Week 12 Recall Questions

Question 1

Prokaryotic cell walls:

What it the function of a cell wall?

Answer 1

Overall cell walls provide

Structure and shape, and protection from osmotic stress, lysis or disintegration, chemicals and biological responses

Question 2

Prokaryotic cell walls:

What is the function of a cell wall in prokaryotes?

Answer 2

Most pro- have cell walls

Function:
Structure (semi-rigid) and shape, protection from osmotic stress, lysis or disintegration, chemicals and biological responses

Determines if cell shape is cocci, bacilli, cubed shaped , helical, spiral.

B/c water can move freely through cell walls, cell wall prevents bursting of cell by counteracting the osmotic pressure from the inside.

Can mechanically make wall harder to protect from pathogens or predators or immune system to attack cells

Type and composition of cell well is a diagnostic trait
— Archaeal cell walls are diff from all other groups
— bacteria are grouped in gram + and gram - based on their cell wall structure

Question 3

Eukaryotic cell walls:

What is the function of a cell wall in eukaryotes?

Answer 3

Function:
- determine shape and size and provide support (outside scaffold) (support stronger than ECM)
- mediate cell to cell interactions
- protection from environmental stress: mechanical, osmotic, pH, pathogens

(Cell wall much more rigid and firm outer structure than ECM)

• Occur is most main eukaryotic groups
  — cell walls of different organisms such as plants, fungi, and protists, are distinctly different. Made from different cell wall components and are used to characterize groups of organisms = part of scientific classification.

Question 4

Prokaryotic cell walls:

What are similarities and differences in the structure of bacterial, plant and fungal cell walls?

Answer 4

Bacterial (unicellular prokaryote):
- only ones that produce peptidoglycan (PG) layer

Plant (multicellular eukaryotes):

Fungal (uni- or multicellular eukaryotes):

Question 5

Prokaryotic cell walls:

How is peptidoglycan constructed?

Answer 5

Is a large polymer

Is made from linked glucose derivatives (NAM + NAG) in long chains, cross linked by shorten polypeptide chains

Process of synthesis of it is still largely unknown

Question 6

Prokaryotic cell walls:

How do common penicillin-based antibiotics work?

Answer 6

Antibiotics are compounds generally produced by microorganisms to defend against bacteria.

Some common antibiotics like penicillin, beta-lactams, interfere with PG cross-linkages

Question 7

Prokaryotic cell walls:

What is the function or teichoic acid?

Answer 7

teichoic acid is a polymer that makes cells walls more resistant to high temps, salt []s, and 1 kind of antibiotic

Question 8

Prokaryotic cell walls:

How does the gram staining procedure work?

Answer 8

1. Cells are stained with crystal violet
2. Then with gram’s iodine, which forms a complex of crystal violet and iodine
3. Cells are rinsed with ethanol
4. counter stained with safranin

Cells that retain crystal violet-iodine complex appear purple when viewed under microscope = gram +

Cells where crystal violet-iodine complex is washed off by ethanol are colourless until stained with safranin which appear pink under the microscope = gram -.

Question 9

Prokaryotic cell walls:

What are similarities and differences between a gram-positive and gram-negative bacterial cell?

Answer 9

Both have peptidoglycan (PG)

Gram +:
- thick PG layer (outside plasma membrane) makes cell wall very rigid
- therefore, during gram strain procedure it traps violet stain, that can’t be washed out = dark purple.
- the stain remains when washed with acid = making this an acid fast stain
- contains teichoic acid polymers, making cells more resistant to high temps, salt []s, 1 kind of antibiotic

Ex:
- harmless/beneficial: Staphylococcus epidermis (part of protective layer of skin), Lactobacillus sp. (use to make yogurt)
- pathogenic: Staphylococcus aureus, S. pneumoniae, Bacillus anthracis (anthrax pathogen)

Gram -:
- all other bacteria are considered gram -.
- thin PG layer covered by second (porous/permeable) membrane.
- appears pink under microscope
- outer membrane covers PG layer and sometimes contains lipopolysaccharides (LPS) with lipid A (endotoxin).
— when lipid A [] in body are very high, immune system can get out of control, sending body into shock and potential death

Ex:
- harmless/beneficial: many E.coli strains
- pathogenic: Salmonella sp., Yersenia pestis (plague bacteria), Treponema pallidum (syphilis), STDs such as chlamydia and gonorrhea.

Question 10

Prokaryotic cell walls:

What are some medically important (pathogenic) examples of bacteria?

Answer 10

E.coli
— if get infected if pathogenic E.coli strain, it starts replicating, entering bloodstream and can result in an out of control immune response caused or triggered by lipid A.

Treponema pallidum (syphilis)
— if left untreated can cause major problems
— but is easily treated with antibiotics, specifically, penicillin.

Question 11

Prokaryotic cell walls:

How do bacteria acquire antibiotic resistance, how does it form?

