H2 Biology 3 - Membrane structure

1. "Fluid" - proteins and phospholipids are free to move within the membrane.

2. Phospholipids are held by weak hydrophobic interactions and can diffuse rapidly in their own layers.

3. "Mosaic" - proteins are embedded within the phospholipid bilayer in a random manner.

1. Act as enzymes to catalyse reactions

2. Act as receptors with specific binding site complementary in shape to signal molecules

3. Cell-cell adhesion; binds cells together to form tissues

4. Act as transport proteins; channel/carrier proteins

1. Cell-cell recognition; hydrocarbon chain acts as marker to distinguish cells

2. Cell-cell adhesion

3. Act as receptor sites for signal molecules

1. Acts as plug, reduces escape, entry of polar molecules/charged ions.

2. Increases stability, flexibility of membrane;

-at low temps, decreases membrane fluidity by restraining phospholipid movement

-at high temps, increases membrane fluidity by hindering close packing of phospholipids

It is the passive movement of polar molecules/charged ions from a region of higher concentration to a region of lower concentration down a concentration gradient, across a selectively permeable membrane via the aid of specific transport proteins.

Amino acid residues with polar/charged R groups make up inner lining of the hydrophilic channel, allowing water-soluble molecules to pass through easily. Channels are selective; certain molecules can pass but not others. Some channels can open/close in response to certain signals.

Has binding sites specific to polar molecule/charged ion; shape of binding site is complementary to molecule. Binding confers a conformational change such that molecule is released to other side of membrane.

It is the active movement of polar molecules/charged ions from a region of lower concentration to a region of higher concentration against a concentration gradient, across a selectively permeable membrane via the aid of specific carrier proteins.

Exocytosis; form of bulk transport where cell secretes macromolecules by fusion of vesicles with plasma membrane in an active process(ATP).

Endocytosis; form of bulk transport where cell takes in macromolecules by forming new vesicles from cell surface membrane in an active process(ATP).

1. Secretory vesicle containing material to be secreted moves towards cell surface membrane.

2. Membrane of secretory vesicle fuses with cell surface membrane.

3. Vesicle opens to exterior, releases contents to extracellular fluid via exocytosis.

1. Cell surface membrane invaginates, forms flask-shaped depression which engulfs materials from exterior of the cell.

2. Invagination is sealed off, encloses extracellular material forming an endocytic vesicle which moves into cell.

2 TYPES - PINOCYTOSIS(smaller fluids), PHAGOCYTOSIS(bigger solids)

It is the process by which cell can obtain solid particles which are too large to be absorbed by diffusion or active transport.

1. Solids taken up by phagocytosis forms a phagocytic vesicle.

2. Lysosome fuses with vesicle and discharges contents into vesicle.

3. Lysosome's hydrolytic enzymes digests particles, digested substances diffuse into cytoplasm from vesicle and absorbed by cytoplasm of cell.

4. Vesicle membrane fuses with plasma membrane; indigestible material released out of cell via exocytosis.

Similar to phagocytosis; vesicles formed are smaller and intake of materials is mainly fluid droplets. Pinocytosis is non-specific compared to phagocytosis in taking in solutes.