Cells, The Living Unit

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Cell Theory

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Cell - the basic functional unit of life-Organismal activity depends on individual and collective activity of cells-Biochemical activities of cells are dictated by structure (i.e. sperm)-Continuity of life has a cellular basis

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Generalized cell has 3 parts

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Plasma membrane- barrier that protects the cell and interacts with the enviroment. - Nucleus- control center. - Nucleus- control center. - Cytoplasm- fluid that contains organelles

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Plasma Membrane

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Separates intracellular fluids from extracellular fluids. - Plays a dynamic role in cellular activity

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Fluid Mosaic Model

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Bilayer of lipids with imbedded, dispersed proteins. - Consists of phospholipids, cholesterol, and glycolipids. - Phospholipids – have two fatty acid groups and a phosphorus group which makes them amphipathic (likes water and lipids)

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Functions of Membrane Proteins

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Transport. - Enzymatic activity. - Receptors for signal transduction. -Intercellular adhesion. - Cell-cell recognition. - Attachment to cytoskeleton and extracellular matrix

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transport

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A protein that spans the membrane may provide a hydrohilic channel across the membrane that is selective for a particular solute. Some transport proteins hydrolize ATP as an energy source to actively pump substances across the membrane. things going through membrane. Important for lymphatic activity

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enzymatic activity

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Protein either breaks down or combine substances to make larger molecules

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receptors for signal transduction

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A membrane protein exposed to the outside of the cell may have a binding site w/ a specific shape that fits the shape of a chemical messenger, such as a hormone. The external signal may cause a conformational change in the protein that initiates a chain of chemical in the cell. "binds to something in environ. Will cause some reaction. Will cause something to happen "downstream" basically signal cascade initiates a chain of chemical in the cell."

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Intercellular joining

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Member proteins of adjacent cells may be hooked together in various kinds of intercellular junctions. Some membrane proteins (CAMs) of this gruop provide temp binding sites that guide cell migration & cell to cell interaction. "cells will like each other provides temporary binding sites that guide cell migration & other cell to cell interaction."

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Cell to Cell Regognition

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

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Attachment to the cytoskeleton & extracellular matrix (ECM)

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Maintain structure shape of cell & fix the location of certain membrane proteins.

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Plasma Membrane Surfaces

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Glycolipids are found only in the outer membrane surface. - 20% of all membrane lipid is cholesterol. - Glycocalyx is a glycoprotein that provides biological markers by which cells recognize one another

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Lipid Rafts

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Make up 20% of the outer membrane surface. - Are concentrating platforms for cell-signaling molecules. Quiltlike patches are more stable and orderly and les fluid than the rest of the membrane and can include or exclude specific proteins to various extents. Because of these qualities, lipid rafts are assumed to be concentrating platforms for molecules needed for cell signaling.

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gycocalyx

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"sugar covering" used to describe the fuzzy, sticky carbohydrate rich area at the cell surface. Your cells are sugar coated. Provides highly specific biological markers by which approaching cells recognize each other. (e.g. sperm recognize the ovum)

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Types of Membrane Junctions

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Tight Junction. - Desmosomes. - Gap Junctions

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Tight Junctions

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Interlocking junctional proteins. Tight junctions and desmosomes serve to anchor cells to one another and deny leakage of the extracellular fluid.

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Desmosomes

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anchoring junction consisting of a plaque scattered along the sides of cells.

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Gap Junction

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a nexus that allows chemical substances to pass between cells

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2 Types of Membrane Transport

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Passive and Active

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Passive Transport

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Does not require the use of ATP. - Always follows the concentration gradient. - 4 types are Simple diffusion, Facilitated diffusion, Osmosis, Filtration

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Active Transport

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Requires use of ATP. - 2 types are Primary active transport & Secondary active transport. - Does not always follow concentration gradient.

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Primary active transport

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transport of substances against a concentraion gradient, across the plama membrane by a solute pump, directly uses entergy of ATP

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Secondary Active transport

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Cotransport (coupled transport) of 2 solutes across the membrane, energy supplied by the ion gradient created by a primary active solute pump (indirectly), symporters move the tranported substances in the same direction, antiporters move transported substanices in opposite directions across the membrane.

