Ch. 2 Cells: The Living Units

  1. 1. Robert Hooke
    2. Matthias Schleiden and Theodor Schwann
    3. Rudolf Virchow
    • 1. 1st observed plant cells with a crude microscope in the late 1600s
    • 2. 1830s, bodly asserted that all living things are composed of cells
    • 3. said that cells arise only from other cells
  2. Cells
    • Are the smallest living units in the body
    • Each cell can: 
    •      -obtain nutrients and other essential substances from surrounding body fluids
    •      -use these nutrients to make the molecules it needs to survive
    •      -dispose of its wastes
    •      -maintain its shape and integrity
    •      -replicate itself
  3. 1. Organelles
    2. Human cells have 3 main parts:
    • 1. the cell's many subunits that carry out functions
    • 2. the plasma membrane, cytoplasm, and the nucleus
  4. Plasma Membrane or Plasmalemma
    is the outer boundary; the boundary fence and security gate; it forms the boundary of the cell and selectively allows materials to pass into and out of the cell
  5. 1. Ribosomes
    2. Endoplasmic reticulum (ER)
    • 1. are the assembly line; they produce proteins for cellular or extracellular function
    • not membrane bound; constructed of proteins plus ribosomal RNA
    • 2. is literally the "network within the cytoplasm" 
    • the ER is an extensive system of membrane-walled envelopes and tubes that twists through the cytoplasm
  6. Golgi Apparatus
    • is a stack of three to ten disc-shaped cisterns, each bound by a membrane it sorts, processes, and packages the proteins and membranes made by the RER
    • *(Fig. 2.7)
  7. Lysosomes
    • are the janitorial crew and recycling center; they break down used proteins and other cellular debris
    • are spherical, membrane-walled sacs containing many kinds of digestive enzymes
    • these enzymes, called acid hydrolases, can digest almost all types of large biological molecules
    • considered the cell's "demolition crew" because they break apart and digest unwanted substances
    • when a cell's internal membrane, protein, or organelles are damaged, they are encircled by a new membrane from the rough ER, forming a vesicle, then nearby lysosomes fuse with this vesicle to digest its contents
  8. 1. Cytoskeleton ("cell skeleton")
    2. Three types of rods:
    • 1. is an elaborate network of rods running throughout the cytosol
    • this network acts as the cell's "bones," "muscles," and "ligaments" by supporting cellular structures and generating various cell movements
    • 2. microfilaments, intermediate filaments, and microtubules, none of which is covered by membrane
  9. Microfilaments
    • the thinnest elements of the cytoskeleton, are strands of the protein actin 
    • also called actin filaments, they concentrate most heavily in a layer just deep to the PM
    • actin filaments interact with another protein called myosin to generate contractile forces within the cell
    • additionally, myosin acts as a motor protein to move some organelles within the cell
  10. Cytoskeletal Elements
    form the framework and infrastructure of the building; they maintain cell shape and structure and transport materials within the cell
  11. Nucleolus
    • is a dark-staining body in the cell nucleus
    • it contains parts of several different chromosomes and serves as the cell's "ribosome-producing machine"
    • specifically, it has hundreds of copies of the genes that code for ribosomal RNA and serves as the site where the large and small subunits of ribosomes are assembled
    • these subunits leave the nucleus through the nuclear pores and join within the cytoplasm to form complete ribosomes
  12. The inner and outer layers of the membrane differ some what in kinds of lipids they contain:
    • Sugar groups are attached to 10% of the outer lipid molecules = "sugar-fats" or glycolipids
    • Cholesterol makes the membrane more rigid and increases its impermeability to water-soluble molecules
    • Proteins make up about half of the PM by weight:
    •      -Integral Proteins
    •      -Peripheral Proteins
  13. Integral Proteins (PM)
    • are firmly embedded in or strongly attached to the lipid bilayer
    • Some integral proteins protrude from one side of the membrane only, but most are transmembrane proteins that span the whole width of the membrane and protrude from both sides (trans=across)
  14. Peripheral Proteins (PM)
    • are not embedded in the lipid bilayer at all
    • they attach rather loosely to the membrane surface 
    • they include a network of filaments that helps support the membrane from its cytoplasmic side and hold it together
  15. Glycocalyx (PM)
    • short chains of carb molecules attach to the integral proteins to form glycoproteins
