Download 4 A/P Biology Summer Packet Plant and Animal Cell Cytoskeleton

4
A/P Biology
Plant and Animal Cell Cytoskeleton Pages 113-138
Name: _____________________________ Date: _________ Period: _________
The cytoskeleton of a plant OR animal cell is composed of specific protein
structures that:
1.) help give the cell shape
2.) help give the cell elasticity
3.) help cell divide (or perform “fission” as in the case of bacteria)
4.) help organize internal structures/inclusions within cell
5.) help conduct signals from the outside of the cell to the inside of the cell
6.) help move materials (cell products) and organelles from one part of the cell to
another part (assist in fusion of organelles -i.e. production of lysosomes)
Eukaryotic and prokaryotic cells contain internal structures of protein filaments arranged
in a network that do everything from guiding Golgi vesicles, lysosomes, and peroxisomes
to their destinations, to chaperoning signal molecules from the outside of the cell to their
ultimate destination. Many of these protein filaments have contractile-like abilities
(meaning that they can shorten - like muscle fibers shorten to perform movement of an
arm or a leg in humans).You might think of these “muscle-like” proteins as cables that
can still be found in San Francisco that help move cable cars from one place to another.
The difference is that these cytoskeleton protein “cables” have many more uses than the
cables of San Francisco.
What are cytoskeleton proteins made up of? There are at least three types of
filaments that make up the cytoskeleton:
a.) microtubules
b.) actin filaments
c.) intermediate filaments
Microtubules: The microtubules are composed of protein
structures that are somewhat spherical (or globular). Two
globular proteins (called tubulins) repeat themselves in a
circular fashion to form a hollow tube (see picture to the
right). When cells divide, these microtubules attach to
specific parts of the DNA to help distribute the genetic
information evenly to the daughter cells. The assembly of
microtubules seems to originate in areas called
microtubule organizing centers (MTOCs). In the
Eukaryotic cells, the major MTOCs are near the nucleus
in a zone called the centrosome. This region often
contains the organelle- the centrioles (used to help the cell
replicate). In Prokaryotic cells (bacteria), there are no true
centrioles, just the centrosome area. As mentioned before,
plant cells do not have centrioles. The tubulins dimers located on either end of the
growing microtubule are less stable than those found in the center of the tubule (more
bonds). This fact seems to make sense in that these microtubules can be rapidly disassembled as chromosomes are pulled away from other chromosomes during anaphase
(mitosis or meiosis).
Page 2 (Cont. A/P Biology Summer packet #4)
Actin filaments: These strands of actin
filaments are also called microfilaments.
These filaments are much thinner (finer) than
the microtubules. Actin filaments play a
different role in the cytoskeleton compared to
the microtubule. These small filaments are
often anchored to the cell surface to provide
the force for movement or shape changes. It
is of no surprise that actin filaments are made
up of globular molecules (see picture to the
right). Globular actin protein is found in
abundance in muscle cells and interacts with
another globular protein (myosin) to help create movement (allow muscle cells to
contract). However, actin filaments are constantly being built up and torn down to
interact with:
a.) other actin filaments in a cross-linked fashion to provide shape changes and
mechanical support for the cell and internal organelles.
b.) other proteins to provide muscle-like contractile forces.
The proteins that associate with actin have been compared to the pulling forces of
winches that pull cables. This is significant because recent evidence shows that these
winches have special signal structures on each cable that links them to a specific structure
or location within the cell. This is like a telephone wire that connects the outside of the
cell (at a specific receptor) to the target of that receptor somewhere inside the cell. To
sum this up microfilaments have three basic “jobs”:
1.) allows cells to change shape (as in amoebas- to move with a “false-foot”)
2.) interacts with other protein molecules to initiate contractile forces (movement of
cell “signal molecules” from outside of cell to inside of cell)
3.) maintain integrity of the cell structure and maintain integrity of cell organelles
Intermediate filaments: The intermediate filaments are fibrous proteins (such as
keratin- keratin is found in wool, fingernails, hair, and the outer layer of human skin).
