molecular biology chapter 15
polyribosome
enable a cell to make many copies of a polypeptide very quickly
frameshift mutation
mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide
Messenger RNA
RNA molecule that carries copies of instructions for the assembly of amino acids into proteins from DNA to the rest of the cell
Missense mutations
still code for an amino acid, but not the correct amino acid
promoter
the DNA sequence where RNA polymerase attaches
transcription initiation complex
the completed assembly of transcription factors and RNA polymerase 2 bound to a promoter
central dogma
the concept that cells are governed by a cellular chain of command: DNA --> RNA --> protein
E site
the exit site, where discharged tRNAs leave the ribosome
primary transcript
the initial RNA transcript from any gene prior to processing
in a eukaryotic cell translation
the nuclear envelope separates transcription from translation
TATA box
A DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex.
deletion
A change to a chromosome in which a fragment of the chromosome is removed.
insertion
A mutation involving the addition of one or more nucleotide pairs to a gene.
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.
aminoacyl-tRNA synthetase
An enzyme that joins each amino acid to the appropriate tRNA.
Alternative RNA splicing
Genes giving rise to two or more different polypeptides depending upon which segments are treated as exons.
Once researchers identified DNA as the molecule responsible for transmitting heritable traits, they asked how information was transferred from the DNA in the nucleus to the site of protein synthesis in the cytoplasm. Which of the following statements correctly describes the mechanism of information transfer that accomplishes this task in eukaryotes?
Messenger RNA is transcribed from a single gene and transfers information to the cytoplasm, where protein synthesis takes place.
poly-A tail
Modified end of the 3' end of an mRNA molecule consisting of the addition of some 50 to 250 adenine nucleotides.
introns
Noncoding segments of nucleic acid that lie between coding sequences.
Which answer correctly compares prokaryotic and eukaryotic codons?
Organisms utilize codons that are nearly universal among all organisms.
RNA splicing
Process by which the introns are removed from RNA transcripts and the remaining exons are joined together.
5' cap
The 5' end of a pre-mRNA molecule modified by the addition of a cap of guanine nucleotide.
template strand
The DNA strand that provides the template for ordering the sequence of nucleotides in an mRNA transcript.
Two mRNAs (mRNA X and mRNA Y) are synthesized with the same exon sequences but poly-A tails of very different lengths. mRNA X is 7,500 bases long. mRNA Y is 6,900 bases long. The mRNA's are added to separate in vitro translation mixtures containing radioactive methionine and the reactions are allowed to proceed for 30 minutes. When the mixtures are analyzed which of the following outcomes will most likely occur?
The mRNA X mixture will contain more radioactive proteins than the mRNA Y mixture.
reading frame
The way a cell's mRNA-translating machinery groups the mRNA nucleotides into codons
Which of the following statements is true about protein synthesis in prokaryotes?
Translation can begin while transcription is still in progress.
CRISPR-Cas9
a bacterial system that can be used either to produce a mutation in a specific gene or to correct a mutation that is already present
signal peptide
a sequence of about 20 amino acids at or near the leading end of the polypeptide
Triplet code
a series of nonoverlapping, three-nucleotide words
gene editing
altering genes in a specific way
signal-recognition particle
binds to the signal peptide and brings the signal peptide and its ribosome to the ER
Ribozymes
catalytic RNA molecules that function as enzymes and can splice RNA
nonsense mutations
change an amino acid codon into a stop codon; most lead to nonfunctional protein
point mutations
changes in just one nucleotide pair of a gene
mutations
changes in the genetic information of a cell
spliceosomes
consist of a variety of proteins and several small nuclear ribonucleoproteins (snRNPs) that recognize the splice sites
George Beadle and Edward Tatum
exposed bread mold to X-rays, creating mutants that were unable to survive on minimal media
extrons
expressed sequence of DNA; codes for a protein
Archibald Garrod
first to suggest that genes dictate phenotypes through enzymes that catalyze specific chemical reactions
wobble
flexible pairing at the third base of a codon
anticodon
group of three bases on a tRNA molecule that are complementary to an mRNA codon
silent mutations
have no effect on the amino acid produced by a codon because of redundancy in the genetic code
Transcription factors
help guide the binding of RNA polymerase and the initiation of transcription
P site
holds the tRNA that carries the growing polypeptide chain
A site
holds the tRNA that carries the next amino acid to be added to the chain
Adrian Srb and Norman Horowitz
identified three classes of arginine-deficient mutants
Terminator
in bacteria, the sequence signaling the end of transcription
mutagens
physical or chemical agents that can cause mutations
Domains
proteins often have a modular architecture consisting of discrete regions
initiation factors
proteins that bring in the large subunit that completes the translation initiation complex
nucleotide-pair substitution
replaces one nucleotide and its partner with another pair of nucleotides
gene expression
the process by which DNA directs protein synthesis, includes two stages: transcription and translation
Ribosomes
the sites of translation
coding strand
the strand of DNA that is not used for transcription and is identical in sequence to mRNA, except it contains uracil instead of thymine
transcription unit
the stretch of DNA that is transcribed
Transcription
the synthesis of RNA using information in the DNA
Translation
the synthesis of a polypeptide, using the information in the mRNA
transfer RNA
transfers amino acids to the growing polypeptide in a ribosome
in prokaryotes translation
translation of mRNA can begin before transcription has finished
ribosomal RNA
type of RNA that combines with proteins to form ribosomes
RNA polymerase
which pries the DNA strands apart and joins together the RNA nucleotides