World without Cats (39 page)

Micromanipulator:
A mechanical device consisting of motors and controls used to position tiny tools and pipettes extremely precisely as the user peers through a microscope.

Morula:
An early stage in embryonic development consisting of a ball of cells.

Nucleotide:
The basic subunit of DNA and RNA. A nucleotide is made up of a sugar molecule (ribose in RNA and deoxyribose in DNA), a phosphate molecule, and a nitrogen-containing organic base. DNA contains the four bases adenine, guanine, cytosine, and thymine. RNA contains the first three, but has uracil instead of thymine.

Oocyte
(pronounced
oh-oh-cyte
): immature egg cell.

Panleukopenia (feline):
A contagious disease of cats characterized by sudden onset, lack of appetite, and vomiting, generally resulting in death of the cat.

Plasmids:
Small, circular, replicating pieces of DNA found in bacteria and in the nuclei of some higher organisms. They are separate from the organism’s chromosome and carry a limited number of genes.

Polymerase chain reaction (PCR)
A laboratory procedure for replicating DNA. It is commonly used with tiny quantities of DNA samples (such as might be found at a crime scene) to amplify the samples, allowing them to be analyzed and subjected to further experimentation that would be impossible with the original, minute quantities of DNA.

Polynucleotide:
A chain of nucleotides in a specific order. The two important polynucleotides, DNA and RNA, carry information in the sequence of the bases in their nucleotides. That sequence in DNA comprises the genetic information passed from generation to generation. RNA obtains its base sequence as it is copied off of a DNA template and is the means by which the information in genes is used to carry out cellular functions such as protein synthesis.

Polypeptide chain:
A chain of amino acids bonded to each other in a unique sequence. A protein molecule is made up of one or more such chains.

Promoter:
A sequence of nucleotides on DNA that signals where the copying of a molecule of RNA is to start.

Pronucleus
: A fertilized ovum has two nuclei, one from the ovum itself, and the other from the spermatozoon that fertilized it. These two nuclei are referred to as pronuclei at this stage. After they fuse and the DNA of the pronuclei undergo recombination, the resulting zygote contains only one nucleus.

Provirus:
A viral genome integrated into the host chromosome and passed on to succeeding cell generations as the chromosome is replicated. Example: FeLV in cats is often present as a provirus.

Protein:
A molecule consisting of one or more polypeptide chains. Proteins have diverse, important functions in living organisms. Most enzymes are made of protein as are muscle fibers, antibodies, and many structural components of skin, connective tissue, and many other components of the organism.

Recombinant DNA:
DNA formed by the breaking of DNA strands from different sources (such as different chromosomes or different parents), and their reconnection into new sequences. Formed naturally in the process of fertilization or artificially in the laboratory.

Retrovirus:
A virus with an RNA genome. In the course of their reproduction such viruses use this RNA to make DNA copies (cDNA) using an enzyme called
reverse transcriptase.

Reverse transcriptase:
An enzyme found in retroviruses that catalyzes the synthesis of cDNA from an RNA template.

Rhinotracheitis
(feline):
An infectious upper-respiratory-tract disease, not unlike a severe cold in humans. Caused by a variety of viruses, including caliciviruses and Feline Viral Rhinotracheitis Virus (FVR).

RNA:
(ribonucleic acid) A polynucleotide having a specific sequence of nucleotides, whose sequence of bases is copied from a DNA template.

RNA interference (RNAi):
The destruction of messenger RNA (mRNA) by a complex process that involves small-interfering RNA (siRNA), double-stranded RNA (dsRNA), and several enzymes. RNAi is thought to play an important role in regulation of cellular function as well as in defense against retroviruses.

Small interfering RNA (siRNA):
Short segments of RNA about 22 nucleotides long. The siRNA is derived from partial digestion of dsRNA by an enzyme named
dicer
. It is an intermediate in the process known as RNA interference (see above).

Stem cells:
Certain undifferentiated cells found in multicellular organisms having the potential to differentiate into any of a wide variety of cells. Two broad categories of stem cells are
embryonic stem cells
and
adult stem cells.
In the course of embryonic development, stem cells play a seminal role, as they differentiate into the various types of cells comprising the organism—muscle, epithelia, nerve cells, etc. In the adult (here, meaning the organism at any age after birth), the primary function of stem cells is to replace cells that die and to repair damaged tissue.

T-cells:
(Also called T-lymphocytes.) See lymphocyte.

Transfer RNA (tRNA):
A class of specific RNA molecules, each of which binds to a specific amino acid and, by pairing with three bases on mRNA, brings the amino acid to its correct position in a growing polypeptide chain.

Vector:
In the context of molecular biology, any agent that can carry a piece of DNA into a cell. It can function in either of two ways:

a) Cloning vector
—
used for reproducing the DNA fragment.

b) Expression vector
—
used for making a gene product (e.g. a polypeptide chain) from the imported gene. Examples: plasmids, bacterial viruses, and retroviruses.

Virogene:
One or more genes found on the host’s chromosome with the information to synthesize a virus or its components.

Virus:
A particle composed of nucleic acid and protein (and, for some viruses, lipid), capable of infecting a cell and using the cell’s biochemical apparatus to reproduce itself. A virus is incapable of reproduction in the absence of a host cell.

Wright’s stain:
A staining procedure used to help distinguish different parts of a cell and to differentiate diverse types of cells. It is commonly used to stain blood smears, allowing the observer to make out the various types of white blood cells.