through outer membranes (typically only by size)
* Generally less susceptible to antibiotics (need ampicillin, not penicillin), not sensitive to lysozyme
* ie... Escerichia, Neisseria, Pseudomonas
33
Describe the characteristics of bacteria without a cell wall.
* Mycoplasmas or termoplasma (type of archaea)
* Shaped by environment
* Highly prone to lysing
* Walking pneumonia
34
Describe the characteristics of an acid fast organism.
* Cell membrane, medium cell wall, lipid layer (mycolic acid)
* Lipid layer protects from drying out, dessication
* Live very long time in the environment (weeks)
* ie... TB, leprosy
35
Gram staining (differential stain) is determined by...
Thickness of cell wall, rather than the number of layers, doesn't always correctly stain
36
Describe the structure of the outer membrane
* LPS layer, inner part is phospholipids
* LPS = core polysaccharide and O polysaccharide - important for protection from antibiotics and some toxins, lipid portion (lipid A)
* LPS replaces most of phospholipids in outer half of membrane
* Endotoxin - toxic part of LPS, fever causing
* Core - same for each type of organism (ie... E. coli)
* O - different depending on strains
37
Explain the difference between an endotoxin and an exotoxin.
Endotoxin is part of bacteria. Exotoxin (ie... botulism) is excreted into environment, and not part of the structure.
38
What is an S-Layer
* Most common cell wall type among archaea, consists of protein or glycoprotein, paracrystalline structure
39
What are 3 types of surface layers on bacteria?
Glycocalyx, capsule, slime layer (often made of polysaccharides)
40
What is a glycocalyx?
Layer outside cell wall, usually made of polysaccharide
41
What is a capsule?
Distinct and gelatinous, enables bavteria to adhere to specific surfaces, allows some organisms to thwart innate defense systems and cause disease
42
What is a slime layer?
Diffuse and irregular. Enables bacteria to adhere to specific surfaces.
43
What are the functions of surface layers of bacteria?
1. Protection from phagocytosis
2. Attachment (ie... to teeth)
3. Resist desiccation
44
What is taxis? What are different types of taxis?
* Taxis = directed movement in response to chemical or physical gradients
* Chemotaxis - response to chemicals
* Phototaxis - response to light
* Aerotaxs - response to oxygen
* Osmotaxis - response to ionic strength
* Hydrotaxis - response to water
45
Describe the structure of flagella.
* Bacteria can have anywhere between 1 and thousands
* Filament composed of flagellin
* Helical in shape, rigid
* Grows from tip out
* MS ring made first, other proteins and hook made next
* Different arrangements: monotrichous/polar (one) peritrichous (everwhere), lophotichous (a bunch on either side), amphitrichous (one on either side)
46
Describe the function of flagella.
* Moves via rotation using energy from PMF
* Move only when they need to: 1000 protons/rotation
* CCW - bundle, run
* CW - unbundle, tumble
* Some are reversible in direction, others are not
47
Describe how eukaryotic flagella are different from bacterial flagella.
* Move via whipping
* Much longer, enclose by cytoplasmic membrane
* Contain cytoskeleton
48
Describe bacterial ribosomes.
* Involved in protein synthesis.
* Two subunits 30S and 50S join to form 70S ribosome, made up of about 50 proteins and 3rRNA. (80S = 60+40S in eukaryotes)
* Polysomes - several ribosomes on mRNA
49
Describe the structure of pili.
* Made of pilin
* Short protein appendaces
50
Describe the function of pili.
* Helps with attachment to surfaces
* Helps with movment
* Often contribute to virulence
* Help with flotation and increase boyancy
* Conjugative (f-pilus) pili - facilitate genetic exchange
* Electricaly conductive pili - conduct electrons toward or away from cell
* Type four pili - help with twitching pili, move along solid surface, ATP driven
* Fimbriae - kind of pili, short, mediate attachment and sitck to surfaces
51
Describe bacterial chromosomes.
* 1 haploid, circular chromosome that supercoils to fit (vs. eukaryotes that are diploid and linear)
* Reprodcuce and mutate faster, genotype = phenotype, adapt to env. faster
* Plasmids - smaller, circular pieces of DNA, usually encode expendable functions - antibiotic resistance
51
Describe bacterial cytoplasms.
* 80% water, 20% salts and proteins
* No organelles
52
Describe the types of cell inclusion bodies.
* Carbon storage - PHP, glycogen
* Polyphosphates - accumulate inorganic phosphate
* Sulfur globules - composed of elemental sulfur
* Magnetosomes - magnetic storage inclusions, super-paramagnetic, have dipole moment (N and S pole), can undergo magnetotaxis
* Help to reduce osmotic stress, take up less space than if stored in a soluble form
53
Describe gas vesicles in bacteria.
* Protein sacs that get air in them, spindle-shaped, hollow but rigid
* For bacteria that want to float, buoyancy
* Vesicle is impermeable to water
54
Describe endospores.
- Structures that allow microbes to survive unfavorable conditions (heat, irradiation, cold, chemicals) - triggered when some nutrient becomes limiting
- Not reproductive but rather domant stage of bacterial life cycle
- Takes time and energy to make spores
- Only produces by bacillales and clostridiales - Gram+
- Location classification: central, subterminal, terminal
- Ideal for dispersal via wind, water, or animal gut
55
Evidence for endosymbiotic theory
1. Double membrane (like G- bacteria)
2. MT chromosome is circular
3. Phylogenetics
4. Make ATP of MT membrane (like bacteria do)
5. Ribosomes are 70S in MT, sensitive to antibiotics
6. MT divide via binary fission (like bacteria do)
7. Size
Hypothesizes that MT and chloroplasts were descendants of respiratory and phototrophic bacterial cells. Over time, the originally free-living symbionts became an intimate part of the eukaryotic cell.
