Lecture 1

PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor

MCAT Prep Exam

Cell Structure...
Outline


Cellular Level of Organization






Prokaryotic Cells
Eukaryotic Cells








Cell theory
Cell size...
Cell Theory
 Cell

was not discovered untill the development of
Microscope
 Detailed study of the cell began in the 1830...
Sizes of Living Things

4
Cell Size
 Cells

range in size from one millimeter down to
one micrometer
 Cells need a large surface area of plasma
me...
Surface to Volume Ratio

6
Microscopy Today: Compound Light
Microscope
 Light

passed through specimen

 Focused
 Max

by glass lenses

magnificat...
Compound Light Microscope
 Diaphragm

– controls
amount of light –
important for image
contrast

 Coarse

Adjustment Kno...
Microscopy Today: Transmission
Electron Microscope
 Abbreviated

T.E.M.

 Uses

a beam of electrons to allow 100 fold hi...
Transmission Electron Microscope

10
Microscopy Today: Immunofluorescence
Light Microscope
 Antibodies

developed against a specific protein

Fluorescent dye ...
Microscopy and Amoeba proteus

12
Cells Under the Microscope
 phase-contrast

light microscope - look at
unstained living animal cells.
 electron microsco...
Autoradiography
 Radioactive

compounds decay or
transform into other compounds or
elements.
 An autoradiograph is an im...
Cell Fractionation and Differential
Centrifugation
 Cell

fractionation is the breaking apart of
cellular components

 D...
Cell Fractionation and Differential
Centrifugation

16
Eukaryotes Vs Prokaryotes
Eukaryotic Cells

Prokaryotic Cells

The cells of “complex” organisms,
including all plants, Pro...
The Structure of Bacteria


Occur in three basic shapes:






Spherical coccus,
Rod-shaped bacillus,
Spiral spirillu...
The Structure of Bacteria

19
The Structure of Bacteria

20
The Structure of Bacteria Cytoplasm &
Appendages


Cytoplasm


Semifluid solution








Bounded by plasma membran...
Eukaryotic Cells


Domain Eukarya includes:



Fungi



Plants





Protists

Animals

Cells contain:


Membrane-bo...
Hypothesized Origin of Eukaryotic Cells

23
Eukaryotic Cells: Organelles
 Eukaryotic


cells are compartmentalized

They contain small structures called organelles
...
Plasma Membrane

25
Animal Cell Anatomy

26
Plant Cell Anatomy

27
Cytosole
 Cytosol,

contains many long, fine filaments
of protein that are responsible for cell
shape and structure and t...
Nucleus
 Command

center of cell, usually near center
 Separated from cytoplasm by nuclear envelope
Consists of double l...
Anatomy of the Nucleus

30
Ribosomes
 Are

the site of protein synthesis in the cell

 Composed

of rRNA and protein



Consists of a large subuni...
Nucleus, Ribosomes, & ER

32
Endomembrane System
 Series

of intracellular membranes that
compartmentalize the cell

 Restrict

enzymatic reactions t...
Endomembrane System:
The Endoplasmic Reticulum



A system of membrane channels and saccules (flattened vesicles)
contin...
Endoplasmic Reticulum

35
Endomembrane System:
The Golgi Apparatus
 Golgi

Apparatus

 Consists

of flattened, curved saccules

 Resembles
 Modi...
Golgi Apparatus

37
Endomembrane System: Lysosomes
 Membrane-bound

vesicles (not in plants)



Produced by the Golgi apparatus



Contain ...
Lysosomes

39
Endomembrane System: Summary
 Proteins

produced in rough ER and lipids from
smooth ER are carried in vesicles to the Gol...
Endomembrane System: A Visual Summary

