MCAT: Foundation 2

Cell Membrane:

a barrier that encases a cell comprised of proteins, cholesterol, and lipids that controls what enters and exits the cell

Amphipathic:

a cell that contains both a hydrophobic and hydrophilic region

Phospholipid Bilayer:

a double layered membrane, the structure of the eukaryote membrane, that has the hydrophobic tails facing in and the hydrophilic head facing out

Extracellular:

space on the outside of the cell (outer leaflet)

Intracellular:

space on the inside of the cell membrane (inner leaflet)

Intercellular:

space in between the two membrane layers

Passive Diffusion:

movement of small, often non polar molecules from outside to inside the cell without the use of energy

Phospholipid

: a lipid with a phosphate head, glycerol backbone, and fatty acid tails

Phosphate Head:

the polar hydrophilic part of the phospholipid that interacts with water

Glycerol Backbone:

the central part of the phospholipid that connects the head and the tail

Fatty Acid Tails:

nonpolar, hydrophobic part of the phospholipids that will not interact with H₂O

Trans Fatty Acids:

straight, linear structure with a double bond that is more solid

Cis Fatty Acids:

A type of unsaturated fatty acid with a bend or kink in the chain

Saturated Fatty Acids:

long linear chains (FA) 

Unsaturated Fatty Acids:

bent and kinked chains

Fluid Mosaic Model:

the model that describes organisms cell membranes

indicating a diverse amount of molecules that can shift and move mimicking “fluid”

function as addition or communication enhancers 

Carbohydrates in the membrane→

function as receptors or transportation of molecules

Proteins in the membrane→

function as a regulator and stabilizer for the cell membrane

Cholesterol in the membrane→

Integral Protein:

proteins the span the entire membrane with corresponding nonpolar and polar regions participating in several differing functions

Peripheral Protein:

proteins found on the outside of the membrane used for communication and support

Lipid Bound Protein:

proteins found in the interior of the cell membrane, wedged into the membrane

Channel Protein:

integral proteins that allow ions and larger polar molecules to enter the membrane using the concentration gradient

Glycoprotein:

protein and sugar that participates in signaling

Carrier Protein:

integral proteins that allow transportation of molecules that commonly couldn’t cross the membrane against the concentration gradient

Membrane Fluidity:

a property that allows the cell membrane to maintain a moveable structure for survival purposes

Membrane fluidity

As temperature increases so does membrane…

Unsaturated FAs increase membrane fluidity 

Membrane fluid Saturation

Cholesterol increases fluidity at lower temperatures and decreases it at higher temperatures

Cholesterol temp. effects on membrane fluidity

Membrane Dynamics:

constantly changing shape and movement of molecules within a cell membrane

Uncatalyzed Phospholipid Movement:

natural movement that occurs with out energy input or protein intervention (lateral)

Trans bilayer Diffusion:

a phospholipid moving from the outer to inner or vice versa within the membrane that is very slow and not common

Lateral Diffusion:

a phospholipid moving from the side to side and front to back within one leaflet, a natural and common, fast occurring transition

Catalyzed Phospholipid Movement:

non natural occurring movements within the phospholipid bilayer that requires energy input 

Flipase:

an enzyme that moves phospholipids from the outer to the inner leaflet that requires ATP

Flopase:

an enzyme that moves phospholipids from the inner to the outer leaflet that requires ATP

Scramblase:

an enzyme the moves phospholipids from the inner to the outer as well as outer to the inner simultaneously that does not require ATP(catalyzed movement)

Diffusion:

high concentration to a low concentration

Hypertonic:

having a high concentration of a solute

Hypotonic:

having a low concentration of a solute

Isotonic:

having an equal concentration of a solute

Passive Transport:

transport across the membrane that does not require energy

Active Transport:

transport across the membrane that requires energy 

maintains resting potential in the cell 

Na⁺/K⁺ pump function→

creating an acidic environment in the stomach

proton/K⁺ exchanger function→

Simple Diffusion:

transport of molecules across the membrane down the concentration gradient 

K⁺ leak channel:

allows potassium to leak outside the cell to create a net negative charge inside the membrane

Facilitated Diffusion:

diffusion down the concentration gradient with the aid of specific channel proteins

Osmosis:

the simple diffusion of water across a cell membrane

Aquaporins:

channel proteins that can facilitate the transport of water across a cell membrane

Primary Active Transport:

pathways that use ATP directly for energy

Secondary Active Transport:

pathways the transport multiple molecules powering the uphill by the downhill of the other

Symport:

molecules are moving in the same direction across the membrane 

Antiport:

molecules are moving in the opposite direction across the membrane

Endocytosis:

contents are brought into a cell via a vesicle being absorbed and fused with the membrane creating a pocket

