AP Bio Midterm Key Terms Ch. 17

Question 1

5’ cap

Answer 1

The 5’ end of a pre-mRNA molecule modified by the addition of a cap of guanine nucleotide.

Question 2

A site

Answer 2

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 3

alternative RNA splicing

Answer 3

A type of 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 correct tRNA.

Question 5

anticodon

Answer 5

A specialized base triplet at one end of a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule.

Question 6

base-pair substitution

Answer 6

A type of point mutation; the replacement of one nucleotide and its partner in the complementary DNA strand by another pair of nucleotides.

Question 7

codon

Answer 7

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 8

deletion

Answer 8

(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 9

domain

Answer 9

(1) A taxonomic category above the kingdom level. The three domains are Archaea, Bacteria, and Eukarya. (2) An independently folding part of a protein.

Question 10

E site

Answer 10

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 11

exon

Answer 11

A coding region of a eukaryotic gene. Exons, which are expressed, are separated from each other by introns.

Question 12

frameshift mutation

Answer 12

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.

Question 13

insertion

Answer 13

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

Question 14

intron

Answer 14

A noncoding, intervening sequence within a eukaryotic gene.

Question 15

messenger RNA (mRNA)

Answer 15

A type of RNA, synthesized from DNA, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein.

Question 16

missense mutation

Answer 16

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.

Question 17

mutagen

Answer 17

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

Question 18

mutation

Answer 18

A rare change in the DNA of a gene, ultimately creating genetic diversity.

Question 19

nonsense mutation

Answer 19

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

Question 20

one gene–one polypeptide hypothesis

Answer 20

The premise that a gene is a segment of DNA that codes for one polypeptide.

Question 21

P site

Answer 21

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 22

point mutation

Answer 22

A change in a gene at a single nucleotide pair.

Question 23

poly-A tail

Answer 23

The modified end of the 3’ end of an mRNA molecule consisting of the addition of some 50 to 250 adenine nucleotides.

Question 24

polyribosome (polysome)

Answer 24

An aggregation of several ribosomes attached to one messenger RNA molecule.

Question 25

primary transcript

Answer 25

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

Question 26

promoter

Answer 26

A specific nucleotide sequence in DNA that binds RNA polymerase and indicates where to start transcribing RNA.

Question 27

reading frame

Answer 27

The way a cell’s mRNA-translating machinery groups the mRNA nucleotides into codons.

Question 28

ribosomal RNA (rRNA)

Answer 28

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.

Question 29

ribosome

Answer 29

A cell 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.

Question 30

ribozyme

Answer 30

An enzymatic RNA molecule that catalyzes reactions during RNA splicing.

Question 31

RNA polymerase

Answer 31

An enzyme that links together the growing chain of ribonucleotides during transcription.

Question 32

RNA processing

Answer 32

Modification of RNA before it leaves the nucleus, a process unique to eukaryotes.

Question 33

RNA splicing

Answer 33

The removal of noncoding portions (introns) of the RNA molecule after initial synthesis.

Question 34

signal peptide

Answer 34

A stretch of amino acids on a polypeptide that targets the protein to a specific destination in a eukaryotic cell.

Question 35

signal-recognition particle (SRP)

Answer 35

A protein-RNA complex that recognizes a signal peptide as it emerges from the ribosome.

Question 36

spliceosome

Answer 36

A complex assembly that interacts with the ends of an RNA intron in splicing RNA, releasing the intron and joining the two adjacent exons.

Question 37

TATA box

Answer 37

A promoter DNA sequence crucial in forming the transcription initiation complex.

Question 38

template strand

Answer 38

The DNA strand that provides the template for ordering the sequence of nucleotides in an RNA transcript.

Question 39

terminator

Answer 39

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.

Question 40

transcription

Answer 40

The synthesis of RNA on a DNA template.

Question 41

transcription factor

Answer 41

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

Question 42

transcription initiation complex

Answer 42

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

Question 43

transcription unit

Answer 43

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

Question 44

transfer RNA (tRNA)

Answer 44

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.

Question 45

translation

Answer 45

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

Question 46

triplet code

Answer 46

A set of three-nucleotide-long words that specify the amino acids for polypeptide chains.

Question 47

wobble

Answer 47

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.