Anatomy Lab Module 2: Cells and Chemistry

Centrosome

- Located: perinuclear cytoplasm (i.e., near nuclease) - Description: Includes pair of centrioles arranged at right angles to one another; also includes centrosome matrix (pericentriolar material), whose texture is different from surrounding cytoplasm - Function: Assists in formation and organization of microtubules; responsible for spindle formation during mitosis - AKA microtubule oranizing center (MTOC) - Pair of centiroles also known as diplosome

Microvillus

- Location: -- Apical surface of some epithelia -- Most developed on absorptive cells in small intestine and kidney proximal convoluted tubule - Description: -- Non-motile, finger-like projection from cell surface (0.1 µm in diameter; 1-2 µm in length) -- Core comprised of 25-30 microfilaments (i.e., actin filaments) -- Actin filament core anchored to terminal web (a complex of micro- and intermediate filaments) located immediately beneath apical plasma membrane -- Visible as "brush border" in light microscope; individual microvilli distinguished only in electron microscope - Function: -- Increase cell surface area -- Facilitate transport and absorption (e.g., nutrients) across membrane - Comment: -- Plural is microvilli -- Microvilli have actin core, lack a basal body, and are not motile; cilia and flagella have microtubule core and are motile -- Stereocilia are long microvilli (not cilia!) found only on epithelium lining epididymis and on cochlear hair cells -- Villi are finger-like protrusions of lamina propria (e.g., in small intestine) covered with microvilli -- Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Inner leaflet of lipid bilayer

- Location: Plasma membrane - Description: -- Sugar-containing membrane protein; specifically, membrane protein conjugated with (i.e., covalently bound to) carbohydrate molecules -- Accounts for >90% of membrane molecules conjugated with carbohydrate molecules - Function: -- Cell-cell interactions (e.g., immune reaction, hormone-cell, sperm-oocyte, developmental interactions) - Comment: -- Carbohydrate molecules attached to glycoproteins and glycolipids contribute to glycocalyx

Cilium

- Location: Apical surface of some epithelia; evident in epithelia lining respiratory system, uterine (Fallopian tube, and ependymal cells) - Motile, hair-like projection from apical cell surface (0.2 µm in diameter; 7-10 µm in length) - Core comprised of a complex of parallel microtubules called the axoneme - Axoneme arises from a basal body (equivalent to centriole) in cytoplasm - Oscillations (bending to-and-fro) of cilia move substances (e.g., mucus, cells, and debris) over cell surface - Ciliary motion (bending) created by axoneme microtubules sliding past one another - Plural is cilia - Axoneme has 9+2 organization of longitudinally arranged microtubules: two central microtubules ("singlets") course through center of axoneme; surrounded by nine microtubule pairs ("doublets") - Microvilli have actin core and are not motile; cilia and flagella have microtubule core and are motile - Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Secretory vesicle of Golgi apparatus

- Location: Between trans-face of Golgi apparatus and plasma membrane - Description: -- Membrane-bound organelle - Function: -- Carries protein products from Golgi apparatus to cell surface for exocytosis

Plasma membrane

- Location: Cell surface - Description: -- Phospholipid bilayer that contains cholesterol and proteins -- Outer surface has attached coat of carbohydrates known as glycocalyx - Function: -- Encloses cell contents -- Communication (receptors) -- Intercellular connections -- Regulates movement of materials into and out of cell - AKA -- Plasmalemma or cell membrane -- Phospholipid bilayer also known as "unit membrane" - Comment: -- Membranes of membrane-bound organelles have structure similar to plasma membrane

Microfilament

- Location: Cortex of cell (terminal web, immediately under plasma membrane); Microvilli and stereocilia (core); Muscle cells - Description: -- Cytoskeletal filaments (6 nm in diameter) -- Composed of actin monomers (G-actin): two actin chains coil around each other to form a thin filament (known as F-actin) - Function: -- Mechanical strength of cell (contributes to terminal web) -- Forms core of microvilli -- Interacts with myosin to produce muscle contraction -- During mitosis, anchors centrosomes at opposite poles of cell - AKA thin filament or actin filament - Comment: -- Terminal web is a complex of micro- and intermediate filaments located in cortex of cell (i.e., immediately subjacent to plasma membrane) -- Cytoskeleton composed of three types of filaments: microfilaments, intermediate filaments, and microtubules -- Nanometer (nm) is 1/1,000,000th of a millimeter

