Cell Structure: A Tour of the Cell

1

• Chapter 7
• Cell Structure A Tour of the Cell

2

• Cell
• A basic unit of living matter separated from its
  environment by a plasma membrane.
• The smallest structural unit of life.

3

• Cell Theory Developed in late 1800s.
• 1. All living organisms are made up of one or
  more cells.
• 2. The smallest living organisms are single
  cells, and cells are the functional units of
  multicellular organisms.
• 3. All cells arise from preexisting cells.

4

• Microscope Features
• Magnification
• Increase in apparent size of an object.
• Ratio of image size to specimen size.
• Resolving power Measures clarity of image.
• Ability to see fine detail.
• Ability to distinguish two objects as separate.
• Minimum distance between 2 points at which they
  can be distinguished as separate and distinct.

5

• Microscopes
• Light Microscopes Earliest microscopes used.
• Lenses pass visible light through a specimen.
• Magnification Highest possible from 1000 X to
  2000 X.
• Resolving power Up to 0.2 mm (1 mm 1/1000 mm).

6

• Types of Microscope
• Electron Microscopes Developed in 1950s.
  Electron beam passes through specimen.
• Magnification Up to 200,000 X.
• Resolving power Up to 0.2 nm (1nm 1/1000,000
  mm).
• Two types of electron microscopes
• 1. Scanning Electron Microscope Used to study
  cell or virus surfaces.
• 2. Transmission Electron Microscope Used to
  study internal cell structures.

7

• Components of All Cells
• 1. Plasma membrane Separates cell contents from
  outside environment. Made up of phospholipid
  bilayers and proteins.
• 2. Cytoplasm Liquid, jelly-like material inside
  cell.
• 3. Ribosomes Necessary for protein synthesis.

8
Procaryotic versus Eucaryotic Cells
Feature Procaryotic Eucaryotic Organisms Bacteri
a All others (animals, plants, fungi, and
protozoa) Nucleus Absent Present DNA One
chromosome Multiple chromosomes Size Small
(1-10 um) Large (10 or more um) Membrane Absent
Present (mitochondria, Bound golgi,
chloroplasts, etc.) Organelles Division Rapid pro
cess Complex process (Binary
fission) (Mitosis)
9

• Relative Sizes of Structures
• 1 nanometer (10-9 m) water molecule
• 10 nanomters (10-8 m) small protein
• 100 nanometers (10-7 m) HIV virus
• 1 micron (10-6 m) cell vacuole
• 10 microns (10-5 m) bacterium
• 100 microns (10-4 m) large plant cell
• 1 millimeter (10-3 m) single cell
  embryo

10
Relative Sizes of Procaryotic and Eucaryotic
Cells and Viruses
11
Relative Sizes of Cells and Other Objects
12

• Prokaryotic Cells
• Bacteria and blue-green algae.
• Small size Range from 1- 10 micrometers in
  length. About one tenth of eukaryotic cell.
• No nucleus DNA in cytoplasm or nucleoid region.
• Ribosomes are used to make proteins
• Cell wall Hard shell around membrane
• Other structures that may be present
• Capsule Protective, outer sticky layer. May be
  used for attachment or to evade immune system.
• Pili Hair-like projections (attachment)
• Flagellum Longer whip-like projection (movement)

13
Procaryotic Cells Lack a Nucleus and other
Membrane Bound Organelles
14

• Eucaryotic Cells
• Include protist, fungi, plant, and animal cells.
• Nucleus Protects and houses DNA
• Membrane-bound Organelles Internal structures
  with specific functions.
• Separate and store compounds
• Store energy
• Work surfaces
• Maintain concentration gradients

15

• Membrane-Bound Organelles of Eucaryotic Cells
• Nucleus
• Rough Endoplasmic Reticulum (RER)
• Smooth Endoplasmic Reticulum (SER)
• Golgi Apparatus
• Lysosomes
• Vacuoles
• Chloroplasts
• Mitochondria

16
Eucaryotic Cells Typical Animal Cell
17
Eucaryotic Cells Typical Plant Cell
18

• Nucleus
• Structure
• Double nuclear membrane (envelope)
• Large nuclear pores
• DNA (genetic material) is combined with histones
  and exists in two forms
• Chromatin (Loose, threadlike DNA, most of cell
  life)
• Chromosomes (Tightly packaged DNA. Found only
  during cell division)
• Nucleolus Dense region where ribosomes are made
• Functions
• House and protect cells genetic information
  (DNA)
• Ribosome synthesis

