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CELL STRUCTURE

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Cytoplasm – located between plasma membrane and nucleus Composed of: Cytosol – fluid (largely water) with dissolved protein, salts, sugars, and other solutes in the cytoplasm Cytoplasmic organelles – metabolic machinery of the cell: either membranous or non-membranous Inclusions - Vary with cell type; e.g., glycogen granules, pigments, lipid droplets, vacuoles, crystals

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Provide most of the cell’s ATP via aerobic cellular respiration Contain their own DNA and RNA Similar to bacteria; capable of cell division called fission

Membranous: Nucleus, Mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus Nonmembranous: Cytoskeleton, centrioles, and ribosomes NUCLEUS • Largest organelle; genetic library with blueprints for nearly all cellular proteins • Responds to signals; dictates kinds and amounts of proteins synthesized • Most cells uninucleate; skeletal muscle cells, bone destruction cells, and some liver cells are multinucleate; red blood cells are anucleate • Three regions/structures NUCLEAR ENVELOPE • Double-membrane barrier; encloses nucleoplasm • Outer layer continuous with rough ER and bears ribosomes • Inner lining (nuclear lamina) maintains shape of nucleus; scaffold to organize DNA • Pores allow substances to pass; nuclear pore complex line pores; regulates transport of large molecules into and out of nucleus NUCLEOLI • Dark-staining spherical bodies within nucleus • Involved in rRNA synthesis and ribosome subunit assembly • Associated with nucleolar organizer regions – Contains DNA coding for rRNA • Usually one or two per cell

MITOCHONDRIA  Double membrane structure with shelf-like cristae

ENDOPLASMIC RETICULUM  Interconnected tubes and parallel membranes enclosing cisternae  Continuous with outer nuclear membrane Two varieties – rough ER and smooth ER

Catalyzes the following reactions the body  liver – lipid and cholesterol metabolism, breakdown of glycogen and detoxification of drugs  testes – synthesis of steroid-based hormones  intestinal cells – absorption, synthesis, and transport of fats  skeletal & cardiac muscle – storage & release of calcium ROUGH ER • External surface studded with ribosomes • Manufactures all secreted proteins • Synthesizes membrane integral proteins and phospholipids • Assembled proteins move to ER interior, enclosed in vesicle, go to Golgi apparatus

SMOOTH ER • Network of tubules continuous with rough ER • Its enzymes (integral proteins) function in – Lipid metabolism; cholesterol and steroid-based hormone synthesis; making lipids of lipoproteins – Absorption, synthesis, and transport of fats – Detoxification of drugs, some pesticides, carcinogenic chemicals – Converting glycogen to free glucose – Storage and release of calcium RIBOSOMES  Made in the nucleolus of the nucleus  Site of protein synthesis  Free ribosomes synthesize soluble proteins  Membrane-bound ribosomes synthesize proteins to be incorporated into membranes

GOLGI APPARATUS  Stacked and flattened membranous sacs  Functions in modification (clipping), concentration, and packaging of proteins (paper dolls)  Transport vessels from the ER fuse with the cis face of the Golgi apparatus  Proteins then pass through the Golgi apparatus to the trans face  Secretory vesicles leave the trans face of the Golgi stack and move to designated parts of the cell

Cell Theory 1. All living organisms are composed of one or more cells. 2. The cell is the basic unit of structure, function, and organization in all organisms. 3. All cells come from pre-existing, living cells.

FIG 4.13

Generalized Cell • All cells have some common structures and functions • Human cells have three basic parts: – Plasma membrane—flexible outer boundary – Cytoplasm—intracellular fluid containing organelles – Nucleus—control center

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Three types of vesicles bud from concave trans face – Secretory vesicles (granules) • To trans face; release export proteins by exocytosis – Vesicles of lipids and transmembrane proteins for plasma membrane or organelles – Lysosomes containing digestive enzymes; remain in cell

LYSOSOMES • Spherical membranous bags containing digestive enzymes • Digest ingested bacteria, viruses, and toxins • Degrade nonfunctional organelles • Breakdown glycogen and release thyroid hormone • Breakdown nonuseful tissue • Breakdown bone to release Ca2+ • Secretory lysosomes are found in white blood cells, immune cells, and melanocytes • Destroy cells in injured or nonuseful tissue (autolysis)

