plasma membranes

Question 1

how does the cell membrane compartmentalise and regulate

Answer 1

• membranes separate the cell / organelle (eukaryotic) contents from the environment
• control what can and cannot move between cells and their surroundings (selectively permeable)

Question 2

describe the structure of a phospholipid and its significance

Answer 2

• amphipathic: hydrophobic and hydrophilic regions
• head (phosphate), polar, hydrophilic
• tails (glycerol and fatty acid), non-polar hydrophobic
• hydrophobic: water repelling, non-polar, cannot form h bonds with water, hide inside membrane, hydrophobic interaction
• hydrophilic: water-attracting, polar, forms h bonds with water, outer surface facing cytoplasm of extracellular fluid
• significance: hydrophobic areas allow for compartments to form, boundary for entire body, ensures that cells and organelles don’t dissolve in water

Question 3

what is the fluid mosaic model

Answer 3

• fluidity: change shape without breaking apart, phospholipids can move freely relative to one another (due to kinks in fatty acid structure)
• not bound together as a polymer (just attraction)
• not a static structure, able to flow and move
• unsaturated hydrocarbon (cis double bond - bending), prevents packing, enhancing fluidity
• lateral / flip-flopping movement of substances across membrane can occur
• mosaic: collage of proteins embedded in membrane (cholesterol, carbohydrates),

Question 4

what are membrane proteins

Answer 4

• determine membranes functions
• particles form bonds with proteins (AA), different bonds, charges and polarities
• embedded: hydrophilic and hydrophobic region, mimics phospholipid structure (amphipathic)
• channel / carrier: allow transport, arrangement of AA chains (varying structure, different substances pass through and allow bonding)
• peripheral: bound to membrane surface, carbohydrates (covalently bonded to proteins or lipids)
• transmembrane integral protein (TIP): penetrate hydrophobic core, span entire membrane, hydrophilic channel
• cholesterol (TIP): temperature buffer, high temperature (restrains movement), low temperature (maintains fluidity, prevents tight packing)
• aquaporin (TIP): transport protein that moves water, water channel

Question 5

what is selective permeability

Answer 5

• permeability of membranes to molecules and ions
• depends on lipid solubility, electrical charge and size
• large charged polar: charge difference across various areas
• small uncharged polar: small, neutral charge across the area of the molecule
• permeable: gases, small uncharged polar (ethanol)
• not permeable: charged polar (AA, ATP), macromolecules

Question 6

what is passive transport

Answer 6

• movement down gradient (high solute to low solute) without energy input
• simple: movement through phospholipids
• facilitated: movement through proteins, channel (simple pathway, aquaporin), carrier (conformational change, forms / breaks bonds as substance moves across)
• rate: movement over time, depends on membrane permeability and gradient magnitude

Question 7

what is an electrochemical gradient

Answer 7

• high conc. to low conc. (attraction of opposite)
• ion moving against voltage gradient (attraction of like)
• two combined forces: ions concentration gradient and electrical charge (membrane potential)
• membrane potential: voltage that exits across a membrane (inside vs outside), causes reactions to occur, stimulus, maintain gradient, potential to do work
• forces work together to guide movement
• proton pump: generate energy by generating voltage (charge separation) across membranes, creates gradient (movement of H+), conc. gradient represent a dual energy source that can drive other processes (uptake of nutrients)

Question 8

describe water movement

Answer 8

• osmosis: water travels passively across membranes to region of highest solute concentration (low water)
• aquaporin: membrane protein with hydrophilic channel
• high water conc. to low water conc., passive
• high water potential to low water potential (not bound, free, high energy)
• higher free energy to lower free energy (not bound, free, high potential)
• water potential: measures concentration of free water
• high: low solute, high free energy / free water
• low: high solute, low free energy / free water

Question 9

describe RBC and plant cells when placed in different solutions

Answer 9

• RBC: lose water and shrink (crenate) or become bloated and burst (lyse)
• plant: shape of plants is maintained by cell turgor (turgidity, does not burst), water continually moves from cells to atmosphere which has low water potential, if it isn’t replaced turgor is reduced
• plasmolysis: contraction of cytoplasm away from the cell wall (shrink)
• hypo: RBC burst, plant cell is turgid and normal
• iso: RBC is normal, plant cell is flaccid
• hyper: RBC shrivelled, plant cells plasmolyse

Question 10

what are the three types of solutions

Answer 10

• isotonic: equal solute concentration
• hypertonic: high solute concentration outside (shrivelled cell, water leaves), hyper to hypo
• hypotonic: low solute concentration outside (water enters, swell / lysis), hypo to hyper