Download Chapter 3 Cells The Basic Units of Life

Cells:
The Basic Units of Life
•
•
•
•
•
•
•
•
•
The Cell: The Basic Unit of Life
Prokaryotic Cells
Eukaryotic Cells
Organelles that Process Information
The Endomembrane System
Organelles that Process Energy
Other Organelles
The Cytoskeleton
Extracellular Structures
• Life requires a structural compartment
separate from the external environment
in which macromolecules can perform
unique functions in a relatively constant
internal environment.
• These “living compartments” are cells.
The average human being is composed of around
100 Trillion individual cells!!!
It would take as many as 50 cells to cover the area of
a dot on the letter.
Discovery of Cells
1665- English Scientist, Robert Hooke, discovered cells
while looking at a thin slice of cork.
He described the cells as tiny boxes or a honeycomb
He thought that cells only existed in plants and fungi
Anton van Leuwenhoek
1673- Used a handmade microscope to
observe pond scum & discovered single-celled
Organisms.
He called them “animalcules”
He also observed blood cells from fish, birds, frogs, dogs,
and humans
Therefore, it was known that cells are found in animals as
well as plants
Between the Hooke/Leuwenhoek discoveries and the mid 19th
century, very little cell advancements were made.
This is probably due to the widely accepted, traditional belief in
Spontaneous Generation.
Examples:
-Mice from dirty clothes/corn husks
-Maggots from rotting meat
19th Century Advancement
Much doubt existed around Spontaneous Generation
Conclusively disproved by Louis Pasteur
Redi’s experiment
Pasteur’s experiment
Development of Cell Theory
1838- German Botanist, Matthias Schleiden, concluded
that all plant parts are made of cells
1839- German physiologist, Theodor Schwann, stated that
all animal tissues are composed of cells.
M. Schleiden
T. Schwann
1858- Rudolf Virchow, German physician, after
extensive study of cellular pathology, concluded
that cells must arise from preexisting cells.
Cell Shapes
11
Cell Shapes 2
•
•
•
•
•
•
•
•
•
Squamous = thin and flat
Polygonal = irregularly angular with 4 or more sides
Cuboidal = squarish
Columnar = taller than wide
Spheroid = round
Discoid = disc-shaped
Stellate = starlike
Fusiform = thick in middle, tapered at ends
Fibrous = threadlike
12
Cell Theory
1.
All organisms are composed of one or more cells
-Organisms can be unicellular or multicellular.
2.
The cell is the basic unit of organization of
organisms.
3.
All cells come from pre-existing cells
-Cells reproduce to make exact copies of
themselves
Exceptions to cell theory
• Protozoans do not have cellular body. They are acellular.
• Bacteria and blue green algae (cynobacteria) do not possess an
organised nucleus. Their genetic material lies uncovered in the
cytoplasm. They also lack membrane bound organelles.
• Some tissues such as connective tissues, have-non-living
material called matrix in which living cells remain embedded.
Cell theory does not cover such cases.
• RBC’s and seive tube cells live without nucleus and other cell
organelles
• Protoplasm is replaced by non-living materials in the surface
cells of skin and cork.
• Viruses do not have a cellular machinery. They consist of a
nucleic acid (DNA or RNA) core surrounded by protein sheath.
They are inert, except, when present in a living cell of some
organism where they multiply by using cell’s mateials and
machinery.
Modern Cell Theory
Modern Cell Theory contains 4 statements, in addition to
the original Cell Theory:
- The cell contains hereditary information(DNA) which is
passed on from cell to cell during cell division.
- All cells are basically the same in chemical composition
and metabolic activities.
- All basic chemical & physiological functions are carried
out inside the cells.(movement, digestion,etc)
- Cell activity depends on the activities of sub-cellular
structures within the cell(organelles, nucleus, plasma
membrane)
-Cell size is limited by the surface area-tovolume ratio.
- The surface of a cell is the area that interfaces
with the cell’s environment. The volume of a
cell is a measure of the space inside a cell.
- Surface area-to-volume ratio is defined as the
surface area divided by the volume. For any
given shape, increasing volume decreases the
surface area-to-volume ratio.
● Because most cells are tiny, with diameters in
the range of 1 to 100 m, microscopes are
needed to visualize them.
● With normal human vision the smallest
objects that can be resolved (i.e., distinguished
from one another) are about 200 m (0.2 mm) in
size.
