IV. THE CYTOPLASM
A. Components
- cyto = Acell@, plasm = Ashaped@ or Amolded@.
- CYTOPLASM - cellular material inside the plasma
membrane & outside the nucleus.
- area where all cellular function takes place.
- consists of:
CYTOSOL - viscous (thick, lots of friction,
jelly-like) semi-transparent fluid that acts as a suspension for other elements.
*mostly HOH, dissolved proteins, sugar, other
solutes (just like Jelly!)
ORGANELLES - see below
INCLUSIONS - @things included@-stored nutrients,
lipids, pigments, crystals-->non-functioning Aother
stuff@.
B. Focus on Organelles (Alittle organs@)
Metabolic Machinery of the cell.
*Function of most cells is to make & deliver
proteins; it is the organelles that do this.
- "Membrane bound" versus "non-membrane bound" organelles:
Membranous System: Membrane-bound structures
within the cytoplasm. Their membrane is similar to lipid
bilayer of cell. In fact, they are continuous. Continuous
with the membranes around the nucleus, too!
Included: the nuclear envelope, the endoplasmic reticulum, the
Golgi apparatus, lysosomes, vacuoles, vesicles, and others. The
system is defined more accurately as the set of membranes that
form a single functional and developmental unit, either being
connected together directly, or exchanging material through
vesicle transport.
Non-membranous System: Protein structures not
surrounded by lipid bilayer.
**some textbooks divide the organelles in this manner. We will not. Instead, we are going to follow
them as they perform their duties: produce proteins, and (sometimes) prepare them for transport out of
the cell.
- Summary of Organelles:
1. Ribosome.
-small, stain dark, tiny protein structures.
* Site of PROTEIN SYNTHESIS: @Building of
proteins@.
* Produce proteins by attaching AAs to each other via
dehydration synthesis.
** They are following the instructions found on the DNA molecule within the nucleus.
** We will discuss this in more detail in the GENETICS MODULE.
** The process is called TRANSLATION.
- 2 types of ribosomes:
FREE FLOATING - make proteins that are to be used within the cell.
MEMBRANE-BOUND RIBOSOMES - synthesize proteins destined for export out of cell or for use in cell
membrane. These are attached to another organelle called the ENDOPLASMIC RETICULUM (see
later).
2. Rough Endoplasmic Reticulum (ER) - @w/in the plasma network that
has roughness to membrane"
- as opposed to Smooth Endoplasmic Reticulum - see later,
quite different function.
-studded w/ ribosomes producing proteins, and putting them in
the inner chambers
* =s a series of CISTERNAE = interconnected tubes that
move proteins through cell.
- RER acts as transport system - @highway@ w/in cell.
* Tubes for secreting proteins -- lots in secreting cells,
cells that produce antibodies, liver cells (secrete blood
proteins).
* puts proteins in a transport vesicle, and sends the
proteins to another organelle: the GOLGI APPARATUS, where they will continue their journey.
- Another function: modifies the proteins (example: adds carbohydrates to proteins, forming
glycoproteins)
3. Golgi Apparatus
- @Packaging warehouse@ of cell.
- modifies, packages, and concentrates proteins & lipids made by rough
ER.
* attach carbohydrates to proteins to form GLYCOPROTEINS.
* proteins are Atagged@ for delivery to a specific Aaddress@,
assorted and accumulated in vesicles = SECRETORY
VESICLES OR GRANULES.
- Also produces LYSOSOMES
4. Mitochondria
- provides majority of the ATP for the cell's use.
* = "Powerhouse@ of the cell. The other organelles get their ATP from the mitochondria.
* Aerobic Respiration: Cell takes in oxygen and glucose, makes a lot of ATP. Majority of this
process happens here.
AEROBIC RESPIRATION - @breathing with oxygen @
- break down glucose by adding oxygen, which produces CO2 (waste), ATP and water.
Glucose + O2
ATP + CO2 + H2O
- Double-membrane, sausage-shaped. Inner membrane = where aerobic respiration occurs.
*CRISTAE = folds of the inner membrane.
* encrusted with enzymes that perform aerobic respiration.
- Cells w/ high energy requirements are characterized by a lot of mitochondria (cells active in
metabolism, liver cells, kidney cells, etc.).
Mitochondria are red due to oxidation process within them; therefore, these tissues are
red!
** INTERESTING SIDE NOTE: Mitochondria contain own genetic material
(DNA & RNA).
They can produce their own enzymes. It is believed that they were an
independent life form in the past, a parasite on cells. Over time, they
took on a symbiotic relationship.
5. Lysosomes
-does digestion for the cell.
- Membrane-bound vesicles that pinch off from the Golgi Apparatus.
Filled with enzymes. Take in materials through phagocytosis.
- filled w/ ACID HYDROLASE (enzyme that hydrolyses). Membrane
surrounding the vesicle is specialized to withstand the hydrolase - or else
cell would digest itself.
- phagocytize and digests:
1. Particles ingested by the cell by endocytosis, especially dangerous stuff (viruses, bacteria, etc.).
2. Worn-out, old non-functional organelles.
3. Break down glycogen.
* Textbooks often refer to them as “suicide sacs”, because if the
hydrolases ever got out, the cell would be destroyed.
* if cell gets low on O2 or too much vitamin A, lysosome
membrane breaks down, releasing hydrolase into cell
- AUTOIMMUNE DISEASE known as RHEUMATOID ARTHRITIS: improper lysosome activity
is part of the destruction we see in joints.
