Ap Biology Unit 6

Antiparallel

DNA strands run in opposite directions (5’ to 3’ and 3’ to 5’)

Semiconservative

Each new DNA molecule consists of one old strand and one new strand

Helicase

Enzyme that unwinds the DNA double helix

DNA polymerase

Synthesizes new DNA by adding nucleotides; reads template 3’ to 5’, synthesizes 5’ to 3’

Leading strand

Synthesized continuously into the replication fork

Lagging Strand

Synthesized discontinuously away from the fork in Okazaki fragments

DNA Ligase

Joins Okazaki fragments together

Topoisomerase

Relieves tension ahead of the replication fork

Transcription

Synthesis of RNA from a DNA template

RNA Polymerase

Enzyme that binds to a promoter and synthesizes mRNA in the 5’ to 3’ direction

Template Strand

DNA strand used to make RNA

5’ Cap

Modified guanine cap added to 5’ end for protection and ribosome attachment

Poly-A Tail

Added to 3’ end for stability

Splicing

Introns are removed, and exons are joined

Translation

Ribosomes in cytoplasm translate mRNA to build a polypeptide

Codon

Three-base sequence on mRNA that codes for an amino acid

tRNA

Transfers amino acids to the ribosome; has an anticodon that matches the mRNA codon

rRNA

Structural components of ribosome

Operon (prokaryotes)

Cluster of genes with a single promoter, operator, and structural genes.

Repressor

Protein that binds to the operator to turn off transcription.

Inducer

Molecule that turns an operon "on" (e.g., lactose in the lac operon).

Point Mutation

Change in one nucleotide

Frameshift Mutation

Insertion or deletion of nucleotides, changing the reading frame.

Misense

Codes for a different Amino Acid

Nonsense

Codes for a premature stop codon