Organelles

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Cell membrane

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The Cell membrane has many jobs for the cell. It provides shape and support. It regulates all that enters and leaves the cell. It is constructed of a bilayer of phospholipids. It is a semi permeable membrane, meaning that it lets some things in and out and not others. Some things are too large to pass through so there are also carrier proteins that regulate transport and diffusion. Carrier proteins move specific molecules through the membrane one at a time. Marker proteins extend across the cell membrane and serve to identify the cell. The immune system uses these proteins to tell friendly cells from foreign invaders. These proteins are used in intercellular communication.

Front 2

Ribosomes

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These ribosomes build proteins for the cell. Ribosomes are found in many places around the cell. Some are floating in the cytoplasm. Those floating ribosomes make proteins that will be used inside of the cell. Other ribosomes are found on the endoplasmic reticulum. They make proteins that will be used inside the cell and proteins made for export out of the cell. A ribosome is not just one piece, but two subunits. When the cell needs to make protein, messenger RNA is created in the nucleus and sent into the cell to the ribosomes. When it is time to make the protein, the two subunits come together and combine with the messenger RNA, lock onto it and start the protein synthesis.

Front 3

Golgi apparatus

Back 3

The function of the golgi apparatus is to modify, sort, and package proteins and other materials from the E.R. for storage in the cell or secretion outside the cell. Once the proteins are produced by the rough E.R. they pass into the sack like cisternae that are the main part of the golgi apparatus. These proteins are then squeezed off into the little blebs which drift off into the cytoplasm.

Front 4

Cilia and flagella

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Cilia and Flagella These are hair-like extentions off of the cell membrane. Their structures are similar except that cilia tend to be small and numerous and flagella tend to be large and fewer. They beat back and forth rhythmically. In unicellular organisms their job is movement. In large multicellular organisms their role is to move fluid past the cell. They have a 9+2 arrangement of microtubles.

Front 5

Vacuoles

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Vacuoles are large areas in the cytoplasm that appear emtpy, but store water, salts, proteins, and carbohydrates. They are usually found in plant cells where they store waste. As a plant cell ages they get larger. In mature cells they occupy most of the cytoplasm.

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Endoplasmic reticulum

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The endoplasmic reticulum is a series of double membranes that loop back and forth between the cell membrane and the nucleus. These membranes fill the cytoplasm but you cannot see them because they are very transparent. The rough E.R. has ribosomes attached to it. This gives it its texture. The smooth does not have ribosomes.

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Nucleus

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The nucleus is a large dark spot in eukaryotic cells that controls cell activity like the brain of a cell. It is surrounded by a nuclear membrane that has many pores in it. Inside is a rope like strand of chromatin. Also inside is the nuclelous which is a knot of chromatin. It manufactures ribosomes. The chromatin is a combination of DNA and histone proteins. It stores the information needed for the manufacture of proteins.

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Centrioles

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A centriole is a barrel shaped organelle found in animal cells. There are two of them during cell division, they move to opposite sides of the cell, and each new paired set of centrioles is composed of the original centriole, plus a newly-made centriole.

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Cytoplasm

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Cytoplasm refers to everything between the cell membrane and the nuclear envelope. It consists of primarily of water. It also contains various organelles as well as salts, dissolved gasses and nutrients. It is where all the chemical reactions take place in the cell.

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Nucleolus

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The nuclelous is found inside the nucleus. A main function of the nucleolus is the production and assembly of ribosome components. The nucleolus is roughly spherical, and is surrounded by a layer of condensed chromatin. No membrane separates the nucleolus from the nucleoplasm.

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Cytoskeleton

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The cytoskeleton helps to maintain cell shape. Its primary importance is in cell movement. The internal movement of cell organelles, as well as cell locomotion and muscle fiber contraction could not take place without the cytoskeleton. The cytoskeleton is an organized network of three primary protein filaments: microtubules, actin filaments, and intermediate fibers.

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Peroxisomes

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Peroxisomes are round in shape, and a cell contains several hundred of them. They are contained in a membrane of proteins and lipids, and their inside contains oxidation enzymes. It is thought that peroxisomes developed due to the increase of oxygen in the environment. Like mitochondrions, peroxisomes are self-replicating. Their "life-span" is only a day. The main function of peroxisomes is to isolate atoms with hydrogen by adding oxygen, making hydrogen peroxide, or to break down hydrogen peroxide by adding oxygen to make water and oxygen gas. Another function of peroxisomes is converting fatty acids to sugars. Peroxisomes also decompose some fatty acids entirely.

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Lysosomes

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Lysosomes are organelles filled with enzymes. One function of lysosomes is the digestion, or breakdown, of lipids, carbohydrates, and proteins into small molecules that can be used by the rest of the cell. Lysosomes are also involved in breaking down organelles that have outlived their usefulness.

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Mitochondria

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Mitochondria are organelles that covert energy stored in food into compounds that the cell can use. This energy is what the cell needs to move, divide, produce, secret products, and contract. They are the power centers of the cell. Mitochondria have a double membrane like the nucleus. The outer membrane is fairly smooth. But the inner membrane is highly convoluted, forming folds called cristae. The cristae greatly increase the inner membrane's surface area. It is on these cristae that food (sugar) is combined with oxygen to produce ATP which is the primary energy source for the cell. In humans, mitochondria are passed on through the egg cell passing on the mom's DNA.

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Chromosomes

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A chromosome is a single long molecule of DNA found in cells. Chromosomes contain one very long, continuous piece of DNA which contains many genes. Eukaryotic cells have large linear chromosomes and prokaryotic cells have smaller circular chromosomes. In eukaryotes nuclear chromosomes are packaged by proteins into a condensed structure called chromatin.