Chapter 3 Cells: The Living Units—BSC 2085

Cell theory

States that all living organisms are made of cells, cells are the basic structural and functional units of life, and cells arise from preexisting cells.

Cell

The basic structural and fuctional unit of life.

Extracellular materials

Materials located outside cells that support, protect, or communicate with cells.

Cellular secretions

Substances produced and released by cells, such as hormones, enzymes, and mucus.

Extracellular matrix

A network of proteins and other materials outside cells that provides structural support and helps cells communicate and adhere to one another.

Plasma membrane

A selectively permeable phospholipid bilayer that separates the cell from its surroundings and regulates what enters and leaves the cell.

Phospholipids

Lipids with a hydrophilic head and hydrophobic tails that form the basic structure of the plasma membrane.

Cholesterol

A membrane lipid that helps stabilize the plasma membrane and regulate its fluidity.

Proteins

Membrane components that perform functions such as transport, communication, enzymatic activity, and cell adhesion.

Transport proteins

Membrane proteins that move specific substances across the plasma membrane.

Receptors

Membrane proteins that bind specific signaling molecules and initiate cellular responses.

Enzyamtic activity

The ability of a protein to catalyze a chemical reaction.

Intercellular junctions

Specialized connections that physically or functionally link neighboring cells.

Tight junctions

Connections between cells that seal adjacent membranes together and prevent substances from passing between the cells.

Desmosomes

Strong cell-to-cell junctions that anchor cells together and resist mechanical stress.

Gap junctions

Channels connecting neighboring cells that allow ions and small molecules to pass directly between them.

Passive transport

The movement of substances across a membrane without cellular energy.

Diffusion

The net movement of particles from an area of higher concentration to an area of lower concentration.

Simple diffusion

Movement of small or nonpolar molecules directly through the phospholipid bilayer without transport proteins or cellular energy.

Facilitated diffusion

Passive movement of substances across a membrane through transport proteins.

Carrier-mediated facilitated diffusion

Facilitated diffusion in which a protein binds a substance and changes shape to move it across the membrane.

Channel-mediated facilitated diffusion

Facilitated diffusion in which substances move through protein channels.

Osmosis

Diffusion of water across a selectively permeable membrane toward the side with a higher concentratioun of solutes that cannot cross the membrane.

Active transport

Movement of substances across a membrane using cellular energy.

Primary active transport

Active transport that directly uses ATP to move substances against their gradients.

Secondary active transport

Active transport that uses the energy stored in an ion concentration gradient.

Symport system

A transport system that moves two substances across a membrane in the same direction.

Antiport system

A transport system that moves two substances across a membrane in opposite directions.

Vesicular transport

The movement of large substances into or out of a cell using membrane-bound vesicles.

Endocytosis

The movement of material into a cell when the plasma membrane surrounds the material and forms a vesicle.

Phagocytosis

Endocytosis in which a cell engulfs large particles or other cells.

Pinocytosis

Endocytosis in which a cell takes in extracellular fluid and dissolved substances.

Receptor-mediated endocytosis

Endocytosis in which specific substances bind to membrane receptors before being brought into the cell.

Vesicular trafficking

Movement of vesicles within a cell to transport materials between cellular compartments.

Exocytosis

Movement of substances out of a cell when a vesicle fuses with the plasma membrane and releases its contents.

Tonicity

The ability of a solution to cause water to move into or out of a cell.

Isotonic solutions

Solutions with the same effective solute concentration as the cell, causing no net movement of water.

Hypertonic solutions

Solutions with a higher effective solute concentration with the cell, causing water to leave the cell.

Hypotonic solutions

Solutions with a lower effective solute concentration than the cell, causing water to enter the cell.

Membrane potential

The difference in electrical charge between the inside and outside of a cell membrane.

Resting membrane potential

The membrane potential of a cell when it is not actively transmitting a signal.

Electrically polarized

Having different electrical charges across the plasma membrane.

Cell adhesion molecules (CAMs)

Membrane proteins that allow cells to attach to other cells or to the extracellular matrix.

Membrane receptors

Membrane proteins that recognize and bind specific signaling molecules.

Contact signaling

Cell communication that occurs when molecules on the surfaces of two cells bind directly to one another.

Chemical signaling

Cell communication in which cells release chemical messengers that bind to receptors on target cells.

G protein-coupled receptors (GCPRs)

Membrane receptors that active G proteins when a signaling molecule binds to them.

G protein

A membrane-associated protein that relays signals from a GPCR to other proteins in side the cell.

Ligand

A signaling molecule that binds specifically to a receptor.

Second messengers

Intracellular molecules that relay and amplify signals from activated membrane receptors.

Cyclic AMP (cAMP)

A second messenger that activates intracellular signaling pathways in response to certain extracelllar signals.