41
Peroxisomes
 Similar

to lysosomes



Membrane-bounded vesicles



Enclose enzymes that rid the cell of toxic peroxides...
Peroxisomes

43
Vacuoles
 Membranous

sacs that are larger than vesicles

Store materials that occur in excess
 Others very specialized ...
Vacuoles

45
Energy-Related Organelles:
Chloroplast Structure
 Bounded
 Inner

by double membrane

membrane infolded



Forms disc-l...
Energy-Related Organelles: Chloroplasts


Serve as the site of photosynthesis



Captures light energy to drive cellular...
Chloroplast Structure

48
Energy-Related Organelles: Mitochondria


Smaller than chloroplast



Contain ribosomes and their own DNA



Surrounded...
Mitochondrial Structure

50
Mitochondrial Origin Hypothesis

51
The Cytoskeleton
 Maintains
 Assists
 Aids

cell shape

in movement of cell and organelles

movement of materials in an...
The Cytoskeleton: Actin Filaments
 Microfilament are rods of actin
 Extremely thin filaments like twisted

pearl

neckla...
The Cytoskeleton: Actin Filament Operation

54
The Cytoskeleton: Intermediate Filaments
 Intermediate

microtubules

 Rope-like

in size between actin filaments and

a...
The Cytoskeleton: Microtubules
 Hollow

cylinders made of two globular proteins called
α and β tubulin
 Spontaneous pair...
The Cytoskeleton: Microtubule Operation

57
The Cytoskeleton

58
Microtubular Arrays: Centrioles
 Short,
 One

hollow cylinders

pair per animal cell



Located in centrosome of animal...
Cytoskeleton: Centrioles

60
Microtubular Arrays: Cilia and Flagella
 Hair-like

projections from cell surface that aid in
cell movement
 In eukaryot...
Structure of a Flagellum

62
Comparison of Prokaryotic and
Eukaryotic Cells

63
Lecture 1

PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor

MCAT Exam Prep

Membrane Struc...
Outline
 Membrane


Models

Fluid-Mosaic

 Plasma

Membrane Structure and Function



Phospholipids



Proteins

 Pl...
Structure and Function:
The Phospholipid Bilayer
 The

plasma membrane is common to all cells

 Separates:


Internal l...
Unit Membrane

67
Membrane Models
 Fluid-Mosaic

Model
 Three components:
 Basic

membrane referred to as phospholipid
bilayer
 Protein ...
The Fluid Mosaic Model

69
Transmembrane Proteins

70
Functions of Membrane Proteins


Channel Proteins:





Carrier Proteins:







Provides unique chemical ID for c...
Membrane Protein Diversity

72
Science Focus: Cell Signaling

73
Types of Transport: Active vs. Passive
 Plasma

membrane is differentially (selectively)
permeable


Allows some materia...
Passage of Molecules Across the
Membrane

75
Types of Membrane Transport: Overview

76
Types of Transport: Diffusion
A

solution consists of:

A solvent (liquid), and
 A solute (dissolved solid)


 Diffusi...
Gas Exchange in Lungs: Diffusion
Across Lung

78
Types of Transport: Osmosis
 Osmosis:

Special case of diffusion
 Focuses on solvent (water) movement rather than
solute...
Types of Transport: Carrier Proteins
 Facilitated

Transport

 Small

molecules

 Can’t

get through membrane lipids

...
Types of Transport: Carrier Proteins
 Facilitated

Transport

 Small

molecules

 Can’t

get through membrane lipids

...
Types of Transport:
Membrane-Assisted Transport
 Macromolecules

transported into or out of
the cell inside vesicles
 Ex...
Cell Surface Modifications: Junctions
 Cell

Surfaces in Animals

 Junctions

Between Cells

 Adhesion


Intercellular...
Cell Surface Modifications
 Extracellular

Matrix



External meshwork of polysaccharides and proteins



Found in clos...
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Lecture 1 cell

