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Cellular Structure
andChapter
Functions
3
LOOKING AT CELLS
Making sense of life’s
most basic Unit
Historical Ideas About Life
• Before 1600 the predominant ideas about
life revolved around the Spontaneous
Generation Theory.
• Spontaneous Generation is the idea that
life appeared from nonliving matter (mold
grows from cheese, mushrooms grow from
dead wood)
Historical Ideas About Life
• The Spontaneous Generation Theory
made sense to people because if they
couldn’t see any mold, but overnight mold
started growing on cheese, the mold must
have appeared.
• The Spontaneous Generation theory was
slowly dismantled after the discovery of
the cell.
What is a Cell
• Robert Hooke - 1665 - discovered cell with
crude “microscope”
– Observed cork cells
– Used term “cell” reminding him of a Monk’s
room or “cell”
What is a Cell
• Anton van Leeuwenhoek - 1674 Develops first quality microscope
• In a pond water sample, Leeuwenhoek
spotted “animacules” in his microscope.
Formation of the Cell Theory
• Once cells were discovered, scientists
began finding them in all kinds of
organisms.
• Scientists began seeing cells before they
were otherwise visible (mold spores, fly
eggs, etc.)
• After seeing this, it became harder to say
life simply “appeared.”
Cell Theory
Scientists formed the cell theory in 1839,
and revised it to the modern cell theory in
1855. The cell theory has three tenants.
1. All living things or organisms are made of
cells and their products.
2. New cells are created when existing cells
divide into two new cells.
3. Cells are the basic building units of all
life.
Cell Theory
With the cell theory in place, biologists could start
looking for cellular explanations of biology,
instead of assuming that actions “just
happened.”
This new idea revolutionized modern biology and
scientists began looking at cells and their
structure in more detail to answer larger
questions.
One major modern addition to the cell theory
important to biology students is the idea that:
Cell Theory
The activity of an organism depends on the total
activity of independent cells.
Cells perform actions – Ex. Heart cells contract so
heart tissues contract, so the heart contracts,
so blood is pumped, so other cells get
nutrients and continue your bodily functions.
(and live)
At a basic level, all biology is based on what each
cell is doing at any given time.
Because of this, biologists began spending
significant resources studying cells.
Two General Categories of Cells
The study of cells led to the discovery of two
very different kinds of cells. These two
cell types create all life.
Eukaryotic cell
-
Cells with a nucleus and organelles
Every living organism EXCEPT bacteria
How do I remember?
-
Eu = True
Karyote = Nucleus
Two General Categories of Cells
B. Prokaryotic Cells
- Lack nucleus and organelles
- Single celled organisms
- Simple cells before other life formed. First life
forms were prokaryotic.
How do I remember?
- Pro = Before
- Sometimes we say pro = No
- Karyote = Nucleus
Prokaryotic Cells
1. Different kinds of bacteria are the only
known organisms who have a
prokaryotic structure.
2. If you are asked about prokaryotes, you
are being asked about bacteria.
3. BACTERIA ONLY!
Prokaryotic Cells
1. Prokaryotes are single celled.
•
They lack advance functioning because their
cells cannot specialize.
2. These are the simplest
form of cells and have
fewer structures than
eukaryotic cells.
3. Prokaryotic cells have
3 main parts.
Prokaryotic Cells
1.Outer Structures
• Pili (pl), Pilus (s) – Hairlike structures that
surround prokaryotic cells for movement.
• Flagella – Longer whip-like structure used for
movement.
There are typically many more
cilia on a cell than flagella.
Cilia usually line the entire outer
surface of a cell, while there
are usually only a few flagella
and they are located on one
end of the organism.
Prokaryotic Cells
2. Wall Structures
• Cell Wall – A tough layer made of protein that
protects and supports the cell
In modern bacteria, the cell wall is made of a protein
matrix called peptidoglycan (important).
When you take antibiotics, the
reason they work is that the
medicine breaks down
peptidoglycan, making the cell
explode.
• Cell Membrane – A
phospholipid bilayer that
controls the movement of
substances in and out of the
cell.
Polymer or Monomer?
Prokaryotic Cells
3. Interior Structures
• Cytoplasm – The gel-like substance that fills the
majority of the inside of cells. Cytoplasm is 70%90% water and is usually clear.
Break it down:
Cyto – Cell
Plasm – Substance
The cytoplasm looks like
nothing in drawings. It is
just a space filler to allow
other materials to “flow”
around the cell.