Smooth endopolasmid reticulum (SER)

- Location: Cytoplasm - Description: -- Membrane-bound organelle -- Subdivision of endoplasmic reticulum (ER), an interconnected system of tubules and flattened sacs (cisternae) -- Lacks attached ribosomes -- Continuous with rough endoplasmic reticulum (RER) -- Special name in skeletal muscle: sarcoplasmic reticulum - Function: -- Synthesizes lipids (especially membrane phospholipids) -- Detoxifies drugs and alcohol -- Metabolizes carbohydrates -- Stores calcium (i.e., in sarcoplasmic reticulum) - Comment: -- ER, which comprises approximately half the total membrane of the cell, has two subdivisions: (1) RER, which has attached ribosomes, and (2) SER, which lacks attached ribosomes

Peroxisome

- Location: Cytoplasm - Description: -- Membrane-bound organelle (<1.0 µm in diameter) -- Contains oxidative enzymes (e.g., catalase) -- Has dense core, called a nucleoid, composed of urate oxidase - Function: -- Formation and breakdown of intracellular hydrogen peroxide (which can be used to oxidize alcohol, formaldehyde, and phenols) -- Breakdown of fatty acids -- Involved in bile acid synthesis in liver - Comment: -- Peroxisomes and lysosomes are structurally similar but contain different enzymes: peroxisomes contain oxidases whereas lysosomes contain acidic hydrolyases -- Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Mitochrondrian

- Location: Cytoplasm - Description: -- Rod-shaped, membrane-bound organelle (0.5-1.0 µm in diameter; up to 7 µm in length) -- Has double membrane (i.e., two lipid bilayers): outer membrane is smooth, inner membrane has complex folds called cristae -- Intermembrane space between outer and inner membrane -- Matrix space enclosed by inner membrane - Function: -- "Powerhouse" of cell (most cells contain numerous mitochondria) -- Synthesizes adenosine triphosphate (ATP), which provides chemical energy for cellular respiration (through oxidative phosphorylation) - Comment: -- Contains mitochondrial DNA that codes for 13 mitochondrial proteins, 16S and 12S rRNA, and 22 tRNAs -- Origin of mitochondria as an organelle: thought to be prokaryotic organisms (like bacteria) that formed symbiotic relationship with anaerobic eukaryotic cells: "mitochondria" received protection and nutrients, the cell received a chemical energy source -- Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Rough Endoplasmic Reticulum (RER)

- Location: Cytoplasm (perinuclear); between nucleus and Golgi apparatus - Description: -- Membrane-bound organelle -- Subdivision of endoplasmic reticulum (ER), an interconnected system of tubules and flattened sacs (cisternae) -- Has attached ribosomes -- Continuous with smooth endoplasmic reticulum (SER) - Function: -- Synthesizes protein for secretion, insertion into plasma membrane, and lysosomal enzymes and other proteins packaged in vesicles - Comment: -- ER, which comprises approximately half the total membrane of the cell, has two subdivisions: (1) RER, which has attached ribosomes, and (2) SER, which lacks attached ribosomes

Outer leaflet of lipid bilayer

- Location: Extracellular (outer) side of lipid bilayer - Description: -- Outer part of lipid bilayer -- Comprised of polar (hydrophilic) heads and non-polar (hydrophobic) fatty acid tails - Function: -- Interacts with extracellular environment - Comment: -- Plasma membrane (also known as plasmalemma) encloses cell; membranes of membrane-bound organelles, sometimes called "cell membranes" have structure similar to plasma membrane -- Hydrophilic refers to an affinity for water; hydrophobic refers to a lack of affinity for water

Membrane channel

- Location: Plasma membrane - Description: Transmembrane protein (a subclass of integral membrane proteins) that forms narrow pore - Function: -- Permits selective passage of water and hydrophilic solutes (e.g., inorganic ions) -- Some channels constantly open -- Other channels open and close with specific stimulus: ligand-gated channels respond to chemical messengers; voltage-gated channels respond to changes in electrical potential of membrane; mechanically regulated channels respond to membrane distension - Comment: -- Hydrophilic refers to an affinity for water; hydrophobic refers to a lack of affinity for water

