cell membranes/ membrane transport/ signal transduction Flashcards
define fluid mosaic model
mixture of lipids, proteins, and carbs, has phospholipid bilayer, molecules in constant motion
explain why phospholipids are amphipathic
because they have a hydrophilic head and a hydrophobic tail
recognize the structure of cholesterol and why it is amphipathic
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
describe the fluidity of a membrane, and how it is affected by the saturation and the length of the hydrocarbon tails
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
explain how cholesterol affects membrane fluidity at different temperatures
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
distinguish between integral, peripheral and anchored membrane proteins
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
location and function of membrane carbohydrates
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
define passive and active transport
passive: high to low, spontaneous
active: low to high, non-spontaneous
define simple diffusion and facilitated diffusion
simple: between hydrophobic solutes, easily passes through lipid bilayer
facilitated: between hydrophilic solutes and require transport proteins
explain osmosis
passive transport of water across a membrane
distinguish between hypotonic, hypertonic and isotonic solutions
hypo: low solute outside, water moves in
hyper: high solute outside, water moves out
iso: solute outside = solute inside
identify 2 types of proteins that participate in facilitated diffusion
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
identify the energy source for primary active transport and for secondary active transport
primary: ATP (adenosine + 3 phosphate groups)
secondary: passive powers active
explain the mechanisms of the Na + -K + ATPase and the Na + -glucose transporter
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
name the processes that allow large molecules to get in and out of the cell
exocytosis and endocytosis
distinguish between phagocytosis, pinocytosis, and receptor mediated endocytosis
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
name the 3 steps of a signal transduction pathaway
reception, transduction, and response
differentiate between autocrine, paracrine and endocrine signals
autocrine: local, signals to itself
paracrine: local, signals to nearby cells
endocrine: very long distance signaling
what type of signal molecules bind to receptor proteins found in the cytoplasm?
cytosilic receptors: recieve hydrophobic signals, easily pass through plasma membrane
what type of signal molecules bind to receptor proteins found in the plasma membrane?
cell-surface receptors: receive hydrophilic signals
describe in detail how ion channel receptors, protein kinase receptors, and G-protein coupled receptors work
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
explain ‘role’ of second messengers in distributing and amplifying the signal during transduction
second messengers spread quickly (distribution), and can activate many targets (amplification)
explain how a cytoplasmic protein kinase cascade works
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
why are there so many steps in a signal transduction pathway?
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
examples of cellular responses that occur as a result of signal transduction pathaways
- turn on/off enzyme activity
- turn on/off genes that code for enzymes
explain how caffeine affects the adenosine receptor and the cAMP phosphodiesterase enzyme
caffeine is a competitive inhibitor to the adenosine receptor and the cAMP phosphodiesterase enzyme
