Chapter 3 quiz San Marcos A and P

Psuedopod

"false foot"; used by the Amoeba for movement

Cells consist of three major compartments:

(1) plasma membrane (=outer cell membrane), (2) the cytoplasm which consists of the cytosol (fluid component) and organelles, (3) the nucleus which contains the genetic material.

Centrosome

(cell center) A region near the nucleus that contains paired organelles called centrioles.

INTERPHASE

(in green), in which the cell grows and carries on its usual activities One of two major periods in the cell life cycle; includes the period from cell formation to cell division.

transcytosis

, moving substances into, across, and then out of the cell, and .

enzymatic activity

-a membrane protein may be an enzyme with its active site exposed to substances in the adjacent solution -a team of several enzymes in a membrane may catalyze sequential steps of a metabolic pathway

ELONGATION

. Using incoming RNA nucleotides as substrates, RNA polymerase aligns them with complementary DNA bases on the template strand and then links them together. As RNA polymerase elongates the mRNA strand one base at a time, it unwinds the DNA helix in front of it, and rewinds the helix behind it. At any given moment, 16 to 18 base pairs of DNA are unwound and the most recently made mRNA is still hydrogen-bonded to the template DNA. This small region—called the DNA-RNA hybrid—is up to 12 base pairs long.

TERMINATION

. When the polymerase reaches a special base sequence called a termination signal, transcription ends and the newly formed mRNA separates from the DNA template.

Ligands

1st messenger Signaling chemicals that bind specifically to membrane receptors. Include most neurotransmitters (nervous system signals), hormones (endocrine system signals), and paracrines (chemicals that act locally and are rapidly destroyed).

number of cells in our body

200 different kinds of cells.

Membrane Proteins

A cell's plasma membrane bristles with this that allow it to communicate with its environment. This makes up about half of the plasma membrane by mass and they are responsible for most of the specialized membrane functions. Some float freely and others are "tethered" to intracellular or extracellular structures and are restricted in their movement. There are two distinct types, integral and peripheral some of these are enzymes

Ribosomal RNA (rRNA)

A constituent of ribosome; exists within the ribosomes of cytoplasm and assists in protein synthesis.

Membrane receptors

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

Glycolipids

A lipid with one or more covalently attached sugars. Found only on the outer plasma membrane surface, these account for about 5% of total membrane lipids. Their sugar groups, make that end of the glycolipid molecule polar, whereas the fatty acid tails are nonpolar.

Tonicity

A measure of the ability of a solution to cause a change in cell shape or tone by promoting osmotic flows of water.

Osmotic pressure

A measure of the tendency of a solvent to move into a more concentrated solution. The force that solutes have to attract water

Selectively permeable membrane

A membrane that allows certain substances to pass while restricting the movement of others; also called differentially permeable membrane.

Selectively permeable membrane

A membrane that allows certain substances to pass while restricting the movement of others; also called differentially permeable membrane. It allows some substances to pass while excluding others. It allows nutrients to enter the cell, but keeps many undesirable substances out. At the same time, it keeps valuable cell proteins and other necessary substances in the cell, but allows wastes to exit.

antiport

A membrane transport process that carries one substance in one direction and another in the opposite direction.

symport (cotransport)

A membrane transport process that carries two substances in the same direction across the membrane.

Gap junction

A passageway between two adjacent cells; formed by transmembrane proteins called connexons. With these the adjacent plasma membranes are very close, and the cells are connected by hollow cylinders called connexons, composed of transmembrane proteins. The many different types of connexon proteins vary the selectivity of the these channels. Ions, simple sugars, and other small molecules pass through these water-filled channels from one cell to the next. These are present in electrically excitable tissues, such as the heart and smooth muscle, where ion passage from cell to cell helps synchronize their electrical activity and contraction.

Transport protein

A protein that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute. Some of these proteins hydrolyze ATP as an energy source to actively pump substances across the membrane.

Signal sequence

A short peptide segment present in a protein being synthesized that causes the associated ribosome to attach to the membrane of rough ER.

Hypertonic solution

A solution that has a higher concentration of nonpenetrating solutes than the reference cell; having greater osmotic pressure than the reference solution (blood plasma or interstitial fluid).

Hypotonic solution

A solution that is more dilute (containing fewer nonpenetrating solutes) than the reference cell. Cells placed in hypotonic solutions plump up rapidly as water diffuses into them.

