Cell Membrane Transport

• Cell membranes transport via facilitated diffusion, active transport, endocytosis, and exocytosis.

Facilitated Diffusion

• A type of diffusion where molecules move from an area of high concentration to an area of low concentration.
• This movement requires the assistance of a channel protein that form protein channels and carrier proteins.

Carrier Proteins

• Bind to specific molecules on one side of the membrane.
• Undergo a conformational change, releases the substance on the other side.
• Examples include glucose and amino acids.

Protein Channels

• Narrow passageways that allows molecules (such as ions) of the correct size and shape to pass through.
• Examples include Na+, K+ and Ca2+.

Active Transport

• Involves the movement of molecules from an area of low concentration to an area of high concentration.
• This process requires the consumption of energy.
• Cells use energy to transport materials against a concentration gradient via a carrier protein.
• Energy is transferred to the carrier protein in the form of ATP.

Sodium-Potassium Pump

• Allows nerve impulses to travel along nerves.
• Maintains the resting membrane potential.
• Transports K+ inside the cell and Na+ outside the cell.

Vesicular Transport

• Vesicular transport is a transport of bulk materials (large particles/whole cells) across the cell membrane in vesicles.
• This is an active process because energy is needed to form the vesicles, move the vesicles in the cytoplasm, and change the shape of the cell:

Endocytosis

• The transport of bulk solids (phagocytosis) and liquids (pinocytosis) into the cell from the external environment via a vesicle.
• Examples include micro-organisms and hormones.
• The cell membrane surrounds extracellular material and folds until particles are fully enclosed.
• The cell membrane folds until the particles are fully enclosed, forming a vesicle that pinches off and is suspended in the cell's cytoplasm.

Exocytosis

• The movement of solids or liquids out of a cell to the external environment via a vesicle.
• Examples include hormones, digestive enzymes, and mucous/wastes.
• Vesicle contents produced in the ER or Golgi are pushed to the edge of the ell.
• The membrane fuses with the cell membrane, and the vesicle contents are pushed to the exterior/extracellular fluid.

Question Set 2.3, P42

• Vesicular transport moves substances in membrane-bound sacs; endocytosis brings liquids or solids into the cell, while exocytosis releases contents out of the cell.
• Facilitated diffusion moves along the concentration gradient from high to low without energy, while active transport moves against the concentration gradient from low to high using ATP.
• Both facilitated diffusion and active transport use carrier proteins, and both are specific to molecules, can be saturated and regulated by hormones.
• Steroids diffuse directly through the membrane due to their lipid solubility, while glucose water solubility requires carrier proteins to enter the cytoplasm.