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Flashcards in Cell Biology Exam 1 Deck (105)
1

Cell Membrane Components

Phospholipids, proteins, cholesterol

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Phospholipids

membranes are variously composed of these special lipids, they are amphipathic molecules with a hydrophobic and phillic end can assemble as micelle, bi-layer and liposome
hydrophobic effect determines the organization of phospholipids

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glycolipids

carbohydrate branches attached to exterior end of lipid replacing the polar head

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glycoprotein

carbohydrate attached to the exterior end of a protein in the cell membrane
nearly all membrane proteins are glycoproteins at somelevel

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Proteins

functional part of the membrane, the ratio of proteins/lipid ratio depends on complexity of membrane functionality, sequence of amino acids assembled in such a way to be folded or wound up,
there are 2 kinds of membrane proteins: Integral Membrane proteins and Peripheral membrane proteins

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Integral membrane proteins

regions of lipid sea, held in position

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Peripheral membrane proteins

located on the surfaces of the lipid sea usually on the cytoplasm side

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Kinds of membrane proteins

structural - give cell structural integrity, ECM
channels - allow for passive transport of molecule through membrane
transporters - active transport of molecule along natural conc gradient
pumps - active transport of molecule against concentration gradient
transducers - couple a membrane receptor to cytoplasmic enzyme
enzymes - perform cellular work by catalyzing rxn

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Cholesterol

added agent involved in cell fluidity, amphipathic steroid, enhances cell membrane stability decreases permeability, helps with packing the phospholipids.

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Fluid Mosaic Model

protein and lipid distribution is asymmetrical, in addition of the obvious barrier function a membrane must be able to engage in recognition, transportation and communication.

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Membrane recognition

cellular adhesion, cellular interactions with prokaryotic organisms, cellular/tissue identity, cellular immunity

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cellular adhesion during growth and development

by cellular density/contact with cell beside it, the part that is recognizable is the stage-specific embryonic antigens (SSEA's)

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cellular adhesion in mature tissues

cell adhesion molecules (CAM's) are what join the cells together

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cadherin

link cells to identical cells

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integrin

links cells to the ECM

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Cellular binding during diaphysis

The ability of a white blood cell to bond to and exit capillary lining linked to the display of interaction of special surface recognition molecules

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cell junctions

adhering or tight junctions by ways of proteins

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cellular interactions with prokaryotic cells

certain bacteria have tiny protein threads, fimbriae, to attack the host cell on the glycolipids

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cellular binding during diapedesis

ability of WBC to bond to, and exit capillary lining linked to the display and interaction of special surface recognition molecules

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cellular/tissue identity

by what carbohydrates are attached can define the type of cells they are "blood typing"

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cellular immunity

cells immune systems express certain proteins on plasma membrane call human leukocyte antigens (HLA), these are used to present foreign material to other defender cells

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antigen presenting cells

HLA cell that put foreign material on outside of membrane for other defender cells to see and attack

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Cell membrane Transportation ways

passive transport, facilitated transport, active transport, vesicular transport

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Passive transport

free passage - completely unaided movement governed by diffusion, unfit for nearly all significant biological molecules, movement through phospholipid sea
openings - various types of channels and pours and is selective, any type of unaided passage governed by diffusion, may be close able - added or subtracted from plasma membrane
commons eg: aquaporins, ion channels and gap junctions

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Aquaporin

a pore for water, more than 10 different forms found where the proteins fold up in lipid by-layer to combin two hemi-phores

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Ion channels

the channels are important for electrically excitable cells such as neurons and muscles, they change membrane potentials
voltage-gated channel - opened by applying voltage
ligand-gated channels - opening by docking a ligand
mechanically-gated channels - opened by physically stressing the cell
chemically-gated channel - opened by the pressence of Ca2+ or phosphorylation of the gate

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Gap junction

special case used to direct cell-to-cell transmission, allows for electrical and metabolic coupling of cells, consists of 6 IMP's termed connexons creating the channel

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Facilitated Transport

facilitated diffusion, various types of IMPs that physically carry a solute across the plasma membrane, selective, non-energy dependant - aided by concentration gradient, uses a translocation mechanism to make a conformational change to IMP to create access, they are simple automatic and efficient.
eg. uniporter, symporter, multiporter

