OpenStax Concepts of Biology Chapter 9 Molecular Biology

codon

three consecutive nucleotides in mRNA that specify the addition of a specific amino acid or the release of a polypeptide chain during translation

deoxyribose

a five-carbon sugar molecule with a hydrogen atom rather than a hydroxyl group in the 2' position; the sugar component of DNA nucleotides

DNA ligase

the enzyme that catalyzes the joining of DNA fragments together

DNA polymerase

an enzyme that synthesizes a new strand of DNA complementary to a template strand

double helix

the molecular shape of DNA in which two strands of nucleotides wind around each other in a spiral shape

gene expression

processes that control whether a gene is expressed

genetic code

the amino acids that correspond to three-nucleotide codons of mRNA

helicase

an enzyme that helps to open up the DNA helix during DNA replication by breaking the hydrogen bonds

lagging strand

during replication of the 3' to 5' strand, the strand that is replicated in short fragments and away from the replication fork

leading strand

the strand that is synthesized continuously in the 5' to 3' direction that is synthesized in the direction of the replication fork

mismatch repair

a form of DNA repair in which non-complementary nucleotides are recognized, excised, and replaced with correct nucleotides

mRNA

messenger RNA; a form of RNA that carries the nucleotide sequence code for a protein sequence that is translated into a polypeptide sequence

mutation

a permanent variation in the nucleotide sequence of a genome

nitrogenous base

a nitrogen-containing molecule that acts as a base; often referring to one of the purine or pyrimidine components of nucleic acids

nontemplate strand

the strand of DNA that is not used to transcribe mRNA; this strand is identical to the mRNA except that T nucleotides in the DNA are replaced by U nucleotides in the mRNA

Okazaki fragments

the DNA fragments that are synthesized in short stretches on the lagging strand

phosphate group

a molecular group consisting of a central phosphorus atom bound to four oxygen atoms

post-transcriptional

control of gene expression after the RNA molecule has been created but before it is translated into protein

post-translational

control of gene expression after a protein has been created

primer

a short stretch of RNA nucleotides that is required to initiate replication and allow DNA polymerase to bind and begin replication

promoter

a sequence on DNA to which RNA polymerase and associated factors bind and initiate transcription

replication fork

the Y-shaped structure formed during the initiation of replication

RNA polymerase

an enzyme that synthesizes an RNA strand from a DNA template strand

rRNA

ribosomal RNA; molecules of RNA that combine to form part of the ribosome

semiconservative replication

the method used to replicate DNA in which the double-stranded molecule is separated and each strand acts as a template for a new strand to be synthesized, so the resulting DNA molecules are composed of one new strand of nucleotides and one old strand of nucleotides

start codon

the AUG (or, rarely GUG) on an mRNA from which translation begins; always specifies methionine

stop codon

one of the three mRNA codons that specifies termination of translation

template strand

the strand of DNA that specifies the complementary mRNA molecule

transcription bubble

the region of locally unwound DNA that allows for transcription of mRNA

tRNA

transfer RNA; an RNA molecule that contains a specific three-nucleotide anticodon sequence to pair with the mRNA codon and also binds to a specific amino acid