These fibers provide strength and stability within the cell AND provide strength to the
adhesive force of skin “sticking” to the cells below them. The intermediate fibers along
with an amorphous
protein gel (below the
fibers), provides
“cement” that often
holds sheets of cells
together. Think of the
stomach not just
hanging around in the
gut somewhere, but
being
Page 3 (Cont. A/P Biology Summer Packer #4)
fixed into position between the pancreas and the diaphragm. “There are several different
types of intermediate filaments, such as keratin in epithelial cells, desmin in muscle cells,
neurofilaments in axons and vimentin in fibroblast cells that are composed of different
protein subunits.” (Taken from: academic.brooklyn.cuny.edu/.../ page/intermediatefil.html)
Below I have inserted a cartoon-type picture of a cell whose cytoskeleton has been
labeled. The diagram below merely shows an overview of the cells, not specific details
of how the cell looks in any true definition.
The picture to the right shows a
little more detail. The different
filaments are arranged in a meshlike framework. We can show
even more detail by looking at
the attachment of a mitochondria
to an actin filament chain and see
how the cell moves mitochondria
from place to place - it HAS to
expend energy (ATP) to do this.
(see picture to right).
Page 4 (Cont. A/P Biology Summer Packet #4)
Understand- I am NOT asking you to memorize all the different proteins involved, the
take-home message is that the cytoskeleton is responsible for the integrity of the cell.
Shape, contortion, integrity, signaling, movement of cell products and cell organelles,
and division are all associated with the cytoskeletal filaments.
Page 5 (Cont. A/P Biology Summer Packet #4)
If we were to stain the different cytoskeletal components with different colors for
microtubules, microfilaments, and intermediate filaments we would see this:
During cell replication, the cytoskeleton works in a fine ballet to attach to DNA fibers
and centrioles while other components of the cytoskeleton hold everything else in place
(see below). This is Metaphase in the cell division cycle.
Intermediate filaments
(green)
Blue filaments (DNA)
Microfilaments (red)
It was originally thought that the Prokaryotic cells (Eubacteria and Archaea
organisms) did not have this actin/tubulins cytoskeleton, but evidence has shown that
Page 6 (Cont. A/P Biology Packet #4)
they have similar protein structures that have repeating units that are near identical to the
Eukaryotic cytoskeleton. This means that we have another piece of evidence that points
toward the evolutionary sequence of all organisms being derived from a single celled
organism.
The idea that the cytoskeleton proteins play an important role in cell function is a
relatively recent finding. It essentially says that if a receptor on the outside of the cell
(see page 7 packet #2- i.e. peripheral proteins may act as receptors- we will look at cell
surface receptors in more detail in packet #5). If a cell surface receptor attaches to an
insulin molecule, it can transmit the presence of that insulin molecule to the DNA inside
the cell by a messenger that attaches to the cable directly associated with the surface
receptor- to the DNA within the nucleus. Such specific communication from one part of
the cell to another could not have been detected 30 years ago because of the lack of
technology (that is to say the scientists back then would have no way of detecting such a
signal). With advances in technology, we are able to detect more and more processes
within the cell. The key to scientists of today understanding the intricacies of the cell’s
function lies in the advances in technology to be able to detect and measure changes
within the cell.
For instance, in a recent article in Scientific American (May, 2011. Pg. 55-59),
The Hidden Organ in Our Eyes., examines the fact that there are other light receptors in
the eye that have nothing to do with perception of images. Rather these receptors work
together with rods and cones to help control circadian rhythms, iris dilation, and blinking
in humans (mimics other functional light receptors in mice, octopus, and tadpoles). Sosignals do not have to be chemical, or even light, but can be temperature, pressure, or
even electrostatic. The take-home message here is NOT to allow yourselves to feel that
all signals are chemical in nature…rather there are other signals the cell responds to that
are OUTSIDE of positive and negative charges that change the configuration of protein
cell surface receptors. Light is one of the most exciting new “triggers” that is being
aggressively investigated.
