Ch 03 - Cells: The Living Units

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cell

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the structural unit of all living things

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cell theory

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the scientific theory describing the properties of cells; the cell is the basic unit of life which organisms depend upon for continuity of life

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1. plasma membrane

2. cytoplasm

3. nucleus

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3 basic parts of a generalized (composite) cell

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plasma membrane

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the outermost boundary of a cell

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fluid mosaic model

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depicts the plasma membrane as a lipid bilayer with proteins "plugged in" to it

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1. membrane lipids

2. membrane proteins

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2 components of the plasma membrane

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1. phospholipids

2. glycolipids

3. cholesterol

4. lipid rafts

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4 types of membrane lipids

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phospholipids

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form the basic structure of the plasma membrane

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hydrophilic

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property of the phospholipid polar head; "water loving"

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hydrophobic

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property of the phospholipid polar tail; "water fearing"

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glycolipids

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lipids of the plasma membrane with attached sugars (glycocalyx)

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cholesterol

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lipid that helps stabilize the plasma membrane

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lipid raft

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assembly of saturated phospholipids covering about 20% of a cell's plasma membrane; more stable and less fluid

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1. integral

2. peripheral

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2 types of plasma membrane proteins

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integral proteins

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transmembrane proteins involved in molecule transport

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peripheral proteins

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membrane proteins attached to integral proteins; help form glycocalyx (exterior) and support cell structure (interior)

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glycoproteins

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proteins of the plasma membrane with attached sugars (glycocalyx)

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glycocalyx

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the sticky, carbohydrate-rich area on a cell surface that provides biological markers for cells to recognize each other; attached to membrane proteins and lipids

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1. sticky glycoproteins

2. wavy contours

3. cell junctions

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3 factors that help bind cells together

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1. tight junctions

2. desmosomes

3. gap junctions

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3 types of cell junctions

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tight junction

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impermeable cell junction where integral proteins fuse adjacent cells together

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desmosomes

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anchoring junctions that prevent cells from separating by acting like a zipper

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gap junction

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a communicating junction between adjacent cells

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1. transportation

2. membrane potential

3. cell environment interactions

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3 features of the plasma membrane:

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interstitial fluid

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extracellular fluid that fills the space between cells

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selective permeability

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allowing some substances to pass while excluding others

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passive processes

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processes in which substances cross the cell membrane without any energy input from the cell

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active processes

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processes in which substances cross the cell membrane using energy provided by the cell (usually ATP)

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1. diffusion

2. filtration

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2 main types of passive transport

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diffusion

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

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concentration gradient

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a measurement of how the concentration of something changes from one place to another

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1. simple diffusion

2. facilitated diffusion

3. osmosis

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3 types of diffusion

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simple diffusion

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form of diffusion in which a substance passes through a membrane without the aid of an intermediary; ex. oxygen in, carbon dioxide out

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facilitated diffusion

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form of diffusion in which certain molecules are transported through the cell membrane with the aid of integral proteins

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1. carrier-mediated

2. channel-mediated

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2 types of facilitated diffusion

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carrier proteins

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integral proteins that transport certain molecules that are too big to pass through membrane channels

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channel proteins

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transmembrane proteins that transport substances through aqueous channels

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osmosis

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the diffusion of a solvent, usually water, through a selectively permeable membrane

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aquaporins

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water-specific channels made by transmembrane proteins that allow water to pass freely and reversibly

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osmolarity

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the total concentration of all solute particles in a solution

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hydrostatic pressure

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the back pressure exerted by water against the membrane

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osmotic pressure

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the tendency of water to move into a cell by osmosis; the osmotic "suck"

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tonicity

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the ability to change the shape or tone of cells by altering water volume

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isotonic solutions

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solute concentration is equal to the cell; no effect

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hypertonic solutions

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solute concentration is greater than the cell; water moves out of the cell

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hypotonic solutions

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solute concentration is less than the cell; water moves in to the cell

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filtration

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passive transportation process in which water and solutes are forced through a membrane by pressure; ex. capillaries and kidneys

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pressure gradient

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solute containing fluids go from greater to lesser pressure

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1. active transport

2. vesicular transport

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2 categories of active membrane transport

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active transport

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the movement of ions or molecules assisted by enzymes and requiring energy (ATP)

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solute pump

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an active transporter that moves solutes "uphill" against a concentration gradient

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symport system

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active transport system in which the transported substances move in the same direction

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antiport system

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active transport system in which transported substances move in opposite directions

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primary active transport

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active transport when fueled by hydrolysis of ATP

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sodium-potassium pump

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Na+ in, K+ out (primary active transport)

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secondary active transport

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active transport driven indirectly by energy stored in ionic gradients created by primary active transport pumps

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vesicular transport

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active transportation process in which large substances are transported inside membranous sacs called vesicles

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endocytosis

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process in which a cell takes in materials from the outside by engulfing and fusing them with its plasma membrane

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clathrin

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coating protein often found in vesicular pits

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1. phagocytosis

2. pinocytosis

3. receptor-mediated endocytosis

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3 types of endocytosis

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phagocytosis

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form of endocytosis in which the cell engulfs some relatively large or solid material; "cell eating" macrophages and WBCs