Remember: Empty-looking
space is the cytoplasm.
Prokaryotic Cells
3. Interior Structures
• Ribosomes - A collection of RNA and protein that
builds new proteins for the cell.
Ribosomes are usually
represented by small dots
floating in the cytoplasm.
They assemble amino
acids into proteins by
using the genetic code
from DNA. This is called
translation (We will spend
a lot of time on this later).
Prokaryotic Cells
3. Interior Structures
• Nucleoid – The region of a cell (usually the center)
that contains most or all of the genetic material in
prokaryotic cells.
Break it down:
Nucleus – Central and most
important part
Oid (suffix) - means similar or like
It is NOT a nucleus, but is similar
(think humanoid: like a human
in some ways, but not truly
human)
The nucleoid is really just a bunch
of wound up circular DNA. Do
not confuse bunched up DNA
with a nucleus.
Prokaryotic Cells
Important things to remember:
1. All prokaryotes are bacteria and all bacteria are
prokaryotes.
2. Prokaryotes do not
have a nucleus
3. Prokaryotes do not
have organelles
4. Prokaryotes DO have a
cell wall (peptidoglycan)
5. Prokaryotes are small.
(compared to
Eukaryotes)
Eukaryotic Cells
1. All other living organisms besides
bacteria are eukaryotic. Animals, plants,
fungi and protists (single celled water
critters) are all eukaryotic.
2. The number one distinguishing feature of
eukaryotes is the big ol’ nucleus.
3. NO BACTERIA!
Eukaryotic Cells
1. Eukaryotes are single celled and multi-cellular.
• Eukaryotic organisms can have very
complicated bodies because their cells can
specialize. (humans)
2. These are the most
advanced cells and
have many different
cell parts.
3. Eukaryotic cells also
have 3 main parts.
Eukaryotic Cells
Eukaryotes are incredibly diverse, so not all
cells feature the same parts, but we will
divide into these three sections
1. Cell Interior (2 parts)
a) Membrane Bound Organelles
b) Other Interior Components
2. Protection and Containment
3. Exterior Structures
Eukaryotic Interior - Organelles
1. Cell Interior: Membrane Bound Organelles
• Nucleolus – The center of the nucleus, made of
protein and RNA, creates ribosomes. –olus suffix
means “small”
• Nucleus – The most visible organelle of the cell.
Houses the cell’s DNA.
The nucleus and nucleolus each
have an extra phospholipid
bilayer (membrane) for
protection and separation from
the rest of the cell. The nuclear
membrane is sometimes called
the nuclear envelope.
All of the cell’s instructions (DNA)
are found here.
Eukaryotic Interior - Organelles
1. Cell Interior: Membrane Bound Organelles
• Mitochondrion – The cell’s “powerhouse.” Makes
Adenosine Triphosphate, or ATP; the molecule that is
used for all cell functions.
Mitochondria (plural) –
Mitochondrion (singular)
Mitochondria are usually represented
by an oval shape with back and
forth ridges inside. These ridges
play a role in cellular respiration,
the chemical process that makes
ATP.
Mitochondria are the most important
cell organelle after the nucleus for
eukaryotes.
Eukaryotic Interior - Organelles
1. Cell Interior: Membrane Bound Organelles
• Ribosomes - A collection of RNA and protein that builds new
proteins for the cell.
• Endoplasmic Reticulum (ER) – A membrane-like system of
tubes, proteins and sacs that makes new membranes, and
helps detoxify the cell.
The ER is always located next to the
nucleus and there are two types,
Rough ER and Smooth ER.
Rough ER has ribosomes located on it,
(the small dots) while Smooth ER
does not.
Other than the presence of the
ribosomes, the smooth ER will look
quite similar to the rough ER.
Eukaryotic Interior - Organelles
1. Cell Interior: Membrane Bound Organelles
• Golgi Apparatus (Golgi Body) – Stacks or folds of membrane
that “package” proteins to ship to other parts of the cell or to
leave the cell. The Golgi Apparatus typically finishes protein
structures created by the ribosome on the Endoplasmic
Reticulum.
The Golgi Apparatus is almost always
floating in the cytoplasm away from
the nucleus.
In our drawing, proteins
(macromolecules) are being
shipped from the smooth ER to the
Golgi Apparatus.
The Golgi Apparatus also creates
organelles called Lysosomes and
helps to form lipid structures
(membranes again) within the cell.