Extra-cellular matrix (ECM) and cell movement components: Prokaryotic cells
(bacteria) have several structures that are related- chemically to cytoskeletal components
of plant and animal cells. Microtubules are found in cilia and flagella and can confer
motility to bacterial cells, various Protist cells, plant cells and animal cells. The flagella
and cilia are actual projections of the cell membrane “filled” with these specialized
microtubules that can drive cells from place to place in a water media. This contractile
function/movement costs energy (ATP) and its intensity, frequency, and direction are
controlled by complex signals that originate either externally or internally. Moreover,
many cells form external complex matrices that are composed of glycoproteins, collagen,
and proteoglycans that allow them to adhere to one another or “other” cells. Many of
these connective components are links to the interior of cells by binding to fibronectin (a
type of glycoprotein) that binds to integrins (a transmembrane protein) that helps the cell
to connect the external signals to the internal cytoskeleton! You are directed to look at
Table 6.1 (pg.113) of your text to “see” the differences in structural components
between bacterial, animal, and plant cells.
Page 7 (Cont. #4 Handout A/P Biology)
Answer the first 15 questions here and on your scan-tron.
_____ 1.) All of the following are functions of the cytoskeleton EXCEPT:
a.) gives cell shape
b.) gives cell elasticity
c.) helps plant cells in absorbing sunlight
d.) helps cells divide
e.) helps move material from one place to another
_____ 2.) Which cytoskeleton component would be used to change the shape of a cell?
a.) microtubules b.) microfilaments c.) intermediate filaments d.) macrofilaments
_____ 3.) Which cytoskeleton component would be used to help the cell move it’s DNA?
a.) microtubules b.) microfilaments c.) intermediate filaments d.) macrofilaments
_____ 4.) Which cytoskeleton component would be used to help cells stick together?
a.) microtubules b.) microfilaments c.) intermediate filaments d.) macrofilaments
_____ 5.) What are MTOCs?
a.) microtubule operations controls
b.) microtubule organization centers
c.) myofibril orcien centers
d.) mechanical organization centers
e.) none of the above are correct
_____ 6.) How might signals from the outside of the cell transported to the interior of the
cell?
a.) signals may be transported along cytoskeletal components
b.) signals can causes an electrical stimulation to the interior of the cell
c.) signals from outside of the cell cannot send messages through the cell membrane
d.) only signal molecules that pass through the cell membrane are able to stimulate
the cell
e.) all of the above are correct
_____ 7.) All of the following structures have cytoskeletal components EXCEPT
(Internet):
a.) eukaryotic cells b.) prokaryotic cells c.) viruses d.) archaebacteria
_____ 8.) The movement of materials from one part of the cell to another part of the cell
utilizing the cytoskeleton:
a.) only occurs in eukaryotic cells
b.) requires energy (ATP)
c.) only occurs in prokaryotic cells
d.) requires cohesion of water
e.) requires a hydrophobic environment
Page 8 (Cont. #4 Handout A/P Biology)
_____ 9.) The cytoskeleton helps the animal and plant cell to maintain:
a.) the cell’s integrity
b.) the osmotic balance
c.) the ionic balance
d.) the energy balance
e.) all of the above are correct
_____ 10.) The ends of the microtubule globular protein subunits are less stable at the
ends of the tubule compared to those that are near the center. Microtubules are
responsible for the movement of chromosomes during mitosis and meiosis. During
Anaphase (look this up in book or Internet) the microtubules pull the chromatids apart.
How do microtubules accomplish this?
a.) the microtubules fold up rapidly to make the tubules shorter
b.) the microtubules are rapidly broken down to become shorter
c.) the microtubules attach to myosin filaments to help them pull chromatids apart
d.) the microtubules dissolve into the chromatids
_____ 11.) What evidence of the cell and cytoskeletons in the Prokaryotic cell and the
Eukaryotic cell intimates that these organisms are evolutionarily related?
a.) the presence of similar cell membrane
b.) the presence of cell surface receptors
c.) the presence of actin/tubulins in the cytoskeleton
d.) the presence of “similar” ribosomes
e.) all of the above are reasonable evidences that these cells are related
12.) How are skin cells of a human normally attached to the rest of the cells? (i.e.