Answer 11

Antibiotics are compounds generally produced by microorganisms to defend against bacteria. Will target diff structures or processes that in bacteria that are diff from eukaryotes

• such as target synthesis of bacterial cell wall
• others target bacterial ribosomes (which are diff from euk- ribos)
• target bacterial membrane that has diff components from euk-
• Some common antibiotics like penicillin, beta-lactams, interfere with cross linking of the short peptides in PG. making PG layer and whole cell weaker.

Antibiotic resistance:
Over years of use of antibiotics, bacteria evolve and become resistant to antibiotics.

Question 12

Prokaryotic cell walls:

How are bacteria able to block the actions of antibiotics?

What are the mechanisms?

Answer 12

Altered target site
Decreased uptake
Enzymatic inactivation or modification
Bypass pathways

Mechanisms:

The builder:
Affects cell wall by reinforcing it with proteins or other structural molecules making wall less permeable.

The pretender:
Altered target site. Change target site for the drug. Such as a side chain or 2. Effects most,u tertiary protein structure.

The cleaner:
A pump (integral membrane protein) pumps antibiotic out of cell, keeping inside clean resulting in decreased uptake of the drug and decreased concentration of the drug and therefore affects drug efficacy.

The inventor:
Bypass pathways, With few tweaks or some major modifications bacteria create a new enzyme that Carries out same reaction as old enzyme. But b/c diff enzyme it is not inhibited by antibiotic

The destroyer:
‘Enzymatic sledgehammer’ and destroys the drug. Degrades, digests or attaches to the drug and inactivates it.

Question 13

Which human actions promote antibiotic resistance?

Answer 13

Taking antibiotics for prolonged time

Question 14

Prokaryotic cell walls:

What are some examples of highly antibiotic resistant strains of bacteria?

Answer 14

Methicillin-resistant Staphylococcus aureus (MRSA) (gram +) or any multidrug-resistant bacterium.

B/c we have used antibiotics wildly for last few decades, it resulted in nightmare bacteria.

Nightmare bacteria are resistant to all antibiotic treatments and can share their genes for resistance with other germs. (Through plasmids and horizontal gene transfer).

Question 15

What are superbugs?

Answer 15

An informal term for a bacterium that has become resistant to serval antibiotics that are used to treat it,

Question 16

Prokaryotic cell walls:

What is the function of a bacterial capsule?

Answer 16

Part of the cell wall is covered by a layer of polysaccharides = this is the capsule.

They are sticky and play important roles in protecting cells in diff environments.

To some extent cells with capsules are protected from desiccation, extreme temps, bacterial viruses, harmful molecules like antibodies or antibiotics.

Question 17

Prokaryotic cell walls:

Is Streptococcus pneumoniae virulent without a capsule?

Answer 17

No it is not. It can easily be eliminated by the body’s immune system. It is ineffective.

Question 18

Prokaryotic cell walls:

What is an endotoxin and what are some examples of bacteria producing endotoxins?

Answer 18

They are the lipid A portion of the LPS molecule of the outer membrane of all gram - bacteria.

When a gram - bacteria lyses, the LPSs of the outer membrane are released; exposure to a specific compound in this layer, known as lipid A, causes endotoxin shock. When a gram - enters the bloodstream, endotoxin overstimulates the hosts immune response, triggering inflammation and often lethal immune response.

Ex: E.coli, salmonella, Shigella

Question 19

What is the Hemolytic Uremic Syndrome?

What is one example of E. coli contamination?

Answer 19

some strains produce toxins, e.g. the shiva toxin (STEC) causing hemolytic uremic syndrome (HUS) resulting in kidney damage.

Question 20

Prokaryotic cell walls:

What are lipopolysaccharides?

What bacterial group are they found in?

Is this group more or less sensitive to antibiotics?

Question 21

Prokaryotic cell walls:

What function does the glycocalyx, the slime layer, the capsule, pili and sex pili have in bacteria?

Answer 21

glycocalyx = sugar coat, polysaccharide layer that covers cell wall
- can refer to capsule or slime later (b/c they are diff forms)
- gen function is protection and adhesion
Ex: is what causes bacteria to stick to teeth

Slime layer (more like a hedge fence)
- polysaccharide rich sheath, more disorganized, loosely attached to cells (bacterium can slip out when needed)
- protects from environmental factors like antibodies], chemicals, drying out, & forms of sterilizations like autoclaving chemicals, likely against antibodies in immune systems
- enables bacteria to attach to smooth surfaces like petri-dishes, surgical implants, catheters

Capsule (more like a wooden fence)
- thick compact carbohydrate layer, firmly attached to cells
- gram + & - bacteria, but more common in gram -
- virulence factor b/c can prevent phagocytosis, protects from water loss (desiccation), other pathogens (viruses) and detergents.
- not a diagnostic trait
- contributes to virulence in some E.coli strains, salmonella, bacillus anthracis, staphylococcus aureus (of MRSA fame)

Pili
- adherence or attachment pili (fimbria)
— usually many, bacteria can attach to each other or to surfaces, important for biofilm establishment, virulence factor
- reason increased attachment is an important virulence factor is b/c when cells stay in a place for longer Period of time, they can multiply, there is longer time for infection, colonization, and nutrient absorption. Which increases likelihood of poor outcome for those infected.

