Lecture 7

Question 1

List the 4 types of bacteria showed on the first slide and their gram stains

Answer 1

Salmonella: Gram negative bacillus
Streptococcus: Gram positive cocci
Listeria: Gram positive Bacillus
Staphylococcus: Gram positive cocci

Question 2

Individual cell shapes of bacteria

Answer 2

Spheres (coccus)
Rods (Bacillus)
Other shapes: Vibrio (crescent shape) and spiral

Question 3

Describe Coccus

Answer 3

Individual cells may occur in various arrangements
coccus: Single cell, alone
Diplococcus: Two cells
Streptococcus: Many cells in a chain
Staphylococcus: Many cells in a cluster

Question 4

Example of a diplococcus

Answer 4

Enterococcus sp.
- Clustering can be variable within species

Question 5

Describe Bacillus

Answer 5

Bacillus: Single cell, alone

Streptobacillus: Many cells in a chain

Question 6

Relationship between bacteria and its name

Answer 6

Many bacteria are named after their shape: Bacillus subtilis
However, bacterial shape is not a very good homologous trait for classification

Question 7

Stains of Escherichia coli and Bacillus megaterium

Answer 7

Coli: Gram negative bacillus
Megaterium: Gram positive streptobacillus

Question 8

Morphological features of bacterial cell

Answer 8

Plasma membrane and the bacterial cell wall
Capsule/slime layer
Flagella and pilus
Sub cellular compartments
Endospores

Question 9

Fimbriae of bacteria

Answer 9

Hairlike appendages that help cells adhere to other cells or to a substrate

Question 10

Capsule of bacteria

Answer 10

Sticky layer of polysaccharide or protein that can help cell adherence and/or evasion of a host’s immune system

Question 11

Internal organization of bacteria

Answer 11

No nucleus or other membrane-bounded organelles; usually no complex compartmentalization

Question 12

Flagella of bacteria

Answer 12

Structures used by most motile bacteria for propulsion; many species can move toward or away from certain stimuli

Question 13

Cell wall of bacteria

Answer 13

Found in nearly all prokaryotes; structure differs in gram positive and gram negative bacteria

Question 14

Circular chromosome of bacteria are

Answer 14

Often accompanied by smaller rings of DNA called plasmids

Question 15

Pilus of bacteria

Answer 15

Appendage that facilitates conjugation

Question 16

Plasma membrane

Answer 16

• Is a lipid bilayer made of fatty acids

Question 17

Single fatty acid

Answer 17

A single fatty acid has a hydrophilic head and a hydrophobic tail
In water, the heads face the water while the tails hide from the water, facing each other. This forms the two layered structure of lipid bilayer

Question 18

Fatty acids (phospholipid) and polarity

Answer 18

Hydrophilic (polar) head
Hydrophobic (non polar) tail

Question 19

Plasma membrane as a barrier

Answer 19

• Permeability barrier
• Very small molecules can diffuse through plasma membrane freely (N2, CO2, O2)

Question 20

Molecules that diffuse slowly or not at all through the membrane

Answer 20

• Some small molecules can diffuse slowly (H2O, glycerol, ethanol)
• Molecules larger than 3-4 carbons and charged molecules can not diffuse at all (Glucose, H+)

Question 21

Peptidoglycan

Answer 21

Bacteria has a peptidoglycan cell walls
- Made of two types of sugars attached in a long, unbranched chain (backbone)
One of the sugars have a short peptide attached (3-5 amino acids)
Different peptidoglycan backbones can attach via their peptides cross-linking

Question 22

Mesh structure

Answer 22

Many peptidoglycan backbone attach to each other to form a mesh structure
- Peptidoglycan exists outside the plasma membrane, surrounding the entire cell

Question 23

How does peptidoglycan and plasma membrane work together

Answer 23

• Make cell wall stronger
• Pep Is rigid and gives mechanical strength to the cell walls. Has large openings and lets molecules diffuse freely due to it not having permeability
  Plasma membrane is a permeability barrier but is not as mechanically strong

