A&P 3: Cells - The Living Units Flashcards
Cells
structural units of all living things
Cell Theory
4 concepts collectively called this; (1) a cell is the basic structural and functional unit of living organisms; define cell properties –> define properties of life (2) activity of an organism depends on both the individual and the collective activities of its cells (3) according to the principle of complementarity of structure and function, the biochemical activities of cells are dictated by their shapes or forms & by the relative number of their specific subcellular structures, & (4) continuity of life from one generation to another has a cellular basis
Generalized (composite) cell
3 main parts of a human cell - plasma membrane, cytoplasm, & nucleus
Plasma membrane
flexible structure that defines the extent of a cell, thereby separating 2 of the body’s major fluid compartments (intracellular & extracellular fluids)
Fluid Mosaic Model
model depicting the plasma membrane as an exceedingly thin (7-10nm) structure composed of a bilayer of lipid molecules with protein molecules plugged into or dispersed in it; constantly changing
Hydrophilic
each lollipop-shaped phospholipid molecule has a polar head that is charged and loves water
Hydrophobic
each phospholipid molecule has an uncharged, nonpolar tail that is made of 2 fatty acid chains and hates water
Glycolipids
lipids with attached sugar groups found only on the outer plasma membrane surface; account for 5% of total membrane lipids
Integral proteins
proteins that are firmly inserted into the lipid bilayer; most are transmembrane proteins (span the entire membrane and protrude on both sides)
Peripheral proteins
proteins not embedded in the lipid bilayer; attach loosely to integral proteins and are easily removed without disrupting the membrane; include a network of filaments that helps support the membrane from its cytoplasmic side; some are enzymes, others are motor proteins involved in mechanical functions, others link cells together
Lipid rafts
20% of the outer membrane surface; dynamic assemblies of saturated phospholipids (which pack together tightly) associated with unique lipids called sphingolipids and lots of cholesterol; more stable, less fluid than the membrane; can include/exclude specific proteins; assumed to be concentrating platforms for cell signaling, membrane invagination, or other functions
Glycocalyx
fuzzy, sticky, carbohydrate-rich area at the cell surface; “sugar-coating”; provides highly specific biological markers by which approaching cells recognize each other
Tight junction
series of integral protein molecules in the plasma membranes of adjacent cells fuse together, forming an impermeable junction that encircles the cell; help prevent molecules from passing through the extracellular space between adjacent cells
Desmosomes
anchoring junctions; mechanical coupling scattered like rivets along the sides of abutting cells to prevent their separation; “binding bodies”; abundant in tissues subjected to great mechanical stress (skin/heart muscle)
Gap junction (nexus)
communicating junction between adjacent cells; cells connected by hollow cylinders (connexons) of transmembrane proteins; ions, simple sugars, and other small molecules can pass through; present in electrically excitable tissues (heart, smooth muscle)
Interstitial fluid
extracellular fluid derived from blood
Selectively (differentially) permeable
describes the plasma membrane; allows some substances to pass while excluding others
Passive processes
substances cross the membrane without any energy input from the cell
Active processes
the cell provides the metabolic energy (usually ATP) needed to move substances across the membrane
Diffusion
tendency of molecules/ions to move from an area of higher concentration to an area where they are in lower concentration
Concentration gradient
difference in the concentration of a particular substance between 2 different areas
Simple diffusion
nonpolar and lipid-soluble substances diffuse directly through the lipid bilayer (oxygen, CO2, and fat-soluble vitamins)
Facilitated diffusion
movement through the plasma membrane by a passive process in which the transported substance either binds to protein carriers in the membrane and is ferried across or moves through water-filled protein channels
Carriers
transmembrane integral proteins that are specific for transporting certain polar molecules or classes of molecules (sugars, amino acids) that are too large to pass through membrane channels
Channels
transmembrane proteins that transport substances, usually ions or water, through aqueous ____ from 1 side of the membrane to the other; selective due to pore size and the charges of the amino acids lining it; leakage or gated
Osmosis
diffusion of a solvent, such as water, through a selectively permeable membrane
Aquaporins (AQPs)
