Download Cells Structure and Function

Cells
How big are cells?
 This is the head of a pin
at 100 µm
 This is the same pin
magnified and your view
is at 20 µm. What you
see are rod-shaped
bacteria.
 Finally, the bacteria
magnified. The view is
0.5 µm
Who discovered cells?
 Robert Hooke
 Hooke was engaged in many
aspects of science, including
chemistry, physics, mechanics,
and his name is attributed to
the discovery of the Law of
Elasticity.
 His most famous discovery
however, involves microscopy.
 In 1665 Hooke published
Microphagia.
 In his book, he described the
first cells, and even coined the
word cells.
 He was looking at dead plant
cells in cork.
Cork cells at 400x magnification
Who discovered cells?
 Anton Van Leeuwenhoek
 Van Leeuwenhoek was a Dutch
trader and scientist, whose
knowledge of glass allowed
him to create his own
microscopes.
 He is known as the father of
microbiology.
 He was the first to describe:
Protozoa
Bacteria
The vacuole of the cell
Spermatozoa (he called these
animalcules)
 And muscle fibers




protozoa
Who discovered cells?
 Matthias Schleiden ,Theodor
Schwann, and Robert Brown
nucleus
 In the 1820’s, improved lenses
brought cells into sharper
focus.
 Brown
 First to identify plant cell
nucleus
 Schleiden
 First to propose that plant cells
may be an independent unit
apart from the plant.
 Schwann
 Reported that cells and their
products made up both plants
and animals.
Onion cells
Who discovered cells?
 Rudolf Virchow
 Studied how cells divide
(mitosis and meiosis)
 Every cell, he decided, must
come from a cell that
already exists.
Cell division
What is the Cell Theory?
 All of these discoveries lead to the cell
theory
 1. Organisms consist of one or more cells.
 2. The cell is the most basic unit of life.
 3. All cells come from other cells.
amoeba
neuron
binary fission
What is a cell?
 The cell is the smallest unit with the
properties of life: metabolism,
response to environment, growth,
and reproduction.
 All cells have three things in
common.
 A plasma membrane separates each
cell from the environment, permits
the flow of molecules across the
membrane, and contains receptors
that affects the cell’s activities.
 A nucleus localizes hereditary
material, which can be copied and
read.
 All cells have some sort of cytoplasm.
Macrophage (a type of
white-blood cell) eating
bacteria
Why aren’t cells bigger?
 The cell is constrained by the
surface-to-volume ratio.
 If a cell expands in diameter
during growth, its volume will
increase more rapidly than its
surface area will.
 A cell that is too large will not
be able to move materials into
and out of the cell interior.
 The smaller the cell, the
more efficiently materials
cross its surface and become
disturbed through the
interior.
Prokaryotic Cells
 Prokaryotes are the smallest known cells and are the
most metabolically diverse forms of life on earth.
 Two domains of prokaryotes exist: Bacteria and
Archaea
 The term prokaryotic means “before the nucleus”
and indicates the existence of bacteria before the
evolution of cells with a nucleus.
 In fact, prokaryotes don’t have ANY organelles.
 Prokaryotes have a rigid cell wall, and sticky
polysaccharides (carbohydrates) help cells attach to
surfaces, such as teeth.
 Many bacteria have the ability to photosynthesize like
plants.
 The bacterial chromosome is a singular, circular
DNA molecule.
 All prokaryotes are unicellular.
Eukaryotic Cells
 Eukaryotic cells (true
nucleus) are larger and
generally more complex
with a nucleus and other
membrane-bound organelles.
 The nucleus contains the
genetic material of the cell.
 All multi-cellular organisms
are eukaryotic.
 Some unicellular organisms
are also eukaryotic.
Plasma Membrane
 In BOTH plant and animal cells
 Lipid bi-layer of plasma membranes forms a boundary between the
inside and outside of the cell.
 Regulates the entry/exit of substances.
 Proteins embedded in the lipid bilayer or positioned at one of its
surfaces serve as channels, pumps, or receptors.
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
Lipid bilayer
The Nucleus
 In BOTH plants and animal cells
 Nuclear envelope
 A nuclear envelope encloses the semi-fluid
intereior of the nucleus called the
nucleoplasm.
 The ribosome-bound outer membrane is
loaded with pores, and it is continuous with
the endoplasmic reticulum.
 Nucleolus
 Dark globular mass where ribosomes are
made.
 Nuclear DNA
 Chromatin refers to the cell’s total collection
of DNA and associated proteins.
 A chromosome is a double-stranded DNA
molecule and its associated proteins.
Endoplasmic Reticulum
 In BOTH plant and animal cells
 The endoplasmic reticulum (ER) is a
collection of interconnected tubes
and flattened sacs that begin at the
nucleus and ramble through the
cytoplasm.
 There are two types of ER
distinguished by the presence or
absence of ribosomes.
 Rough ER
Has ribosomes on its surface and
looks “rough”
 Lipids for use outside the cell (like
hormones) are manufactured here
 Smooth ER
 Has NO ribosomes on its surface and
looks “smooth”
 Lipids for use inside the cell (like
more cytoplasm) are manufactured
here.

