Chapter 3 Cellular Level of Organization

Cell

The basic unit of structure and function in living things

Cell theory

A widely accepted explanation of the relationship between cells and living things. There are 3 components: 1. All living things are composed of cells, 2. Cells are the basic units of structure and function in living things, and 3. New cells are produced from existing cells

Cytoplasm

A jellylike fluid inside the cell in which the organelles are suspended

Cytoskeleton

network of protein filaments within some cells that helps the cell maintain its shape and is involved in many forms of cell movement

Extracellular material

any fluid outside the cell contributing to body mass. Generally comprised of body fluids and secretions; interstitial, blood plasma, cerebrospinal fluid, gastric fluid, saliva, mucus, serous fluids, and extracellular matrix

Extracellular fluid (ECF)

Fluid outside of cells
Includes tissue (interstitial) fluid

Cellular secretions

intestinal and gastric fluids, saliva, mucus, and serous fluids; substances that aid in digestion and some that act as lubricants

Extracellular matrix (ECM)

The meshwork surrounding animal cells, consisting of glycoproteins, polysaccharides, and proteoglycans synthesized and secreted by the cells.

Plasma Membrane

A selectively-permeable phospholipid bilayer forming the boundary of the cells; the membrane is embedded with protein and cholesterol and forms the boundary of every cell; it acts as a selective barrier, thereby regulating the cell's chemical composition.

Intracellular fluid

fluid inside cells

Fluid mosaic model

Structural model of the plasma membrane where molecules are free to move sideways within a lipid bilayer.

Selective permeability

A property of the plasma membrane that allows some substances to cross more easily than others.

Cell recognition

Membrane receptors allow cells to identify each other; for example MHC glycoproteins on plasma membranes are different for each person so organ transplants are difficult to achieve

Integral Proteins

Proteins that span the membrane.

Transmembrane proteins

Integral proteins that span the membrane.

Peripheral proteins

The proteins of a membrane that are not embedded in the lipid bilayer; they are bound to the surface of the membrane

Glycolipids

carbohydrates covalently bonded to lipids

Glycoproteins

proteins that have carbohydrates covalently bonded to them

Glycocalyx

a glycoprotein-polysaccharide covering that surrounds the cell membranes of some bacteria, epithelia and other cells; can be important for cell-to-cell communication

Receptors

Special structures (usually proteins) that allow living organisms to sense the conditions of their internal or external environment.

Channel proteins

have a hydrophilic channel that certain molecules or ions can use as a tunnel

Passive transport

the movement of substances across a cell membrane without the use of energy by the cell; Requires NO energy, Movement of molecules from high to low concentration, Moves with the concentration gradient

Active transport

Energy-requiring process that moves material across a cell membrane against a concentration difference

Facilitated transport

The movement of molecules across the cell membrane without the use of ATP, but with the help of a protein.

Diffusion

Movement of molecules from an area of higher concentration to an area of lower concentration.

Concentration Gradient

A difference in the concentration of a substance across a distance.

Solubility

A measure of how much solute can dissolve in a given solvent at a given temperature and pressure.

Simple diffusion

movement of a solute from an area of high concentration to an area of low concentration without the use of ATP

Carrier-mediated facilitated diffusion

a carrier (usually protein) moves a solute down its concentration gradient across the plasma membrane

Channel-mediated facilitated diffusion

a solute moves down its concentration gradient across the lipid bilayer through a channel protein; mostly ions selected on basis of size and charge

Osmosis

diffusion of water across a selectively permeable membrane

Aquaporins

water channel proteins

Osmolarity

total concentration of all solute particles in a solution

Hydrostatic pressure

the pressure within a blood vessel that tends to push fluid out of the vessel

Osmotic pressure

pressure that must be applied to prevent osmotic (water) movement across a selectively permeable membrane

Tonicity

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

Isotonic

when the concentration of two solutions is the same

Hypotonic

when comparing two solutions, the solution with the lesser concentration of solutes

Hypertonic

when comparing two solutions, the solution with the greater concentration of solutes

Cell junctions

connections between cells that hold the cells together as a unit

Tight junction

a type of intercellular junction between animal cells that prevents the leakage of material through the space between cells

Desmosomes

Anchoring junctions that prevents cells subjected to mechanical stress from being pulled apart; button like thickenings of adjacent plasma membranes connected by fine protein filaments

Gap junctions

channels that run between membrane pores in adjacent cells, allowing substances to pass between cells

Active Transport

Energy-requiring process that moves material across a cell membrane; usually against a concentration difference

Primary active transport

Active transport in which ATP is hydrolyzed, yielding the energy required to transport an ion or molecule against its concentration gradient.

Sodium potassium pump

a carrier protein that uses ATP to actively transport 3 sodium ions out of a cell and 2 potassium ions into the cell

Secondary active transport

Form of active transport which does not use ATP as an energy source; rather, transport is coupled to ion diffusion down a concentration gradient established by primary active transport.