Isotonic solution

A solution with a concentration of nonpenetrating solutes equal to that found in the reference cell.

Carriers

A transmembrane integral protein that changes shape to envelop and transport a polar substance across the cell membrane.

Carrier

A transmembrane protein that changes shape to envelop and transport a polar substance across the cell membrane.

Channel

A transmembrane protein that forms an aqueous pore, allowing substances to move from one side of the membrane to the other.

Secondary active transport

A type of active transport in which the energy needed to drive the transport process is provided by the electrochemical gradient of another molecule (which moves "downhill" through the transport protein at the same time as another molecule is moved "uphill" against its gradient). Also called cotransport or symport (when the two transported molecules move in the same direction) or antiport (when the two transported molecules move in opposite directions).

primary active transport

A type of active transport in which the energy needed to drive the transport process is provided directly by hydrolysis of ATP.

generalized cell

All cells have some common structures and functions .

Exons

Amino acid-specifying informational sequences (separated by introns) in the genes of higher organisms.

Cistern

Any cavity or enclosed space serving as a reservoir.

Tight junction

Area where plasma membranes of adjacent cells are tightly bound together, forming an impermeable barrier. These help prevent molecules from passing through the extracellular space between adjacent cells. For example, these junctions between epithelial cells lining the digestive tract keep digestive enzymes and microorganisms in the intestine from seeping into the bloodstream.

Chromosomes

Barlike bodies of tightly coiled chromatin; visible during cell division.

Pinocytosis

Cell drinking

Desmosome

Cell junction composed of thickened plasma membranes joined by filaments. serve as anchoring junctions

Multinucleate cell

Cell with more than one nucleus, e.g., skeletal muscle cells, osteoclasts.

Inclusions

Chemical substances that may or may not be present, depending on cell type. Examples include stored nutrients, such as the glycogen granules in liver and muscle cells; lipid droplets in fat cells; and pigment (melanin) granules in certain skin and hair cells.

Nucleus

Control center of a cell; contains genetic material; (2) clusters of nerve cell bodies in the CNS; (3) center of an atom; contains protons and neutrons. genetic library, it contains the instructions needed to build nearly all the body's proteins. Additionally, it dictates the kinds and amounts of proteins to be synthesized at any one time in response to signals acting on the cell. hree recognizable regions or structures: the nuclear envelope (membrane), nucleoli, and chromatin

Ribosomes

Cytoplasmic organelles at which proteins are synthesized. small, dark-staining granules composed of proteins and a variety of RNAs . Each UNIT has two globular subunits that fit together like the body and cap of an acorn. sites of protein synthesis

Mitochondria

Cytoplasmic organelles responsible for ATP generation for cellular activities.

Nucleoli

Dense spherical bodies in the cell nucleus involved with ribosomal RNA (rRNA) synthesis and ribosomal subunit assembly.

osmosis

Diffusion of a solvent through a selectively permeable membrane from a dilute solution into a more concentrated one.

Phagocytosis

Engulfing of foreign solids by (phagocytic) cells.

Integral proteins

Firmly inserted into the lipid bilayer. Some protrude from one membrane face only, but most are transmembrane and span the entire membrane and protrude on both sides. Whether transmembrane or not, all of these have both hydrophobic and hydrophilic regions. This structural feature allows them to interact with both the nonpolar lipid tails buried in the membrane and the water inside and outside the cell. Some of these proteins are involved in transport, and cluster together to form channels.

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.

Nucleosome

Fundamental unit of chromatin; consists of a strand of DNA wound around a cluster of eight histone proteins.

CHANNEL-MEDIATED FACILITATED DIFFUSION

In carrier-mediated diffusion, the diffusing substance attaches to a membrane (protein) carrier that moves it across the membrane. Channels are transmembrane proteins that transport substances, usually ions or water, through aqueous channels from one side of the membrane to the other (Figure 3.7c and d). Channels are selective due to pore size and the charges of the amino acids lining the channel. Leakage channels are always open and simply allow ions or water to move according to concentration gradients. Gated channels are controlled (opened or closed), usually by chemical or electrical signals. Like carriers, many channels can be inhibited by certain molecules, show saturation, and tend to be specific. Substances moving through them also follow the concentration gradient (always moving down the gradient).

