Plasma membrane, cytoskeleton and transport WK2

Question 1

Describe the structure and function of plasma membrane (have diagram look over)

Answer 1

-Border of cell separating internal and external environments
-selective, differentially, permeable lipid bilayer
-Controls entry and exit ions, e.g. Na+, K+, Ca+
-Passive/active control of substance into cell

Question 2

Describe membrane lipids. Mention phospholipids

Answer 2

-75% of membrane lipids are phospholipids
-Amphipathic molecules arranged in bilayer
-Hydrophilic (polar) phosphate heads face H2O on each side of membrane
-Hydrophobic fatty acid tails directed towards centre

Question 3

What are two types of membrane lipids? Describe them in the bilayer

Answer 3

Cholesterol
-Holds phospholipids still, can stiffen membrane

Glycolipids
-Phospholipids with short carbohydrate chains on extracellular face
-Contributes to glycocalyx-carbohydrate coating on cell surface

Question 4

Describe integral membrane proteins

Answer 4

penetrate membrane
-Transmem proteins pass through
-Hydrophilic regions contact cytoplasm + extracellular
-Hydrophobic regions pass through lipid of membrane
-Some drift in membrane other anchored to cytoskeleton

Question 5

Describe peripheral membrane proteins

Answer 5

adhere to one face of membrane
-do not penetrate membrane
-usually tethered to cytoskeleton

Question 6

Provide functions of protein membranes

Answer 6

-Anchoring proteins (support)

-Recognition proteins (self)

-Secondary messenger systems-communicate within cell receiving chem message

-Enzymes: catalyse reactions
-Receptor proteins: bind chem signals

-Carrier proteins: bind solutes and transfer them across membrane

-Cell-adhesion molecules: mechanically link cell to extracellular material

-Channels: allow hydrophilic solutes and water to pass through membrane

Question 7

Define pumps, cell-adhesion molecules and cell-identity markers

Answer 7

Pumps- carriers that consume ATP
Cell-identity marker: glycoproteins acting as identification tags
Cell-adhesion molecules: mechanically link cell to extracellular material

Question 8

Define the types of channels

Answer 8

Ligan gated- respond to chem messengers

-Voltage gated- respond to charge changes

-Mechanically gated- respond to physical stress on cell

Question 9

Describe structure and functions of glycocalyx

Answer 9

Fuzzy coat external to plasma membrane
-Protection, Immunity to infection, Defence against cancer, Transplant compatibility

Question 10

Describe the process of a secondary-messenger system

Answer 10

-Chem message binds to surface receptor
-Receptor activate G protein (intracellular protein that obtains energy from GTP
-G protein relays signal to adenylate cyclase which converts ATP to cAMP
-cAMP activate cytoplasmic kinases
-Kinases add phosphate group to other enzymes turning some on/off
-Up to 60% of drugs work through G proteins and second messengers (medicinal etc)

Question 11

Describe structure and function of microvilli

Answer 11

-Made of microfilaments (provide strength and anchor microvilli to cell)
.Increase SA
.Increase exposure to extracellular fluid
.Absorb materials from extracellular fluid

Question 12

Describe structure and function of cilia

Answer 12

-Made of microtubules (movement)
-Hair-like processes, beat freely in saline layer at cell surface (mucous on top)
-nonmotile cilium on most cells monitor nearby conditions e.g. sensory cells of nose
.Balance (inner ear) light detection (retina)
.Motile cilia- respiratory tract, reproductive tract, ventricles of brain
.Beat in waves to sweep material across surface in one direction
.Axoneme-core of motile cilium
.2 central microtubules surrounded by ring of 9 pairs that anchor cilium to cell

Question 13

Describe structure and function of cytoskeleton

Answer 13

Network of protein filaments and cylinders
-Determines cell shape
-Supports structure
-Organises cell contents
-Direct movement of materials within cell
-Contributes to movement of cell as whole
Composed of: microfilaments, intermediate fibers, microtubules

Question 14

Define functions of microfilaments, intermediate fibers, microtubules. Organise from thinnest to thickest walls.

