Chapter 3: Cells - The Living Units

• basic structural and functional unit of living organisms
• activity of an organism depends on both the individual and the collective activities of its cells
• Principle of Complementarity of Structure and Function, the biochemical activities of cells are dictated by their shapes or forms, and by the relative number of their specific sub-cellular structures
• Continuity of life from one generation to another has a cellular basis

• all cells are composted of carbon, hydrogen, nitrogen, oxygen and trace amounts of several other elements - all cells have the same basic parts and some common functions
• Human cell has three main parts: plasma membrane, cytoplasm, nucleus

• defines the extent of a cell, thereby separating two of the body's major fluid compartments - the intracellular fluid within cells and the extracellular fluid outside cells
• Cell membrane is commonly used as a synonym for plasma membrane

fluid mosaic model of membrane structure depicts the plasma membrane as an exceedingly thin structure composed of a double layer of lipid molecules with protein molecules "plugged into" it

• forms the basic "fabric" of the membrane
• Constructed largely of phospholipids, with smaller amounts of glycolipids, cholesterol, and areas called lipid rafts

• hydro=water
• philic=loving
• phobic=fear

Largely constructs the lipid bilayer with a charged and polar, hydrophilic head and a uncharged and nonpolar , hydrophobic tail (made of two fatty acid chains)

lipids with attached sugar groups

a cell's plasma membrane bristles with proteins that allow it to communicate with its environment - two distinct populations of membrane proteins, integral and peripheral

20% of membrane lipid, wedged between the phospholipid tails to stabilized the membrane, while decreasing the mobility of the phospholipids and the fluidity of the membrane

firmly inserted into the lipid bilayer - some protrude from one membrane face only, but most are transmembrane proteins that span the entire membrane and protrude on both sides

NOT embedded in the lipid bilayer - they attach loosely to integral proteins and are easily removed without disrupting the membrane

(20% of the outer membrane contains) dynamic assemblies of saturated phospholipids associated with unique lipids called sphingolipids and lots of cholesterol - quilt-like lipid rafts are more stable and less fluid than the rest of the membrane, and they can included or exclude specific proteins to various extents

many of the proteins that abut the extracellular fluid are glycoproteins with branching sugar groups - the fuzzy, sticky, carbohydrate-rich area at the cell surface - provides highly specific biological markers by which approaching cells recognize each other

• Three factors act to bind cells together
• 1 Glycoproteins in the glycocalyx act as an adhesive
• 2 Wavy contours of the membranes of adjacent cells fit together in a tongue-and-groove fashion
• 3 Special cell junctions form

impermeable junctions prevent molecules from passing through the intercellular space - a series of integral protein molecules in the plasma membranes of adjacent cells fuse together, forming and impermeable junction that encircles the cell

anchoring junctions bind adjacent cells together like a molecular "Velcro" and help form an internal tension-reducing network of fibers - mechanical couplings scattered like rivets along the sides of abutting cells to prevent their separation -

Communicating junctions allow ions and small molecules to pass for intercellular communication - cells are connected by hollow cylinders called connexons

Like a rich, nutritious"soup", interstitial fluid contains thousands of ingredients, including amino acids, sugars, fatty acids, vitamins, regulatory substances such as hormones and neurotransmitters, salts, and waste products

allows some substances to pass while excluding others

substances cross the membrane without ny energy input from the cell

the cell provides the metabolic energy (usually ATP) needed to move substances across the membrane

the tendency of molecules or ions to move from an area where they are in higher concentration

the difference in the concentration of a particular substance between two different areas

nonpolar and lipid-soluble substances diffuse directly through the lipid bilayer

Passive transport process in which the trasnported substance either binds to protein carriers in the membrane and is ferried across, or moves through water-filled protein channels

transmembrane integral proteins that are specific for transporting certain polar molecules or classes of molecules, such as sugars and amino acids, that are too large to pass through membrane channels

• transmembrane proteins that transport substances, usually ions water, through aqueous channels from one side of the membrane to the other
• Leakage channels are always open and simply allow ions or water to move according to concentration gradients
• Gated channels are controled by chemical or electrical signals

diffusion of a solvent, such as water, through a selectively permeable membrane - even though water is highly polar, it passes via osmosis through the lipid bilayer

transmembrane proteins which allow single-file diffusion of water molecules

total concentration of all solute particles in a solution

pressure of fluid in a solution - back pressure exerted by water against the membrane

a measure of the tendency of water to move into a more concentrated solution - tendency of water to move into the cell by osmosis

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

have the same concentration of nonpenetrating solutes as those found in cells (0.9% saline or 5% glucose)

have a higher concentration of nonpenetrating solutes than seen in the cell - cells immersed in hypertonic solutions lose water and shrink, or crenate

are more dilute than cells

Like carrier-mediated facilitated diffusion, requires carrier proteins that combine specifically and reversibly with the transported substances - distinguished according to their source of energy: primary active transport, secondary active transport

move solutes, most importantly ions, "uphill" against a concentration gradient

the two transported substances move in the same direction

transported substances "wave to each other" as they cross the membrane in opposite directions

hydrolysis of ATP results in the phosphorylation of the transport protein - causes the protein to change its change in such a manner that it "pumps" the bound solute across the membrane