CARRIER-MEDIATED FACILITATED DIFFUSION

In channel-mediated diffusion, the diffusing substance moves through a membrane channel. are 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. Alterations in the shape of the carrier allow it to first envelop and then release the transported substance, allowing it to bypass the nonpolar regions of the membrane. Essentially, the carrier protein changes shape to move the binding site from one face of the membrane to the other

2 types of diffusion

In channel-mediated diffusion, the diffusing substance moves through a membrane channel. In carrier-mediated diffusion, the diffusing substance attaches to a membrane (protein) carrier that moves it across the membrane.

Second messenger

Intracellular molecule generated by the binding of a chemical (hormone or neurotransmitter) to a receptor protein; mediates intracellular responses to the chemical messenger.

Cyclic AMP

Intracellular second messenger that mediates the effects of the first (extracellular) messenger (hormone or neurotransmitter); formed from ATP by a plasma membrane enzyme (adenylate cyclase).

Cytoskeleton

Literally, cell skeleton. An elaborate series of rods running through the cytosol, supporting cellular structures and providing the machinery to generate various cell movements. microfilaments, intermediate filaments, and microtubules

Messenger RNA (mRNA)

Long nucleotide strands that reflect the exact nucleotide sequences of the genetically active DNA and carry the DNA's message.

Exocytosis

Mechanism by which substances are moved from the cell interior to the extracellular space as a secretory vesicle fuses with the plasma membrane.

Passive (transport) processes

Membrane transport processes that move substances down their concentration gradients (e.g., diffusion). They are driven by kinetic energy and so do not require cellular energy (such as ATP). The two main types of transport are diffusion (dĭ-fu′zhun) and filtration.

The plasma membrane

Membrane, composed of phospholipids, cholesterol, and proteins, that encloses cell contents; outer limiting cell membrane. the outer boundary of the cell which acts as a selectively permeable barrier. Separates two of the body's major fluid compartments: intracellular and extracellular

Endoplasmic reticulum (ER)

Membranous network of tubular or saclike channels in the cytoplasm of a cell.

Peroxisomes

Membranous sacs in cytoplasm containing powerful oxidase enzymes that use molecular oxygen to detoxify harmful or toxic substances, such as free radicals.

Golgi apparatus

Membranous system close to the cell nucleus that packages protein secretions for export, packages enzymes into lysosomes for cellular use, and modifies proteins destined to become part of cellular membranes. principal "traffic director" for cellular proteins. Its major function is to modify, concentrate, and package the proteins and lipids made at the rough ER and destined for export from the cell.

Centriole

Minute body found in pairs near the nucleus of the cell; active in cell division. form the bases of cilia and flagella

Intron

Noncoding segment or portion of DNA that ranges from 60 to 100,000 nucleotides long.

INITIATION

Once properly positioned, RNA polymerase pulls apart the strands of the DNA double helix so transcription can begin at the start point in the promoter.

Gene

One of the biological units of heredity located in DNA; transmits hereditary information. as a segment of a DNA molecule that carries instructions for creating one polypeptide chain.

Transcription

One of the two major steps in the transfer of genetic code information from a DNA base sequence to the complementary base sequence of an mRNA molecule.

Translation

One of the two major steps in the transfer of genetic code information, in which the information carried by mRNA is decoded and used to assemble polypeptides.

Microtubules

One of three types of rods in the cytoskeleton of a cell; hollow tubes made of spherical protein that determine the cell shape as well as the distribution of cellular organelles. Hollow tubes made of spherical protein subunits called tubulin (radiate from a small region of cytoplasm near the nucleus called the centrosome or cell center (see Figure 3.2). are remarkably dynamic organelles, constantly growing out from the centrosome, disassembling, and then reassembling at the same or different sites. determine the overall shape of the cell, as well as the distribution of cellular organelles. Mitochondria, lysosomes, and secretory vesicles attach to the these like ornaments hanging from tree branches. form centrioles, cilia, flagella

M (mitotic) phase

One of two major periods in the cell life cycle; involves the division of the nucleus (mitosis) and the division of the cytoplasm (cytokinesis).

Lysosomes

Organelles that originate from the Golgi apparatus and contain strong digestive enzymes.

fluid mosaic model

Our current idea of plasma membrane structure consists of a double layer of lipids with embedded proteins.

Facilitated diffusion

Passive transport process used by certain large or charged molecules (e.g., glucose, Na+) that are unable to pass through the plasma membrane unaided. Involves movement through channels or movement facilitated by a membrane carrier.