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Glucose Tansporter

part of family of similar proteins GLUT 1 thru 5, stimulated by insulin and inhibited by ATP,

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Bi-Chloride Antiporter

this anion transporter exchanges a HCO3 for a Cl- in RBCs

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Active Transport

a carrier mediated transport system requiring ATP, works against the concentration gradient, selective
two broad types are primary and secondary where sec. does not use ATP directly often called co-transporter

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Sodium Potassium pump

the main pump, hydrolysis of ATP is used to run the pump, an antiporter IMP the moves 3 Na out for 2 K in, is electrogenic b/c it moves ionic species, high level of Na is used for secondary co-transports systems

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Calcium Pump

a uniporter IMP that moves Ca2+ out per ATP, in all cells, primary active transporter

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Hydrogen Potassium Pump

an antiporter IMP that moves H+ out and K in per ATP, primary active transport

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Sodium-Glucose Symporter

an IMP that moves 2 Na+ in with 1 Glucose in, glucose levels usually higher in cells so to move in against its gradient sodium is used, since it is then dependant on the sodium pump it is a secondary active transport

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Sodium-Hydrogen Antiporter

an IMP that moves H+ out and Na+ in, secondary active transport, relies on sodium gradient by the Na/K pump, common in kidney tubule cells

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Sodium-Calcium Antiporter

an IMP that moves Ca2+ out and Na+ in, actually faster than the Calcium pump, econdary active transport, relies on sodium gradient created by Na/K pump

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Vesicular Transport

utilizing membrane sphere (vesicles) to shuttle material to and from the cell membrane, technically requires energy, broken down into endocytosis and exocytosis

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Exocytosis

vesicles originate at the golgi apparatus and shuttles along the cytoskeleton to the plama membrane so it is moving things out also known as secretion.

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Endocytosis

vesicles bud off of plasma membrane towards the interior as form of bulk transport, moving things IN using an endosome, there is 3 types; phagosytosis, pinocytosis and receptor-mediated endocytosis

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phagosytosis

involves the engulfment of particulate, gobling of stray material, formation of pseudopodia that envaginate and fuse to form a phagocytic vesicle termed a phagosome

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pinocytosis

a fluid phase endocytosis, non-specific internalization common in all cells, involves invagination of membrane to create pinocytotic vesicles

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transcytosis

termed used to describe the shuttling of a endocyte across the cell to another surface

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receptor-mediated endocytosis

highyl specific internalization, receptor IMP are required, that must bind to a ligand before internalization
multistep process: receptor binding, clathrin pulls membrane down, pulls to create a cage called coated pit, endosome is formed and fuses with CURL vesicle

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CURL

Compartment the Uncouples Receptor and Ligand

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LDL receptor- LDL endocytosis

receptor that takes in cholesterol to the cell which is synthesized to be used by golgi apparatus and put back into the cell membrane

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Cell Membrane Communication 5 categories

endocrine secretion, neuro-endocrine secretion, paracrin secretion, autocrine secretion, synaptice transmission (neuronal secretion)

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Endocrine Secretion

the process involves the synthesis and exocytosis of a hormone from a source cell->released hormone enters ECM then into bloodstream where it circulates throughout the body -> then exits blood capillaries and in EC to land on or enter target cells
receptors at target cells determine sensitivity

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peptide hormone

water soluble, receptor located on the cell surface, typically transemembrane IMPs

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steroid hormone

lipid soluble and can easily cross the plasma membrane, receptors located in either cytoplsm or nucleus inside cell, protein with ligand or DNA binding site, directly turn gene expression on

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Autocrine Secretion

synthesis and exocytois of a chemical signal from a cell-> released chemical enters ECM where it stays locally -> then lands on the same cell as a target

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Paracrine Secretion

involves the synthesis and exocytosis of a chemical signal loosely called a hormone from a source cell -> released chemical enters ECM where it stays locally -> then lands on nearby target cells
receptors on target cells determine sensitivity
eg. Endothelial cells lining blood vessels can secrete stimulants to the underlying smooth muscle cells to induce vasoconstriction
During fetal development target tissues secrete nuerotrophic factor which serves as a chemo-attractent molecule. Nerve Growth Factor

