Topic 2: Cell Physiology I

Question 1

The Cell Membrane

Answer 1

• Phospholipid Bilayer
• Membrane Proteins
• Membrane Carbohydrates

Question 2

Phospholipid Bilayer

Answer 2

• continuous layer around the cell

- barrier to water soluble substances – NOT to small molecules (O2 & CO2) and lipid soluble molecules

Question 3

Membrane Proteins

Answer 3

• Transport Proteins
• Receptor Proteins
• Enzymes
• Joining Proteins
• Identifying Proteins

Question 4

Transport Proteins

Answer 4

• Channels

- Carrier Proteins

Question 5

Channels

Answer 5

• form pore in membrane
• selectively permit channel-mediated facilitated diffusion of water & specific ions
• Can be:
• -gated: can open or close – when signaled
• -non-gated (= leakage channels): always open

Question 6

Carrier Proteins

Answer 6

• bind solute + carry it across membrane

- allow protein carrier-mediated facilitated transport OR active transport

Question 7

Receptor Proteins

Answer 7

• can bind specific extracellular molecules (= ligands) e.g. hormones, neurotransmitters (nt)
• e.g. glucose uptake:
• -insulin binds to receptor on skel. muscle or adipose tissue
• -triggers movement of more glucose transporters to cell membrane
• -⇑ glucose movement from blood into cells

Question 8

Enzymes

Answer 8

• control chemical reactions on outer or inner surface
• e.g. acetylcholinesterase
• e.g.2: Na+/K+- ATPase - all cells have these

Question 9

Joining Proteins

Answer 9

• control anchor cell membrane to cytoskeleton or an adjacent cell
• junctional proteins between cells forming:
• -desmosomes, tight junctions, and gap junctions
• extracellular fibers (usually glycoproteins)

Question 10

Identifying Proteins

Answer 10

e. g. Major Histocompatibility Complex (MHC) proteins
- on surface of all cells except rbc
- identify cell as “self” (part of the body) – not foreign

Question 11

Membrane Carbohydrates

Answer 11

• glycoproteins and glycolipids

- differs for every cell type - allow cells to recognize type e.g. sperm recognizes egg

Question 12

Membrane Transport

Answer 12

movement of material between the intra and extra cellular fluids

Question 13

Solute vs Solvent

Answer 13

• substance dissolved in a solution

- Solvent – substance solute is dissolved in e.g. water

Question 14

-Types of transport

Answer 14

• Passive Transport

- Active Processes

Question 15

Passive Transport

Answer 15

• no energy required (no ATP)
• movement from a high to low concentration (i.e. down its conc. gradient)
• the greater the difference in concentration = the more molecules want to move

Question 16

Passive Transport Types

Answer 16

Solute movement:
-Simple diffusion 
-Facilitated diffusion
-Facilitated transport 
Solvent movement:
-Osmosis

Question 17

Simple diffusion

Answer 17

• solute diffuses directly through cell membrane bilayer

- small and lipid soluble molecules (O2, CO2, etc.)

Question 18

Facilitated diffusion

Answer 18

-ions diffuse through membrane via protein channels

Question 19

Facilitated transport

Answer 19

• large, charged or water soluble molecules
• diffuse across membrane using a specific carrier protein – must bind to protein to be transported
  e. g. glucose into liver or skeletal muscle

Question 20

d) Osmosis

Answer 20

• movement of H2O across a semipermeable membrane (permeable to H2O) due to [H2O] difference (H2O moves down it’s concentration gradient) via pores (channels) or across the membrane bilayer
• note:
• [solute] depends on the number of ions or molecules not the type

Question 21

high [H2O]

Answer 21

low [solute] (dilute solution)

Question 22

low [H2O]

Answer 22

high [solute] (concentrated solution)