water moves freely and reversibly through water-specific channels constructed by these transmembrane proteins which allow single-file diffusion of water molecules; particularly abundant in red blood cells and in cells involved in water balance (kidney tubule cells)
Osmolarity
total concentration of all solute particles in a solution
Hydrostatic pressure
back pressure exerted by water against the membrane
Osmotic pressure
tendency of water to move into the cell by osmosis
Tonicity
ability of a solution to change the shape or tone of cells by altering the cells’ internal water volume; “tension”
Isotonic solutions
solutions with the same tonicity; same concentrations of nonpenetrating solutes as those found in cells (0.9% saline or 5% glucose)
Hypertonic solutions
have a higher concentration of nonpenetrating solutes than seen in the cell; cells crenate/shrink when immersed in these solutions
Hypotonic solutions
more dilute (contain a lower concentration of nonpenetrating solutes) than cells; cells placed in these solutions lyse/burst
Active transport
requires carrier proteins that combine specifically and reversibly with the transported substances; always follows the concentration gradient (b/c driving force is kinetic energy)
Solute pumps
active transporters; move solutes (most importantly, ions) uphill/against gradient; cells must expend energy
Symport system
2 transported substances move in the same direction
Antiport system
transported substances cross the membrane in opposite directions
Primary active transport
hydrolysis of ATP results in the phosphorylation of the transport protein; causes the protein to change its shape in such a manner that it pumps the bound solute across the membrane
Sodium-potassium pump
carrier (pump) is an enzyme called NA+ -K+ ATPase; operates almost continuously as an antiporter; simultaneously drives Na+ out of the cell against a steep concentration gradient and pumps K+ back in
Electrochemical gradients
ions diffuse according to these, which recognize the effect of both electrical and concentration (chemical) forces
Secondary active transport
a single ATP-powered pump can indirectly drive __ ___ ___ of several other solutes
Vesicular transport
fluids containing large particles and macromolecules are transported across cellular membranes inside membranous sacs called vesicles
Clathrin
coating found on the cytoplasmic face of the plasma membrane pit is most often this bristlelike protein
Phagocytosis
“cell eating”; the cell engulfs some relatively large or solid material, such as a clump of bacteria, cell debris, or inanimate particles (asbestos fibers, glass)
Phagosome
endocytic vesicle; “eaten body”
Amoeboid motion
“changing shape”; flowing of cytoplasm into temporary extensions which allows one to creep along
Pinocytosis
“cell drinking”; AKA fluid-phase endocytosis; a bit of infolding plasma membrane surrounds a very small volume of extracellular fluid containing dissolved molecules
Receptor-mediated endocytosis
main mechanism for the specific endocytosis and transcytosis of most macromolecules by body cells; allows cells to concentrate material that is present only in small amounts in the extracellular fluid
Caveolae
“little caves”; tubular or flask-shaped inpocketings of the plasma membrane seen in many cell types involved in a unique kind of receptor-mediated endocytosis; capture specific molecules (folic acid, tetanus toxin) from the extracellular fluid in coated vesicles and participate in some forms of transcytosis; smaller than clathrin-coated vesicles; also, their cage-like protein coat is thinner; closely associated with lipid rafts
Exocytosis
vesicular transport processes that eject substances from the cell interior into the extracellular fluid accounts for hormone secretion, neurotransmitter release, mucus secretion, and in some cases, ejection of wastes
Membrane potential
voltage across the membrane
Resting membrane potential
-50 to -100 millivolts (mV)
Polarized
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
Cell Adhesion Molecules (CAMs)
thousands found on almost every cell in the body; play key roles in embryonic development and wound repair & in immunity; these sticky glycoproteins (cadherins and integrins) act as molecular Velcro that cells use to anchor themselves to molecules and to each other, arms that migrating cells use to haul themselves past one another, SOS signals that rally WBC’s to a nearby infected/injured area, mechanical sensors that respond to changes in tension/fluid movement at the cell surface, & transmitters of intracellular signals that direct cell migration, proliferation, and specialization
Membrane receptors
huge, diverse group of integral proteins and glycoproteins that serve as binding sites
Ligands
chemicals that bind specifically to plasma membrane receptors; include most neurotransmitters, hormones, and paracrines
Paracrines
