3-1 New Unit: Cells

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3-12 Some History… Robert Hooke looks at a thin slice of cork under a microscope Anton van Leeuwenhoek observes small living organisms in pond water 1839-Mathias Schleidan concludes that all plants are made up of cells 1839-Theodor Schwann concludes that all animals are made up of living cells Rudolph Virchow proposes that all cells come from existing cells

3-13 Cell Theory All living things are composed of cells Cells are the basic units of structures and function in living things New cells are produced from old cells

3-14 Cell Characteristics What characteristics do we use to define a cell? All cells have two things in common 1. The are surrounded by a barrier called a cell membrane 2. At some point in their lives the contain genetic material.

3-15 Prokaryotes vs. Eukaryotes Cells can be split up in two broad categories, depending on whether they contain a nucleus Prokaryotic cells have genetic material that is not contained in the nucleus Eukaryotic cells contain a nucleus in which their genetic material is separated from the rest of the cell.

3-16 Prokaryote

3-17 Eukaryote

3-18 Functions of the Cell Basic unit of life Protection and support Movement Communication Cell metabolism and energy release

3-19 Cell Characteristics Plasma Membrane –Outer cell boundary Cytoplasm –Cytosol –Cytoskeleton Organelles –Specialized structures that perform specific functions

3-20 Cell Membrane ALL cells are surrounded by a thin flexible barrier called the cell membrane Many cells have an additional barrier called the cell wall The cell membrane regulates what goes in and out of the cell The cell membrane is called a lipid bilayer

3-21 Cytoplasm Cellular material outside nucleus but inside plasma membrane Cytosol: Fluid portion Cytoskeleton: Supports the cell –Microtubules –Microfilaments –Intermediate filaments

3-22 Organelles Small specialized structures for particular functions Most have membranes that separates interior of organelles from cytoplasm Related to specific structure and function of the cell

3-23 Nucleus DNA dispersed throughout Consists of : –Nuclear envelope: Separates nucleus from cytoplasm and regulates movement of materials in and out –Chromatin: Condenses to form chromosomes during cell division –Nucleolus: Assembly site of large and small ribosomal units

3-24 Centrioles In specialized zone near nucleus: Each unit consists of microtubules Before cell division, centrioles divide, move to ends of cell and become spindle fibers

3-25 Ribosomes Sites of protein synthesis Composed of a large and small subunit Types –Free –Attached to endoplasmic reticulum

3-26 Endoplasmic Reticulum Types –Rough Attached ribosomes Proteins produced and modified –Smooth Not attached ribosomes Store enzymes, Manufacture lipids

3-27 Golgi Apparatus Modification, packaging, distribution of proteins and lipids for secretion or internal use Flattened membrane sacs stacked on each other

3-28 Function of Golgi Apparatus

3-29 Mitochondria Provide energy for cell Major site of ATP synthesis Membranes –Cristae: Infoldings of inner membrane –Matrix: Substance located in space formed by inner membrane

3-30 Lysosomes -Small organelles filled with enzymes -Involved in digestion or breakdown of lipids carbohydrates, and proteins. -Also involved in breaking down old organelles, and removing “junk” of the cell.

3-31 Chloroplasts Capture energy from sunlight and convert it into chemical energy during photosynthesis Found in plants and other organisms.

3-32 Vacuoles Store materials such as water, salts, proteins, and carbohydrates. Plants use vacuoles as support for heavy structures Contracting vacuoles are found in some animals and single celled organisms to pump out excess water.

3-33 Cilia Appendages projecting from cell surfaces Capable of movement Moves materials over the cell surface

3-34 Flagella Similar to cilia but longer Usually only one exists per cell Move the cell itself in wavelike fashion Example: Sperm cell

3-35 Microvilli Extension of plasma membrane Increase the cell surface Normally many on each cell One tenth to one twentieth size of cilia Do not move

3-36 Organelle DNA Some organelles have their own DNA These include the mitochondria, ribosomes, and chloroplasts What implications do you think this has? Evolutionary?

3-37 Endosymbiosis Proposed by Lynn Margulis in Suggests that mitochondria and chloroplasts were once free living organisms and were taken into other cells as endosymbiotes.