19
Structure of Cell Nucleus
20

• Endoplasmic Reticulum (ER)
• Network within the cell
• Extensive maze of membranes that branches
  throughout cytoplasm.
• ER is continuous with plasma membrane and outer
  nucleus membrane.
• Two types of ER
• Rough Endoplasmic Reticulum (RER)
• Smooth Endoplasmic Reticulum (SER)

21

• Rough Endoplasmic Reticulum (RER)
• Flat, interconnected, rough membrane sacs
• Rough Outer walls are covered with ribosomes.
• Ribosomes Protein making machines.
• May exist free in cytoplasm or attached to ER.
• RER Functions
• Synthesis of cell and organelle membranes.
• Synthesis and modification of proteins.
• Packaging, and transport of proteins that are
  secreted from the cell.
• Example Antibodies

22
Rough Endoplasmic Reticulum (RER)
23

• Smooth Endoplasmic Reticulum (SER)
• Network of interconnected tubular smooth
  membranes.
• Smooth No ribosomes
• SER Functions
• Synthesis of phospholipids, fatty acids, and
  steroids (sex hormones).
• Breakdown of toxic compounds (drugs, alcohol,
  amphetamines, sedatives, antibiotics, etc.).
• Helps develop tolerance to drugs and alcohol.
• Regulates levels of sugar released from liver
  into the blood
• Calcium storage for cell and muscle contraction.

24
Smooth Endoplasmic Reticulum (SER)
25

• Golgi Apparatus
• Stacks of flattened membrane sacs that may be
  distended in certain regions. Sacs are not
  interconnected.
• First described in 1898 by Camillo Golgi (Italy).
• Works closely with the ER to secrete proteins.
• Golgi Functions
• Receiving side receives proteins in transport
  vesicles from ER.
• Modifies proteins into final shape, sorts, and
  labels proteins for proper transport.
• Shipping side packages and sends proteins to cell
  membrane for export or to other parts of the
  cell.
• Packages digestive enzymes in lysosomes.

26
The Golgi Apparatus Receiving, Processing, and
Shipping of Proteins
27

• Lysosomes
• Small vesicles released from Golgi containing at
  least 40 different digestive enzymes, which can
  break down carbohydrates, proteins, lipids, and
  nucleic acids.
• Optimal pH for enzymes is about 5
• Found mainly in animal cells.
• Lysosome Functions
• Molecular garbage dump and recycler of
  macromolecules (e.g. proteins).
• Destruction of foreign material, bacteria,
  viruses, and old or damaged cell components.
• Digestion of food particles taken in by cell.
• After cell dies, lysosomal membrane breaks down,
  causing rapid self-destruction.

28
Lysosomes Intracellular Digestion
29

• Lysosomes, Aging, and Disease
• As we get older, our lysosomes become leaky,
  releasing enzymes which cause tissue damage and
  inflammation.
• Example Cartilage damage in arthritis.
• Steroids or cortisone-like anti-inflammatory
  agents stabilize lysosomal membranes, but have
  other undesirable effects (affect immune
  function).
• Diseases from mutant lysosome enzymes are
  usually fatal
• Pompes disease Defective glycogen breakdown in
  liver.
• Tay-Sachs disease Defective lipid breakdown in
  brain. Common genetic disorder among Jewish
  people.

30

• Vacuoles
• Membrane bound sac.
• Different sizes, shapes, and functions
• Central vacuole In plant cells. Store starch,
  water, pigments, poisons, and wastes. May occupy
  up to 90 of cell volume.
• Contractile vacuole Regulate water balance, by
  removing excess water from cell. Found in many
  aquatic protists.
• Food or Digestion Vacuole Engulf nutrients in
  many protozoa (protists). Fuse with lysosomes to
  digest food particles.

31
Central Vacuole in a Plant Cell
32
Interactions Between Membrane Bound Organelles of
Eucaryotic Cells
33

• Chloroplasts
• Site of photosynthesis in plants and algae.
• CO2 H2O Sun Light -----gt Sugar O2
• Number may range from 1 to over 100 per cell.
• Disc shaped structure with three different
  membrane systems
• 1. Outer membrane Covers chloroplast surface.
• 2. Inner membrane Contains enzymes needed to
  make glucose during photosynthesis. Encloses
  stroma (liquid) and thylakoid membranes.
• 3. Thylakoid membranes Contain chlorophyll,
  green pigment that traps solar energy. Organized
  in stacks called grana.

