membrane structure and function

Question 1

functions of the fluid phospholipid bilayer

Answer 1

• maintains internal/external environment
• prevents passage of water-soluble molecules (eg. ions, sugars, amino acids)
• allows passage of very small uncharged molecules (o2, co2)
• allows passage of lipid-soluble molecules (alcohol, fatty acids, steroids)

Question 2

which kind of fatty acids increase and decrease fluidity?

Answer 2

• unsaturated fatty acids have kinks, so they prevent the fatty acids from packing tightly together. therefore they increase fluidity
• saturated fatty acids have no kink, so they can pack tightly together. therefore they decrease fluidity

Question 2

how do temperature and cholesterol affect fluidity of membrane?

Answer 2

• warm temp=membrane becomes more fluid bc phospholipids have more kinetic energy. SO, cholesterol stabilizes phospholipids, which prevents the membrane from getting TOO fluid
• cold temp=membrane becomes more rigid because phospholipids pack together more closely. SO, cholesterol maintains space between phospholipids and prevents tight packing, which maintains fluidity

Question 3

what are integral proteins

Answer 3

• transmembrane proteins
• have hydrophobic amino acids embedded in the lipid bilayer
• have hydrophilic amino acids that interact with water

Question 4

peripheral proteins

Answer 4

• only found on one side of the membrane
• have fewer hydrophobic amino acids

Question 5

what are the 7 types of membrane proteins?

Answer 5

1. transport proteins (allow material to cross membrane)
2. receptors (receive chemical signal and pass on to nucleus)
3. enzymes (increase rate of chemical reactions)
4. cell adhesion or anchoring proteins (bind cells together)
5. recognition proteins (protrude from surface and identify cells in an immune response)
   6+7. glycoproteins and peripheral proteins (allow membrane to interact with ECM and cytoskeleton)

Question 6

what type of membrane protein has a membrane transport function

Answer 6

transport proteins

Question 7

what type of membrane protein has a signal transduction function

Answer 7

receptors

Question 8

what type of membrane protein has a enzymatic activity function

Answer 8

enzymes

Question 9

what type of membrane protein has a intercellular joining function

Answer 9

cell adhesion or anchoring proteins

Question 10

what type of membrane protein has a cell-cell recognition function

Answer 10

recognition proteins

Question 11

what type of membrane protein has a attachment to cytoskeleton and ECM function

Answer 11

glycoproteins and peripheral proteins

Question 12

define diffusion

Answer 12

net movement of molecules from an area of high concentration to an area of low concentration. no energy is required.

Question 13

why does diffusion occur?

Answer 13

molecules have KE and are in constant motion, they move randomly collide, which leads to even distribution.

Question 14

examples of simple diffusion?

Answer 14

• gases like O2 and CO2
• lipid-soluble molecules like drugs, alcohol, steroids
• small uncharged molecules

Question 15

compare and contrast the functions of the three types of transport proteins and provide an example for each

Answer 15

1. carrier proteins
   - opens one side at a time, binds to specific ions/molecules and undergoes a conformational change to transport them across the membrane
   - passive transport
   - ex: GLUT (glucose transporters for facilitated diffusion of glucose)
2. channel proteins
   - form a corridor through the cell membrane that allows SPECIFIC ions to pass through membrane (each channel is structured to accommodate a particular ion based on size and charge)
   - passive transport
   - ex: ion channels (Na+, K+)
3. pump proteins
   - open one side at a time. specific molecule binds while its open on one side. ATP breaks down into ADP and Pi, the Pi binds to protein, energizing the pump and causing it to undergo conformational change, which allows pump to move molecule against its concentration gradient.
   - loss of phosphate reverts protein shape
   - active transport
   - ex: Na+/K+ pump, proton pump

Question 16

Describe the molecular movement in diffusion, osmosis, and facilitated diffusion

Answer 16

diffusion: molecules are constantly and randomly moving around due to KE, causing them to collide with each other. this leads to even distribution of molecules. even when they reach equilibrium, the net movement is the same in both directions.

osmosis: water moves from an area of low solute concentration to an area of high solute concentration (high water concentration to low water concentration). the movement of water continues until the concentration of solutes is equal on both sides of the membrane (or until other factors prevent further movement).

facilitated diffusion: the passive movement of larger or charged molecules across the cell membrane through specialized transport proteins. molecules move from an area of high concentration to an area of low concentration, but because these molecules are too large or polar (charged) they need help to pass through (channel proteins or carrier proteins).

Question 17

what happens to an animal cell and a plant cell placed in an isotonic solution?

Answer 17

animal cell: no change in cell size, normal
plant cell: no change in cell size, flaccid and plant may wilt

Question 18

what happens to a plant and animal cell placed in a hypertonic solution?

Answer 18

animal cell: cells shrink in size, cell shrivels/crenates
plant cell: membrane pulls away from cell, plasmolysis (lethal)

Question 19

what happens to an animal and plant cell placed in a hypotonic solution?

Answer 19

animal cell: cell swells and may burst (lysis)
plant cell: swells and presses against cell wall, normal for plant cell

Question 20

compare passive transport, active transport, co-transport, and bulk transport, including the
direction of transport, size of molecules, and energy requirements

Answer 20

passive:
- down concentration gradient
- typically small, non-polar molecule like O2, CO2 and water. can also move large molecules with facilitated diffusion
- no energy required

active:
- against concentration gradient
- typically larger or charged molecules like K+, Na+, and large nutrients
- requires ATP

co-transport:
- one molecule moves down its concentration gradient while the other moves against it. the molecule moving down its gradient releases energy, this energy is used by the protein to change shape, allowing it to actively transport the other molecule against its concentration gradient.
- typically smaller molecules
- use of stored gradient (indirectly requires ATP)

bulk transport:
- into cell (endocytosis) or out of cell (exocytosis)
- large molecules such as lipids, proteins, or even whole cells
- requires ATP for the formation of vesicles and the movement of materials in or out of the cell.

Question 21

Explain the processes of exocytosis and endocytosis

Answer 21

exocytosis: vesicles carrying material fuses with membrane to release contents outside of cell

endocytosis: membrane dips in engulfing material, then pinches and fuses to form vesicle surrounding material.

Question 22

what are the three types of endocytosis?

Answer 22

1. phagocytosis “cellular eating”
   - membrane reaches out and engulfs other cells/particles in phagocytic vacuole
   - used by protists as food gather strategy
   - used by host defence cells to get rid of germs
2. pinocytosis “cellular drinking”
   - membrane takes in extracellular fluid and dissolved solutes
3. receptor mediated endocytosis
   - binding of specific molecules to receptors triggers pinching in.

Question 23

what is a membrane potential?

Answer 23

a membrane potential is a voltage difference across a cell membrane caused by a difference in charges inside vs outside the cell.