AP Biology Chapter 16 Vocab

transformation

A change in genotype and phenotype due to the assimilation of external DNA by a cell.

bacteriophages

viruses that infect bacteria

phages

nickname for a virus that infects bacteria.

double helix

the form of native DNA, referring to its two adjacent anti-parallel polynucleotide strands wound around an imaginary axis into a spiral shape.

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.

origins of replication

site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides.

replication fork

A Y-shaped region on a replicating DNA molecule where the parental strands are being unwound and new strands are growing.

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.

single-strand binding proteins

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.

topoisomerase

a protein that breaks, swivels, and rejoins DNA strands. During DNA Replication, they help to relieve strain in the double helix ahead of the replication fork.

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.

primase

an enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template.

DNA polymerases

an enzyme that catalyzes the elongation of new DNA (for example at the replication fork) by the addition of nucleotides to the 3' end of an existing chain. There are several different of these; number III and number I play major roles in DNA replication in prokaryotes.

leading strand

the new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5'-3' direction.

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.

Okazaki Fragments

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.

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 (such as a growing DNA chain.)

mismatch repair

the cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides.

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.

nucleotide excision repair

A repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide.

telomeres

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.

telomerase

an enzyme that catalyzes the lengthening of telomeres in eukaryotic cells.

nucleoid

A dense region of DNA in a prokaryotic cell.

chromatin

The complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing, it exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope.

heterochromatin

Eukaryotic chromatin that remains highly compacted during interphase and is generally not transcribed.

euchromatin

The less condensed form of eukaryotic chromatin that is available for transcription.

Xeroderma Pigmentosum

a skin disorder that results from a defect in the nucleotide excision repair enzymes. These individuals are hypersensitive to sunlight. UV light produces thymine dimers between adjacent thymine nucleotides, which buckles the DNA double helix and interferes with DNA replication, causing skin cancer.

Thymine Dimers

when there's two thymine that are bound together.

antiparallel

the direction in which the strands of the double helix run; one goes 5'-3' and the other goes 3'-5'

3' end

has a free hydroxyl group attached to deoxyribose

5' end

has a free phosphate group attached to deoxyribose

nucleoside triphosphate

what ATP is, exactly like DNA but it has a ribose instead of a deoxyribose.

X-Ray Crystallography

X-Rays are diffracted as they pass through aligned fibers of purified DNA. The diffraction pattern can be used to deduce the three dimensional shape of the molecules. What Wilkins and Franklin used to study the structure of DNA

purine

one of the two types of nitrogenous bases found in nucleotides, characterized by a six-membered ring fused to a five-membered ring. Adenine and Guanine are these.

pyrimidine

one of two types of nitrogenous bases found in nucleotides, characterized by a six-membered ring. Cytosine, thymine, and uracil are these.

adenine

a compound that is one of the four constituent bases of nucleic acids. A purine derivative, it is paired with thymine in double-stranded DNA

thymine

a compound that is one of the four constituent bases of nucleic acids. A pyrimidine derivative, it is paired with adenine in double-stranded DNA.

guanine

one of the four constituent bases of nucleic acids. A purine derivative, it is paired with cytosine in double-stranded DNA

cytosine

a compound found in living tissue as a constituent base of nucleic acids. It is paired with guanine in double-stranded DNA.

Chargaff's rule

states that DNA from any cell of all organisms should have a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases and, more specifically, that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine. AKA base pairing rule

Hydrogen bonds

hold nitrogenous bases together

deoxyribose

the sugar component of DNA nucleotides, having one fewer hydroxyl group than ribose, the sugar component of RNA nucleotides.

nitrogenous base

a nitrogen containing molecule that has the same chemical properties as a base. They are particularly important since they make up the building blocks of DNA and RNA: adenine, guanine, cytosine, thymine and uracil.

nucleic acids

a polymer consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular activities. The two types are DNA and RNA.

Interphase

When two strands of DNA unwind and expose their bases

histones

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.