Hydrostatic pressure

Pressure of fluid in a system. back pressure exerted by water against the membrane.

Mitosis

Process during which the chromosomes are redistributed to two daughter nuclei; nuclear division. Consists of prophase, metaphase, anaphase, and telophase.

Autolysis

Process of autodigestion (self-digestion) of cells, especially dead or degenerate cells.

G protein

Protein that relays signals between extracellular first messengers (such as hormones or neurotransmitters) and intracellular second messengers (such as cyclic AMP) via an effector enzyme.

signal transduction

Proteins in the cell membrane that bind hormones and relay messages into the interior of the cell

signal transduction

Receptors for hormones or other chemical messengers and relay messages to the cell interior

Genetic code

Refers to the rules by which the base sequence of a DNA gene is translated into protein structures (amino acid sequences).

Cell cycle

Series of changes a cell goes through from the time it is formed until it reproduces itself.

Transfer RNA (tRNA)

Short-chain RNA molecules that transfer amino acids to the ribosome.

organelles

Small cellular structures (ribosomes, mitochondria, and others) that perform specific metabolic functions for the cell as a whole. are the metabolic machinery of the cell. Each type of organelle carries out a specific function for the cell—some synthesize proteins, others generate ATP, and so on. The are the little "organs" of the cell. each one of these plays a role in the normal functioning of the cell.

Channels

Small, water-soluble molecules or ions can move through these pores, bypassing the lipid part of the membrane. protiens act as carriers that bind to a substance and then move it through the membrane (Figure 3.4a).

SNAREs

Soluble Neuronal Attachment protein Receptors. General term for attachment proteins. VESICULAR or target

Cholesterol

Some 20% of membrane lipid is made up of this. Like phospholipids, this has a polar region (its hydroxyl group) and a nonpolar region (its fused ring system). It wedges its plate like hydrocarbon rings between the phospholipid tails, which stabilize the membrane, while decreasing the mobility of the phospholipids and the fluidity of the membrane.

Chromatin

Structures in the nucleus that carry the hereditary factors (genes).

cell theory

The cell is the structural and functional unit of life. The activity of an organism depends on the activities of its cells. The activities of cells depend on their form and relative numbers of subcellular structures. Cells can only arise from other cells.

Cytoplasm

The cellular material surrounding the nucleus and enclosed by the plasma membrane. A jellylike fluid inside the cell in which the organelles are suspended. consists of three major elements: the cytosol, organelles, and inclusions

electrochemical gradient

The combined difference in concentration and charge; influences the distribution and direction of diffusion of ions. crucial for cardiac, skeletal muscle, and neuron function

Concentration gradient

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

Concentration gradient

The difference in the concentration of a particular substance between two different areas. The constant random and high-speed motion of molecules and ions (a result of their intrinsic kinetic energy) results in collisions. With each collision, the particles ricochet off one another and change direction. The overall effect of this erratic movement is to scatter or disperse the particles throughout the environment. The greater the difference in concentration of the diffusing molecules and ions between the two areas, the more collisions occur and the faster the particles diffuse.

Cytokinesis

The division of cytoplasm that occurs after the cell nucleus has divided. begins during late anaphase and is completed after mitosis ends. A contractile ring made of actin filaments (Focus Figure 3.3, final phase) draws the plasma membrane inward to form a cleavage furrow over the center of the cell. The furrow deepens until it pinches the cytoplasmic mass into two parts, yielding two daughter cells. Each is smaller and has less cytoplasm than the mother cell, but is genetically identical to it. The daughter cells then enter the interphase portion of the life cycle until it is their turn to divide.

Nuclear envelope

The double membrane barrier of a cell nucleus. separated by a fluid-filled space (similar to the mitochondrial membrane). The outer membrane is continuous with the rough ER of the cytoplasm and is studded with ribosomes on its external face. The inner membrane is lined by the nuclear lamina, a network of lamins (rod-shaped proteins that assemble to form intermediate filaments) that maintains the shape of the nucleus and acts as a scaffold to organize DNA in the nucleus

transmembrane potential

The electrical potential difference (voltage) across a cell's plasma membrane

Telophase

The 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.

Prophase

The first stage of mitosis, consisting of coiling of the chromosomes accompanied by migration of the two daughter centrioles toward the poles of the cell, and nuclear membrane breakdown. Nuclear envelope breaks up, spindle forms, nucleoli disappear, and the chromosomes coil and condense.

