Download Plant/Animal Cell Info

Plant Cell Illustration
Animal Cell Illustration
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Golgi Apparatus: A series (stack) of flattened, membrane-bound sacs (saccules)
involved in the storage, modification and secretion of proteins (glycoproteins) and
lipids destined to leave the cell (extracellular) and for use within the cell (intracellular).
The Golgi apparatus is abundant in secretory cells, such as cells of the pancreas.
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Golgi Vesicle: A membrane-bound body that forms by "budding" from the Golgi
apparatus. It contains proteins (glycoproteins), such as digestive enzymes, and migrates
to the cell (plasma) membrane. Golgi vesicles fuse with the cell membrane and
discharge their contents into the exterior of the cell through a process called exocytosis.
Some Golgi vesicles become lysosomes which are involved in intracellular digestion.
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Lysosome: A membrane-bound organelle containing hydrolytic (digestive) enzymes.
Lysosomes originate as membrane-bound vesicles (called Golgi vesicles) that bud from
the Golgi apparatus. They are primarily involved with intracellular digestion.
Lysosomes fuse with vesicles (small vacuoles) formed by endocytosis. The contents of
these vesicles are digested by lysosomal enzymes. Autodigestion by lysosomes also
occurs during embryonic development. The fingers of a human embryo are webbed
initially, but are separated from each other by lysosomal enzymes. Cells in the tail of a
tadpole are digested by lysosomal enzymes during the gradual transition into a frog.
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Mitochondrion: Membrane-bound organelle and the site of aerobic respiration and
ATP production. Energy from the step-by-step oxidation of glucose (called the Krebs
or citric acid cycle) is used to produce molecules of adenosine triphosphate (ATP). The
Krebs cycle starts when a 2-carbon acetyl group combines with a 4-carbon group to
form a 6-carbon citrate. Including glycolysis (which occurs outside the mitochondria), a
total of 38 ATP molecules are generated from one molecule of glucose.
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In eukaryotic cells, including the cells of your body, ATP is produced within special
membrane-bound organelles called mitochondria. During this process, electrons are
shuttled through an iron-containing cytochrome enzyme system along membranes of
the cristae which result in the phosphorylation of ADP (adenosine diphosphate) to form
ATP (adenosine triphosphate). ATP is the vital energy molecule of all living systems
which is absolutely necessary for key biochemical reactions within the cells. The actual
synthesis of ATP from the coupling of ADP (adenosine diphosphate) with phosphate
(PO4)
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Chloroplast: Membrane-bound organelle and the site of photosynthesis and ATP
production in autotrophic plant cells. Like mitochondria, chloroplasts contain their own
circular DNA molecules. In fact, chloroplast DNA, including the protein-coding RBCL
gene, is often used at the family level to show the relationships between genera and
species within plant families. Intron regions from chloroplast DNA are also used to
construct family trees. Introns are sections of messenger RNA that are removed prior to
translation at the ribosome. Comparative DNA between different genera and species of
a plant family can be shown with computer generated evoltionary trees called
cladograms.
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Endoplasmic Reticulum: A complex system of membrane-bound channels extending
throughout the cytoplasm of cells. Like the emergency room of a hospital, the
endoplasmic reticulum is often abbreviated as ER.
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Smooth Endoplasmic Reticulum: Does not contain attached ribosomes.
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Rough Endoplasmic Reticulum: Studded (dotted) with attached ribosomes on the side
of the membrane that faces the cytoplasm.
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Ribosome: Organelle site of protein synthesis. The ribosome is composed of large and
small subunits separated by a central groove. A strand of messenger RNA (m-RNA)
fits into the groove and the ribosome moves along the m-RNA in a 5' to 3' direction.
Molecules of cloverleaf-shaped transfer-RNA (t-RNA), each with a unique amino acid,
temporarily attach to the m-RNA at the ribosome in a process called translation.
