1.8 - Membranes and Transports

Question 1

What does the hydrophobic region of the lipid layer of cell membrane o?

Answer 1

The hydrophobic region decides whether or not water is allowed to come in/go out of the cell

Question 2

What is membrane fluidity dependent on?

Answer 2

Membrane fluidity is dependent of whether the phospholipids contained in the lipid dbilayer are saturated or unsaturated

Question 3

What is temperature fluidity dependent on?

Answer 3

Temperature fluidity is dependent on cholesterol (steroid with a 4-ring chain)

• Cholesterol inserts itself into the membrane to prevent phospholipids from clumping at low temperatures, and to help them get closer together at high temperatures. This helps to keep the fluidity at an acceptabl level in both temperature extremes

Question 4

What are the 6 membrane protein functions?

Answer 4

1. Allow/transport molecules into cell
2. Enzymatic activity (chemical reactions)
3. Signal transduction (turning proteins on/off)
4. Cell-cell recognition (cells joining together to create tissue)
5. Intercellular joining (hooking together with neighbouring cells’ membrane proteins)
6. Attachment to the cytoskeleton and extra-cellular matrix (ECM) (Microfilaments/other parts of cytoskeleton bond to membrane proteins)

Question 5

What are the 3 forms of transportation across membranes?

Answer 5

1. Active transport
2. Facilitated diffusion
3. Diffusion

Question 6

What are the 2 forms of passive transport?

Answer 6

Facilitated diffusion and diffusion

Question 7

What is facilitated diffusion?

Answer 7

Facilitated diffusion is the movement of a larger/chemcially charged molecule across membranes with the help of a protein (piggy-backing onto protein for help “crossing the border”)

Question 8

What are permeases?

Answer 8

Permeases are carriere proteins used to transport large/electrically charged molecules across membranes during facilitated diffusion

Question 9

What is a concentration gradient?

Answer 9

A concentration gradient occurs when the concentration of molecules is higher in one area than another

Question 10

What is diffusion?

Answer 10

Diffusion is movement from an area of high concrentation to low concentration. This transport does NOT reqeuire energy

Question 11

What is active transport?

Answer 11

Active transport is pumping against concentration gradients (transport from a low concentration area to a high concentration area). This transport requires ATP (energy)

Question 12

What factors affect diffusion rates?

Answer 12

• How high the concentration of molecules is
• The temperature
• The distance that the molecules must travel
• The size of the molecules (big ones move slowly, small ones move quickly)
• If molecules are charged (opposite charges (+/-) attract, like charges (+/+) repel)

Question 13

What is dynamic equilibrium?

Answer 13

Dynamic equilibrium occurs when molecules are still in motion, but no concentration gradient exists (all the same concentration, no higher/lower)

Question 14

What is required for simple diffusion across bilayers?

Answer 14

To diffuse across bilayers, different molecules can/cannot enter the cell without help from a protein

Question 15

What is osmosis?

Answer 15

Osmosis is the movement of water molecules from a solution with a high concentration of water molecules to a solution with a lower concentration of water molecules, through a cell’s partially permeable membrane.

• Osmosis = water molecules travelling through a selectively permeable membrane to an area with a high concentration of solutes (salt/water)

Question 16

What is an isotonic solution?

Answer 16

An isotonic solution meas there is the same concentration of solute and solvent inside the cell as ouside (equilibrium/homeostasis)

Question 17

What is a hypotonic solution?

Answer 17

A hypertonic solution means the fluid inside has a higher concentration of solutes (or a lower concentration of water molecules) than outside the cell, so water will flow out of the cell

• Cells will BURST! Water rushing in, cells will bloat and explode

Question 18

What is a hypertonic solution?

Answer 18

A hypertonic solution means the fluid inside has a higher concentration of water molecules (or a lower concentration of solutes) than outside the cell, so water will flow out of the cell

• Cells will SHRIVEL! Water will rush out, cells will dry up and be thirsty

Question 19

What is the sodium-potassium pump?

Answer 19

The sodium-potassium pump is a revolving door into/out of the cell that is powered by ATP. First, 3 sodum ions enter the protein (which acts like a revolving door). In doing so, they change the shape of the protein, which opens the door into the cell. The sodium ions are then deposited into the cell, while 2 potassium ions enter the doorway. The doorway then changes shape and opens out of the cell, and the potassium ions are then deposited outside of the cell.

• The inside of the cell is negative, and the outside of the cell is positive

Question 20

What is an electrochemical gradient?

Answer 20

An electorchemical gradient is a concenetration gradient with ions

• Ex: with sodium-potassium pump, there is a high concentration of potassium ions insided the cell, and a high concentration of sodium ions outside the cell (and low concentrations of each ion in the opposite ions “high concentration area”)

Question 21

What is endocytosis?

Answer 21

Endocytosis is the process by which cells absorb molecules (like proteins) by engulfing them. The engulging process is carried out by the lysosome (aka the grim reaper, responsible for clean up within the cell)

• Taking stuff from outside the cell and sucking it in

Question 22

What are the 3 kinds of endocytosis?

Answer 22

1. Phagocytosis
2. Pinocytosis
3. Receptor mediated endocytosis

Question 23

What is phagocytosis?

Answer 23

Phagocytosis is the process of taking up/eating solids

Question 24

What is pinocytosis?

Answer 24

Pinocytosis is the process of taking up/eating liquids

Question 25

What is receptor mediated endocytosis?

Answer 25

Receptor medidated endocytosis is the process of taking up/eating specific substances using receptors/docking stations located on the plasma membrane

Question 26

What is exocytosis?

Answer 26

Exocytosis is the process by which a cell directs the contents of secretory vesicles out of the cell membrane

• Making stuff inside the cell and spitting it out