Cell Transport and Signalling Flashcards by Mary Rose Carvajal

♣ Also called plasma membrane
♣ 8 to 10 nm thick
♣ a phospholipid bilayer
♣ barrier against movement of water molecules and water-soluble substances

Cell Membrane

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♣ Cell membrane is composed of phospholipid bilayer

♣ It is fluid-like

Fluid Mosaic Model

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♣ Lipid-soluble substances diffuse easily

♣ Water and water-soluble substances passes through transport proteins

Membrane Transport

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allow free movement of water and selected ions

Channel Proteins

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conformational change to transport molecules

Carrier Proteins

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random movement of substance through intermolecular spaces or in combination with a carrier
Normal kinetic motion of matter
“downhill”

Passive Transport

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Movement across the membrane in combination with a carrier protein
against the concentration gradient
Requires additional energy
“Uphill”

Active Transport

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♣ simple movement though the membrane
♣ caused by the random motion or kinetic movement of the molecules
♣ cell membrane pores
♣ lipid matrix of the membrane (for lipid soluble substances)

Diffusion

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♣ Occurs downhill from an electrochemical gradient
♣ Via membrane opening or intermolecular spaces
♣ No interaction with carrier proteins
♣ Governed by Fick’s Law of Diffusion

Simple Diffusion

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The rate of diffusion is determined by

the amount of substance
velocity of kinetic motion
number and sizes of openings

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Predicts the rate of diffusion of molecules across a biological membrane

Fick’s Law of Diffusion

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According to Fick’s Law, diffusion is_________ at higher concentration gradients

Fast

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According to Fick’s Law, diffusion is _______ at higher permeability

Fast

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According to Fick’s Law,diffusion is _______ at higher areas for diffusion

Fast

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According to Fick’s Law, diffusion is ______ when diffusing membrane is thicker

Slow

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2 important characteristics of Simple Diffusion

selectively permeable

2. Voltage or ligand -gated channels

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♣ molecular conformation of the gate or of its chemical bonds responds to the electrical potential across the cell membrane; Eg Na and K Pump

Voltage-Gated Channels

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♣ Also called chemical gating
♣ Channels are opened by a chemical substance with the protein
♣ Causes conformational/structural change in the channel
♣ Example: Acetylcholine Channel

Ligand-Gated Channels

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♣ Also called uniport
♣ Occurs downhill from an electrochemical gradient
♣ Does not require metabolic energy (passive)
♣ More rapid than simple diffusion
♣ carrier-mediated process
♣ NOT governed by Fick’s law of diffusion

Facilitated Diffusion

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♣ Net movement of water through a semipermeable membrane caused by a concentration

Osmosis

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homogeneous mixture composed of two or more substances

Solution

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undergoes diffusion from an area of high solute concentration to an area of low solute concentration.

Solute

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undergoes osmosis from an area of low solute concentration to an area of high solute concentration.

Solvent

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concentration of all osmotically active
particles (osmoles) per liter of solution (osmol/L)
colligative property that can be measured by freezing point depression

Study These Flashcards

Osmolarity

- concentration of all osmotically active particles (osmoles) per kg of solvent (osmol/kg) - determines osmotic pressure between solutions

Osmolality

Two solutions that have the same osmolarity

Isosmotic

Solution with the higher osmolarity

Hyperosmotic

Solution with the lower osmolarity

Hyposmotic

- The exact amount of pressure required to stop osmosis - pressure which needs to be applied to a solution to prevent the inward flow of water across a semipermeable membrane - calculated using Van't Hoff's Law

Osmotic Pressure

Van't Hoff's Law physiologic implications

♣ osmotic pressure is HIGHER with higher osmolality ♣ osmotic pressure is HIGHER with higher temperature ♣ the higher the osmotic pressure of a solution, the greater the tendency for water to flow into the solution

- measure of the osmotic pressure of two solutions separated by a semipermeable membrane - influenced only by solutes that cannot cross the membrane

Tonicity

OSMOLARITY vs TONICITY

OSMOLARITY accounts for all solutes. | TONICITY accounts for only non-permeating solutes

♣ Transport of glucose, amino acids, and other polar molecules through the cell membrane ♣ Mediated by carrier proteins in cell membrane

