The Structure & Function of Cells

Most cells are of this type (body cells, plant cells, Protists, etc.) The Cell is the basic functional unit of ALL living things. There are 2 basic categories of cells: 1. Eukaryotic Cells= contain plasma membrane (cell membrane), organelles, nucleus, cytoplasm Most cells are of this type (body cells, plant cells, Protists, etc.) Evolutionarily this is a recent advancement

Bacteria cells are of this type 2. Prokaryotic Cells = contain plasma membrane (cell membrane) and cytoplasm but NO ORGANELLES, NO NUCLEUS Bacteria cells are of this type Ribosomes are the only other real internal structure The oldest of cell types are prokaryotic Question #1

Animal Cell

Plant Cell Polysome On Endoplasmic Reticulum = Rough

IMPORTANT PARTS OF THE CELL Cell OR Plasma Membrane: separates the internal metabolic events from the external environment surrounding the cell Function= control the movement of materials into and out of the cell Structure= a double phospholipid membrane (Lipid Bilayer), Polar hydrophilic “water loving” heads pointing toward outside and inside of the cell; Nonpolar hydrophobic “water fearing” tails point toward the inside of the membrane. Question #2

“Fluid Mosaic Model” of the Cell Membrane

2. Integral Proteins: extend into the membrane Fluid Mosaic Model= describes the structure of the cell membrane. PROTEINS are scattered throughout the flexible lipid bilayer. These proteins can be of 3 different types: Question # 8 1. Peripheral Proteins: attached loosely to the inner or outer surface of the membrane 2. Integral Proteins: extend into the membrane 3. Transmembrane Proteins: an integral protein that spans across the membrane and appears at both surfaces

Phospholipid Bilayer with Embedded Proteins

Proteins in the plasma membrane provide a wide range of functions including: Question #9 Channel Proteins: provide passageways through the membrane for certain water soluble substances (i.e. polar & charged molecules) Transport Protein: use energy to transport materials across the membrane against a concentration gradient Recognition Proteins(Glycoproteins): used to distinguish the identity of neighboring cells Adhesion Proteins: attach cells to neighboring cells, provide stability Receptor Proteins: provide a binding site for hormones or other chemical triggers Electron Transfer Proteins: transfer electrons from one molecule to another during chemical reactions

Features of the Plasma Membrane It is Semi-Permeable = only small, uncharged, polar, hydrophobic molecules pass freely across the membrane Permeable = H2O , CO2 , O2 , lipid soluble hydrocarbons NON-Permeable = large molecules, glucose, all ions

Lets water flow freely, restricts the flow of glucose molecules Water passes freely raising the water level on side 2

Types of Membrane Proteins

Features of the Plasma Membrane Cholesterol= provide some rigidity to the fluid nature of the membrane in animal cells. Act as a “Cellular Antifreeze” to keep a cell from freezing in cold temps. or melting in warm temps. Question #11

Features of the Plasma Membrane 4. Glycocalyx= carbohydrate coat covering the outer surface of the cell membrane. Used for cell to cell recognition. Features of the Plasma Membrane

ORGANELLES OF THE CELL Organelle = a structure in the cytoplasm (semi-fluid medium between nucleus and cell membrane) of the cell that serves a specific function related to the metabolism of the cell Nucleus: contains DNA, the hereditary information of the cell. Surrounded by a nuclear envelope Normal DNA = Chromatin: spread out in a threadlike matrix Chromosomes: visible when the cell begins to divide

The Pores in the Nuclear Envelope: NEW SLIDE!!!!! Nuclear Envelope = Nuclear Membrane Provide for the movement of: Proteins into the nucleus mRNA out of the nucleus Ribosome subunits out of the nucleus Endomembrane System: Connects the nucleus to the cell membrane Nuclear Envelope (Pores) --> Rough ER --> Golgi --> Smooth ER --> Lysosomes --> Cell Membrane Question # 3 Question # 6

Nucleolus: produces rRNA & multiple copies of genes ; concentrations of DNA in the process of manufacturing the components of Ribosomes ORGANELLES OF THE CELL Question # 4 Synthesis & Storage of Ribosomes

Ribosomes: assemble amino acids into proteins in the cytoplasm ORGANELLES OF THE CELL Question # 14 Has large and small subunits Cells producing secretory products have many ribosomes

ORGANELLES OF THE CELL Endoplasmic Reticulum (ER): stacks of flattened sacs involved in the production of various membranes & products (#13), looks like a maze when viewed in cross-section, often connected to the nucleus Rough ER: has ribosomes on it, specializes in protein synthesis; manufacture membranes and other secretory products (#14) Smooth ER: NO ribosomes, specializes in the production of lipids, detoxification, storage & release of ions etc. (depends on the cell type) (#14)

ORGANELLES OF THE CELL Golgi Apparatus(Complex or Body): a group of flattened sacs arranged like a stack of bowls has a Cis and Trans face (opposite fat vs thin ends) Function to modify and package proteins and lipids, products of Rough ER Puts the products into Vesicles Contents of vesicles get released outside the cell Question # 14