PEROXISOMES       FIG 4.18

Membranous sacs containing powerful oxidases and catalases Detoxify harmful or toxic substances Catalysis and synthesis of fatty acids Neutralize dangerous free radicals (highly reactive chemicals with unpaired electrons) Oxidases convert to H2O2 (also toxic) Catalases convert H2O2 to water and oxygen

PLASMA MEMBRANE • Lipid bilayer and proteins in constantly changing fluid mosaic • Plays dynamic role in cellular activity • Separates intracellular fluid (ICF) from extracellular fluid (ECF) MEMBRANE LIPIDS • 75% phospholipids (lipid bilayer) – Phosphate heads: polar and hydrophilic – Fatty acid tails: nonpolar and hydrophobic (Review Fig. 2.16b) • 5% glycolipids – Lipids with polar sugar groups on outer membrane surface • 20% cholesterol – Increases membrane stability PHOSPHOLIPIDS  Modified triglycerides with two fatty acid groups and a phosphorus group  Polar molecule  Forms the basis for cell membranes

MEMBRANE PROTEINS • Allow communication with environment • ½ mass of plasma membrane • Most specialized membrane functions • Some float freely • Some tethered to intracellular structures • Two types: – Integral proteins; peripheral protein

Glycolipids- lipids with bound carbohydrates (sugars) Glycocalyx: sugar protein area abutting the cell that provides highly specific biological markers by which cells recognize one another. Allows the immune system to determine what is self and what is nonself.

Phospholipid bilayer

FLUID MOSAIC MODEL Phospholipid bilayer: hydrophobic tails and hydrophilic heads – Integral proteins: Firmly inserted into membrane (most are transmembrane) – Have hydrophobic and hydrophilic regions – Can interact with lipid tails and water – Function as transport proteins (channels and carriers), enzymes, or receptors

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Peripheral proteins: Loosely attached to integral proteins Include filaments on intracellular surface for membrane support Function as enzymes; motor proteins for shape change during cell division and muscle contraction; cell-to-cell connections

Cholesterol: 20% of membrane lipids, increases mobility

Glycocalyx: “sugar coating”; each cell has a unique pattern of sugars o Specific biological markers for cell to cell recognition o Allows immune system to recognize "self" and "non self" o Cancerous cells change it continuously Glycolipids: found only in the outer membrane surface Lipid Rafts: Membrane area that are rich in lipids.  Composed of sphingolipids (contains alcohols and an amine group) and cholesterol  Concentrating platforms for cellsignaling molecules  20% of outer membrane  ADDS to the FLUIDITY of the MEMBRANE

CYTOSKELETON • The “skeleton” of the cell • Dynamic, elaborate series of rods running through the cytoplasm

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Filtration - Usually across capillary walls Diffusion  Simple diffusion  Facilitated diffusion  Osmosis

Molecule will passively diffuse through membrane if  It is lipid soluble, or  Small enough to pass through membrane channels, or  Assisted by carrier molecule DESMOSOME: resist shearing forces found in simple and stratified squamous epithelium and bind muscles cells to one another.

1.Simple Diffusion  nonpolar and lipid-soluble substances diffuse directly through the lipid bilayer; rate of diffusion is not regulated EXAMPLES:  fat soluble vitamins  O2 (concentration is higher in the blood than tissue)  CO2 (concentration is higher in the tissue than blood)

MICROFILAMENTS • Dynamic strands of the protein actin • Attached to the cytoplasmic side of the plasma membrane • Braces and strengthens the cell surface • Attach to CAMs and function in endocytosis and exocytosis, cell motility INTERMEDIATE FILAMENTS • Tough, insoluble protein fibers with high tensile strength • Resist pulling forces on the cell and help form desmosomes • E.g neurofilaments in nerve cells; keratin filaments in epithelial cells MICROTUBULES • Dynamic, hollow tubes made of the spherical protein tubulin • Determine the overall shape of the cell and distribution of organelles

GAP JUNCTION: directly connects the cytoplasm of two cells  allows various molecules and ions to pass freely between cells

3 MEMBRANE JUNCTIONS • Tight junction – impermeable junction that encircles the cell • Desmosome – anchoring junction scattered along the sides of cells • Gap junction – a nexus that allows chemical substances to pass between cells TIGHT JUNCTION: maintain the polarity of cells; prevent the passage of molecules and ions through the space between cells

