Chapter 17 Flashcards
One gene-one polypeptide hypothesis
Premise that a gene is a segment of DNA that codes for one polypeptide
Transcription
The synthesis of RNA under the direction of DNA; the synthesis of RNA on a DNA template
Messenger RNA (mRNA)
A type of RNA, synthesized from DNA, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein
Translation
The actual synthesis of a polypeptide, which occurs under the direction of mRNA
Ribosomes
Sites of translation that are complex particles that facilitate the orderly linking of amino acids into polypeptide chains
organelle constructed in the nucleolus and functioning as the site of protein synthesis in the cytoplasm; consists of rRNA and protein molecules, which make up two subunits
RNA processing
Modification of RNA before it leaves the nucleus, a process unique to eukaryotes
Primary transcript
An initial RNA transcript; also called pre-mRNA when transcribed from a protein-coding gene
Triplet code
A set of three-nucleotide-long words that specify the amino acids for polypeptide chains
Template strand
The DNA strand that provides the template for ordering the sequence of nucleotides in an RNA transcript
Codons
A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code
Reading frame
The way a cell’s mRNA-translating machinery groups the mRNA nucleotides into codons
RNA polymerase
An enzyme that links together the growing chain of ribonucleotides during transcription
Promoter
A specific nucleotide sequence in DNA that binds RNA polymerase and indicates where to start transcribing RNA
Terminator
In prokaryotes, a special sequence of nucleotides in DNA that marks the end of a gene. It signals RNA polymerase to release the newly made RNA molecule, which then departs from the gene
Transcription unit
A region of a DNA molecule that is transcribed into an RNA molecule
Transcription factors
A regulatory protein that binds to DNA and stimulates transcription of specific genes
Transcription initiation complex
The completed assembly of transcription factors and RNA polymerase bound to the promoter
TATA box
A promoter DNA sequence crucial in forming the transcription initiation complex
5’ cap
The 5’ end of a pre-mRNA molecule modified by the addition of a cap of guanine nucleotide
poly-A tail
The modified end of the 3’ end of an mRNA molecule consisting of the addition of of some 50 to 250 adenine nucleotides
RNA splicing
The removal of noncoding portions (introns) of the RNA molecule after initial synthesis
Introns
A noncoding, intervening sequence within a eukaryotic gene
Exons
A coding region of a eukaryotic gene. Exons, which are expressed, are seperated from each other by introns
Spliceosome
A complex assembly that interacts with the ends of an RNA intron in splicing RNA, releasing the intron and joining the two adjacent exons
Ribozymes
An enzyme-like RNA molecule that catalyzes reactions during RNA splicing
Alternative RNA splicing
A type of regulation at the RNA-processing level in which different mRNA molecules are are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns
Transfer RNA (tRNA)
An RNA molecule that functions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognizing the appropriate codons in the mRNA
Anticodon
A specialized base triplet at one end of a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule
Aminoacyl-tRNA synthase
An enzyme that joins each amino acid to the correct tRNA
Wobble
A violation of the base pairing rules in that the third nucleotide (5’ end) of a tRNA anticodon can form hydrogen bonds with more than one kind of base in the third position (3’ end) of a codon
Ribosomal RNA (rRNA)
The most abundant type of RNA, which together with proteins forms the structure of ribosomes, Ribosomes coordinate the sequential coupling of tRNA molecules to mRNA codons
P site
One of ribosome’s three binding sites for tRNA during translation. The P site holds the tRNA carrying the growing polypeptide chain. (P stands for peptidyl tRNA)
A site
One of a ribosome’s 3 binding sites for tRNA during translation. the A site holds the tRNA carrying the next amino acid to be added to the polypeptide chain (A stands for aminoacyl tRNA)
E site
One of a ribosome’s three binding sites for tRNA during translation. The E site is the place where discharged tRNAs leave the ribosome (E stands for exit)
Polyribosomes / polysomes
An aggregation of several ribosomes attached to one messenger RNA molecule
Signal peptide
A stretch of amino acids on a polypeptide that targets the protein to a specific destination in a eukaryotic cell
Signal-recognition particle (SRP)
A protein-RNA complex that recognizes a signal peptide as it emerges from the ribosome
Point mutations
A change in a gene at a single nucleotide pair
Missense mutations
The most common type of mutation, a base-pair substitution in which the new codon makes sense in that it still codes for an amino acid
Nonsense mutation
A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein
Insertion
A mutation involving the addition of one or more nucleotide pairs to a gene
Deletion
- A deficiency in a chromosome resulting from the loss of a fragment through breakage
- A mutational loss of one or more nucleotide pairs from a gene
Frameshift mutation
A mutation occurring when the number of nucleotides inserted or deleted is not a multiple of three, resulting in the improper grouping of the following nucleotides into codons
Mutagens
A chemical or physical agent that interacts with DNA and causes a mutation
Domains
- A taxonomic category above the kingdom level
2. An independently folding part of a protein
Mutations
A change in the DNA of a gene, ultimately creating genetic diversity
Base-pair substitution
A type of point mutation; the replacement of one nucleotide and its partner in the complementary DNA strand by another pair of nucleotides
