Biology Review Cell Biology 2 Much of the text material is from, Essential Biology with Physiology by Neil A. Campbell, Jane B. Reece, and Eric J. Simon (2004 and 2008). I dont claim authorship. Other sources are noted when they are used. Note 3 Outline Cell theory Microscopy Cells and their components 4 Cell Theory 5 Cells were first described in 1665 by the British scientist, Robert Hooke, from microscopic examination of thin slices of cork from Mediterranean oak trees. Over the next two centuries, cells have been found in all organisms that were examined. The accumulation of evidence led to cell theory: all organisms are com- posed of cells. Cell theory was later expanded to encompass observations that cells arise from previously existing cellsthat is, cells do not spontaneously form. 6 Cellular Structure of CorkRobert Hookes drawing. 7 Microscopy 8 Microscopic World of Cells Every cell in a living organism is intricate and extremely complex. The most elaborate machine, if it were reduced to the size of a cell, would seem simple in comparison. Cells must be very small for materials to to move in and out to meet their metabolic needs. 9 Microscopic World of Cells (continued) Organisms are single-cellular (bacteria, archaea, and some pro- tista) or multi-cellular (other protista, fungi, plants, and animals). The human body has many trillions of cells that work cooperatively to perform their functions, which is a focus of this course on human physiology. 10 Light Microscope The light microscope was invented during the Renaissance, about 400 years ago. Visible light passes through a specimenthe lens enlarges the image and projects it onto the retina of the human eye, film camera, or elec- tronic sensing device. Modern light microscopes have compound lenses to reduce chromatic (color) aberration and spherical aberration to improve the quality of the viewed image. 11 Light Microscope (continued)A modern lab and classroom version. 12 Magnification and Resolving Power Two key aspects of microscopes are their magnification and resolving power. Magnification is the increase in an objects apparent size compared to its actual size. Resolving power is the ability to show two or more objects as distinct entities. Due to limitations in resolving power (about 0.2 m), the maximum useful magnification of a light microscope ranges between X400 and X1000. 13 Red blood cells and a stained white blood cell.Light Micrograph 14 Another Light Micrograph Coronal cross section of a rat brain under low-power magnification (about X10). 15 Do you have experience using a light microscope? If so, what did you discover? 16 Electron Microscope Electron microscopes use electron beams rather than light to access a very small world. Resolving power is much higher than for light microscopes, allowing for much higher useful magnifications. Electron micrographs can be produced at magnifications of X100,000 or higher. The study of cells advanced rapidly when electron microscopes were developed in the 1950s. 17 Electron Microscope (continued)A somewhat dated, electron microscopy laboratory. 18 Types of Electron Microscopes Scanning electron microscopes are used to study the surfaces of cells. Transmission electron microscopes are used to explore the inter- nal structures of cells. Electron microscopes are used with prepared (dead) specimens, while light microscopes are suited for either live or prepared speci- mens. 19 Electron MicrographA collection of pollens. 20 Another Electron MicrographEscherichia coli (E. coli). 21 Cells and Their Components 22 Prokaryotic and Eukaryotic CellsEukaryotic cell Plants, animals, and fungi (animal cell shown)Prokaryotic cell Bacteria and archaea (bacterium shown) Not to scale: A prokaryotic cell is about 1000 times smaller in volume than a eukaryotic cell. 23 Cell Comparisons Prokaryotic cells first appeared about 3.5 billion years ago; eukary- otic cells appeared about 1.8 billion years later. Eukaryotic cells are much largerthey are about ten times the dia- meter of prokaryotic cells and their volume is even greater (by about a thousand times). The DNA in eukaryotic cells is in the nucleus surrounded by a mem- brane, while the DNA in prokaryotic cells is in an unenclosed central region. Prokaryotic and eukaryotic use different processes for copying their DNA (replication versus transcription). 24 How do some types of prokaryotic cells affect our lives? 25 Cell Comparisons (continued) Eukaryotic cells have several types of membrane-enclosed organ- elles with specialized functions, while prokaryotic cells have far fewer. Eukaryotic cells use aerobic respiration and anaerobic respiration for chemical energy production, while prokaryotic cells only use an- aerobic respiration. Organelle = a compartment within a cell that has a specialized function, for example, ribosome, lysosome, Golgi apparatus, or mitochondrion. (http://sis.nlm.nih.gov/enviro/iupacglossary/glossaryo.html) Most of these membrane-enclosed organelles, as we will discuss, are unique to eukaryotic cells. 