Transfer-RNA anticodons hook up with m-RNA codons and the amino acids bond
together by dehydration synthesis. As the ribosome moves toward the 3' end of the mRNA strand, the amino acid chain (polypeptide) grows longer and longer. Finally the
completed polypeptide leaves the ribosome site and moves away to become a protein
utilized within the cell or secreted from the cell. The simplified animated gif images
below illustrate this remarkable process. A series of several ribosomes moving along
the same m-RNA strand is called a polyribosome. Ribosomes are composed of
ribosomal RNA and they are not membrane-bound. They occur in prokaryotic as well
as eukaryotic cells. In eukaryotic cells, ribosomal RNA is synthesized in the nucleolus.
The large and small subunits of ribosomes are synthesized by specific genes. One gene
in the nucleolus codes for the smaller subunit of the ribosome. The gene is called SSU
rDNA or small subunit ribosomal DNA. Base sequences from this gene are sometimes
used to compare taxa at the species level. The results from comparative DNA studies
using mitochondrial and chloroplast DNA are illustrated in computer generated
evoltionary trees called cladograms.
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Nucleolus: Dark-staining body within the nucleus where ribosomal RNA is
synthesized. Plant nuclei in onion root tip cells may have several nucleoli.
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Nucleus: Membrane-bound organelle containing chromatin, a term applied to all the
chromosomes collectively when they are in a tenuous (threadlike) stage. During the
prophase of mitosis, the chromosomes become shorter and thicker, and appear as
distinct doubled bodies called "chromosome doublets."
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Cell (Plasma) Membrane: The living membrane that surrounds the cytoplasm of all
cells. It is composed of a phospholipid bilayer with embedded glycoproteins. In the
"sandwich model" the two phospholipid layers are sandwiched between two layers of
protein. The membranes of organelles are also composed of a phospholipid bilayer,
including vacuoles, nuclei, mitochondria and chloroplasts. [Riubosomes are not
membrane-bound.] Embedded glycoproteins in plasma membranes include membrane
transport "carrier molecules" and cell recognition antigens. The plasma membrane is
permeable to water molecules by osmosis, but not to other molecules and ions by
simple diffusion. Ions pass through the plasma membrane via carrier molecules by
active transport and facilitated diffusion. Active transport requires ATP.
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Cell Wall: A cellulose layer that surrounds the plasma membrane of plant cells.
Because it is very porous, the cell wall is permeable to molecules and ions that cannot
pass through the plasma membrane by simple diffusion. During plasmolysis, the cell
membrane loses water and its contents shrink up into a ball, while the outer cell wall
remains intact. Shrubs and trees have a thickened secondary cell wall containing lignin,
a brown phenolic polymer that imparts great strength and hardness to wood. Ironwoods
such as lignum vitae sink in water because of the density of their heavy, thick-walled,
lignified cells.
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Vacuole: A membrane-bound, fluid-filled sac inside plant and animal cells. Contractile
vacuoles of protists, such as the Paramecium, are specialized organelles for expelling
excess water. Food vacuoles of the Amoeba digest smaller cells captured by
phagocytosis. Plant cells have large central vacuoles that occupy much of the cell
volume.
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Large Central Vacuole: A membrane-bound, fluid-filled sac that occupies much of
the volume of a plant cell. For this reason, the chloroplasts, nucleus and other
organelles are displaced to the periphery of the cytoplasm (around the central vacuole).
In addition to water, this large vacuole stores salts, water soluble pigments
(anthocyanins), and potentially toxic molecules in the form of crystals.
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Centrioles Nonmembrane-bound organelles that occur in pairs just outside the
nucleus of animal cells. Each centriole is composed of a cylinder or ring of 9 sets of
microtubule triplets with none in the middle (9 + 0 pattern). During cell division a pair
of centrioles moves to each end of the cell, forming the poles of the mitotic spindle.
Centrioles also give rise to basal bodies that control the origin of cilia and flagella in
motile cells of protists. In cross section, flagella and cilia have 9 sets of microtubule
doublets surrounding a pair of single microtubules in the center (9 + 2 pattern). This
characteristic pattern also occurs in motile cells of higher organisms, such as human
sperm.
