Chapter 6 A Tour of the Cell

1
Chapter 6A Tour of the Cell
2
I. Microscopes - Led to the discovery of cells

• Light Microscope Visible light is focused on a
  specimen and light passing through is refracted
  with objective and ocular lens
• Magnification How much larger the object
  appears to be
• Resolution Minimum distance between two points
  that can be distinguished
• Robert Hooke (1665) Described cells using a
  light microscope

3

• Electron Microscope Electron beams refracted
  instead of light
• Resolving power inversely related to wavelength
  electron beams have shorter wavelengths ? higher
  resolution
• Transmission Electron Microscope (TEM) Thin
  slices of specimen are stained and viewed
• Scanning Electron Microscope (SEM) - Scans
  surface producing a 3D image
• Use on dead objects only

4
Light v.s. Electron Microscope
5
II. Cell Organelle Isolation

• Cell Biology integrates the study of cell
  structure (Cytology) with the study of cell
  function

6

• Cell Fractionation Techniques which involves
  centrifuging disrupted cells at various speeds
  and durations to isolate various cell components
• Pellet Nuclei and other large particles settle
  at the bottom
• Supernatant is decanted into another tube and
  centrifuged at a faster speed to separate smaller
  organelles
• Metabolic function of each organelle is then
  studied

7
III. Cell Overview

• Prokaryotic Cells
• Kingdom Monera (bacteria/cyanobacteria)
• No true nucleus, lacks nuclear envelope
• Genetic material in nucleoid region
• No membrane bound organelles

8
(No Transcript)
9

• Eukaryotic Cells
• Found in Kingdoms Protista, Fungi, Plantae and
  Animalia
• True nucleus bounded by nuclear envelope
• Genetic Material within nucleus
• Contains cytoplasm with cytosol and membrane
  bound organelles

10
(No Transcript)
11
(No Transcript)
12
C. Cell Size

• Mycoplasms (smallest bacteria) 0.1-1.0
  micrometer most bacteria 1.0-10 micrometers
  most eukaryotic cells 10-100 micrometers in
  diameter
• Lower limits of cell size limited to metabolic
  requirements enough DNA and cellular components
  to sustain life and reproduce
• Upper limits surface-to-volume ratio

13
D. Compartmental Organization

• Provide localized environmental conditions
  necessary for specific metabolic processes
• Membranes house enzymes that participate in
  chemical reactions
• Isolate reactions from other chemical processes

14
IV. Nucleus Control center, contains most genes

• Nuclear Envelope A double membrane which
  encloses nucleus
• Two lipid bilayer membranes separated by space,
  each containing specific proteins
• Nuclear Lamina A network of protein filaments
  on nuclear side that stabilizes shape
• Perforated by pores

15

• Chromatin Complex of DNA and histone proteins
• Chromosomes Long threadlike association of
  genes composed of chromatin
• Chromosome number characteristic of species
• Human somatic cells contain 46 sex cells
  contain 23
• Nucleolus Spherical regions in nucleus that
  synthesize molecular ingredients of ribosomes

16
(No Transcript)
17
V. Ribosomes site of protein synthesis

• Complexes of RNA and protein
• Free Ribosomes Ribosomes suspended in cytosol
• Proteins produced will function in cytosol
• Bound Ribosomes Attached to endoplasmic
  reticulum
• Make proteins that are destined for membrane
  inclusion or export

18
(No Transcript)
19
VI. Endomembrane System

• Vesicles Membrane enclosed sacs that pinch
  off portions of membranes that move from one site
  to another
• Membranes are dynamic and change in composition,
  thickness and behavior

20

• Endomembrane System Includes
• Nuclear Envelope
• Endoplasmic Reticulum
• Golgi Apparatus
• Lysosomes
• Vacuoles
• Plasma Membrane

21
VII. Endoplasmic Reticulum Network of tubules
and sacs (cisternae) which sequesters its
internal lumen (cisternal space) from the cytosol

• Most extensive portion of the endomembrane system
• Continuous with outer membrane of nuclear
  envelope
• Two distinct regions of ER

22
1. Smooth ER (lacks ribosomes)

• Synthesize lipids, phospholipids and steroids
  (adrenal glands, ovaries, testes)
• Participate in carbohydrate metabolism
  (liver-glycogen-glucose conversion removes P
  from glucose phosphate)
• Detoxifies drugs and poisons
• Enzymes catalyze addition of hydroxyl to drugs
  and poison water soluble for excretion
• Increase in response to excessive drugs/alcohol
  increased tolerance
• Stores calcium ions needed for muscle contraction
• In a muscle cell, ER membrane pumps Ca2 from
  cytosol into cisternal space
• Nerve impulse - Ca2 leaks from the ER back into
  cytosol and triggers muscle contraction