Sodium-potassium pump

A primary active transport protein that uses ATP to move sodium ions out of the cell and potassium ions into the cell.

Cytoplasm

Everything inside the plasma membrane except the nucleus.

Cytosol

The fluid portion of the cytoplasm surrounding the organelles.

Inclusions

Nonliving materials stored in the cytoplasm, such as pigments, lipid droplets, and glycogen granules.

Organelles

Specialized structures within most cells that perform specific functions.

Mitochondria

Organelles that produce most of the cell's ATP through aerobic cellular respiration.

Ribosomes

Structures that synthesize proteins by linking amino acids according to genetic instructions.

Free ribosomes

Ribosomes suspended in the cytosol that produce proteins primarily used within the cell.

Membrane-bound ribosomes

Ribosomes attached to the rough ER that produce proetins destined for secretion, membranes, or certain organelles.

Rough endoplasmic reticulum

A membrane network covered with ribosomes that synthesizes and begins processing proteins.

Smooth endoplasmic reticulum

A membrane network without ribosomes that synthesizes lipids, helps detoxify substances, and stores calcium ions.

Glogi apparatus

Modifies, sorts, and packages proteins and lipids for transport within or outside the cell.

Lysosomes

Membrane-bound organelles containing digestive enzymes that break down cellular wasste, damaged organelles, and engulfed materials.

Peroxisomes

Organelles that break down fatty acids and detoxify harmful substances, producing and breaking down hydrogren peroxide.

Free radicals

Highly reactive molecules that can damage cellular components by reacting with proteins, lipids, and DNA.

Cytoskeleton

A network of protein fibers that maintains cell shape, organizes organelles, and assissts with cell movement and intracellular transport.

Microfilaments

The thinnest cytoskeletal fibers, made primarily of actin; help with cell shape, movement, and muscle contraction.

Intermediate filaments

Strong cytoskeletal fibers that provide mechanical strength and help stabilize cell structure.

Microtubules

Hollow cytoskeleton fibers that help maintain cell shape, move organelles, and form structures involved in cell division and movement.

Centrosome

A region near the nucleus that organizes microtubules and forms the mitotic spindle during cell division.

Centrioles

Cylindrical structures within the centrosome that help organize microtubules.

Cilia

Short, numerous projections that move substances across the cell surface.

Flagella

Long, usually single projections that propel a cell through fluid.

Basal bodies

Structures that anchor cilia and flagella to the cell and organize their microtubules.

Microvilli

Small membrane projections that increase a cell's surface area for absorption.

Nucleus

The organelle that contains most of a cell's DNA and controls gene expression.

Nuclear envelope

A double membrane surrounding the nucleus that separates nuclear contents from the cytoplasm.

Nuclear pores

Openings in the nuclear envelope that regulate movement of substances between the nucleus and cytoplasm.

Nucleoli

Regions inside the nucleus where rRNA is produced and ribosomal subunits are assembled.

Chromatin

A complex of DNA and proteins that contains the cell's genetic material.

Histone proteins

Proteins around which DNA winds to help package and organize DNA.

Nucleosomes

Basic units of chromatin consisting of DNA awrapped around a group of histone proteins.

Chromosomes

Condensed structures of DNA and proteins that contain genes and become especially visible during cell division.

Cell cycle

The sequence of events through which a cell grows, replicates its DNA, and divides.

Interphase

The period of the cell cycle during which a cell grows, performs normal functions, and prepares for division.

Gap 1 subphase

The phase in which the cell grows, performs normal functions, and produces materials needed for DNA replication.

Synthesis phase

The phase in which the cell replicates its DNA.

Replication fork

The Y-shaped region where the DNA double helix separates and new DNA strands are synthesized.

DNA polymerase

An enzyme that adds complementary nucleotides to a growing DNA strand during DNA replication.

Semiconservative replication

DNA replication in which each new DNA molecule contains one original strand and one newly synthesized strand.

Gap 2 subphase

The phase in which the cell continues growing and prepares proteins and stuctures needed for cell division.

Cell division

The process by which one cell divides to produce new daughter cells.

Mitosis

Nuclear division in which duplicated chromosomes are separated into two genetically similar nuclei.

Prophase

The stage of mitosis in which chromosomes condense, the mitotic spindle forms, and the nuclear envelope breaks down.

Metaphase

The stage of mitosis in which chromosomes align along the cell's equator.

Anaphase

The stage of mitosis in which sister chromatids separate and move toward opposite poles of the cell.

Telophase

The stage of mitosis in which chromosomes reach opposite poles, decondense, and new nuclear envelopes form.

Cytokinesis

Division of the cytoplasm that produces two separate daughter cells.

Cleavage furrow

A groove that forms in the plasma membrane during cytokinesis and pinches the cell into two daughter cells.