AP Biology - Chapter 5 Vocabulary

SHS

Amphipathic

A molecule that has both a hydrophilic region and a hydrophobic region. An example of this would be a phospholipid bilayer.

Fluid Mosaic Model

Also known as a phospholipid bilayer. The membrane is a mosaic of protein molecules embedded in a fluid phospholipid bilayer. Proteins are not randomly distributed in the membrane.

Hydrophobic interactions

Weaker attractions that are weaker than covalent bonds. These interactions hold cell membranes together.

Integral proteins

Proteins that penetrate the hydrophobic interior of the lipid bilayer. The majority of these are transmembrane proteins. These proteins transport molecules that cannot move across the membrane on their own.

Peripheral proteins

Proteins that are not embedded in the lipid bilayer. These proteins are loosely bound to the surface of the membrane, often to exposed parts of integral proteins.

Glycolipids

Short, branched membrane carbohydrates that are covalently bonded to lipids.

Glycoproteins

Membrane carbohydrates that are covalently bonded to proteins.

Selective permeability

The ability to allow some substances to cross more easily than others. This ability to regulate transport across cellular boundaries is essential to the cell’s existence.

Transport proteins

Proteins that span the cell membrane. Transport specific ions and a variety of polar molecules that cannot move through the cell membrane on their own.

Aquaporins

A type of channel protein that facilitates the passage of water molecules through the cell membrane. Most of these proteins consist of four identical polypeptide subunits.

Diffusion

The movement of particles of any substance so that they spread out into the available space. A substance will diffuse from where it is more concentrated to where it is less concentrated. This movement requires no energy.

Concentration gradient

The region along which the density of a substance increases or decreases.

Passive transport

The diffusion of a substance across a biological membrane that requires no energy. Three types of this movement consist of diffusion, osmosis, and facilitated diffusion.

Osmosis

The movement of water across a selectively permeable membrane and the balance of water between the cell and its environment. Crucial to organisms.

Osmoregulation

The control of solute concentrations and water balance in organisms.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water. This factor depends in part on its concentration of solutes that cannot cross the membrane relative to that inside the cell.

Isotonic

A solution that has the same solute concentration as a submerged animal cell. There will be no net movement of water across the plasma membrane.

Hypertonic

A solution that has a higher concentration in comparison to a submerged animal cell. Water will move out of the cell, causing it to shrivel and die.

Hypotonic

A solution that has a lower concentration in comparison to a submerged animal cell. Water will move into the cell, causing it to swell and lyse (burst).

Turgid/Turgidity

A FIRM state of a cell. This state is healthy for most plant cells. It is determined by the turgor pressure, which opposes excess water uptake.

Flaccid

Occurs when a plant’s cells and their surroundings are isotonic. Cells become LIMP and the plant wilts.

Plasmolysis

As a plant cell shrivels, its plasma membrane pulls away from the cell wall at multiple places. This causes the plant to wilt and can lead to plant death. This process also occurs in hypertonic environments.

Cytolysis

When an animal cell (which lacks a cell wall) is placed in a hypotonic solution, water enters the cell faster than it leaves, causing the cell to swell and eventually burst.

Facilitated Diffusion

A form of passive transport that allows polar molecules and ions to cross the lipid bilayer of the membrane to diffuse passively with the help of transport proteins that span the membrane.

Ion channels

Channel proteins that transport ions through the cell membrane.

Gated channels

Ion channels that open or close in response to a stimulus. This stimulus is electrical.

Active transport

A type of membrane transport that requires work/energy in the form of ATP. This occurs primarily when transport proteins move solutes against their concentration gradients, from the side where they are less concentrated to the side where they are more concentrated.

Sodium-potassium pump

A protein that uses ATP to transport sodium ions and potassium ions across the plasma membrane of animal cells. In other words, sodium ions are exchanged for potassium ions.

Membrane potential

The voltage across a membrane that ranges from 50-200 millivolts. This acts as the battery or energy source that affects the traffic of all charged substances across the membrane.

Electrochemical gradient

The combination of forces that acts on an ion. These forces include chemical forces (ion’s concentration gradient) and electrical forces.

