ch. 3 membrane physiology

Question 1

plasma membrane

Answer 1

encloses the intracellular contents

selectively permits specific substances to enter or leave the cell

responds to changes in cell’s environment

trilaminar structure under electron microscopy

fluid lipid bilayer embedded with proteins

Question 2

phospholipids

Answer 2

most abundant membrane component

head contains charged phosphate group [hydrophilic]

2 nonpolar fatty acid tails [hydrophobic]

assemble into lipid bilayer with hydrophobic tails in center and hydrophilic heads in contact with water

Question 3

cholesterol

Answer 3

placed between phospholipids to prevent crystallization of fatty acid chains

helps stabilize phospholipids position

provides rigidity, esp. in cold temps

Question 4

membrane proteins

Answer 4

integral proteins - embedded in the lipid bilayer, have hydrophilic and hydrophobic regions, transmembrane proteins extend through entire thickness of membrane

peripheral proteins - found on inner or outer surface of membrane, polar molecules, anchored by weak chemical bonds to polar parts of integral proteins or phospholipids

Question 5

membrane carbohydrates

Answer 5

located on outer surface of membrane

short-chain carbohydrates bound to membrane proteins [glycoproteins] or lipids [glycolipids]

important roles in self-recognition and cell-to-cell interactions

Question 6

diffusion

Answer 6

random collisions and intermingling of molecules as a result of their continuous, thermally induced random motion

new movement of molecules from an area of higher concentration to an area of lower concentration

equilibrium is reached when there is no concentration gradient and no net diffusion

Question 7

osmosis

Answer 7

water moves across a membrane by osmosis, from an area of lower salute concentration to an area of higher salute concentration

driving force is water concentration gradient

hydrostatic pressure opposes osmosis

osmotic pressure is pressure required to stop the osmotic flow

Question 8

tonicity

Answer 8

the effect of solute concentration on cell volume

isotonic solution - same concentration of nonpenetrating solutes as in normal cells, cell volume remains constant

hypotonic solution - lower solute concentration than in normal cells, cell volume increases perhaps to the point of lysis

hypertonic solution - higher solute concentration than in normal cells, cell volume decreases causing crenation

Question 9

phospholipid bilayer impermeable to

Answer 9

large, poorly lipid-soluble molecules [proteins, glucose, and amino acids]

small, charged molecules [ions]

Question 10

mechanisms for transporting molecules [proteins, glucose, amino acids, and ions] in/out of cells

Answer 10

channel transport - highly selective, transmembrane proteins form narrow channels, gated channels can be open or closed, leak channels are open at all times, permits passage of ions or water [aquaporins], movement through channels is faster than carrier-mediated transport

carrier-mediated transport - transmembrane proteins that can undergo reversible changes in shape, binding sites can be exposed to either side of membrane, transport small water-soluble substances, facilitated diffusion or active transport

vesicular transport - transport between ICF and ECF of large particles wrapped in membrane-bound vesicles, endocytosis incorporates outside substances into cell, exocytosis releases substances into the ECF, the rate of endocytosis and exocytosis must be balanced to maintain a constant membrane surface area and cell volume, caveolae may play a role in transport of substances and cell signaling

Question 11

opening and closing of membrane receptor channels

Answer 11

chemically gates [ligand gated] - respond to binding to an extracellular chemical messenger to a specific membrane receptor

voltage gated - respond to changes in the electrical current in the plasma membrane

mechanically gated - respond to stretching or other mechanical deformation of the channel

Question 12

facilitated diffusion

Answer 12

passive carrier-mediated transport from high to low concentration, does not require energy

transported molecule attaches on binding site on protein carrier

carrier protein changes conformation, exposing bound molecule to other side of membrane [lower concentration side]

bound molecule detaches from carrier

carrier returns to original conformation [binding site on higher concentration side]

Question 13

active transport

Answer 13

carrier-mediated transport that moves a substance against its concentration gradient

requires energy

primary active transport; energy is directly required, ATP is split to power the transport process

secondary active transport; ATP is not used directly, carrier uses energy stored in the form of an ion concentration gradient built by primary active transport

Question 14

endocytosis

Answer 14

internalization of extracellular material within a cell

pinocytosis: a droplet of ECF is taken up nonselectively

receptor-mediated endocytosis - highly selective process enables cells to import specific large molecules, triggered by bonding of a molecule to a specific surface

phagocytosis - large multimolecular particles are internalized

Question 15

exocytosis

Answer 15

primary mechanism for secreting substances into the extracellular fluid

secretory vesicles bud off of golgi complex

vesicle and plasma membrane fuse, releasing contents of vesicle into extracellular fluid

Question 16

NA+ - K+ ATPase pump

Answer 16

pumps 3 NA+ out of cell for every 2 K+ in

splits ATP for energy

phosphorylation induces change in shape of transport protein

maintains Na+ and K+ concentration gradients across the plasma membrane

helps regulate cell volume

Question 17

secondary active transport

Answer 17

simultaneous transport of a nutrient molecule and an ion across the plasma membrane by a cotransport protein

nutrient molecule is transported against its concentration gradient

driven by simultaneous transport of an ion along its concentration gradient

Question 18

direct intercellular communication

Answer 18

gap junction, transient direct linkup of surface markers, nanotubes

Question 19

indirect intercellular communication

Answer 19

intercellular chemical messengers; synthesized by specialized cells to serve a designated purpose, bind with specific receptors on target cells

Question 20

categories of chemical messengers

Answer 20

paracrines - local chemical messenger whose effect is exerted only on neighboring cells

neurotransmitters - used by neurons which communicate directly with the cells they innervate

hormones - long-range chemical messengers that are secreted into the circulations by endocrine gland

neurohormones - hormones released into the circulation by neurosecretory neurons

pheromones - chemical signals released into the environment to reach sensory cells of other animals

cytokines - regulatory peptides made by almost any cell, generally involved in development and immunity

Question 21

signal transduction

Answer 21

extracellular chemical messengers bind with receptors to trigger a biochemical chain of events inside the target cell

the process by which incoming signals are conveyed to the target cell’s interior for execution

lipophilic extracellular messengers - pass through target cell’s plasma membrane to bind to intracellular receptors; (1) produce second messenger cyclic GMP or (2) alter gene transcription

Question 22

phosphorylating enzymes

Answer 22

protein kinase phosphorylates a target cell protein

phosphorylated protein changes shape and function [is activated]

tyrosine kinase [ie insulin receptor] phosphorylates its own tyrosine residues [autophosphorylation]

activated protein kinase sites phosphorylate cytoplasmic proteins to lead to the cellular response

Question 23

membrane potential

Answer 23

the separation of charges across the plasma membrane

measured in millivolts

attractive force causes separated positive and negative charges to accumulate along the inner and outer surfaces of the membrane

Question 24

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