3. CHAPTER 6 CELLULAR STRUCTURE

4. WHY STUDY CELLS?
Intro to Cells

5. Brief
Hitory

6. First to debunk spontaneous generation
" I put in four flasks with wide mouths one sneak, some fish of river, four small eels of Arno river and a piece of calf and I locked very well the mouths of the flasks with paper and string. Afterward, I placed in other four flasks the same things and left the mouths of flasks open. Short time later the meat and the fishes inside the open flasks became verminous, and after three weeks I saw many flies around these flasks, but in the locked ones I never seen a worm "
Great researcher
Based on observation
Viper venom!
First to debunk spontaneous generation

7. Lazzaro Spallanzani
1765
Louis Pasteur
1862

8. "Omnis cellula e cellula"... "All cells only arise from
pre-existing cells".
-Rudolf Virchow

9. Cell Theory – original 1839 Schleiden and Schwann
All organisms are made up of cells
The cell is the basic living unit of organization for all organisms
All cells from pre-existing cells
Biogenesis -Not spontaneous generation or abiogenesis

10. The Modern Cell Theory:
   1. all known living things are made up of cells.    2. the cell is structural & functional unit of all living things.    3. all cells come from pre-existing cells by division.    4. cells contains hereditary information which is passed from cell to cell during cell division.    5. All cells are basically the same in chemical composition.    6. all energy flow (metabolism & biochemistry) of life occurs within cells.

11. Biological Diversity and Unity
DNA is universal “language”
Cells are most basic unit of
structure and function
Lowest level of structure
capable of performing all
life activities and being
self-sustaining
Cells

12. Activities of Life Reproduction Growth and development
Energy utilization
Response to stimuli
homeostasis

13. MICROSCOPY

14. HOW DO WE STUDY CELLS?
Robert Hooke 1665
Leewenhoek 1674

15. Microscopes
Light microscope (LM) - visible light passes through specimen and then through glass lenses.
lenses refract light - image is magnified into the eye
Specimen can be alive!

16. Magnification = the ratio of an object’s image to its real size.
Resolving power = a measure of image clarity
minimum distance 2 points can be separated and still be viewed as two separate points
7X X X X

17. minimum resolution is about 2 microns (small bacterium)
LIGHT MICROSCOPE
minimum resolution is about 2 microns (small bacterium)
magnify effectively to about 1,000 times
At higher magnifications, the image blurs
HOW
BIG

19. ELECTRON MICROSCOPE 1950’S 2.0 nm resolution 100X > than light
Organelles
Only on dead cells

20. electron microscope (EM)-
beam of electrons through the specimen or onto its surface - shorter wavelengths of light
greater resolution

21. Transmission electron microscopes (TEMs)-
Transmission electron microscopes (TEMs)- study internal ultrastructure
electron beam through thin section of specimen
image focused and magnified by electromagnets
thin sections stained with atoms of heavy metals
Dead; may leave debris/artifacts
Tracheal cells

22. SEM has great depth of field, image seems 3-D
Scanning electron microscopes (SEMs)- useful for studying surface structures
surface covered with a thin film of gold
beam excites electrons on surface
secondary electrons collected and focused on screen
SEM has great depth of field, image seems 3-D
Dead,debris/artifacts

23. LM’s -less resolution but living
cytology- study of cell structures
Cytology + biochemistry = modern cell biology

24. ISOLATING ORGANELLES Cell Fractionation Separate organelles from cell
Use varying densities of parts
Ultracetrifuge
HEAVIEST?
LIGHTEST?

25. Ultracentrifuge – molecular level
130,000 rpm
Forces>1 million g’s
Why in a BIG thick
lead-lined housing?

26. Microcentrifuge Biotechnology research
Cells at protein and genetic level
Microcentrifuge

27. Homogenization- disrupts cell
Ultracentrifuge- spins to separate heavier pieces into pellet with lighter particles in supernatant

28. END MICROSCOPY

29. PROKARYOTE
vs.
EUKARYOTE

30. CELLS
ALIVE

31. Amoebas
Animals

32. Plant Cells

33. Cell characteristics – All Cells
Plasma membrane
Cytosol
Semi-fluid substance w/ “solutes”
Cytoplasm = cytosol + organelles(euk’s)
Contain chromosomes w/ genes in DNA
Ribosomes
Protein synthesis; carry out gene instructions

34. Types of Cells Prokaryotic vs. Eukaryotic Cells
Location of chromosomes
Prokaryotic Cells
Nucleoid region
1 main Circular chromosome + plasmids
Ribosomes
Eukaryotic Cells
Nucleus; isolated
Linear chromosomes
Membrane bound organelles
Ribosomes
Human Cells

35. CELL SIZE

36. Remember the agar block lab?
Same time = same depth of diffusion

37. Limited by SA/ Vol ratio
Volume increases by factor of 3; SA by 2
Smaller objects have greater SA:Vol ratio
What cell organelle governs this?
Why is a huge single-cell organism not possible?