Amoeboid motion

The flowing movement of the cytoplasm of a phagocyte. their cytoplasm flows into temporary extensions that allow them to creep along.

Osmolarity

The number of solute particles present in 1 liter of a solution. More specifically the individual number of atoms ions and molecules in the solution

hydrostatic pressure

The pressure of water against the walls of its container.

Diffusion

The spreading of particles in a gas or solution with a movement toward uniform distribution of particles; driven by kinetic energy.

Diffusion

The spreading of particles in a gas or solution with a movement toward uniform distribution of particles; driven by kinetic energy. Is an important means of passive membrane transport for every cell of the body. Because filtration generally occurs only across capillary walls, we will discuss it later in conjunction with capillary transport.

Anticodon

The three-base sequence complementary to the messenger RNA (mRNA) codon.

Codon

The three-base sequence on a messenger RNA molecule that provides the genetic information used in protein synthesis; codes for a given amino acid.

Receptor-mediated endocytosis

The type of endocytosis in which engulfed particles attach to receptors before endocytosis occurs. Unfortunately, flu viruses, diphtheria, and cholera toxins also use this route to enter our cells.

Simple diffusion

The unassisted transport across a plasma membrane of a lipid-soluble or very small particle.

simple diffusion

The unassisted transport across a plasma membrane of a lipid-soluble or very small particle.

Anaphase

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

Microvilli

Tiny projections on the free surfaces of some epithelial cells; increase surface area for absorption. increase the plasma membrane surface area tremendously and are most often found on the surface of absorptive cells such as intestinal and kidney tubule cells. have a core of bundled actin filaments that extend into the terminal web of the cell. Actin is sometimes a contractile protein, but this appears to function as a mechanical "stiffener." major function is to increase the cell's surface area for absorption of substances.

Cilia

Tiny, hairlike projections that move in a wavelike manner to propel substances across the exposed cell surface.

Aquaporins

Transmembrane proteins that form water channels. particularly abundant in red blood cells and in cells involved in water balance such as kidney tubule cells

Vesicular transport

Transport of large particles and macromolecules into or out of a cell or between its compartments in membrane-bound sacs. via endo and excocytosis

Cell Junctions

Typically, three factors act to bind cells together: Glycoproteins in the glycocalyx act as an adhesive. Wavy contours of the membranes of adjacent cells fit together in a tongue-and-groove fashion. Special cell junctions form (Figure 3.5).

Phagosome

Vesicle formed as a result of phagocytosis.

Secretory vesicles (granules)

Vesicles that migrate to the plasma membrane of a cell and discharge their contents from the cell by exocytosis.

Membrane potential

Voltage across the plasma membrane.

BODY FLUIDS

also called extracellular fluids, include interstitial fluid, blood plasma, and cerebrospinal fluid. These fluids are important transport and dissolving media.

The nucleus

an organelle that controls cellular activities. Typically the nucleus lies near the cell's center.

MEMBRANE-BOUND RIBOSOMES

are attached to membranes, forming a complex called the rough endoplasmic reticulum (Figure 3.16). They synthesize proteins destined either for incorporation into cell membranes or lysosomes, or for export from the cell.

peripheral proteins

are not embedded in the lipid bilayer. Instead, they attach loosely to integral proteins and are easily removed without disrupting the membrane. These proteins include a network of filaments that helps support the membrane from its cytoplasmic side (Figure 3.4c). Some of these proteins are enzymes. Others are motor proteins involved in mechanical functions, such as changing cell shape during cell division and muscle cell contraction. Still others link cells together.

Extracellular materials

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

Cells

are the smallest structural unit of the human body that possess all the functions and activities that biologists describe as "life". There is a system of internal membranes, the endomembrane system, which includes the endoplasmic reticulum (rough and smooth), the Golgi apparatus, secretory vesicles, and lysosomes, AND the membrane surrounding the nucleus. The rough endoplasmic reticulum (RER) is involved with protein synthesis. The other form of endoplasmic reticulum lacks ribosomes so it is called smooth endoplasmic reticulum or SER. Although the SER is continuous with the RER, it plays no role in protein synthesis (because it lacks ribosomes). Instead the SER is involved with lipid metabolism and synthesis of cholesterol and steroid hormones. It also plays a crucial role in detoxification of drugs, alcohol and other toxic substances.

