Think About it What s the smallest part of any living thing that still counts as being alive? Prokaryotic v. Eukaryotic Cells Can we just keep dividing living things into smaller and smaller parts, or is there a point at which what s left is no longer alive? The smallest living unit of any organism is the cell. The Discovery of the Cell The cell theory states: Exploring the Cell 1.All living things are made up of cells. 2.Cells are the basic units of structure in living things. 3.New cells are produced from existing cells. 1
Prokaryotes and Eukaryotes All cells: Contains DNA (biological information) surrounded by a thin, flexible barrier called a cell membrane BUT How are prokaryotic and eukaryotic cells different? What is a Nucleus? 2 categories of cells depending on whether they contain a nucleus. Nucleus - large membrane-enclosed structure that contains DNA (cell s genetic material) Controls many of the cell s activities. Eukaryotic cells - DNA in nucleus (separates the genetic material from the rest of the cell) Eu = Nu Prokaryotic cells - DNA in cytoplasm Pro = No Prokaryotes Prokaryotic cells Smaller/simpler than eukaryotic cells. Grow, reproduce, and respond to the environment All characteristics of life Example: Bacteria Eukaryotes Eukaryotic cells Larger/ more complex than prokaryotic cells. Dozens of structures and internal membranes. Highly specialized. Examples: plants, animals, fungi, protists 2
BACTERIA Escherichia coli 3
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Cell Structure At first glance, a factory is a puzzling place, and the sheer diversity of activity can be confusing. if you take your time and watch carefully, what might at first seem like chaos begins to make sense. The same is true for the living cell. Cell Structure 5
Cell Organization Organelles: little organs Specialized cell structures All have different jobs Cytoplasm: the fluid portion of the cell outside the nucleus Here come the Organelles!!!!!! The Nucleus Control center of the cell contains cell s DNA DNA - coded instructions for making proteins and other important molecules The Nucleus Nuclear envelope has thousands of pores, which allow material in and out Chromosomes genetic information passed from one generation to the next 6
Cell Walls Support and Protection Not in all cells Have cell walls: prokaryotes, plants, algae, fungi Do not have cells walls Animals Outside the cell membrane Allow water, oxygen, CO 2, and other substances to pass through easily Cell Membranes IN ALL CELLS Regulates what enters and leaves the cell Protects and supports the cell Has 2 layers called a lipid bilayer Properties of Lipids 2 parts to the Phospholipid Hydrophobic (water-hating) Tail Hydrophilic (water-loving) Head In membrane, form lipid-bilayer Tails facing in towards each other Heads facing out to watery environment inside and outside the cell. Fluid Mosaic Model Fluid Mosaic Model: many different kinds of molecules make up the cell membrane proteins are embedded in the lipid bilayer some of the proteins form channels (move materials in/out of cell) carb chains act as chemical ID cards allowing cells to identify one another 7
The Fluid Mosaic Model Permeable substances are able to cross a membrane Impermeable substances cannot pass across it most biological membranes are semipermeable, meaning that some substances can pass across and others cannot Vacuoles Vacuoles: large and saclike structures that store materials H 2 O, NaCl, proteins, and carbs Only in plant cells Liquid-filled vacuole increases rigidity support for leaves and flowers Vesicles Vesicles: smaller storage structures move materials around the cell Lysosomes Lysosomes: filled with enzymes that function as the cell s cleanup crew removes junk that clutter up the cell breaks down fats, carbs, and proteins that can be used by the rest of the cell breaks down old organelles 8
The Cytoskeleton Cytoskeleton: network of filaments that give cells shape and organization help transport materials around the cell two protein filaments that make up the cytoskeleton microfilaments (Smaller) microtubules (Larger) Ribosomes Ribosomes: small particles of RNA (nucleic acid) and protein found throughout the cytoplasm in all cells make proteins by following instructions from DNA Endoplasmic Reticulum Endoplasmic Reticulum: Builds many cell parts cell membrane, proteins, lipids and carbs Endoplasmic Reticulum Rough ER: has ribosomes on surface Makes proteins Smooth ER: NO ribosomes on surface Makes lipids and carbs 9
Golgi Apparatus Golgi apparatus: sorts and packages what the ER makes Packages can be stored, or leave the cell How proteins and other materials are shipped to their final destination inside/outside the cell Organelles That Capture and Release Energy Chloroplasts (Plants only) Mitochondria (Plants and Animals) All living things require a source of energy Chloroplasts Chloroplasts capture the energy from sunlight and convert it into food in a process called photosynthesis contain the green pigment chlorophyll Mitochondria Mitochondria: power plants of the cell that convert chemical energy ALL eukaryotic cells, including plants, contain mitochondria Take food and make it useable as energy in the body 10
Different Types of Cells Different types of cells have different functions The structure of a cell is based on its function. Cells differ in numbers of organelles Cells differ in types of organelles Cell Transport Passive Transport Passive transport- the movement of materials across the cell membrane without using energy Passive Transport Diffusion: the process by which solute particles move from an area of high concentration to an area of lower concentration. Solution Solute + solvent Concentration amount of substance in a given volume Cytoplasm: A solution of many different substances (solutes) dissolve in water. 11
Passive Transport Diffusion Down concentration gradient From higher concentration to lower concentration Affected by size (more you have, the longer it takes) Simple Diffusion Suppose a substance is present in unequal concentrations on either side of a cell membrane. TYPES of diffusion: Simple diffusion Diffusion through the lipid bilayer (small molecules like O 2, CO 2 ) Facilitated diffusion Diffusion through a channel protein (small molecules) EXAMPLE : Osmosis water molecules through aquaporins Simple Diffusion If the substance can cross the cell membrane, its particles will tend to move toward the area where it is less concentrated until it is evenly distributed. Simple Diffusion At that point, the concentration of the substance on both sides of the cell membrane is the same, and equilibrium is reached. 12
Simple Diffusion Even when equilibrium is reached, particles of a solution will continue to move across the membrane in both directions. Because almost equal numbers of particles move in each direction, there is no net change in the concentration on either side. Facilitated Diffusion Cell membranes have proteins that act as channels! Facilitated diffusion: Molecules that cannot directly move across the membrane pass through special protein channels in a process. Osmosis: An Example of Facilitated Diffusion OSMOSIS: the movement of water through cell membranes extremely important process movement of water molecules from an area of higher concentration to an area of lower concentration The inside of a cell s lipid bilayer is hydrophobic or waterhating. (Water molecules struggle to get through!) Aquaporins - water channel proteins 13
How Osmosis Works Isotonic: the concentrations of solutes is the same inside and outside the cell Hypotonic: the solution has a lower solute concentration than the cell Hypertonic: the solution has as higher solute concentration than the cell Active Transport = NEED ENERGY Active Transport Active transport- the movement of materials against a concentration difference low concentration to high concentration Requires energy (ATP) Carried out by transport proteins, or protein pumps Examples: endocytosis and exocytosis 14
Endocytosis vs. Exocytosis Endocytosis Endocytosis: Taking material into cell by means of pockets through cell membrane Exocytosis: Many cells also release large amounts of material from the cell membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell. Exocytosis 15