40. Eukaryotes generally much bigger
LIMITS TO SIZE---
Eukaryotes generally much bigger
Logistics of carrying out metabolism sets limits on cell size
SA to Volume ratio?
smallest bacteria, mycoplasmas
0.1 to 1.0 micron
Most bacteria 1-10 microns
Eukaryotes typically microns
Micron = 1 micrometer = 1/1,000,000 meter
1000 microns = 1 millimeter
Human hair = apx. 20 microns

41. Size must be low to sustain life
enough DNA to program metabolism
enough ribosomes for protein synthesis
enough enzymes for metabolism
enough cellular components

42. plasma membrane functions as a selective barrier
Controls movement in and out of cell
maintains homeostasis - correct environment
bilayer of phospholipids + proteins
Amphipathic
hydrophyllic
hydrophobic
Volume of cytoplasm determines need for exchange
Chemical exchange rate may be inadequate to maintain a cell with a very large volume
Surface area must accommodate the volume
Larger organisms do not generally have larger cells than smaller organisms - simply more cells

43. COMPARTMENTALIZATION
Internal membranes compartmentalize the functions of a eukaryotic cell
eukaryotic - extensive and elaborate internal membranes, compartments
membranes embedded w/ many enzymes;
participate in metabolism
provide different local environments;
facilitate specific metabolic functions
isolate reactions

46. TOUR OF THE CELL
BUCKLE
UP!

47. The Nucleus and Ribosomes

48. Nucleus contains a eukaryotic cell’s genetic library
contains most of genes in euk. Cell
largest organelle
double membrane
unique environment
membranes fuse to form pores/envelope
large macromolecules & particles pass
unique chemical signals
viruses may break code

49. Nuclear lamina--nuclear side; lined by intermediate filaments
maintains shape of nucleus
DNA and histone proteins = CHROMATIN
Nucleolus – rRNA synthesis
NUCLEUS - directs protein synthesis; synthesizes mRNA
appears as grainy mass
During division coils into chromosomes
Characteristic number in eukaryotic species
Humans 46; onion 16, chimps 48
Nucleolus – rRNA synthesis
region in nucleus;
ribosomal RNA (rRNA) synthesized;
w/ proteins forms ribosomal subunits; ,000/min
pass from the nuclear pores to cytoplasm combine to form ribosomes during Prot Syn
Make multiple copies of genes
maybe more than one per cell

50. Ribosomes build a cell’s proteins
Ribosomes contain rRNA and protein
A ribosome = two subunits combined to carry out protein synthesis; no membrane!
Free and Bound and prokaryotic
Cell types that synthesize large quantities of proteins (e.g., pancreas) have large numbers of ribosomes and prominent nuclei.
free ribosomes = suspended in the cytosol and synthesize proteins that function within the cytosol/cell
bound ribosomes = attached to the outside of the endoplasmic reticulum.
synthesize proteins that are either included into membranes or for export from the cell
Ribosomes can shift between roles depending on the polypeptides they are synthesizing
3 types of ribosomes:
free/cytoplasmic
bound/ER
prokaryotic
Many drugs interact with ribosomes
antibiotics may paralyze prok. types and not Euk. - tetracycline / streptomycin

51. The Endomembrane System
membranes either in direct contact or connected via transfer of vesicles
= membrane bound sacs
diverse functions and structures
system includes:
nuclear envelope, ER, Golgi, lysosomes, vacuoles, and plasma membrane

52. ER manufactures membranes and performs many other biosynthetic functions
membranous tubules and internal, fluid-filled spaces = cisternae; storage area
Lumen is center of ER
continuous with N. E.
cisternal space of ER is continuous w/ space between two membranes of n. e.

53. 2 connected regions of ER--
Smooth ER lacks ribosomes
Rough ER (bound ribosomes)
Smooth ER rich in enzymes
plays role in variety of metabolic processes
no ribosomes; tubular
synthesizes lipids, phospholipids, steroids, sex hormones and adrenal steroids
catalyzes a key step in transport of glucose from stored glycogen in liver
permitting glucose to exit cell
smooth ER of liver helps detoxify drugs and poisons and alcohols
Frequent exposure = increase of smooth ER,
Muscle cells rich in enzymes that pump calcium ions from the cytosol to the cisternae
nerve impulse stimulates a muscle cell, calcium rushes from the ER into the cytosol, triggering contraction
enzymes then pump the calcium back, readying the cell for the next stimulation.
Rough ER abundant in cells that secrete proteins
New polypeptides thread into cisternal space through pores formed by a protein in ER membrane
glycoproteins, oligosaccharide is attached; mailing labels
secretory proteins packaged in transport vesicles; carried to next stage
RER makes its own membrane
Membrane bound proteins are synthesized directly into membrane
Enzymes in RER also synthesize phospholipids from precursors in cytosol
As ER membrane expands, parts can be transferred as transport vesicles to other components of endomembrane system

