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What is the transmembrane domain (TMD)?
largely hydrophobic (uncharged) alpha-helical peptide sequence that spans the membrane
What does the TMD consist of?
amino acids with hydrophobic side chains
TMD permanently attaches the protein to what?
Plasma membrane
What interacts with the hydrophobic TMD?
hydrophobic fatty acid tails
The TMD can facilitate what?
protein-protein interactions
What do lipid bilayers NOT allow?
many compounds cannot pass through freely
What type of molecules can cross membranes relative easily?
small, uncharged
What are examples of small and uncharged molecules?
H2O
O2
CO2
NO
What type of compounds cannot easily cross lipid bilayers?
large
polar
charged
What are examples of large, polar, and charged compounds?
Ca+
Na+
K+
glucose
What are the 4 basic mechanisms for moving molecules across membranes?
simple diffusion
diffusion through channel
facilitated diffusion
active transport
What does passive movement of substances across cell membranes rely on?
concentration gradient
What is a concentration gradient?
molecular concentrations of substances across the membrane
Molecular concentrations move from _______ across the membrane
high to low
low to high
high to low
What does simply diffusion only work for?
very small and uncharged molecules (H2O, O2, CO2)
What are aquaporins?
specific water channels
H2O moves through in single file down the concentration gradient
Channels are formed by what?
integral membrane proteins - multiple subunits that line an aqueous pore
Channels are effective for what?
small charged molecules - ions
(Na+, K+, Ca2+, Cl-)
Ions move ______ concentration gradients
down
Channels are selective
only allow certain types of ions to pass (uniporter)
What are often gated?
ion channels
What does it mean to be gated?
can be turned on/off in response to different signals/stimuli
What are the two types of gated ion channels?
voltage-gated (Na+ & K+)
ligand-gated (neurotransmitters)
Voltage-gated channels respond to what?
changes in charge across membrane
Under non-depolarized conditions, neurons have what?
low [Na+] inside
Ligand-gated channels respond to what?
binding of specific molecule on its surface (ligand)
What does the binding of a ligand produce?
conformational change in structure of the receptor/channel
What is tetrodotoxin (TTX)?
a very potent neurotoxin; Na+ channel blocker
How does TTX work?
inhibits firing action potentials in neurons by binding to voltage-gated sodium channels in nerve cell membranes
blocks Na+ ion passage into the neuron
prevents the nervous system from carrying messages to muscles
What is curare?
competitive antagonist of the nicotinic acetylcholine receptor (nAChR)
What does curare do?
occupies same position on receptor as ACh with ≥ affinity
elicits no response
What is an example of curare?
non-depolarizing muscle relaxant
What was curare used as?
a paralyzing poison + hunting tool
In facilitated diffusion, compounds bind to integral membrane called a
facilitative transporter
In facilitated diffusion, what allows for a compound to be released on the other side of the membrane?
a change in transporter conformation
Most animal cells import glucose from the blood into cells _____ via _______
down a concentration gradient
facilitative transporter
4 steps of importing glucose
transporter ready to accept glucose molecule
glucose accepted by the transporter
The intracellular side of the transporter opens
glucose released, cycle repeats
What is the solution to moving substances from a LOW concentration to a HIGH concentration? (against the concentration gradient)
chemical gradient of a 2nd molecule that would NOT reach extracellular/intracellular equilibrium
Symporter
both molecules are transported in the same direction
Describe the Na+ Glucose Symporter
2Na+ & 1 glucose bind to outward binding site of transporter
conformation change in transporter occurs (occluded conformation)
transporter adopts inward-facing conformation
2Na+ dissociate in the cytosol
glucose gets pushed in
Antiporter
the concentration gradient of one molecule is used to transfer a 2nd molecule in OPPOSITE directions
What is an example of an antiporter?
Na+/H+ exchanger
Where is the Na+/H+ exchanger located?
in the nephron of the kidney
How does the Na+/H+ exchanger work?
transports Na+ into the cell
forces H+ out of the cell
maintains pH and Na levels in specific kidney cells
Active transporter
an integral membrane protein a compound specifically binds to
What causes a change in conformation of the transporter? (active)
hydrolysis of an ATP molecule
What does the hydrolysis of an ATP molecule allow for in active transportation?
molecule is released on other side of membrane
What does active transport require?
energy input in the form of ATP
What maintains cellular [Na+] and [K+] using ATP?
the Na+/K+ ATPase
Describe the Na+/K+ pump
3Na+ exit cell, 2K+ enter cell
important to maintain higher Na+ concentration OUTSIDE than INSIDE the cell
How do cells achieve and sustain the Na+ chemical gradient for non-stop activity of Na+ glucose symporter?
spend energy (ATP)
What are two mechanisms in which molecules move across membranes?
passive
active
What are the passive mechanisms?