striatum germinativum or basale) of the epidermis (stratified squamous) to the underlying
papillary layer of the dermis?) (Internet)
a.) by using sugar molecules as cement
b.) by using connective tissue as cement
c.) by using lipid molecules as cement
d.) by using DNA molecules as cement
13.) A mutated mouse that has eyes that do NOT have functioning rods and cones, still
behave like a normal mouse in terms of being quiescent during the day and active at
night. Since these animals cannot “see images”/perceive light, how do they manage to
maintain proper circadian rhythm? (Scientific American)
a.) they can look around them and see what other mice are doing
b.) they can hear the different movements around them and determine day and night
c.) they can feel the vibration of the earth around them that tells them if it is day or night
d.) they have other receptors in the eyes that detect light but do not allow them to see
images
Page 9 (Cont. Handout #4 AP Biology)
14.) If you take the mice in the above example and remove their eyes, predict how would
their circadian rhythms respond? (Scientific American)
a.) there would be no change in their circadian rhythms
b.) their circadian rhythms would be disrupted
c.) they would have to rely on other clues to maintain their circadian rhythms
d.) the animals would die without visual cues for circadian rhythm
15.) The secondary photoreceptor in the eye that help control circadian rhythm is called
melanopsins. If these cells (and these cells only-cones and rods are active) are disabled,
speculate what would happen to the circadian rhythm? (Scientific American)
a.) there would be no change in their circadian rhythms
b.) their circadian rhythms would be disrupted
c.) they would have to rely on other clues to maintain their circadian rhythms
d.) the animals would die without visual cues for circadian rhythm
Answer the following questions on this handout only!
16.) Animal cells and plant cells have many of the same organelles. Plant and animals
cells also share similar cytoskeletal components. If the plant cell has a cell wall, why
does it need microfilaments (often used in shape changes)?
17.) If you look at the way a single celled amoeba moves you see the cytoplasm flowing
into a false-foot (pseudopodia). The physical changes in shape of the cell membrane
MUST be the result of the workings of which type(s) of protein(s) in the cytoskeleton?
(Explain why you included one or more of the different proteins of the cytoskeleton.)
18.) In comparing the structure of the microtubule to the microfilaments, we notice that
the microtubule is larger. Speculate why the microtubule would be larger and why
microtubules would be manufactured in one specific region in the cell rather than all over
the cell.
Page 10 (Cont. Handout #4 AP Biology)
19.) Scientist knew 30 years ago that cells reacted rapidly to cell signal molecules.
Scientists came up with explanations for this rapid response to cell signals by explaining
that signal molecules within the cell (such as cyclic AMP) transferred/activated the cell.
However, scientist ignored (1) the need to explain how the cyclic AMP molecule knew
where to go and (2) explain away the time it should have taken for cyclic AMP to diffuse
from the source of the receptor to the place where it was to “tell” the cell what to do.
How does the discovery of the cytoskeleton help explain the rapid response to external
cell signal. YOU MUST answer this question explaining how the cyclic AMP molecule
knew where to go AND why simple diffusion could not explain the rapid response to a
cell stimulus (hint- look at results of egg experiment, Handout #1…look at the depth of
the stain into the egg whites.).
20.) White blood cells are responsible for defending the body from foreign bacteria and
virus particles. Most white blood cells can move through the blood vessels and between
cells to “survey” the body for foreign invaders. Which part of the cytoskeleton is most
active to help white blood cells move between other cells? When a white blood cell
attacks bacteria, it can surround the bacteria and enclose it to be destroyed. Again, which
cytoskeleton molecules are at work here?
21.) Glucose Uptake Over Time in Guinea Pig Red Blood Cells
Concentration of
Radioactive Glucose
Into RBCs in mM
15 day old guinea
pig
1-monh old guinea
pig
Incubation time (min.)
Draw a conclusion about the uptake of glucose in the red blood cell of the 15 day old
guinea pig versus the 3-month old guinea pig RBCs.
Date: __________________
Lesson Plan for Handout #4
AP Biology
Objective: TLWD ability to determine how the three different types of cytoskeletal
components help the cell maintain its integrity, transfer signal, and transfer molecules
within the cells when given handout #4.
Content: Plant, animal, and Prokaryotic cytoskeletal components.
Method: Power point, white board, discussion
Homework: Handout #4
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