26 Some Animal Cell Types 1. Blood 2. Purkinje (cerebellum) Images 1 and 2,Image 3,Image 4,3. Adipose 4. Intestinal 27 Components of Eukaryotic Cells ComponentAnimal cell Plant cell Plasma membrane x x Nucleus x x Chromosomes x x Cytoplasm x x Ribosomes x x Endoplasmic reticulum x x Golgi apparatus x x Lysosomes x Rare Mitochondria x x Cytoskeleton x x Vacuoles and vesicles x x Flagella and cilia x Rare Centrioles x x Cell wall -- x Chloroplasts -- x Central vacuole -- x 28 Plasma Membrane A plasma membrane separates the intracellular space of a cell from its surrounding extracellular space. The plasma membrane defines the cell boundary. The membrane is a double layer (bilayer) of phospholipid molecules. Computer generated graphic 29 Plasma Membrane (continued) The glycerol heads with their attached phosphate groups orient toward the fluids in the intracellular and extracellular spaces because they are hydrophilic. The two lipid tails attached to the glycerol molecule orient inward since they are hydrophobic. Phospholipid membranes are self-organizing because of their hydrophilic and hydrophobic properties. 30 Plasma Membrane (continued) Chemical receptors and other protein molecules are embedded in the plasma membrane. The plasma membrane is not a static structure of molecules fixed in place. Phospholipids and most proteins are drift about in the plane of the membrane, much like icebergs floating in the high-latitude oceans. Therefore, the plasma membrane is described as a fluid mosaic. 31 Selective Permeability, Membrane Transport The plasma membrane and membranes that enclose organelles are selectively permeable. The membranes allow some substances to pass while blocking others from entering a cell. Some substances can diffuse across the plasma membrane including O 2, CO 2, and some nutrients. The passage of other substances requires the use of transport proteins through the plasma membrane. Glucose, a major source for cellular energy, is attached to a transport protein to enter cells. 32 Nucleus The nucleus of a cell has the genetic code of life in the form of DNA. The nucleus is enclosed in a double membrane known as the nuclear envelopeit is similar in molecular structure to the cells plasma mem- brane. Pores in the nuclear envelope permit the passage of material between the nucleus and cytoplasm (messenger RNA and components of ribo- somes). Electron micrograph 33 Nucleus (continued) DNA molecules and proteins in the nucleus form long fibers called chromatin. Each fiber makes-up one chromosomehumans usually have 46 chromosomes in somatic cells of their bodies. A ball-like mass in the nucleus, called the nucleolus, produces the components of ribosomes. 34 Cytoplasm The cytoplasm is the region between the cells plasma membrane and its nucleus. It contains organelles suspended in a fluid known as cytosol. Each type of organelle performs specific functions, as we will discuss. Most organelles in eukaryotic cells have their own phospholipid mem- branes. Electron micrograph 35 Ribosomes Ribosomes are found in the cytoplasm, and often in close proximity to the cell nucleus. These organelles synthesize the polypeptides that make up proteins from amino acids. Computer generated graphic 36 Ribosomes (continued) The genetic information of DNA is transferred via messenger RNA (mRNA) to the ribosomes to provide instructions for the synthesis of polypeptides that form proteins. Some ribosomes synthesize proteins for use in the cytoplasm or plasma membrane. Other ribosomes make proteins for secretion by the cell for use by other cells. 37 Endoplasmic Reticulum The endoplasmic reticulum (ER) synthesizes many types of biological molecules. ER is made-up of an elaborate system of tubes and sacs in the cyto- plasm. The two types of endoplasmic reticulum are rough ER and smooth ER. Electron micrograph 38 Rough ER Rough ER has the appearance of roughness due to the ribosomes that stud its surface. Rough ER produces proteins found in the plasma membranes of cells and organelles, and for secretion by the cell. Cells that secrete substantial amounts of proteins, such as salivary glands of the mouth, are rich in rough ER. Products are sent to other locations in the cell in membrane covered packages called transport vesiclesthe vesicles bud and separate from the ER. 39 Smooth ER Smooth ER lacks the ribosomes that stud the surface of rough ER. One function is the synthesis of steroids in the testes, ovaries, and adrenal glands. 40 Smooth ER (continued) Smooth ER in liver cells (known as hepatocytes) produce enzymes that detoxify drugs and poisons in the blood. The amount of smooth ER increases (up-regulates) with exposure to certain drugs. The body increases its tolerance to the drug, which requires higher dosages to achieve the same physiological effect. One hallmark of addiction is increased drug tolerance (along with a psychological component). 