34
Chloroplasts Trap Solar Energy and Convert it to
Chemical Energy
35

• Chloroplasts
• Contain their own DNA, ribosomes, and make some
  proteins.
• Can divide to form daughter chloroplasts.
• Type of plastid Organelle that produces and
  stores food in plant and algae cells.
• Other plastids include
• Leukoplasts Store starch.
• Chromoplasts Store other pigments that give
  plants and flowers color.

36

• Mitochondria (Sing. Mitochondrion)
• Site of cellular respiration
• Food (sugar) O2 -----gt CO2 H2O ATP
• Change chemical energy of molecules into the
  useable energy of the ATP molecule.
• Oval or sausage shaped.
• Contain their own DNA, ribosomes, and make some
  proteins.
• Can divide to form daughter mitochondria.
• Structure
• Inner and outer membranes.
• Intermembrane space
• Cristae (inner membrane extensions)
• Matrix (inner liquid)

37
Mitochondria Harvest Chemical Energy From Food
38
Origin of Eucaryotic Cells

• Endosymbiont Theory Belief that chloroplasts and
  mitochondria were at one point independent cells
  that entered and remained inside a larger cell.
• Both organelles contain their own DNA
• Have their own ribosomes and make their own
  proteins.
• Replicate independently from cell, by binary
  fission.
• Symbiotic relationship
• Larger cell obtains energy or nutrients
• Smaller cell is protected by larger cell.

39

• The Cytoskeleton
• Complex network of thread-like and tube-like
  structures.
• Functions Movement, structure, and structural
  support.
• Three Cytoskeleton Components
• 1. Microfilaments Smallest cytoskeleton fibers.
  Important for
• Muscle contraction Actin myosin fibers in
  muscle cells
• Amoeboid motion of white blood cells

40
Components of the Cytoskeleton are Important for
Structure and Movement
41

• Three Cytoskeleton Components
• 2. Intermediate filaments Medium sized fibers
• Anchor organelles (nucleus) and hold cytoskeleton
  in place.
• Abundant in cells with high mechanical stress.
• 3. Microtubules Largest cytoskeleton fibers.
  Found in
• Centrioles A pair of structures that help move
  chromosomes during cell division (mitosis and
  meiosis).
• Found in animal cells, but not plant cells.
• Movement of flagella and cilia.

42

• Typical Animal Cell

43
Cilia and Flagella

• Projections used for locomotion or to move
  substances along cell surface.
• Enclosed by plasma membrane and contain
  cytoplasm.
• Consist of 9 pairs of microtubules surrounding
  two single microtubules (9 2 arrangement).
• Flagella Large whip-like projections.
• Move in wavelike manner, used for locomotion.
• Example Sperm cell
• Cilia Short hair-like projections.
• Example Human respiratory system uses cilia to
  remove harmful objects from bronchial tubes and
  trachea.

44
Structure of Eucaryotic Flagellum
45
Cell Surfaces

• A. Cell wall Much thicker than cell membrane,
• (10 to 100 X thicker).
• Provides support and protects cell from lysis.
• Plant and algae cell wall Cellulose
• Fungi and bacteria have other polysaccharides.
• Not present in animal cells or protozoa.
• Plasmodesmata Channels between adjacent plant
  cells form a circulatory and communication system
  between cells.
• Sharing of nutrients, water, and chemical
  messages.

46
Plasmodesmata Communication Between Adjacent
Plant Cells
47
Cell Surfaces

• B. Extracellular matrix Sticky layer of
  glycoproteins found in animal cells.
• Important for attachment, support, protection,
  and response to environmental stimuli.
• Junctions Between Animal Cells
• Tight Junctions Bind cells tightly, forming a
  leakproof sheet. Example Between epithelial
  cells in stomach lining.
• Anchoring Junctions Rivet cells together, but
  still allow material to pass through spaces
  between cells.
• Communicating Junctions Similar to
  plasmodesmata in plants. Allow water and other
  small molecules to flow between neighboring
  cells.

