A&P Ch. 3 Cell Membranes

Three Basic Parts of All Cells

1. Plasma Membrane- outermost boundary, selectively permeable

2. Cytoplasm- intracellular fluid

3. Nucleus- controls cellular activities, contains genes/DNA- some cells do not have (RBC)

Plasma Membrane

forms a boundary between the two main fluid compartments (intracellular and extracellular fluid), phospholipid bilayer with proteins randomly dispersed through it (fluid mosaic model)

Three Parts of Cell Membranes

1. Lipids

2. Proteins

3. Carbohydrates

Phospholipids

forms basic structure of membrane

polar phosphate head- hydrophilic (face outside)

non polar fatty acid tails (2)- hydrophobic (faces inside)

Cholesterol

provides structure to stiffen the membrane, increase stability, throughout the tails

Types of Proteins by Location

1. Integral proteins- embedded in the plasma membrane, Transmembrane proteins- span the entire width of the membrane

2. Peripheral proteins- loosely attached to integral protein

Transport proteins

moves substances in or out of cells, selectively, 1 or 2 at a time (usually integral-transmembrane)

Receptor Proteins

receive and relay to cell interior when bound or exposed to chemical messengers, changes shape when binds, changes cellular activity (usually integral in nature)

Enzymes

proteins that catalyze chemical reactions

Cell-Cell Recognition Proteins

allow body cells to recognize other body cells, immune system (belongs or doesn’t)

Attachment Proteins

helps hold some membrane proteins in place or maintains cell shape, usually inside of the cell, but can be outside depending on function

Intercellular Junction Proteins

proteins used to link cells together, allows cells to adhere and interact with one another temporarily or permanently

Carbohydrates on cell membrane

short branched carbohydrates are on the outside of the cell, attached to lipids or proteins (glycolipids, glycoproteins)

creates the glycocalyx- sugar coating, allows for identification and prevents large substances from entering cell

Cell Junctions

a class of proteins that provide contact or adhesion between two or more cells, can be permanent or temporary

Tight Junction

type of cell junction, proteins in cell membranes of neighboring cells fuse together and interlock- impermeable

Desmosomes

anchoring junctions from one cell to another (neighboring), prevents separation, not as tight as tight junctions

Cadherins- protein filaments that extend from cell surface and link to cadherins on another cell surface-overlap (velcro)

Gap Junctions

type of cell junction, “communication“ junctions, hollow cylinders formed by proteins to connect neighboring cells and move intercellular fluid of one cell into another, so cells can share certain substances (selective)

Passive Membrane Transport

movement of molecules across the membrane down their concentration gradient (diffusion), no ATP required, KE drives

Three Factors Determining Speed of Diffusion

1. Concentration- greater concentration difference between two areas leads to faster diffusion

2. Molecular size- smaller molecules diffuse faster

3. Temperature- higher temp. results in faster diffusion rates

Three Types of Diffusion

1. Simple Diffusion- diffusion of substance directly through lipid bilayer (no proteins involved), small/nonpolar particles

2. Facilitated Diffusion- diffusion of molecules through the membrane with use of a protein

3. Osmosis

Types of Facilitated Diffusion

1. Carrier-Mediated- transmembrane proteins are used to carry large molecules through the membrane, transport protein must change shape to move substance

2. Channel-Mediated- transmembrane proteins form channels for molecules to pass through, size of channel determines what can pass

Leaky Channel

type in channel-mediated facilitated diffusion, always open, molecule can pass freely at any time

Gated Channel

type in channel-mediated facilitated diffusion, have a gate on both sides of the proteins, only opens when binds to a certain chemical

Osmosis

the diffusion of water through a selectively permeable membrane, can occur without proteins or use of aquaporin proteins, if concentrations are = : no net movement of water

Osmolarity

total concentration of all solute particles in a solution (high osmolarity = greater # of solute particles)

Tonicity

ability of a solution to change the shape of a cell by altering the cells internal water volume- always refers to the solution

Isotonic Solutions

have the same concentration as inside of the cell, no movement of water- cell will remain the same size and shape

Hypertonic Solutions

have a higher concentration than inside of the cell, water moves out- cell shrinks (crenates)

Hypotonic Solutions

have a lower concentration than inside the cell, water will move in- cell swells and can lyse

Active Membrane Transport

movement of molecules across the plasma membrane that requires energy (ATP) and transport proteins- substances are moving against their concentration gradient

primary, secondary, vesicular

Primary Active Transport

uses ATP from ATP hydrolysis, transport proteins called pumps use ATP (phosphate tail) to pump a substance against a concentration gradient, creates own concentration gradient on either side of the membrane- ex: Na+ and K+ ATPase pump

Secondary Active Transport

uses energy stored in concentration gradients of ions created by primary active transport, transport protein does not directly use ATP, need primary for this to happen

Vesicular Transport

movements of fluids with large particles and macromolecules inside membraneous sacs called vesicles (needs energy)

Endocytosis

vesicular transport used to bring substance into the cell

Phagocytosis

type of endocytosis, cell engulfs large and/or solid material, specific, material binds to receptors on cell surface, vesicle fuses w/ lysosome and contents are broken down by digestive proteins (clean up)

Pinocytosis

type of endocytosis, cell brings in a small volume of extracellular fluid containing small solute particles, no receptor needed, nonspecific, cell “samples“ surroundings to know external environment

Receptor-Mediated Endocytosis

type of endocytosis, allows endocytosis of specific substances, *for small particles- binds to receptor proteins to form a vesicle filled with substance

Exocytosis

vesicular transport used to remove substances from the cell

secretory vesicle- created around the substance to be removed, travels to plasma membrane, fuses with it, and dumps contents out of the cell

hormone secretion, neurotransmitter release, waste removal

Membrane Potential

the difference of electrical voltage across the plasma membrane due to the separation of oppositely charged particles

Resting Membrane Potential

voltage difference across cell membrane when cell is at rest

average = -70mV

important for neurons and muscle cells

Four Charged Particles that Contribute to Membrane Potentials

1. Na+

2. K+

3. Cl-

4. Proteins (-)

Key Ion for creating Membrane Potential

Potassium (K+), leaky channel, K+ leaks out due to concentration gradient and proteins remain inside the cell, not all K+ leaves the cell, some is brought back in due to electrical gradient, when inside gets too negative

Contact Signaling

cellular recognition by physical contact between cells- receptors of cells bind to one another

Chemical Signaling

when a chemical messenger binds a specific receptor and initiates a response by the cell

specific response is linked to the cell’s internal machinery, not the ligand (hormones, other molecules)