Cells Essay, Research Paper

Proteins made from ribosomes attached to the rough

endoplasmic reticulum enter the lumen of the ER and move

to the smooth endoplasmic reticulum. A small vacuole

(vesicle) pinches off the smooth ER and carries the protein

to the Golgi apparatus, where it is further processed.

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Mitochondria are bounded by a double membrane. The inner

membrane is folded to form little shelves, called cristae,

which project into the matrix, an inner space filled with

a gel-like fluid.

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A vacuole is a large membrane-enclosed sac that usually

functions as a storage area. Plant vacuoles contain not

only water, sugars, and salts but also pigments and toxic

substances. The pigments are responsible for many of the

red, blue, or purple colors of flowers and some leaves.

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The green pigment chlorophyll, found within the grana,

makes chloroplasts and leaves green. Chlorophyll absorbs

solar energy, and chloroplasts convert this energy into

ATP molecules.

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Chloroplasts carry on the process of photosynthesis, in

which light energy is used to produce food molecules, such

as glucose. Chloroplasts take in carbon dioxide, water,

and solar energy in order to produce glucose and oxygen.

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The energy-related organelles, chloroplasts and

mitochondria, convert one form of energy into another.

While chloroplasts are unique to plant cells, mitochondria

are found in both plant and animal cells.

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Chloroplasts carry on photosynthesis, during which light

energy (photo) is used to produce food molecules, like

glucose (synthesis). Chloroplasts take in carbon dioxide,

water, and solar energy in order to produce glucose and

give off oxygen.

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Mitochondria are often called the powerhouses of the cell:

just as a powerhouse burns fuel to produce electricity,

the mitochondria convert the chemical energy of glucose

products into the chemical energy of ATP molecules.

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Chromatin, a threadlike material, contains DNA and is

found within the nucleus. At the time of cell division,

chromatin condenses into rodlike structures called

chromosomes.

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The middle lamellae, a region between cell walls, contains

a sticky substance, usually pectin. Lignin is a substance

found in secondary cell walls that makes them even

stronger than primary cell walls.

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Autodigestion is important during development. For

example, when a tadpole becomes a frog, the enzymes within

lysosomes digest the cells of the tail, and the fingers of

a human embryo are at first webbed, but they are freed

from one another by lysosomal action.

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Lysosomes, vesicles formed by the Golgi apparatus, contain

hydrolytic enzymes that can digest macromolecules.

Macromolecules are sometimes brought into a cell in

vesicles formed at the cell membrane. A lysosome can fuse

with such a vesicle and digest its contents into simpler

molecules, which then enter the cytoplasm.

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Special vacuoles (membrane-enclosed sacs) called

peroxisomes are often attached to smooth ER, and these

contain enzymes capable of detoxifying drugs.

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A chloroplast is bounded by a double membrane. Inside the

structure, there is even more membrane organized into

flattened sacs called thylakoids. The thylakoids are

piled up like stacks of coins, and each stack is called a

granum. There are membranous connections between the

grana called lamellae. The fluid-filled space about the

grana is called the stroma.

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Inside the chloroplast, there is membrane organized into

flattened sacs called thylakoids. The thylakoids are

piled up like stacks of coins, and each stack is called a

granum. The fluid-filled space about the grana is called

the stroma.

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The nucleus is a large organelle that has a nuclear

envelope, chromatin and nucleoli. The nuclear envelope is

a double membrane that keeps the contents of the nucleus

separate from the cell’s cytoplasm. Pores in the nuclear

envelope allow large molecules to pass into and out of the

nucleoplasm, the fluid interior of the nucleus.

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Ribosomes are the site of protein synthesis in the

cytoplasm. They can be attached to the endoplasmic

reticulum or lie free within the cytoplasm. When several

ribosomes are making the same protein, they are arranged

in a functional group called a polysome.

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Both plant and animal cells have cell membranes, nuclear

membranes, mitochondria, and vacuoles. Chloroplasts are

found in plant cells but not in animal cells.

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All plants have a cell wall, located outside the cell

membrane. The primary cell wall contains cellulose

whereas the secondary cell walls contain lignin. The

middle lamella, a region between cell walls, contains a

sticky substance, usually pectin.

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In the process of aerobic cellular respiration,

mitochondria convert the chemical energy of glucose

(carbohydrate) into the chemical energy of ATP molecules.

In the process, mitochondria use up oxygen and give off

carbon dioxide and water.

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Smooth ER, which lacks ribosomes, produces different

molecules in different cells. It is abundant in the

testes and adrenal cortex, both of which produce steroid

hormones. In the liver, smooth ER is involved in the

detoxification of drugs, including alcohol.

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The Golgi apparatus is composed of a stack of about a

half dozen or more saccules (flattened vacuoles, which

look like hollow pancakes). One side of the stack, called

the inner face, is directed toward the nucleus and the

ER. The other side of the stack, called the outer face,

is directed toward the cell membrane.

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