cell membranes/ membrane transport/ signal transduction

Question 1

define fluid mosaic model

Answer 1

mixture of lipids, proteins, and carbs, has phospholipid bilayer, molecules in constant motion

Question 2

explain why phospholipids are amphipathic

Answer 2

because they have a hydrophilic head and a hydrophobic tail

Question 3

recognize the structure of cholesterol and why it is amphipathic

Answer 3

structure: 4 hydrocarbon rings, and one hydroxl (-OH) group. it is amphipathic because it has a small part of the molecule that is water soluble, but the rest is insoluable

Question 4

describe the fluidity of a membrane, and how it is affected by the saturation and the length of the hydrocarbon tails

Answer 4

fluidity: membrane integrity depends on lipid composition
length of hydrocarbon tails: longer=less fluid (more solid/gel-like) shorter=more fluid
saturation: saturated=less fluid non-saturated=more fluid

Question 5

explain how cholesterol affects membrane fluidity at different temperatures

Answer 5

higher temperatures: cholesterol acts as glue and holds the phospholipids together to prevent melting
lower temperatures: acts as anitfreeze and prevents phospholipids from packing too closely

Question 6

distinguish between integral, peripheral and anchored membrane proteins

Answer 6

integral: transmembrane
peripheral: no contact with the hydrophobic region of the membrane, interact with polar head groups through weak, non-covalent interactions
anchored: completely attached to a lipid that is embedded in the membrane

Question 7

location and function of membrane carbohydrates

Answer 7

location: only on the outer surface of the plasma membrane, or on the lumenal surface of an organelle
function: cell-cell recognition, cell-cell adhesion, signaling sites

Question 8

define passive and active transport

Answer 8

passive: high to low, spontaneous
active: low to high, non-spontaneous

Question 9

define simple diffusion and facilitated diffusion

Answer 9

simple: between hydrophobic solutes, easily passes through lipid bilayer
facilitated: between hydrophilic solutes and require transport proteins

Question 10

explain osmosis

Answer 10

passive transport of water across a membrane

Question 11

distinguish between hypotonic, hypertonic and isotonic solutions

Answer 11

hypo: low solute outside, water moves in
hyper: high solute outside, water moves out
iso: solute outside = solute inside

Question 12

identify 2 types of proteins that participate in facilitated diffusion

Answer 12

channel: hydrophilic tunnels, can be gated (open/closed based on stimulus), some are not gated
carrier: binds to the transported substance, changes shape upon binding to transported substance

Question 13

identify the energy source for primary active transport and for secondary active transport

Answer 13

primary: ATP (adenosine + 3 phosphate groups)
secondary: passive powers active

Question 14

explain the mechanisms of the Na + -K + ATPase and the Na + -glucose transporter

Answer 14

Na K ATPase: there are 3 Na on the outside of the cell, 2 K on the inside, it goes against the concentration gradient, most abundant transport protein, in normal conditions, Na would be in high concentration on the outside and low concentration on the inside, and K is the opposite
Na glucose transporter: wants to absorb glucose into intestinal cells to be sent to the blood stream. there is a passive transport of Na into the cell, then an active transport of one glucose into the cell. the transporter is mediating passive transport of glucose into the blood stream

Question 15

name the processes that allow large molecules to get in and out of the cell

Answer 15

exocytosis and endocytosis

Question 16

distinguish between phagocytosis, pinocytosis, and receptor mediated endocytosis

Answer 16

phagocytosis: ‘cellular eating’ bring substance in through phagosome, fuses with lysosome, contents digested
pinocytosis: ‘cellular drinking’ continuous, spontaneous, non-specific intake of fluids and dissolved substance
receptor mediated endocytosis: transmembrane receptor protein on a cell surface which binds to a specific ligand. clathrin protein in cytosol binds to the inner surface of the plasma membrane and exerts a pulling force, which forms a vesicle

Question 17

name the 3 steps of a signal transduction pathaway

Answer 17

reception, transduction, and response

Question 18

differentiate between autocrine, paracrine and endocrine signals

Answer 18

autocrine: local, signals to itself
paracrine: local, signals to nearby cells
endocrine: very long distance signaling

Question 19

what type of signal molecules bind to receptor proteins found in the cytoplasm?

Answer 19

cytosilic receptors: recieve hydrophobic signals, easily pass through plasma membrane

Question 20

what type of signal molecules bind to receptor proteins found in the plasma membrane?

Answer 20

cell-surface receptors: receive hydrophilic signals

Question 21

describe in detail how ion channel receptors, protein kinase receptors, and G-protein coupled receptors work

Answer 21

ion channel: signal binds, gate opens, ions pass through membrane via passive transport
protein kinase: (kinase-phosphorylate target proteins) signal binds, receptor changes shape, receptor adds phosphate to targets, can phosphorylate multiple targets 
G protein (GPCR): signal binds, changes shape, activates G protein, drops GDP, picks GTP, changes shape (subunits dissociate), activates effector protein, triggers a multitude of chemical reactions

Question 22

explain ‘role’ of second messengers in distributing and amplifying the signal during transduction

Answer 22

second messengers spread quickly (distribution), and can activate many targets (amplification)

Question 23

explain how a cytoplasmic protein kinase cascade works

Answer 23

activated by cAMP, it adds phosphate groups to multiple cellular enzymes. by doing this, it can activate enzymes, also inhibit enzymes. these kinase enzymes always phosphorylate but dont always activate their targets. PKA also inhibits glycogen synthase

Question 24

why are there so many steps in a signal transduction pathway?

Answer 24

because of the idea of amplification. it is the idea that one signal can have a huge response. for example, one epinephrine caused the production of 10,000 glucose molecules

Question 25

examples of cellular responses that occur as a result of signal transduction pathaways

Answer 25

• turn on/off enzyme activity

- turn on/off genes that code for enzymes

Question 26

explain how caffeine affects the adenosine receptor and the cAMP phosphodiesterase enzyme

Answer 26

caffeine is a competitive inhibitor to the adenosine receptor and the cAMP phosphodiesterase enzyme