Denniston, 8e

Glossary of Key Terms in Chapter Twenty

aminoacyl tRNA (20.6) the transfer RNA covalently linked to its cognate amino acid.

aminoacyl tRNA binding site of ribosome (A-site) (20.6) a pocket on the surface of a ribosome that holds the aminoacyl tRNA during translation.

aminoacyl tRNA synthetase (20.6) an enzyme that recognizes one tRNA and covalently links the appropriate amino acid to it.

anticodon (20.4) 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 (20.2) 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 pair (20.2) 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.

bioinformatics (20.10) an interdisciplinary field that uses computer information sciences and DNA technology to devise methods for understanding, analyzing, and applying DNA sequence information.

cap structure (20.4) a 7-methylguanosine unit covalently bonded to the 5’ end of a mRNA by a 5’-5’ triphosphate bridge.

carcinogen (20.7) any chemical or physical agent that causes mutations in the DNA that lead to uncontrolled cell growth or cancer.

central dogma (20.4) a statement of the directional transfer of the genetic information in cells:

DNA  RNA  Protein.

chromosome (20.2) a piece of DNA that carries all the genetic instructions, or genes, of an organism.

cloning vector (20.8) a DNA molecule that can carry a cloned DNA fragment into a cell and that has a replication origin that allows the DNA to be replicated abundantly within the host cell.

codon (20.4) a group of three ribonucleotides on the mRNA that specifies the addition of a specific amino acid onto the growing peptide chain.

complementary strands (20.2) 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 (20.5) a term used to describe the fact that different triplet codons may be used to specify a single amino acid.

deletion mutation (20.7) a mutation that results in the loss of one or more nucleotides from a DNA sequence.

deoxyribonucleic acid (DNA) (20.1) 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 (20.1) 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.

DNA polymerase III (20.3) the enzyme that catalyzes the polymerization of daughter DNA strands using the parental strand as template.

double helix (20.2) the spiral staircaselike structure of the DNA molecule characterized by two sugar-phosphate backbones wound around the outside and nitrogenous bases extending into the center.

elongation factor (20.6) a protein that facilitates the elongation phase of translation.

eukaryote (20.2) an organism having cells containing a true nucleus enclosed by a nuclear membrane and having a variety of membrane-bound organelles that segregate different cellular functions into different compartments.

exon (20.4) the protein-coding sequences of a gene that are found on the final mature mRNA.

genome (20.2) the complete set of genetic information in all the chromosomes of an organism.

hybridization (20.8) a technique for identifying DNA or RNA sequences that is based on specific hydrogen bonding between a radioactive probe and complementary DNA or RNA.

initiation factors (20.6) 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 (20.7) a mutation that results in the addition of one or more nucleotides to a DNA sequence.

intron (20.4) a noncoding sequence within a eukaryotic gene; it must be removed from the primary transcript to produce a functional mRNA.

lagging strand (20.3) the DNA strand that is replicated discontinuously from many RNA primers.

leading strand (20.3) the DNA strand that is replicated continuously from a single RNA primer.

messenger RNA (mRNA) (20.4) an RNA species produced by transcription, which specifies the amino acid sequence for a protein.

mutagen (20.7) any chemical or physical agent that causes changes in the nucleotide sequence of a gene.

mutation (20.7) any change in the nucleotide sequence of a gene.

nucleosome (20.2) the first level of chromosome structure consisting of a strand of DNA wrapped around a small disk of histone proteins.

nucleotide (20.1) 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) (20.6) a pocket on the surface of the ribosome that holds the tRNA bound to the growing peptide chain.

point mutation (20.7) 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 (20.4) a tract of 100-200 adenosine monophosphate units covalently attached to the 3’ end of a eukaryotic mRNA molecule.

polysome (20.6) complexes of many ribosomes all simultaneously translating a single mRNA.

post-transcriptional modification (20.4) 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 (20.4) the RNA product of transcription in eukaryotic cells, before post-transcriptional modifications are carried out.

prokaryote (20.2) an organism with simple cellular structure in which there is no true nucleus enclosed by a nuclear membrane and there are no true membrane-bound organelles in the cytoplasm.

promoter (20.4) 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 (20.1) a family of nitrogenous bases that are components of DNA and RNA and consist of a six-sided ring fused to a five-sided ring. The common purines in nucleic acids are adenine and guanine.

pyrimidine (20.1) 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 (20.7) 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 (20.6) 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.

replication fork (20.3) the point at which new nucleotides are added to the growing daughter DNA strand.

replication origin (20.3) the region of a DNA molecule where DNA replication always begins.

restriction enzyme (20.8) a bacterial enzyme that recognizes specific nucleotide sequences on a DNA molecule and cuts the sugar-phosphate backbone of the DNA at or near that site.

ribonucleic acid (RNA) (20.1) single-stranded nucleic acid molecules that are composed of phosphate groups, ribose, and the nitrogenous bases uracil, cytosine, adenine, and guanine.

ribonucleotide (20.1) 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) (20.4) the RNA species that are a structural and functional component of the small and large ribosomal subunits.

ribosome (20.6) 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 (20.4) the enzyme that catalyzes the synthesis of RNA molecules using DNA as a template.

RNA splicing (20.4) 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 (20.7) 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 (20.6) 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 (20.4) the synthesis of RNA from a DNA template.

transfer RNA (tRNA) (20.4) 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 (20.4) 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 (20.6) 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.