Cell membranes and transport
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Cell Membranes and Transport. What is going on in this picture?. Phospholipids. Phospholipids. Fatty acid chains A phosphate group Glycerol backbone. Polar heads Nonpolar fatty acids. The Fluid Mosaic Model. Fluid Mosaic Model. Transports: Small molecules Between the phospholipids

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Cell Membranes and Transport

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Cell Membranes and Transport


What is going on in this picture?


Phospholipids


Phospholipids

  • Fatty acid chains

  • A phosphate group

  • Glycerol backbone.

    • Polar heads

    • Nonpolar fatty acids


The Fluid Mosaic Model


Fluid Mosaic Model

  • Transports:

    • Small molecules

    • Between the phospholipids

  • Large molecules?!


Composition of the Plasma Membrane

  • Lipid bilayer

  • Peripheral proteins

  • Integral proteins

  • Cholesterol

  • Glycoproteins

  • Alpha helix protein


Homeostasis

  • Maintaining a Balance

    • Nutrients

    • Water

    • Wastes

  • Selectively permeable


Diffusion

Cell membrane

Outside cell

Inside cell


Diffusion

Cell membrane

diffusion

Outside cell

Inside cell


Diffusion

Cell membrane

Outside cell

Inside cell

EQUILIBRIUM


Facilitated Diffusion

Cell membrane

diffusion

Protein channel

Outside cell

Inside cell


Facilitated Diffusion

Cell membrane

diffusion

Protein channel

Outside cell

Inside cell

EQUILIBRIUM


Osmosis

CONCENTRATED SOLUTION

DILUTE SOLUTION

Cell membrane partially permeable.

Sugar molecule

VERY Low conc. of water molecules. High water potential.

VERY High conc. of water molecules. High water potential.

Outside cell

Inside cell


Osmosis

Cell membrane partially permeable.

Low conc. of water molecules. High water potential.

OSMOSIS

High conc. of water molecules. High water potential.

Outside cell

Inside cell


Osmosis

Cell membrane partially permeable.

OSMOSIS

Outside cell

Inside cell

EQUILIBRIUM. Equal water concentration on each side. Equal water potential has been reached. There is no net movement of water


Cellular Transport - Passive

  • No energy is needed to move particles

  • Types of passive transport:

    • Diffusion

    • Facilitated diffusion

    • Osmosis


What determines the rate of diffusion?

  • Steepness of the concentration gradient

  • Temperature

  • Surface area

  • Type of molecule or ion diffusing


What’s the Point?


Cell Concentrations

  • Hypertonic solutions

    • More dissolved solute, less water

  • Hypotonic solutions

    • Less dissolved solute, more water

  • Isotonic solutions

    • Equal amounts of dissolved solute and water


Cell Concentrations – Isotonic

  • If the outside solution is isotonic to the inside of the cell…

    • The inside of the cell has the same amount of dissolved solute as outside the cell

  • So the water moves…

    • IN and OUT at equal rates!


Cell Concentrations – Hypotonic

  • If the outside solution is hypotonic to the inside of the cell…

    • The outside of the cell has less solute and more water than the inside of the cell

  • So the water moves…

    • INTO the cell until equilibrium is reached.


Cell Concentrations – Hypertonic

  • If the outside solution is hypertonic to the inside of the cell…

    • The outside of the cell has more solute and less water than the inside of the cell

  • So the water moves…

    • OUT of the cell until equilibrium is reached.


Overcoming Osmosis

  • Contractile vacuoles

  • Turgor pressure


Cellular Transport - Active

  • Active transport

    • Energy is needed to move particles UP the concentration gradient


Cellular Transport - Active

  • Carrier proteins

  • Endocytosis

    • Pinocytosis

    • Phagocytosis

  • Exocytosis


Active/Passive

Molecules That Move Across the Membrane

Direction

Energey Needed?

Protein Needed?

Diffusion

Osmosis

Facilitated Diffusion

Active Transport

How Molecules Cross the Membrane


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