Damn Near Everything There Is To Know About Cells: Essay, Research Paper

Damn Near Everything There Is To Know About Cells:

Biology Cell Report

There are many parts of a cell, they all have specific duties, and are all

needed to continue the life of the cell. Some cells exist as single-celled

organisms that perform all of the organism’s metabolism within a single cell.

Such single-celled organisms are called unicellular. Other organisms are

made up of many cells, with their cells specialized to perform distinct

metabolic functions. One cell within an organism may be adapted for movement,

while another cell carries out digestion. The individual cells no longer

carry out all life functions, but rather depend on each other. Many-celled

organisms are called multicellular. When a group of cells function together to

perform an activity, they form a tissue. The cells of a human are organized

into tissues such as muscle and nerve tissues. Plant tissues include those

of the stem and root. Many cells in tissues are linked to each other at

contact sites called cell junctions. Cell junctions help maintain differences

in the internal environment between adjacent cells, help anchor cells together,

and allow cells to communicate with one another by passing small molecules from

one cell to another. Groups of two or more tissues that function together

make up organs. An organ system is a group of organs that work together to

carry out major life functions.

Eukariotic Cell Structure:

Boundaries and Control:

Plasma Membrane – The plasma membrane is sometimes called the cell membrane, or

the cellular membrane. It is the outermost part of the animal cell, and it’s

purpose is to enclose the cell, and change shape if needed. The cell membrane

is capable of allowing materials to enter and exit the cell. Oxygen and

nutrients enter, and waste products such as excess water leave. The plasma

membrane helps maintain a chemical balance within the cell.

Cell wall – The cell wall is an added boundary to the cell. It is relatively

inflexible, and surrounds the plasma membrane. The cell wall is much thinker

than the plasma membrane and is made of different substances in different

organisms. The cells of plants, fungi, almost all bacteria, and some protists

have cell walls. Animal cells have no cell walls. Plant cells contain

cellulose molecules, which form fibers. This fibrous cellulose of plants

provides the bulk of the fiber in our diets. Chitin, a nitrogen-containing

polysaccharide, makes up the cell walls of fungi.

Nucleus – The nucleus of the cell is the organelle that manages cell functions

in a eukariotic cell. The nucleus contains DNA, the master instructions for

building proteins. DNA forms tangles of long strands called chromatin, which is

packed into identifiable chromosomes when the cells are ready to reproduce.

Also within the nucleus is the nucleolus, a region that produces tiny cell

particles that are involved in protein synthesis These particles, called

ribosome’s, are the sites where the cell assembles enzymes and other proteins

according to directions of the DNA.

Assembly, Transport, and Storage:

Cytoplasm – The material that lies outside the nucleus and surrounds the

organelles is the cytoplasm, a clear fluid that is a bit thinner than toothpaste

gel. It usually constitutes a little more than half the volume of a typical

animal cell.

Endoplasmic Reticulum – The endoplasmic reticulum (ER) is a folded membrane that

forms a network of interconnected compartments inside the cell. The ER

membranes contain the enzymes for almost all of the cell’s lipid synthesis, they

serve as the site of lipid synthesis in the cell. The ER functions as the

cell’s delivery system. Some parts of the ER are studded with ribosome’s. In

the cell, the sites of protein assembly are the ribosome’s.

Golgi Apparatus – The Golgi apparatus’s main purpose is to store materials. The

Golgi apparatus is a series of closely stacked, flattened membrane sacs that

receives newly synthesized proteins and lipids from the ER and distributes them

to the plasma membrane and other cell organelles. Proteins are transferred from

the ER to the Golgi apparatus in small, membrane-bound transport packages.

These packages, called vesicles, have pinched off from the membrane of the ER

and contain proteins. The Golgi apparatus modifies the proteins chemically,

then repackages them in new vesicles for their final destination in the cell.

They may be incorporated into the cell structures, expelled, or remain stored

for later usage.

Vacuole – A vacuole is a sac of fluid surrounded by a membrane. Vacuoles often

store food, enzymes, and other materials needed by cells, and some vacuoles

store waste products. A plant cell has one large vacuole that stores water and

other substances.

Lysosomes – In addition to the assembly and storage of macromolecules, cells

also can disassemble things. Lysosomes, organelles that contain digestive

enzymes, digest excess or worn out cell parts, food particles, and invading

viruses or bacteria.

Mitochondria – Mitochondria are organelles in which food molecules are broken

down to release energy. This energy is then stored in other molecules that can

power cell reactions easily. A mitochondrion has an outer membrane and a highly

folded inner membrane. As with ER, the folds of the inner membrane provide a

large surface area in a small space. Energy is produced on the inner folds.

Chloroplasts – Chloroplasts transform light energy directly into usable chemical

energy and store that energy in food molecules. These foods include sugars and

starches. Chloroplasts contain the molecule chlorophyll, a green pigment that

traps the energy from sunlight and gives plants their green color. The

chloroplast belongs to a group of plant organelles called plastids, which are

used for storage. Some plastids store starches or lipids, whereas others

contain pigments, molecules that give color.

Structures for Support and Locomotion:

The cytoskeleton is a network of thin, fibrous elements that act as a sort of

scaffold to provide support for organelles. It also helps maintain cell shape

in a manner similar to the way poles maintain the shape of a tent. The

cytoskeleton is usually composed of microtubules and microfilaments.

Microtubules are thin, hollow cylinders made of protein. Microfilaments are

thin, solid protein fibers. Microtubules and microfilaments make up most of the

sytoskeleton.

Cilia – Cilia are only contained in some cells. They are short, numerous,

hairlike projections out of the plasma membrane. Cilia tend to occur in large

numbers on a cell’s surface, and their beating activity is usually coordinated.

Flagella – Flagella are longer projections that move with a whiplike motion.

Cells that have flagella only have one or two per cell. In single-celled

organisms, cilia and flagella are the major means of locomotion. Sperm cells of

animals and some plants move by means of flagella. Organisms that contain many

cells, including humans, have cilia that move fluids over a cell’s surface,

rather than moving the cell itself.