General Biology Ch 5

Front 1

Plasma Membrane

Back 1

The biomembrane that separates the internal contents of a cell from its external environment.

Front 2

8 Important Functions of Cellular Membranes

Back 2

Selective uptake and export of ions and molecules; cell compartmentalization; protein sorting; anchoring of the cytoskeleton; producion of energy intermediates such as ATP and NADPH; Cell signaling; Cell and nuclear division; adhesion of cells to each other and to the extra-cellular matrix

Front 3

Fluid Mosaic Model of Cell Membrane

Back 3

PM exhibits properties that resemble a fluid because lipids and proteins can move relative to each other within the membrane.

Front 4

Transmembrane Proteins

Back 4

Have one or more regions which are embedded in the phospholipid bilayer and span the membrane from one leaflet to the other.

Front 5

Lipid Anchors

Back 5

This involves the covalent attachment of a lipid to an amino acid side chain within a protein. The fatty acyl tails keep the protein firmly bound to the membrane.

Front 6

Integral Membrane Proteins

Back 6

Refers to transmembrane proteins and lipid anchors, named as they are because they cannot be released from the membrane without disrupting the integrity of the membrane.

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Peripheral Membrane Proteins

Back 7

AKA extrinsic proteins, do not interact with the hydrophobic interior of the phospholipid bilayer,instead they are noncovalently bound to regions of integral membrane proteins that project out from the membrane, or they are bound to the polar head groups of phospholipids, and are bound to the membrane by hydrogen and/or ionic bonds.

Front 8

Membrane Fluidity

Back 8

individual molecules remain in close association yet have the ability to readily move within the membrane.

Front 9

Glycosylation

Back 9

Refers to the process of covalently attaching a carbohydrate to a protein or lipid.

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Glycolipid

Back 10

A carbohydrate attached to a lipid

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glycoprotein

Back 11

a carbohydrate attached to a protein

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Carbohydrates in the PM

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The carbohydrates that are attached to lipids and proteins have well-defined structures that serve in some cases as recognition signals for other cellular proteins. Also plays a role in cell surface recognition.

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Cell coat or glycocalyx

Back 13

the carbohydrate-rich zone on the cell surface that shields the cell from mechanical and physical damage, and protects them from harsh conditions of the extracellular environment and degradation by the extracellular proteases which are enzymes that digest proteins.

Front 14

Selective Permeability of the PM

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Ensures that essential molecules such as glucose and amino acids enter cell, metabolic intermediates remain in the cell, and waste products exit, this allows the cell to maintain a favorable internal environment.

Front 15

Selective Permeability contd.

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High: Gases and very small uncharged polar molecules get in easily; water and urea get in pretty easily; polar organic molecules get in sometimes; and ions and charged polar molecules and macro-molecules have a hard time getting in :Very Low

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Diffusion

Back 16

Occurs when a solute moves from a region of high concentration to a region of lower concentration.

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Passive Diffusion

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Term to describe this process when it occurs through a membrane without the aid of a transport protein

Front 18

Transmembrane Gradient

Back 18

When this exists, it means that the concntration of a solute is higher on one side of amembrane than the other.

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Ion electrochemical gradient

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a dual gradient that has both an electrical gradient and chemical gradient. ex. Na+ an electrical gradient could exist in which the amount of net positive charge outside a cell is greater than inside, at the same time a chemical gradient could exist in which the concentration of Na+ outside is greater than inside.

Front 20

Passive Transport

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Refers to the diffusion of a solute across a membrane in a process that is energetically favorable and does not require an input of energy. Process tends to dissipate a pre-existing gradient

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Facilitated Diffusion

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Involves the aid of transport proteins which facilitate the movement of various nutrients and in some types of cells- water across the membrane.

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Osmosis

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The process in which water diffuses through a membrane from the hypotonic compartment into the hypertonic compartment.

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Isotonic

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When the solute concentrations on both sides of the plasma membrane are equal

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Hypertonic

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When the solute concentration inside the cell is higher relative to the outside of the cell

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Hypotonic

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When the solute concentration outside the cell is higher relative to the inside of the cell

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Crenation

Back 26

Cell shrinkage; occurs in a hypertonic solution; solute concentration is higher outside the cell, cells shrink because water exits the cell.

Front 27

Lysis

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cells burst; occurs in a hypotonic solution; solute concentration is lower outside the cell, the cells swell and may even rupture because water is taken into the cell

Front 28

Channel Proteins

Back 28

Transmembrane proteins that form an open passageway for the facilitated diffusion of ions or molecules across the membrane. Solutes move directly through PM via these to the other side.

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Aquaporin

Back 29

a channel protein that allows the passage of water across the membrane.

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Gated

Back 30

Referring to channel proteins, term means they can open to allow the diffusion of solutes and close to prohibit diffusion.

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Ligand-gated channels

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Are controlled by the noncovalent binding of small molecules, such as hormones or neurotransmitters, and are important in the transmission of signals between nerve and muscle cells or between two nerve cells.

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Protein Transporters

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AKA Carriers, bind their solutes in a hydrophilic pocket and undergo a conformational change that switches the exposure of the pocket to the other side of the membrane. Are much slower than channels

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Uniporters

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bind a single moleculeor ion and transport it across the membrane

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Symporters

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bind tow or more ions or molecules and transport them in the same direction

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Antiporters

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bind two or more ions or molecules and transport them in opposite directions

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Pump

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A transporter that directly couples its conformational changes to an energy source, such as ATP hydrolysis

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Active Transport

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The movement of a solute across a membrane against its gradient-that is, from a region of low concentration to higher concentration. It is energetically unfavorable and requires the input of energy.

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Secondary Active Transport

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Involves the utilization of a pre-existing gradient to drive the active transport of a solute. For ex. an H+/sucrose symporter can utilize an H+ electrochemical gradient, established by an ion pump to move sucrose against its concentration gradient.

Front 39

Sodium Potassium Pump

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Every time one ATP is hydrolyzed, this ATPase functions as an anti-porter that pumps three Na+ into the extra-cellular environment and two K+ into the cytosol. Results in the net export of one positive charge

Front 40

Exocytosis

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A process in which material inside the cell is packaged into vesicles and excreted into the extracellular environment. These vesicles are usually derived from the Golgi apparatus.

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Endocytosis

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The plasma membrane invaginates or folds inward to form a vesicle that brings substances into the cell.

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Receptor-mediated endocytosis

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A receptor is specific for a given cargo and stimulates the bindingof coat proteins to the membrane which initiates the formation of a vesicle.

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Pinocytosis

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"cell drinking" involves the formation of membrane vesicles from the PM as a way for cells to internalize the extracellular fluid. Is especially important for cells that are actively involved in nutrient absorption

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Phagocytosis

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"cell eating" an extreme form of endocytosis involving the formation of an enormous membrane vesicle that engulfs a large particle such as a bacterium.