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Synaptic Transmission (Neuronal Secretion)

transmitting end of neurone; small intercellular space or ECM; and a receiving cell
receptors postsynaptic side determine sensitivity, selectivity due to physical construction of synapse

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4 Basic Categories of chemical signalling (reception)

steroid hormone receptor mechanism, ligand-gated receptor mechanism, G-protein receptor mechanism, enzymatic receptor mechanism

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Steroid Hormone Receptor Mechanism

b/c steroids are lipid soluble they pass thru membrane, receptor is inside cell and has a steroid DNA and Gene-regulatory domain

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Ligand-gates Receptor Mechanism

involves a external receptor site as an IMP where ligand binds to the receptor to open the channel

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Nicotininc Acetylcholine Receptor

receptor has ligand attach and IMP undergoes a conformational change to allow for Na and K to pass, stimulates an action potential by secondarily activating voltage gated K channels nearby creating an Excitatory post synaptic potential, the Ach is broken down by acetylcholinesterase

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receptor

an IMP that receives a primary messenger and indigoes a conformational change which convey message further

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transducer

a PMP that relays/converts signal from receptor to amplifier

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amplifier

IMP that boost signal by activation many secondary messengers

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secondary messengers

cytosolic signalers formed by phosphorylated precursor that activate internal agent

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internal effector

cytosolic protein that activate other proteins by phosphorylating them

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cAMP

cyclic adenosine monophosphate system

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protein phosphorylation

when a protein is phosphorylated and it changes its conformation and is thereby activated

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protein kinase

enzyme that phosphorylate other proteins

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protein phosphotase

enzyme that de-phosphorylate other proteins

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The Mechanism of G-Protein-Linkes Receptor

External signal (first messenger)
Receptor
Transducer
Amplifier
Phosphorylated precursor
Second Messenger
Internal Effector
Cellular Response

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3 major types of transducer G-proteins

Gs - stimulatory, and activates adenylate cyclase
Gi - inhibitory, and inhibits adenylate cyclase
Gp - stimulatory, and activates phospholipase C

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What are the G-Proteins subunits?

alpha subunit - the most variable and functionally important
beta and gamma - are similar, these bind the molecule together and hold it in the cell membrane

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Amplifiers relavent to this course

these PMPs produce many copies of the second messenger
adenylate cyclase - converts ATP into cAMP
phospholipase C - converts PIP2 into IP3 and DG,

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Second Messengers relevant to this course

cAMP - stimulates A-kinase

IP3, DG, and Ca2+- variously stimulates C-kinase and calcium/calmodulin kinase

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Internal effectors relevant to this course

A-kinase - activated by cAMP

C-kinase- activated by DG

Ca2+/calmodulin kinase - activated by Ca2-

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The Activation of the cAMP Signal Transduction

with the activation of adenylate cyclase by activated G-protein, cAMP made.
cAMP diffuse in cytosol and binds to A-kinase, this releases a catalytic component (c) from the regulatory cap (r)
A-kinase phosphorylates cellular proteins, thus activating them, conformational change allows this to happen

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In-Activation of the cAMP Signal Transduction

system shuts down by a number of mechanisms that relate to the continual recycling of molecules, done by phosphatase enzymes available in the cell
-GTP -> GDP then causing G-protein to become quiet
-protein-P _> protein then returning them to resting conformation
-cAMP ->AMP thus eliminating the second messenger

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The Activation of the IP3, DG, Ca2+ Signal Transduction

-with the activation of PL-C by activated G-protein IP3 and DG are made by cannibalizing the membrane phospholipid called PIP2.
-IP3 enters cytosol, DG moves thru membrane, IP3 stimulate the release of ER stored Ca2+, DG binds to near C-kinase
-Ca2+ binds to the Ca2+/calmodulin kinase, this phosphorylates the proteins, fairly fast acting but temporary
-C-kinase phosphorylates cytosolic proteins, this is somewhat slow