  1. 1. Lecture 1 PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor MCAT Prep Exam Cell Structure and Function 1
  2. 2. Outline  Cellular Level of Organization     Prokaryotic Cells Eukaryotic Cells       Cell theory Cell size Organelles Nucleus and Ribosome Endomembrane System Other Vesicles and Vacuoles Energy related organelles Cytoskeleton  Centrioles, Cilia, and Flagella 2
  3. 3. Cell Theory  Cell was not discovered untill the development of Microscope  Detailed study of the cell began in the 1830s  A unifying concept in biology  States that: All organisms are composed of cells  All cells come only from preexisting cells  Cells are the smallest structural and functional unit of organisms  Cells carry genetic information in the form of DNA  3
  4. 4. Sizes of Living Things 4
  5. 5. Cell Size  Cells range in size from one millimeter down to one micrometer  Cells need a large surface area of plasma membrane to adequately exchange materials.  The surface‑ area‑ to‑ volume ratio requires that cells be small 5
  6. 6. Surface to Volume Ratio 6
  7. 7. Microscopy Today: Compound Light Microscope  Light passed through specimen  Focused  Max by glass lenses magnification about 1000X objects separated by 0.2 µm, 500X better than human eye  Resolves  Resolution is limited by the wavelength of light (nanometer) 7
  8. 8. Compound Light Microscope  Diaphragm – controls amount of light – important for image contrast  Coarse Adjustment Knob – focuses the image  Fine Adjustment Knob – finely focuses the image 8
  9. 9. Microscopy Today: Transmission Electron Microscope  Abbreviated T.E.M.  Uses a beam of electrons to allow 100 fold higher magnification  Because it uses beam of electrons, its resolution is at the atomic level (picometer)  Tissue  Can must be fixed and sectioned living specimen be examined by T.E.M? 9
  10. 10. Transmission Electron Microscope 10
  11. 11. Microscopy Today: Immunofluorescence Light Microscope  Antibodies developed against a specific protein Fluorescent dye molecule attached to antibody molecules  Specimen exposed to fluorescent antibodies   Ultra-violet specimen light (black light) passed through Fluorescent dye glows in color where antigen is located  Emitted light is focused by glass lenses onto human retina   Allows in cell mapping distribution of a specific protein 11
  12. 12. Microscopy and Amoeba proteus 12
  13. 13. Cells Under the Microscope  phase-contrast light microscope - look at unstained living animal cells.  electron microscope - look at organelles e.g. ribosomes.  fluorescence microscope - look at a living cell expressing green fluorescent protein or to do confocal microscopy.
  14. 14. Autoradiography  Radioactive compounds decay or transform into other compounds or elements.  An autoradiograph is an image on an xray film or nuclear emulsion produced by the pattern of decay emissions (e.g., beta particles or gamma rays) from a distribution of a radioactive substance  Autoradiography can also uses radioactive molecule to study biochemical activity, 14
  15. 15. Cell Fractionation and Differential Centrifugation  Cell fractionation is the breaking apart of cellular components  Differential  Allows separation of cell parts  Separated  Works centrifugation: out by size & density like spin cycle of washer  The faster the machine spins, the smaller the parts that are settled out 15
  16. 16. Cell Fractionation and Differential Centrifugation 16
  17. 17. Eukaryotes Vs Prokaryotes Eukaryotic Cells Prokaryotic Cells The cells of “complex” organisms, including all plants, Protists, fungi and animals Contain a nucleus and membrane bound organelles “Simple” organisms, including bacteria and cyanobacteria (blue-green algae) Lack a nucleus and other membrane-encased organelles. Can specialize for certain functions, such as absorbing nutrients from food or transmitting nerve impulses; multicellular organs and organisms Usually exist as single, virtually identical cells Cell Wall present in Plants and Fungi only Ribosome: 40s, 60S Cell Wall Ribosome: 30S, 50S 17
  18. 18. The Structure of Bacteria  Occur in three basic shapes:     Spherical coccus, Rod-shaped bacillus, Spiral spirillum (if rigid) or spirochete (if flexible). Cell Envelope includes:   Plasma membrane - lipid bilayer with imbedded and peripheral protein Cell wall - maintains the shape of the cell 18
  19. 19. The Structure of Bacteria 19
  20. 20. The Structure of Bacteria 20