48
Different Animal Cell Junctions
49
Important Differences Between Plant and Animal
Cells
Plant cells Animal cells Cell wall
None (Extracellular matrix) Chloroplasts No
chloroplasts Large central vacuole No central
vacuole Flagella rare Flagella more usual No
Lysosomes Lysosomes present No
Centrioles Centrioles present
50
Differences Between Plant and Animal Cells
Animal Cell
Plant Cell
51

• Typical Plant Cell

52
Summary of Eucaryotic Organelles

• Function Manufacture
• Nucleus
• Ribosomes
• Rough ER
• Smooth ER
• Golgi Apparatus
• Function Breakdown
• Lysosomes
• Vacuoles

53
Summary of Eucaryotic Organelles

• Function Energy Processing
• Chloroplasts (Plants and algae)
• Mitochondria
• Function Support, Movement, Communication
• Cytoskeleton (Cilia, flagella, and centrioles)
• Cell walls (Plants, fungi, bacteria, and some
  protists)
• Extracellular matrix (Animals)
• Cell junctions

54

• The Cell Membrane and Cell Transport

55

• Functions of Cell Membranes
• 1. Separate cell from nonliving environment.
  Form most organelles and partition cell into
  discrete compartments.
• 2. Regulate passage of materials in and out of
  the cell and organelles. Membrane is selectively
  permeable.
• 3. Receive information that permits cell to sense
  and respond to environmental changes.
• Hormones
• Growth factors
• Neurotransmitters
• 4. Communication with other cells and the
  organism as a whole. Surface proteins allow cells
  to recognize each other, adhere, and exchange
  materials.

56

• I. Fluid Mosaic Model of the Membrane
• 1. Phospholipid bilayer Major component is a
  phospholipid bilayer.
• Hydrophobic tails face inward
• Hydrophilic heads face water
• 2. Mosaic of proteins Proteins float in the
  phospholipid bilayer.
• 3. Cholesterol Maintains proper membrane
  fluidity.
• The outer and inner membrane surfaces are
  different.

57
Membrane Phospholipids Form a Bilayer
58
The Membrane is a Fluid Mosaic of Phospholipids
and Proteins
Notice that inner and outer surfaces are different
59

• A. Fluid Quality of Plasma Membranes
• In a living cell, membrane has same fluidity as
  salad oil.
• Unsaturated hydrocarbon tails INCREASE membrane
  fluidity
• Phospholipids and proteins drift laterally.
• Phospholipids move very rapidly
• Proteins drift in membrane more slowly
• Cholesterol Alters fluidity of the membrane
• Decreases fluidity at warmer temperatures (gt
  37oC)
• Increases fluidity at lower temperatures (lt 37oC)

60

• B. Membranes Contain Two Types of Proteins
• 1. Integral membrane proteins
• Inserted into the membrane.
• Hydrophobic region is adjacent to hydrocarbon
  tails.
• 2. Peripheral membrane proteins
• Attached to either the inner or outer membrane
  surface.
• Functions of Membrane Proteins
• 1. Transport of materials across membrane
• 2. Enzymes
• 3. Receptors of chemical messengers
• 4. Identification Cell-cell recognition
• 5. Attachment
• Membrane to cytoskeleton
• Intercellular junctions

61
Membrane Proteins Have Diverse Functions
62

• C. Membrane Carbohydrates and Cell-Cell
  Recognition
• Found on outside surface of membrane.
• Important for Cell-cell recognition Ability of
  one cell to recognize other cells.
• Allows immune system to recognize self/non-self
• Include
• Glycolipids Lipids with sugars
• Glycoproteins Proteins with sugars
• Major histocompatibility proteins (MHC or
  transplantation antigens).
• Vary greatly among individuals and species.
• Organ transplants require matching of cell
  markers and/or immune suppression.

63
(No Transcript)
64

• The cell plasma membrane is Selectively Permeable
• A. Permeability of the Lipid Bilayer
• 1. Non-polar (Hydrophobic) Molecules
• Dissolve into the membrane and cross with ease
• The smaller the molecule, the easier it can cross
• Examples O2 , hydrocarbons, steroids
• 2. Polar (Hydrophilic) Molecules
• Small polar uncharged molecules can pass through
  easily (e.g. H2O , CO2)
• Large polar uncharged molecules pass with
  difficulty (e.g. glucose)
• 3. Ionic (Hydrophilic) Molecules
• Charged ions or particles cannot get through
• (e.g. ions such as Na , K , Cl- )

65

• Transport Proteins in the membrane Integral
  membrane proteins that allow for the transport of
  specific molecules across the phospholipid
  bilayer of the plasma membrane.
• How do they work?
• May provide a hydrophilic tunnel (channel)
• May bind to molecule and physically move it
• Are specific for the atom/molecule transported

66

• III. Passive transport Diffusion of molecules
  across the plasma membrane
• A. Diffusion The net movement of a substance
  from an area of high concentration to area of low
  concentration.
• Does not require energy.
• B. Passive transport The diffusion of substance
  across a biological membrane.
• Only substances which can cross bilayer by
  themselves or with the aid of a protein
• Does not require the cells energy

67
Passive Transport Diffusion Across a Membrane
Does Not Require Energy
68

• IV. Osmosis
• The diffusion of water across a semi-permeable
  membrane.
• Through osmosis water will move from an area with
  higher water concentration to an area with lower
  water concentration.
• Solutes cant move across the semi-permeable
  membrane.