54. The Golgi Apparatus finishes, sorts, and ships cell products
Receives transports vesicles from ER
Modifies contents
Warehousing, sorting, and shipping
Abundant in secretory cells
Produces lysosomes and cell wall

55. Endomembrane System Sumanisc
endomembrane system plays key role in synthesis (and hydrolysis) of macromolecules in cell
each component modifies macromolecules for their various functions
Sumanisc
Endomembrane System

56. Golgi consists of stacks of flattened membranous sacs - cisternae
Cis side of Golgi receives material by fusing with vesicles, while the trans side, buds off (blebs) vesicles that travel to other sites
cis -----> trans movement; polarity
Golgi manufacture its own
macromolecules, including pectin and other noncellulose polysaccharides
material is moved from cisterna to cisterna, each with own set of enzymes
Finally, Golgi tags, sorts, and packages materials into transport vesicles

57. Lysosomes are digestive sacs
lysosome - a membrane-bound sac of hydrolytic enzymes that digests macromolecules.
hydrolyze food, organelles, proteins, fats, polysaccharides, nucleic acids, viruses
proteases, nucleases, lipases, etc.
enzymes work best at pH 5
Proteins in membrane pump hydrogen ions from cytosol to lumen of lysosomes; lo to hi
massive leakage from lysosomes can destroy a cell by autodigestion
create a space where the cell can digest macromolecules safely; recycles
in animal cells only
lysosomal enzymes and membrane are synthesized by RER and transferred to Golgi
some lysosomes bud from trans face of Golgi
Can fuse w/ food vacuoles of phagocytosis
Monomers of digested polymers pass out to cytosol to become nutrients of cell
Lysosomes can fuse with another organelle or part of the cytosol
Recycling, or autophagy, renews the cell
Lysosomes play a critical role in programmed destruction of cells in multicellular organisms
allows reconstruction during the developmental process
webbing
brain cell pruning
frog tail
Several inherited diseases due to lack of a functioning version of normal hydrolytic enzyme
Lysosomes engorged with indigestable substrates
Pompe’s disease- glycogen in liver
Tay-Sachs - lipids in brain; death
PKU - protein in brain; retardation
cystic fibrosis - fluid in lungs; death

58. Vacuoles have diverse functions in cell maintenance
Vesicles and vacuoles (larger versions)
membrane-bound sacs
Food vacuoles, from phagocytosis, fuse with lysosomes
Contractile vacuoles, in freshwater protists
pump excess water out of cell
Central vacuoles in plant cells;
Store water and solutes
membrane of plant cell’s central vacuole = tonoplast
selective in transport of solutes into vacuole
functions of central vacuole: stockpiling proteins or inorganic ions, depositing metabolic byproducts/waste, storing pigments, and storing defensive compounds against herbivores
also increases SA:Vol ratio for whole cell

59. Other Membranous Organelles

61. Mitochondria and chloroplasts are main energy transformers of cells
convert energy to usable forms for work
Mitochondria = sites of cell. respiration, generate ATP from catabolism of sugars, fats, and other fuels in presence of oxygen
Chloroplasts - found in plants and eukaryotic algae; sites of photosynthesis
convert solar energy to chemical energy and synthesize new organic compounds from CO2 and H2O.
Mitochondria and chloroplasts not part of endomembrane system
Both have small quantities of DNA that direct the synthesis of polypeptides produced by own internal ribosomes
Grow and reproduce as semiautonomous organelles
Almost all eukaryotic cells have mitochondria
1 very large mitochondrion or hundreds to thousands
number related to aerobic metabolic activity
dynamic: moving, changing shape, and dividing
Mitochondria
smooth outer membrane;highly folded inner membrane = cristae
creates a fluid-filled space between them
Cristae- surface area for enzymes that synthesize ATP
inner membrane encloses mitochondrial matrix, a fluid-filled space with DNA, ribosomes, and enzymes

62. PLASTIDS -
Amyloplasts/leucoplasts - store starch in roots and tubers
Chromoplasts store pigments
Chloroplast
produces sugar via photosynthesis
color from chlorophyll pigment
in leaves and other green structures of plants and in eukaryotic algae