What are the active mechanisms?
How are TTX and curare related?
toxins that interfere with movement through ion channels
ECM components are produced and secreted by what?
cells
ECM components are assembled into what?
an extracellular network
What are the major components of the ECM?
proteins - collagen
glycoproteins - laminin, fibronectin
proteoglycans
What are proteoglycans?
proteins with a polysaccharide chain?
What are the functions of the ECM?
cell adherence
cell communication
cell shape
mechanical support
structural integrity
barrier
Anchor membrane proteins - integrins
interact with ECM components
what do anchor proteins assist in?
tissue formation
coordinated cell function
cell communication
What is the ECM abundant in?
connective tissues (tendons, ligaments, dermis)
What cells have walls?
NON-ANIMAL
bacteria
plants
fungi
Plant cell walls = ?
ECM
Plant cell walls are composed of what?
cellulose
hemicellulose
pectin
protein
Plant cell walls provide what?
structural support to cell + whole organism
Plant cell walls protect cells from what?
mechanical damage
pathogen attack
Membrane proteins play a major role in what?
signal transduction
converts extracellular signal → intracellular signal(s)
Signal transduction allows cell to do what?
rapidly respond to events happening in their environment
grow
divide
survive
move
differentiate
What are ligands?
small molecules that bind to receptor
What does ligand binding change?
conformation of receptor protein
What does the ligand not do?
enter the cell
What side of the receptor protein is affected by the conformation change?
cytosolic side
What can conformation changes activate?
other proteins in cytosol/membrane bound
What are the 3 stages to signal transduction?
ligand binds to receptor
signal transduction → 2nd messenger (cAMP, Ca, G-protein)
cellular response: growth, division, glucose→glycogen
What are some diseases caused by signal transduction defects?
cancer
diabetes
brain disorders
Glycogenolysis
how epinephrine activates glycogen→glucose
Where is epinephrine made?
in the adrenal glands
What does epinephrine bind to?
receptor on liver cell (hepatocyte)
___________ will recruit G-protein and allow the binding of GTP to turn it on
active receptor
The yellow subunit of the G-protein dissociates and turns ON what?
Adenyl cyclase → causes accumulation of cAMP inside cells
At the end of glycogenolysis, what enzyme will release glucose units?
phosphorylase-P
Function of mitochondria
ATP synthesis
apoptosis
Function of chloroplast
photosynthesis
ATP synthesis
What is the Endosymbiotic Theory?
organelles from eukaryotic cells with two membranes represent formerly free-living prokaryotes taken on inside the other in endosymbiosis
What is the supporting evidence of the Endosymbiotic Theory
binary fission of mitochondria & plastids
circular DNA inside organelles similar to bacteria
Describe aerobic respiration
converts in presence of oxygen energy stored in food into chemical energy stored in ATP
by-product: CO2
Describe photosynthesis
building carbs using sun energy and CO2
What is the chemical equation for aerobic respiration?
CH2O + O2 → CO2 + H2O + ATP
What is the chemical equation for photosynthesis?
CO2 + H2O → CH2O + O2
What does the Outer mitochondrial membrane - OMM contain?
enzymes w/diverse metabolic functions (lipid metabolism)
porins → large channels permeable (PASSIVE) to many molecules when opened (ATP, sucrose)
What is the protein:lipid ration in the Inner mitochondrial membrane?
3:1
Cristae
double-layered folds in the IMM
increase membrane surface area
contain machinery for aerobic respiration and ATP formation
What is the IMM rich in?
cardiolipin
What is cardiolipin?
phospholipid
characteristic of bacterial membranes
needed for optimal function of many enzymes
The mitochondria has 2 _________
aqueous compartments
What are the 2 aqueous compartments of the mitochondria?
intermembrane space separates OMM + IMM
matrix → high protein content, gel-like space containing ribosomes and genome (DNA)
What does cellular respiration use to produce ATP?
chemical energy stored in carbs and lipids
What kind of reaction is involved in cellular respiration?
catabolic