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Chapter 4: The Nucleus - Definitions

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Organelle
is a specialized cell part that carries out specific functions to
ensure a cell's survival
Cell Membrane
separates the inside of a cell from its external environment
Cytoplasm
is a jelly-like substance that contains the organelles and other life-supporting materials, such as water and sugar
Ribosome
are small organelles that do not have a membrane
Endoplasmic Reticulum
is a network of membrane-covered channels within a cell
Golgi Body
is a specialized organelle that sorts and packages proteins for transport
Mitochondria
are organelles that are specialized to provide energy for cells by changing sugar called glucose into usable energy
Vesicles
are membrane-covered sacs that form off the ends of the endoplasmic reticulum
Vacuoles
are membrane-covered storage containers within cells
Chloroplast
trap the energy from the Sun and make glucose
Cell Wall
is a tough, rigid structure that surrounds the cell membrane. The cell wall provides support for the plant cell and prevents the cell from bursting when a plant is in a very moist environment
Nucleus
controls the functions of a living cell
Nuclear Membrane
protects the contents of the nucleus
Nucleolus
is a membrane-free organelle that floats in the interior of the nucleus
Nuclear Pores
are openings in the nuclear membrane that allow only certain materials into and out of the nucleus
Proteins
are essential materials required for the cell to carry out the activities necessary for its survival
DNA (Deoxyribonucleic Acid)
The instructions in the nucleus are carried in long, two stranded molecules called deoxyribonucleic acid. The DNA molecule looks like a twisted ladder. The two strands, or sides, of the DNA ladder wrap around each other in a spiral shape that scientists call a double helix. The word "helix" comes
from a Greek word meaning to wrap. The sides of the DNA ladder are made of sugar and phosphate. The steps of the ladder are made of four nitrogen bases, which are represented by the letters A (adenine), G (guanine), C (cytosine), and T (thymine).
DNA message
Everything that occurs within a cell is the result of how the bases on the DNA molecule are arranged. This arrangement is known as the DNA message.
Chromatin
Chromatin is a substance that contains DNA and proteins.
Within each strand of chromatin is one molecule of DNA
Chromosome
When a eukaryotic cell is ready to divide, each strand of chromatin coils up into a very compact, X-shaped structure called a chromosome.
Gene
are small segments of DNA located at specific places on a
chromosome. Genes store the information needed to produce 90 000 to 100 000 different proteins used in the cells of your
body.
Enzymes
Thousands of different, specialized proteins called enzymes speed up the hundreds of chemical reactions that occur within each cell.
Hormones
proteins act as chemical messengers
RNA
The DNA message for a specific protein is copied into a small
molecule called ribonucleic acid or RNA.
Gene Mutation
is a change in the order of the A, G, C, and T bases in a gene. Gene mutations can be positive, negative, or neutral.
Deletion
one base is missing
Addition
an extra base is added
Substitution
one base is substituted for another
Positive Mutation
Errors in the sequence of DNA bases may produce proteins that could be beneficial to an organism and therefore to the survival of its species.
Negative Mutation
Harmful mutations, known as negative mutations, can cause a species to become extinct.
Neutral Mutation
errors in the base sequence of DNA appear to have no effect on the organism
Gene Therapy
Researchers are testing new techniques called gene therapy to
treat mutated genes. In one form of gene therapy, researchers replace a mutated gene with a healthy copy of the gene. Because the technique is risky, gene therapy is currently being tested on diseases without known cures.
Sickle Cell Anemia
is a negative mutation, but some researchers have found that people living in Africa with this mutation may be less likely to contract a potentially fatal disease called malaria.
Cystic Fibrosis
is another genetic disease caused by a mutation. In cystic fibrosis, mucus builds up because the protein that normally functions to transport chloride ions into and out of the cell is not made correctly. Since the protein malfunctions, chloride
ion levels build up, affecting the thickness of mucus in the lungs, causing respiratory problems, and making breathing difficult
Mutagens
are substances or factors that can cause mutations in DNA.