Week 3: Cell Structure and Function Flashcards
List the three domains into which living organisms are classified. Are organisms in different domains related? Explain.
Bacteria, archaea, Eykarya. Yes, organisms share a universal common ancestor.
Describe and compare the basic cellular organization of prokaryotic and eukaryotic cells. Is one group organized while the other is not? Explain.
Eukaryotic cells have a “true nucleus” that is membrane-enclosed. Also contains other membrane enclosed intracellular structures. Prokaryotic cells are “before nucleus”, lack a membrane- enclosed nucleus and other membrane -enclosed structures. Both have DNA and organization (think paper bag vs. backpack).
In a single sentence, describe the basic structure of the cell membrane. Of what types of molecules is it composed, and how are they arranged?
The cell membrane is composed of a fluid phospholipid layer that contains proteins. Composed of phospholipids arranged a tail to tail layer with the hydrophobic heads inward and the hydrophobic heads facing the outside.
Phospholipids
- membrane foundation
- two layers
- not covalently linked
- fluid and flexible
- hydrophilic heads and hydrophobic tails
In a single sentence, describe the basic function of the cell membrane.
Protects and creates structure for the cell to maintain internal environment while facilitating transportation of molecules in and out of the cell.
Describe the fluid mosaic model of membranes.
explains the fluid structure of the plasma membrane of animal cells as a mosaic of components such as phospholipids, proteins, cholesterol, and carbohydrates. Everything’s fits together like a puzzle.
Integral proteins
proteins that are inserted into the membrane
Peripheral proteins
associated with the membrane surface
What purpose to proteins serve in the plasma membrane?
Enzymes, transportation proteins, receptor proteins.
Describe the semipermeable nature of the cell membrane.
Maintains the cell’s interior as a distinctly different environment. movement into and out of the cell is regulated, not everything can cross the membrane.
How does active transport differ from passive transport?
PassiveActive transport does not require energy and can only move substance down their concentration gradient. While active transport requires energy usage (ATP) and can move substances against their concentration gradient
Describe and differentiate between the processes of diffusion and facilitated diffusion. How are they similar? How are they different?
Diffusion: movement of substance directly across phospholipid bilayer.
Facilitated diffusion: movement of substance across phospholipid bilayer via transport protein.
Both are passive transport, both only work in the direction down the concentration gradient. Differ in facilitation needs a transport protein.
Osmosis
involves the movement of water across the membrane through a specific water channel protein
Aquaporins
Channels used to move water via osmosis.
Hypertonic
solution has more solute and less water
hypotonic
solution has less solute and more water
Describe the process of osmosis using the terms hypertonic and hypotonic.
Movement of water across the membrane and down its concentration gradient. Occurs through channels called aquaporins. Net moment is from hypotonic solution to hypertonic solution.
List 3 types of passive transport
diffusion, facilitated diffusion, osimosis
What is group translocation? How is it important in gathering molecules such as glucose within a cell?
Form of active transport, the transported substance is chemically altered during the process and the membrane is impermeable by this modified substance. Example, glucose is converted to glucose-g-phosphate.
How does a bacterial cell membrane differ from its eukaryotic counterpart?
- Different phospholipid composition: different chemical groups that are immunologically important
- Lacks sterols: such has cholesterol or ergosterol
-Involved in energy transformations: capture of energy and storage for ATP
- Heavily infolded: increases surface area, facilitates transport and energy transformations.
List at least five bacterial cellular structures that are external to the cell membrane.
flagella
sheath
pili
glycocalyx
cell wall
List at least five bacterial cellular structures that are internal to the cell membrane.
Endospores
DNA
Ribosomes
gas vesicle
granules
What is the key function of the bacterial cell wall?
Provide structure/shape and protect from osmotic pressure. Also assists in attachment and resistance to antimicrobial drugs.
What molecule that is possessed only by bacteria is present in virtually all bacterial cell walls?
peptidoglycan
Most bacteria have one of two main types of cell wall. What are these two cell wall types?