Question 23

Osmotic Pressure

Answer 23

• pressure that must be applied to prevent movement of H2O from a pure H2O solution (S1) across a semipermeable membrane into another solution (S2)
• the greater [solute] in solution the greater OP and lower [H2O] ⇒ water will want to move in (down gradient)
• OP is used as a measure of the [solute] of a solution
• high OP = high [solute] (low [H2O])

Question 24

Tonicity

Answer 24

• response of a cell immersed in a solution

- depends on [solute] (and permeability of cell membrane to solute)

Question 25

Tonicity classification

Answer 25

- Hypotonic solution - Hypertonic solution - Isotonic solution

Question 26

Hypotonic solution

Answer 26

- ECF has lower OP (higher [H2O]) than ICF (cytosol) - cell swells (takes in water) + may burst - swelling can rupture cell = lysis - if rbc = hemolysis

Question 27

Hypertonic solution

Answer 27

- ECF has higher OP (lower [H2O]) than ICF (cytosol) | - cell shrinks (loses H2O)

Question 28

Isotonic solution

Answer 28

- ECF and ICF have equal OP - cell neither swells nor shrinks - rbc - all [solutes] within equals a 0.9% saline solution (= normal saline)

Question 29

Tonicity uses

Answer 29

- injecting 10% sucrose solution (hypertonic) will move water to blood stream e. g. use to ⇓ brain edema (swelling)

Question 30

Osmosis role in [Solute] regulation

Answer 30

- Concentration of solutes in body fluids must be maintained within narrow limits or cells will die e. g. If body loses H2O (e.g. sweat) ⇒ ⇑ [blood] ∴ blood OP ⇑ ⇒ fluid moves from tissues to blood - response = thirst and ⇓ renal H2O loss which leads to ⇓ urine production

Question 31

Major body fluids

Answer 31

- extracellular fluids=blood plasma, interstitial fluid | - intracellular fluid

Question 32

Bulk Flow

Answer 32

- movement of fluid (+ solutes) due to a pressure gradient (high pressure to low pressure) e. g. cell membrane, blood vessel wall (= blood pressure) e. g. Capillary – if blood has higher pressure than ISF, fluid flows out of the capillary (= filtration)

Question 33

hydrostatic pressure

Answer 33

Pressure of a fluid pressing against a surface

Question 34

Active Processes

Answer 34

Require energy (ATP)

Question 35

Active Process types

Answer 35

- Active Transport | - Vesicular Transport

Question 36

Active Transport

Answer 36

- substances move against conc. gradient (low to high) | - always protein carrier-mediated

Question 37

Active Transport types

Answer 37

- Primary (1°) Active Transport | - Secondary (2°) Active Transport

Question 38

Primary (1°) Active Transport

Answer 38

- molecular pumps - ATP breakdown is directly part of transport process e. g. Na+/K+-ATPase Pump – 3 Na+ out of cell and 2 K+ in per ATP

Question 39

Secondary (2°) Active Transport

Answer 39

- cotransport (use of ATP is indirect) e. g. glucose entry at small intestine - 2 steps: - Na+ gradient established by Na+/K+-ATPase (ATP use step) - glucose & Na+ both must bind to carrier and are cotransported into the cell ⇒ Na+ moving down its concentration gradient drives in glucose against its concentration gradient (transport step)

Question 40

Vesicular Transport

Answer 40

substance is surrounded by a membrane within a cell (vesicle)

Question 41

Vesicular Transport types

Answer 41

- Endocytosis | - Exocytosis

Question 42

Endocytosis

Answer 42

- movement into a cell | - phagocytosis or pinocytosis

Question 43

Phagocytosis

Answer 43

- large items into cell (e.g. bacteria) | - = “cell eating"

Question 44

Pinocytosis

Answer 44

- fluids (+ dissolved substances) | - = “cell drinking”

Question 45

Exocytosis

Answer 45

- movement out of cell - vesicles containing hormones, enzymes, neurotransmitters, etc. - fuse with cell membrane releasing contents into ECF (triggered by a rise in cytosolic Ca++)