Most investigated example of a primary active transport system - the carrier, or "pump" is a an enzyme called sodium-potassium ATPhase

the combined difference in concentration and charge; influences the distribution and direction of diffusion of ions

fluids containing large particles and macromolecules are transported across cellular membranes inside membranous sacs called vesicles

moving out of the cell

moving substances into the cell

the cell engulfs some relatively large or solid material, such as a clump of bacteria, cell debris, or inanimate particles and enclosing wit within a membrane sac called phagosome

the cell "drinks" a drop of extracellular fluid containing solutes into tiny vesicles - no receptors are used, so the process is nonspecific

main mechanism for the specific endocytosis and transcytosis of most macromolecules by body cells - Extracellular substances bind to specific receptor proteins, enabling the cell to ingest and concentrate specific substances (ligands) in protein-coated vesicles

vesicular transport processes that eject substances from the cell interior into the extracellular fluid

state of a plasma membrane of an unstimulated neuron or muscle cell in which the inside of the cell is relatively negative in comparison to the outside; the resting state

a huge and diverse group of integral proteins and glycoproteins that serve as binding

cellular material between the plasma membrane and the nucleus, is the site of most cellular activities

specialized cellular compartments or structures, each performing its own job to maintain the life of the cell

• site of ATP synthesis: powerhouse of the cell
• Rodlike, double-membrane structures; inner membrane folded into projections call cristrae

• The sites of protein synthesis
• Dense particles consisting of two subunits, each composed of ribosomal RNA and protein - free or attached to rough endoplasmic reticulum

• Site of lipid and steroid (cholesterol) synthesis, lipid metabolism, and drug detoxification
• Membranous system of sacs and tubules; free of ribosomes

• Sugar groups are attached to proteins within the cisterns - proteins are bound in vesicles for transport to the Golgi apparatus and other sites - external face synthesizes phospholipids
• Membranous system enclosing a cavity, the cistern, and coiling through the cytoplasm - externally studded with ribosomes

• packages, modified, and segregates proteins for secretion from the cell, inclusion in lysosomes, and incorporation into the plasma membrane - TRAFFIC DIRECTOR
• a stack of flattened membranes and associated vesicles close to the nucleus

• the enzymes detoxify a number of toxic substances - catalase (most important enzyme) breaks down Hydrogen Peroxide
• Membranous sacs of catalase and oxidase enzymes

• sites of intracellular digestion
• membranous sacs containing acid hydrolases

Support the cell and give it shape - involved in intracellular and cellular movements - form centrioles and cilia and flagella, if presentcylindrical structures made of tubulin proteins

• involved in muscle contraction and other types of intracellular movement - help form the cell's cytoskeleton
• fine filaments composed of the protein actin

• the stable cytoskeletal elements; resist mechanical forces acting on the cell
• Protein fibers; composition varies

• Organize a microtubule network during mitosis (cell division) to form the spindle and asters - form the bases of cilia and flagella
• paired cylindrical bodies, each composed of nine triplets of microtubules

• Coordinated movement creates a unidirectional current that propels substances across cell surfaces
• short cell-surface projections; each cilium composed of nine pairs of microtubules surrounding a central pair

• Propels the cell
• like a cilium, but longer - only example in humans is the sperm tail

• increase surface area for absorption
• tubular extensions of the plasma membrane; contain a bundle of actin filaments

• Control center of the cell - responsible for trasnmitting genetic information and providing hte instructions for proteins synthesis
• largest organelle - surrounded by the nuclear envelope; contains fluid nucleoplasm, nucleoli, and chromatin

have many nuclei - skeletal muscle cells,bone destruction cells, and some live cells are multinucleate

cells without a nucleus - red blood cells are anucleate

• separates the nucleoplasm from the cytoplasm and regulates passage of substances to and from the nucleus
• double-membrane structure pierced by pores - outer membrane continuous with the endoplasmic reticulum

allow movement - selectively permeable but substances pass much more freely than elsewhere

• site of ribosome subunit manufacture
• dense pherical (non-membrane-bounded) bodies, composed of ribosomal RNA and proteins

• DNA constitues the genes
• granular, threadlike material composed of DNA and histone proteins - when a cell is preparing to divide, the chromatin threads coil and condense enormously to form short, barlike bodies called chromosomes "colored bodies"

series of changes a cell goes through from the time it is formed until it reproduces

in which the cell grows and carries on its usual activities - the period from cell formation to cell division

during  the cells divides into two cells - two distinct events: mitosis and cytokinesis

• the division of the nucleus
• Described as four phases: prophase, metaphase, anaphase, and telophase

period of a cell's life when it carries out its normal metabolic activities and grows - not a part of mitosis

First step of mitosis, consiting of coiling of the chromosomes accompanied by migration of the two daughter centrioles toward the poles of the cell, and nuclear membrane breakdown

two chromoes are at opposite poles of the cell - chromosomes cluster at the midline of the cell - enzymes act to separate the chromatids from each other

third stage of mitosis, meiosis I, and meiosis II in which daughter chromosomes move toward each pole of a cell

final phase of mitosis - begins when migration of chromosomes to the poles of the cell has been completed and ends with the formation of two daughter nuclei

division of the cytoplasm - a contractile ring of actin microfilaments forms the cleavage furrow and pinches the cell apart

life begins as a single cell; fertilized egg

development of specific and distinctive features in cells

programmed cell death

accelerated growth

decrase in size of an organ or body tissue