Gram-positive bacteria and gram-negative bacteria
Name, describe, and compare the two main types of bacterial cell walls.
Gram positive: NAM and NAM joined by short peptide interbridges.
Gram negative: NAM and NAM directly joined together.
What cellular feature determines the shape of a bacterial cell?
The rigid cell wall.
From a human perspective, why is knowing the shape of bacterial cells important?
Aids in identification of different bacteria.
Name and describe the two basic shapes of bacterial cells.
Coccus/Cocci: Spherical bacteria
Bacillus/Bacilli: rod shaped
Name and describe the most common variations on these basic bacterial shapes.
Coccobacilli: very short rods, easily mistaken for cocci.
Vibrio: short curved rod
Spirillum: long curved rod forming spirals, rigid cell shape.
Spirochete: long helical cell, flexible cell wall, unique mobility.
What two classes of macromolecules are represented in the molecule peptidoglycan?
N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG)
Briefly describe the structure of the glycan chains of peptidoglycan.
Chains are formed by alternating NAM and NAG with covalent linkages. Theses chains are millions of sugars long.
Briefly describe the structure of the cross-links between peptidoglycan’s glycan chains.
Short peptides are attached from NAM to NAM. They are tetra- or penta-peptides, 4 or 5 amino acids long.
How do these cross-links differ between the two main types of bacterial cell walls?
In gram-negative cells the NAM and NAM are directly connected, lacking a peptide chain. In gram- positive cells NAM and NAM are joined by short peptide interbridges.
Describe the basic structure of the Gram-positive cell wall.
Thick layer of peptidoglycan. May contain up to 30 interconnected layers/sheets of glycan chains.
How much does the cell wall contribute to the dry mass of a Gram-positive cell?
40-80% cells dry weight
Compare the permeability of the Gram-positive cell wall to the cell membrane.
permeable to many substances
What is teichoic acid? To what types of molecules is it attached, and how is it named in each of these cases?
homopolymers of phosphorylated subunits. They protrude from the gram- positive cell wall. Negatively charged. Some attach to the peptidoglycan “wall teichoic acids” some attach to the plasma membrane “lipoteichoic acids”.
What are the key roles of teichoic acid?
Specific to gram-positice cells. Helps bacteria adhere to host cells, adhesin.
What is an adhesin?
occurs when adhesive molecules expressed on the bacterial surface bind to host surface receptors
Describe the basic structure of the Gram-negative cell wall.
Thin layer of peptidoglycan with an additional membrane external to the peptidoglycan called the outer membrane. The region in between the cell wall and the cytoplasmic membrane is the periplasm
Compare and contrast the terms cell wall and cell envelope.
The cell wall is the periplasm, peptidoglycan, and outer membrane. The envelope encompasses the cell wall and the cell membrane.
Compare the permeability of the various portions of the Gram-negative cell envelope. Include a discussion of porin channels. Is this relevant to the treatment of Gram-negative bacterial infections? Explain.
The Gram-negative cell envelope is less permeable than gram-positive cells. The porins allow the movement of small hydrophilic molecules into the periplasmic space (excludes many molecules, including some antibiotics). Yes, this makes it more difficult for them to be treated than a gram-positive cell because it takes more invasive methods to treat them.
What is the periplasm, and what metabolic processes occur in the periplasm?
It is the space between the inner and outer membrane of a gram-negative cell. Contains peptidoglycan and periplasm (which is a substance rich in water, nutrients, digestive enzymes, enzymes building peptidoglycan and other substances secreted by the cell). Enzymes break down larger nutrient molecules into smaller molecules that can be absorbed.
Describe the nature of the Gram-negative cell wall’s LPS layer.
The outer leaflet of a gram-negative cell wall is composed lipopolysaccharides (“LPS” layer). The lipid portion of LPS is called “lipid A.” Lipid A functions as an endotoxin.
What is an endotoxin, and what effects does it have on the human body?
A toxin that is present inside a bacterial cell and is released when the cell disintegrates; Dead cell disintegrates and releases lipid A; triggers various body responses in humans like fever, vasodilation, inflammation, shock, blood clotting, etc.
