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