41 Golgi Apparatus The Golgi apparatus works with the endoplasmic reticulum to refine, store, and distribute molecules synthesized by the cell. Products synthesized in the ER reach the Golgi apparatus via trans- port vesicles. Enzymes in the Golgi apparatus modify many of the products synthe- sized by the ER. Electron micrograph 42 Golgi Apparatus (continued) The Golgi apparatus is named for its discoverer, Camillo Golgi. They work with the ER to refine, store, and distribute chemical products. The Golgi apparatus tags proteins with addresses of their destinations within the cell. Vesicles that bud from the Golgi apparatus distribute products to other organelles. Other products are sent to the plasma membrane for secretion by the cell. 43 Lysosomes Lysosomes are membrane-enclosed sacs of enzymes for digestion to prevent self-destruction of the cell. The enzymes breakdown macromolecules including proteins, glycogen, fats, and nucleic acids. Molecules from this process nourish the cell. Electron micrograph 44 Lysosomes (continued) Other lysosomes function as recycling centers by engulfing and digest- ing damaged organelles and making some of these molecules available for the synthesis of new organelles. Lysosomes in white blood cells ingest bacteriatheir enzymes destroy bacterial cell walls. Another type of lysosome destroys the webbing that joins the fingers in human embryos. 45 Mitochondria Mitochondria perform cellular respiration to harvest chemical energy for cellular work. The processes, known as the Krebs or citric acid cycle and the elec- tron transport chain, are aerobic since as require a continuing supply of oxygen molecules. Sugars and other types of food molecules are converted to a form of energy known as ATP. Electron micrograph 46 Mitochondria (continued) The inner membrane of a mitochondrion contains enzymes and other molecules for cellular respiration. The membrane has many folds to increase its surface area and maxi- mize ATP output. Mitochondria may have been invaders in the earliest eukaryotic cells. Now, a symbiotic relationship exists between mitochondria and eukary- otic cells. Mitochondriaplural; mitochondrionsingular. Symbiotic = an interaction between dissimilar organisms, especially when they benefit each other. 47 Mitochondria (continued) Mitochondrial DNA is passed through maternal lineage from mother to daughter. The DNA maintains remarkable stability from generation to generation. These aspects enable mitochondrial DNA to be used in tracing popula- tion groups 10,000 years or more back in time as they have migrated. 48 Cytoskeleton Microtubules of several different proteins form a network of fibers known as the cytoskeleton. The cytoskeleton is found in the cytoplasm. It provides structural support for a cell and a means for specialized movements. Color enhanced electron micrograph 49 Cytoskeleton (continued) Microtubules also hold the organelles in place in the cytoplasm and guide the movement of vesicles. Other microtubules guide the movement of individual chromosomes when cells divide. 50 Cytoskeleton (continued) Unlike a bony skeleton, a cytoskeleton can be rapidly dismantled in one location to reform in a new location of the cell. This process occurs through the removal and replacement of its pro- tein units. It contributes to the crawling motion of single-cell amoeba and move- ment of white blood cells. 51 Vacuoles and Vesicles Vacuoles and vesicles are membrane enclosed sacs that bud from a cells plasma membrane, endoplasmic reticulum, and Golgi appar- atus. They differ in their functionsfor example, vacuoles in the plasma membrane of a cell engulf food molecules for transportation to the lysosomes. Electron micrographIn neurons, vacuoles known as synaptic vesicles store neurotransmitters to com- municate with other neurons, muscles, and glands. 52 Flagella Some eukaryotic cells have appendages and specialized microtub- ules that enable movement. Flagella (singular: flagellum) propel cells by an undulating, whip-like motion. Flagella usually occur singlyfor example, in sperm that must travel the length of the female reproductive tract to fertilize an egg released by an ovary. Human sperm, Electron micrograph 53 Cilia Cilia, which are usually shorter and more numerous than flagella, pro- duce motion through rhythmic back-and-forth movements (think of the rows of oars on an ancient galley ship). The cilia of cells in the oviducts (fallopian tubes) can sweep a fertilized egg along the reproductive path for implantation in the uterus.Electron micrograph 54 Cilia (continued) Tobacco smoke can damage or destroy the cilia in the bronchial tubes, which interferes with the bodys normal means for removing pollutants from the lungs. Smokers cough is the bodys compensatory attempt to cleanse the respiratory system. 55 Extracellular Matrix Most animal cells secrete a thick, sticky substance called extracel- lular matrix. It helps hold cells together in tissues, and provides protective and supportive functions. 56 Cell Junctions The cells in many animal tissues are connected by cell junctions. Tight junctions bind cells to form a leak-proof sheet of tissue such as in the small intestine and large intestine to prevent fluids from leaking into the abdominal cavity. Anchoring junctions bind cells together while allowing some molecules to pass among the spaces between them. Communicating junctions contain channels to permit water and other small molecules to flow among neighboring cells. 57 Centrioles Centrioles are can-shaped structures of microtubules in the cyto- plasm that support cell division. We will cover their functions when we discuss mitosis and meiosis in the next lecture. Computer generated graphic 58 Can you describe the components of an animal eukaryotic cell and their basic functions?