UNIT III – CELL STRUCTURE & FUNCTION Hillis – Ch 4,5 Baby Campbell – Ch 4,5 Big Campbell – Ch 6,7,11

I. DISCOVERY OF CELLS History of Microscopes Cell Theory Anton van Leeuwenhoek Robert Hooke Cell Theory All living things are made of cells. Cells are the smallest working unit. All cells come from pre-existing cells through cell division.

I. DISCOVERY OF CELLS, cont. Types of Microscopes Compound Light Microscope Magnification Resolution Advances in light microscopy include Confocal Fluorescent Phase Contrast Super-resolution Electron Microscope Scanning Electron Microscope (SEM) Transmission Electron Microscope (TEM)

I. DISCOVERY OF CELLS, cont. Cell Size Metabolic needs impose both upper & lower limits on cell size How small? Must have enough space for DNA, enzymes Mycoplasma sp. - < 1 μm How large? Surface Area to Volume Ratio Adaptations

II. CELL TYPES Prokaryotic Cells Typically smaller than euks Bacteria Kingdom No true nucleus – DNA found as a single chromosome in region called nucleoid

II. CELL TYPES, cont Prokaryotic Cells

II. CELL TYPES, cont Eukaryotic Cells Larger, more complex Contain true nucleus, membrane-bound organelles suspended in cytosol Composed of Nucleus Ribosomes Endomembrane System ER Golgi Apparatus Lysosomes Vacuoles Mitochondria/Chloroplasts Peroxisomes Cytoskeleton

III. EUKARYOTIC CELL STRUCTURES

III. EUKARYOTIC CELL STRUCTURES, cont Control center of eukaryotic cell Double membrane that protects nucleus; continuous with ER Contains pores Site of ribosome production DNA wrapped in protein

III. EUKARYOTIC CELL STRUCTURES, cont Suspended in cytosol or found on rough ER Site of protein production in a cell

III. EUKARYOTIC CELL STRUCTURES, cont Endomembrane System Endoplasmic Reticulum Interconnected network continuous with nuclear envelope Rough ER Smooth ER

III. EUKARYOTIC CELL STRUCTURES, cont Endomembrane System, cont “Cell postmaster” Receives transport vesicles from ER; modifies, stores, and ships products Receiving side is known as the cis face; shipping side is known as the trans face

III. EUKARYOTIC CELL STRUCTURES, cont Endomembrane System, cont Sacs containing hydrolytic enzymes Used for recycling cellular materials, destroying pathogens

III. EUKARYOTIC CELL STRUCTURES, cont Endomembrane System, cont Storage sac Plants typically have large, central vacuole surrounded by membrane called tonoplast. Absorbs water and helps plant cell to grow larger Some protists have contractile vacuole to pump out excess water

III. EUKARYOTIC CELL STRUCTURES, cont Site of oxidative respiration Contain own DNA, ribosomes Found in virtually all euk cells Enclosed by 2 membranes; inner membrane has folds called cristae to increase surface area

III. EUKARYOTIC CELL STRUCTURES, cont Type of plastid that carries out photosynthesis by converting solar energy to chemical energy (glucose) Contain membranous system of flattened sacs called thylakoids – stack is called a granum Fluid surrounding thylakoids is called stroma Contains DNA, ribosomes

III. EUKARYOTIC CELL STRUCTURES, cont Endosymbiont Theory

III. EUKARYOTIC CELL STRUCTURES, cont Membrane-bound compartments that use O2 to carry out metabolism H2O2 is produced; broken down by _________________

III. EUKARYOTIC CELL STRUCTURES, cont Provides structural support to cell Allows for movement Attachment site for organelles, enzymes More extensive in animal cells Composed of three types of proteins Actin More fixed Keratin

III. EUKARYOTIC CELL STRUCTURES, cont Cytoskeleton, cont

IV. CELL BOUNDARIES Cell Wall Found in Rigid structure; protects, maintains shape of cells Prevents excess water uptake Plant cell wall Cellulose Pectin - Sticky polysaccharide found between cell walls of adjacent cells Plasmodesmata - Perforations between adjacent cell walls that allow for movement of materials from one cell to another

IV. CELL BOUNDARIES, cont Extracellular Matrix of Animal Cells Holds cells together, protects & supports cells Allows for communication between cells Composed primarily of glycoproteins – proteins with covalently-bonded carbohydrate chains attached Must abundant glycoprotein in most animals is collagen

