Download CELLS PLUS VOLUME

Robert Hooke 1665
coined the word `cell’ for the box-like structures of cork
M J Schleiden
a lawyer turned botanist &
Theodore Scwann
an animal embryologist
met at dinner party in 1837
•1839 formally espoused cell theory
•the cells are of universal occurrence and are
• the basic units of an organism
1849 Cell division described
1858 Rudolph Virchow forcefully states the
paradigm of cell theory
``All cells come from previous cells’’
Omnis cellula e cellula
Thus:
all individuals derived from a single
celled organism are related &
all cells in a multi-celled organism are
descended from one fertilized egg.
Basics of the Cell Theory
• all known living things (systems) are composed of
cells
• cells arise only from other cells
(not spontaneously - experiments of Redi and
Pasteur)
• all energy flow (metabolism & biochemistry) of life
occurs within cells
• cells contain DNA as genetic info - (for
subsequent generations)
Some important facts about cells:
- their diversity : many sizes, shapes, and types
(165+ in humans)
- their similarity: have same basic structural plan
- surrounded by cell membrane
- contain nuclei
(bacteria = genophore)
- similar sub-cell parts (ORGANELLES)
- all contain same macromolecules
Different Shapes & Forms
Scanning electron micrograph of
human red blood cells
Sickle cells
Why are cells so small?
a. Efficiency: smaller cells have larger
surface area
b. Specialization: Having numerous
small cells permits specialization
How large cells can be?
•As an object increases in size its volume increases as the cube of its linear
dimensions while surface area increases as the square
Surface area = L X B
Square of two linear dimensions
Volume = L X B X H
Cube of three linear dimensions
•As these cubes illustrate the surface area to volume ratio of a small object
is larger than that of a large object of similar shape
•This ratio limits how large cells can be
Getting around this problem
Divide to become
multicelled - Embryo
long and thin or skinny
and flat
many protists, nerve cells, muscle
cells
Smaller Particles React Faster Than Larger
Particles
• Granular sugar dissolves easier than sugar
cubes
• Everything that the cell needs or has to get rid
of has to go through the cell membrane, the
amount of which relates to the surface area
• Surface must allow sufficient exchange to
support the contents of the cell
• stops growing when its surface area is
insufficient to meet the demands of the cell's
volume
Cells Have Evolved Two Basic
Architectural Plans
Cells without a nucleus
Cells with a nucleus
“karyon” = kernel or nut; “pro” = before ; “eu” = good or true; • Eukaryotes - “cells with a true nucleus”
• Prokaryotes - “cells with no defined nucleus”
Prokaryotes
• Cells whose nucleus
is not enclosed in a membrane
• Lack other organelles too
• First to evolve, The oldest accepted prokaryote fossils
date to 3.5 billion years
• Contain
a circular chromosome
Plasmids with satellite DNA
Ribosomes
food storage granules
Prokaryotic cell-Bacterium
A general prokaryotic cell
Eukaryotes
• Cells whose nucleus is enclosed in a membrane
• Evolved later. Eukaryotic fossils date to between 750 million years and
possibly as old as 1.2-1.5 billion years.
Fine structure of an animal cell- based on electron microscope
studies
Eukayotic cell as seen with an electron microscope
Organelles
• Mitochondria and chloroplasts are
energy-transducing organelles
• Both seem to share many properties
with bacteria:
– contain 70S ribosomes (whereas rest of
eukaryote cells contain 80S ribosomes)
– divide by binary fission
– contain circular DNA without nucleus, etc.
Endosymbiont Theory
Symbiosis = "living together“
• Chloroplasts and Mitochondria derived from ancient
colonization of large bacteria (became the eukaryotic cell)
by smaller bacteria
• Host cells acquired respiration from the precursor of the
mitochondrion, and oxygenic photosynthesis from the
precursor of the chloroplast
• Also acquired much of their genetic information
• Eventually, organelles lost ability to exist as separate
organisms, cannot have independent existence from cell
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Some protists
Why double membrane of chloroplast?
Invagination
Outer membrane of
organelle originally
belonged to the host cell.
Why double membrane?
Images with electron microscope
Mitochondrium
Cutaway view of mitochondrion
Inner membrane more active
Centrifugation
• A centrifuge is a device for separating
particles from a solution according to their
size, shape, density, viscosity of the
medium and rotor speed
• In biology, the particles are usually cells,
sub cellular organelles, viruses, large
molecules such as proteins and nucleic
acids
• Instrumental in working out the functions of
organelles
Centrifuge