Answer 14

Microfilaments:
-Forms terminal web

Intermediate filaments:
-within skin cells, made of protein keratin
-Give cell shape, resists stress

Microtubules:
-Maintain cell shape, hold organelles, make axonemes of cilia and flagella; form mitotic spindle

Question 15

Differentiate between active, passive and carrier-mediated membrane transport

Answer 15

-membrane is selectively permeable

Passive mechanisms require no ATP
-Random molecular motion of particles provides necessary energy
-Filtration, diffusion, osmosis

Active mechanisms consume ATP
-Active transport and vesicular transport

Carrier-mediated mechanisms
-use membrane protein to transport substances across membrane

Question 16

Describe/define filtration

Answer 16

Particles driven through membrane by physical pressure
-Allows delivery water/nutrients to tissues
-Allows removal of waste from capillaries in kidneys

Question 17

Describe simple diffusion

Answer 17

Net movement of particles from high conc to lower
- from constant, spontaneous molecular motion
-Molecules collide/bounce off each other
-Substances diffuse down their conc gradient
-Doesn’t require membrane

Question 18

What factors effect diffusion rate through membrane

Answer 18

-Temp: increase motion of particles
-Molecular weight: larger molecules move slower
-Steepness of concentrated gradient: increase difference= increase rate
-Membrane SA: increase= increase rate
-Membrane permeability: increase= increase rate

Question 19

Define osmosis. Effect of aquaporins. What are some real world examples of osmotic imbalance

Answer 19

Net flow of H2O through selectively permeable membrane
-From more concentrated to less
-Osmotic imbalance underlie diarrhea, constipation, edema
-More aquaporins in cell=increase speed as enhance osmosis

Question 20

Define what is meant by specificity in carrier mediate transport

Answer 20

-Transport proteins specific for particular solutes
-Solute (ligan) binds to receptor site on carrier protein
-Solute released unchanged on other side of membrane

Question 21

Define what is meant by saturation in carrier mediated transport

Answer 21

-solute conc rises, rate of transport rises till transport maximum (Tm) reached
-Tm: rate at which all carriers are occupied

Question 22

What are the three types of carriers

Answer 22

-Uniport: carries one types of solute e.g. Ca+ pump
-Symport: carries two/more solutes simultaneously in same direction e.g. Sodium glucose transporters
-Antiport: carries two/more solutes in opposing directions (counter) e.g. Na+-K+ pumps remove Na bring in K

Question 23

Define and list the three mechanisms of carrier-mediated transport

Answer 23

Facilitated diffusion
-Solute particle enters channel of membrane protein
-Solute binds to receptor site where carrier changes conformation
-carrier releases solute on other side of membrane (no ATP)

Primary active transport
-Carrier moves solute through membrane up to its conc gradient
- use ATP e.g. Ca pump/Na K pump)

Secondary active transport
-Carrier moves solute through membrane but uses ATP indirectly
E.g. Sodium-glucose transporter (symport)

Question 24

Describe process of Na K pump

Answer 24

-Each cycle consumes 1 ATP and exchanges 3 Na for 2 k
-k conc kept higher, Na conc lower within cell
Half of daily calories used for Na K pump

Question 25

Function of Na K pump

Answer 25

-Maintains Na conc gradient allows for secondary active transport
-Regulates solute conc, thus osmosis and cell vol
-Maintains neg. charged resting membrane potential
-Produces heat

Question 26

Describe vesicular transport and it’s types

Answer 26

Moves large particles through membrane in vesicles-enclosures of membrane

Endocytosis- processes that bring material into cell

Phagocytosis-engulfs large particles
Membrane caves in then pinches off pinocytic vesicle

Pinocytosis-takes in ECF containing molecules useful to cell

Receptor-mediated endocytosis-particles bind to specific receptors on plasma membrane

Exocytosis-discharging material from the cell