Chapter 3 Cells: The Living Units

Cell

Smallest structural and functional unit of life.

Plasma membrane

A membrane that separates the internal environment of a cell from its external environment.

Cytoplasm

Intracellular fluid containing organelles and many solutes such as Na+, K+, and Cl-.

Nucleus

Organelle that contains the genetic material (DNA) of a cell.

Extracellular matrix

Substance that acts as glue to hold cells together; composed of various types of proteins.

Hydrophilic

• Molecules or atoms that are charged (polar)

• dissolve in water (water-soluble).

• Literally means water-loving.

Hydrophobic

• Molecules or atoms are not charged (nonpolar)

• Will not dissolve in water (lipid-soluble)

• Literally means water-fearing.

Integral protein

• membrane protein

• firmly inserted into the lipid bilayer

• protrude from only one membrane face or span the entire membrane and protrude from both sides (transmembrane protein).

• have both hydrophobic and hydrophilic regions.

Peripheral protein

• membrane protein

• not embedded into the lipid bilayer

• loosely attached to integral proteins

• hydrophilic.

Glycocalyx

• glycolipids and glycoproteins sticking out of the cell's surface

• cell-to-cell communication and recognition.

Tight junctions

• specialized connection

• integral proteins on adjacent cells fuse to form an impermeable junction encircling the cell

• prevents fluids and molecules from moving between cells.

Desmosomes

• Cell junction

• proteins of neighboring cells interlock like a zipper

• allows give between cells

• reduces the possibility of tearing under tension.

Gap junctions

• Transmembrane proteins from adjacent cells connect

• creates tunnels that allow small molecules or electrical signals to pass from cell to cell.

Passive process

• strategy

• materials cross the plasma membrane of a cell

• does not require energy input from the cell.

Active process

• strategy

• materials cross the plasma membrane of a cell

• requires energy input from the cell.

Diffusion

The tendency of molecules or ions to move from an area of higher concentration to an area of lower concentration due to the kinetic energy of all atoms/molecules.

• passive process

• does not require energy.

Concentration gradient

• difference in concentration, often across a membrane

• one side is higher in the concentration of a molecule/ion while the other side is lower in the concentration of a molecule/ion

Selectively (differentially) permeable

barrier allows some substances to pass across it while excluding others

Simple diffusion

Nonpolar and lipid-soluble substances diffuse directly through the plasma membrane.

• passive process

• does not require energy.

Facilitated diffusion

The substance diffuses across the plasma membrane through a transport protein (either a carrier or channel protein).

• passive process

• does not require energy.

Carrier proteins

• Transmembrane integral proteins

• specific for transporting certain polar molecules or classes of molecules by altering their shapes

• first envelopes substance

• then releases substance across the membrane

• changes shape to move the substance across the hydrophobic bilayer.

Channel protein

• Transmembrane integral proteins

• transport substances, usually ions or water, through aqueous channels from one side of the membrane to the other

• are selective for the specific substance allowed to cross.

• Can be leakage (always open) or gated (closed until stimulated to open).

Leakage channel

• channel protein

• always open for its specific material to cross the plasma membrane.

Gated channel

• channel protein

• usually closed unless stimulated to open by a mechanical, chemical, or electrical signal.

Ligand-gated ion channel

• ion channel

• opens in response to small molecules that bind to proteins or glycoproteins.

Voltage-gated ion channel

• ion channel

• opens when there is a change in charge across the plasma membrane.

Osmosis

• diffusion of a solvent through a selectively permeable membrane

• Water follows solute.

Aquaporin

A water-specific protein channel.

Osmolarity

The total concentration of all solute particles in a solution.

Tonicity

• solution's ability to change the shape or tone of cells by altering the cell's internal water volume

• ability of a solution to cause a cell to lose or gain water.

Isotonic solution

• Definition: A fluid with the same solute concentration as the inside of a cell.

• Water movement: Water moves equally in and out of the cell.

• Effect on cell: The cell maintains a stable size and shape.

Hypertonic solution

• Definition: A fluid with a higher solute concentration than the cell.

• Water movement: Water flows out of the cell and into the surrounding solution.

• Effect on cell: The cell loses water and shrinks (shrivels).

Hypotonic solution

• Definition: A fluid with a lower solute concentration than the cell.

• Water movement: Water flows into the cell from the surrounding solution.

• Effect on cell: The cell gains water, swells, and can even burst.

Active transport

• strategy

• moves substances across the plasma membrane

• moves solutes AGAINST their concentration gradients

• moves from an area of lower concentration to an area of higher concentration.

• requires energy.

Antiporter

• carrier protein

• transports two molecules across the plasma membrane in opposite directions.

Symporter

• carrier protein

• transports two molecules across the plasma membrane in the same direction.

Primary active transport

The energy to do work comes directly from hydrolysis of ATP.

Sodium-potassium pump

• Carrier transport protein

• directly uses ATP to eject 3 sodium ions out of the cell

• followed by bringing 2 potassium ions into the cell

• both against their concentration gradients.

Electrochemical gradient

• combined difference in concentration and charge

• influences the distribution and direction of diffusion of ions.

Secondary active transport

• Transport is driven indirectly by energy stored in concentration gradients of ions created by primary active transport pumps.

• coupled systems, such as symporters and antiporters.

Vesicular transport

• fluids containing large particles and macromolecules are transported across plasma membranes inside bubble-like, membranous sacs called vesicles

• active process

• requires energy.

Endocytosis

Bringing an externally located material across the plasma membrane in a vesicle into the cell.

Phagocytosis

• cell engulfs a relatively large or solid material and brings it into the cell.

• type of endocytosis.

Pinocytosis

• cell engulfs a small volume of extracellular fluid and brings it into the cell

• type of endocytosis.

Receptor-mediated endocytosis

• type of endocytosis

• engulfed particles attach to receptors before endocytosis occurs.

Exocytosis

• Vesicular transport process

• ejects substances from inside the cell into the extracellular fluid.

Voltage

An electrical charge/difference between two points.

Polar

Having a charge.

Resting membrane potential (RMP)

A charge difference across the plasma membrane of a cell.

Contact signaling

cells that touch recognize each other by each cell's unique surface membrane receptors.

Chemical signaling

Interaction between receptors and ligands that cause changes in cellular activities.

Ligand

A chemical messenger molecule that binds to a receptor surface of another molecule.