Cell Biology Fine Structures: Exam II

what molecules easily pass through the cell membrane?

hydrophobic molecules (O2, CO2, N2, steroid hormones)

what molecules partially pass through the cell membrane?

small uncharged polar molecules (H2O, urea, glyceral)

what molecules have difficulty passing through the cell membrane?

large uncharged polar molecules (glucose, sucrose)

what molecules require transport proteins to pass through the cell membrane?

Ions

passive transport

molecules moves freely down concentration gradient w/out energy use

active transport

molecules move against the gradient

tonicity

determines cell swelling or shrinking based on solute concentration differences

osmolarity

the total solute concentration in a solution

isotonic

no net water movement

hypertonic

high solute concentration outside cell, water moves out of the cell (shrinks)

hypotonic

low solute concentration outside cell, water moves in, cell swells and may burst (lysis)

passive diffusion

solute moves freely through membrane (O2, CO2)

facilitated diffusion

requires channel or carrier protein (glucose, ions)

primary active transport

uses direct ATP (Na+/K+ pump)

secondary active transport

uses pre-existing gradient (glucose/Na symporter); indirectly uses ATP

ATP driven pumps

P-type, F-type, V-type

sodium-potassium pumps

uses ATP to actively transport 3 Na+ out and 2 K+ in; maintains resting membrane potential in nerve cells

what diseases can be caused by genetic mutations in ABC genes?

cystic fibrosis, anemia/drug response issues, neurological diseases

functions of bacterial ABC transporters

nutrient uptake, antibiotic resistance (efflux pumps remove harmful substances)

transport issues in gram-negative bacteria

can be immunogenic (trigger immune responses)

structure of phospholipids

glycerol backbone, two fatty acid tails (hydrophobic), phosphate-linked head group (hydrophilic)

amphipathic nature/membrane formation

hydrophobic tails face inward, hydrophilic heads face outwards, forms semi-permiable bilayer

factors affecting membrane fluidity

unsaturated fatty acids increase fluidity; cholesterol stabilizes membrane, reduces fluidity at high temps, increases at low temps; higher temp increases fluidity, lower temps decrease it

biological importance of phospholipid bilayer

creates controlled internal environment for biochemical reactions, enable compartmentalization

carbohydrates in membranes

attached to lipids/proteins (glycolipids/glycoproteins), important for cell recognition and signaling

integral membrane proteins

proteins permanently embedded in membrane, facilitate movement of molecules and detect signals

peripheral membrane proteins

proteins loosely attached to to membrane surfaces, assist in signaling

ectoenzymes

function on outer surface of the plasma membrane, many are glycoproteins

endoenzymes

active on the inner surface of the plasma membrane, aid in internal cellular processes

lipid rafts

Microdomains in plasma membrane that cluster specific lipids & proteins to regulate signaling

aquaporins

selectively allow water transport across cell membranes; maintain osmotic balance, prevent ion movement

detergents and membranes

insert into bilayer, disrupt hydrophobic interactions, increases cell permeability or causes cell lysis

heterokaryons

fusion of different cells into one cell with multiple nuclei, used to study membrane protein mobility

fluorescence recovery after photobleaching (FRAP)

technique used to study protein and RNA movement by tracking fluorescence recovers from a bleached spot

types of ion channels

voltage-gated, ligand-gated, mechanically-gated

types of signaling

Juxtacrine, paracrine, endocrine, synptic

juxtacrine signaling

short distance, requires direct contact between signaling and receiving cells

paracrine signaling

signals diffuse to nearby cells; local signaling

endocrine signaling

long distance, hormones are released into bloodstream to reach target cells

synaptic signaling

neurons release neurotransmitters that diffuse across a synaptic cleft to reach target cells

examples of second messengers

cAMP, Ca2+ ions, IP3

cAMP

activates protein kinase A (PKA)

IP3

helps release calcium from cell storage

signal transduction pathways

reception, transduction, response

reception pathway

ligand binds to receptor

transduction pathway

signal is amplified inside the cell

response pathway

cell undergoes change (gene expression alteration, enzyme activation)

GPCR’s

G protein-coupled receptors, important for cell communication and drug targets in medicine

G proteins

molecular switches that relay extracellular to intracellular pathways by cycling between GDP bound (inactive) and GTP bound (active) states

signal activation

ligand binds to GPCR, GTP replaces GDP and activates downstream signaling

inactivation

Ga hydrolyzes GTP to GDP

cAMP pathway

adenylyl cyclase enzyme binds to activated Gsa and produces cAMP, cAMP activates PKA and leads to protein phosphorylation which regulates metabolism, gene expression, and stress response

phospholipid bilayer

two layers of phospholipids, tails face inwards away from water, heads face outward and interact with aqueous environment; forms semi-permeable membrane

phosphodiesterase

breaks down cAMP after inactivation, stops the signal

role of calcium in signaling

regulate muscle contraction, neurotransmitter release, and gene expression

Ca2+ regulation

Ca-ATPases pump Ca2+ out of cytosol into endoplasmic/sarcoplasmic reticulum, prevents calcium build up in the cell; Ca2+ ions released from ER into cytosol via IP3 signaling

antagonists

block receptors; bind to receptors without activating them, prevents natural ligand from triggering a response

agonists

drugs or molecules that activate receptors, mimic natural ligand effects

signal amplification

small signal triggers large response through cascades, each step activates multiple molecules, signal effect increases exponentially

second messenger

molecules produced when ligand binds to a receptor, amplify signal, leads to cascade of intracellular changes

cAMP

second messenger produced from ATP by the enzyme adenylyl cyclase

receptor-mediated endocytosis

remove receptors, less ligands can bind, decreases cell responsiveness

desensitization

modify receptors to lower affinity for ligands, makes them less responsive

membrane stability and adaptability

hydrophobic interactions keep phospholipids in place, proteins anchor cytoskeleton and enable communication, cholesterol adds rigidity

voltage-gated channel

open when membrane potential changes (Na+, K+ for neuron signaling, heart rhythm)

ligand-gated channel

open when a molecule binds, activated by neurotransmitter receptors

mechanically-gated channel

open due to pressure or vibrations

P-type pump

self-phosphorylating using ATP (Na+/K+ pump, Ca2+ pump)

F-type pump

use proton gradients to make ATP (ATP synthase)

V-type pump

pump protons into organelles (lysosomes, vacuoles)