Chpt 3 - Cell Biology part 1

Generalized Cell, Plasma Membrane, Cell-Environment interactions

functions of cell

cell metabolism, energy use, synthesis of molecules, communication (chemical and electrical signals), reproduction and inheritance, autophagy

fluid membrane

-how cells create boundary for themselves

-fluid mosaic model of different proteins embedded in the phospholipid bilayer, hydrophilic portions maximally exposed to water, hydrophobic portions in nonaqueous environment inside membrane

-creates potential because of gradient

example of electrochemical gradient

sodium gradient because there is a difference in both teh chemical concentration and the electrical charge of sodium (Na+) ions across the cell membrane, with much more outside than inside

example of electrical gradient

movement of sodium (Na+) across membrane of a resting neuron because negative interior of cell strongly attracts sodium ions inward

function of membrane proteins

attachment to itself, regulate movement in and out of cell, communication

marker molecules

allow cells to identify other cells or other molecules (ex: different marker molecule in organ transplant)

attachment proteins

anchor cells to other cells

examples of transport proteins

channel proteins, receptor proteins, ATP-powered pumps

channel proteins (transport protein)

form passageways, allowing specific ions or molecules to enter or exit; may be leaked or gated; ex: Potassium K+ channels are always open while ligand-gated sodium Na+ channels are closed until ligand bonds

carrier proteins

integral proteins that move ions from one side to the other, changes shape when specific chemical attaches to binding site and then moves chemical across membrane; resumes original shape

ATP-powered pumps

move specific ions or molecules across membrane using breakdown of ATP; have binding sites for specific ions, and hydrolysis of ATP to ADP release ennergy to chaneg shape to move substance; releases ion and phosphate

receptor proteins

function as binding sites for chemical signals in the extracellular fluid; binding of chemical signals to receptors triggers cellular response

enzymes

catalyze chemical reactions either inside or outside cells

why are plasma membranes selectively permeable

maintain homeostasis, so lipid soluble molecules can dissolve but large, nonlipid solubule molecules and ions need transport proteins or vesicles to pass through

lipid soluble molecules that can dissolve through bilayer

O2, CO2, and steroids

non-lipid soluble molecules and ions that need transport

potassium, glucose, sodium

transport mechanisms

passive transport, active transport, vesicular transport

passive transport

movement of substance from high to low concentration (diffusion, osmosis, facilitated diffusion)

active transport

movement of substances against concentration gradient (low to high) requiring ATP (ex: sodium-potassium pump)

what does the rate of active transport depend on

-concentration of substate

-number of ATP pumps

-amount of ATP

describe steps of Sodium-Potassium pump

1. 3 sodium and 1 ATP bind to pump

2. sodium binding stimulates hydrolysis of ATP and pump changes shape

3. 3 sodium released to extracellular fluid

4. 2 potassium ions bind to changed pump shape

5. triggered release of phosphate

6. pump resumes shape, 2 potassium ejected

secondary active transport

use of potential energy in concentration gradient of one substance to help move another substance against its gradient (ex: more sodium outside cell than inside cell in sodium/potassium pump, and sodium moves back into cell with transport protein, but concentration gradient strong enough to move glucose against its concentration gradient)

vesicular transport

movement of larger substances by formation or release of membrane-bound vesicle; requires ATP (ex: endocytosis, exocytosis, transcytosis)

endocytosis

large substances movement into cell by being enclosed by membrane (ex: phagocytosis, pinocytosis)

phagocytosis

solid particle ingested and large vesicle is formed

pinocytosis

dissolved molecules ingested and small vesicles are formed

exocytosis

movement out of cell, sacs fuse with membrane and release contents to outside

transcytosis

movement through a cell by a combination of endocytosis on one surface and exocytosis on opposite surface

pressure required to prevent net movement of water into a solution

osmotic pressure

hypertonic solution

solution with greater solute concentration than inside a cell

hypotonic solution

solution with a lower solute concentration than inside a cell