Question 24

Peptidoglycan surrounds the

Answer 24

Plasma membrane

Question 25

Osmotic pressure in bacteria

Answer 25

Concentration of chemicals in cytoplasm is higher compared to the surrounding environment - creates osmotic pressure for water to move from environment into cell. Cell will burst if too much water enters Pep gives mechanical strength to cell envelope to prevent the bursting

Question 26

Two types of bacterial cell wall

Answer 26

Gram positive cell wall - Thick layer of peptidoglycan - Relatively simpler structure Gram negative cell wall - Thin layer of peptidoglycan - A second lipid bilayer surrounds the peptidoglycan layer (outer membrane)

Question 27

Gram stain purpose

Answer 27

To stain gram positive and negative cells to appear different under a light microscope

Question 28

Gram stain procedure

Answer 28

1. Stain all cells with dark purple dye, crystal violet 2. Destain with ethanol - Gram negative cells become clear whereas gram positive remain purple because of thick pep 3. Stain again with lighter pink dye safranin Gram positive cells appear purple Gram negative cells appear pink

Question 29

Examples of gram negative bacteria

Answer 29

E coli Chlamydias Spirochetes Cyanobacteria

Question 30

Gram positive bacteria

Answer 30

S.Aureus and B.subtillis

Question 31

Staining gram negative does not always mean

Answer 31

The bacteria has a gram negative cell wall - Some group such as chlamydias don't have a peptidoglycan cell wall but still stain pink

Question 32

Peptidoglycan is the target for

Answer 32

Many antibiotics (pencillin, vancomycin) - Stopping petidoglycan synthesis stops bacterial growth

Question 33

How does the effectiveness of antibiotics depend on the cell wall structure

Answer 33

Gram positive have peptidoglycan exposed to environment, antibiotics have easier access Gram negative have outer membrane, blocking many antibiotics from accessing the peptidoglycan

Question 34

Gram stain only takes

Answer 34

10 minutes to do

Question 35

Capsule and slime layer

Answer 35

A layer outside the bacterial cell wall Made of sugars and/or peptides (species dependent) Can be rigid (capsule) or more soft and flexible (slime layer) Resists dehydration, resists immune system of host organism, adherence to surfaces

Question 36

Sub cellular structures

Answer 36

Do not have organelles Can still have complex sub cellular structures made of lipid bilayers and protein shells such as thylakoid membrane and carboxysomes

Question 37

Thylakoid membrane and Carboxysomes

Answer 37

Thylakoid - Multiple folds of lipid bilayer inside cyanobacteria - Conversion of light energy to chemical energy (ATP) Carboxysomes - Polygonal structures made of protein shell, found inside cyanobacteria - Fixation of CO2 into organic molecules

Question 38

Flagella

Answer 38

Long whip like structure attached to the bacterial cell wall Rotation of flagella makes cell move Very dissimilar structure from a eukaryotic flagella - Analogous structures due to convergent evolution

Question 39

Chemotaxis:

Answer 39

Bacteria has systems to move 'towards good things' and 'away from bad things'

Question 40

Fimbriae and pilus

Answer 40

Other string like structures are also found on bacterial surfaces Fimbriae - Shorter and more numerous - Attachment to surfaces and to other cells Pilus - A long tubular structure - Connects two bacterial cells to facilitate exchange of genetic material (form of horizontal gene transfer)

Question 41

Endospores

Answer 41

Survival mechanism deployed by some gram positive bacteria Can withstand huge amounts of stress such as UV radiation Vegetative cells (normally growing cells) form endospores to survive unfavorable environmental condition - Vegetative cells die in the unfavorable condition while the endospores persist

Question 42

Endospores grow back to vegetative cells once

Answer 42

Environmental condition is restored

Question 43

Would bacillus spores survive space travel and contaminate other planets

Answer 43

Only a fraction of bacillus endospores survived 1.5 years of exposure to outer space and were able to grow back into vegetative cells

Question 44

PROTECT experiment by ESA

Answer 44

* Bacillus subtilis spores were loaded on a spacecraft and delivered to the International Space Station on February 7, 2008 * Bacillus spores were exposed to outer space for 1.5 years before they were brought back to earth