Sepsis is a term describing the presence of bacteria in the blood or other body tissues. How might treating sepsis with antibiotics potentially exacerbate a patient’s problems if the bacterium is Gram-negative?
If they are gram-negative and they do succeed in killing the bacteria, that will cause the gram-negative cells to release the endotoxin Lipid A which could cause symptoms of disease in a human, making the human feel worse.
What diseases are caused by members of the genus Mycobacterium? In what way does the cell wall of this genus differ from most bacteria? Does this affect the treatment of Mycobacterium infections? Explain.
Causes tuberculosis and leprosy. Cell wall is 60% mycolic acid which is a waxy lipid. It adds an extra layer of protection against environmental conditions including antibiotics making it hard to treat.
In terms of cell walls, how do bacteria of the genus Mycoplasma differ from most bacteria? Is the cell membrane modified as well? How does this affect cell shape? How do bacteria of this genus compare to their ancestors in terms of their cell walls? Explain.
They lack cell walls which makes them naturally resistant to antibiotics that target cell walls. They are variable in shape. They have sterols in membrane to confer strength and rigidity (produced from cholesterol obtained from the environment). Osmotic protection normally granted by cell wall is less important because they colonize osmotically protected environments.
A bacterial infection can be effectively controlled by tossing the infected individual in an incinerator. Do antimicrobial compounds offer a better means of control? Explain.
Yes since human cells lack peptidoglycan in their cell walls antimicrobials tat target theses features work to kill bacteria without affecting human cells.
Beta-lactams such as penicillin interfere with bacterial function by targeting what cellular feature? How does this cause bacterial death?
Inhibits cell wall synthesis by covalently binding to transpeptidase enzymes that crosslink NAM. Only works on newly synthesized peptidoglycan not already formed cell walls. With this inhibition the growing bacteria have a weekend cell wall and burst from osmotic pressure.
Not effective on gram-negative bacteria as transpeptidase enzymes is in the periplasmic space where porin channels have the ability to exclude it. In gram-positive it is right on the outer layer since there’s no extra layer protecting it.
Would you expect penicillin to have a greater effect on a rapidly growing bacterial population or a population barely growing at all? Explain.
Rapidly growing, because it specifically works on newly synthesized peptidoglycan.
Compare the mechanisms of penicillin and vancomycin. How are they similar and how are they different?
Vancomycin inhibits crosslinking of glycan chains in gram-positive cells. Does not bind to transpeptidase directly but instead binds to the terminus of pentapeptide to block transpepidase. While penicillin acts on the synthesis of crosslinking of NAM. Both work by weakening the cell wall so it bursts from osmotic pressure. But they act on different cell wall linkages.
Compare the mechanism of bacitracin to that of either penicillin or vancomycin. How are they similar and how are they different?
Bacitracin inhibits the growth of the cell wall by blocking transport of NAM and NAG. Like the other two the cell bursts from osmotic pressure. In comparison it works by inhibiting the building blocks of the cell wall being available vs the other two who prevent linkage of the building blocks.
What type of molecule is lysozyme? Do you produce it? If so, where? How do you benefit from lysozyme production?
Enzymes, produced in many human body fluids like tears and saliva. Destroys the structural integrity of glycan chains by breaking the covalent bonds between NAM and NAG. Prevents bacteria from entering the mucous membrane of the human body.
Compare the mechanism of lysozyme to that of penicillin. How are they similar and how are they different?
Unlike penicillin, lysozyme acts on walls that are already formed. Lysozyme destroys the structural integrity of glycan chains (breaks the bond between NAM and NAG). It results in lysis due to osmotic pressure like penicillin though.
Would you expect lysozyme to have notably different effects on rapidly growing and slowly growing bacterial populations? Explain.
No, because lysozyme acts on all walls. It does not affect wall synthesis and therefore would not have a different effect.
What is the purpose of a Gram-stain?
used to differentiate between gram positive and gram negative bacteria.
List the various steps in a Gram-stain procedure, explaining what is occurring at each step.
