Definitions for Chapter 16—The Molecular Basis of Inheritance

3’—designation for one of the five carbon atoms which make up deoxyribose or ribose.  A 3’ carbon is exposed at one end of the sugar phosphate backbone of a DNA or RNA molecule; this end is designated the 3’ end.

5’—designation for one of the five carbon atoms which make up deoxyribose or ribose.  A 5’ carbon is exposed at one end of the sugar phosphate backbone of a DNA or RNA molecule; this end is designated the 5’ end.

Adenine—One of the nucleotides that make up DNA and RNA.

Antiparallel—term used to describe DNA molecules, in which the two sugar-phosphate backbones are oriented in opposite directions with respect to the 3’ and 5’ carbon molecules in the deoxyribose.

Avery, Oswald—American scientist who was among the first to demonstrate that DNA was the genetic material rather than protein.

Bacteriophage—a virus which specializes in attacking bacteria.

Chargaff, Erwin—Austrian-American biochemist who discovered that the amounts of adenine and thymine, and the amounts of guanine and cytosine in DNA were almost exactly the same.  These rules (now called Chargaff’s rules) helped Watson and Crick determine the structure of the DNA molecule.

Chargaff’s rules-- the amounts of adenine and thymine, and the amounts of guanine and cytosine in DNA are almost exactly the same.  Often expressed as “A = T, C = G.” 

Crick, Francis—British chemist who, along with James Watson, first described the structure of DNA.

Cytosine—one of the nucleotides that make up DNA and RNA.

DNA ligase—enzyme which fills in the gaps between sections of DNA (Okazaki fragments) on the lagging strand during DNA replication

DNA polymerase—enzyme which assembles nucleotides to build a strand of DNA, using a complementary strand as a template.

Escherichia coli—common intestinal bacterium of mammals, often used in experiments.

Franklin, Rosalind—British chemist who conducted X-ray diffraction experiments on DNA and helped to discover its basic double helix structure.

Griffith, Frederick—British scientist who attempted to find a vaccine against pneumonia, and whose work first demonstrated bacterial transformation and the central role of DNA to heredity.

Guanine—one of the nucleotides that make up DNA and RNA.

Helicase—an enzyme which untwists the double helix and separates the template DNA strands at the replication fork during DNA replication.

Hershey, Alfred—American scientist who definitively established that DNA, and not proteins, was the genetic material of the cell.

Nuclease—an enzyme which can cut a DNA molecule; some nucleases cut out damaged parts of DNA molecules which can then be repaired by DNA polymerase and DNA ligase.

Nucleoside triphosphate—nucleotide with three attached phosphate groups.  The phosphate groups may be hydrolyzed to supply energy to power replication.

Okazaki fragments—sections of DNA molecule on the lagging strand.  Okazaki fragments are created because the DNA polymerase can only read DNA in one direction; because the two strands of DNA are anti-parallel, the lagging strand is constructed in segments.

Origin of replication—specific sequence of nucleotides which is recognized by replication enzymes as a starting point for replication.

Pauling, LInus—American biochemist who attempted to determine the structure of DNA, but was unable to do so before Watson and Crick.  Pauling won two Nobel Prizes during his lifetime, a Nobel Prize in Chemistry, and the Nobel Peace Prize.

Primer—a short stretch of RNA with an exposed 3’ on the end of a DNA molecule which serves as the starting point for DNA replication.

Pyrophosphate—chemical which is the result of hydrolysis of phosphate groups on a nucleoside triphosphate.  Pyrophosphates are also hydrolyzed to power replication.

Replication—the process of copying DNA before cell division.

Replication bubble—structure formed by replication enzymes at origins of replication where copying of the DNA molecule is in progress.

Replication fork—structures at the ends of a replication bubble consisting of strands of DNA having been separated by replication enzymes.

Semi-conservative—term used to describe DNA replication, in which new DNA molecules consist of one strand from the parent molecule, and a new strand complementary to that strand.

Single-strand binding protein—enzymes which keep unpaired template strands of the DNA molecule apart during replication.

Streptococcus pneumoniae—bacterium that causes pneumonia, subject of transformation studies by Frederick Griffith.

T-2—bacteriophage which attacks Escherichia coli, making it convenient for use in experiments.

Telomere—a repeating sequence of nucleotides at the end of a DNA molecule which are shortened during replication; these sequences protect the DNA molecule from being damaged during the replication process.  Human telomeres are typically repeating sequences of TTAGGG.

Telomerase—an enzyme which catalyzes the lengthening of telomeres in eukaryotic germ cells, and which has been found to be active in some somatic cancer cells.

Template—a strand of DNA from an already-existing molecule which is used to determine the order of the nucleotides on a new strand.

Thymine—nucleotide found in DNA but not RNA.  In RNA, thymine is replaced by uracil.

Topoisomerase—an enzyme which relieves the strain on the DNA molecule caused by the untwisting of the double helix ahead of the replication fork during replication.

Transformation—change in genotype and phenotype due to the assimilation of foreign DNA by a cell, first demonstrated by Frederick Griffith.

Watson, James—American chemist who, along with Francis Crick, first described the structure of the DNA molecule.

Wilkins, Maurice—British chemist whose work on DNA was instrumental in Watson and Crick’s discovery of the structure of the molecule.

X-ray crystallography—technique for determining the structure of complex molecules.  X-rays are passed through aligned fibers of the purified molecule, and the diffraction pattern can be used to deduce the three-dimensional shape of the molecule.