  21. 21. The Structure of Bacteria Cytoplasm & Appendages  Cytoplasm  Semifluid solution      Bounded by plasma membrane Contains water, inorganic and organic molecules, and enzymes. Nucleoid is a region that contains the single, circular DNA molecule. Plasmids are small accessory (extrachromosomal) rings of DNA Appendages    Flagella – Provide motility Fimbriae – small, bristle-like fibers that sprout from the cell surface Sex pili – rigid tubular structures used to pass DNA from cell to cell 21
  22. 22. Eukaryotic Cells  Domain Eukarya includes:   Fungi  Plants   Protists Animals Cells contain:  Membrane-bound nucleus that houses DNA  Specialized organelles  Plasma membrane  Much larger than prokaryotic cells  Some cells (e.g., plant cells) have a cell wall 22
  23. 23. Hypothesized Origin of Eukaryotic Cells 23
  24. 24. Eukaryotic Cells: Organelles  Eukaryotic  cells are compartmentalized They contain small structures called organelles Perform specific functions  Isolates reactions from others   Two  classes of organelles: Endomembrane system:  Organelles that communicate with one another    Via membrane channels Via small vesicles Energy related organelles Mitochondria & chloroplasts  Basically independent & self-sufficient  24
  25. 25. Plasma Membrane 25
  26. 26. Animal Cell Anatomy 26
  27. 27. Plant Cell Anatomy 27
  28. 28. Cytosole  Cytosol, contains many long, fine filaments of protein that are responsible for cell shape and structure and thereby form the cell’s cytoskeleton 28
  29. 29. Nucleus  Command center of cell, usually near center  Separated from cytoplasm by nuclear envelope Consists of double layer of membrane  Nuclear pores permit exchange between nucleoplasm & cytoplasm   Contains chromatin in semifluid nucleoplasm Chromatin contains DNA of genes, and proteins (Histones)  Condenses to form chromosomes   Chromosomes are formed during cell division  Nucleolus  is a dense structure in the nucleus Synthesize ribosome RNA (rRNA) 29
  30. 30. Anatomy of the Nucleus 30
  31. 31. Ribosomes  Are the site of protein synthesis in the cell  Composed of rRNA and protein  Consists of a large subunit and a small subunit  Subunits made in nucleolus  May be located:  On the endoplasmic reticulum (thereby making it “rough”), or  Free in the cytoplasm 31
  32. 32. Nucleus, Ribosomes, & ER 32
  33. 33. Endomembrane System  Series of intracellular membranes that compartmentalize the cell  Restrict enzymatic reactions to specific compartments within cell  Consists of:  Nuclear envelope  Membranes of endoplasmic reticulum  Golgi apparatus  Vesicles  Several types  Transport materials between organelles of system 33
  34. 34. Endomembrane System: The Endoplasmic Reticulum   A system of membrane channels and saccules (flattened vesicles) continuous with the outer membrane of the nuclear envelope Rough ER   Studded with ribosomes on cytoplasmic side Protein anabolism   Synthesizes proteins Modifies and processes proteins    Adds sugar to protein Results in glycoproteins Smooth ER     No ribosomes Synthesis of lipids Site of various synthetic processes, detoxification, and storage Forms transport vesicles 34
  35. 35. Endoplasmic Reticulum 35
  36. 36. Endomembrane System: The Golgi Apparatus  Golgi Apparatus  Consists of flattened, curved saccules  Resembles  Modifies stack of hollow pancakes proteins and lipids  Receives vesicles from ER on cis (or inner face)  Modifies them and repackages them in vesicles  Release the vesicles from trans (or outer face)  Within cell  Export from cell (secretion, exocytosis) 36
  37. 37. Golgi Apparatus 37
  38. 38. Endomembrane System: Lysosomes  Membrane-bound vesicles (not in plants)  Produced by the Golgi apparatus  Contain powerful digestive enzymes and are highly acidic  Digestion of large molecules  Recycling of cellular debris and resources  Autolysis may occur in injured or dying cell to cause apoptosis (programmed cell death, like tadpole losing tail) 38
  39. 39. Lysosomes 39
  40. 40. Endomembrane System: Summary  Proteins produced in rough ER and lipids from smooth ER are carried in vesicles to the Golgi apparatus.  The Golgi apparatus modifies these products and then sorts and packages them into vesicles that go to various cell destinations.  Secretory vesicles carry products to the membrane where exocytosis produces secretions.  Lysosomes fuse with incoming vesicles and digest macromolecules. 40
  41. 41. Endomembrane System: A Visual Summary 41
  42. 42. Peroxisomes  Similar to lysosomes  Membrane-bounded vesicles  Enclose enzymes that rid the cell of toxic peroxides  Participate in the metabolism of fatty acids and many other metabolites 42
