Download Glossary of Key Terms in Chapter Two

Glossary of Key Terms in Chapter Seventeen
aminoacyl tRNA (17.6) the transfer RNA covalently linked to its cognate amino acid.
aminoacyl tRNA binding site of ribosome (A-site) (17.6) a pocket on the surface of a ribosome that
holds the aminoacyl tRNA during translation.
aminoacyl tRNA synthetase (17.6) an enzyme that recognizes one tRNA and covalently links the
appropriate amino acid to it.
anticodon (17.4) a sequence of three ribonucleotides on a tRNA that are complementary to a codon on the
mRNA; codon-anticodon binding results in the tRNA bringing the correct amino acid to the site of
protein synthesis.
antiparallel strands (17.2) a term describing the polarities of the two strands of the DNA double helix;
on one strand, the sugar-phosphate backbone advances in the 5’  3’ direction while on the opposite,
complementary strand, the sugar phosphate backbone advances in the 3’  5’ direction.
base pairs (17.2) a hydrogen-bonded pair of bases within the DNA double helix; the standard base pairs
always involve a purine and a pyrimidine; in particular, adenine always base pairs with thymine and
cytosine with guanine.
cap structure (17.4) a 7-methylguanosine unit covalently bonded to the 5’ end of a mRNA by a 5’-5’
triphosphate bridge.
carcinogen (17.7) any chemical or physical agent that causes mutations in the DNA that lead to
uncontrolled cell growth or cancer.
central dogma (17.4) a statement of the directional transfer of the genetic information in cells:
DNA  RNA  Protein.
chromosome (17.2) a piece of DNA that carries all the genetic instructions, or genes, of an organism.
codon (17.4) a group of three ribonucleotides on the mRNA that specifies the addition of a specific amino
acid onto the growing peptide chain.
complementary strands (17.2) the opposite strands of the double helix are hydrogen bonded to one
another such that adenine and thymine or guanine and cytosine are always paired.
degenerate code (17.5) a term used to describe the fact that different triplet codons may be used to
specify a single amino acid.
deletion mutation (17.7) a mutation that results in the loss of one or more nucleotides from a DNA
sequence.
deoxyribonucleic acid (DNA) (17.1) the nucleic acid molecule that carries all of the genetic information
of an organism; the DNA molecule is a double helix composed of two strands, each of which is
composed of phosphate groups, 2’-deoxyribose, and the nitrogenous bases thymine, cytosine, adenine,
and guanine.
deoxyribonucleotide (17.1) a nucleotide composed of a nitrogenous base in -N-glycosidic linkage to the
1’ carbon of the sugar 2’-deoxyribose and with one, two, or three phosphoryl groups esterified at the
hydroxyl of the 5’ carbon.
double helix (17.2) the spiral staircaselike structure of the DNA molecule characterized by two sugarphosphate backbones wound around the outside and nitrogenous bases extending into the center.
elongation factor (17.6) a protein that facilitates the elongation phase of translation.
exon (17.4) the protein-coding sequences of a gene that are found on the final mature mRNA.
initiation factors (17.6) proteins that are required for formation of the translation initiation complex,
which is composed of the large and small ribosomal subunits, the mRNA, and the initiator tRNA.
insertion mutation (17.7) a mutation that results in the addition of one or more nucleotides to a DNA
sequence.
intron (17.4) a noncoding sequence within a eukaryotic gene; it must be removed from the primary
transcript to produce a functional mRNA.
messenger RNA (mRNA) (17.4) an RNA species produced by transcription, which specifies the amino
acid sequence for a protein.
mutagen (17.7) any chemical or physical agent that causes changes in the nucleotide sequence of a gene.
mutation (17.7) any change in the nucleotide sequence of a gene.
nucleotide (17.1) a molecule composed of a nitrogenous base, a five-carbon sugar, and one, two, or three
phosphoryl groups.
peptidyl tRNA binding site of ribosome (P-site) (17.6) a pocket on the surface of the ribosome that
holds the tRNA bound to the growing peptide chain.
