Cells
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Cells BIOLOGY OCTOBER 2014 What are cells? The basic unit of life. The smallest things that can carry out life processes. Some organisms are made up of a single cell (Ex. Bacteria and Archaea) Others are made up of trillions of cells. (larger organisms) Size of cells The largest cell in the human body is the ovum, or egg cell. The smallest cell in the human body is the sperm. Roughly 1 mm in diameter and just visible to the naked eye 60 micrometers (0.002 inches) in length, and not visible to the naked eye The longest cells in the human body is the neuron (nerve cell), which can be over a meter long. Links the brain to other parts of the body. So, how do we see cells? Microscope Anton van Leeuenhoek Developed a simple microscope in the 1600s Several types of modern microscope Compound light microscope Uses light and lenses to magnify images These are the ones we’ll be using Electron microscopes SEM, TEM, and STM Read about these in your book. Magnification The power of magnification is the product of the magnifications of the individual lenses Eyepiece x objective An eyepiece with magnification of 10x and an objective lens with magnification of 40x would equal 10 x 40 =400x magnification 1. Ocular Lens (Eyepiece) This is what you look through to see the image. It contains a lens (usually 10x magnification) 2. Arm Structural piece Holds the parts of the microscope in the proper places. THE ARM IS NOT A HANDLE Never carry the microscope by the arm alone. One hand around the arm, the other hand underneath the base to support it. Microscopes are very expensive. Use the utmost care when transporting it. 3. Stage This is the flat portion where you put the slide. A hole in the stage allows light to pass through the slide 4. Course Focus Moves the stage up and down. Doing so brings the object into focus. Move it until the image becomes visible. It will still be a bit blurry. Note about the Course Focus: Using the course focus to try to get a better image could result in the stage moving the slide up into the objective. This could crack the slide and/or objective lens, and could be a VERY expensive mistake. 5. Fine Focus Makes tiny adjustments to the stage. Once you have found the image, use the fine focus to make it clear. 6. Base Bottom of the microscope. Structural and support. Remember, one hand underneath the base and the other holding the arm. 7. Light Source A light bulb Sends light through the slide. 8. Diaphragm Allows you to adjust the mount of light that come through. 9. Slide Clips Little metal pieces that hold the slide in place. Make sure that the slide is under the clips. You do not want the slide moving after you have just found the image 10. Objectives Each is a different lens that magnifies the image. Most microscopes have several of these ranging from 4x to 200x Begin on the lowest objective to find the image, then increase to zoom it in. 11. Rotating Nosepiece Holds the objectives Twist to change magnification. 12. Body Tube Holds eyepiece The cell theory Developed with the contributions from 4 scientists (guaranteed matching question!) Robert Hooke Matthias Schleiden Theodor Schwann Rudolf Virchow Robert Hooke 1600 English scientist Looked through a microscope at cork (dead oak bark) Noticed small compartments Called these compartments “cells” Matthias Schleiden 1800s German Botanist (studied plants) Observed that all of the plants he saw were made of cells Theodor Schwann 1800s German physiologist (studied how body works) Interesting facts: Coined the term “metabolism” Important cells in the nervous system are named after him (Schwann cells-protect neurons) Discovered pepsin-the enzyme that breaks down food in the stomach Through his work, he determined that all animals were made of cells Rudolf Virchow 1800s German doctor Interesting facts: First to recognize leukemia cells Credited in a lot of early cancer research First person to determine that disease can pass from other animals to humans and vice versa. Used his research to determine that cells come from other cells. Types of Cells Some cells have small, specialized structures called organelles. Each has a specific function for the cell. Organelle=little organ Similar to the organs in your body, each of which does some job to keep you functioning, organelles work together to keep the cell functioning. 