The scale of life
The scale of life
Two Types of Cells
• Prokaryotic Cells:
– No nucleus
– No organelles
– Mostly unicellular organisms
– Cell wall or membrane
Specialized features of some prokaryotic cells:
- A cell wall just outside the plasma membrane (made of
carbohydrates).
- Some bacteria have another membrane outside the cell
wall, a polysaccharide-rich phospholipid membrane.
- Some bacteria have an outermost slimy layer made of
polysaccharides and referred to as a capsule.
Some bacteria, including cyanobacteria, can carry on
photosynthesis. The plasma membrane is infolded and has
chlorophyll.
Some bacteria have flagella, locomotory structures shaped like a
corkscrew.
Some bacteria have pili, threadlike structures that help bacteria
adhere to one another during mating or to other cells for food and
protection.
Three types of prokaryotic cells
1. Bacteria without Cell Walls – Mycoplasma- PPLO
• Lack a rigid cell wall during their entire life cycle
• Smallest known organisms – smallest genomes (other
than viruses)
– Diameter ranges from 0.15 m to 0.30 m
• Do not stain with the Gram stain.
• May be saprophytic or parasitic.
• Pleomorphic
– Tiny pleomorphic cocci, short rods, short spirals,
and sometimes doughnut shape
• Mycoplasma pneumoniae
– Atypical pneumonia in humans.
23
2. Kingdom Eubacteria
•
•
•
•
Unicellular (single-cell)
Prokaryotes (no membrane-bound organelles)
Cell Walls contain peptidoglycan, not cellulose
First appeared approximately 3.7 BYA
Nutrition
Autotrophs- manufacture organic compounds
– Photoautotrophs- use light energy & CO2
– Chemoautotrophs-use inorganic substances like H2S,
NH3, and other nitrogen compounds
• Heterotrophs- obtain energy by consuming organic
compounds
– parasites- get energy from living organisms
– saprobes (saprophytes)- get energy from dead, decaying
matter; also called decomposers.
• Bacteria cells digest foods by releasing enzymes (which are
usually poisonous) outside the cells and into their food. This is
called Extra-cellular digestion.
•
• The digested foods are then absorbed by diffusion or active
transport.
Oxygen Preferences
• obligate aerobes must have oxygen
• obligate anaerobes cannot live in oxygen
• facultative anaerobes can grow with or without
oxygen
General Characteristics
• are found almost everywhere
• are often pathogenic (they make us sick!)
• are divided into groups according to:
– their shape
– grouping
– cell wall
– ability to absorb stains
Shapes
• Coccus = spherical (coccus came from the Greek
word for berries!)
• Bacillus = rod-shaped
• Spirilla = spiral-shaped.
Examples of Spherical-shaped cells
Cyanobacteria
Gram negative phototrophs
- Oxygenic photosynthesis 12H2O + 6CO2 
C6H12O6 + 6H2O + 6O2
- Existed for  2.3 bya
- Largest and one of the most important groups
of bacteria on Earth
Extremely diverse group
- Unicellular, colonial & filamentous form
- Some species fix N2 in heterocysts
- Some species produce akinete
Analogous to a endospore
- Most species are found in fresh water
▪ Marine
▪ Damp soil
▪ Temporarily moistened desert rocks
▪ Endosymbionts in lichens, plants, various protists or
sponges
Two Types of Cells
• Eukaryotic Cells:
– Nucleus
– Organelles surrounded
by membranes
– Mostly multicellular
– organisms
– Cell wall or membrane
Eukaryotic cells Prokaryotic cells
Vesicles:
Mitochondria:
Chloroplasts:
Plasma membrane
with steriod
Golgi apparatus:
Endoplasmic
reticulum:
Differentation:
Ribosomes:
Cytoskeleton:
Vacoules:
Number of
chromosomes:
Present
Present
Present (in plants)
Present
Absent
Absent
Yes
Usually no
Present
Absent
Present
Absent
Tissue and organs
80S especially in
Mitochondria and
chloroplast
Present
Present
Radimentary
More than one
One
70S
May be absent
Present
DNA complexed
histones:
True Membrane
bound Nucleus:
Yes
No
Present
Absent
Cell wall:
Chemically simpler
Nucleolus:
Mitosis Occurs:
Genetic
Recombination:
Present
Yes
Mitosis and fusion
gametes
Microscopic in size;
membrane bound;
usually arranged as
nine doublets
surrounding two
singlets
Flagella:
Lysosomes and
peroxisomes:
Microtubules:
Usually chemically
complexed
Absent
No
Partial, undirectional
transfers DNA
Submicroscopic in
size, composed of
only one fiber
Present
Absent
Present
Absent or rare
Cell Organelles
• Cytoplasm:
– Structure: gel-like material found inside the cell,
made of water, salts, and organic materials.