1) crystal violet stain (all cells purple, primary stain)
2) Iodine (all cells purple, mordant)
3) Alcohol (gram poss=purple, gram neg=collarless, decolorizer)
4) safranin (gram poss=purple, gram neg= red/pink, counterstain)
What cellular process determines the types of cell groupings a particular bacterial species will characteristically form?
Cell Division
Why might one bacterial species form chains of cells, whereas another species forms irregular clusters?
Based on cell division and their plane of division.
From a human perspective, why is knowing the characteristic groupings of bacterial species important?
Aids in identification of bacteria since we know how different bacteria divides.
Coccus/Cocci
Spherical bacteria
Bacillus/Bacilli
rod shaped
Coccobacilli
very short rods, easily mistaken for cocci.
Vibrio
short curved rod
Spirillum
long curved rod forming spirals, rigid cell shape.
Spirochete
long helical cell, flexible cell wall, unique mobility.
Chains
plane of division parallel to the last plain of division. Pairs or chains, broth works better as not crushed/stacked on solid media.
Packets
each plane of division is perpendicular to the last.
Clusters
plane of division is randomly oriented relative to the last plane.
sworms
ormed by myxobacteria, move as a pack. Form when nutrients are scare so can move through the macroscopic world.
Biofilms
dental plaque, rapidly dividing.
List and briefly describe two different “multicellular associations” found in certain bacterial species.
Sworms: formed by myxobacteria, move as a pack. Form when nutrients are scare so can move
through the macroscopic world.
Bioflims: an assemblage of surface-associated microbial cells, rapidly dividing, dental plaque.
What is a glycocalyx, and where is it located relative to other cellular features?
Gelatinous, stick substance external to the cell wall.
Of what substance is a glycocalyx normally formed?
Most are polysaccharides. But some are polypeptides or a combination of both.
Describe and compare a capsule to a slime layer.
Capsule: distinct and gelatinous, composed of organized repeating units of organic chemicals firmly attached to the cell wall.
Slime layer: irregular and diffuse, stickly, lose water soluble.
What are the key functions of a glycocalyx?
-protects from desiccation
-aids in attachment (important in biofilm formation)
-avoid detection from the immune system (chemicals in capsules are often similar to chemicals in the host body, not immediately detected as foreign.)
S strain
strain of streptococcus pneumoniae, smooth appearance, possess a glycocalyx, pathogenic.
R strain
strain of streptococcus pneumoniae, rough appearance, cells lack a glycocalyx, non-pathogenic.
What is a sheath? What are its key functions? What types of bacteria possess a sheath?
Linear chain of cells, attaches bacteria to solid objects in favorable habitats, and protects from predators. Some aquatic bacteria have sheaths.
What is the key function of bacterial flagella? Do all bacteria possess flagella?
Responsible for bacterial motility, not present in all bacteria.
Describe the location of a bacterial flagellum relative to the cell membrane and cell wall.
Extends from the cytoplasmic membrane and exits the outer membrane of the cell wall.
List the basic structure of a bacterial flagellum.
Filament, hook, basal body
Filament
Long and hollow, composed of the protein “flagellin”. Cells secretes the protein up through the hollow core and the tube is created in a spiral like fashion. Not covered by a membrane and does not contain microtubules.
Hook
curve structure composed of different protein then the filament. Base of the filament is inserted into the hook and it creates a curve so that it does not spin.
Basal Body
composed of several different proteins. Anchors the filament and hook to the cell wall and plasma membrane. Gram neg vs pos attachment differs. Acts as motor.
Compare a bacterial flagellum to a eukaryotic flagellum. Structurally, are they more similar or more different?
More different. Bacterial flagellum is not covered by a membrane and does not contain microtubules.
Describe the mechanism by which a flagellum’s filament is lengthened.
Lengthened in a circular motion out of the filament.
What is the function of the basal body of a bacterial flagellum? How does it work? How does this compare to eukaryotic flagella?
Acts as the motor
How variable are the number and arrangement of bacterial flagella? From a human perspective, why is this important?