Ribosomes
 In BOTH plant and animal
cells
 Made in the nucleolus and
located throughout the
cytoplasm and on the rough
ER.
 They help make proteins.
 They are made of a small and
large subunit that assists in
threading protein.
Golgi Bodies
 In BOTH plants and animal
cells
 In the golgi bodies (also
golgi apparatus), proteins
and lipids undergo final
processing, sorting, and
packaging.
 The membranes of the
golgi are arranged in stacks
of flattened sacs whose
edges break away as
vesicles.
Lysosomes
 In BOTH plant and animal
cells
 They are rare in plant cells but
are there at times.
 Lysosomes are vesicles that bud
from the golgi bodies.
 They carry powerful enzymes
that can digest the contents of
other vesicles, worn-out cell
parts, or bacteria and foreign
particles.
 They are programmed for celldeath (apoptosis).
Peroxisomes
 In BOTH plants and animal
cells
 Vesicles like lysosomes that
contain enzymes that break
down fatty acids and amino
acids.
Central Vacuole
 In PLANTS ONLY
 Accumulates a watery solution
of ions, amino acids, sugars,
and toxic substances.
 Vacuoles enlarge during growth
and greatly increase the cell’s
outer surface area.
 The enlarged cell, with more
surface area, has an enhanced
ability to absorb nutrients.
Mitochondria
 In BOTH plants and animals
 Are the primary organelles for making useable
energy for the cells.
 Each mitochondrion has two membranes, and inner
folded membrane (cristae) surrounded by a smooth
outer membrane.
 Inner and outer compartments formed by the
membranes are important in energy transformation.
 Mitochondria resemble bacteria in size and
biochemistry.
 Like bacteria they have their own DNA and divide on
their own apart from the cell.
 They have ribosomes.
 Endosymbiosis is a theory that explains how
mitochondria may have once been independent
prokaryotic cells that were engulfed by another cell
but became permanent.
Chloroplasts
 In PLANTS ONLY
 Oval or disk-shaped organelle,
bound by a double membrane, and
specialized for photosynthesis.
 In the innermost membrane, stacked
disks (thylakoids), pigments and
enzymes trap sunlight energy to form
ATP and NADPH.
 Sugars and starches are formed in the
fluid substance (stroma) surrounding
the stacks.
 Pigments such as chlorophyll (green)
confer distinctive colors to the
chloroplasts.
Chromoplasts
 In PLANTS ONLY
 store red and brown
pigments that give color to
flowers, autumn leaves,
fruits, and roots.
Cell Walls
 In PLANTS CELLS only
 Cell walls are carbohydrate
frameworks (cellulose) for
mechanical support in
bacteria, protistans, fungi,
and plants.
 Cell walls have an inner and
outer wall.
 It makes plant parts stronger,
more waterproof, and less
inviting to insects.
Cytoskeleton
 In BOTH plant and animal cells
 Supporting matrix of protein
fibers
 Maintains cell shape and acts as a
scaffold upon which organelles
are attached.
 Composed of microfiliments,
microtubules and many other
supportive proteins.
These animal cells are stained
to show the cytoskeleton.
microtubules (green),
microfilaments (red), and nuclei
(blue).
How do cells move?
 Cells can move with a variety of
structures.
 Cilia
 These are short, numerous, hair-like
extensions of the cell membrane.
 Found on free-living cells.
 Flagella
 Long, not usually numerous.
 Found in one-celled protozoans and
spermatazoa.
 Pseudopods
 “false feet”
 Temporary lobes that project from the cell,
used in locomotion and cell capture.