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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.
Plasma
membrane
Cytoplasm
Hereditary
material
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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.
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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).
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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
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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.
5
Cells
Cell size
Does small cell sizes have advantages?
The surface area increases as the square
2
(10 )of the diameter of a sphere, but the
volume increases as the cube (103 ).
small cube - surface area
10 m
6 x (10 m x 10 m) = 600 m2
small cube - volume
10 m x 10 m x 10 m = 1000 m3
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Cells
big cell - surface area
2
6 x (30 m x 30 m) = 5400 m
big cell - volume
30 m x 30 m x 30 m = 27000 m
3
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Cells
Comparing different sizes
Surface area
1 small = 600 m
2
2
27 small = 16.200 m
2
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
8
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
9
Structure of prokaryotes
Strong cell wall made of
carbohydrate matrix and peptide
units.
Slime capsule (some times with pili),
not always present.
10
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
11
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
12
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
13
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
14
Structure of eukaryotes
the nucleolus
an assembly plant for ribosomal
subunits
ribosomal proteins are made in the
cytoplasm
ribosomal RNA made in the nucleus
15
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
16
Organelles
Ribosomes
Made of two parts.
Made in the nucleus.
Assist in the manufacture of
proteins.
Golgi apparatus
17
Organelles
Mitochondrion
Lysosome
18
Organelles
Chloroplast
19
Cells
State two similarities between
prokaryotic and eukaryotic cells.
State two differences between
the eukaryotic nucleus and the
prokaryotic nuclear material.
20
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
21
mitochondria divide by simple fission
The Plant Cell Wall
22