Exocytosis:

contents are brought out of the cell into the extracellular area via a vesicle that fuses with the membrane and creates an opening for the contents to escape

Phagocytosis:

the process where a cell binds to an item and proceeds to engulf it by pulling the item inward and surrounding the contents with its membrane

Opsin receptors:

used to bind to bacteria that has been coated in immunoglobulin G (IgG)

“Complement system”:

proteins are used to tag bacteria for death

Scavenger Receptors:

bind to molecules that are produced by bacteria

Toll-like receptors:

bind to specific molecules that are produced by bacteria

Membrane Potential:

the difference in a cells charge across the cell membrane, caused by distribution of ions in and out of a cell

Equilibrium Potential:

the membrane voltage at which a specific ion is at electrochemical equilibrium, no net movement of ions across the membrane

Permeability:

how easily an ion can run across the membrane depending on the state of ion channels

the ion cannot have an equilibrium potential 

If an ion does not have a concentration gradient AND permeability

Exocytosis:

exiting the cell

Endocytosis:

entering the cell

Waste Proteins:

vesicle removal of contents from the cell mending with the membrane and releasing the contents from the cell to the extracellular space

Membrane Proteins:

proteins that are formed inside the cell and migrate to the membrane 

Phagocytosis:

the engulfment of solid, insoluble products into a cell

Pinocytosis:

the engulfment of dissolved ions and solutes in a liquid medium

Receptor Mediated Exocytosis:

engulfment of specific molecules into a cell through membrane bound receptors

Cell Junctions:

connection pathways for differing cells

Gap Junctions:

connecting tunnel pathways between cells that allows the transport of water and ions as well as spreading the electrochemical signals secreted by other parts of the body

Tight Junctions:

cell connection via physical touch and possess an impermeable layer in between the cells

Desmosomes:

thread like connections between cells that holds two cells together through the cytoskeleton but does not allow contents from the inside to flow, but the space in between the cells is flexible

Plasmodesmata:

plasma membrane lined connecting channel for plant proteins that allows transport of water, ions, and small molecules between

Connexins:

proteins the form gap junctions in vertebrates (smaller component)

Innexins:

proteins the form gap junctions in invertebrates

Claudins:

transmembrane proteins in vertebrate tight junctions that seals the cells together to prevent leakage

Cadherin:

Calcium dependent adhesion molecule that mediates desmosomes binding with neighboring cells

Cytoplasmic Plaque:

dense protein structure on the cytoplasmic side of the desmosomes that anchors cytoskeleton filaments to junctions

Membrane Receptors:

integral proteins that communicate with the extracellular portion of the cell

Ligand:

any molecule that specifically binds to a receptor to trigger a biological response

Ligand-receptor complex:

the complex that forms when the ligand is bonded to the receptor

Signal Transduction:

the cell responding to an outside signal and creates an intracellular response

“Lock and Key” Model:

the idea that receptors have a specific site and shape for a ligand to bind

Induced Fit Model:

the idea that the receptor and ligand can form a newer shape and change conformationally once bonded

Ligand Gated Ion Channels:

trans-membrane ion channels that open or close in response to allosterically binding to a ligand and turn the extracellular signal into an intracellular electric signal

G-protein Coupled Receptors:

a large class of receptors that detect molecules outside the cell and activate an internal signal transduction pathways, spread in the membrane 7 times and contains multiple subunits

Alpha subunit of GCPR:

activated when coupled to the receptor and binds to GDP or GTP, dissociates from the complex, activates or inhibits target proteins

Beta subunit:

bound to the gamma subunit and stabilizes the complex, after activation the dimer can activate other signaling channels

Gamma Subunit:

bound to the beta subunit and anchors the complex as well as aiding in signaling for the G protein

Lipid Anchors:

modifications on the alpha and beta subunits that tether the G protein to the inner leaflet

Regulator of G signaling Protein:

accelerate GTP hydrolysis on the alpha subunit, turning off the signal faster 

General Pathway of G-protein

1. Ligand binds GPCR

2. GPCR activates G-protein (α exchanges GDP for GTP)

3. α and βγ split and activate effectors

4. RGS helps α hydrolyze GTP → inactivation

5. Subunits reassemble and await next signal

Enzyme Linked Receptors:

membrane receptors that have intrinsic enzymatic activity, when bonded with a ligand relay an enzymatic function

RTKs:

an enzyme linked receptor that transfers phosphate groups to tyrosine residues on proteins

Voltage Gated Ion channels:

transmembrane proteins that open or close in response to changes in membrane potential, allow ions to rapidly leave or enter the cell

Stretch Activated Channels:

ion channels that open in response to mechanical deformation of the membrane and allow ions to pass when it is distorted