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3-39 Cell Membrane Passive Transport and Active Transport Inheritance

3-40 Lipid Bilayer Two layers of lipids = bilayer

3-41 Lipid Bilayer Hydrophobic = water fearing Hydrophilic = water loving

3-42 Lipid Bilayer Also contains proteins and carbohydrates Proteins = channels and pumps Carbs = identification

3-43 Lipid Bilayer In order to survive, every cell must take in and eliminate substances This means the cell membrane must allow certain substances to penetrate it. It is called selectively permeable

Functions of the Cell Membrane Isolates the cytoplasm from the external environment Regulates the flow of materials into and out of the cell Communicates with other cells

The Fluid Mosaic Model Currently accepted model of the cell membrane Phospholipid bilayer –Hydrophilic “head” – exposed to the outside –Hydrophobic “tail” – hides inside Membrane proteins are randomly dispersed in phospholipid bilayer

Fluidity of the Membrane The lipids and proteins can drift throughout the membrane Membrane is NOT stiff/rigid Cholesterol makes the membrane stronger by limiting the movement of phospholipids

Membrane as a Mosaic Lipid bilayer has membrane proteins “stuck” in it Integral proteins –Go through the membrane (both sides) Peripheral proteins – attached to the surface of the membrane

Diffusion Movement of molecules from high to low concentration until equilibrium is reached. Passive Transport= no energy required What substances may diffuse across membrane? Nonpolar (non-charged) molecules; small polar molecules

Diffusion Each substance diffuses down its OWN concentration gradient and is unaffected by concentration gradients of other substances

Diffusion Does all movement stop once equilibrium is reached?? –NO!! –Equal rates in all directions

Osmosis Def’n: –The passive transport of water across a selectively permeable membrane –Hyper-, hypo-, iso- tonic RELATIVE TERMS!! Always referring to solute concentration Water moves from areas of lower concentration of solutes (hypotonic) to areas of higher solute concentration (hypertonic)

Osmosis in Plant and Animal Cells Animal Cells: –Plasmolysis Occurs when a cell is in a hypertonic solution –Water goes from cell into solution –Cytolysis Occurs when a cell is in a hypotonic solution –Water goes from solution into cell Plant Cells: –Turgid –Flaccid

Facilitated Diffusion Def’n: –The diffusion of large molecules across the cell membrane using transport proteins –Glucose; ions Does NOT require an input of energy –Solute is still moving down its concentration gradient

Facilitated Diffusion Transport proteins are specific for their solutes Transport proteins can become saturated Some are gated channels: –Chemical or electrical stimulus causes them to open

Example Which direction will sucrose move? Which direction will glucose move? Which direction will fructose move?

Active Transport Def’n: –The pumping of solutes against their gradients –Requires an input of energy by the cell –Used so cells can “stockpile” extra supplies

Electrogenic Pumps Voltage across membranes = stored energy that can be used for cellular work Sodium-Potassium Pump: –3 Na+ OUT of the cell for every 2 K+ pumped in –Net transfer of one positive charge from cytoplasm to ECF Very important for transferring signals between nerve cells

Sodium-Potassium Pump

Cotransport Substance that has been pumped across a membrane can do work as it “leaks” back by diffusion Another substance “hitches a ride”

Endocytosis & Exocytosis Def’n: –The movement of large molecules (polysaccharides, proteins, etc.) across the membrane –Endocytosis = cell takes in macromolecules –Exocytosis = cell secretes macromolecules

Endocytosis Cell takes in macromolecules by forming vesicles made from the plasma membrane Phagocytosis = “cell eating” –Large molecules Pinocytosis = “cell drinking” –Small molecules & liquids Receptor-mediated endocytosis = seeks out specific molecules

Endocytosis

Exocytosis The cell secretes macromolecules by the fusion of vesicles with the plasma membrane Used to release hormones, chemical signals, etc.

Signal Transduction Pathway We’ll discuss this later… But for now: –The cell’s plasma membrane is an important player in a cell’s ability to sense and respond to environmental change