Nucleus

- Location: Generally centrally located in cell; sometimes eccentric (i.e., off to one side) - Description: -- Largest organelle (5-10 µm in diameter) -- Spherical or ovoid structure -- Nuclear envelope has double membrane (i.e., two lipid bilayers) -- Contains cellular DNA and nucleolus - Function: -- DNA replication -- DNA transcription into mRNA -- Ribosomal RNA synthesis and ribosome subunit assembly (in nucleolus) - Comment: -- Cells that lack a nucleus (e.g., red blood cells) termed anucleate; cells that have multiple nuclei (e.g., skeletal muscle cells) termed multinucleate -- Staining of DNA with basic histological dyes like hematoxylin depends on transcriptional activity: DNA undergoing active transcription, called euchromatin, stains lightly because it is less folded and, therefore, less dense; transcriptionally inactive DNA, or heterochromatin, is tightly packed and condensed and, therefore, stains more darkly -- Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter

Polar heads of lipid bilayer

- Location: Hydrophilic region of lipid bilayer of plasma membrane - Description: -- Hydrophilic part of membrane phospholipids -- Comprised of a head group (choline or charged amino acid, e.g., serine or ethanolamine), phosphate, and glycerol - Function: -- Membrane surface charge -- Intracellular signaling - Comment: -- Plasma membrane phospholipid molecules are amphipathic (i.e., polar lipids): they have a hydrophilic (polar) head and two hydrophobic (non-polar) tails (usually comprised of fatty acids) -- Hydrophilic refers to an affinity for water; hydrophobic refers to a lack of affinity for water

Cholesterol molecules in lipid bilayer

- Location: Hydrophobic region of lipid bilayer of plasma membrane - Description: -- Steroid molecules (a type of lipid) -- Accounts for approximately 20% of plasma membrane lipids - Function: -- Strengthens membrane and stabilizes it at extreme temperatures -- Prevent over-dense packing of fatty acid tails by filling gaps between fatty acid tails - Comment: -- Hydrophilic refers to an affinity for water; hydrophobic refers to a lack of affinity for water

Fatty acid tails of lipid bilayer

- Location: Hydrophobic region of lipid bilayer of plasma membrane - Description: -- Non-polar (hydrophobic) tails of phospholipid molecule -- Comprised of two long-chain fatty acids (14-24 carbon atoms in length) -- In most mammalian cells, one fatty acid chain is saturated, the other is unsaturated - Function: -- Length and saturation of fatty acid tails influences fluidity and flexibility of membrane (presence of unsaturated fatty acids increases fluidity and flexibility) - Comment: -- Hydrophilic refers to an affinity for water; hydrophobic refers to a lack of affinity for water -- Unsaturated means fatty acid has one or more cis double bonds, which introduce "kinks" into the fatty acid and prevent close packing of the hydrophobic tails

Membrane channel pore

- Location: Membrane channel protein - Description: Narrow pore - Function: Permits selective passage of water and hydrophilic solutes (e.g., inorganic ions) Comment: Hydrophilic refers to an affinity for water; hydrophobic refers to a lack of affinity for water

Nuclear pore

- Location: Nuclear envelope - Description: -- Opening in nuclear envelope (30-100 nm in diameter) -- Formed by ring of proteins - Function: -- Allows for, and regulates, passage of materials between cytoplasm and nucleus - Comment: -- Nanometer (nm) is 1/1,000,000th of a millimeter

Nucleolus

- Location: Nucleus - Description: -- Dark staining, granular region of nucleus (1-3 µm in diameter) -- Usually spherical in shape -- 1-3 nucleoli present depending on synthetic activity of cell - Function: -- Ribosomal RNA synthesis and ribosome assembly - Comment: -- Stains darkly with basic histological dyes like hematoxylin -- Micrometer (µm) is 1/1,000 of a millimeter

Glycocalyx

- Location: Outer surface of plasma membrane - Description: -- "Fuzzy coat" on extracellular (outer) surface of plasma membrane -- Comprised of carbohydrates attached to membrane glycolipids and glycoproteins - Function: -- Protection against mechanical and chemical damage -- Immunity to infection -- Defense against cancer -- Transplant compatibility -- Cell adhesion -- Embryonic development - Also known as: -- Cell "coat" - Comment: -- Glycocalyx visible in light microscope using histological stains (e.g., ruthenium red) -- Greek: glyco = sweet (denoting sugars); kalyx = husk or shel