Eukaryotic Interior - Organelles
1. Cell Interior: Membrane Bound Organelles
• Lysosomes – A sac-like organelle that breaks down molecules
within a cell. Lysosomes frequently “digest” food, waste, and
worn out organelles.
The name: lysis – to separate
some – body; to separate a body
(molecule).
Lysosomes also move materials in and
out of the cell, destroy invading
bacteria and viruses, and
sometimes kill their own cell. This
gave them the nickname “suicide
sacks.”
Lysosomes contain hydrolase. What is
hydrolase?
Hydrolase is an enzyme that breaks
down molecules by adding water.
Eukaryotic Interior - Organelles
1. Cell Interior: Membrane Bound Organelles
• Vesicles/Vacuoles – Membrane bound sacks that function
as storage containers for materials inside the cell.
Lysosomes are a version of a vesicle.
Vesicles and Vacuoles have their
own phospholipid bilayer that
separates the contents from the
inner cell environment.
Vesicles and Vacuoles are
considered organelles because
they have the membrane.
Vesicles are for transport of
materials and Vacuoles are for
storage of materials.
– See drawing
Eukaryotic Interior - Components
1. Cell Interior: Other Cellular Components
• Cytoplasm – The same as in prokaryotes, the cytoplasm is the
gel-like substance that fills the majority of the inside of cells. All
organelles “float around” within the cytoplasm.
• Cytoskeleton – A network of protein
tubes and fibers that provide
structure to the inside of the cell and
hold the cell together.
Cyto – Cell, Skeleton – Skeleton (duh)
The Cytoskeleton is made of
microfilaments and microtubules.
The filaments (bone) are primarily
for structure and the microtubules
help move molecules around the cell
(vessels).
Eukaryotic Interior - Components
1. Cell Interior: Other Cellular Components
• Centrioles – Technically part of the cytoskeleton, the centrioles
are a bundle of microtubules that are used during cell division.
(they look like churros)
Centrioles attach to the chromosomes
(DNA) in the nucleus and help to pull the
cell apart.
They usually just sit there when the cell isn’t
dividing.
During division, small spindle fibers attach
to the chromosomes and centrioles.
Eukaryotic Interior – Components
Plant Specific
1. Cell Interior: Membrane Bound Organelles
• Chloroplasts – The organelle that carries out photosynthesis in
plants and protists. Chloroplasts give plants and protists their
green color.
Chloroplasts use sunlight, water and carbon
dioxide to produce glucose (carbohydrate).
Plastids – Any type of “plast” is a plastid. These
organelles are responsible for photosynthesis
in all organisms (even brown and red ones).
Chloro is the green kind of plastid.
•
Central Vacuole - Plants also have larger
vacuoles than other organisms for water
storage. In many cases, the central vacuole is
larger than the rest of the cell combined.
Vacuoles help maintain the plant’s shape (they
don’t have muscles). Plants begin to wilt when
their vacuoles empty out.
Eukaryotic Protection and Containment
2. Protection and Containment
• Cell Membrane – Semi-permeable phospholipid bilayer that
separates the cell from the outside environment. Also controls
what materials go into and out of the cell.
Without the cell membrane,
the cell would simply be
stuff floating in water.
The cell membrane also
contains protein groups,
cholesterol and
carbohydrate chains.
The proteins assist molecules
that could not otherwise
pass through the
membrane. (more on this
later)
The cellular envelope is present in ALL
cells and has an almost identical structure
across all organism types.
Eukaryotic Protection and Containment
2. Protection and Containment
• Cell Wall (Plants and Fungi ONLY) – Layer of rigid, tough
material that helps protect and support the cell. The cell wall is
typically thick.
In plants the cell wall is made
of cellulose (fiber)
In fungi the cell wall is made of
chitin (also found in
crustacean shells or insect
exoskeletons)
The presence of the cell wall is
what makes veggies
crunch. You are shattering
the cell walls with your
teeth.
Eukaryotic Exterior Structures
3. Exterior Structures – Found only in certain cells.
• Flagella – Longer whip-like structure used for movement.
Eukaryotic flagella function in roughly the same manner as
prokaryotic flagella.
Cilia (pl), Cilium (s) – Smaller projections used
for sense or locomotion.
Cilia are used by many types of cells
sometimes as sense organs (touch or
chemical), and sometimes to move (similar
to prokaryotic pili)
Labeled Prokaryote
Labeled Animal Cell
Labeled Plant Cell
Cellular Structure
andChapter
Functions
3
LOOKING AT CELLS
Making sense of life’s
most basic Unit