Carrier-Mediated Transport

Characteristics of Carrier-Mediated Transport

♣ Stereospecificity ♣ Saturation ♣ Competition

Each carrier protein is specialized to transport a specific substance

Stereospecificity

Transport rate increases as solute concentration increases until all carriers are saturated (transport maxima, Tmax)

Saturation

Structurally related solutes compete for transport sites on carrier molecules

Competition

♣ Occurs uphill against an electrochemical gradient ♣ Requires direct input of metabolic energy (active) ♣ Carrier-mediated transport that exhibits stereospecificity, saturation and competition

Primary Active Transport

♣ Transport Na+ from ICF to ECF and K+ from ECF to ICF -against electrochemical gradients ♣ Energy provided from terminal bonds of ATP ♣ Usual stoichiometry is 3NA+/2K+

Na+/K+-ATPase

Functions of Na+/K+-ATPase

♣ CONTROL OF CELL VOLUME - large numbers of proteins and other osmotically active particles are present inside the cell ♣ ELECTROGENIC NATURE - net of one positive charge is moved from the interior of the cell to the exterior for each cycle of the pump; creates an electrical potential across the cell membrane

♣ Transport of two or more solutes is coupled ♣ One of the solutes (usually Na+) is transported downhill and provides energy for the uphill transport of other solute(s) ♣ Metabolic energy is provided indirectly from the Na+ gradient ♣ inhibition of Na+/K+-ATPase inhibits secondary active transport

Secondary Active Transport

Types of Secondary Active Transport

1. Co-Transport | 2. Countertransport

- also called symport | - occurs if the solutes move in the same direction across the cell membrane

Co-Transport

- called exchange transport or antiport | - occurs if the solutes move in opposite directions across the cell membrane

Countertransport

Transport of hormones along the blood stream to a distant target organ

Endocrine Signaling

♣ Also called synaptic transmission | ♣ Transport of neurotransmitter from a presynaptic cell to a postsynaptic cell

Neurocrine Signaling

♣ Release and diffusion of local hormones with regulatory action on neighboring target cells

Paracrine Signaling

♣ A cell secretes hormones or chemical messengers that binds to the same cell

Autocrine Signaling

♣ Also called contact-dependent signaling ♣ transmitted via oligosaccharide, lipid or protein components of a cell membrane ♣ occurs between adjacent cells linked by gap junctions

Juxtacrine Signaling

2 Basic Classes of Receptor

Plasma Membrane receptors | Nuclear receptors

♣ Ion-channel linked ♣ G-protein coupled receptors ♣ Catalytic receptors ♣ Transmembrane receptors

Plasma Membrane receptors

♣ hormone-receptor complex binds to DNA and regulates the transcription of specific genes ♣ Early primary response -->gene activation to stimulate other genes --> biological effect

Nuclear receptors

♣ Process by which an extracellular signal activates a membrane receptor ♣ second messengers ♣ Involves small molecules in complicated networks within the cell ♣ Results to single amplification ♣ Alteration of intracellular molecules creating a response

Signal Transduction

♣ Family of integral transmembrane proteins that possess seven transmembrane domains ♣ Heterotimeric complexes - α, β, and γ subunits ♣ Linked with more than 1000 different receptors

G Protein-Coupled Signal Transduction Pathways

♣ Mediate direct and rapid synaptic signaling between electrically excitable cells ♣ neurotransmitters bind to the receptors and either open or close the ion channel ♣ Chemical electrical signal response ♣ Examples: Voltage gated-channels in NMJ, ryanodine receptor, Arachidonic acid, caffeine

Ion Channel Linked Signal Transduction Pathway

♣ Kinase is an enzyme that modifies other proteins by phosphorylation ♣ Phosphorylation usually results in a functional change of the target protein

Protein Kinases

♣ calcium (Ca2+) binding causes conformational alterations in calmodulin; Eg. Muscle cells

Calmodulin-dependent Protein Kinases

♣ Adenylyl cyclase facilitates the conversion of ATP to cAMP ♣ Increased cAMP activates protein kinase A

cAMP-dependent Protein Kinases

♣ Binding of ANP causes dimerization and activation of guanylyl cyclase, which metabolizes GTP to cGMP ♣ cGMP activates cGMP-dependent protein kinases; phosphorylates proteins on specific serine and threonine residues

cGMP-dependent Kinases

Cell Transport and Signalling Flashcards

(59 cards)