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Cells. What is a cell? A cell is a membrane bound unit containing hereditary material and other compounds that make metabolism, growth and reproduction possible. Hereditary material. Plasma membrane. Cytoplasm. Cells. Overview of cell structure Cells are surrounded by a plasma membrane.

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cells
Cells
  • What is a cell?

A cell is a membrane bound unit containing hereditary material and other compounds that make metabolism, growth and reproduction possible.

Hereditary

material

Plasma

membrane

Cytoplasm

cells1
Cells
  • Overview of cell structure
    • Cells are surrounded by a plasma membrane.
    • DNA the hereditary material is packaged in one or more chromosomes located in a nuclear region or nucleus.
    • The cytoplasm contains molecules and organelles needed for cellular activities.
    • Ribosomes are the factories in which proteins are manufactured.
cells2
Cells
  • How were cells discovered?
    • 1665 Robert Hooke

Examined cork in simple microscope.

Saw empty compartments and

called them ‘cellulae’ (small rooms).

    • 1650 - 1700 Anton Van Leeuwenhoek

Made his own microscope that could magnify 200 X.

Observed living things.

Called them ‘Animacules’ (little animals).

cells3
Cells
  • Formation of the cell theory
    • 1838 Matthias Schleiden

Concludes that all plants are made of cells or their derivatives.

He called this theory phytogenesis

    • 1839 Theodore Schwann

All animal tissue is made of cells and within an organism these cells are identical.

    • The theory they presented from these observations is often called the Schleiden and Schwann Cell Theory
cells4
Cells
    • 1855 Rudolph Virchow

Studied pathenogens and concluded

‘omnis cellula e cellua’ which means that all cells arise from pre-existing cells.

  • Principles of the Cell Theory
    • All organisms are composed of one or more cells.
    • Cells are the basic unit of life.
    • Cells arise only by division of a previously existing cell.
cells5
Cells
  • Cell size
    • Does small cell sizes have advantages?
    • The surface area increases as the square (10 )of the diameter of a sphere, but the volume increases as the cube (10 ).

small cube - surface area

small cube - volume

2

3

10 m

2

6 x (10 m x

10 m) = 600 m

3

10 m x 10 m x 10 m = 1000 m

cells6
Cells

2

6 x (30 m x 30 m) = 5400 m

  • big cell - surface area
  • big cell - volume

3

30 m x 30 m x 30 m = 27000 m

cells7
Cells

2

  • Comparing different sizes
    • Surface area

1 small = 600 m

27 small = 16.200 m

1 big = 5400 m

    • Volume is the same for 1 big and 27 small
    • The ratio of surface to volume
      • 27 small 16200/27000 = 0,6
      • 1 big 5400/27000 = 0,2
      • surface area of small is 3X greater

2

2

cell size
Cell size
  • Why aren´t cells larger?
    • limitations of molecular diffusion
      • faster passage through small cells
      • more efficient communication
    • limitations of surface/volume ratio
      • with in size greater in volume
      • interaction occurs only at surface
      • insufficient exchange of materials at plasma membrane
structure of prokaryotes
Structure of prokaryotes
  • Strong cell wall made of carbohydrate matrix and peptide units.
    • Slime capsule (some times with pili), not always present.
structure of prokaryotes1
Structure of prokaryotes
  • Simple interior organization
    • lack internal compartmentalization
    • reactions not separated, one metabolic unit
    • lack membrane-bound organelles
    • infolding of plasma membrane
  • Rotating flagella
    • cell movement - screw like motion
structure of prokaryotes2
Structure of prokaryotes
  • Ribosomes in the cytoplasm
    • protein synthesis
  • Circular nuclear matter (DNA)
    • located in the nucleoid region
  • Plasmids
    • small independent circular DNA
  • Mesosome
    • infolding of plasma membrane often associated with photosynthesis
structure of eukaryotes
Structure of eukaryotes
  • More complex than prokaryotes
  • They are compartmentalized
    • possess internal membrane bound organelles
      • ribosomes
      • rough endoplasmic reticulum (rER)
      • lysosomes
      • Golgi apparatus (complex)
      • mitochondria
      • nucleus
      • chloroplasts
structure of eukaryotes1
Structure of eukaryotes
  • Nucleus the largest organelle
    • the nuclear envelope
      • double layer of membranes,
      • outer continuous with ER
      • nuclear pores
      • restrict passage of molecules to proteins and RNA
    • chromosomes - chromatid
      • contain hereditary material
      • divided into linear chromosomes, associated with histone protein
structure of eukaryotes2
Structure of eukaryotes
  • the nucleolus
    • an assembly plant for ribosomal subunits
      • ribosomal proteins are made in the cytoplasm
      • ribosomal RNA made in the nucleus
organelles
Organelles
  • Endoplasmic reticulum
      • Thin membrane not visible in the light microscope.
      • Divides interior into compartments.
      • Cytoskeleton, holds the cell shape.
    • Rough ER
      • covered with ribosomes
      • manufactures proteins for export
    • Smooth ER
      • lacks ribosomes
      • carbohydrate and lipid synthesis
organelles1
Organelles
  • Ribosomes
    • Made of two parts.
    • Made in the nucleus.
    • Assist in the manufacture of proteins.
  • Golgi apparatus
organelles2
Organelles
  • Mitochondrion
  • Lysosome
organelles3
Organelles
  • Chloroplast
cells8
Cells
  • State two similarities between prokaryotic and eukaryotic cells.
  • State two differences between the eukaryotic nucleus and the prokaryotic nuclear material.
endosymbiosis
Endosymbiosis
    • Symbiosis is two organisms living in close association.
  • Mitochondria and chloroplasts are thought to be ancient bacteria that became incorporated into eukaryotic cells.
    • Evidence supporting Theory:
      • both are surrounded by double membranes
      • mitochondria and bacteria hvae similar size
      • mitochondrial ribosomes resemble bacterial ribosomes
      • both have circular DNA like bacteria
      • mitochondria divide by simple fission