Cell functions and structures

• Anton van Leewenhoek


  Dutch microscope inventor. The first person to observe microorganisms, leading to the discovery of cells
• Anton van Leewenhoek's microscope


  • Rather simple, but powerful enough to enable him to open up a whole new world – the world of microscopic organisms, which had never before been seen
• Robert Hooke


  Used a microscope to examine a thin slice of cork. Closeup reminded him of tiny rooms where monks lived (monasteries), named them cells
• Cell theory


  Schleiden, Schwann and Virchow
• Cell theory


  1. Schleiden -1838 botanist concluded that all plants are composed of cells

  2. Schwann- 1839 zoologist came to the same conclusion about animals

  3. Virchow- - 1855 physician studied how disease affects living things, reasoned that cells come only from other cells
• Three points of cell theory


  • All living things are composed of one or more cells
  • Cells are the basic units of structure and function in an organism
  • Cells come only from the reproduction of existing cells
• Cell Diversity


  • Variety of shapes (short or long, circular or oval)
  • Variety of sizes (some large enough to be seen by the unaided eye, prokaryotic cells are smaller than eukaryotic cells)
  • Variety of internal structures called organelles
• Cell shapes


  • In nerve cells, the long extensions reach out in different directions to receive and transmit nerve impulses
  • The flat shape of dead skin cells cover the body surface
  • White blood cells can change their shape, leave the blood, and entering areas surrounding the blood vessels, allows them to move through narrow openings and destroy the bacteria
• Cell membrane


  The thin membrane that surrounds the entire cell
• Nucleus


  The large organelle near the center of the cell that contains the majority of the cell's genetic information and directs most of the activities of the cell
• Organelles


  Cell components that perform specific functions for the cell
• Organisms whose cells contain a membrane-bound nucleus and other organelles


  • Eukaryotes (plants, animals, fungi, protists)
• Organisms whose cells lack a nucleus or membrane-bound organelles

  • Prokaryotes (bacteria and archaea)
• Mitochondria


  Scattered throughout the cytosol, they are the sites of chemical reactions that transfer energy from organic compounds to ATP
• Mitochondria


  • Numerous in cells that need high energy requirements
  • Have their own DNA and new mitochondria arise only when existing ones grow and divide
  • Surrounded by 2 membranes (smooth outer membrane and inner membrane with many long folds called cristae)
• Ribosomes


  Most numerous and not surrounded by membranes, important in the synthesis of proteins
• Ribosomes


  • Each ribosome is a collection of 2 organic compounds which are proteins and RNA
  • Some are free within the cytosol, some are attached to the ER
  • Proteins to be used within the cytosol are produced on the free ribosomes, proteins to be inserted into membranes or exported from the cell are produced on the ribosomes attached to the ER
• Endoplasmic Reticulum (ER)


  A system of membranous tubules and sacs that functions primarily as an intracellular highway, a path along which molecules move from one part of the cell to another
• Types of ER


  • Smooth ER (involved in synthesis of steroids, regulation of calcium levels, breakdown of toxic substances)
  • Rough ER (prominent in cells that make large amounts of proteins to be exported or inserted into the cell membrane)
• Golgi Apparatus


  A collection of smooth, membrane-bound sacs that works with the ER in preparing materials for release by the cell and also modifies proteins for export
• Lysosomes


  Small, spherical organelles that enclose hydrolytic enzymes within single membranes, can digest proteins, carbohydrates, lipids, DNA, and RNA, as well as old organelles, viruses and bacteria
• Lysosomes


  • Common in cells of animals, fungi and protists but rare in plant cells
  • In multicellular organisms, they play a role during early development (e.g. forming spaces between fingers)
• Cytoskeleton


  A network of long protein strands located in the cytosol that helps maintain cell structure and movement of organelles
• Components of the cytoskeleton


  • Microfilaments (composed of actin, contribute to cell movement and muscle contraction)
  • Microtubules (largest strands, form spindle fibers during cell division)
• Cilia and Flagella


  Hair-like organelles that extend from the cell surface and assist in movement
• Differences between cilia and flagella


  • Cilia (short and numerous on a cell, found in many eukaryotic cells, help propel tiny organisms and trap particles in respiratory tract)
  • Flagella (long and less numerous, found on many cells including sperm, can swiftly propel unicellular organisms or specialized cells)
• Nucleus


  Most important structure within a eukaryotic cell, stores hereditary information in DNA, synthesizes RNA and ribosomes
• Nucleus


  • Surrounded by a double membrane called the nuclear envelope
  • Contains fine strands of chromatin (DNA and protein) that form chromosomes when the cell is about to divide
  • Maintains its shape with the help of a protein skeleton called the nuclear matrix
• Nucleolus


  A spherical area within the nucleus where ribosomes are synthesized and partially assembled before passing through the nuclear pores to the cytosol
• Cell Wall


  A rigid structure that covers plant cells, lies outside the cell membrane, provides support and protection
• Components of cell walls


  • Long chains of cellulose (complex carbohydrates)
  • Embedded in proteins and other carbohydrates that harden the entire structure
• Types of cell walls


  • Primary walls (constructed first as the cell expands)
  • Secondary walls (developed between the primary wall and cell membrane when the cell reaches max size, tough and woody)
• Vacuoles


  Fluid-filled organelles in plant cells that store enzymes, metabolic wastes, and other materials
• Vacuoles


  • May occupy up to 90% of a plant cell's volume
  • Can store toxic wastes away from the rest of the cell, providing defense against plant-eating animals
• Plastids


  Organelles in plant cells that are surrounded by 2 membranes and contain DNA, can store starch, fats, or pigments
• Chloroplasts


  The type of plastid that contains the thylakoid system where photosynthesis occurs
• Differences between plant and animal cells


  • Plant cells have a cell wall and chloroplasts, animal cells do not
  • Plant cells have a large vacuole, animal cells do not
  • Animal cells have centrioles, centrosomes, and lysosomes that plant cells do not
• Homeostasis and transport are important processes that occur within cells, with differences between active and passive transport
• Organelles


  • Surrounded by 2 membranes
  • Contain DNA
• Plastids


  • Store starch
  • Store fats
  • Contain pigments that absorb visible light