Active and Bulk Transport

Active Transport

• passive transport is useful for many metabolic functions, but often materials need to be concentrated

this requires moving them against a concentration gradient

• adenosine triphosphate (ATP) provides the energy needed in this and many other processes of living cells

ATP

• ATP is similar to the structure of a nucleotide, except that it contains 3 phosphate groups attached to a ribose sugar

energy is released when the high-E bond between the 2nd and 3rd phosphate group is broken

Adenosine Triphosphate

Active Transport Mechanism• active transport is the movement of

molecules and ions against a concentration gradient

molecules and ions bind to a protein carrier which uses energy from ATP to pump molecules or ions across the cell membrane

the molecule to be transported attaches to an open binding site on one side of the carrier protein

ATP is converted to ADP + P on the carrier protein and releases energy

the energy causes a change in the shape of the protein that carries the solute to the other side of the membrane

Na+/K+ Pump • The Na+/K+ pump is utilized in neurons

(nerve cells)Na+ ions must be higher outside the cell,

while K+ ions must be lower outside the cell for a nerve transmission to occur

Binding of the phosphate from ATP changes the shape of the protein, alternately providing binding sites for three Na+ ions to be transported out for every two K+ ions to be transported into the cell

http://www.youtube.com/watch?v=Kd3LorZcJew&feature=related

Cystic Fibrosis

• Cystic fibrosis is a disease in which the protein for active transport of Cl- ions out of cells is faulty, resulting in a buildup of Cl- ions and reduced reabsorption of Na+ ions

• This results in dehydration of lung and digestive tissue, increased mucous, and reduced ability to defend against bacteria.

http://www.youtube.com/watch?v=5n29ZCvtCI8&feature=related

Bulk Transport vesicles are required for movement

of large particles (i.e. proteins, polysaccharides) in and out of cells, requiring energy from ATP.

Endocytosis• endocytosis

involves the pinching in of a portion of the cell membrane to form a vesicle inside the cytoplasm which then travels to the needed location within the cell.

• two types: phagocytosis and pinocytosis

Phagocytosis

• Phagocytosis (cell eating) is the bulk transport of solids into the cell

• Involves the use of pseudopods to engulf particles (i.e. macrophages WBC engulf entire bacteria) which eventually encloses them in a vesicle within the cell’s cytoplasm

• Lysosomes containing digestive enzymes may fuse with the phagocytic vesicle to digest the particles it contains

Electron Micrograph of Macrophage Phagocytosis of E. coli

Pinocytosis• pinocytosis (cell drinking) is the bulk transport of (liquid)

extracellular fluid into vesicles in the cell, forming a pinocytic vesicle

• molecule binds to receptor protein on cell membrane exterior

Receptor-Mediated Endocytosis

receptor-molecule complexes move within membrane

vesicles form when enough accumulate (i.e. insulin)

Hypercholesterolemia• Hypercholesterole

mia is a condition in which receptor proteins on liver cells used to remove excess cholesterol is absent or reduced in number.

• This leads to heart and artery disease

http://www.youtube.com/watch?v=UIjkAPn2CRE

Exocytosis • exocytosis moves large amounts of material

out of the cell in a process which is the reverse of endocytosis

• some cells produce substances for export like proteins (i.e. hormones, enzymes)

vesicles form around proteins created in the endoplasmic reticulum

vesicles merge with the Golgi body where the protein is modified and packaged for export

new vesicles are formed by the Golgi body which move to and merge with the cell membrane, expelling the protein from the cell (i.e. hormones expelled into blood, digestive enzymes into lumen of small intestine)

http://www.youtube.com/watch?v=bD4z27ASN1M&feature=fvsr