Transcript Cells - gcate.org

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.
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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
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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
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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
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Structure of prokaryotes
Strong cell wall made of
carbohydrate matrix and peptide
units.
Slime capsule (some times with pili),
not always present.
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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
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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
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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
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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
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Structure of eukaryotes
the nucleolus
an assembly plant for ribosomal
subunits
ribosomal proteins are made in the
cytoplasm
ribosomal RNA made in the nucleus
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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
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Organelles
Ribosomes
Made of two parts.
Made in the nucleus.
Assist in the manufacture of
proteins.
Golgi apparatus
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Organelles
Mitochondrion
Lysosome
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Organelles
Chloroplast
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Cells
State two similarities between
prokaryotic and eukaryotic cells.
State two differences between
the eukaryotic nucleus and the
prokaryotic nuclear material.
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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
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mitochondria divide by simple fission
The Plant Cell Wall
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