chemicals that act locally and are rapidly destroyed
G protein-linked receptors
exert their effect indirectly through a G protein
G protein
a regulatory molecule that acts as a middleman or relay to activate or inactivate a membrane-bound enzyme or ion channel
Second messengers
intracellular chemical signals which connect plasma membrane events to the internal metabolic machinery of the cell
Cyclic AMP
important 2nd messenger; typically activates protein kinase enzymes, which transfer phosphate groups from ATP to other proteins
Cytoplasm
“cell-forming material”; the cellular material between the plasma membrane and the nucleus; site of most cellular activities
Cytosol
viscous, semitransparent fluid in which the other cytoplasmic elements are suspended; complex mixture with properties of both a colloid and a true solution
Organelles
metabolic machinery of the cell; each type carries out a specific function for the cell
Inclusions
chemical substances that may or may not be present, depending on cell type; examples - stored nutrients (glycogen granules in liver/muscle cells), lipid droplets in fat cells, pigment (melanin) granules in certain skin/hair cells, and crystals
Mitochondria
threadlike or lozenge-shaped membranous organelles; squirm/elongate/change shape almost continuously; power plants of a cell, providing most of its ATP supply
Cristae
shelflike inner membrane of a mitochondrion
Ribosomes
small, dark-staining granules composed of proteins and a variety of RNAs called ribosomal RNAs; each has 2 globular subunits that fit together like the body/cap of an acorn; sites of protein synthesis; some float freely in cytoplasm, others are attached to ER
Endoplasmic reticulum
extensive system of interconnected tubes and parallel membranes enclosing fluid-filled cavities (cisterns)
Cisterns
fluid-filled cavities of the ER
Rough ER
externally studded with ribosomes, which manufacture proteins secreted from cells; abundant and well developed in most secretory cells, antibody-producing plasma cells, and liver cells (produce most blood proteins); = cell’s membrane factory, where integral proteins and phospholipids that form part of all cellular membranes are manufactured
Smooth ER
continuous with the rough ER, consists of tubules arranged in a looping network; no role in protein synthesis; metabolize lipids, synthesize cholesterol, synthesize lipid components of lipoproteins (in liver cells), synthesize steroid-based hormones; absorb, synthesize, and transport fats, detoxify drugs, certain pesticides, and cancer-causing chemicals (in livers/kidneys), break down stored glycogen to free form glucose (esp in liver cells)
Golgi Apparatus
stacked, flattened membranous sacs, shaped like hollow dinner plates, associated with swarms of tiny membranous vesicles; principle traffic director for cellular proteins; modifies, concentrates, and packages the proteins/lipids made at the rough ER and destined for export from the cell
Secretory vesicles (granules)
vesicles containing proteins destined for export pinch off from the trans face (shipping side of the Golgi Apparatus) as these, which migrate to the plasma membrane and discharge their contents from the cell
Peroxisomes
spherical membranous sacs containing a variety of powerful enzymes (most important = oxidases, catalases); especially numerous in liver/kidney cells, which are very active in detoxification
Free radicals
highly reactive chemicals with unpaired electrons that can scramble the structure of biological molecules
Lysosomes
“disintegrator bodies”; spherical membranous organelles containing activated digestive enzymes; AKA acid hydrolases
Autolysis
a lysosome digesting itself; basis for desirable destruction of cells
Endomembrane system
system of organelles that work together mainly to (1) produce, degrade, store, and export biological molecules, (2) degrade potentially harmful substances; includes ER, Golgi apparatus, secretory vesicles, lysosomes, & the nuclear membrane
Cytoskeleton
“cell skeleton”; elaborate network of rods running through the cytosol and hundreds of accessory proteins that link these rods to other cell structures; provides machinery to generate various cell movements; includes microfilaments, intermediate filaments, and microtubules
Microfilaments
thinnest elements of the cytoskeleton; semiflexible strands of the protein actin (“ray”); involved in cell motility or changes in cell shape
Intermediate filaments
tough, insoluble protein fibers that resemble woven ropes; made of twisted units of tetramer (4) fibrils, they have a diameter between microfilaments and microtubules; most stable & permanent of the cytoskeletal elements; high tensile strength; attach to desmosomes; main job: act as internal guy-wires to resist pulling forces exerted on the cell
Microtubules