Intermediate filaments

are tough, insoluble protein fibers that resemble woven ropes. Made of twisted units of tetramer (4) fibrils, they have a diameter between those of microfilaments and microtubules most stable and permanent of the cytoskeletal elements and have high tensile strength. They attach to desmosomes, and their main job is to act as internal guy-wires to resist pulling forces exerted on the cell. Because their protein composition varies in different cell types, there are numerous names for these cytoskeletal elements—for example, they are called neurofilaments in nerve cells and keratin filaments in epithelial cells.

smooth er

continuous with the rough ER and consists of tubules arranged in a looping network. Its enzymes (all integral proteins integrated into its membranes) play no role in protein synthesis. Instead, the enzymes catalyze reactions involved with the following tasks: Metabolize lipids, synthesize cholesterol and phospholipids, and synthesize the lipid components of lipoproteins (in liver cells) Synthesize steroid-based hormones such as sex hormones (testosterone-synthesizing cells of the testes are full of smooth ER) Absorb, synthesize, and transport fats (in intestinal cells) Detoxify drugs, certain pesticides, and cancer-causing chemicals (in liver and kidneys) Break down stored glycogen to form free glucose (in liver cells especially)

osmosis transport

diffusion of a solvent such as water through a specific chanel protein (aquaphorin) or through the bilayer

Attachment to the cytoskeleton and extracellular matrix

elements of the cytoskelaton (internal support) and the extracellular matrix may anchor to membrane proteins, which help maintain cell shape and fix the location of certain membrane proteins. Others play a role in cell movement or binds adjacent cells together.

Glycocalyx

enriched both by glycolipids and by glycoproteins secreted by the cell. A layer of externally facing glycoproteins and glycolipids (a "cell coat") on or near a cell's plasma membrane; its components determine blood type and are involved in cellular interactions. sugar residues of the this provide biological markers that allow cells to recognize each other.

FREE RIBOSOMES

float freely in the cytosol. They make soluble proteins that function in the cytosol, as well as those imported into mitochondria and some other organelles.

extracellular fluid

fluid compartment outside the cell referred to as interstitial fluid in tissues bathes the cell plasma

intracellular fluid

fluid compartment within the cells cytosol 62% of the body is intracellular fluid

free radicals

highly reactive chemicals with unpaired electrons that can scramble the structure of biological molecules.

coat proteins

in general is that they play a significant role in all forms of endocytosis.

Contact signaling

in which cells come together and touch, is the means by which cells recognize one another. It is particularly important for normal development and immunity. Some bacteria and other infectious agents use this to identify their "preferred" target tissues.

endomembrane system

is a system of organelles (most described above) that work together mainly to (1) produce, degrade, store, and export biological molecules, and (2) degrade potentially harmful substances. It includes the ER, Golgi apparatus, secretory vesicles, and lysosomes, as well as the nuclear membrane—

Interstitial fluid

is the fluid in tissues that bathes all of our cells, and has major and endless roles to play. Like a rich, nutritious "soup," interstitial fluid contains thousands of ingredients, including amino acids, sugars, fatty acids, regulatory substances, and wastes. To remain healthy, each cell must extract from this mix the exact amounts of the substances it needs depending on present conditions.

THE EXTRACELLULAR MATRIX

is the most abundant extracellular material. Most body cells are in contact with a jellylike substance composed of proteins and polysaccharides. Secreted by the cells, these molecules self-assemble into an organized mesh in the outside space, where they serve as a universal "cell glue" that helps to hold body cells together this is particularly abundant in connective tissues—in some cases so abundant that it (rather than living cells) accounts for the bulk of that tissue type. Depending on the structure to be formed, this in connective tissue ranges from soft to rock-hard.

nucleoplasm

jellylike fluid in which other nuclear elements are suspended. Like the cytosol, the nucleoplasm contains dissolved salts, nutrients, and other essential solutes.