DIFFUSION: Molecules move along or down their concentration gradient

TYPES OF TRANSPORT I. Passive – no energy input required from cell – Substance moves down its concentration gradient

2.Facilitated Diffusion  Unable to pass through lipid bilayer; rate of diffusion can be regulated  Protein carriers: lipid-insoluble macromolecules  Water-filled protein channels: small, polar or charged molecules  Two types: o Leakage channels  Always open o Gated channels

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Controlled by chemical or electrical signals

EXAMPLES: -water -sugars -amino acids -ions

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Occurs when water concentration different on the two sides of a membrane Occurs when the concentration of a solvent is different on opposite sides of a membrane Diffusion of water across a semipermeable membrane Osmolarity – total concentration of solute particles in a solution Tonicity – how a solution affects cell volume

Solution: homogeneous mixtures (liquid, gas or solid) Solvent: substances present in a larger amount Solute: substances present in a smaller amount

AQUAPORIN (WATER CHANNEL) • Aquaporins selectively conduct water molecules in and out of the cell, while preventing the passage of ions and other solutes. • The narrow pore acts to weaken the hydrogen bonds between the water molecules allowing the water to interact with the positively charged arginine, which also acts as a proton filter for the pore.

3.Osmosis (Diffusion of Water) • Movement of solvent (e.g., water) across selectively permeable membrane • Water diffuses through plasma membranes – Through lipid bilayer – Through specific water channels called aquaporins (AQPs)

FILTRATION: The passage of water and solutes through a membrane by hydrostatic pressure  Pressure gradient pushes solutecontaining fluid from a higher-pressure area to a lower-pressure area Example:  Blood forces fluid out of capillaries  Kidneys force urine to be excreted

EFFECTS OF SOLUTION OF VARYING TONICITY Isotonic – solutions with the same solute concentration as that of the cytosol. Hypertonic – solutions having greater solute concentration than that of the cytosol. ***Cells will shrink when placed in a hypertonic solution. Hypotonic – solutions having lesser solute concentration than that of the cytosol. ***Cells will expand and eventually burst when placed in a hypotonic solution.

II. Active - cell provides ATP for transport

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Occurs only in living cell membranes

Active transport Vesicular transport Both require ATP to move solutes across a living plasma membrane because o Solute too large for channels o Solute not lipid soluble o Solute not able to move down concentration gradient

ACTIVE TRANSPORT • Uses ATP to move solutes across a membrane • Requires carrier proteins • As you continue in your health studies, an understanding of these transporters is essential to understand disease processes and their treatment • Requires carrier proteins (solute pumps) • Bind specifically and reversibly with substance • Moves solutes against concentration gradient • Requires energy .TYPES OF ACTIVE TRANSPORT • Primary active transport – hydrolysis of ATP phosphorylates the transport protein causing conformational change – e.g. Na+/K+-pump • Required energy directly from ATP hydrolysis • Secondary active transport – use of an exchange pump (such as the Na+/K+ pump) indirectly to drive the transport of other solutes UP their concentration gradient • Primary and Secondary transport systems can either be Symporters – two substances are moved across a membrane in the same direction (aka co-transporters) Antiports – two substances are moved across a membrane in opposite directions (aka exchangers)

MEMBRANE POTENTIALS • Membrane potentials are due to a separation of electric charges (ions) across a resistive barrier (membrane). • Resting membrane potential (voltage) – when the membrane potential of a cell does not change in time. The two most important ion transport proteins for determination of membrane potentials are ion channels and ion pumps

VESICULAR TRANSPORT: • Transport of large particles and macromolecules across plasma membranes • Uses ATP and GTP for energy Exocytosis – moves substance from the cell interior to the extracellular space Endocytosis – enables large particles and macromolecules to enter the cell Exocytosis—transport out of cell Endocytosis—transport into cell • Phagocytosis, pinocytosis, receptormediated endocytosis Transcytosis—transport into, across, and then out of cell Vesicular trafficking—transport from one area or organelle in cell to another

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Phagocytosis Pseudopods engulf solids and bring them into cell's interior Form vesicle called phagosome

Used by macrophages and some white blood cells  Move by amoeboid motion o Cytoplasm flows into temporary extensions o Allows creeping...