Vesicular Transport

Transport of large particles and macromolecules across plasma membranes using endocytosis and exocytosis

Transcytosis

moving substances into, across, and then out of a cell

Endocytosis

A process in which a cell engulfs extracellular material through an inward folding of its plasma membrane.

Phagocytosis

A type of endocytosis in which a cell engulfs large particles or whole cells

Pinocytosis

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

Receptor-mediated endocytosis

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

Exocytosis

Process by which a cell releases large amounts of material (e.g. mucus, hormones, waste)

Membrane potential

the voltage difference across a membrane

Resting membrane potential

An electrical potential established across the plasma membrane of all cells by the Na+/K+ ATPase and the K+ leak channels. IN most cells, the resting membrane potential is approximately -70 mV with respect to the outside of the cell.

Adhesion Molecules

allow cells to adhere to other cells

Membrane receptors

A large, diverse group of integral proteins and glycoproteins that serve as binding sites for signaling molecules.

Contact signaling

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

Chemical signaling

The specific interaction of hormones and neurotransmitters with cell surfaces for the purpose of changing cell activity.

Ligand; chemical messenger

Neurotransmitters, hormones, proteins, peptides; ligands can bind to receptors

Secondary messengers

conveys message of a neurotransmitter or hormone from cell membrane surface to inside the cell in order to regulate metabolism and development

Organelles

A tiny cell structure that carries out a specific function within the cell

Mitochondria

Powerhouse of the cell, organelle that is the site of ATP (energy) production

Ribosomes

site of protein synthesis

Endoplasmic Reticulum (Rough)

A system of membranes that is found in a cell's cytoplasm and that assists in the production, processing, and transport of proteins and in the production of lipids.

Endoplasmic Reticulum (Smooth)

Storage of lipid (triglycerides), glycogen, calcium; detoxification of drugs; toxins are neutralized

Golgi Apparatus

stack of membranes in the cell that modifies, sorts, and packages proteins from the endoplasmic reticulum

Peroxisomes

Break down fatty acids and produce hydrogen peroxide

Lysosomes

cell organelle filled with enzymes needed to break down certain materials in the cell

Autolysis

self-destruction of cells; decomposition of all tissues by enzymes of their own formation without microbial assistance

Microfilaments

Fine, threadlike proteins found in the cell's cytoskeleton

Intermediate filaments

Threadlike proteins in the cell's cytoskeleton that are roughly twice as thick as microfilaments

Microtubules

A hollow rod composed of tubulin proteins that have spiralled to make a tube; makes up part of the cytoskeleton in all eukaryotic cells and is found in cilia and flagella and spindle fibers

Motor proteins

A protein that interacts with cytoskeletal elements and other cell components, producing movement of the whole cell or parts of the cell.

Centrosome

A structure in animal cells containing centrioles from which the spindle fibers develop.

Centrioles

a minute cylindrical organelle near the nucleus in animal cells, occurring in pairs and involved in the development of spindle fibers in cell division.

Cilia

The hairlike projections on the outside of cells that move in a wavelike manner

Flagella

A long, whip-like filament that helps in cell motility. Many bacteria are flagellated, and sperm are flagellated.

Nucleus

A part of the cell containing DNA and RNA and responsible for growth and reproduction

Multinucleate

many nuclei

Anucleate

without a nucleus

Nuclear envelope

Double membrane perforated with pores that control the flow of materials in and out of the nucleus.

Nucleolus

Found inside the nucleus and produces ribosomes

Chromatin

granular material visible within the nucleus; consists of DNA tightly coiled around proteins

Histone protein

A simple protein bound to DNA, involved in the coiling of chromosomes

Nucleosomes

Bead-like structures formed by histones and DNA

Chromosomes

threadlike structures made of DNA molecules that contain the genes

Cell division

Process by which a cell divides into two new daughter cells

Interphase

Cell grows, performs its normal functions, and prepares for division; consists of G1, S, and G2 phases

G (0) phase

when a cell leaves the cell cycle and stop division usually to mature and become a fully functional cell

S phase

The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated.

G (2) phase

cell grows and synthesizes structures other than DNA

Mitotic phase

stage of the cell cycle when a cell is actively dividing

DNA replication

The process in which DNA makes a duplicate copy of itself.

Replication fork

a Y-shaped point that results when the two strands of a DNA double helix separate so that the DNA molecule can be replicated

DNA polymerase

Enzyme involved in DNA replication that joins individual nucleotides to produce a DNA molecule

Semiconservative Replication

Method of DNA replication in which parental strands separate, act as templates, and produce molecules of DNA with one parental DNA strand and one new DNA strand

Mitosis

cell division in which the nucleus divides into nuclei containing the same number of chromosomes

Prophase

first and longest phase of mitosis, during which the chromosomes become visible and the centrioles separate and take up positions on the opposite sides of the nucleus