Greatly variable, aids in identification and characterization of bacteria.
how fast does flagella rotate?
over 100,000 rpm, about 60 cell lengths per second
Would you describe the flagellum-mediated movement of a bacterium as graceful? Explain.
No, it is sporadic movies in series of “runs” and “tubmles” looks like a drunken stagger.
Would you expect all organisms to be beautiful, elegant, and perfect? Why or why not?
No, because as long as the organism is meeting its needed functions that’s all that matters. They don’t have the cognitive function to prioritize beauty and elegance.
Describe the roles of runs and tumbles in the flagellum-mediated movement of a bacterium. What causes runs? What causes tumbles?
Counterclockwise rotation= propelled forward “run”
Clockwise rotation= reversal of rotation “tumble”
How are flagella coordinated in a bacterium with numerous flagella?
They align and rotate as a single unit.
How can runs and tumbles result in the direction movement of a bacterium termed chemotaxis?
Receptors on the cell surface detect chemicals. Attractant concentration increasing= tumbles suppressed (run is lengthened). Attractant concentration decreasing= no suppression of tumbles. Results in indirect movement towards attractant or away from repellent.
Chemotaxis
Movement in response to a chemical stimulus.
How are chemotaxis, phototaxis, aerotaxis, and magnetotaxis similar, and how are they different? How might each be of benefit to bacteria capable of that type of movement?
Similar in that they represent reasons that direct bacteria movement, different in that the reason for this movement response varies. Propels the bacteria towards something they need or away from something that could harm them.
Chemotaxis
movement in response to a chemical signal
Aerotaxis
movement in response to O2 concentrations
Phototaxis
movement in response to light
Magnetotaxis
movement in response to Earth’s magnetic field, Move downward into sediments with low O2 concentrations.
Thermotaxis
movement
in response to variations in
temperature
How does an endoflagellum differ from a “normal” flagellum? Why types of bacteria possess endoflagella?
between its cytoplasmic membrane and its outer membrane, results in corkscrew movement.
Virulence factors
bacteria-associated molecules that are required for a bacterium to cause disease while infecting eukaryotic hosts such as humans
Describe the structure of a pilus. Do all bacteria possess pili? How many are typically possessed?
- specialized type of fimbriae.
- Possess one or a few.
-Shorter and thinner than flagella, but longer than other fimbriae.
What is the key function of a sex pilus?
Used for conjugation in bacteria (akin to sexual reproduction). Forms a temporary cytoplasmic bridge between bacteria. Combines genetic material from two different sources increasing genetic variation.
Of what benefit is conjugation to bacteria?
increases genetic variation which increases natural selection and thus promotes evolution.
Briefly describe the process of conjugation.
Conjugation is the process by which one bacterium transfers genetic material to another through direct contact. During conjugation, one bacterium serves as the donor of the genetic material, and the other serves as the recipient.
What are the key functions of fimbriae?
- adhesion, especially for biofims. Helps adhere to each other and to substrates via fimbriae and glycocalyces.
- Communication within biofilms, act as electrical wires conduction singlas.
-Rarely used for mobility.
Describe the structure of fimbriae. Do all bacteria possess fimbriae? How many are typically possessed?
- Numeros sticky, rod-like, hollow protein extensions.
- shorter and thinner than flagella
- often hundreds per cell
- possessed by many but not all cells
- main purpose is adhesion to other bacteria and to substrates, rarely used for movement.
YOPS proteins (yersinia outer proteins)
Interfere with host cytoskeleton function
Inhibit cell signaling pathways
Suppress host inflammatory
response
Inhibit phagocytosis
What virulence factors does Yersinia pestis possess?
Possess adhesion to attach bacterium to target cells, capsule acts a s antiphagocytic factor, type III secretory system injects YOPS protein into immune cells of host.
What virulence factors does Helicobacter pylori possess?
powerful flagella for burrowing, protein inhibits acid production in stomach, adhesins, enzymes inhibit phagocytic killing (urease to degrade urea).