IV. CELL BOUNDARIES, cont Intracellular Junctions in Animal Cells Tight Junctions – Press membranes together very tightly; prevents leakage of fluid Desmosomes (Anchoring Junctions) – Fasten cells together in sheets Gap Junctions – Allow for movement of cytoplasm from one cell to another; important in communication between cells

IV. CELL BOUNDARIES, cont Cell (Plasma) Membrane Selectively-permeable barrier found in all cells Composed primarily of phospholipid bilayer Fluid Mosaic Model “Fluid” – Not a rigid structure. Organization due to high concentration of water inside & outside cell

IV. CELL BOUNDARIES, cont Organization of Plasma Membrane

IV. CELL BOUNDARIES, cont Fluidity of Plasma Membrane

IV. CELL BOUNDARIES, cont Cell Membrane, cont Proteins - “Mosaic” – Assortment of different proteins embedded in bilayer; determine most of membrane’s specific functions. Act as channels, pumps, enzymes in metabolism, binding sites, etc Integral Proteins – Embedded in phospholipid layer Peripheral Proteins – Bound to surface of membrane

IV. CELL BOUNDARIES, cont Membrane Proteins

IV. CELL BOUNDARIES, cont Cell Membrane, cont Carbohydrates “ID tags” that identify cell. Enable cells to recognize each other and foreign cells. May be bonded to lipids (glycolipids) or proteins (glycoproteins)

IV. CELL BOUNDARIES, cont

V. CELL TRANSPORT

V. CELL TRANSPORT, cont Passive Transport – Movement of materials from high to low concentration. No energy output required. Diffusion Random movement of a substance across membrane down concentration gradient No net movement once equilibrium is reached

V. CELL TRANSPORT, cont Passive Transport, cont Facilitated Diffusion Passive transport of molecules across cell membrane with the help of transport proteins Utilized by large molecules, charged particles, polar molecules Water

V. CELL TRANSPORT, cont Passive Transport, cont Osmosis – Diffusion of water across a membrane. Tonicity refers to tendency of cell to gain or lose water. If the solution is Isotonic relative to the cell – Solute concentration is same on both sides of membrane. No net movement of water. Hypertonic relative to the cell – Concentration of solute is greater outside cell → water moves out of cell until equilibrium is reached. Cell may shrivel. Hypotonic relative to the cell – Concentration of solute is lower outside cell → water moves into cell until equilibrium is reached. Cell may swell to bursting point.

V. CELL TRANSPORT, cont Passive Transport / Osmosis, cont Water Potential Used to predict the passive movement of water Designated as Ψ Water always moves from an area of higher water potential → lower water potential ΨS = ΨP =

V. CELL TRANSPORT, cont Passive Transport/Osmosis, cont Osmoregulation Cells must have mechanism to prevent excess loss, uptake of water Cell wall, contractile vacuole Plasmolysis – Seen in plants; excessive water loss causes cell membrane to pull away from cell wall

V. CELL TRANSPORT, cont

V. CELL TRANSPORT, cont Active Transport Movement of materials against concentration gradient. Requires energy output by cell Carrier Proteins – Na+ / K+ Pump

V. CELL TRANSPORT, cont Active Transport, cont Proton Pump

V. CELL TRANSPORT, cont Active Transport, cont Exocytosis Secretion of biomolecules by fusion of vesicles with cell membrane. Biomolecules “spit out”. Hormones, neurotransmitters, etc

V. CELL TRANSPORT, cont Active Transport, cont Endocytosis – “Sucking In”. Cell membrane surrounds, engulfs particle or biomolecule, pinches in to form vesicle. Phagocytosis – “Sucking in” food particles Pinocytosis – “Sucking in” fluid droplets Receptor-mediated Endocytosis – Very specific

VI. CELL SIGNALING Autocrine Signaling

VI. CELL SIGNALING, cont Coordinates cell activities, development Typically involves 3 steps: Reception – Target cell’s detection of signal molecule due to binding of signal molecule to receptor protein in cell membrane Transduction – Binding of signaling molecule changes receptor protein; triggers a sequence of events within cell Response – Results in specific cellular response; for example, activation of genes, enzyme catalysis, etc.

VI. CELL SIGNALING, cont Reception Typically involves G Proteins

VI. CELL SIGNALING, cont Transduction Typically multi-step pathway Relay molecules are usually protein kinases

VI. CELL SIGNALING, cont Transduction Non-protein molecule known as cAMP is often second messenger

VI. CELL SIGNALING, cont Response Nuclear May “turn on” or “turn off” genes Cytoplasmic May regulate enzyme activity Apoptosis Controlled cell suicide

VI. CELL SIGNALING, cont Regulation