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In-Activation of the IP3, DG, Ca2+ Signal Transduction

this system is shut down by a number of mechanisms that relate to the continual recycling of molecules, done by various phosphotase enzymes
GTP->GDP, thus causing it to become quiet
IP3->IP2 thus eliminating this second messenger
Ca2+ re-pumped back into ECM and into ER
Protein-P->Protein thus returning them to resting conformation

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Enzyme Receptor Mechanism

this process involves an external receptor that spans the membrane and can directly phophorylate cytosolic proteins
-external, ligand binding domain
-membrane-spanning domain
-internal, catalytic domain
most of these are tyrosine kinases because they add phosphates to tyrosine residues on proteins of the cell interior by using ATP

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Nucleoplasm

the contents of the nucleus

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Cytoplasm

the bulk of the cell including the cell organelles and fluid

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Cytosol

fluid inside cell mostly water, amino acids, proteins, fatty acids, lipids, nucleotides, simple sugars and complex carbohydrates

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Sytoskeleton

an array of proteins that can criss cross the interior

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Organelles

ER, Golgi Apparatus, lysosomes, mitochondria

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Functions of the Endoplasmic Reticulum (Smooth and Rough)

Protein synthesis
Hydroxylation (Smooth but some Rough)
Glycosylation (Rough but some smooth)
Glycogenolysis (Smooth)
Sterol Metabolism (Smooth)
Lipid Synthesis (Both)
Calcium Storage (Smooth)

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Hydroxylation

addition od hydfroxyl group to lipid-soluble toxins, converting them to water-soluble molecules that can be easily disposed of
can be done to complete the synthesis of certain molecules

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Glycosylation

addition of sugar residue (to specific amino acids) in peptide chains, usually done on rough endoplasmic reticulum bound ribosomes

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Glycogenolysis

breakdown of glycogen to glucose

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Sterol Metabolism

steroid hormone synthesis in endocrine glands
cholesterol synthesis and availability for membrane stability

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Lipid Synthesis

new phospholipids added to cytoplasmic side of ER bilayer
the special enzyme used to flip the new lipid to the cisternal side to prevent mono-lipid layer formation is the flippase

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Calcium Storage

common muscle cells as a way to sequester Ca2+ during the resting state

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alpha helices

amino acid chain that has commonly spiraled into large sections

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globular

when the alpha helices fold up further this is what they form

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5 kinds of proteins based on their structure

tripartite (transmembrane) single pass, hydrophilic region extends from both sides, single hydrophobic region spanning the membrane, hydrophobic regions as an alphas helix
multipass (transmember) IMP -multiple helices spanning over lipid by-layer, may contain polar or charged amino acids that contribute to formation of an aqueous pore
non-spanning IMP - embedded in one side
PMP ionically bonded to another IMP or PMP
PMP ionically bonded to an phospholipid

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Extra-Cellular Matrix

structural proteins in between cell that connect them and hold them together

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Stage-specific embryonic antigens

family of glycolipids expressed in embryogenesis
linked to specific stages of development
affect the further growth of the embryo

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cell adhesion molecules

family of glycoproteins involved in maintaining tissue integrity

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diffusion

the net movement of molecules from an area of high concentration to an area of low concentration

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osmosis

thee diffusion of water across a semi-permeable membrane

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transport maximum

the maximum rate of penetration allowed through a cell

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Donnan Effect

imbalance in distribution of mobile ions and causing water to achieve its own equilibrium by moving

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Donnan Swelling

it the cell is unable to move molecules out it this is what happens

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Polarized cells

since the cell is then constantly moving Na+ out of the cell and the Proteins -ve and Cl- inside create differences in charges from the inside to the outside.

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Electrical potential across cell

the net potential across the plasma membrane is about 60-mV

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Action Potential

There is a voltage at which enough gates open to briefly overwhelm the pumps, and cause very serious membrane action to occur
this is a self-propagating wave of depolarization due to sequential ionic gating

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Digoxin

poison found in Digitalis Foxglove plant. The toxin binds top the sodium pump in cardiac muscle cells and inhibits it. Therefore a higher level of Ca is in the heart causing strong heart beat, can be used for congestive heart failure

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Residual Bodies

any indigestible materials persist as permanent phagosomes