    • these sugars project from the external cell surface, forming glycocalyx (sugar-coating)
    • glycocalyx is sticky and may help cells bind when they come together
    • glycocalyx is also a distinctive biological marker by which approaching cells recognize each other
  16. 1. Diffusion
    2. Simple Diffusion
    • 1. is the tendency of molecules in a solution to move down their concentration gradient; that is, the molecules move from a region where they are more concentrated to a region where they are less concentrated
    • 2. Small, uncharged molecules, such as oxygen, carbon dioxide, and fat-soluble molecules, can pass freely through the lipid bilayer of the PM
  17. Osmosis
    the diffusion of water molecules across a membrane
  18. Facilitated Diffusion
    • Most water-soluble or charged molecules (glucose, amino acids, ions) cannot pass through the lipid bilayer by simple diffusion
    • Such substances can cross the PM only by means of specific transport mechanisms that use the integral proteins to carry or pump molecules across the membrane or to form channels through which specific molecules pass
    • Some of these molecules move down their concentration gradient, diffusing through the PM by moving through a specific integral protein
  19. Active Transport
    other integral proteins move molecules across the PM against their concentration gradient
  20. Vesicular or Bulk Transport
    • transports macromolecules through PM
    • two general types:
    •      -exocytosis
    •      -endocytosis
  21. 1. Endocytosis
    2. Three types:
    • 1. is the mechanism by which large particles and macromolecules enter cells
    • 2. Phagocytosis, Pinocytosis, Receptor-Mediated Endocytosis
  22. Vesicle
    • a membrane walled sac
    • the membranous vesicle is pinched off from the PM and moves into the cytoplasm
  23. Exocytosis
    • is a mechanism by which substances move from the cytoplasm to the outside of the cell
    • Ex. accounts for most secretion processes, such as the release of mucus or protein hormones from the gland cells of the body
  24. 1. Cytoplasm "cell-forming material"
    2. Most cellular activities are carried out in the cytoplasm, which consist of three major elements:
    • 1. is the part of the cell that lies internal of the PM and external to the nucleus
    • 2. cytosol, organelles, and inclusions
  25. Cytosol
    • is the jellylike, fluid containing substance within which the other cytoplasmic elements are suspended
    • it consists of water, ions, and many enzymes
    • in many cell types, it makes up about half the volume of the cytoplasm
  26. Typically, the cytoplasm contains about nine types of organelles:
    • mitcohondria
    • ribosomes
    • rough and smooth endoplasmic reticulum
    • Golgi apparatus
    • lysosomes
    • peroxisomes
    • the cytoskeleton
    • Centrioles
  27. RER
    • consists mainly of stacked membrane-enclosed cavities called cisterns ("fluid-filled cavities)
    • ribosomes stud the external faces of the membranes of the rough ER, assembling proteins
    • the ribosomes attach to the membrane when protein is being made, then detach when the protein is completed
  28. The RER has several functions:
    • the ribosomes make all protein that are secreted from cells; thus, rough ER is especially well developed in gland cells that secrete a large amount of protein (Ex. mucous)
    • it makes the digestive enzymes that will be contained in lysosomes
    • it makes both the integral proteins and phospholipid molecules of the cell's membrane
    • all cell membranes start out as RER membrane ("membrane factory")
  29. SER
    • because no ribosomes are attached to its membranes, the smooth ER is not a site of protein synthesis
    • most of its functions is related to lipid metabolism, the making or breaking down of fats
    • SER is abundant in cells that make lipid steroid hormones from cholesterol and in liver cells that detoxify lipid soluble drugs
    • another important function is storing calcium ions, ionic calcium is a signal for the beginning of many cellular events (ex. muscle contractions and glandular secretion)
    • The calcium concentration in the cytosol is kept low when such events are not occurring, because most calcium ions are pumped into the ER and held there until the cells need them
  30. The Golgi apparatus follows three pathways:
    • *(Fig. 2.8)
    • A. occurs in gland cells, the protein product is contained in secretory vesicles; these vesicles ultimately release their contents to the cell's exterior by exocytosis
    • B. common in all cells, the membrane of the vesicle fuses to and contributes to the PM, whose components are constantly being renewed and recycled
