BISC 303 primary

Phosphodiester Bond

Covalent linkage between the 3' carbon of one nucleotide and the 5' carbon of the next.

Helicase

Enzyme that unwinds the DNA double helix during replication initiation. Single-Strand Binding Proteins (SSBPs) Proteins that bind to single-stranded DNA to prevent re-annealing at the replication fork.

DNA Polymerase III

Primary elongation enzyme that synthesizes new DNA 5' to 3' by adding dNTPs to a 3'-OH group.

DNA Polymerase I

Enzyme that removes RNA primers and fills the gaps with DNA nucleotides.

DNA Ligase

Enzyme that covalently joins Okazaki fragments by sealing sugar-phosphate backbones.

Spo11

Conserved protein that initiates meiotic recombination by introducing double-strand breaks in DNA

Heteroduplex DNA

Region of a double-stranded DNA molecule where one strand comes from the maternal parent and the other from the paternal parent.

Gene Conversion

Non-Mendelian allele inheritance resulting from mismatch repair within heteroduplex DNA during recombination.

Depurination

Spontaneous DNA lesion involving the hydrolysis of a purine base (A or G) from the deoxyribose backbone.

Deamination

Loss of an amino group from a base, such as Cytosine converting to Uracil.

Luria-Delbrück Fluctuation Test

Experiment demonstrating that bacterial mutations arise spontaneously prior to environmental selection.

Transition Mutation

Point mutation replacing a purine with another purine, or a pyrimidine with another pyrimidine.

Transversion Mutation

Point mutation replacing a purine with a pyrimidine or vice versa.

Missense Mutation

Base substitution that changes a codon to specify a different amino acid.

Nonsense Mutation

Base substitution that changes an amino-acid-coding codon into a stop codon (UAA, UAG, UGA).

Frameshift Mutation

Insertion or deletion of nucleotides not in multiples of three, altering the reading frame downstream.

Amorphic (Null) Mutation

Loss-of-function allele that completely eliminates gene function.

Hypomorphic Mutation

Loss-of-function allele that reduces but does not completely eliminate gene function.

Haploinsufficiency

Dominant condition where one wild-type allele does not produce enough gene product for normal function.

Hypermorphic Mutation

Gain-of-function allele that produces excess protein or an overactive protein.