Chapter 7: Cell Membrane

Question 1

Selective Permeability

Answer 1

Cell allows some substances to travel “across” the membrane

Question 2

Amphipathic

Answer 2

When a molecule has hydrophobic AND hydrophilic regions (exp phospholipid bilayer; most common kind of membrane lipid)

Most cell membrane proteins and lipids are amphipathic

Question 3

Fluid mosaic model of cell membranes

Answer 3

Made of mosaic of protein molecules bobbing in a fluid bilayer of phospholipids

Proteins occur in patches based on shared, specialized function

More densely packed in some areas of the membrane than others

Question 4

Fluid phospholipid bylayer

Answer 4

Must be fluid to work properly

Membrane lipids can move about the membrane laterally; they don’t have to stay in the same position.

Held together primarily by hydrophobic interactions

Fluid becomes more rigid/solid as temp drops (unless it’s made of phospholipids with kinked/unsaturated tails)

Question 5

Cholesterol “fluidity buffer” in the membrane

Answer 5

Found in the cell membrane

Makes the membrane less fluid at lower temperatures bc it impedes the close packing of lipids; helps membrane resist temp-based changes in fluidity

Question 6

2 major membrane proteins

Answer 6

Integral Protein

Peripheral Protein

Question 7

Integral (membrane) protein

Answer 7

Proteins that penetrate the hydrophobic interior of the phospholipid bilayer (transmembrane)

Question 8

Peripheral Proteins

Answer 8

Loosely bound to the surface of cell membrane

Sometimes bound to the exposed part of integral proteins

Question 9

Integrin

Answer 9

Type of integral transmembrane protein

Enhances strength of the membrane

Question 10

Transmembrane Protein Structure

Answer 10

May have N terminus region (sticking out of the membrane), secondary alpha helix region (within the hydrophobic part of the bilayer) and a C terminus (inside the cell cytosol)

p/ 129 bacteriorhodopsin

Question 11

Glycolipids and glycoproteins

Answer 11

Types of molecular markers used by cells to identify one another

Question 12

Nonpolar molecules vs phospholipid bilayers

Answer 12

Non polars like hydrocarbons, CO2, and O2 can dissolve in the bilayer and pass through it without any help from the cell

Question 13

polar molecules vs phospholipid bilayers

Answer 13

Polars can’t get through the hydrophobic part of the bilayer without help from transport proteins

Passive transport

Question 14

Transport/Channel Proteins

Answer 14

Help materials pass through the membrane:

exp. Aquaporins: used to transport H2O

Question 15

Tonicity

Answer 15

The ability of a surrounding solution to cause a cell to gain or loose water

Depends on the concentration of solutes that cannot pass through the cell membrane

If there is a higher concentration of non penetrating solutes in the surrounding solution, water will tend to leave the cell and vice versa;

Free water goes to where the solutes are

Question 16

Plasmolysis

Answer 16

When the environment around the PLANT cell wall is hypertonic and the water leaves the cells, causing the membrane to shrivel but the cell wall stays in tact.

Causes plants to wilt

Question 17

Facilitated Diffusion/Passive Transport:

Channel Proteins

Answer 17

No energy req by the cell; materials being moved DOWN their concentration gradients

Basically and open protein gate that material can flow through to pass through the cell membrane

exp. aquaporins transport water
ion channels transport ions (some have gates)

Question 18

Facilitated Diffusion/Passive Transport:

Carrier Proteins

Answer 18

No energy req by the cell; materials being moved DOWN their concentration gradients

Change shape to allow materials to travel through the membrane

Question 19

Active transport

Answer 19

Energy IS req by the cell; materials being moved UP their concentration gradients

ATP may give up a phosphate group to activate the transport protein, which changes shape to facilitate the transport exp NaK pump

Question 20

Membrane potential

Answer 20

Potential energy of the cell membrane

Requires active transport the maintain desired balance of negative and positively charged ions inside and outside of the cell

Involves effects of ions’ concentration gradient and electrochemical gradiant (charge attractions/repulsion)

Question 21

Electrogenic Pump

Answer 21

Transport protein that generates voltage across the cell membrane (by pumping ions in or out of the cell)

exp. NaK pump in ANIMALS
Proton pump in PLANTS, FUNGI, BACTERIA (transports hydrogen ions)

Question 22

Cotransport

Answer 22

When the activity of a one pump or some passive transport of a material down its concentration gradient indirectly drives the active transport of some other material
???

Question 23

Bulk transport

Answer 23

Active, req energy, transport of large materials like proteins and polysaccharides

Exocytosis: when vesicle buds OFF the golgi and travels along the microtubules to the plasma membrane where it can fuse with in and then pass on its contents; exportation

Endocytosis: reverse of exocytosis

Question 24

3 types of endocytosis

Answer 24

phagocytosis: Eating
Pinocytosis: Drinking
receptor mediated endocytosis: cholesterol processing

Question 25

Ligand

Answer 25

Any molecule that binds specifically to a receptor site of another molecule

Involved in receptor mediated endocytosis

Question 26

What can pass/diffuse through the membrane without help

Answer 26

Nonpolar molecules (like hydrocarbons, CO2, H2O)

Partly because they are small enough to fit but mostly because they are hydrophobic

Question 27

What can NOT pass/diffuse through the membrane without help

Answer 27

Polar/hydrophilic molecules (like mean polar bears and sugars) and ions

These diffuse very slowly and need help to move through the membrane