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Simple diffusion

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nonpolar and lipid-soluble substances pass directly through membrane

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Facilitated diffusion

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Transported substances bind carrier proteins or pass through protein channels

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Carrier Proteins

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Are integral transmembrane proteins. - Show specificity for certain polar molecules including sugars and amino acids

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Osmosis

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Occurs when the concentration of a solvent is different on opposite sides of a membrane . - Diffusion of water across a semipermeable membrane

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Osmolarity

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total concentration of solute particles in a solution

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Filtration

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The passage of water and solutes through a membrane by hydrostatic pressure. Pressure gradient pushes solute-containing fluid from a higher-pressure area to a lower-pressure area

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Tonicity

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how a solution affects cell volume

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Isotonic –

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solutions with the same solute concentration as that of the cytosol

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Hypertonic –

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solutions having greater solute concentration than that of the cytosol

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Hypotonic –

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solutions having lesser solute concentration than that of the cytosol

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Active Transport

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Uses ATP to move solutes across a membrane. - Requires carrier proteins. - Symport system – two substances are moved across a membrane in the same direction. - Antiport system – two substances are moved across a membrane in opposite directions

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Vesicular Transport

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Large particles, macromolecules, and fluids are transorted across plasma and intracellular membranes. Used for exocytosis, endocytosis, transcytosis, & vesicular trafficing.

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Exocytosis

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– moves substance from the cell interior to the extracellular space

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Endocytosis –

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enables large particles and macromolecules to enter the cell

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Transcytosis –

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moving substances into, across, and then out of a cell

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Vesicular trafficking

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– moving substances from one area in the cell to another

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Trafficking into and throughout the cell

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Endocytosis via clathrin-coated pits. - Pinocytosis (Fluid-phase endocytosis) – the plasma membrane infolds, bringing extracellular fluid and solutes into the interior of the cell . - Receptor-mediated endocytosis – clathrin-coated pits provide the main route for endocytosis and transcytosis. - Phagocytosis- englufing of foreign bodies (bacteria, dead cells) by phagocytes of the immune system. - Coatomer-coated vesicles- accounts for nearly all intracellular trafficking

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Membrane Potential

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Voltage across a membrane. - Resting membrane potential – the point where K+ potential is balanced by the membrane potential. - Results from Na+ and K+ concentration gradients across the membrane. - Differential permeability of the plasma membrane to Na+ and K+. - Steady state – potential maintained by active transport of ions

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Generation and Maintenance of Membrane Potential

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Resting Membrane Potential is established when K+ movement out of the cell equals K+ movement into the cell. K+ goes out via leakage and creating an neg. charge inside the cell, thereby attracting K+ back into the cell.

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Roles of Membrane Receptors

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Contact signaling – important in normal development and immunity. - Electrical signaling – voltage-regulated “ion gates” in nerve and muscle tissue. - Chemical signaling – neurotransmitters bind to chemically gated channel-linked receptors in nerve and muscle tissue

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Cytoplasm

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Cytoplasm – material between plasma membrane and the nucleus. - Cytosol –water with dissolved protein, salts, sugars. - Cytoplasmic organelles – metabolic machinery of the cell. Inclusions – chemical substances such as pigment

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Cytoplasmic Organelles

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Membranous: Mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus. - Nonmembranous: Cytoskeleton, centrioles, and ribosomes

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Mitochondria

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Double membrane structure with shelflike cristae. - Provide most of the cell’s ATP via aerobic cellular respiration. - Contain their own DNA and RNA. - Believed to have arisen from bacteria- symbiotic relationship

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Endo Membrane System

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System of organelles that function to: Produce, store, and export biological molecules. - Degrade potentially harmful substances. - System includes: Nuclear envelope, smooth and rough ER, lysosomes, vacuoles, transport vesicles, Golgi apparatus, and the plasma membrane

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Ribosomes

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2 globular subunits containing protein and rRNA. - Site of protein synthesis. - Free ribosomes synthesize soluble proteins. - Membrane-bound ribosomes synthesize proteins to be incorporated into membranes

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Endoplasmic Reticulum

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Interconnected tubes and parallel membranes enclosing cisternae. - Continuous with the nuclear membrane. - Two varieties – rough ER and smooth ER

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Rough ER

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External surface studded with ribosomes. - Manufactures all secreted proteins. - Responsible for the synthesis of integral membrane proteins and phospholipids for cell membranes