  43. 43. Peroxisomes 43
  44. 44. Vacuoles  Membranous sacs that are larger than vesicles Store materials that occur in excess  Others very specialized (contractile vacuole)   Plants cells typically have a central vacuole Up to 90% volume of some cells  Functions in:  Storage of water, nutrients, pigments, and waste products  Development of turgor pressure  Some functions performed by lysosomes in other eukaryotes  44
  45. 45. Vacuoles 45
  46. 46. Energy-Related Organelles: Chloroplast Structure  Bounded  Inner by double membrane membrane infolded  Forms disc-like thylakoids, which are stacked to form grana  Suspended in semi-fluid stroma  Chlorophyll  Green photosynthetic pigment  Chlorophyll capture solar energy 46
  47. 47. Energy-Related Organelles: Chloroplasts  Serve as the site of photosynthesis  Captures light energy to drive cellular machinery  Photosynthesis  Synthesizes carbohydrates from CO2 & H2O  Makes own food using CO2 as only carbon source  Inorganic molecules (Energy-poor compounds) are converted to organic molecules (energy-rich compounds)  Only plants, algae, and certain bacteria are capable of conducting photosynthesis 47
  48. 48. Chloroplast Structure 48
  49. 49. Energy-Related Organelles: Mitochondria  Smaller than chloroplast  Contain ribosomes and their own DNA  Surrounded by a double membrane  Inner membrane surrounds the matrix and is convoluted (folds) to form cristae.  Matrix – Inner semifluid containing respiratory enzymes  Break down carbohydrates  Involved in cellular respiration  Produce most of ATP utilized by the cell  Contain their own DNA and ribosome i.e. they are semiautonomous  Inherited from Oocyte 49
  50. 50. Mitochondrial Structure 50
  51. 51. Mitochondrial Origin Hypothesis 51
  52. 52. The Cytoskeleton  Maintains  Assists  Aids cell shape in movement of cell and organelles movement of materials in and out of cells  Three types of macromolecular fibers  Microfilament  Intermediate Filaments  Microtubules  Assemble and disassemble as needed 52
  53. 53. The Cytoskeleton: Actin Filaments  Microfilament are rods of actin  Extremely thin filaments like twisted pearl necklace  Support for microvilli in intestinal cells  Intracellular traffic control For moving stuff around within cell  Cytoplasmic streaming   Function in pseudopods of amoeboid cells  Important component in muscle contraction 53
  54. 54. The Cytoskeleton: Actin Filament Operation 54
  55. 55. The Cytoskeleton: Intermediate Filaments  Intermediate microtubules  Rope-like in size between actin filaments and assembly of fibrous polypeptides  Functions:  Support nuclear envelope  Cell-cell junctions, like those holding skin cells tightly together 55
  56. 56. The Cytoskeleton: Microtubules  Hollow cylinders made of two globular proteins called α and β tubulin  Spontaneous pairing of α and β tubulin molecules form structures called dimers  Dimers then arrange themselves into tubular spirals of 13 dimers around  Assembly:   Under control of Microtubule Organizing Center (MTOC) Most important MTOC is centrosome  Function:    Provide framework for movement of organelle within cell Direct separation of chromosomes during cell division (e.g. Centrioles are composed of microtubules) Provide locomotion and movement (e.g. flagella and cilia) 56
  57. 57. The Cytoskeleton: Microtubule Operation 57
  58. 58. The Cytoskeleton 58
  59. 59. Microtubular Arrays: Centrioles  Short,  One hollow cylinders pair per animal cell  Located in centrosome of animal cells  Oriented at right angles to each other  Separate during mitosis to determine plane of division 59
  60. 60. Cytoskeleton: Centrioles 60
  61. 61. Microtubular Arrays: Cilia and Flagella  Hair-like projections from cell surface that aid in cell movement  In eukaryotes, cilia are much shorter than flagella Cilia move in coordinated waves like oars  Flagella move like a propeller or cork screw  61
  62. 62. Structure of a Flagellum 62
  63. 63. Comparison of Prokaryotic and Eukaryotic Cells 63
  64. 64. Lecture 1 PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor MCAT Exam Prep Membrane Structure and Function 64
  65. 65. Outline  Membrane  Models Fluid-Mosaic  Plasma Membrane Structure and Function  Phospholipids  Proteins  Plasma Membrane Permeability  Diffusion  Osmosis  Transport Via Carrier Proteins  Cell Surface Modifications 65