*if too little is produced, leading to an accumulation of wastes.
- TAY-SACHS DISEASE = genetic, heritable, rare but seen in Jewish populations from central
Europe. Lack enzyme to digest glycolipids from nerve cells.
6. Peroxisomes
- Similar to lysosomes, but smaller, not from Golgi apparatus.
- contain POWERFUL oxidase enzymes, which use oxygen to detoxify many
lipid-based molecules, alcohol, and others.
- Also, detox FREE RADICALS--very reactive chemicals w/ unpaired e-s.
- Lots in kidney & liver cells.
7. Smooth ER (SER)
- less common, but liver, testes, intestine, & kidney cells have a lot.
- Continuation of Rough ER.
- No ribosomes = no protein synthesis.
- Different functions in different cells:
Liver - cholesterol synthesis
Testes - testosterone production
Intestine - absorb & synthesis of fat
Liver & kidney - detox of drugs (chemicals, alcohol,
pesticides, etc.).
Notice that they are all related to lipid-based
or soluble molecules!
8. Cytoskeleton - the cell=s internal skeleton (frame).
- Inner scaffolding attached to anchor proteins in PM.
- made of long, fibrous proteins running through cytosol
.
- Functions: (among others)
* Gives the cell its shape.
* Anchors the organelles
* Forms some other structures, such as cilia,
flagella, and centrioles
* Fibrous proteins arranged thin strands (filaments) or thick tube (microtubules)
9. Centrioles
- Many cytoskeleton tubes attach here, at center
near nucleus.
-contain paired structures called CENTRIOLES,
which is a collection of microtubules of the
cytoskeleton.
* Important role in cellular division and
MITOSIS, among other things.
We'll see this in more detail during the
Mitosis module.
10. Cilia & Flagellum
- See earlier section entitled "3. Special Features of the PM - a. Extensions" for a description of
these 2 structures.
If cilia, there are many, probably covering this whole surface.
If flagellum, then just one, and much longer.
But....all work the same (not true of microvillus).
They are formed in a similar manner to centrioles; in fact, a centriole makes up the base. Microtubules
then project out into the plasma membrane. But now, they can cause movement.
Summary Table
Classification & Name
Function
Special Features
Non-Membranous Organelles
Ribosomes
Protein structures that
perform translation (protein
synthesis in the cytoplasm).
Cytoskeleton
Series of proteins tubules
that give cell shape, and
hold organelles in place.
Attach to anchor proteins embedded in the
plasma membrane.
Also help form cilia & flagellum.
Centrioles
Protein tubules that have
special role in mitosis.
Basal body of cilia and flagellum is a modified
centriole.
Produce proteins for
export, and modify them
(this modification can be
several things, all of which
get them ready to function!)
RERs have ribosomes attached, which perform
synthesis of proteins for (mostly) transport out of
cell. RER places them in its cisternae (inner
branching chambers).
Golgi
Package proteins for
export, and further modify
proteins.
Places proteins in Secretory Vesicles, for ex[port
out of cell.
Mitochondria
Produce ATP
Contain inner membrane with shelf-like
structures called cristae. Studded with
enzymes that perform aerobic respiration.
Smooth Endoplasmic
Reticulum
Break down toxins, produce
lipid-based molecules
Continuous with RER; simply has no ribosomes
attached (see below).
Membrane-bound Organelles
Rough Endoplasmic
Reticulum
(RER)
(SER)
Liver, testes, small intestines: Roles vary.
Lysosomes
Digestive vesicles
Contain hydrolytic enzymes. Fuses with
Phagosome.
Peroxisome
Digestive vesicles
Contain oxidative enzymes.
V. NUCLEUS
-Control center of the cell.
- AKernel@ or APit@.
- most cells have 1 nucleus; some have many (MULTINUCLEATE; skeletal muscle cells).
*some are ANUCLEATE = no nucleus.
** Red Blood Cells; cells that don=t do any metabolism.
- Largest organelle in the cell: some people consider it another organelle.
-contain 3 structures:
A. Nuclear Envelope
- 2 nuclear membranes, forming an envelope.
* Double membrane = 2 phospholipid bilayers.
Between them is a fluid-filled space called the
PERINUCLEAR CISTERNAE (Aaround the
nucleus space@).
*outer membrane of the envelope is continuous
w/ the rough ER; it also has ribosomes attached.
- Encloses the NUCLEOPLASM – similar to cytoplasm, supports 2
other organelles (see below).
- also is selectively permeable -------> has NUCLEAR PORES.
IMAGE NEED: cell w/ envelope
(eric sent one)
B. Chromatin
-@bumpy threads@
-composed of DNA + HISTONES = proteins
clumped together in bodies called
NUCLEOSOMES (Anuclear bodies@).
DNA is a very long molecule that is in a shape
called a "double helix".
Histones are proteins that are very "sticky" to
DNA.
DNA is "wrapped" around the histones.
* The genetic information is on the DNA
molecule
* The ribosomes will use this info to make proteins
* Histones help regulate this process (turn it "on" and "off")
DNA + Histones = Chromatin
WE WILL LOOK AT THIS MORE CLOSELY
DURING THE GENETICS AND MITOSIS
MODULES
C. Nucleoli (Alittle nuclei@)
- Large dark structures within the nucleus.
- Produces ribosomes.
*large and obvious in growing cells that are
making large amounts of proteins.