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phagosome

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a membrane-bound vesicle in a phagocyte containing the phagocytized material

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amoeboid motion

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cell movement by the flowing of cytoplasm into temporary extensions that allows them to creep along

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pinocytosis

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form of endocytosis in which a cell ingests a small volume of ECF; "cell drinking"

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receptor-mediated endocytosis

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form of endocytosis in which only specific molecules are ingested into the cell

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exocytosis

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vesicular transport process that ejects substances from the cell interior into the extracellular space

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membrane potential

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potential energy (voltage) of the cell membrane; used for cell signaling

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resting membrane potential

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potential energy of a cell membrane during its resting state; slightly negative

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1. cell adhesion molecules (CAMs)

2. plasma membrane receptors

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2 classes of glycocalyx molecules:

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cell adhesion molecules (CAMs)

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membrane proteins involved in binding with other cells or with the extracellular matrix

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membrane receptors

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integral proteins and glycoproteins that serve as binding sites on the cell surface

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1. contact signaling

2. electrical signaling

3. chemical signaling

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3 forms of interaction of membrane receptors:

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contact signaling

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process by which cells recognize one another by their membrane receptors

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chemical signaling

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the process by which membrane receptors respond to ligands (neurotransmitters, hormones, or paracrines)

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ligands

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chemicals that bind specifically to plasma membrane receptors; neurotransmitters, hormones, and paracrines

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G protein-linked receptors

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membrane receptors that exert their effect indirectly through a G protein and second messengers; ex. cyclic AMP

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electrical signaling

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process by which changes in membrane potential signal channel proteins to open or close

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cytoplasm

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the site of most cellular activities, the intracellular fluid between the plasma membrane and the nucleus

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1. cytosol

2. organelles

3. inclusions

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3 major elements of the cytoplasm

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cytosol

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viscous, semitransparent fluid in which the cytoplasmic elements are suspended

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organelles

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the metabolic machinery of the cell; each type carries out a specific function

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inclusions

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chemical substances that may or may not be present in a cell, depending on cell type; ex. glycogen in liver cells, lipid in fat cells, pigment in skin cells, etc.

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mitochondria

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powerhouse of the cell, providing most of its ATP supply; self-replicating

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matrix

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gel-like substance inside the mitochondria

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cristae

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ridges inside a mitochondrion

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ribosomes

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sites of protein synthesis in a cell; small, dark-staining granules composed of proteins and rRNAs

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endoplasmic reticulum (ER)

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network of interconnected tubes and parallel membranes enclosing fluid-filled cavities in a cell

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cisterns

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fluid-filled cavities enclosed by the endoplasmic reticulum

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rough endoplasmic reticulum

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houses ribosomes that manufacture all proteins secreted from cells; also manufactures proteins and phospholipids for cell membranes

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smooth endoplasmic reticulum

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site of lipid synthesis, lipid metabolism, and drug detoxification in a cell

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Golgi apparatus

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modify, concentrate, and package the proteins made in the rough ER; ex. secretory vesicles, plasma membrane components, lysosomes

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secretory vesicles (granules)

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pinch off from the Golgi apparatus and migrate to the plasma membrane to discharge their contents

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peroxisomes

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contain enzymes that detoxify harmful chemicals and neutralize free radicals; numerous in kidney and liver cells

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free radicals

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highly reactive chemicals with unpaired electrons

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lysosomes

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contain enzymes that digest foreign substances engulfed by the cell; the "demolition crew"

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autolysis

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the destruction of cells or tissues by their own enzymes

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endomembrane system

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the system of organelles that work together to produce, degrade, store, and export biological molecules, and degrade harmful substances

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cytoskeleton

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the "cell skeleton"

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1. microfilaments

2. intermediate filaments

3. microtubules

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3 types of rods in the cytoskeleton

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microfilaments

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"beaded" cytoskeleton elements involved in cell shape and cell movement

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intermediate filaments

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rope-like tough, insoluble protein fibers of the cytoskeleton; stabilize and resist pulling forces in a cell

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microtubules

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hollow tubes made of spherical proteins that determine the overall shape of a cell and the distribution of organelles; make up centrioles

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motor proteins

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move and reposition organelles along the microtubules

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centrosome

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the microtubule organizing center located near the cell nucleus

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centrioles

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small, barrel-shaped organelles in the centrosome made of microtubules; form the bases of cilia and flagella

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cilia

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whiplike, cellular extensions that move substances in one direction across cell surfaces

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flagella

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cell projections that propel the cell itself; ex. a sperm's tail

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basal bodies

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centrioles forming the bases of cilia and flagella

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microvilli

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minute, fingerlike extensions of the plasma membrane that increase surface area

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nucleus

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the organelle that is the cell's control center, contains most of the cell's genetic material

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multinucleate

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having many nuclei

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anucleate

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cells without a nucleus; cannot reproduce

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1. nuclear envelope

2. nucleoli

3. chromatin

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3 regions of the nucleus

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nuclear envelope

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a double membrane barrier that surrounds the cell nucleus