phosphodiester bond (17.2)
point mutation (17.7) the substitution of a single base in a codon; this may or may not alter the genetic
code of the mRNA resulting in the substitution of one amino acid in the protein.
poly(A) tail (17.4) a tract of 100-200 adenosine monophosphate units covalently attached to the 3’ end of a
eukaryotic mRNA molecule.
polysome (17.6) complexes of many ribosomes all simultaneously translating a single mRNA.
post-transcriptional modification (17.4) alterations of the primary transcripts produced in eukaryotic
cells; these include addition of the poly(A) tail to the 3’ end of the transcript, addition of the cap
structure to the 5’ end of the mRNA, and RNA splicing.
primary transcript (17.4) the RNA product of transcription in eukaryotic cells, before post-transcriptional
modifications are carried out.
promoter (17.4) the sequence of nucleotides immediately before a gene that is recognized by the RNA
polymerase and signals the start point and direction of transcription.
purine (17.1) a family of nitrogenous bases that are components of DNA and RNA and consist of a sixsided ring fused to a five-sided ring. The common purines in nucleic acids are adenine and guanine.
pyrimidine (17.1) a family of nitrogenous bases that are components of nucleic acids and consist of a
single six- sided ring. The common pyrimidines of DNA are cytosine and thymine; the common
pyrimidines of RNA are cytosine and uracil.
pyrimidine dimer (17.7) two adjacent pyrimidine bases in a DNA strand become covalently linked to one
another; as a result of this ultraviolet light induced damage, there can be no hydrogen bonding to the
opposite, complementary strand.
release factor (17.6) a protein that binds to the termination codons in the empty A-site and causes the
peptidyl transferase to hydrolyze the bond between the peptide and the peptidyl tRNA.
ribonucleic acid (RNA) (17.1) single-stranded nucleic acid molecules that are composed of phosphate
groups, ribose, and the nitrogenous bases uracil, cytosine, adenine, and guanine.
ribonucleotide (17.1) a nucleotide composed of a nitrogenous base in -N-glycosidic linkage to the 1'
carbon of the sugar ribose and with one, two, or three phosphoryl groups esterified at the hydroxyl of
the 5' carbon of the ribose.
ribosomal RNA (rRNA) (17.4) the RNA species that are a structural and functional component of the
small and large ribosomal subunits.
ribosome (17.6) an organelle composed of a large and a small subunit, each of which is made up of
ribosomal RNA and proteins; it functions as a platform on which translation can occur and has the
enzymatic activity that forms peptide bonds.
RNA polymerase (17.4) the enzyme that catalyzes the synthesis of RNA molecules using DNA as a
template.
RNA splicing (17.4) removal of portions of the primary transcript that do not encode protein sequences.
semiconservative replication (20.3) DNA polymerase reads each parental strand of DNA and produces a
complementary daughter strand; thus, all newly synthesized DNA molecules consist of one parental
and one daughter strand.
silent mutation (17.7) a mutation that changes the sequence of the DNA but does not alter the amino acid
sequence of the protein encoded by the DNA.
termination codon (17.6) a triplet of ribonucleotides with no corresponding anticodon on a tRNA. As a
result, translation will end, since there is no amino acid to transfer to the peptide chain.
transcription (17.4) the synthesis of RNA from a DNA template.
transfer RNA (tRNA) (17.4) small RNAs that bind to a specific amino acid at the 3' end and mediate its
addition at the appropriate site in a growing peptide chain; this is accomplished by recognition of the
correct codon on the mRNA by the complementary anticodon on the tRNA.
translation (17.4) the synthesis of a protein from the genetic code carried on the mRNA; the process
occurs on ribosomes and the code of the mRNA is decoded by the anticodon of the tRNA.
translocation (17.6) movement of the ribosome along the mRNA during translation; each time an amino
acid is added to the chain, the ribosome moves to the next codon on the mRNA.