Glycolipid

- Location: Outer surface of plasma membrane - Description: -- Sugar-containing lipid molecule; specifically, membrane lipids conjugated with (covalently bound to) carbohydrate molecules -- May account for 5% of lipid molecules in outer membrane layer - Function: -- Protect membrane from harsh extracelullar conditions (e.g., low pH and degradative enzymes) -- Contribute to electrical properties of cell -- Cell-cell recognition -- Binding of cell to extracellular matrix and other cells - Comment: -- Carbohydrate molecules attached to glycoproteins and glycolipids contribute to glycocalyx

Peripheral membrane protein

- Location: Plasma membrane - Description: -- Protein molecule associated with either intracellular (cytoplasmic) or extracellular surface of membrane and does not extend into lipid bilayer -- Usually associated with transmembrane protein and anchored to cytoskeleton (if on intracellular surface) - Function: -- Cell signaling -- Regulation of transmembrane proteins (e.g., ion channels) -- Enzyme activity

Integral membrane of protein

- Location: Plasma membrane - Description: -- Protein that is partially or completely embedded within plasma membrane -- Transmembrane proteins, a subclass of integral membrane proteins, traverse both sides of lipid bilayer -- Hydrophobic regions of integral membrane protein interact with interior (i.e., hydrophobic region) of lipid bilayer -- Hydrophilic regions of integral membrane protein exposed to hydrophilic regions on either side of lipid bilayer - Function: -- Receptors for specific molecules -- Enzyme activity Membrane channel (for water or hydrophilic solutes) -- Cell-identity marker -- Cell adhesion - AKA Intrinsic membrane protein - Comment: -- Integral membrane protein distinguished from peripheral membrane protein (attached to inner or outer surface by weak electrostatic forces) -- Hydrophilic refers to an affinity for water; hydrophobic refers to a lack of affinity for water

Glycoprotein

- Location: Plasma membrane - Description: -- Sugar-containing membrane protein; specifically, membrane protein conjugated with (i.e., covalently bound to) carbohydrate molecules -- Accounts for >90% of membrane molecules conjugated with carbohydrate molecules - Function: -- Cell-cell interactions (e.g., immune reaction, hormone-cell, sperm-oocyte, developmental interactions) - Comment: -- Carbohydrate molecules attached to glycoproteins and glycolipids contribute to glycocalyx

Lipid bilayer

- Location: Plasma membrane; Membrane-bound organelles (endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria, nucleus, and plasmids) - Description: -- 75% of lipids in plasma membrane are phospholipids -- Double layer of phospholipids with a polar (hydrophilic) head and two non-polar (hydrophobic) tails -- Polar (hydrophilic) head comprised of a head group (choline or charged amino acid, e.g., serine or ethanolamine), phosphate, and glycerol -- Non-polar tails comprised of fatty acids - Function: -- Forms semipermeable membrane around cell and membrane-bound organelles -- Separates aqueous intracellular and extracellular compartments -- Membrane surface charge - Comment: -- Lipid bilayer also known as "unit membrane" -- Plasma membrane (also known as plasmalemma) encloses cell; membranes of membrane-bound organelles, sometimes called "cell membranes" have structure similar to plasma membrane -- Hydrophilic refers to an affinity for water; hydrophobic refers to a lack of affinity for water

Microtubules

- Location: cytoplasm, cilia and flagella, centromere (in the centrosome) - Description: -- Cytoskeletal filament (25 nm in diameter) -- Composed of tubulin protein monomers that polymerize to form tubule - Function: -- Mechanical strength -- Organelle movement (e.g., microtubules act like railroad track) -- Chromosome movement (microtubules form spindle during cell division) - Comment: -- Cytoskeleton composed of three types of filaments: microfilaments, intermediate filaments, and microtubules -- Nanometer (nm) is 1/1,000,000th of a millimeter

