Mod 2 Chap 5: Plasma Membranes Flashcards

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1
Q

Describe the roles of membranes within cells.

A
  • may house pigments essential for chemical reactions e.g. Chlorophyll on thylakoid membranes of chloroplasts
  • can form vesicles to transport substances e.g proteins from RER to Golgi
  • compartmentalisation (all components needed for a specific function held in one place)
  • folded membranes increases surface area
  • contain enzymes for a specific chemical reaction
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2
Q

Describe the roles of membranes on the surface of cells.

A
  • contain antigens so the organism’s immune system recognises the cell as ‘self’, so does not attack it
  • may release chemicals to signal to other cells
  • separate cell’s components from extracellular environment
  • regulates transport of materials in and out of cells
  • contains receptors for chemical signals, released by other cells
  • may contain enzymes involved in metabolic pathways
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3
Q

What are cell membranes PARTIALLY permeable to?

A
  • v small molecules that can diffuse easily across by moving between structural components of membrane e.g. O2
  • lipid-soluble molecules can dissolve in lipid bi-layer and pass through
  • large polar molecules pass proteins in membrane e.g. Glucose, water
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4
Q

Name the components of the Fluid-Mosaic Model of the plasma membrane and describe their roles.

A

Intrinsic / Integral proteins: are transmembrane (embedded in both layers of membrane), have amino acids w/ hydrophobic R-groups on their external surfaces, which interact w/ hydrophobic core of membrane, holding them in place. Examples:

  • Channel proteins: provide hydrophilic channel allowing passive movement of polar molecules + ions down conc gradient through membranes.
  • Carrier proteins: have role in both passive transport (down a conc gradient) + active transport (against a conc gradient) into cells, this often involves shape of protein changing
  • Glycoproteins: embedded in surface membrane w/ attached carb (sugar) chains, have role in cell adhesion + as receptors for chemical signals (= process of cell communication / cell signalling).

Extrinsic / Peripheral proteins: present in one side of bilayer (can be either, some move between two), normally have hydrophilic R-groups on outer surfaces + interact w/ polar heads of phospholipids / w/ intrinsic proteins.

Cholesterol: a lipid w/ a hydrophilic end + a hydrophobic end, like a phospholipid, regulates fluidity of membranes, positioned between phospholipids in a membrane bilayer so hydrophobic-hydrophilic interactions pull them together, makes cholesterol add stability to membrane without being too rigid, stop phospholipid molecules grouping + crystallising, which stops membrane being too solid.

Glycolipids: similar to glycoproteins, lipids w/ attached carb (sugar) chains, called cell markers / antigens, can be recognised by immune system as self (part of organism) or non self (belonging to another organism).

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5
Q

Describe the process of cell communication / cell signalling, carried out by glycoproteins.

A
  • when chemical binds to receptor, a response is elicited from cell
  • causes a direct response / sets off cascade of events in cell
  • (some drugs act by binding to cell receptors)

Example of this process:
- receptors for peptide hormones such as Insulin + glucagon, which affect uptake + storage of glucose by cells

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6
Q

Describe diffusion as a method of movement for molecules.

A

The net movement of molecules or ions from a region of high concentration to a region of low concentration until they are spread out evenly.

Simple Diffusion:

  • a passive process, no energy required
  • particles able to diffuse across plasma membrane: small non polar molecules that are small enough to fit between phospholipids e.g. O2 + CO2, or water small enough to fit through too, despite being polar
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7
Q

Describe the factors affecting the rate of diffusion.

A
  • concentration gradient: steeper the conc gradient = faster rate of diffusion
  • size of particles: larger particles = slower rate
  • thickness of membrane: thicker membrane = slower rate
  • surface area: larger SA:V ratio = faster rate
  • temperature: higher temp = more KE molecules have = faster their movement = faster rate
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8
Q

Describe the difference between simple diffusion and facilitated diffusion.

A

Simple: diffusion in the absence of a barrier or membrane.

Facilitated: diffusion across a membrane through protein channels.

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9
Q

Describe facilitated diffusion as a method of movement for molecules across membranes.

A
  • large polar molecules can only enter cell by facilitated diffusion, down their conc gradient w/ aid of proteins
  • uses proteins to facilitate (allow) diffusion

The two types of proteins used:

  • channel proteins
  • carrier proteins

Membranes with channel proteins are selectively permeable.

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10
Q

Describe how channel proteins work in facilitated diffusion.

A
  • charged ions / polar molecules like water cannot diffuse through non polar centre of phospholipid bilayer
  • channel proteins form pores to allow them to pass through
  • each is specific to one type of ion (so membrane is selectively permeable here)
  • some can open and close pores, acting like gates
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11
Q

Describe how carrier proteins work in facilitated diffusion.

A
  • allow diffusion of larger polar molecules e.g. Sugar and amino acids
  • molecule attaches to specific binding site on carrier protein
  • this causes carrier protein to change shape to ‘deliver’ molecule through membrane
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12
Q

Describe a practical investigation into the factors affecting diffusion rates in model cells.

A

Investigating factors of: temp and concentration

  • dialysis tubing used as a membrane
  • one end of tubing tied, fill with a solution, then tie other end = model cell
  • place into another solution/s (of various concentrations / sizes of solute molecules)
  • measure changes over time in conc of solute molecules, inside and out of model cell
  • calculate rate of diffusion across tubing (changes in conc divided by time)
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13
Q

Describe active transport as a method of movement for molecules.

A

The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration.

  • a process requiring energy and carrier proteins
  • energy needed as particles are being moved up a conc gradient (opposite direction to diffusion)
  • metabolic energy supplied by ATP
  • carrier proteins span membranes + act as ‘pumps’
  • a selective process, specific substances transported by specific carrier proteins
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14
Q

Describe HOW the process of diffusion occurs for movement of molecules.