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Cytoplasm: All the contents of a cell within the plasma membrane. The nucleus and its
contents (nucleoplasm) are generally excluded from the cytoplasm. The semifluid
medium between the nucleus and the plasma membrane is called cytosol.
Hypertonic and Hypotonic: When comparing two solutions, such as the inside of a red blood
cell (RBC) with the solution they are placed in, the solution with the greater salt concentration
is hypertonic, while the solution with the lower salt concentration is hypotonic. Compared
with the RBCs, a 10% NaCl solution is hypertonic while a 0.1 % NaCl is hypotonic. Since the
latter solution is almost pure water, the blood cells are actually hypertonic by comparison.
Osmosis: Movement of water molecules from a region of high concentration to a region of
lower concentration through a differentially permeable cell membrane. In biology, this
definition should include water molecules and cell membrane.
Diffusion: Movement of molecules or ions (charged atoms) from a region of high
concentration to a region of lower concentration. This definition does not include a cell
membrane and refers to molecules of any substance, not specifically water. Examples of
diffusion include perfume molecules in the air, ether molecules in a classroom, sugar
molecules in a cup of coffee, methylene blue molecules in a bowl of clear gelatin, etc.
Active Transport: Movement of molecules and ions through a cell membrane against a
diffusion gradient (i.e. from a low to a higher concentration). This movement involves carrier
proteins (channels) in the cell membrane and requires energy in the form of ATP (adenosine
triphosphate). Active transport occurs during a nerve impulse or action potential (wave of
depolarization) when a nerve cell membrane suddenly becomes permeable to sodium ions.
The inflow of sodium ions moves quickly along the nerve cell axon, activating an adjacent
nerve cell or muscle. As sodium ions rapidly move across the membrane to the inside of the
axon, the polarity of the membrane changes. This reversal in polarity causes the sodium
channels to close and the potassium channels to open. Now potassium ions move from inside
the axon to the outside of the axon in a wave of repolarization.
During a lethal injection, a fatal dosage of potassium chloride is administered intravenously.
The large influx of potassium ions interrupts the wave of depolarization (action potential) to
the heart muscle resulting in cardiac arrest. A paralyzing agent, such as pancuronium bromide
or tubocurarine chloride, plus a lethal dosage of a general anesthetic, such as sodium
thiopental (sodium pentothal) are usually given before the potassium chloride is administered.
Tubocurarine is the active ingredient of curare, an extract from the bark and stems of the
South American vine (Chondodendron tomentosum). Amazonian Indians use the gummy
extract to coat the poison darts of their blowguns. The alkaloid D-tubocurarine blocks
acetylcholine receptor sites at neuromuscular junctions, causing relaxation and paralysis of
muscles, including respiratory organs and the heart.
Diagram Of Osmosis Through A Cell Membrane
Osmosis: Movement of water molecules (blue circles) through a cell membrane (red) from a
region of high concentration (inside cell) to a region of lower concentration (outside cell).
Inside the cell the solution is hypotonic with a low solute (salt) concentration. Outside the
membrane the solution is hypertonic with a high solute (salt ion) concentration shown by the
orange circles. The membrane is not permeable to the salt ions. Since the concentration of
water molecules per unit area is higher inside the cell than outside, water moves out of the
cell.
The internal body fluids of a marine fish are hypotonic compared with the hypertonic sea
water; therefore, water molecules diffuse out of the fish through the gill region. To cope
with this steady loss of water, the marine fish has greatly reduced urine with little or no
water loss, continuously drinks water, and excretes excess salt through the gills by active
transport. Conversely, a freshwater fish is hypertonic compared with the water of a lake or
pond; therefore, it continually absorbs water through the gill region. To cope with this
steady influx of water molecules, the freshwater fish has copious urine, drinks very little
water, and absorbs salts through the gills by active transport.