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Smooth ER

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Catalyzes the following reactions in various organs of the body. - lipid and cholesterol metabolism. - synthesis of steroid-based hormones . - absorption, synthesis, and transport of fats. - storage and release of calcium

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Golgi Apparatus

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Stacked and flattened membranous sacs. - Functions in modification, concentration, and packaging of proteins. - 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

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Lysosomes

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Spherical membranous bags containing digestive enzymes (acid hydrolases). - Digest ingested bacteria, viruses, and toxins. - Degrade nonfunctional organelles & nonuseful tissue. Secretory lysosomes are found in white blood cells & immune cells

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Peroxisomes

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Membranous sacs containing oxidases and catalases. - Detoxify harmful or toxic substances. - Neutralize dangerous free radicals. - Free radicals – highly reactive chemicals with unpaired electrons (i.e., O2–)

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Cytoskeleton

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The “skeleton” of the cell. - Dynamic, elaborate series of rods running through the cytosol. - Consists of microtubules, microfilaments, and intermediate filaments

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Microtubules

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Dynamic, hollow tubes made of the spherical protein tubulin. - Determine the overall shape of the cell and distribution of organelles

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Microfilaments

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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

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Intermediate Filaments

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Tough, insoluble protein fibers with high tensile strength. - Resist pulling forces on the cell and help form desmosomes

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Centrosome/ Centrioles

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Centrosome- microtubule organizing complex (MTOC) near the nucleus where microtubules are anchored at one end. - Centriole- small barrel-shaped organelles located in the centrosome near the nucleus. - Organize mitotic spindle during mitosis. - Form the bases of cilia and flagella

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Cilia

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Whiplike, motile cellular extensions on exposed surfaces of certain cells. - Move substances in one direction across cell surfaces

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Nucleus

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Contains nuclear envelope, nucleoli, chromatin. - Gene-containing control center of the cell- dictates what proteins are made. - Has DNA that encodes nearly all cellular proteins

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Nuclear Envelope

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Selectively permeable membrane containing pores. - Encloses nucleoplasm (contains essential solutes). - Outer membrane is continuous with the rough ER and is studded with ribosomes. -Inner membrane is lined with the nuclear lamina, which maintains the shape of the nucleus. - Pore complex regulates transport of large molecules into and out of the nucleus

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Nucleoli

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Dark-staining spherical bodies within the nucleus. - Site of ribosome production

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Chromatin

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Threadlike strands of DNA and histones. - Arranged in fundamental units called nucleosomes. - Form condensed, barlike bodies of chromosomes when the nucleus starts to divide

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Cell Cycle

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Interphase: Growth (G1), synthesis (S), growth (G2). - Mitotic phase: Mitosis and cytokinesis

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2 Main periods of the cell cycle

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Interphase and cell division

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Interphase

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The period of cell formation to cell division (inappropriately dubbed the resting phase). Three subphases: G1 (gap 1):metabolic activity and vigorous growth. G0: cells that permanently cease dividing. S (synthetic):DNA replication. G2 (gap 2) – preparation for division

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DNA Replication

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takes place when the DNA helix uncoils, and the hydrogen bonds between its base pairs are broken. Then each nucleotide strand of the DNA acts as a template for the construction of a complementary nucleotide strand.

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Cell Division

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Essential for body growth and tissue repair. - Mitosis:nuclear division. - Cytokinesis:division of the cytoplasm due to cleavage furrow formed in late anaphase by contractile ring

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Mitosis

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The phases of mitosis are: Prophase, Metaphase, Anaphase, &Telophase

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Early Prophase

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Asters are seen as chromatin condenses into chromosomes

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Late Prophase

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Nucleoli disappear. Centriole pairs separate and the mitotic spindle is formed

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Metaphase

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Chromosomes cluster at the middle of the cell with their centromeres aligned at the center of the cell. This arrangement of chromosomes along a plane is called the metaphase plate

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Anaphase

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Centromeres of the chromosomes split. Motor proteins in kinetochores pull chromosomes toward poles

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Telophase and Cytokinesis

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Centromeres of the chromosomes split. Motor proteins in kinetochores pull chromosomes toward poles

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Control of Cell Division

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Surface-to-volume ratio of cells. Chemical signals such as growth factors and hormones. Contact inhibition