Unit 1.3 Cell membranes and transport Flashcards
Why is it called fluid mosaic model?
Fluid - components (proteins) free to move in membrane
Mosaic - proteins different shapes + sizes, scattered randomly
Tell me all about the plasma membrane… visually and informatively
- First off, it’s practically the cell surface membrane soooo
Visuals + info of the Fluid Mosaic Model:
Phospholipid bilayer
Well it’s the whole layer within the hydrophilic heads
- Aware of hydrophobic tail too within
Extrinsic protein
Positioned as “out of the bilayer”
- Acts as enzymes, receptors, etc.
- They have a charge on the whole thing
Intrinsic protein
The whole body positioned within the bilayer
- Transport proteins that are either:
1. Channel proteins - for facilitated diffusion
2. Carrier proteins - for active transport
- They have a charge however only on the outside and not within bilayer
Glycoprotein
Kinda seems to be like extrinsic protein, just not an extrinsic protein
- Has a carbohydrate chain
- Only on outer edge
- Usually receptors/antigens
Glycolipid
Just like glycoprotein, except it’s not a protein, it’s the phospholipid molecule
- Has a carbohydrate chain
- Only on outer edge
- Facilitate cellular recognition
Cholesterol (only animal cells btw)
Hexagons that have swapped with phospholipid molecule, if u know u know
- Regulated fluidity
Phospholipid molecule
The literally whole bilayer thing, the one with the philic head and phobic tail
- Hydrophilic, polar, phosphate head
- Hydrophobic, non-polar fatty acid
- Tails arrange themselves in centre, away from tissue fluid + cytoplasm
How are proteins positioned within fluid mosaic?
Location of charged regions (+/-)
Charge regions are polar + associate with phosphate heads
- Extrinsic would be mostly charged
- Intrinsic not charge in middle
What can/can’t pass through cell surface membrane/fluid mosaic/plasma membrane?
Can:
- Small molecules e.g. O2
- Non-polar/lipid soluble e.g. Vitamin A
Why:
Small - fit between phospholipid molecules
Non-polar - dissolves in fatty acid tails
Can’t:
- Large e.g. glucose C6H12O6
- Polar e.g. ions
Why:
State the opposite of above
What are the 3 factors affecting membrane permeability
- Temperature
- pH
- Solvents e.g. ethanol
How does temperature affect permeability?
Freezing - ice crystals cause gaps in membrane
Normal temp ranges - increasing temp increases KE, increases fluidity, permeability + diffusion
Hot - proteins denature, bilayer melts, gaps/porous
How do pH affect permeability?
Extremes - H bonds in protein break, changes tertiary structure (3D shape), protein denatures
How do solvents e.g. ethanol, affect permeability?
Dissolves fatty acid tails, gaps in membrane, porous, increases permeability
What are the 3 types of transport
- Simple diffusion
- Facilitated diffusion
- Active transport
Tell me about simple diffusion
Substances:
- Small, non-polar (O2, Vit A + D)
Process:
- Movement of molecules from area of higher conc., to one of lower conc. down conc. gradient, until concentrations equal/evenly distributed
Factors affecting rate:
- Temp, diffusion distance, conc. gradient, surface area
Graph = Diagonal - rate directly proportional to concentration
Tell me about facilitated diffusion
Substances:
-Large molecules e.g. glucose
Process:
- As for simple diffusion, but molecules pass through channel protein
Factors affecting rate:
- As above, plus number + type of channel protein
Graph = Diagonal then straight, as it indicated the channels are used up
Tell me about one type of facilitated diffusion, and ofc details
Co-transport
- Actively pump ion out, build conc. gradient, it diffuse back in, bringing another molecule
Tell me about active transport
Substances:
- Polar molecules e.g. ions
Process:
- Molecules move from lower conc., to an area of higher conc., against conc. gradient, through carrier proteins, using ATP
Factors affecting rate:
- As above, minus conc. gradient, plus rate of respiration + conc. ATP
Tell me about osmosis
Diffusion of water molecules from area of higher ψ to a lower ψ, down ψ gradient, across selectively permeable membrane
Water potential - Concentration of free water molecules, able to move in/out of a system
What are the 3 different water potentials in either plant or animal cells?
- Low ψ (hypertonic)
- Same ψ (isotonic/insipient plasmolysis)
- High ψ (hypotonic)
Tell me about low water ψ in both animal and plant cells
Low ψ:
- Concentrated solution/ hypertonic
- Higher ψ inside cells than solution
- Water leaves cells by osmosis
Animal = Crenated, H2O out
Plant = Plasmolysed, cell contents shrinks, pulls away from cell wall ψ = 0
Visuals for plant:
- Shrunken vacuole
- Cell membrane pulled away from cell wall
Tell me about the same water ψ in both animal and plant cells
Same ψ:
- Isotonic
- No net osmosis
- When no change, ψsol = ψcell
Tell me about high water ψ in both animal and plant cells
High ψ:
- Dilute/pure water, hypotonic
- Higher ψ in solution than cell
- Water enters cell by osmosis
Animal = Lysed, H2O in
Plant = Turgid, strong cell wall
Visuals for plant:
- Vacuole filled with water
- Cytoplasm pushes out against cell wall
- Positive pressure potential as cell wall pushes back
Explain point of insipient plasmolysis
When 50% of sample of plant cells plasmolysed
ψP = 0, therefore ψsol = ψcell
- Cell has just enough water for membrane to pull away from the wall
- Since pressure potential = 0, water potent. of cell equal to solute potent. of surrounding solution
- 50% of cells show signs of plasmolysis when at equilibrium
What can increase rate of diffusion?
- Larger area
- Difference in concentration
- Thinner the surface
What are the 4 types of active transport?
- Ion pumps
- Exocytosis
- Pinocytosis
- Phagocytosis
What are ion pumps?
Ion pumps:
- Proteins that can actively accumulate specific ions on one side of the membrane
- E.g. Gain potassium ions in exchange of sodium ions
What is exocytosis?
Exocytosis:
- Vesicles budded from golgi or endoplasmic reticulum, can fuse with plasma membrane, expelling their contents
What is pinocytosis?
Pinocytosis:
- Ingestion of a fluid/suspension into the cell
- Plasma membrane encloses some of the fluid and pinches off to form a vesicle
What is phagocytosis?
Phagocytosis:
- Ingestion of solids from outside cell
- Plasma membrane encloses a particle and buds off to form a vacuole
- Lysosomes will fuse with it to enable digestion of the contents
What does the influence of cyanide do to transport?
- Cyanide is a strong poison which inhibits respiration by inhibiting the enzyme cytochrome oxidase
- Which catalyses the formation of ATP from ADP and inorganic phosphate.
- As a result of that, no ATP is produced and the cell dies