The lipid bilayer

made up of about 75% phospholipds -characterized by have a polar "head" which means it is water-loving (hydrophilic) and can interact with the water component of body fluids. The other part of the phospholipid molecule consists of two fatty acid tails which are nonpolar and hydrophobic (water-fearing). Notice that the tails of the fatty acids point inward toward each other, where as the polar heads are facing the watery environment inside and outside the cell. Thus, the plasma membrane effectively separates the intracellular fluid (ICF) from the extracellular fluid (ECF). About

intercellular joining

membrane proteins of adjacent cells may hook together in various kinds of intercellular junctions Some membrane proteins of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions

cell adhesion molecules (CAMs)

molecular velcro that cells use to anchor themselves to molecules in the extracellular space and to each other

Solute pump

move solutes, most importantly ions, "uphill" against a concentration gradient. Enzyme-like protein carrier that mediates active transport of solutes such as amino acids and ions uphill against their concentration gradients.

sodium-potassium pump

moves Na+ out of the cell and K+ into the cell. pump A primary active transport system that simultaneously drives Na+ out of the cell against a steep gradient and pumps K+ back in. Also called Na+-K+ ATPase. concentration of K+ inside the cell is some 10 times higher than that outside, and the reverse is true of Na+

vesicular trafficking

moving substances from one area (or membranous organelle) in the cell to another

Anucleate

no nucleus, cells cannot reproduce and therefore live in the bloodstream for only three to four months before they deteriorate. Without a nucleus, a cell cannot produce mRNA to make proteins, and when its enzymes and cell structures start to break down (as all eventually do), they cannot be replaced.

Active (transport) processes

occurs whenever a cell uses energy to move solutes across the membrane. Membrane transport processes for which ATP is directly or indirectly required, e.g., solute pumping and endocytosis. refers specifically to solute pumping.

CELL DIVISION

or the mitotic phase (in yellow), during which it divides into two cells

resting membrane potential

osmosithe electrical charge of a neuron when it is not active

The integral membrane proteins

play a very strategic role in selectivity. They are inserted into the lipid bilayer, and many go all the way through it from inside to outside. These are called transmembrane proteins. Most of the integral membrane proteins play a role in transport. They can serve as pores or channels, as carriers, receptors, or as enzymes. Peripheral membrane proteins attach loosely to the integral membrane proteins on both the inside and outside of the plasma membrane. The glycoproteins on the extracellular surface help to form a "glycocalyx" important for cell reinforcement of cell structure, adhesion, recognition, and other functions. The proteins on the intracellular surface are part of a "cytoskeleton" that helps give support to the cells among other functions.

Caveolae

pouchlike infoldings that sequester bits of extracellular fluid containing a high concentration of Ca2+ close to the membrane; when calcium channels open here Ca2+ influx occurs rapidly

permeability of the cells

property that determine what substances can enter or leave the cytoplasm of the cell. 2 types: freely and impermeable

histone proteins

provide the means to pack DNA in a compact, orderly way, and they play a role in gene regulation.

cell-cell recognition

some glycoproteins serve as identification tags that are specifically recognized by other cells

Replication

still being studied but appears to involve a sequence of events Uncoiling: Enzymes unwind the DNA molecule, forming a replication bubble. Separation: The two DNA strands separate as the hydrogen bonds between base pairs are broken. The point at which the strands unzip is known as the replication fork. Assembly: With the old (parental) strands acting as templates, the enzyme DNA polymerase positions complementary free nucleotides along the template strands, forming two new strands. Because the polymerases work in one direction only, the two new strands, called leading and lagging strands, are synthesized in opposite directions. Two new (daughter) DNA molecules result from one parental DNA molecule. Since each new molecule consists of one old and one new nucleotide strand, this mechanism is known as semiconservative replication. Restoration: Ligase enzymes (not illustrated in Figure 3.29) splice short segments of DNA together, restoring the double helix structure.

CELLULAR SECRETIONS

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

Tonicity

the ability of a surrounding solution to cause a cell to gain or lose water

matrix

the gel-like substance within the mitochondrion.

The cytoplasm

the intracellular fluid packed with organelles, small structures that perform specific cell functions.

phosphorylated

the recipient of the phosphate group

Chanel mediated facilitated diffusion

through a channel protein. mostly ions selected on basis of size and charge

secretory vesicle

vesicle fusing with the plasma membrane, releasing materials to be secreted from the cell protein-coated membranous sac

Carrier-mediated facilitated diffusion

via protein carrier specific for one chemical; binding of substrate causes transport protein to change shape

Cytosol

viscous, semitransparent fluid substance of cytoplasm in which other elements are suspended

Receptors for signal transduction

• A membrane protein exposed to the outside of the cell may have a binding site that fits the shape of a specific chemical messenger, such as a hormone. • When bound, the chemical messenger may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell.