Cell Structure & Function Flashcards
What is visible light used for in compound light microscopy?
Illuminate cells
What are 4 types of light microscopy?
1) Bright-field
2) Phase-contrast
3) Dark-field
4) Flourescence
What are the 2 types of lenses in a bright-field microscope?
Ocular and objective
What is the maximum magnification of a bright-field microscope?
2000x
Define magnification
The ability to make an object larger
Define resolution
The ability to distinguish two adjacent objects as separate and distinct
How are magnification and resolution related?
Inversely
How do you calculate magnification?
Ocular magnification times objective magnification
What happens to resolution as wavelength decreases?
It increases
What happens to resolution as energy decreases?
It decreases
What is a way to improve contrast?
Staining
What is simple staining?
Only one dye is used to colour a specimen
Define chromophore
The coloured portion of a dye
What is a basic dye?
- A positively charged chromophore
- Binds to negatively charged molecules on cell surface
What is an acidic dye?
- Negatively charged chromophore
- Repelled by cell surface; stains background
What are 3 examples of differential stains?
- The Gram stain
- Acid fast stain
- Endospore stain
During a gram stain, what colour will the gram positive cell be and what colour will the gram negative cell be?
- Gram positive is purple
- Gram negative is pink
What does an acid fast stain detect?
Mycolic acid in the cell wall of Mycobacterium
In an acid fast stain, what colour will the Mycobacterium be and what colour will everything else on the slide be?
- Mycobacterium will be pink
- Everything else will be blue
In an endospore stain, what colour will the endospores be and what colour will all the other cells be?
- Endospores will be green
- Other cells will be pink
What does phase-contrast microscopy allow for the visualization of?
Live samples
Does phase-contrast microscopy involve a stain?
No
What kind of image will be produced by a phase-contrast microscope?
Dark cells on a light background
What kind of image will be produced by a dark field microscope?
A bright object on a dark background
What is dark field microscopy used to observe?
Bacteria that don’t stain well
What is fluorescence microscopy used to observe?
Specimens that fluoresce
What is the name of a fluorescent dye and what does it bind to?
DAPI binds to DNA
How can cells be observed in 3D?
By using differential interference contrast (DIC) microscopy or confocal scanning laser microscopy (CSLM)
What happens in a DIC microscope?
A polarizer is used to create two distinct beams of polarized light
What is the resolution for CSLM?
0.1 micrometer
What do electron microscopes use to image cells and structures?
Electrons
Since the wavelength of an electron is much shorter than the wavelength of light, what does that mean for resolution?
Higher resolution
What are the 2 types of electron microscopes?
1) Transmission electron microscope
2) Scanning electron microscope
What must be done to a cell before it can be viewed with a transmission electron microscope?
It must be fragmented (sliced) and then stained
What must a cell be stained with before it can be viewed with a transmission electron microscope and why?
Metals such as lead or uranium because they bind to cell structures and make them more electron dense
What must a cell be stained with before it can be viewed with a scanning electron microscope?
A thin film of heavy metal such as gold
Do prokaryotes have membrane bound organelles?
Nope
Between bacteria and archaea, which have the capacity to be pathogenic?
Bacteria
Are archaea ever pathogenic?
No
What is a coccus shape?
Spherical
What is a bacillus shape?
Rod
What is a spirillum shape?
Spiral
Is it common or uncommon for cells to have a shape that is not coccus, bacillus, or spirillum?
Uncommon
Can morphology (shape) predict any characteristics of a cell?
Generally no
What is an advantage to being small?
More surface area relative to cell volume
What does a greater surface-to-volume ratio mean?
- Greater nutrient exchange per unit cell volume
- Tend to grow faster
What is generally the smallest a cell can be and still be able to live?
0.15 micrometer
What is another name for the cytoplasmic membrane?
Plasma membrane
On a phospholipid, which part is hydrophobic and which is hydrophilic?
Hydrophobic – fatty acid tail
Hydrophilic – glycerol-phosphate head
Define amphipathic and give an example
- Has both polar and nonpolar characteristics
- Ex: proteins embedded in the plasma membrane
What does an ester phospholipid consist of?
- Glycerol
- 2 fatty acids
- Phosphate
- Possibly a side chain
What is the general diameter of the cytoplasmic membrane?
8 - 10 nm
What stabilizes the plasma membrane?
Hydrogen bonds and hydrophobic interactions
Why is the plasma membrane fluid?
So protein channels can move from side to side
Does a gram negative or gram positive bacteria have an extra outer membrane?
Gram negative
Does the membrane proteins bind substrates and process large molecules for transporting gram-positive or gram-negative bacteria?
Gram negative
How are integral membrane proteins connected to the plasma membrane?
Firmly embedded in the membrane
How are peripheral membrane proteins connected to the plasma membrane?
One portion is anchored in the membrane
Where are ether linkages found?
Phospholipids in archaea
Where are ester linkages found?
Bacteria and Eukarya phospholipids
What is lacking in archaeal lipids and what replaces them?
Fatty acids replaced by isoprenes
Are arachaeal plasma membrane lipids always in a bilayer?
No, they can be a monolayer, bilayer, or a mixture
What is a major difference between lipid monolayers and lipid bilayers?
Monolayer membranes are extremely heat resistant
What kind of archaea are monolayers typically found in?
Hyperthermophilic (ones that live in environments over 80 C)
What types of molecules can cross the plasma membrane?
Polar and charged
What is the purpose of transport proteins?
Carry solutes against their concentration gradient
What does a protein anchor do?
Hold transport proteins in place
Do carrier-mediated systems happen for just any substance?
NO! They are highly specific
What are 3 major classes of transport systems in prokaryotes?
1) Simple transport
2) Group translocation
3) ABC system
Define uniporter
Transport in one direction across the membrane
Define symporter
Function as co-transporter (2 molecules going in the same direction across the membrane)
Define antiporter
Transport a molecule across the membrane while simultaneously transporting another molecule in the opposite direction
What does ABC stand for in ABC transport?
ATP-binding cassette
What is ABC transport involved in the uptake of?
Organic compounds, inorganic nutrients, and trace metals
What do gram-negatives employ for ABC transport?
Periplasmic-binding proteins
What do gram-positives employ for ABC transport?
Substrate-binding lipoproteins
What is the texture of the cell wall of bacteria and archaea?
Rigid to help determine cell shape
Is the cell wall of bacteria and archaea a major permeability barrier?
No
What is the main function of the cell wall in bacteria and archaea?
Protect the cell from osmotic changes
What is a bacteria cell relative to its surroundings?
Hypertonic, so H2O goes into the cell
What does the cell wall prevent?
Cell expansion and toxic substances
What are the differences in cell wall structure between gram-positives and gram-negatives?
- Gram-positive has only peptidoglycan
- Gram-negative has peptidoglycan and LPS (lipopolysaccharide)
What does peptidoglycan do for the cell wall?
Provide strength
What is the backbone of peptidoglycan composed of?
NAM and NAG connected by glycosidic linkages
What is the difference between gram-positive and gram-negative peptidoglycan?
It is cross-linked differently
What is not present in the peptidoglycan of gram-negative bacteria?
An interbridge
Is NAG involved in interbridges?
Nope
What percentage of gram-positive cell walls is peptidoglycan?
Up to 90%
What is commonly embedded in the cell wall of gram-positives?
Teichoic acids
What are crosslinks in peptidoglycan formed by?
Peptides
What is the shape of a peptidoglycan strand?
Helical
What does LPS consist of?
Core polysaccharide and O-polysaccharide
What does LPS replace?
Phospholipids in outer half of outer membrane
What is periplasm?
The space located between cytoplasmic and outer membrane
What does periplasm contain?
Many proteins
What are porins?
Channels for movement of hydrophilic low-MW substances
Do archaeal cell walls have peptidoglycan and an outer membrane?
Not usually
What is found in the cell wall of some archaea?
Pseudomurein
What is the most common cell wall type of archaea?
S-layer
What does the S-layer consist of?
Protein or glycoprotein
What are archaea resistant to since they lack peptidoglycan?