23
2. Rough ER and Protein Synthesis

• Studded with ribosomes
• Manufactures secretory proteins and membrane
• Ribosomes synthesize secretory proteins
• Growing polypeptide is threaded through ER
  membrane into lumen ( cisternal space)
• Protein folds into its native conformation
• If destined to be glycoprotein, enzymes catalyze
  the covalent bonding of an oligosaccharide to
  protein
• Protein departs in a transport vesicle pinched
  off from transitional ER adjacent to rough ER

24
(No Transcript)
25

• Glycoprotein Protein covalently bonded to a
  carbohydrate
• Oligosaccharide Small polymer of sugar units
• Transport vesicles Membrane vesicle in transit
  from 1 part of cell to another

26
3. Rough ER and Membrane Production

• ER membranes grow in place as proteins and
  phospholipids are assembled
• Newly expanded ER membrane can be transported as
  a vessicle to another part of the cell

27
VIII. Golgi Apparatus Organelle made of
stacked, flattened membranous sacs (cisternae),
that modifies, stores and routes products of the
ER

• Vesicles may transport substance between Golgi
  and other cellular structures

28

• Distinct Polarity two poles
• Cis face receives products by accepting transport
  vesicles from ER. Vesicles fuse with Golgi and
  empties contents into cisternal space.
• Trans face pinches off vesicles from the Golgi
  and transports molecules to other sites

29

• Enzymes in Golgi modify products of ER in stages
  as they move through the Golgi stack from cis to
  trans face each cisternae contains a unique set
  of enzymes
• Alters some membrane phospholipids
• Modifies the oligosaccharide portion of
  glycoprotein
• Makes certain macromolecules
• Targets products for various parts of cell
• Adds ID tags
• Golgi budded vesicles have external molecules
  that recognize docking sites of certain
  organelles
• Sorts products for secretion

30
IX. Lysosomes Membrane enclosed bag of
hydrolytic enzymes that digest macromolecules

• Enzymes include lipase, carbohydrases, proteases,
  and nucleases
• Optimal pH5
• Membrane Importance
• Sequesters destructive hydrolytic enzymes from
  cytosol
• Maintains optimal pH by pumping H in from cytosol

31
Functions of Lysosomes

• Intracellular digestion
• Phagocytosis Cellular process of ingestion
  where plasma membrane engulfs particulate
  substances and pinches off to form a
  particle-containing vacuole
• Examples amoeba, human macrophages
• Recycles cells own organic material
• May engulf other cellular organelles or part of
  the cytosol and digest them (autophagy)
• Resulting monomers are released into the cytosol
  where they are recycled
• Programmed cell destruction during metamorphosis
  and development

32
(No Transcript)
33
Lysosomes and Human Disease

• Storage diseases result from lack of a specific
  lysosomal enzyme
• Pompes disease lack carbohydrase, which breaks
  down glycogen. Glycogen accumulates in liver
  causing damage
• Tay-Sachs disease missing lysosomal lipase.
  Lipids accumulate in the brain

34
X. Vacuoles Membrane enclosed sac larger than
a vesicle or lysosome

• Food Vacuole Formed by Phagocytosis site of
  intracellular digestion in some protists and
  macrophages
• Contractile vacuole found in freshwater
  protozoa pumps excess water from cell

35
C. Central vacuole Large vacuole found in most
mature plant cells

• Enclosed by a membrane called the tonoplast
• Develops by the coalescence of smaller vacuoles
  derived from the ER and Golgi apparatus

36

• Many Functions
• Stores organic compounds
• Stores inorganic ions
• Sequesters dangerous metabolic by-products from
  the cytoplasm
• Contains soluble pigments in some cells (flowers)
• Plant protection from predators (poisonous or
  unpalatable)
• Plant growth absorbs water and elongates cell
• Contributes to the large ratio of membrane
  surface area to cytoplasmic volume

37
XI. Peroxisomes Contain specialized enzymes
for metabolic pathways contain
peroxide-producing oxidases

• Transfer H from the various substrates to oxygen
  producing hydrogen peroxide
• RH2 O2 oxidases gt R H2O2
• Contains catalase, an enzyme that converts toxic
  hydrogen peroxide to water
• 2H2O2 catalase gt 2H2O O2
• Peroxisomal reactions have many functions
• Break down fatty acids into smaller molecules
  (acetyl CoA)
• Detoxification of alcohol and other harmful
  compounds
• Convert lipids to carbohydrates in germinating
  seeds

38
XII. Mitochondria and Chloroplasts Energy
Transformers

• General Characteristics
• Enclosed by double membranes
• Membrane not part of endomembrane system
• Contains ribosomes and some DNA that program a
  small portion of their own proteins synthesis
• Semiautonomous grow and reproduce within cell

39
B. Mitochondria Sites of cellular respiration

• Unique proteins embedded in phospholipid bilayer
• Convoluted inner membrane contains enzymes that
  are involved in cellular respiration. Infoldings
  (cristae) increases surface area

40
3. Inner and outer membranes divide the
mitochondrion into two internal compartments

