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Cells
Cells are the basic unit of life and come in two main types - prokaryotic and eukaryotic. Prokaryotic cells like bacteria lack membrane-bound organelles and have no nucleus, while eukaryotic cells like animal and plant cells contain organelles and a membrane-bound nucleus. Key differences include prokaryotes having a cell wall and single circular chromosome while eukaryotes may lack a cell wall and have multiple linear chromosomes with histones. The development of the microscope allowed scientists like Hooke, van Leeuwenhoek, and Schwann to observe cells and establish that all living things are made of these basic cellular units.
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Cells
- 2. Cell – thebuilding blocks The cell is the basic unit of life; living cells are made of cells. Cells Tissue Organ System Organism They are viewed using a microscope.
- 3. The Cell Theory ConceptEvidence 1. Living cells are made of cells Observations by microscopists 2. Cells are the smallest unit of life Discovery of viruses Biochemical investigations of organelles 3. Cells come from pre-existing cells Pasteur’s observation Observation on the behaviour of cells at division 4. Cells contain a blueprint for growth, development and behaviour Observations on the behaviour of chromosomes 5. Cells are the site of the chemical reactions of life Discovery of enzymes Discovery of biochemical events Discovery of cell ultrastructure
- 4. The Discovery ofCell 1590 Hans and Zacharias Jansen constructed the first crude compound microscope 1665 Robert Hooke looked at a slice of cork under a compound microscope and discovered the cork was made up of small “boxes” that he named cells 1680 Anton von Leeuwenhoek looked at blood and pond water under a microscope. He saw moving microscopic creatures that he named “Animalcules.” 1824 Henri Dutrochet came to the conclusion that all living things are made of cells. In other words, cells are the “building blocks” of life
- 5. The Discovery ofCell continued… 1826 Pierre Turpin observed cell division 1838 Matthias Schleiden studied plant tissue under a microscope and discovered all plants were composed of “cells” 1839 Theodor Schwann studied animal tissue under a microscope and found that animals were also composed of cells Hugo von Mohl described the process of mitosis in plant cells 1855 Rudolph Virchow stated that all living cells come from other living cells 1873 Anton Schneider observed chromosomes inside of a cell during cell division
- 6. Relative Sizes ofMolecules vis-à-vis Cell Biological Entity Size Molecules 1 nm Cell Membrane thickness 10nm Virus 100nm Bacteria 1 um Cell Organelles Up to 10um Cells Up to 100 um
- 7. Microscopy and Magnification Microscope– an instrument used to see objects that are too small for the naked eye. Compound Microscopes - are designed with a compound lens system. Electron Microscope (EM)– use a beam of highly energetic electrons to examine objects on a very fine scale. Transmission EM – yields the size, shape and arrangement of the particles which make up the specimen as well as their relationship to each other on the scale of atomic diameters. Scanning EM – yields the surface features of an object or "how it looks", its texture; detectable features limited to a few manometers Magnification - the process of enlarging the size of something, as an optical image. Magnification = size of image___ size of specimen
- 8. Cell Surface Area:Volume Ratio Surface area - units squared (m2) Volume – units cubed (m3) General Principle: As the cell gets bigger in size, the surface area:volume ratio becomes lesser. The rate of metabolism of a cell is a function of its mass, whereas the rate of exchange of materials and heat energy that metabolism generates is a function of the cell’s surface area. rate of metabolism : cell mass rate of exchange of materials and heat : cell’s surface
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- 10. Types of Cells Prokaryote– unicellular organisms whose cell lacks membrane bound nucleus and organelles ex. Bacterial cell Eukaryote – unicellular to unicellular organisms whose cell contain a membrane bound nucleus and organelles ex. Animal and plant cell N.B. Both unicellular and multicellular organisms can do the basic life processes.
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- 12. Prokaryotic Cell Structure Prokaryoticcells are not as complex as eukaryotic cells. They have no true nucleus as the DNA is not contained within a membrane or separated from the rest of the cell, but is coiled up in a region of the cytoplasm called the nucleoid. Capsule - Found in some bacterial cells, this additional outer covering protects the cell when it is engulfed by other organisms, assists in retaining moisture, and helps the cell adhere to surfaces and nutrients. Cell Wall - Outer covering of most cells that protects the bacterial cell and gives it shape. Cytoplasm - A gel-like substance composed mainly of water that also contains enzymes, salts, cell components, and various organic molecules. Cell Membrane or Plasma Membrane - Surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell. Pili - Hair-like structures on the surface of the cell that attach to other bacterial cells. Shorter pili called fimbriae help bacteria attach to surfaces. Flagella - Long, whip-like protrusion that aids in cellular locomotion. Ribosomes - Cell structures responsible for protein production. Plasmids - Gene carrying, circular DNA structures that are not involved in reproduction. Nucleiod Region - Area of the cytoplasm that contains the single bacterial DNA molecule.
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- 14. Eukaryotic Cell Structure OrganelleFunction Nucleus The “brains” of the cell, the nucleus directs cell activities and contains genetic material called chromosomes made of DNA. Mitochondria Make energy out of food Ribosomes Make protein Golgi Apparatus Make, process and package proteins Lysosome Contains digestive enzymes to help break food down Endoplasmic Reticulum Called the "intracellular highway" because it is for transporting all sorts of items around the cell. Vacuole Used for storage, vacuoles usually contain water or food. (Are you are thirsty? Perhaps your vacuoles need some water!) Plant cells also have: Chloroplasts Use sunlight to create food by photosynthesis Cell Wall For support
- 15. Characteristic Prokaryotes Eukaryotes Sizeof cell Typically 0.2-2.0 m m in diameter Typically 10-100 m m in diameter Nucleus No nuclear membrane or nucleoli (nucleoid) True nucleus, consisting of nuclear membrane & nucleoli Membrane-enclosed organelles Absent Present; examples include lysosomes, Golgi complex, endoplasmic reticulum, mitochondria & chloroplasts Flagella Consist of two protein building blocks Complex; consist of multiple microtubules Glycocalyx Present as a capsule or slime layer Present in some cells that lack a cell wall Cell wall Usually present; chemically complex (typical bacterial cell wall includes peptidoglycan) When present, chemically simple Plasma membrane No carbohydrates and generally lacks sterols Sterols and carbohydrates that serve as receptors present Cytoplasm No cytosketeton or cytoplasmic streaming Cytoskeleton; cytoplasmic streaming Ribosomes Smaller size (70S) Larger size (80S); smaller size (70S) in organelles Chromosome (DNA) arrangement Single circular chromosome; lacks histones Multiple linear chromosomes with histones Cell division Binary fission Mitosis Sexual reproduction No meiosis; transfer of DNA fragments only (conjugation) Involves meiosis
- 16. Eukaryotic and ProkaryoticCell Structure Cell Structure Prokaryotic Cell Typical Animal Eukaryotic Cell Cell Membrane Yes Yes Cell Wall Yes No Centrioles No Yes Chromosomes One long DNA strand Many Cilia or Flagella Yes, simple Yes, complex Endoplasmic Reticulum No Yes (some exceptions) Golgi Complex No Yes Lysosomes No Common Mitochondria No Yes Nucleus No Yes Peroxisomes No Common Ribosomes Yes Yes