69
(No Transcript)
70

• Osmotic Pressure Ability of a solution to take
  up water through osmosis.
• Example The cytoplasm of a cell has a certain
  osmotic pressure caused by the solutes it
  contains.
• There are three different types of solution when
  compared to the interior (cytoplasm) of a cell
• 1. Hypertonic solution Higher osmotic pressure
  than cell due to
• Higher solute concentration than cell or
• Lower water concentration than cell.
• 2. Hypotonic solution Lower osmotic pressure
  than cell due to
• Lower solute concentration than cell or
• Higher water concentration than cell.
• 3. Isotonic solution Same osmotic pressure than
  cell.
• Equal concentration of solute(s) and water than
  cell.

71

• V. Cells depend on proper water balance
• Animal Cells
• Do best in isotonic solutions.
• Examples
• 0.9 NaCl (Saline)
• 5 Glucose
• If solution is not isotonic, cell will be
  affected
• Hypertonic solution Cell undergoes crenation.
  Cell shrivels or shrinks.
• Example 5 NaCl or 10 glucose
• Hypotonic solution Cell undergoes lysis. Cell
  swells and eventually bursts.
• Example Pure water.

72

• V. Cells depend on proper water balance
• Plant Cells Do best in hypotonic solutions,
  because the cell wall protects from excessive
  uptake of water.
• Hypertonic solution Cell undergoes plasmolysis.
  Cell membrane shrivels inside cell wall.
• Isotonic solution Cell becomes flaccid or wilts.
• Hypotonic solution Turgor. Increased firmness
  of cells due to osmotic pressure.
• This is the reason why supermarkets spray fruits
  and vegetables with pure water, making them look
  firm and fresh.

73
(No Transcript)
74

• VI. Facilitated Diffusion
• Some substances cannot cross the membrane by
  themselves due to their size or charge.
• Membrane proteins facilitate the transport of
  solutes down their concentration gradient.
• No cell energy is required.
• Transport Proteins
• Specific Only transport very specific molecules
  (binding site)
• Glucose
• Specific ions (Na, K, Cl- )

75
Facilitated Diffusion Uses a Membrane Transport
Protein
76

• VI. Active Transport
• Proteins use energy from ATP to actively pump
  solutes across the membrane
• Solutes are moved against a concentration
  gradient.
• Energy is required.
• Example
• The Na-K ATPase pump
• Energy of ATP hydrolysis is used to move Na out
  of the cell and K into the cell

77
(No Transcript)
78

• Endocytosis
• Moving materials into cell with vesicles.
• Requires use of cell energy.
• 1. Pinocytosis (Cell drinking) Small droplets
  of liquid are taken into the cell through tiny
  vesicles.
• Not a specific process, all solutes in droplets
  are taken in.
• 2. Phagocytosis (Cell eating) Large solid
  particles are taken in by cell.
• Example Amoebas take in food particles by
  surrounding them with cytoplasmic extensions
  called pseudopods.
• Particles are surrounded by a vacuole.
• Vacuole later fuses with the lysosome and
  contents are digested.

79
Endocytosis Uses Vesicles to Move Substances into
the Cell
80

• Endocytosis
• 3. Receptor mediated endocytosis Highly
  specific. Materials moved into cell must bind to
  specific receptors first.
• Example Low density lipoproteins (LDL)
• Main form of cholesterol in blood.
• Globule of cholesterol surrounded by single layer
  of phospholipids with embedded proteins.
• Liver cell receptors bind to LDL proteins and
  remove LDLs from blood through receptor mediated
  endocytosis.
• Familial hypercholesterolemia Genetic disorder
  in which gene for the LDL receptor is mutated.
  Disorder found in 1 in 500 human babies
  worldwide. Results in unusually high levels of
  blood cholesterol.

81
Blood Cholesterol is Taken Up by Liver Cells
through Receptor Mediated Endocytosis
82

• Exocytosis
• Used to export materials out of cell.
• Materials in vesicles fuse with cell membrane
  and are released to outside.
• Tear glands export salty solution.
• Pancreas uses exocytosis to secrete insulin.