  66. 66. Structure and Function: The Phospholipid Bilayer  The plasma membrane is common to all cells  Separates:  Internal living cytoplasmic from  External environment of cell  Phospholipid bilayer:  External surface lined with hydrophilic polar heads  Cytoplasmic surface lined with hydrophilic polar heads  Nonpolar, hydrophobic, fatty-acid tails sandwiched in between 66
  67. 67. Unit Membrane 67
  68. 68. Membrane Models  Fluid-Mosaic Model  Three components:  Basic membrane referred to as phospholipid bilayer  Protein molecules  Float around like icebergs on a sea  Membrane proteins may be peripheral or integral   Peripheral proteins are found on the inner membrane surface Integral proteins are partially or wholly embedded (transmembrane) in the membrane  Some have carbohydrate chains attached  Cholesterol 68
  69. 69. The Fluid Mosaic Model 69
  70. 70. Transmembrane Proteins 70
  71. 71. Functions of Membrane Proteins  Channel Proteins:    Carrier Proteins:     Provides unique chemical ID for cells Help body recognize foreign substances Receptor Proteins:    Combine with substance to be transported Assist passage of molecules through membrane Cell Recognition Proteins:   Tubular Allow passage of molecules through membrane Binds with messenger molecule Causes cell to respond to message Enzymatic Proteins:  Carry out metabolic reactions directly 71
  72. 72. Membrane Protein Diversity 72
  73. 73. Science Focus: Cell Signaling 73
  74. 74. Types of Transport: Active vs. Passive  Plasma membrane is differentially (selectively) permeable  Allows some material to pass  Inhibits passage of other materials  Passive Transport:  No ATP requirement  Molecules follow concentration gradient  Active Transport  Requires carrier protein  Requires energy in form of ATP 74
  75. 75. Passage of Molecules Across the Membrane 75
  76. 76. Types of Membrane Transport: Overview 76
  77. 77. Types of Transport: Diffusion A solution consists of: A solvent (liquid), and  A solute (dissolved solid)   Diffusion Net movement of solute molecules down a concentration gradient  Molecules move both ways along gradient  Molecules move from high to low  Equilibrium:  When NET change stops  Solute concentration uniform – no gradient  77
  78. 78. Gas Exchange in Lungs: Diffusion Across Lung 78
  79. 79. Types of Transport: Osmosis  Osmosis: Special case of diffusion  Focuses on solvent (water) movement rather than solute  Diffusion of water across a differentially (selectively) permeable membrane  Solute concentration on one side high, but water concentration low  Solute concentration on other side low, but water concentration high  Water diffuses both ways across membrane but solute can’t  Net movement of water is toward low water (high solute) concentration   Osmotic pressure is the pressure that develops due to osmosis 79
  80. 80. Types of Transport: Carrier Proteins  Facilitated Transport  Small molecules  Can’t get through membrane lipids  Combine  Follow  Active with carrier proteins concentration gradient Transport  Small molecules  Move against concentration gradient  Combining  Requires with carrier proteins energy 80
  81. 81. Types of Transport: Carrier Proteins  Facilitated Transport  Small molecules  Can’t get through membrane lipids  Combine  Follow  Active with carrier proteins concentration gradient Transport  Small molecules  Move against concentration gradient  Combining  Requires with carrier proteins energy 81
  82. 82. Types of Transport: Membrane-Assisted Transport  Macromolecules transported into or out of the cell inside vesicles  Exocytosis – Vesicles fuse with plasma membrane and secrete contents  Endocytosis – Cells engulf substances into pouch which becomes a vesicle  Phagocytosis  Pinocytosis vesicle – Large, solid material into vesicle – Liquid or small, solid particles go into  Receptor-Mediated using a coated pit – Specific form of pinocytosis 82
  83. 83. Cell Surface Modifications: Junctions  Cell Surfaces in Animals  Junctions Between Cells  Adhesion  Intercellular filaments between cells  Tight  Junctions Form impermeable barriers  Gap  Junctions Junctions Plasma membrane channels are joined (allows communication) 83
  84. 84. Cell Surface Modifications  Extracellular Matrix  External meshwork of polysaccharides and proteins  Found in close association with the cell that produced them  Plant  Cell Walls Plants have freely permeable cell wall, with cellulose as the main component  Plasmodesmata penetrate cell wall  Each contains a strand of cytoplasm  Allow passage of material between cells 84
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