largest diameter; hollow tubes of spherical protein subunits called tubulins; most radiate from a small region of cytoplasm near the nucleus called the centrosome (cell center); stiff, bendable; determines overall shape of the cell and distribution of cellular organelles
Motor proteins
tiny protein machines (kinesins, dyneins, etc) continually move and reposition the organelles along the microtubules
Centrosome
Cell center; acts as a microtubule organizing center; organizes the mitotic spindle during cell division
Centrioles
small, barrel-shaped organelles oriented at right angles to each other; made of 9 triplets of microtubules; also form the bases of cilia and flagella
Cilia
“eyelashes”; whiplike, motile cellular extensions that occur, typically in large numbers, on the exposed surfaces of certain cells; move substances in 1 direction across cell surfaces
Flagella
projections formed by centrioles; substantially longer than cilia; only cell with this in human body is sperm; propels itself
Basal bodies
centrioles forming the bases of cilia and flagella
Microvilli
“little shaggy hairs”; minute, fingerlike extensions of the plasma membrane that project from an exposed cell surface; increase the plasma membrane surface area tremendously; most often found on the surface of absorptive cells (intestinal/kidney tubule cells); have a core of bundled actin filaments that extend into the terminal web of the cytoskeleton
Nucleus
control center of the cell; contains genes; “pit, kernel”; contains instructions needed to build nearly all the body’s proteins; dictates the kinds/amounts of proteins to be synthesized at any one time in response to signals acting on the cell
Multinucleate
having many nuclei
Anucleate
cells without nuclei; can’t reproduce; live in bloodstream for 3-4 months before they deteriorate
Nuclear envelope
nucleus bounded by this double-membrane barrier separated by a fluid-filled space; outer part continuous with rough ER, studded with ribosomes; inner lined by nuclear lamina (network of lamins = rod-shaped proteins that assemble to form intermediate filaments) that maintain the shape of the nucleus and acts as a scaffold to organize DNA
Nuclear pores
nuclear envelope is punctuated by these at various points; regulates entry/exit of molecules and large particles into/out of the nucleus
Nucleoli
dark-staining spherical bodies found within the nucleus where ribosomal subunits are assembled; not membrane bounded; 1-2 per nucleus typically, but there may be more; usually large in growing cells that are making large amounts of tissue proteins
Chromatin
system of bumpy threads weaving through the nucleoplasm; composed of 30% DNA, 60% globular histone proteins, & 10% RNA chains (newly formed or formin)
Histone proteins
globular proteins which package and regulate the DNA within chromatin
Nucleosomes
fundamental units of chromatin; consist of flattened disc-shaped cores or clusters of 8 histone proteins connected like beads on a string by a DNA molecule
Chromosomes
short, barlike bodies; “colored bodies”; compact, prevent chromatin from tangling/breaking; chromatin coils/condense into these when a cell is preparing to divide
Cell cycle
series of changes a cell goes through from the time it is formed until it reproduces
Interphase
period from cell formation to cell division; metabolic/growth phase; sometimes called resting phase
G1 (gap 1 subphase)
cell is metabolically active, synthesizing proteins rapidly, growing vigorously; most variable phase of interphase in terms of length; virtually no activities directly related to cell division occur; as this phase ends, centrioles start to replicate in preparation for cell division
G0 phase
cells that permanently cease dividing
S phase
DNA is replicated, ensuring 2 future cells being created will receive identical copies of the genetic material; new histones made, assembled into chromatin; must be done right or there is no correct mitotic phase
G2 (gap 2 subphase)
brief, final phase of interphase; enzymes/proteins needed for division are synthesized, moved to their proper sites
RNA primer
DNA can’t start a new strand from scratch, they can only add nucleotides to a strand that already exists; this problem is solved by formation of a short, complementary ___ ______, about 10 bases long, by a primase enzyme
DNA polymerase
positions complementary nucleotides along the template strand and then covalently links them together; works in only 1 direction
Leading strand
synthesized continuously once primed, following the movement of the replication fork
Lagging strand
constructed in segments in the opposite direction; requires that a primer initiate replication of each segment
Semiconservative replication
because each new molecule consists of 1 old and 1 new nucleotide strand, this mechanism of DNA replication is called this
M (mitotic) phase
mitosis + cytokinesis
Mitosis
division of the nucleus; lasts an hour or less in human cells
