Chapter 17

Question 1

gene expression

Answer 1

The process by which information encoded in DNA directs the synthesis of proteins or, in some cases, RNAs that are not translated into proteins and instead function as RNAs.

Question 2

5′ cap

Answer 2

A modified form of guanine nucleotide added onto the 5′ end of a pre-mRNA molecule.

Question 3

alternative RNA splicing

Answer 3

A type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns.

Question 4

aminoacyl-tRNA synthetase

Answer 4

An enzyme that joins each amino acid to the appropriate tRNA.

Question 5

anticodon

Answer 5

A nucleotide triplet at one end of a tRNA molecule that base-pairs with a particular complementary codon on an mRNA molecule.

Question 6

A site

Answer 6

One of a ribosome’s three 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)

Question 7

coding strand

Answer 7

Nontemplate strand of DNA, which has the same sequence as the mRNA except it has thymine (T) instead of uracil (U)

Question 8

codon

Answer 8

A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.

Question 9

deletion

Answer 9

(1) A deficiency in a chromosome resulting from the loss of a fragment through breakage. (2) A mutational loss of one or more nucleotide pairs from a gene.

Question 10

domain

Answer 10

(1) A taxonomic category above the kingdom level. The three domains are Archaea, Bacteria, and Eukarya. (2) A discrete structural and functional region of a protein.

Question 11

E site

Answer 11

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.)

Question 12

exon

Answer 12

A sequence within a primary transcript that remains in the RNA after RNA processing; also refers to the region of DNA from which this sequence was transcribed.

Question 13

frameshift mutation

Answer 13

A mutation occurring when nucleotides are inserted in or deleted from a gene and the number inserted or deleted is not a multiple of three, resulting in the improper grouping of the subsequent nucleotides into codons.

Question 14

insertion

Answer 14

A mutation involving the addition of one or more nucleotide pairs to a gene.

Question 15

intron

Answer 15

A noncoding, intervening sequence within a primary transcript that is removed from the transcript during RNA processing; also refers to the region of DNA from which this sequence was transcribed.

Question 16

messenger RNA (mRNA)

Answer 16

A type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein. (In eukaryotes, the primary RNA transcript must undergo RNA processing to become mRNA.)

Question 17

missense mutation

Answer 17

A nucleotide-pair substitution that results in a codon that codes for a different amino acid.

Question 18

mutagen

Answer 18

A chemical or physical agent that interacts with DNA and can cause a mutation.

Question 19

mutation

Answer 19

A change in the nucleotide sequence of an organism’s DNA or in the DNA or RNA of a virus.

Question 20

nonsense mutation

Answer 20

A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.

Question 21

nucleotide-pair substitution

Answer 21

A type of point mutation in which one nucleotide in a DNA strand and its partner in the complementary strand are replaced by another pair of nucleotides.

Question 22

point mutation

Answer 22

A change in a single nucleotide pair of a gene.

Question 23

poly-A tail

Answer 23

A sequence of 50−250 adenine nucleotides added onto the 3′ end of a pre-mRNA molecule.

Question 24

polyribosome (polysome)

Answer 24

A group of several ribosomes attached to, and translating, the same messenger RNA molecule.

Question 25

primary transcript

Answer 25

An initial RNA transcript from any gene; also called pre-mRNA when transcribed from a protein-coding gene.

Question 26

promoter

Answer 26

A specific nucleotide sequence in the DNA of a gene that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.

Question 27

P site

Answer 27

One of a 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.)

Question 28

reading frame

Answer 28

On an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis.

Question 29

ribosomal RNA (rRNA)

Answer 29

RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA.

Question 30

RNA polymerase

Answer 30

An enzyme that links ribonucleotides into a growing RNA chain during transcription, based on complementary binding to nucleotides on a DNA template strand.

Question 31

RNA processing

Answer 31

Modification of RNA primary transcripts, including splicing out of introns, joining together of exons, and alteration of the 5′ and 3′ ends.

Question 32

RNA splicing

Answer 32

After synthesis of a eukaryotic primary RNA transcript, the removal of portions of the transcript (introns) that will not be included in the mRNA and the joining together of the remaining portions (exons).

Question 33

signal peptide

Answer 33

A sequence of about 20 amino acids at or near the leading (amino) end of a polypeptide that targets it to the endoplasmic reticulum or other organelles in a eukaryotic cell.

Question 34

signal-recognition particle (SRP)

Answer 34

A protein-RNA complex that recognizes a signal peptide as it emerges from a ribosome and helps direct the ribosome to the endoplasmic reticulum (ER) by binding to a receptor protein on the ER.

Question 35

silent mutation

Answer 35

A nucleotide-pair substitution that has no observable effect on the phenotype; for example, within a gene, a mutation that results in a codon that codes for the same amino acid.

Question 36

spliceosome

Answer 36

A large complex made up of proteins and RNA molecules that splices RNA by interacting with the ends of an RNA intron, releasing the intron and joining the two adjacent exons.

Question 37

start point

Answer 37

In transcription, the nucleotide position on the promoter where RNA polymerase begins synthesis of RNA.

Question 38

TATA box

Answer 38

A DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex.

Question 39

template strand

Answer 39

The DNA strand that provides the pattern, or template, for ordering, by complementary base pairing, the sequence of nucleotides in an RNA transcript.

Question 40

terminator

Answer 40

In bacteria, a sequence of nucleotides in DNA that marks the end of a gene and signals RNA polymerase to release the newly made RNA molecule and detach from the DNA.

Question 41

transcription

Answer 41

The synthesis of RNA using a DNA template.

Question 42

transcription factor

Answer 42

A regulatory protein that binds to DNA and affects the transcription of specific genes.

Question 43

transcription initiation complex

Answer 43

The completed assembly of transcription factors and RNA polymerase bound to a promoter.

Question 44

transcription unit

Answer 44

A region of DNA that is transcribed into an RNA molecule.

Question 45

transfer RNA (tRNA)

Answer 45

An RNA molecule that functions as a translator between nucleic acid and protein languages by picking up a specific amino acid and carrying it to the ribosome, where the tRNA recognizes the appropriate codon in the mRNA.

Question 46

translation

Answer 46

The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule. There is a change of “language” from nucleotides to amino acids.

Question 47

triplet code

Answer 47

A genetic information system in which a series of three-nucleotide-long words specifies a sequence of amino acids for a polypeptide chain.

Question 48

wobble

Answer 48

Flexibility in the base-pairing rules in which the nucleotide at the 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.