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.