AP Biology Vocabulary & Roots: Ch. 16
1. Bacteria-One of two prokaryotic domains, the other being Archaea.
2. bacteriophage- A virus that infects bacteria; also called a phage.
3. bacterium- Member of the prokaryotic domain Bacteria.
4. chromatin- The complex of DNA and proteins that makes up a eukaryotic chromosome. When
the cell is not dividing, chromatin exists in its dispersed form, as a mass of very long, thin fibers
that are not visible with a light microscope.
5. deoxyribose- The sugar component of DNA nucleotides, having one fewer hydroxyl group than
ribose, the sugar component of RNA nucleotides.
6. DNA ligase-A linking enzyme essential for DNA replication; catalyzes the covalent bonding of
the 3' end of one DNA fragment (such as an Okazaki fragment) to the 5' end of another DNA
fragment (such as a growing DNA chain).
7. DNA polymerase- An enzyme that catalyzes the elongation of new DNA (for example, at a
replication fork) by the addition of nucleotides to the 3' end of an existing chain. There are several
different DNA polymerases; DNA polymerase III and DNA polymerase I play major roles in DNA
replication in prokaryotes.
8. double helix-The form of native DNA, referring to its two adjacent antiparallel polynucleotide
strands wound around an imaginary axis into a spiral shape.
9. euchromatin- The less condensed form of eukaryotic chromatin that is available for
transcription.
10. helicase-An enzyme that untwists the double helix of DNA at the replication forks, separating
the two strands and making them available as template strands.
11. heterochromatin- Eukaryotic chromatin that remains highly compacted during interphase and
is generally not transcribed.
12. histone-A small protein with a high proportion of positively charged amino acids that binds to
the negatively charged DNA and plays a key role in chromatin structure.
13. lagging strand-A discontinuously synthesized DNA strand that elongates by means of Okazaki
fragments, each synthesized in a 5'3' direction away from the replication fork.
14. leading strand-The new complementary DNA strand synthesized continuously along the
template strand toward the replication fork in the mandatory 5'3' direction.
15. mismatch repair-The cellular process that uses specific enzymes to remove and replace
incorrectly paired nucleotides.
16. nuclease-An enzyme that cuts DNA or RNA, either removing one or a few bases or hydrolyzing
the DNA or RNA completely into its component nucleotides.
17. nucleoid- A dense region of DNA in a prokaryotic cell.
18. nucleosome- The basic, bead-like unit of DNA packing in eukaryotes, consisting of a segment
of DNA wound around a protein core composed of two copies of each of four types of histone.
19. nucleotide excision repair-A repair system that removes and then correctly replaces a damaged
segment of DNA using the undamaged strand as a guide.
20. Okazaki fragment- A short segment of DNA synthesized away from the replication fork on a
template strand during DNA replication, many of which are joined together to make up the lagging
strand of newly synthesized DNA.
21. origin of replication-Site where the replication of a DNA molecule begins, consisting of a
specific sequence of nucleotides.
22. phage-A virus that infects bacteria; also called a bacteriophage.
23. primase-An enzyme that joins RNA nucleotides to make the primer using the parental DNA
strand as a template.
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24. primer-A short stretch of RNA with a free 3' end, bound by complementary base pairing to the
template strand, that is elongated with DNA nucleotides during DNA replication.
25. pyrimidine- One of two types of nitrogenous bases found in nucleotides, characterized by a sixmembered ring. Cytosine (C), thymine (T), and uracil (U) are pyrimidines.
26. radioactive isotope-An isotope (an atomic form of a chemical element) that is unstable; the
nucleus decays spontaneously, giving off detectable particles and energy.
27. repetitive DNA-Nucleotide sequences, usually noncoding, that are present in many copies in a
eukaryotic genome. The repeated units may be short and arranged tandemly (in series) or long and
dispersed in the genome.
28. replication fork- A Y-shaped region on a replicating DNA molecule where the parental strands
are being unwound and new strands are growing
29. semiconservative model- Type of DNA replication in which the replicated double helix
consists of one old strand, derived from the old molecule, and one newly made strand.
30. single-strand binding protein- A protein that binds to the unpaired DNA strands during DNA
replication, stabilizing them and holding them apart while they serve as templates for the synthesis
of complementary strands of DNA.
31. telomerase-An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells.
32. telomere- The tandemly repetitive DNA at the end of a eukaryotic chromosome’s DNA
molecule that protects the organism’s genes from being eroded during successive rounds of
replication. See also repetitive DNA.
33. template strand-The DNA strand that provides the pattern, or template, for ordering the
sequence of nucleotides in an RNA transcript.
34. topoisomerase-A protein that breaks, swivels, and rejoins DNA strands. During DNA
replication, topoisomerase helps to relieve strain in the double helix ahead of the replication fork.
35. transformation- A change in genotype and phenotype due to the assimilation of external DNA
by a cell.
36. X-ray crystallography-A technique that depends on the diffraction of an X-ray beam by the
individual atoms of a crystallized molecule to study the three-dimensional structure of the molecule.
Word Roots
helic- = a spiral (helicase: an enzyme that untwists the double helix of DNA at the replication forks)
liga- = bound or tied (DNA ligase: a linking enzyme for DNA replication)
-phage = to eat (bacteriophages: viruses that infect bacteria)
semi- = half (semiconservative model: type of DNA replication in which the replicated double helix
consists of one old strand, derived from the parent molecule, and one newly made strand)
telos- = an end (telomere: the protective structure at each end of a eukaryotic chromosome)
trans- = across (transformation: a phenomenon in which external DNA is assimilated by a cell)
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