    • C. also common in all cells the vesicle leaving the golgi apparatus is a lysosome that remains inside the cell
  31. 1. Mitochondria
    2. Enclosed by two membrane
    • 1. these organelles produce the energy for cellular function
    • Bean like structure; in reality they are long and threadlike (mitos=thread)
    • 2. the outer membrane is smooth and featureless, and the inner membrane folds inward to produce shelflike cristae, these protrude into the matrix, the jellylike substance within the mitochondrion
  32. Peroxisomes (toxic waste removal system)
    • they are membrane-walled sacs that resemble small lysosomes
    • they contain a variety of enzymes, most importantly oxidases and catalases
    • oxidases use oxygen to neutralize aggressively reactive molecules called free radicals, converting these to hydrogen peroxide
    • free radicals are normal by-products of cellular metabolism, but if allowed to accumulate they can destroy the cell's proteins, membranes, and DNA
    • Hydrogen peroxide is also reactive and dangerous, but it is converted by catalase into water and oxygen
    • this catalase-driven reaction breaks down poisons that have entered the cell, such as alcohol
    • abundant in liver and kidney cells
  33. Intermediate Filaments
    • are tough, insoluble protein fibers, with a diameter between those of microfilaments and microtubules
    • they are the most stable and permanent of the cytoskeletal elements 
    • their most important property is high tensile strength, that is, they act like strong guy-wires to resist pulling forces that are placed on the cell
    • they also function to link adjacent cells together by attaching specific cell junctions called desmosomes
  34. Microtubules
    the elements with the largest diameter, are hollow tubes made of spherical protein subunits called tubulins
  35. 1. Inclusions
    2. Lipid Droplets
    3. Glycosomes
    • 1. are temporary structures in the cytoplasm that may or may not be present in a given cell type
    • ex. pigments, crystals of protein, and food stores
    • the food stores, by far the most important kind, are lipid droplets and glycosomes
    • 2. are spherical drops of stored fat, their appearance can be mistaken for lysosomes but the difference is they lack a surrounding membrane
    • small lipid droplets are found in liver cells and large ones in fat cells
    • 3. store sugar in the form of glycogen, which is a long branching chain of glucose molecules, the cell's main energy source
  36. 1. Nucleus
    2. Multinucleate
    3. Anucleate
    4. The main parts of the nucleus are the:
    • 1. is the control center of the cell
    • its genetic material, deoxyribonucleic acid (DNA), directs the cell's activities by providing the instructions for protein synthesis
    • avg. 5μm in diameter=larger than any of the cytoplasmic organelles
    • it generally conforms to the overall shape of the cell
    • 2. most cells have one nucleus but some have many=multinucleate (ex. skeletal muscle)
    • 3. no nucleus (ex. red blood cell)
    • 4. nuclear envelope, nucleolus, and chromatin and chromosomes
  37. 1. Nuclear envelope
    2. Nuclear lamina
    3. Nuclear Pore
    • 1. consists of 2 parallel membranes separated by a fluid-filled space
    • the outer membrane is continuous with the RER and has ribosomes on its external face
    • it forms anew from RER after every cell division, so it is evidently a specialized part of the RER
    • 2. the inner membrane is lined by protein filaments, which maintain the shape of the nucleus
    • 3. at various points, the two layers of the nuclear envelope fuse, and nuclear pores penetrate the fused regions
    • each 34
  38. 1. DNA
    2. Four bases
    • 1. is a double helix that resembles a spiral staircase
    • it is composed of four kinds of subunits called nuclelotides, each of which contains a distinct base
    • 2. thymine (T), adenine (A), cytosine (C), and guanine (G)
  39. 1. The Cell Life Cycle
    2. Can be divided into two major periods:
    • is the series of changes a cell undergoes from the time it forms until it reproduces itself
    • 2. Interphase and mitotic phase
  40. In most cell types, division involves two distinct events:
    • Mitosis, division of the nucleus
    • Cytokinesis division of the entire cell into two cells
  41. 1. Mitosis ("the stage of threads")
    2. Four consecutive phases:
    • 1. is the series of events during which the replicated DNA of the original cell is parceled out into two new cells, culminating in the division of the nucleus
    • the chromosomes are evident as thick rods or threads
    • typically last about 2 hours
    • 2. Prophase, Metaphase, Anaphase, and Telophase
Card Set
Ch. 2 Cells: The Living Units