– Function: holds the organelles, keeps them
separate.
• Cell wall:
– Structure: a tough outer covering made of
cellulose, small holes are present that allow
materials to enter and exit the cell.
– Function: maintains shape, supports,
strengthens
– Only plant cells have cell walls.
• Cell membrane: a protective covering that
surrounds the cell.
– Materials entering the cell must pass through
the cell membrane. Some materials can easily
enter while others cannot cross at all.
– Selectively permeable.
– Made of a phosopholipid bilayer: The heads of
the lipids are hydrophilic (water loving) while the
tails are hydrophobic (water fearing).
– Both plant and animal cells have cell
membranes
• Nucleus:
– Structure: round, large organelle. Surrounded
by a membrane. Contains the DNA, nucleolus,
and chromatin.
– Function: controls the cell
– Nickname: “brain”
• Nuclear membrane: surrounds and protects the
nucleus.
• Ribosomes:
– Structure: made of RNA
– Function: produce proteins
– Location: attached to the endoplasmic
reticulum.
– Nickname: food source
• Endoplasmic Reticulum:
Structure: made of membranes, flattened sacs
Location: located next to the nuclear membrane
Nickname: highway, subway system, …
Smooth ER: does not contain ribosomes, makes
lipids and membrane proteins, transports
proteins
– Rough ER: contains ribosomes, makes proteins.
–
–
–
–
• Golgi Body:
– Structure: stack of membranes.
– Function: packages proteins from the ER and
distribute them around or outside of the cell.
– Nickname: UPS or shipping center, …
• Mitochondria:
– Structure: outer membrane is a phospholipid
bilayer, inner membrane is permeable to oxygen,
carbon dioxide, and water. Wrinkled
appearance
– Function: transform the energy in food to energy
the cell can use to drive chemical reactions.
– Nickname: “powerhouse” of the cell.
• Lysosomes:
– Structure: sac filled with enzymes and liquids.
– Function: involved in digestion of old cell
organelles as well as breaking large molecules
into smaller ones.
– Location: found in all animal cells, rare in plant
cells.
– Nickname: garbage person, stomach.
• Vacuoles:
– Structure: cell membrane surrounding a fluid.
– Function: storage area
• Plant cells: very large organelle, contains
pigments, waste, salts, water. Maintains turgor
pressure
• Animal cells: smaller organelle, primarily
responsible for general storage.
– Nickname: storage tank.
Difference Between Plant Cell And
Animal Cell
•
•
•
•
•
•
•
•
•
•
•
PLANT CELL
************
Shape
Size
Cell Wall
Vacuole
Plastid
Centrosome
Mitochondria
Amino Acid
Cell Division
•
•
•
•
•
•
•
•
•
•
•
ANIMAL CELL
**************
Shape
Size
Cell Wall
Vacuole
Plastid
Centrosome
Mitochondria
Amino Acid
Cell Division
Plant cell
1. Rectangular in shape.
2. Plant cell is covered by a
thick cell wall.
Cell wall is made up of
cellulose and hemicellulose.
3. Plant cell is larger than
Animal cell.
4. Vacuole is big, prominent
and permanent.
5. Plastids are present .
6. Centrosome is absent.
7. The number of
Mitochondria is less in plant
cell than animal cell.
8. Cell Division occurs by cell
plate .
Animal cell
-Spherical in shape
- Animal cell is covered by a
thin cell membrane.
It is made up of Lipoprotein.
- Animal cell is smaller than
plant cell.
- Vacuole is small, temporary
and not so prominent.
-Plastids are absent.
-Centrosome is present.
-The number of Mitochondria
is approximately more in
animal cell.
-Cell Division occurs by
furrow in spite of cell plate.
Plant cell
9. Nucleus is pushed to one
side of the cell by central
vacuole.
10. Crystals are mostly
present.
11. Can synthesize all amino
acids, coenzymes and
vitamins.
12. Glyoxysomes may be
present.
13. Store carbohydrates as
starch.
Animal cell
- The nucleus is mostly located
in the centre of the cell.
-Crystals mostly lacking.
-Incapable of synthesizing all
amino acids, coenzymes and
vitamins.
-Glyoxysomes not present.
- Carbohydrates are stored as
glycogen.