AP Biology - Unit 4: Membranes & Transport

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57 Terms

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Fluid Mosaic Membrane

composed of several elements (integral membrane protein, cholesterol, carrier protein, peripheral membrane protein, channel protein, lipid bilayer)

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Phospholipid bilayer

Phosphate (polar), glycerol, fatty acids, polar heads, non-polar tails

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Fluidity of phospholipid bilayer depends on…

  • Degree of saturation of the fatty acids in phospholipid  

  • Steroids like cholesterol in membrane alter fluidity depending on temperature

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Fluid Mosaic elements

Glycoprotein, polysaccharide, cholesterol, extracellular fluid, glycolipid, cytoplasm, filaments of cytoskeleton (actin + microtubules)

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Bilayer

barrier to passage of water and water soluble molecules 

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Glycolipids & glycoproteins

cell & tissue identity markers;  indicate self vs. other 

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Glycoprotein

protein with attached carbohydrate chains, present in cell membranes, extracellular matrix, and secreted proteins; they play roles in cell signaling, immune response, and cell adhesion.

ex: antibodies, hormones, and enzymes

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Glycolipid

lipid molecule that contains a carbohydrate group attached to it; plays not only a structural role to maintain membrane stability but also facilitates cell-cell communication acting as receptors, anchors for proteins and regulators of signal transduction

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Cytoskeleton

holds membrane in shape, position proteins (microtubules) & move membrane & organelles (actin)

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Microtubules

position proteins

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Actin

move membrane & organelles

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Cell Identity markers

Glycoprotein/glycolipid (ex: blood type, tissue type)

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Cell to Cell Adhesion 

Intercellular junction; forces things thru membrane not around

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Catalyze reactions

enzyme, product, substrate; in series on the membrane

ex: smooth ER, mitochondria

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Gates, Channels, Pumps 

Transport proteins & ATP; membranes are selectively permeable by regulating movement of ions or molecules by shape

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Receptor

Receptor proteins

Ex: hormone, neurotransmitter, causes internal activity change

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Attach to cytoskeleton

Proteins attach to cytoskeleton and extracellular matrix; gives cell structure

changes shape of cell

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Signaling Between Cells steps

  • Initiating cell releases signal molecule (hormone, NTS)

  • To intercellular fluid or blood stream

  • Signal molecule binds to protein receptor of target cell

  • Leads to change in internal activity of target cell

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Paracrine signaling

allows cells to communicate with each other by releasing signaling molecules that bind to and activate surrounding cells; injured cell, local mediator, mast cell releases histamine to target cells

  • Nearby cell – signal thru intercellular fluid

  • Walls of blood vessels expand

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Contact-dependent signaling

requires cells to be in direct membrane-membrane contact, membrane-bound signal molecule connects signaling and target cells

  • Infected cell presenting piece of pathogen

  • Helper T cell will destroy

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Neuronal signaling

synapses permit information transfer by interconnecting neurons to form the circuitry on which neural processing depends; neuron (sending cell) sends signaling molecule (neurotransmitter) to target cell through synapse

  • target cell can be neuron, muscle, gland

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Endocrine signaling

the signaling molecules (hormones) are secreted by specialized endocrine cells and carried through the circulation to act on target cells at distant body sites; endocrine cell secretes hormone through blood to receptor on target cells, or other glands/muscle

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Passive transport

Ions & molecules move down the gradient. High to Low (no energy required from cell), spread b/c of their molecular motion 

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Diffusion

ions move down gradient w/o energy from cell depending on permeability via protein channels specific to each ion

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Facilitated Diffusion

larger molecules use a shape specific carrier protein BUT can become saturated b/c it only carries one at a time

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Osmosis

movement of water from high to low water conc but depends on solute conc.; moves through aquaporin channels

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Hyperosmotic solution

High solute concentration, low water concentration, water moves out of the cell → cells shrink

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Isosmotic solution

Equal solute concentration, equal water concentration, water moves both in and out of the cell → cell normal, suitable

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Hyposmotic solution

Low solute concentration, high water concentration, water moves into the cell → cells swell/expand

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Cytolysis

animal cell bursting

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Turgid

plant cell swelling

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Plasmolysis

plant cell shrinking

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Why does solute matter? 

  • More solute, less room for water so it lowers water potential

  • More solute, less water available because it is busy with Hydrogen bonding & keeping non-polar molecules excluded

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Hydrostatic pressure

the pressure that any fluid in a confined space exerts

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Osmotic equilibrium

occurs when the fraction of water molecules in solution matches the fraction of pure water molecules that have enough energy to overcome the pressure difference

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Why does pressure matter?

More pressure more water potential 

BUT Plant cells can fight back against osmosis because of cell wall

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Water potential purpose

To quantify the effect of  solute concentration and internal pressure on the direction of water movement

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Ψ

(water potential)

ΨP      +         Ψs

(Pressure potential + solute potential)

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Water will always move from 

high water potential to low water potential

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Water potential calculation

Ψ         =         ΨP      +       Ψs    which is –i x C x R x T

(Water potential = Pressure potential given + -i  x  C  x  R  x  T

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i

# ions produced by dissociation 

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C

concentration of solute 

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R

.0831

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T

273 + oC = K

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Bulk passage

Movement of large particles/quantities by engulfing (active transport)

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Endocytosis

into cell via a vesicle 

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Phagocytosis

solid (cell “eating”) 

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Pinocytosis

liquid (cell “drinking”) 

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Exocytosis

out of cell via vesicle (ex: wastes, product) 

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Receptor Mediated Endocytosis

uses protein receptors along membrane to pick up only appropriate molecules for endocytosis

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Sodium-Potassium Pump

pumps Na out of cell and K in – both move up their gradients; requires energy form cells (ATP) → active transport

Ex: neurons

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B/c phosphate groups are large and charged

they change the shape of the protein to open/close gate

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Coupled transport

Uses Na K pump to set up gradient that provides potential & kinetic energy to drive a coupled pump that will transport another molecule (sugar) → secondary active transport

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Charge changes the shape of the protein so…

it drags another molecule with it

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Proton pump

1st establishing proton gradient provides potential energy to drive ATP synthase to store energy in ATP (active transport)

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Passive transport

Osmosis, diffusion, and facilitated diffusion

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