A
  • particles in a gas / liquid have KE, so are moving randomly
  • so unequal distribution of particles eventually becomes even, equilibrium is reached so movement is equal in both directions
  • particles are moving at high speeds so are constantly colliding, slowing down their overall movement
  • means that over short distance, diffusion is fast, but as diffusion distance increases, rate of diffusion slows as more collisions have taken place
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15
Q

Describe HOW the process of active transport occurs for movement of molecules into or out of a cell.

A
  • molecule / ion to be transported binds to receptors in channel of carrier protein
  • ATP binds to carrier protein + is hydrated into ADP and phosphate
  • binding of phosphate to carrier protein causes protein to change shape, opening up to other side of cell
  • molecule or ion is released to other side of cell
  • phosphate molecule released from carrier protein + recombined w/ ADP to form ATP
  • carrier protein returns to original shape
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16
Q

Describe Bulk Transport as another form of active transport.

A
  • another form of active transport
  • where large molecules e.g. Enzymes / hormones / whole cells are too large to move through channel / carrier proteins, so move into / out of cell via bulk transport
17
Q

Describe Endocytosis as a form of Bulk Transport.

A
  • the bulk transport of material INTO cells
  • two types: Phagocytosis (for solids), + Pinocytosis (for liquids), but process = same for both
  • cell surface membrane first invaginates (bends inwards) when in contact w/ material to be transported
  • membrane enfolds material until membrane fuses, forming a vesicle
  • vesicle pinches off + moves into cytoplasm to transfer material for further processing inside cell
    ATP energy required for this
18
Q

Describe Exocytosis as a form of Bulk Transport.

A
  • reverse of Endocytosis (transport OUT OF cells)
  • vesicles, usually formed by Golgi apparatus, move towards + fuse w/ cell surface membrane
  • contents of vesicles then release outside of cell
    ATP energy required for this
19
Q

Describe osmosis as a method of movement for water molecules.

A

The net movement of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane.

20
Q

Describe the relationships between the water potential of a solution and its concentration.

A

Pure water: has a high no. of free water molecules and no solute molecules, SO has Water Potential (Psi) = 0 kPa

Concentrated solution: has a low no. of free water molecules, as most are bound to solute molecules, SO has a negative Water Potential (Psi)

The more concentrated the solution, the more negative the Water Potential (Psi)

21
Q

Describe how osmosis is caused between solutions of different concentrations / water potentials.

A
  • when solutions of diff concentrations (so diff water potentials), are separated by partially permeable membrane, water molecules can move been the solutions but solutes usually can’t
  • so will be a net movement of water from solution w/ higher water potential (less concentrated) to solution w/ lower water potential (more concentrated)
  • this net movement continues until water potential = equal on both sides of membrane (equilibrium is reached)
22
Q

Describe the effects of osmosis on plant cells.

A

TURGIDITY:

  • water moves into plant cell, down water potential gradient, by osmosis
  • cell swells and contents press outwards onto cell wall
  • cell wall exerts pressure back against hydrostatic pressure
  • no more net entry of water, so cell is TURGID

EQUILIBRIUM:

  • water potential outside cell equal to water potential inside cell
  • so no net movement of water, there is an equilibrium

PLASMOLYSIS:

  • water potential inside cell > water potential outside cell
  • water moves out of plant cell, down water potential gradient, by osmosis
  • cell membrane starts to shrink away from cell wall
  • cell is FLACID
  • if water continues to leave cell, plasma membrane pulls away from cell wall
  • cell is PLASMOLYSED
23
Q

Describe the effects of osmosis on animal cells.

A

CELL BURSTING / CYTOLYSIS:

  • water potential outside cell greater than water potential inside cell
  • net movement of water into cell, increases hydrostatic pressure
  • cell surface membrane cannot stretch much and cell bursts, (CYTOLYSIS)

EQUILIBRIUM:

  • water potential outside cell = water potential inside cell
  • no met movement of water, there is an equilibrium

CRENATION:

  • water potential outside cell is lower than water potential inside cell
  • net movement of water out of cell
  • cell shrivels and puckers, (CRENATION)
24
Q

Describe a practical investigation into the effects of solutions of different water potentials on plant and animal cells.

A
  • pieces of potato / onion can be placed into sugar / salt solutions w/ diff concentrations (so diff water potentials)
  • water will move into / out of cells depending on water potential of solution relative to water potential of plant tissue
  • as plant tissue gains / loses water it will increase / decrease in mass and size
25
Q

What are the factors that affect membrane structure and permeability?

A
  • temperature

- presence of solvents

26
Q

Describe temperature as a factor affect membrane structure and permeability.

A
  • phospholipids in a cell membrane are constantly moving
  • when temp increases, phospholipids have more KE + so move more
  • makes membrane more fluid, so begins to lose its structure, will eventually real down completely
  • loss of structure increases permeability of membrane, so easier for particles to cross it
  • carrier + channel proteins in membrane denatured at high temps, increasing membrane permeability too
27
Q

Describe solvents as a factor that affect membrane structure and permeability.

A
  • water (polar solvent) = essential in formation of phospholipid bilayer
  • many organic solvents are less polar than water, or are non polar
  • these will dissolve membranes, disrupting cells
  • pure or v strong alcohols are toxic as they destroy cells in body, less concentrated solutions of alcohols will not dissolve membranes but can still cause damage
  • non polar alcohol molecules can enter cell membrane between phospholipids, which disrupts membrane
  • makes membrane more fluid + more permeable, in neuronal membranes for e.g., this means nerve impulses are no longer transmitted as normal
  • also happens to neurones in brain, explain behavioural changes after alcohol consumption