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Vacuoles, Vesicles, and Cytoskeleton Defined

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Andrew Jones

on 17 September 2012

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Transcript of Vacuoles, Vesicles, and Cytoskeleton Defined

Cytoskeleton The Cytoskelton is a network of protein filaments
that gives a eukaryotic cell its shape and support. Its main functions are:
It supports the cell and maintains shape.
It controls the positions and movements of organelles within the cell.
It is involved with bulk movements of the cytoplasm called cytoplasmic streaming.
It interacts with extracellular structures, helping to anchor the cell in place. Vacuole Occur in many eukaryotic cells, but particularly those of plants and fungi. Functions: 1. Storage: like all cells, plant cells produce a variety of toxic by-products and waste products. Plants store many of these in vacuoles. The storage of these toxins create a natural defense system sometimes deterring animals from eating them. 2. Structure: In many plant cells, enormous vacuoles take up more than 90 percent of the cell volume and grow as the cell grows. The presence of dissolved substances in the vacuole causes water to enter it from the cytoplasm, making the vacuole swell like a water-filled balloon. The resistance to this swelling, called TURGOR PRESSURE, causes the cell to stiffen from the increase in water pressure and also helps support the cell as a whole. 3. Reproduction: Some pigments in the petals and fruits of flowering plants are contained in vacuoles. These pigments are visual cues that help attract animals, which assist in pollination and seed dispersal. 4. Catabolism: The vacuoles in the seeds of some plants contain enzymes that hydrolyze stored seed proteins into monomers. These monomers in turn are used as the building blocks and sources of energy for the developing plant seedling. Contractile Vacuole Contractile Vacuoles are in many freshwater protists. Their function is to get rid of the excess water that rushes into the cell because of the imbalance in solute concentration between the interior of the cell and its freshwater environment. The contractile vacuole enlarges as water enters then abruptly contracts, forcing the water out of the cell through a special pore structure. Vacuoles work with the cell membrane
to move materials in and out of the cell. They also work with the lysosomes of a cell to digest cellular materials. Vesicle Vacuoles are basically vesicles filled
with mostly water. A vesicle is a small bubble in a cell. This bubble
is similar to a plasma membrane, consisting of a
lipid bi-layer. Vesicles interact closely with the endomembrane
system (nuclear envelope, endoplasmic reticulum, Golgi apparatus, and lysosomes) by transporting substances between the various organelles of the system. e.g. transport proteins from the rough endoplasmic reticulum to the Golgi apparatus. Under a microscope, vesicles seem to be static. However, these membranes and the materials they contain are in constant motion. Functions: 1. Transportation: Vesicles are involved in the
process of carrying waste to the cell wall and disposing
of it (exocytosis) as well as harboring in nutrients from
outside of the cell wall (endocytosis). 3. Enzyme Storage: Vesicles can hold and store enzymes used throughout the cell. e.g. enzymes that are used to make plant cell walls. 2. Metabolism: Vesicles can act as chemical reaction chambers. The membrane of vesicles harbor reactions from the cytosol in the cell allowing the reactions to take place. Microfilaments These are the thinnest
filaments of the cytoskeleton. Microfilaments are assembled from actin
monomers that attach at one end
and detach at the other. The shortening
(detachment)and lengthening (assembly) of
the microfilaments creates the property of
dynamic instability. They act as tracks for the movement
of myosin molecules that attach to
the filaments and "walk" along
them. The interactions of these two proteins
accounts for the contraction of muscles. Intermediate filaments Intermediate filaments are tough,
rope-like protein assemblages
8-12 nm in diameter. Intermediate filaments are more permanent
than the other two types of filaments and do
not show dynamic instability. There are two major structural
functions:

1. They anchor cell structures in
place.

2. They resist tension. Microtubules Microtubules are the largest diameter
components of the cytoskeletal system.
They are long, hollow, unbranched
cylinders about 25 nm in diameter
and up to several micrometers long. Microtubules have two roles:

1. They form a rigid internal skeleton
for some cells or cell regions.

2. They act as a framework along which
motor proteins can move structures
within the cell. Microtubules are assembled from
dimers of the protein tubulin.
Thirteen chains of tubulin dimers
surround the hollow microtubule. Microtubules show dynamic instability
with (+) and (-) ends and associated
proteins. Microtubules often form an
interior skeleton for projections
that come out of the plasma.
e.g. cilia and flagella
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