Electrogenic pump

A transport protein that generates voltage across a membrane. The sodium-potassium pump is an example of this. These pumps store energy by generating voltage across membranes. However, these pumps still use ATP through active transport.

Proton pump

The main electrogenic pump of plants, fungi, and bacteria. The pumping of H+ transfers positive charge from the cytoplasm to the extracellular solution.

Cotransport

A mechanism in which a transport protein couples the downhill diffusion of a solute to the uphill transport of a second substance against its concentration gradient. The downhill diffusion provides energy for the transport of a substance against its concentration gradient.

Bulk transport

An energy-intensive active transport mechanism that moves large molecules, cell parts, or whole cells into or out of a cell in bulk. The two types of this transport are endocytosis and exocytosis.

Endocytosis

The process by which the cell takes in molecules and particulate matter by forming new vesicles from the plasma membrane. The three types of this process are phagocytosis, pinocytosis, and receptor-mediated endocytosis.

Phagocytosis (1)

Process by which a cell engulfs a particle by extending pseudopodia around it and packaging it within a membranous sac called a food vacuole. The particle will be digested after the food vacuole fuses with a lysosome containing hydrolytic enzymes.

Pinocytosis (2)

When a cell continually “gulps” droplets of extracellular fluid into tiny vesicles, formed by infoldings of the plasma membrane, which obtain molecules dissolved in the droplets. The parts of the plasma membrane that form vesicles are lined on their cytoplasmic side by a fuzzy layer of coat protein; the pits and resulting vesicles are called coated pits.

Receptor-mediated (3)

A specialized type of pinocytosis that enables the cell to acquire bulk quantities of specific substances, even though those substances may not be very concentrated in the extracellular fluid.

Exocytosis

The process by which cells secrete certain biological molecules by the fusion of vesicles with the plasma membrane.

Cell Signaling

The process by which a cell detects, transmits, and responds to chemical or physical signals from its environment or other cells

Local signaling

Process in which signaling molecules are secreted by the signaling cell to target cells in the immediate vicinity. In animals, it is called paracrine signaling.

Long-distance signaling

Animal and plant cells use molecules called hormones for this type of signaling. For example, in animals, specialized cells release hormones through endocrine signaling.

Reception (1)

The target cell’s detection of a signaling molecule coming from outside the cell. A chemical signal is “detected” when the signaling molecule binds to a receptor protein located at the cell’s surface, or, in some cases, inside the cell.

Transduction (2)

A step or series of steps that converts the signal to a form that can bring about a specific cellular response. This process usually requires a sequence of changes in a series of different molecules, which is known as a signal transduction pathway.

Response (3)

Almost any imaginable cellular activity, such as catalysis by an enzyme, rearrangement of the cytoskeleton, or activation of specific genes in the nucleus.

Hormones

Molecules that are used for long-distance signaling.

STP, Signal Transduction Pathway

A sequence of changes in a series of different molecules to convert a signal into a response.

Ligand

A molecule that specifically binds to another molecule. These molecules that bind generally cause a receptor protein to undergo a change in shape.

G protein-coupled receptor GPCR

A cell surface transmembrane receptor that works with the help of a G protein. Many signaling molecules use this, and are remarkably similar in structure.

G protein

A protein that binds the energy-rich molecule GTP, which is similar to ATP.

Ligand-gated channel

A membrane receptor with a region that can act as a “gate” for ions, opening or closing the channel when the receptor assumes alternative shapes.

Protein kinase

An enzyme that transfers phosphate groups from ATP to a protein.

Phosphorylation cascade

A series of proteins in a pathway that are phosphorylated in turn, with each protein adding a phosphate group to the next. This sequence transmits signals through the kinase proteins.

Second messenger

Small, nonprotein, water-soluble molecules or ions. They are involved in many signaling pathways and can readily spread through the cell by diffusion. The most common second messengers are cyclic AMP and calcium ions.

Cyclic AMP

In an experiment, Sutherland discovered that epinephrine binding to the plasma membrane of a liver cell increases the cytosolic concentration of this molecule. It is known as cyclic adenosine monophosphate, which broadcasts the signal to the cytoplasm.