Sex pili
- necessary for Bactria conjugation: binds two cells, they pull close to each other and exchange genetic material (plasmids)
- invoked in horizontal gene transfer
- longer than regular pili

Question 22

Prokaryotic cell walls:

What the difference between adherence pili and sex pili?

Answer 22

Pili attach the cell to surfaces or other cells.

Sex pili attaches 1 bacterium to another during mating

Question 23

What is a biofilm?

What are some advantages of biofilms to bacteria?

Are there any disadvantages?

Answer 23

A microbial community consisting of a diverse microorganisms (bacteria, archaea, unicellular eukaryotes like yeasts) attached to a surface.
All organisms are cooperating and exchanging genetic information.
The diff bacteria show a type of communication called quorum sensing to coordinate their behaviour and growth.
Colony produces a different kind of extracellular matrix, mostly based of polysaccharides (like glycocalyx), 3D colony.
Attachment is a prerequisite for biolfilms.

Advantages:
- for microorganisms- sharing nutrients and often genetic material, protection against environment (desiccation, pH, etc)
- positive direct impact on human health, intestinal tract = help with digestion, prevent harmful bacteria from colonizing.
- remediation of oil spills, tailings, cleaning of wastewater.

Disadvantages:
- negative direct impact on human health when colonizing teeth, implants like catheters and prothese, contact lenses leading to infection
- found in many ‘wet rooms’ like bathrooms and kitchens
- problem in spread of antibiotic resistance, rapid horizontal gene transfer

Question 24

How are humans impacted by biofilms?

Question 25

Eukaryotic cell walls:

What are the components of cell walls in eukaryotes?

Give an example for each kind of cell wall.

Answer 25

Plants:
Function: support and protection
Components
- cellulose fibres (a linear glucose polymer, glucose joined together by beta 1-4 glycosidic bonds)
- hemicellulose (polysaccharide) function mostly in keeping cellulose fibrils together.
- pectin (polysaccharide)
— in jellies and pudding = gives squishy but stable consistency.
Relatively thin in cell walls of leaves but in woody parts or the stems, cell wall is massive; as thick as the whole diameter of the cell.

Protists:
Many plant-like protists such as diatoms or ‘algae’ have cell walls.
Composition:
- varies but usually cellulose microfibrils or other polysaccharides (sometimes proteins)
- often minerals like silica or calcium carbonate
— causes cell wall to look like mini shells. These shells can sink to bottom of lakes & oceans & make up thick sediment layers that can used as diatomaceous earth.

Fungal (more closely related to animals than plants):
Components:
- main component is chitin (polysaccharide- made of glucose monomers bound together by beta 1-4 glycosidic bonds), which is a diagnostic trait
- proteins

Question 26

Eukaryotic cell walls:

What eukaryotic groups have a cell wall, which one does not?

Answer 26

Animals/animal cells: extracellular matrix

Plants: plant cell wall

Fungi: fungal cell wall

Protists (unicellular eukaryotes): different cell walls

Question 27

Eukaryotic cell walls:

What is the Extracellular Matrix (ECM) and what function does it have?

Answer 27

Is a macromolecular base substance of connective tissue, secreted by fibroblasts and other connective tissue cells, consists of proteins, polysaccharides, and proteoglycans. Rarely faces external environment: main function is binding of cells and tissues (so we don’t fall apart).

Cells secrete ECM through exocytosis

Function:
Is layer between cells and around out cells, is glue that keeps them together and provide some outside structure to keep shape. Protects from external environment and communicates info about external environment.

Question 28

Eukaryotic cell walls:

What are important components of the ECM?

Answer 28

Collagen

Proteoglycans: (glycoproteins) comprise the network between collagen fibres and determine how soft or solid ECM is. 95% polysaccharide, 5% proteins. Smallish. Non-covalently attached to long polysaccharide molecules.
Ex: cartilage proteoglycans are very connected & can absorb water to make soft and elastic. In bones network has mineral crystals embedded and can be very hard

Fibronectins

Intigrins

Question 29

Eukaryotic cell walls:

What is the function of collagen?

Give some examples for the human body.

Answer 29

Collagen (fibrous protein) is for structure. Is triple helix of diff polypeptide chains, provide elastic but firm structure typically for tissues.

In humans, ECM is below epidermal cells. As get older, becomes less firm, collagen get more fragmented and start to see wrinkles. But it is overall firm yet squishness of humans. Provides structural support to maintain shape

Question 30

Eukaryotic cell walls:

What functions do fibronectins and integrins have in the ECM?

Answer 30

Fibronectin (glycoproteins) connect membrane and cytoskeleton. Collagen connected to fibronectin and then fibronectin is connected to integrins, which is connect to cytoplasm and cytoskeleton. = maintains structure

Integrins (proteins) anchor the ECM and convey stimuli. Receptor molecules, convey mechanical stimuli to cells inside (Such as when being squished).

Importantly they are connected to fibronectins that anchor the cell to ECM. B/c of this cells aren’t moving all over the place = cell is neatly organized into tissues.