Chapter 8 Cell Structure

Cell Theory Schleiden, Schwann, and Virchow were the three scientists whose work led to the formation of the cell theory: All living things are made of one or more cells. Cells are the basic units of structure and function in organisms. All cells arise from existing cells.

Cell Size Small cells function more efficiently than large cells. Substances do not need to travel as far to reach the center of a smaller cell.

Common Features of All Cells Structure Function Cell Membrane Outer boundary; regulates what enters & exits a cell Cytoplasm (cytosol) Cell’s interior Cytoskeleton Web of protein fibers that hold the cell together & keep the membrane from collapsing Ribosomes Cellular structures on which proteins are made DNA Provides the instructions for making proteins

Two Major Types of Cells: Prokaryotes & Eukaryotes Smallest, most simple cell; early prokaryotes lived at least 3.5 billion years ago No nucleus & no membrane-bound organelles Example = Bacteria DNA – single, circular molecule located in the center of the cell Flagella – In prokaryotes S: long thread-like structures F: movement

Two Major Types of Cells: Prokaryotes vs. Eukaryotes Early eukaryotes evolved 2.5 billion years ago Cells that have a nucleus & organelles Organelles – internal structures that carry out specific functions Vesicles – in eukaryotes S: envelopes; pods F: move substances around the cell (vehicle) Cilia – in eukaryotes S: short, hair-like structures F: movement

Cell Membrane Located in prokaryotic and eukaryotic cells S: Phospholipid bilayer: double layer of phospholipids F: Protection; barrier between cell & its environment; maintain homeostasis Selective Permeability – determines what enters or leaves the cell.

Cell Membrane Proteins are embedded in the cell membrane. Marker Proteins – advertise cell type; protein with a carbohydrate attached Receptor Protein – recognizes & binds to substances outside of the cell Transport Proteins – helps substances move across the cell membrane (like a gate) Marker protein

Cell Organelles Nucleus (Control Center) Nuclear Envelope/Membrane Eukaryotic (Plant and Animal) S: large mass in the middle of the cell F: stores the cell’s DNA Nuclear Envelope/Membrane S: surrounds the nucleus; envelope F: controls movement in/out of the nucleus through nuclear pores Nucleolus S: area inside the nucleus F: assembles ribosomes

Cell Organelles Ribosomes Endoplasmic Reticulum (E.R.) Prokaryotic & Eukaryotic S: can be “free” (floating in cytoplasm) or attached to ER F: make proteins Endoplasmic Reticulum (E.R.) Eukaryotic Rough ER S: network of tubes; ribosomes sprinkled on surface F: Move proteins made by attached ribosomes into the ERinto vesicles) Smooth E.R. S: smooth surface; network of tubes with no ribosomes attached F: makes lipids & breaks down toxins

Cell Organelles Golgi Apparatus –Packaging & Distribution (UPS) Eukaryotic S: flattened sacs; look like a stack of pancakes F: Modifies & Re-packages proteins into new vesicles & sends them to the cell membrane to be released outside of the cell

Cell Organelles Mitochondria--Powerhouse Eukaryotic S: Double membrane organelle; complex matrix inside F: Convert energy from food to make energy called ATP- called cellular respiration Muscle cells (require lots of energy) may contain hundreds or thousands of mitochondria

Cell Organelles Lysosomes – Garbage Disposal S: small round pods F: contain digestive enzymes; break down old cell parts and food

Structures of Plant Cells Plant cells are also eukaryotic cells; they have 3 additional structures that are NOT found in animal cells Cell wall – S: thick wall that surrounds the cell membrane; make of cellulose F: helps support the shape of a plant cell, protects the cell from damage, & connects it with neighboring cells Chloroplasts – S: Green pods containing stacks of thylakoids F: use sunlight to make carbohydrates from carbon dioxide (CO2) and water (H2O) Central Vacuole – S: large, membrane-bound sac that takes up most of the cell’s space F: stores water, nutrients, ions, and wastes

Cytoplasm and Microtubules Location: prokaryotic and eukaryotic Structure: thick, jelly-like substance Function: interior of cell; organelles float around in it Microtubules Location: eukaryotic cells Structure: “rails” like train tracks that go around the cell Function: support, highway system for the cell

Microscopes: Compound Light Microscope Body Tube Revolving Nose Piece Objective Lens Stage Clips Diaphragm Light Source Ocular Lens/Eye Piece (10X) Arm Stage Course Adjustment Knob Fine Adjustment Knob Base

Determining Total Magnification: Microscopes Magnification – the quality of making an image appear larger than its actual size Resolution – a measure of the clarity of an image (how clear or fuzzy the image looks) Determining Total Magnification: Formula: Ocular Lens x Objective Lens = Example: 10 x 4 = 40X (Scanning Power) What would be the total magnification if you used the high power objective lens? 10 x 40 = 400X

Cell Size Small cells have a large surface area-to-volume ratio Which means…not much volume (inside) and substances do not have to travel as far to enter or leave a cell!!