64. floating membranous sacs in stroma = THYLAKOIDS stacked into grana
Chloroplast has 2 membranes
innermost membrane surrounds fluid-filled space = STROMA w/ DNA, ribosomes, & enzymes for PS
floating membranous sacs in stroma = THYLAKOIDS stacked into grana
Dynamic- change shape, reproduce by binary fission

65. Peroxisomes - single membrane
contain enzymes to break down H2O2
Some break fatty acids down for mitochondria for fuel
Some detoxify alcohol and other harmful compounds
Glyoxysomes = Specialized peroxisomes,
in plants only,
convert fatty acids to sugars in seeds = easier energy and carbon source

66. The Cytoskeleton

67. CYTOSKELETON = a network of fibers throughout cytoplasm
maintains shape of the cell; oppose forces
organizes structures and activities of cell
provides anchorage for organelles
dynamic, dismantles and reassembles as needed

68. cytoskeleton - major role in cell motility changes in cell location
limited movements of parts of cell
interacts with motor proteins- dynein
In cilia and flagella
also in muscle cells
circulate materials
within cell by
cytoplasmic
streaming
kinesin
Cilia
flagella

69. three main types of fibers in the cytoskeleton:
microtubules
microfilaments
intermediate filaments

70. Actin

71. Actin and keratin

72. globular protein called tubulin
Microtubules = thick, hollow
globular protein called tubulin
grow or shrink as more tubulin molecules are added or removed
move chromosomes during cell division
Act as tracks to move organelles
May grow from a centrosome near the nucleus
resist compression to the cell

73. Cilia and Flagella are microtubules
move unicellular and small multicellular organisms thru water
may move fluid over a surface
EX: cilia sweep mucus carrying trapped debris from the lungs
Cilia usually in large #’s on cell surface
flagella - usually just one or a few

74. Flagellum - undulatory movement
Force - parallel to the flagellum’s axis

75. Cilia move like oars
force perpendicular to cilia’s axis

76. In animal cells, centrosome has a pair of centrioles, each with 9 triplets of microtubules arranged in a ring
centrioles replicate during cell division

77. “9 + 2”
Cilia and flagella

78. Site of controversy
Basal body same structure as centriole
Basal body

79. bending driven by arms of motor protein called dynein
Hydrolysis of ATP causes bending of protein
Dynein arms
alternately grab,
move and release
outer microtubules
both have same ultrastructure
a core of microtubules sheathed by membrane
9 doublets of microtubules arranged around a pair at the center, the “9 + 2” pattern.
anchored in cell by a basal body a structure identical to centriole
Micro-
Tubule
sliding
Motor
protein

80. Microfilaments= thinnest fibers; solid, globular protein actin
microfilament of actin subunits
resist tension = pulling
interact with myosin for muscle contraction
A contracting belt- divides cytoplasm animal cells during cell division

81. microvilli increase SA lung tissue, intestinal lining, etc;
Absorptive surfaces
anchored to
intermediate
filaments.

82. contraction causes amoeboid movement
Pseudopodia, cellular extensions, extend and contract through assembly and contraction of actin subunits into microfilaments

83. In plant cells - actin-myosin interactions drive cytoplasmic streaming
a circular flow of cytoplasm
speeds the distribution of materials within the cell.

84. Intermediate filaments - for bearing tension
built from keratin
reinforce cell shape and fix organelle location

85. Cell Surfaces and Junctions

86. Plant cells are encased by cell walls
cell wall - in prokaryotes, fungi, and some protists; multiple functions
In plants - protects, maintains shape, prevents excess uptake of water; turgor
supports plant against force of gravity
thickness and composition differs from species to species and among cell types

87. consists of microfibrils of cellulose in a matrix of proteins and other polysaccharides
mature cell wall consists of a primary cell wall, a middle lamella with sticky polysaccharides- pectin- holds cell together, and layers of secondary cell wall

89. Extracellular matrix (ECM) of animal cells
glycoproteins, especially collagen, embedded in network of proteoglycans
fibronectins bind to integrin proteins in membrane to connect ECM to cytoskeleton microfilaments
permit interaction of changes inside and outside cell

90. The ECM can regulate cell behavior
Embryonic cells migrate along specific pathways by matching the orientation of their microfilaments to the “grain” of fibers in the extracellular matrix.
ECM can influence activity of genes in nucleus via a combination of chemical and mechanical signaling pathways
This may coordinate all the cells within a tissue.

91. Intercellular junctions
Connections between cells
Plant cells have plasmodesmata, channels for direct exchange of cytosol

93. Animal have 3 main types of intercellular links:
tight junctions, membranes are fused, form continuous belts around cells-prevents leakage of extracellular fluid
Desmosomes fasten cells together into strong sheets - keratin intermediate filaments
Gap junctions provide cytoplasmic channels between adjacent cells

95. THE END!