Lysozyme and penicillin
Define cytoplasm
Material bounded by plasma membrane
Define protoplast
The plasma membrane and everything within it
Define nucleoid
The region that contains the genome
What kind of ribosome is found in bacteria?
70S
What kind if ribosome is found in eukarya?
80S
What components make up a ribosome?
30S small subunit (40S in eukarya) and 50S large subunit
What are capsules and slime layers made of?
Polysaccharides and proteins
What is the purpose of capsules and slime layers?
Assist in attachment to surface
What do capsules and slime layers protect against?
Phagocytosis and desiccation
What is the function of fimbriae?
Enable organisms to stick to surfaces or form pellicles
What are fimbriae?
Filamentous protein structures
What is the difference between fimbriae and pili?
Pili are typically longer
What is the function of pili?
Assist in surface attachment
What are inclusion bodies?
Aggregates in cytoplasm
What are polyphosphates?
Accumulations of inorganic phosphate
What are magnetosomes?
Magnetic storage inclusion bodies
What are polyphosphates used for?
Storage of phosphate and energy
What is the function of magnetosomes?
Give the cell magnetic properties, allowing it to orient itself in a magnetic field
What do gas vesicles do?
Convey bouyancy
What are gas vesicles made of?
Protein
HOW do gas vesicles function?
By decreasing cell density
What are gas vesicles impermeable to?
Water
What are endospores?
Highly differentiated cells resistant to heat, harsh chemicals, and radiation
What kind of bacteria produce endospores?
Some gram positives, NEVER GRAM NEGATIVES
Why is an endospore metabolically inactive?
It is dormant
Where is an endospore formed?
Inside a mother cell
What do the spore coat and cortex protect against?
Chemicals, enzymes, physical damage, and heat
What 5 things can endospores resist?
1) Boiling for hours
2) UV and gamma radiation
3) Chemical disinfectants
4) Desiccation
5) Age
What are the 7 stages of the life cycle of a spore-forming bacterium?
1) Asymmetric cell division
2) Septation
3) Mother cell engulfs the forespore
4) Formation of the cortex
5) Coat synthesis
6) Endospore matures
7) Mother cell is lysed
What does septation divide the cell into?
Forespore and mother cell
What is the core wall?
Highly cross-linked peptidoglycan layer
What is the cortex?
Loosely cross-linked peptidoglycan layer
What does the coat protect the spore from?
Chemicals and enzymes
What happens after the mother cell is lysed?
A mature spore is released
What are flagella and what do they do?
Hollow protein filaments that assist with motility
Define monotrichous
Single flagellum
Define amphitrichous
Flagella at opposite ends
Define lophotrichous
Multiple flagella in a single tuft
Define peritrichous
Flagella distributed all around cell
What 3 parts does a flagellum consist of?
1) Filament
2) Hook
3) Basal body
What are the 4 rings that the basal body passes through?
1) L ring – LPS layer
2) P ring – peptidoglycan
3) MS ring – membrane
4) C ring – cytoplasm
Where does energy to power the flagella come from?
Proton motive force
Where is there a high [H+]?
Outside the cytoplasmic membrane
Where is there a low [H+]?
Inside the cytoplasmic membrane
___ forms a channel that allows H+ to move into the cytoplasm
Mot proteins
What part of a flagella is made first?
MS ring
What part of a flagella is made last?
Filament
What does gliding motility require?
Surface contact
Define taxis
Directed movement in response to chemical or physical gradients
Define chemotaxis
Response to chemicals
Define phototaxis
Response to light
Define aerotaxis
Response to oxygen
Define osmotaxis
Response to ionic strength
Define hydrotaxis
Response to water (to rehydrate cell)
What are attractants and repellants sensed by in E. coli?
Chemoreceptors
How do you measure chemotaxis?
Insert a capillary tube containing an attractant or a repellent into a medium of motile bacteria
What do eukaryotic cells need since they have a lower surface area to volume ratio?
More sophisticated transport mechanisms
Give 5 pieces of evidence that support the hypothesis that mitchondria and chloroplasts evolved from bacteria.
1) Semi-autonomous
2) Circular chromosomes
3) 70S ribosomes
4) Two membranes
5) Outer membrane has porins
