campbell biology chapter 7

hypertonic

"SALTY" Referring to a solution that, when surrounding a cell, will cause the cell to lose water.

isotonic

"SAME" Referring to a solution that, when surrounding a cell, causes no net movement of water into or out of the cell

hypotonic

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

List the functions of membrane proteins (main six)

1. Transport of specific solutes in/out cell. 2. Enzymatic activity, sometimes catalyzing one of a number of steps of a metabolic pathway. 3. Signal transduction, relaying hormonal messages to the cell. 4. Cell-to-cell recognition, allowing other proteins to attach two adjacent cells together. 5. Intercellular joining of adjacent cells with gap or tight junctions. 6. Attachment to the cytoskeleton and extracellular matrix, maintaining cell shape and stabilizing the location of certain membrane proteins.

aquaporins

A channel protein in a cellular membrane that specifically facilitates osmosis, the diffusion of free water across the membrane

glycolipids

A lipid with one or more covalently attached carbohydrates.

plasmolysis

A phenomenon in walled cells 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

Selective permeability

A property of biological membranes that allows them to regulate the passage of substances across them

peripheral proteins

A protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer

glycoproteins

A protein with one or more covalently attached carbohydrates

concentration gradient

A region along which the density of a chemical substance increases or decreases

ion channels

A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient

gated channels

A transmembrane protein channel that opens or closes in response to a particular stimulus

Transport proteins

A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane

integral proteins

A transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqueous solution on one or both sides of the membrane (or lining the channel in the case of a channel protein).

sodium-potassium pump

A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell

phagocytosis

A type of endocytosis in which large particulate substances or small organisms are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells)

pinocytosis

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

Explain the role of membrane carbohydrates in cell-to-cell recognition

Cells can recognize other cells by binding to the surface molecules (usually carbohydrates) on the plasma membrane. The carbohydrates are usually branched oligosaccharides that form glycolipids when bonded with lipids and glycoproteins when formed with proteins.

Describe how plant cells and animal cells regulate water balance

Cells without cell walls are immersed in an isotonic environment that experiences no net water movement. Water molecules move at the same rate in each direction through osmosis (in hypertonic environment the cell would shrivel and die; in hypotonic, the cell would expand and burst). Cells with cell walls osmoregulate to control water balance using the contractile vacuole to force water out of the cell. The cell wall keeps the cell from bursting, but cannot keep it from shrinking.

endocytosis

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

Distinguish between carrier proteins and channel proteins

Channel proteins are transport proteins that have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane (Ex: aquaporins for water). Carrier proteins are transport proteins that bind to molecules and change shape to shuttle them across the membrane.

Explain how transport proteins facilitate diffusion

Channel proteins provide hydrophilic corridors for specific molecules. Ion channels open/close depending on chemical/physical stimulus. Other transport proteins translocate the solute binding site and solute across the membrane while the protein changes shape.

Define diffusion and explain why it is a spontaneous process

Diffusion is the tendency of molecules of any substance to spread out in the available space. It is driven by heat (kinetic energy) of molecules. Diffusion decreases free energy and increases entropy by creating a randomized mixture.

amphipathic

Having both a hydrophilic region and a hydrophobic region

Explain how hydrophobic molecules cross cell membranes

Hydrophobic molecules can dissolve in the lipid bilayer which makes it easy for them to cross.

Explain how large molecules like proteins and polysaccharides are transported across a cell membrane

Large molecules use vesicles to cross the membrane. The vesicle is moved by the cytoskeleton to the plasma membrane. When the two membranes come in contact, the bilayers fuse and split the contents to the outside.

flaccid

Limp. Lacking turgor (stiffness or firmness), as in a plant cell in surroundings where there is a tendency for water to leave the cell. (A walled cell becomes flaccid if it has a higher water potential than its surroundings, resulting in the loss of water.)

Explain how membrane fluidity is influenced by temperature and membrane composition

Many of the membrane proteins drift in the phospholipid bilayer. Some move directional while others never move because they are anchored to the cytoskeleton. When temperatures become cooler, the membranes become solid and the phospholipids are packed more tightly. Membranes with more unsaturated fats are more fluid than those with more saturated fats because the double bonds in unsaturated fatty acids prevent tight packing.

Distinguish among osmosis, facilitated diffusion, and active transport

Osmosis is the diffusion of water across a selectively permeable membrane. Facilitated diffusion is the passive movement of molecules down their concentration gradient via transport proteins. Active transport requires the cell to expend metabolic energy (usually ATP) to enable the cell to maintain internal concentrations of small molecules that would otherwise diffuse across the membrane.

Define osmosis and predict the direction of water movement based on differences in solute concentrations

Osmosis is the diffusion of water across a selectively permeable membrane. Water movement goes from hypotonic solution to hypertonic solution. When isotonic, the water moves at equal rates.

Explain why phospholipids are amphipathic molecules

Phospholipids have both hydrophobic regions and hydrophilic regions. The molecules in its bilayer are arranged so the hydrophobic fatty acid tails are sheltered from water while the hydrophilic fatty acids interact with water.

Distinguish between pinocytosis and receptor-mediated endocytosis

Pinocytosis is when a cell creates a vesicle around a droplet of extracellular fluid and all included solutes are taken into the cell. Receptor-mediated endocytosis enables a cell to acquire bulk quantities of specific materials that may be in low concentrations in the environment. This happens when ligands bind to special receptors on the membrane surface and the receptor proteins are in regions coated with coat proteins that bring the bound substances into the cell.

osmoregulation

Regulation of solute concentrations and water balance by a cell or organism

turgid

Swollen or distended, as in plant cells. (A walled cell becomes turgid if it has a lower water potential than its surroundings, resulting in entry of water.)

tonicity

The ability of a solution surrounding a cell to cause that cell to gain or lose water

Exocytosis

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

Explain why concentration gradient of a substance across a membrane represents potential energy

The concentration gradient drives diffusion (potential energy drives kinetic energy).

fluid mosaic model

The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids

osmosis

The diffusion of free water across a selectively permeable membrane

The "fluid mosaic model" is used to describe the structure of membranes. What does the "fluid" component refer to? The "mosaic" component?

The fluid mosaic model explains various observations regarding the structure of functional cell membranes. The model describes the cell membrane as a two-dimensional liquid that restricts the lateral diffusion of membrane components.

Active transport

The movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring an expenditure of energy

receptor-mediated endocytosis

The movement of specific molecules into a cell by the infolding of vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.

facilitated diffusion

The passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific transmembrane transport proteins, requiring no energy expenditure.

diffusion

The random thermal motion of particles of liquids, gases, or solids. In the presence of a concentration or electrochemical gradient, diffusion results in the net movement of a substance from a region where it is more concentrated to a region where it is less concentrated

Passive transport

diffusion of a substance across a membrane with no energy investment

Bulk transport across the plasma membrane occurs by ___________ and _____________

exocytosis, endocytosis

Cellular membranes are

fluid mosaics of lipids and proteins

Active transport uses energy to what?

move solutes against their gradient

Membrane structure results in ______________ _________________

selective permeability

in contrast to transmembrane proteins, a variety (many of which behave as integral membrane proteins) of proteins are anchored in what?

the plasma membrane by covalently attached lipids or glycolipids