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Nucleic Acid Either of two kinds of molecules 
(DNA and RNA), formed by chains of 
nucleotides, that carry genetic information. 
Nucleotide A subunit of DNA or RNA that includes 
one base, one phosphate molecule, and one 
sugar molecule (deoxyribose in DNA, ribose in 
RNA). See base. 
Nucleus In eukaryotic cells, the membrane-bound 
organelle that contains the genetic material. 
Organelle A specialized structure having a definite 
function in a cell; for example, the nucleus, a 
mitochondrion, a ribosome. 
Peroxisome A membrane-bound organelle that both 
generates and breaks down hydrogen peroxide. 
Phospholipid A fatty compound that contains 
phosphate. Phospholipids make up much of the 
outer membranes of cells and organelles. 
Prokaryotic Cell A cell that does not have a 
membrane around its nuclear region; for 
example, a bacterium. 
Protein A molecule made up of a number of amino 
acids arranged in a specific order determined by 
the genetic code. Proteins are essential for all 
life processes. 
Receptor A specialized molecule of a cell’s 
membrane that receives information from the 
environment and conveys it to other parts of the 
cell. The information is transmitted in the form 
of a specific chemical that must fit the receptor 
like a key in a lock. 
Recombinant DNA Technology A body of tech- 
niques for cutting apart and splicing together 
different pieces of DINA. When segments of 
foreign DNA are transferred into another cell or 
organism, the substance for which they code 
may be produced along with substances coded 
for by the native genetic material of the cell or 
organism. Thus, these cells become “factories” 
for the production of the protein coded for by 
the inserted DINA. 
Replication The duplication of hereditary 
material prior to cell division. 
Respiration Within cells, the breakdown of food 
molecules to liberate metabolieally useful energy. 
Ribosome An organelle that contains RNA and 
protein, and is the site of protein synthesis. 
RNA ( ribonucleic acid ) A single-stranded nucleic 
acid that contains the sugar ribose. There are 
several forms of RNA, including messenger 
RNA, transfer RNA, and ribosomal RNA (all 
involved in protein synthesis), as well as several 
small RNA’s whose functions are still being clar- 
ified. Certain viruses have RNA, instead of 
DNA, as their genetic material. 
Second Messenger System A multi-step signal 
amplification process used by the cell to 
transmit, for example, signals from many 
hormones that cannot enter the cell directly. 
Steroid A molecule related to cholesterol. Many 
important hormones, such as estrogen and 
testosterone, are steroids. 
Transcription The transfer of information from var- 
ious parts of the DNA molecule to new strands of 
messenger RNA, which then carry this informa- 
tion from the nucleus to the cytoplasm. 
Translation The conversion of the genetic instruc- 
tions for a protein from nucleotides of 
messenger RINA into amino acids. 
Vesicle A small, membrane-bound, spherical sac in 
the cytoplasm of a eukaryotic cell. 