Lysosomes: Acidic pH; vesicles that contain hydrolytic digestive enzymes to digest macromolecules . NOT FOUND IN PLANT CELLS ORGANELLES OF THE CELL

ORGANELLES OF THE CELL Peroxisomes: breakdown various substances O2 + H2  H2O2 Common in liver and kidney cells ORGANELLES OF THE CELL

ORGANELLES OF THE CELL Mitochondria: carry out cellular respiration Energy in the form of ATP is obtained from carbohydrates ORGANELLES OF THE CELL Double membrane sac with Cristae (folding inner membraene)

Chloroplasts: carry out photosynthesis in plants; this is where plants incorporate energy from the sun to make carbohydrates ORGANELLES OF THE CELL Thylakoids (Grana): System of flattened sacs inside chloroplast

ORGANELLES OF THE CELL MAINTAIN CELL SHAPE & Anchors Organelles Cytoskeleton: internal structure of the cytoplasm MAINTAIN CELL SHAPE & Anchors Organelles Microtubules = provide support and motility, made of protein tubulin (spindle fibers during cell division; cilia & flagella) (#10) Intermediate Filaments = support, maintain cell shape Microfilaments = made of protein actin, involved in cell motility

Internal Anatomy of a cell

ORGANELLES OF THE CELL Flagella and Cilia: protrude from the cell membrane, used for movement Flagella = long and few Cilia = short and many Both arranged in “9+2” arrangement

Centrioles and Basal Bodies: Microtubule organizing centers ORGANELLES OF THE CELL

Cell Wall: found only in plants; outside of plasma membrane, provides support, made of Cellulose ORGANELLES OF THE CELL

ORGANELLES OF THE CELL Vacuoles and Vesicles: fluid filled, single membrane bound bodies Transport Vesicles= move materials between organelles Food Vacuoles= temporary food storage Storage Vacuoles= store starch, pigments, and toxins Central Vacuole= fill up most of the interior in plant cells, maintain rigidity of the cell (Plant) Contractile Vacuoles= collect and pump excess water out of a cell (Plant or Animal)

ORGANELLES OF THE CELL Cell Junctions: serve to anchor cells to one another Desmosomes= act as “spot welds” to hold adjacent animal cells together in high stress tissues (skin, heart muscle) Tight Junctions= “stitched seams” between animal cells, prevent movement of material between the cells (cells lining the digestive tract). Gap Junctions= narrow tunnels between animal cells, allow passage of small ions and molecules, communication through electrical impulses Plasmodesmata= narrow channels between plant cell

Types of Cell Junctions Desmosome Tight Junction Gap J unction

Plants = cell walls, large vacuole, chloroplasts Animal = lysosomes, centrioles Plant vs. Animal Cells Animal Cell Plant Cell

Prokaryotes vs. Eukaryotes Prokaryotes: No nucleus, No Organelles, Single stranded “naked” DNA, Only Bacteria Eukaryotes: Have a nucleus, Lots of Organelles, DNA in chromosomes, All other cells

The Movement of Substances The cell membrane and the membrane of other organelles are Semi-permeable = only certain substances can cross the membrane Selective Permeability= allowing only specific substances to pass Water = solvent; dissolved particles = solute Movement of substances may be from higher to lower concentrations (down or with the concentration gradient) or the reverse (up or against the gradient) The movement of substances may be active or passive

Selective Permeability

Solute concentrations may be compared: Hypertonic= higher concentration of solutes Hypotonic= lower concentration of solutes Isotonic= equal concentration of solutes ………relative to another region.

Other Types of Movement Bulk Flow= collective movement of substances in the same direction in response to some force or pressure (blood moving through a vessel)

Passive vs. Active Transport Passive Transport= Movement of molecules down a concentration gradient (high  low) Does not require the cell to expend any energy! 1. Diffusion: due to the random nature of molecules in motion (dye in a beaker of water) Rates of diffusion are determined by: Concentration gradient Shape and size of the molecules Temperature (higher temp. = faster diffusion time) Liquid vs. gas (slower in liquids)

Passive Transport 2. Osmosis: the diffusion of water molecules across a semi-permeable membrane Osmotic Pressure = force water exerts against the inside of a cell Turgor Pressure = pressure water exerts against the inside of a plant cell, used for structural support

Passive Transport 3. Dialysis: diffusion of solutes across a semi-permeable membrane 4. Plasmolysis: movement of water out of a cell, results in the collapse of the cell 5. Facilitated Diffusion: use channel proteins embedded in the membrane to transport solutes

Active Transport Active Transport= requires the cell to expend energy to move substances against the concentration gradient (low high) Usually utilizes transport proteins to move: small ions (Na+, K+, Cl-, H+), amino acids, simple sugars

Active Transport Exocytosis: Large particles are released from the cell by vesicles forming and fusing with the cell membrane Endocytosis: Large particles enter the cell by vesicles forming and fusing with the cell membrane Phagocytosis = cell eating (white blood cells attacking bacteria) Pinocytosis = cell drinking Receptor Mediated Endocytosis = special receptors attract certain molecules (cholesterol transport in the blood, hormones)