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Powerpoint Presentation: Biological Membranes
Powerpoint Presentation: Pore Proteins

 

Cells Index

Cells
Cell Structure
The Light Microscope and the Electron Microscope
Eukaryote Cell Ultrastructure
The Plant Cell Wall

Cells
Cell Structure
The Light Microscope and the Electron Microscope
Eukaryote Cell Ultrastructure
The Plant Cell Wall

Active Transport

  • Uses energy

  • Faster than diffusion

  • Can move against a concentration or electrochemical gradient

  • Uses carrier proteins - very specific arrow selective transport

Evidence of active transport in marine algal cells

 

Concentration / m mol dm-3

Ion

Sea water

Cell sap

Sodium (Na+)

488

257

Potassium (K+)

012

337

Chloride (Cl-

523

543

 

Phagocytosis

Also works using receptor molecules.

Phagocytic white blood cells (neutrophils and macrophages) recognise and engulf microbes this way.

Phagocytosis I

Phagocytosis II

 

CELLS

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Membrane Transport Proteins

Passive Transport - Facilitated diffusion

Driving forces

  1. Diffusion: along a concentration gradient.

  2. Electrochemical gradient: A membrane potential is set up due to a voltage (potential difference) across the membrane.

    Positive ions are encouraged to move in and negative ions are encouraged to move out.

 

Electrochemical gradient

 

The difference between diffusion and facilitated diffusion.

Diffusion may occur through any part of the plasma membrane, e.g. N2 gas molecules.

Facilitated diffusion uses pores, e.g. glucose molecules

 

Facilitated diffusion

 

Types of pore

Channel Proteins:

Proteins that permit the passive movement of molecules or ions of appropriate size (dialysis) through an aqueous pore.

Channel Proteins

 

Carrier proteins: Bind to specific solutes to transport them across a membrane

Carrier proteins

 

Uniport pore: One type of molecule transported

Uniport pore

 

Coupled pores: Two molecules transported together

Symport: Both molecules move in the same direction eg Glucose and Na+ in the kidney and intestine epithelial cells.

symport

Antiport: Molecules move in opposite directions (one in the other out), eg Na+ (out) and K+ (in).

Antiport I

Antiport II

ATPase is an antiport pore protein.

ATP is made on the mitochondria inner membranes by throwing an ATPase into reverse.

 

Exocytosis and Endocytosis

  • Transferring large molecules or particles or large volumes in and out of the cell.

  • Mediated by special proteins

Endocytosis may form small vesicles by invaginating the plasma membrane = Pinocytosis

Endocytosis may also occur when a large cell flows round and engulfs a smaller cell = Phagocytosis.

Exocytosis and Endocytosis

 

Exocytosis may be continuous as a cell makes material for secretion.

Exocytosis may be regulated, vesicles are stored in the cytoplasm waiting for a signal to be released.

Endocytosis uses protein coated pits which form coated vesicles.

The plasma membrane has receptor molecules on the outer surface.

When the specific molecule attaches to the receptors the membrane invaginates.

 

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