Exam 1 - Chapter 2 Lecture

All cells must have a

cell membrane

Major functions of the cytoplasmic membrane

1. Permeability barrier

2. Protein anchor

3. Energy conservation

Cell membrane as a permeability barrier

Prevents leakage & functions as a gateway for transport of nutrients into, and wastes out of, the cell

Cell membrane is the site of proteins that participate in...

transport, bioenergetics, and chemotaxis

How does the cell membrane function in energy conservation?

Site of generation and dissipation of the proton motive force

Passive transport

Follows concentration gradient (energy-independent)

Active transport

Accumulate solutes against concentration gradient (energy-dependent)

Simple transport

Driven by the energy in the proton motive force

ABC Transporter

Periplasmic binding proteins are involved and energy comes from ATP

Group translocation

Chemical modification of the transported substance driven by phosphoenolpyruvate (common in bacteria and archaea)

3 classes of transport systems

simple transport, ABC transporter, group translocation

Antiporter

A carrier protein that transports two molecules across the plasma membrane in opposite directions.

Symporter

Transporter that carries two different ions or small molecules, both in the same direction

Functions of the cell wall

1. Withstand osmotic/turgor pressure to prevent cell lysis

2. Maintain cell shape & rigidity

Do all microbial cells have a cell wall?

No, but most do

Gram stain classification of bacteria is based on...

organization and cell wall structures

Cells without a cell wall are more sensitive to...

changes in osmotic/turgor pressure

Gram positive cell wall

Has one layer of membrane and a thick cell wall/peptidoglycan layer

Gram negative cell wall

Has 2 membrane layers with a thin cell wall/peptidoglycan layer in between

Peptidoglycan is not found in...

Archaea or Eukarya

What structure is shown?

Peptidoglycan

The gram + cell wall is more...

1. Rigid

2. Resistant to salt, dryness, and osmotic changes

3. Sensitive to peptidoglycan inhibitors

The gram - cell wall is more...

1. Flexible

2. Sensitive to salt, dryness, and osmotic changes

3. Resistant to peptidoglycan inhibitors

Gram - cell wall impact on transport

Makes it harder to transport nutrients due to 2 membrane layers

LPS

Additional protection in gram - cell wall that can trigger immune response

Bacterial Capsules/Slime Functions

1. Assist in attachment to surfaces

2. Role in development and maintenance of biofilms

3. Contribute to infectivity

4. Prevent dehydration/dessication

Bacterial Capsules/Slime

Coating on outside of cell wall present in some cells which can be lost by the cell

Capsules vs slime

Capsules: More rigid and more permanently attached to the cell wall

Slime: More loose and easier to lose

Fimbriae

Filamentous extracellular structures that help mediate attachment, used mostly for adhesion to surfaces and other cells (different from flagella!)

Pili

A type of fimbriae that can be used for adhesion or genetic exchange

What are the names for pili used for genetic exchange?

F-pili

Conjugative pili

Sex pili

Function of cell inclusions

1. Energy reserves

2. Carbon or phosphorus reservoirs

3. Special functions

4. Reduces osmotic stress

Cell inclusions are enclosed by...

thin protein membrane

Gas vesicles

Allow buoyant cyanobacteria to float to surface for exposure to air, sun, etc. or sink beneath the surface for darkness, to avoid predators, etc.

Bacterial endospore

Survival structures to endure unfavorable growth conditions (not for reproduction) - allow a cell to stay dormant for years until conditions become favorable to return to a vegetative cell

Life cycle of endospore-forming bacterium

1. Vegetative cell

2. Sporulation: develops endospore

3. Mature endospore

4. Germination: Conversion from endospore back to vegetative cell

How many parents yield 1 endospore?

1

What structure is shown?

Endospore

Endospore structures

1. Exosporium

2. Endospore coat

3. Outer spore membrane

4. Cortex

5. Inner membrane

6. Core

7. DNA

Bacterial flagella

Functions in cell motility but not present in all motile cells

What arrangement of flagella is shown?

Peritrichous flagella

What arrangement of flagella is shown?

Polar flagella

What arrangement of flagella is shown?

Lophotrichous flagella

Peritrichous flagella

flagella that cover the surface of a cell

Polar flagella

flagella only at the end of a cell (one or both ends)

Lophotrichous flagella

multiple flagella on either end

Movement in peritrichously flagellated prokaryotic cells

1. Bundled flagella rotate counterclockwise to facilitate cell runs

2. Flagella spread apart and rotate clockwise to facilitate cell tumbles

3. Random reorientation

4. Repeat

Movement in polarly flagellated prokaryotic cells (reversible)

1. Flagella rotates counterclockwise for cell run

2. Flagella rotates clockwise & cell reverses

Movement in polarly flagellated prokaryotic cells (unidirectional)

1. Flagella rotates clockwise for cell run

2. Rotation stops and random reorientation occurs

3. Clockwise rotation for cell run (repeat)

Chemotaxis in Peritrichously Flagellated Bacteria

1. No attractant present: cell runs and tumbles randomly - random movement; no net movement

2. Attractant present: Directed movement - cell runs, tumbles, and runs in direction of attractant (tumbles to reorient towards attractant); net movement toward attractant

Chemotaxis

Response to chemicals

Osmotaxis

response to ionic strength

Hydrotaxis

response to water

Aerotaxis

response to oxygen

Phototaxis

response to light

T/F: Only motile cells can perform taxis

True

T/F: Cells must have flagella to perform taxis

False

Eukaryotes compared to prokaryotes

Bigger and more complex cells; evolved from prokaryotes

Cilia

Extracellular structures that are functionally equivalent to flagella but different in chemical composition and motion

Cilia composition

Made of microtubules

Cilia motion

waving/undulation motion (no rotation)