Module 3: Plasma Membrane - Anatomy

Question 1

cells

Answer 1

• simplest unit of life
• all organisms are composed of cells
• all physiological processes are based on cell activity

Question 2

Plasma Membrane

Answer 2

• surrounds cell, defines boundaries
• made of proteins and lipids
• selectively permeable

Question 2

Extracellular fluid (ECF)

Answer 2

Fluid outside of cells includes tissue fluid

Question 2

Cytoplasm

Answer 2

• organelles
• cytoskeleton
• inclusions (stored or foreign particles)
• cytosol (intracellular fluid, ICF)

Question 2

Plasma Membrane: Glycocalyx

Answer 2

carbohydrate chain + protein –> glycoprotein
carbohydrate chain + lipid –> glycolipid

functions:
- protection
- cell adhesion
- immunity to infection
- fertilization
- defense against cancer
- transplant compatibility

Question 2

Plasma Membrane: Lipids (98%)

Answer 2

Phospholipids
- 75% of membrane lipids
- amphipathic molecules arranged in a bilayer
- Hydrophilic phosphate heads face water on each side of the membrane
- hydrophobic tails are directed toward the center, avoiding water
- drift laterally, keeping membrane fluid
Cholesterol
- 20% of lipids
- stabilizes membrane at warmer temperatures
- keeps membrane fluid at lower temperature
Glycolipids
- 5% of lipids
- Phospholipids with short carbohydrate chains on extracellular surface
- contribute to GLYCOCALYX-carbohydrate coating on cell surface

Question 3

Plasma Membrane: Proteins (2%)

Answer 3

Integral proteins
- transmembrane proteins pass completely through the membrane
- Some drift in membrane; others are anchored to cytoskeleton

Peripheral proteins
- adhere to one face of the membrane
- often anchored to transmembrane
- often anchored to transmembrane protein and/or cytoskeleton
functions:
- stability
- receptors
- enzymes
- molecule transfer (cytochrome c)

Question 3

Plasma membrane: Border of a cell

Answer 3

Composed of
- a bilayer of phospholipids with embedded and attached proteins
- has intracellular and extracellular faces
Functions
- defines cell boundaries
- governs interactions with other cells
- controls passage of materials in and out of cell: Selectively Permeable

Question 4

Selectively Permeable Membranes

Answer 4

• plasma membranes limit what can get into our cells
• some things easily cross these phospholipid bilayers, but most things do not

Question 4

Concentration Gradient

Answer 4

the difference between the regions of high concentration and low concentration

Question 5

passive transport

Answer 5

• requires NO energy
• high to low
• along/down the concentration gradient

Question 6

active transport

Answer 6

• requires energy
• low to high
• against the concentration gradient

Question 7

passive transport: diffusion

Answer 7

the passive net movement of solute particles from regions of high to low solute concentration (down the gradient)

Question 8

diffusion: factors that affect rate

Answer 8

• temperature
• molecular weight
• steepness of the concentration gradient
• membrane surface area
• membrane permeability

Question 9

passive transport: osmosis

Answer 9

the passive net movement of water particles across a selectively permeable membrane from regions of:
- high water potential to low water potential
- low solute concentration to high solute concentration (when solute cant pass)

Question 10

osmosis

Answer 10

• passive
• along water potential gradient
• no ATP is required
• may or may not be facilitates by aquaporins

Question 11

passive transport: filtration

Answer 11

• particles are driven through membrane by physical pressure

examples:
- filtration of water and small solutes through gaps in capillary walls
(allows delivery of water and nutrients to tissues)
(allows removal of waste from capillaries in kidneys)

Question 12

Active transport

Answer 12

• against the concentration gradient (low to high concentration)
• using membrane protein pumps
• using energy
  either directly from ATP hydrolysis –> primary transport
  or indirectly from ATP hydrolysis –> secondary transport

Question 13

Primary Active Transport

Answer 13

• uses energy directly from the breakdown of ATP
• phosphorylation of pump occurs

ion pumps
- maintain internal (ions)
ex) Ca2+ Pump in plasma membrane of RBCs

Question 14

Primary Active Transport

Answer 14

Sodium-Potassium ATPase
- carrier protein
- co-transporter
- anti-porter
- active transporter

Moved Na+ and K+ up concentration gradient
- pumps 3 Na+ out
- pumps 2 K+ in

Question 15

Secondary Active Transport

Answer 15

• moves substances against concentration gradient
• uses energy from movement of second substance down its gradient
• kinetic energy providing “power” to pump other substance
• dependent on Na+/K+ pumps for energy

two types
- symport
- antiport

Question 16

Vesicular Transport

Answer 16

a cell uses two mechanisms to move large molecules across membranes

exocytosis is used to export bulky molecules such as proteins or polysaccharides

endocytosis is used to import substances useful to the livelihood of the cell

in both causes, material to be transported is packaged within a vesicle that fuses with the membrane

Question 17

endocytosis: phagocytosis

Answer 17

the engulfment of a particle by wrapping cell membrane around it, forming a vacuole

Question 18

endocytosis: pinocytosis

Answer 18

the same thing except that fluids are taken into small vesicles

Question 19

endocytosis: receptor-mediated endocytosis

Answer 19

uses receptors in a receptor-coated pit to interact with a specific protein, initiating the formation of a vesicle