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Flashcards in Cell Transport and Signalling Deck (59):
1

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

Cell Membrane

2

♣ Cell membrane is composed of phospholipid bilayer
♣ It is fluid-like

Fluid Mosaic Model

3

♣ Lipid-soluble substances diffuse easily
♣ Water and water-soluble substances passes through transport proteins

Membrane Transport

4

allow free movement of water and selected ions

Channel Proteins

5

conformational change to transport molecules

Carrier Proteins

6

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

Passive Transport

7

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

Active Transport

8

♣ 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

9

♣ 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

10

The rate of diffusion is determined by

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

11

Predicts the rate of diffusion of molecules across a biological membrane

Fick's Law of Diffusion

12

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

Fast

13

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

Fast

14

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

Fast

15

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

Slow

16

2 important characteristics of Simple Diffusion

1. selectively permeable
2. Voltage or ligand -gated channels

17

♣ 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

18

♣ 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

19

♣ 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

20

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

Osmosis

21

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

Osmolarity

25

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

Osmolality

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Two solutions that have the same osmolarity

Isosmotic

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Solution with the higher osmolarity

Hyperosmotic

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Solution with the lower osmolarity

Hyposmotic

29

- 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

30

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

31

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

Tonicity

32

OSMOLARITY vs TONICITY

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

33

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

Carrier-Mediated Transport

34

Characteristics of Carrier-Mediated Transport

♣ Stereospecificity
♣ Saturation
♣ Competition

35

Each carrier protein is specialized to transport a specific substance

Stereospecificity

36

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

Saturation

37

Structurally related solutes compete for transport sites on carrier molecules

Competition

38

♣ 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

39

♣ 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

40

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

41

♣ 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

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Types of Secondary Active Transport

1. Co-Transport
2. Countertransport

43

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

Co-Transport

44

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

Countertransport

45

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

Endocrine Signaling

46

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

Neurocrine Signaling

47

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

Paracrine Signaling

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

Autocrine Signaling

49

♣ 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

50

2 Basic Classes of Receptor

Plasma Membrane receptors
Nuclear receptors

51

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

Plasma Membrane receptors

52

♣ 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

53

♣ 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

54

♣ 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

55

♣ 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

56

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

Protein Kinases

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

Calmodulin-dependent Protein Kinases

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

cAMP-dependent Protein Kinases

59

♣ 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