Golgi apparatus

- Location: cytoplasm; adjacent to rough endoplasmic reticulum (RER) - Description: -- Membrane-bound organelle -- Series of flattened sacs (cisternae) -- Three subdivisions: (1) cis-face (closest to, and contiguous with RER), (2) intermediate face, and (3) trans-face (farthest from RER) - Function: -- Transport vesicles, containing newly synthesized proteins from RER, fuse with cis-face -- Modifies, packages, and sorts newly synthesized proteins -- Modified proteins packaged at trans-face into vesicles that become: lysosomes (contain hydrolytic enzymes), secretory vesicles (undergo exocytosis), or vesicles that add new plasma membrane - Comment: -- Golgi apparatus also called Golgi network or stack -- cis-face also known as receiving region -- trans-face also known as "transport" or "shipping" region

Intermediate filament

- Location: cytoplasm; nuclear envelope - Description: -- Cytoskeletal filaments (8-12 nm in diameter) -- More than 50 different intermediate filaments (IFs) in human cells, including: cytokeratins (epithelial cells), desmin (muscle), vimentin (mesodermal cells), neurofilaments and peripherins (neurons), glial fibrillary acidic protein (glial cells), and nuclear lamins (nuclear envelope) - Function: -- Maintain cell shape and rigidity -- Anchor organelles -- Structural support for nuclear envelope (nuclear lamins) -- Structural support for apical cytoplasm (terminal web, immediately subjacent to plasma membrane) -- Cytoplasmic IFs connected to plasma membrane at cell junctions (e.g., tonofilaments associated with desmosomes and hemidesmosomes) by IF-associated proteins - Comment: -- Epidermolysis bullosa simplex (EBS) a disorder associated with mutations in some keratin genes can result in blister formation in epidermis -- Cytoskeleton composed of three types of filaments: microfilaments, intermediate filaments, and microtubules -- Nanometer (nm) is 1/1,000,000th of a millimeter

Membrane-bound ribosome

- Location: outer aspect of rough endoplasmic reticulum (RER); outer aspect of outer nuclear envelope - Description: Ribosomes attached to membrane-bound organelles (i.e., outer side of RER and nuclear envelope) - Function: Membrane-bound ribosomes involved in translating protein destined for secretory vesicles, lysosomes, or insertion into membranes

Free ribosome

Location: • Cytoplasm Description: • Not attached to rough endoplasmic reticulum or outer aspect of nuclear envelope • Multiple, free ribosomes attached to mRNA are called polyribosomes Function: • Polyribosomes represent sites of cytoplasmic protein synthesis * Carries out protein synthesis for proteins to be used inside the cell.

Endocytic vesicle

Location: • Plasma membrane and cytoplasm Description: • Membrane-bound vesicle • Two types of endocytic vesicle: phagosome (>250 nm in diameter) and pinocytic vesicle (<150 nm in diameter) • Phagosome engulfs relatively large particles (e.g., bacteria, dust, cellular debris) • Pinocytic vesicle engulfs extracellular fluid; also used to recycle plasma membrane • Receptor-mediated endocytic vesicle, a specialized pinocytic vesicle, involved in uptake of specific molecules (e.g., low-density lipoprotein (LDL) receptors or insulin receptors regulate, respectively, uptake of LDL and insulin across endothelial Function: • Moves large particles, fluid, or molecules through plasma membrane and into cell Comments: • Endocytosis is process by which plasma membrane surrounds extracellular substances and internalizes (i.e., brings substance into cell) material within a membrane-bound vesicle • Nanometer (nm) is 1/1,000,000th of a millimeter

Lysosome

Location: cytoplasm Description: -- Membrane-bound organelle (0.3-0.8 µm in diameter) -- Contains acidic hydrolytic enzymes (which are mostly glycoproteins) -- Formation: (1) acidic hydrolytic enzymes synthesized in rough endoplasmic reticulum, (2) transported through Golgi apparatus, (3) packaged into vesicles released from trans-face of Golgi apparatus as (primary) lysosomes, and finally (4) fuse with vesicle containing material to be degraded to form secondary lysosome (also called a phagolysosome) -- Primary lysosomes: moderately electron-dense in transmission electron micrographs (TEMs) -- Secondary lysosomes (phagolysosomes): moderately electron-dense in TEM but contain extremely electron-dense material Function: Digests macromolecules, microorganisms, old or damaged organelles Comment: -- Lysosomes and peroxisomes structurally similar but contain different enzymes: lysosomes - acidic hydrolases; peroxisomes - oxidases -- Micrometer (µm), also known as a micron, is 1/1,000 of a millimeter