2 main types of cells Differentiated by whether they have organelles or not. Prokaryotic Cells The simpler of the 2 cell types Lack organelles Prokaryotic means “Before nucleus” Most unicellular organisms are prokaryotic Bacteria, Archaea Eukaryotic Cells Much more complicated Contain membrane-bound organelles Eukaryotic=“True nucleus” Most of the organisms you are familiar with Plants, animals, fungi Mostly multicellular, though some are unicellular The nucleus controls the cell and contains DNA The Plasma Membrane Flexible boundary between the cell and its environment. Jobs: Provides protection, allows materials to enter and exit the cell Key in homeostasis-process of keeping proper internal conditions Cell needs nutrients. These are acquired as they pass through the membrane. Selective Permeability- Membrane allows some materials to enter, while keeping others out. Similar to a screen on a window (lets air in, prevents birds, insects, etc.) Some materials, such as water, enter and exit freely. Other particles can only enter and exit at certain times. Structure of the Plasma Membrane Phospholipid bilayer Phospholipids are large molecules of fatty acids 2 parts Polar head-attracted to water (also a polar molecule) Nonpolar tail The head is hydrophilic (attracted to water) The tail is hydrophobic (avoids water) This causes the heads and tails to orient in a certain way Water exists outside the cell and inside the cell Fluid Mosaic Model Fluid=The cell membrane is fluid, meaning it is constantly moving. Mosaic=The membrane has a “pattern” Proteins are embedded in the membrane Proteins do several jobs, including transport and support Proteins in the Plasma membrane Transport proteins- move needed materials into and out of the cell Some proteins help cells to identify chemical signals and each other. Others in the inner membrane help give the cell support by attaching to internal structures Eukaryotic Cell Structure Eukaryotic Cells have many different parts Structures Organelles Each portion does something for the cell. Cellular boundaries Plasma membrane Job: Protection and selectively allows materials to enter and exit. Found in: All cells Cell wall-rigid structure outside the plasma membrane Job: additional support and protection Found in: Plants, fungi, some protists, and many prokaryotic cells Cellular Control Nucleus-control center of the cell Job: Central in formation of proteins, controls the activity of organelles Found in: All eukaryotic cells The nucleus contains the instructions for making proteins Chromatin-strands of DNA Forms chromosomes Nucleus also contains an organelle called the nucleolus Makes ribosomes (to be discussed soon) Cytoplasm Jelly-like fluid within the cell. Outside of the nucleus Suspends the organelles Found in all cells Assembly Endoplasmic Reticulum (E.R.) Job: Site of chemical reations Found in: Most eukaryotic cells 2 types: Smooth E.R. Rough E.R. Many biochemical reactions, including production and storage of lipids Similar to Smooth E.R., but studded with ribosomes Ribosomes Job: Making Proteins Found in: most eukaryotic cells, and some prokaryotic cells Can be free-floating in the cytoplasm, or attached to R.E.R. Sorting and Packaging Golgi apparatus Job: Modifies proteins. Sorts them and packages them into organelles called vesicles. Found in: Most eukaryotic cells Vesicles Job: Movement of proteins Found in: Most eukaryotic cells Storage and recycling Vacuoles Job: Storage of materials, including food, water, enzymes Found in: Most eukaryotic cells and some prokaryotic cells Large one called central vacuole found in plant cells for storage of water. Plant cells typically have one large one, animal cells have many small ones Lysosomes Job: Break down materials in a cell, including food particles, invaders such as viruses and bacteria worn out or broken down cell parts Found in most eukaryotic cells Energy Chloroplasts Job: Convert light energy to chemical energy that can be used Found in: Plant cells and some unicellular organisms Contain a pigment called chlorophyll, which traps light energy Mitochondria Job: Transfer energy from food into usable energy Found in: Most eukaryotic cells Support Cytoskeleton Job: Gives cell shape, supports cell, allows some cells to move. Found in: most eukaryotic cells Cytoskeleton is made up of 2 main parts: Microtubules-thin, hollow cylinders made up of protein Microfilaments- smaller, solid protein fibers Centrioles Job: assist in cell division Found in: most eukaryotic cells Made up of microtubules Locomotion Cilia and flagella Some cells, especially unicellular organisms, are capable of movement They use cilia and flagella to move around their liquid environment Cilia-short, hair-like structures Used similar to rowboat Cells typically have many of these Flagella-longer whip-like projections Used like a motor on a boat. Cells typically have only 1 or 2