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nuclear pores

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pores regulating molecules entering and exiting the nucleus

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nucleoli

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dark-staining spherical bodies within the nucleus where ribosomes are produced

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chromatin

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mass of genetic material inside the nucleus composed of DNA and proteins that condense to form chromosomes

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histone proteins

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proteins that package and regulate DNA

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nucleosomes

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eight histone proteins surrounded by a DNA molecule; the fundamental unit of chromatin

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chromosomes

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coiled and condensed chromatin threads during mitosis; carry genetic information in the form of genes

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cell cycle

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

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1. interphase
2. mitotic phase (cell division)

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2 major periods of the cell cycle

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interphase

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the period from cell formation to cell division; cell grows and gets ready to divide

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1. G1

2. S

3. G2

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3 subphases of the interphase period

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G1 (gap 1) phase

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subphase when the cell is active, synthesizing proteins rapidly and growing vigorously

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S (synthetic) phase

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subphase when DNA is replicated

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G2 (gap 2) phase

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subphase when substances needed for division are synthesized and moved to their proper sites; the cell is ready to divide

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semiconservative replication

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the mechanism of DNA replication, one old and one new nucleotide strand

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1. mitosis
2. cytokinesis

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2 distinct events of the M (mitotic) phase

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mitosis

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division of the nucleus

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cytokinesis

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division of the cytoplasm

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1. prophase
2. metaphase
3. anaphase
4. telophase

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4 phases of mitosis

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prophase

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chromatin condenses to chromosomes, nucleolus and nuclear envelope disappear, centrioles move to opposite ends; stage 1 of mitosis

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metaphase

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chromosomes align at the equator; stage 2 of mitosis

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anaphase

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chromosomes split into two and are pulled along mitotic spindles to the separate poles; stage 3 of mitosis

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telophase

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chromosomes unwind into chromatin, nuclear envelope and nucleolus reappear, cytokinesis; stage 4 of mitosis

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gene

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the segment of a DNA molecule that codes for a single polypeptide chain

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triplet

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each sequence of three nucleotide bases; the "word" that specifies a particular amino acid

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uracil

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replaces thymine on all forms of RNA

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exon

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amino acid-specifying informational sequence

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intron

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separate exons; noncoding segments believed to serve as a reservoir of ready-to-use DNA segments

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1. mRNA (messenger)
2. rRNA (ribosomal)
3. tRNA (transfer)

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3 types of RNA

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messenger RNA (mRNA)

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the form of RNA in which genetic information transcribed from DNA is transferred to the cytoplasm; short-lived

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ribosomal RNA (rRNA)

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form of RNA that, along with proteins, forms ribosomes

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transfer RNA (tRNA)

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form of RNA that ferries amino acids to a ribosome

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1. transcription

2. translation

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2 major steps of polypeptide synthesis

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transcription

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DNA's information is encoded in mRNA

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promoter

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special DNA sequence where mRNA synthesis starts

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polymerase

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the enzyme that oversees the synthesis of RNA

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1. initiation

2. elongation

3. termination

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3 basic phases of RNA transcription

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initiation

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RNA polymerase pulls apart strands of DNA so transcription can begin at the promoter; phase 1 of RNA transcription

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elongation

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RNA polymerase aligns nucleotides with DNA and links them together; phase 2 of RNA transcription

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termination

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RNA polymerase reaches the termination signal and transcription ends; phase 3 of RNA transcription

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termination signal

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DNA base sequence that signals transcription to end

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translation

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the language of nucleic acids is translated into the language of proteins; step 2 of polypeptide synthesis

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genetic code

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the rules by which a base sequence of a gene is translated into an amino acid sequence

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codon

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the corresponding three-base sequence on mRNA for each DNA triplet

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anticodon

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the complementary three-base sequence on tRNA for every mRNA codon

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1. initiation

2. elongation

3. termination

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3 events of RNA translation

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ubiquitins

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mark doomed proteins for attack by attaching to them in an ATP-dependent reaction

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proteasome

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giant complex of enzymes that break down proteins that aren't accessible by lysosomes

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extracellular materials

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any substances contributing to body mass that are found outside the cells

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1. body fluids

2. cellular secretions

3. extracellular matrix

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3 classes of extracellular materials:

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cell differentiation

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the development of specific and distinctive features in cells

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apoptosis

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programmed cell death; eliminates unnecessary or damaged cells

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atrophy

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decrease in size of an organ or body tissue

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1. wear-and-tear theory
2. mitochondrial theory
3. autoimmune theory
4. genetic theory

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4 theories of cell aging

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wear-and-tear theory

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theory of cell aging that attributes aging to chemicals and free radicals damaging cells over time

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mitochondrial theory

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theory of cell aging in which free radicals destroy mitochondria and glucose cross-links proteins

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autoimmune theory

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theory of cell aging in which cell damage results from autoimmune disorders and weakening

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genetic theory

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theory of cell aging that suggests that cessation of mitosis and cell aging are programmed into our genes

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telomere

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long strings of nucleotides that cap the ends of chromosomes; once they've deteriorated the "stop mitosis" sign is given