Cytokinesis
division of the cytoplasm
Mitotic phases
prophase, metaphase, anaphase, telophase
Cleavage furrow
contractile ring of actin filaments draws the plasma membrane inward to form this over the center of the cell
Cyclins
regulatory proteins whose levels rise and fall during each cell cycle
Cdks (cyclin-dependent kinases)
present in a constant concentration in the cell and are activated by binding to particular cyclins
MPF (M-phase promoting factor)
threshold amount of a protein complex required to give the okay signal to pass the G2 checkpoint and enter M phase; later inactivated
Gene
segment of a DNA molecule that carries instructions for creating one polypeptide chain
Triplet
each sequence of 3 nucleotide bases that specifies a particular amino acid
Exons
amino-acid specifying informational sequences; often separated by introns
Introns
noncoding, often repetitive segments that range from 60-100,000 nucleotides; reservoir of ready-to-use DNA segments for genome evolution, as well as a rich source of small RNA molecules
mRNA
messenger RNA; relatively long nucleotide strands resembling “half-DNA” molecules; carries a transcript of the code to the cytoplasm, where protein synthesis occurs
rRNA
ribosomal RNA; along with proteins, forms the ribosomes, which consist of 2 subunits (1 large, 1 small); subunits combine to form functional ribosomes
tRNA
transfer RNA; small, roughly L-shaped molecules that ferry amino acids to the ribosomes; decode mRNA’s message for amino acid sequence in the polypeptide to be built
Transcription
transfers info from a DNA base sequence to the complementary base sequence of an mRNA molecule; done in the nucleus
Promoter
special DNA sequence that contains the start point (beginning of the gene to be transcribed); specifies where mRNA synthesis starts and which DNA strand will be the template strand
RNA Polymerase
enzyme that oversees the synthesis of mRNA correctly at the promoter
DNA-RNA hybrid
at any given moment during transcription, 16-18 base pairs of DNA are unwound and the most recently made mRNA is still hydrogen-bonded to the template DNA; this small region is up to 12 base pairs long
Termination Signal
when the polymerase reaches this special base sequence, transcription ends and the newly formed mRNA separates from the DNA template
Translation
step of protein synthesis in which the language of nucleic acids (base sequence) is translated into the language of proteins (amino acid sequence)
Genetic code
rules by which the base sequence of a gene is translated into an amino acid sequence
Codon
for each triplet, the corresponding 3-base sequence on mRNA is called this; = stop signs that call for termination of polypeptide synthesis
Anticodon
3-base sequence complementary to the mRNA codon calling for the amino acid carried by a particular tRNA; form hydrogen bonds with complementary codons
Initiator tRNA
small ribosomal subunit binds to a special methionine-carrying _____ ____ then to the new mRNA to be decoded
Signal sequence
when a short leader peptide called an ER ___ ____ is present in a protein being synthesized, the associated ribosome attaches to the membrane of the rough ER; cargo = ribosome & mRNA, guided to appropriate receptor sites on the ER membrane by a signal recognition particle
Antisense RNAs
made on the DNA strand complementary to the template strand for mRNA; can intercept and bind to the protein-coding mRNA strand and prevent it from being translated into protein
MicroRNAs
small RNAs that can use RNA interference machinery to interfere with and suppress mRNAs made by certain exons, thus effectively silencing them
Riboswitches
folded RNAs that code, like mRNA, for a particular protein; has a special region that acts like a switch to turn protein synthesis on or off in response to metabolic changes in their immediate environment
Autophagy
“self-eating”; sweeps up bits of cytoplasm and excess organelles into double-membrane vesicles called autophagosomes; delivered to lysosomes for digestion
Ubiquitins
proteins that mark doomed proteins for attack (proteolysis) by attaching to them in an ATP-dependent reaction
Proteasomes
giant waste-disposal complexes composed of protein-digesting enzymes that helps recycle ubiquitins
Extracellular materials
any substances contributing to body mass found outside cells (body fluids, cellular secretions, extracellular matrix)
Cell differentiation
development of specific and distinctive features in cells
Apoptosis
programmed cell death
Hyperplasia
accelerated growth
Atrophy
decrease in the size of an organ or body tissue; can result from loss of normal stimulation or from diseases like muscular dystrophy
Telomeres
nonsensical strings of nucleotides that cap the ends of chromosomes and provide protection from fraying, fusing with other chromosomes, inappropriate repair, and losing important genetic information