• Intermembrane space
• Narrow space between inner and outer
  mitochondrial membranes
• Cytosol solute concentration (outer membrane
  permeable)
• Mitochondrial Matrix
• Compartment enclosed by inner mitochondrial
  membrane
• Contains enzymes that catalyze many metabolic
  steps for cellular respiration some are
  embedded in membrane

41
4. Plastids A group of plant and algae
organelles

• Amyloplasts Colorless plastids that store
  starch (roots, tubers)
• Chromoplasts Plastids containing pigments other
  than chlorophyll responsible for color of fruits
  flowers and autumn leaves
• Chloroplasts Chlorophyll-containing plastids
  sites of photosynthesis
• Found in eukaryotic algae, green plants
• Dynamic structures that change shape, move, divide

42
5. Structure of Chloroplasts

• Intermembrane Space Space between double
  membrane

43
b. Thylakoid space Thylakoids form another
membrane system separates chloroplasts into 2
compartments thylakoid space and stroma

• Thylakoid Space Space inside the thylakoid
• Thylakoid flattened membranous sacs inside the
  chloroplasts
• Chlorophyll contained in thylakoid membrane
• Function in the light reactions (light ? chemical
  energy)
• Grana stacks of thylakoids

44
c. Stroma

• Photosynthetic reactions that use chemical energy
  to convert carbon dioxide to sugar occur in
  stroma (dark reaction)
• Viscous fluid outside the thylakoid

45

• Cytoskeleton Network of fibers throughout the
  cytoplasm that forms a dynamic framework for
  support, shape, and motility

46
A. Microtubules

• Straight, hollow fibers
• Constructed from globular proteins alpha tublin
  and beta tublin
• Function
• Cellular Support
• May radiate from centrosome
• May radiate from bundles near plasma membrane
• Tracks for organelle movement interact with
  motor molecules
• Separation of chromosomes during cell division
• Make up centrioles in animal cells located in
  centrioles, replicated during cell division

47
(No Transcript)
48
(No Transcript)
49

• Cilia and Flagella Locomotor organelles
• Propel single-celled organisms and sperm
• Draw fluids across surface of stationary cells

50

• Ultrastrucutre of cilia and flagella
• Extensions of plasma membrane w/core of
  microtubules
• 9 2 pattern
• Each doublet has a pair of attached microtubules
• Each doublet is connected to the center by a ring
  of radial spokes
• Doublets attached to neighbors by side arms
  dynein large protein molecules powered by ATP
• Linear displacement of dynein side arms is
  translated into a bending by resistance of the
  radial spokes
• Working against resistance, dynein-walking
  distorts the microtubules, causing them to bend
• Basal bodies anchor microtubule assemblies

51
(No Transcript)
52
B. Microfilaments (Actin)

• Solid rods built from globular proteins linked
  into long chains
• Participate in muscle contraction w/myosin, a
  motor molecule
• Provide cellular support (microvilli)
• Responsible for localized contraction of cells
• Pinches animal cell in 2 during cell division
• Amoeboid movement
• Cytoplasmic streaming

53
(No Transcript)
54
Intermediate Filaments

• Constructed from keratin subunits
• More permanent than microfilaments and
  microtubules
• Reinforce cell shape and fix organelle position

55
XIV. Plant Cell Walls

• Chemical composition varies among cells and
  species
• Cellulose fibers embedded in a matrix of other
  polysaccharides and proteins
• Function to protect plant cells, maintain shape,
  and prevent excess water uptake
• Has membrane-lined channels, plasmodermata that
  connect cytoplasm of neighboring cells
• Development
• Primary cell wall pectin cement cells together
• Strengthening
• Secrete hardening substance into primary wall
• Add a secondary wall between plasma membrane and
  primary wall

56
(No Transcript)
57
IV. Extracellular Matrix functions in support,
adhesion, movement and development in animal cells

• Meshwork of macromolecules outside the plasma
  membrane
• Locally secreted by cells
• Composed mostly of glycoproteins (collagen,
  proteoglycans, fibronectins)
• Fibronectin binds to transmembrane receptor
  proteins integrin
• Bond on their cytoplasmic side of microfilaments
  in the cytoskeleton
• Integrate cytoskeletal responses to ECM
  changes/vice versa

58
(No Transcript)
59

• Function
• Provide support and anchorage of cells
• Embryonic cell Migration
• Helps control gene activity response to
  environment

60
XVI. Intercellular Junctions Direct physical
contact among cells

• Plasmodermata Channels that perforate cell
  walls for cytoplasmic exchange

61

• Tight Junctions Block intercellular transport
  (epithelial layers)
• Desmosomes Rivet cells together, but permit
  substances to pass freely through intracellular
  spaces
• Gap Junctions Intercellular junctions
  specialized for material transport between
  cytoplasm of adjacent cells (animal embryos,
  cardiac muscle)

62
(No Transcript)