Chapter 7: Membrane Structure and Function

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Phospholipids are amphipathic. Explain what this means

Has both a hydrophillic and hydrophobic region

The currently accepted model of the membrane is the fluid mosaic model. Describe the model.

Various proteins embedded or attached to a double layer of phospholipids

Describe decreasing temperatures affect on membrane fluidity

membrane remains fluid until phospholipids settle into a closely packed arrangement and membrane solidify

Describe phospholipids with unsaturated hydrocarbon chains affect on membrane fluidity

because of kinks, cannot pack together as closely as saturated hydrocarbon tails. makes membrane more fluid

cholesterol

"fluidity buffer" resisting changes in membrane fluidity

Integral proteins

penetrate hydrophobic interior of the lipid bilayer. majority are transmembrane proteins, which span the membrane.

Peripheral Proteins

not embedded in the lipid bilayer; appendages loosely bound to the surface of the membrane, often exposed to integral proteins.

Transport Proteins

spans membrane.
provide hydrophilic channel.
hydrolyze ATP.
shuttle substances from one side to the other.

Enzymatic Activity

Active side exposed to substances in solution organized to carry out sequential of a metabolic pathway

Signal Transduction

Binding site with specific shape such as hormone cause protein to change shape, relay message

cell-cell recognition

glycoproteins serve as identification tags that membranes of other cells recognize

intracellular joining

membrane proteins hook together in various junctions

Attachement to cytoskeleton and ECM

non covalently bonded to membrane protein helps stabilize location of certain membranous proteins

Membranes and carbs are important in cell-cell recognition. What are 2 examples of this?

1. glycolipids
2. glycoproteins

Glycolipids

Lipid with one or more covalent attached carb

glycoprotein

a protein with one or more covalently attached carb

Channel protein

a hydrophilic channel that molecules or atomic ions use as a tunnel through the membrane

carrier protein

hold onto their passengers and change shape in a way that shuttles them across the membrane

Are transport proteins site specific?

Specific for the substance it translocates, allowing only a certain substance to cross membrane.

Red blood cells transport glucose across membrance

Aquaporins

Allows entry up to 3 billion water molecules per second, passing single file through its central channel.

How is CO2 moved across the cell?

Cell takes in O2 for cellular respiration and expels CO2

How is glucose moved across the cell?

red blood cells transport glucose 50,000x faster than glucose alone in cell membranes

How is O2 moved across the cell?

cells takes O2 for cellular respiration

How is H2O moved across the cell?

Thru aqaporin allows 3 billion water molecules to enter per second

Diffusion

the movement of molecules of any substance so that they spread evenly into the available space

Concentration gradient

region along which the density of a chemical substances increases or decreases, each substance diffuses down its own concentration gradient to expand.

passive transport

diffusion of a substance across a biological membrane because the cell doesnt have energy to make it happen

osmosis

the diffusion of free water across a selectively permeable membrane, whether artificial or cellular

Isotonic

a solution, that when surrounding a cell, causes no movement of water into or out of the cell

hypertonic

a solution that when surrounding a cell, will case the cell to lost water

hypotonic

a solution that, when surrounding a cell, will cause the cell to take up water

turgid

swollen or distended, as in plant cell (a walled cell becomes turgid f it has a lower water potential than its surroundings, resulting in entry of water)

flaccid

limp. lacking turgor as in a plant cell in surroundings where there is a tendency for water to leave the cell (higher water potential than surroundings)

plasmolysis

a phenomenon in walled calls in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment

What is facilitated diffusion? is it active or passive?

polar molecules and ions impeded by the lipid bilayer oft he membrane diffuse passively with the help of transport membranes that span the membrane

it is passive

Why do red blood cells burst when placed in a hypotonic solution, but not the plant cell?

RBC swells in hypotonic and bursts. plant cell have turgid and healthiest in hypotonic. water to pump a cell solute across a membrane against its gradient uptake is work. cell must expend energy.

Describe Active Transport. What type of transport proteins are involved, and what is the role of ATP in this process?

ATP transfers its terminal phosphate group directly to the transport protein

Sodium potassium pump

exchanges NA+ for K+

Summarize steps of sodium potassium pump

1. cytoplasmic Na+ binds to the sodium potassium pump. Affinity for NA+ is high when protein is in this shape

2. Na+ binding stimulates phosphorilation by ATP

3. Phosphorilation leads to a change in protein shape, reducing its affinity for NA+ which is released outside

4. New shape has a high affinity for K+ which binds on extracellular side and triggers release of phosphate group

5.loss of phosphate group restores the proteins original shape, which has a lower affinity for K+

6. K+ is released, affinity for A+ is high again, and the cycle repeats

What is membrane potential?

the difference in electrical charge (voltage) across a cells plasma membrane due to the differential distribution of ions. membrane potential effects the activity of excitable cells and the transmembrane movement of all charged substances.

1. What are the two forces that drive the diffusion of ions across the membrane?

2. What is the combination of the 2 forces called?

1. chemical and electrical force.
2. electrochemical gradient

What is cotransport

the coupling of the downhill diffusion one substance to the uphill transport of another against its own concentration gradient. sodium-glucose cotransporters on the surface of the intestinal cells and passed thru cells int he blood

exocytosis

the cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane

endocytosis

cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane

receptor-mediated endocytosis

the movement of specific molecules into a cell by the inward budding of vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of substance

Phagocytosis

A type of endocytosis in which large particular substances or small organisms are taken up by a cell. it is carried out by some protists and by certain immune cells of animals

pinocytosis

a type of endocytosis in which the cell ingests the extracellular fluid and its dissolved solutes.

ligand

a molecules that binds specifically to take in cholesterol for membrane synthesis another molecule, usually a larger one. and synthesis of other steroids.

this is an example of active transport

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