Genes and Proteins

Question 1

7-methylguanosine cap

Answer 1

modification added to the 5’ end of pre-mRNAs to protect mRNA from degradation and assist translation

Question 2

Aminoacyl tRNA synthetase

Answer 2

enzyme that “charges” tRNA molecules by catalyzing a bond between the tRNA and a corresponding amino acid

Question 3

Anticodon

Answer 3

three-nucleotide sequence in a tRNA molecule that corresponds to an mRNA codon

Question 4

CAAT box

Answer 4

(GGCCAATCT) essential eukaryotic promoter sequence involved in binding transcription factors

Question 5

Central dogma

Answer 5

states that genes specify the sequence of mRNAs, which in turn specify the sequence of proteins

Question 6

Codon

Answer 6

three consecutive nucleotides in mRNA that specify the insertion of an amino acid or the release of a polypeptide chain during translation

Question 7

Colinear

Answer 7

in terms of RNA and protein, three “units” of RNA (nucleotides) specify one “unit” of protein (amino acid) in a consecutive fashion

Question 8

Consensus

Answer 8

DNA sequence that is used by many species to perform the same or similar functions

Question 9

Core enzyme

Answer 9

prokaryotic RNA polymerase consisting of α, α, β, and β’ but missing σ; this complex performs elongation

Question 10

Degeneracy

Answer 10

(of the genetic code) describes that a given amino acid can be encoded by more than one nucleotide triplet; the code is degenerate, but not ambiguous

Question 11

Downstream

Answer 11

nucleotides following the initiation site in the direction of mRNA transcription; in general, sequences that are toward the 3’ end relative to a site on the mRNA

Question 12

Exon

Answer 12

sequence present in protein-coding mRNA after completion of pre-mRNA splicing

Question 13

FACT

Answer 13

complex that “facilitates chromatin transcription” by disassembling nucleosomes ahead of a transcribing RNA polymerase II and reassembling them after the polymerase passes by

Question 14

GC-rich box

Answer 14

(GGCG) nonessential eukaryotic promoter sequence that binds cellular factors to increase the efficiency of transcription; may be present several times in a promoter

Question 15

Hairpin

Answer 15

structure of RNA when it folds back on itself and forms intramolecular hydrogen bonds between complementary nucleotides

Question 16

Holoenzyme

Answer 16

prokaryotic RNA polymerase consisting of α, α, β, β’, and σ; this complex is responsible for transcription initiation

Question 17

Initiation site

Answer 17

nucleotide from which mRNA synthesis proceeds in the 5’ to 3’ direction; denoted with a “+1”

Question 18

Initiator tRNA

Answer 18

in prokaryotes, called tRNAMetf
; in eukaryotes, called tRNAi; a tRNA that interacts with a start codon, binds directly to the ribosome P site, and links to a special methionine to begin a polypeptide chain

Question 19

Intron

Answer 19

non–protein-coding intervening sequences that are spliced from mRNA during processing

Question 20

Kozak’s rules

Answer 20

determines the correct initiation AUG in a eukaryotic mRNA; the following consensus sequence must appear around the AUG: 5’-GCC(purine)CCunderlineAUGend underlineG-3’; the bolded bases are most important

Question 21

Nonsense codon

Answer 21

one of the three mRNA codons that specifies termination of translation

Question 22

Nontemplate strand

Answer 22

strand of DNA that is not used to transcribe mRNA; this strand is identical to the mRNA except that T nucleotides in the DNA are replaced by U nucleotides in the mRNA

Question 23

Octamer box

Answer 23

(ATTTGCAT) nonessential eukaryotic promoter sequence that binds cellular factors to increase the efficiency of transcription; may be present several times in a promoter

Question 24

Peptidyl transferase

Answer 24

RNA-based enzyme that is integrated into the 50S ribosomal subunit and catalyzes the formation of peptide bonds

Question 25

Plasmid

Answer 25

extrachromosomal, covalently closed, circular DNA molecule that may only contain one or a few genes; common in prokaryotes

Question 26

Poly-A tail

Answer 26

modification added to the 3' end of pre-mRNAs to protect mRNA from degradation and assist mRNA export from the nucleus

Question 27

Polysome

Answer 27

mRNA molecule simultaneously being translated by many ribosomes all going in the same direction

Question 28

Preinitiation complex

Answer 28

cluster of transcription factors and other proteins that recruit RNA polymerase II for transcription of a DNA template

Question 29

Promoter

Answer 29

DNA sequence to which RNA polymerase and associated factors bind and initiate transcription

Question 30

Reading frame

Answer 30

sequence of triplet codons in mRNA that specify a particular protein; a ribosome shift of one or two nucleotides in either direction completely abolishes synthesis of that protein

Question 31

rho-dependent termination

Answer 31

in prokaryotes, termination of transcription by an interaction between RNA polymerase and the rho protein at a run of G nucleotides on the DNA template

Question 32

rho-independent

Answer 32

termination sequence-dependent termination of prokaryotic mRNA synthesis; caused by hairpin formation in the mRNA that stalls the polymerase

Question 33

RNA editing

Answer 33

direct alteration of one or more nucleotides in an mRNA that has already been synthesized

Question 34

Shine-Dalgarno sequence

Answer 34

(AGGAGG); initiates prokaryotic translation by interacting with rRNA molecules comprising the 30S ribosome

Question 35

Signal sequence

Answer 35

short tail of amino acids that directs a protein to a specific cellular compartment

Question 36

Small nuclear RNA

Answer 36

molecules synthesized by RNA polymerase III that have a variety of functions, including splicing pre-mRNAs and regulating transcription factors

Question 37

Splicing

Answer 37

process of removing introns and reconnecting exons in a pre-mRNA

Question 38

Start codon

Answer 38

AUG (or rarely, GUG) on an mRNA from which translation begins; always specifies methionine

Question 39

TATA box

Answer 39

conserved promoter sequence in eukaryotes and prokaryotes that helps to establish the initiation site for transcription

Question 40

Template strand

Answer 40

strand of DNA that specifies the complementary mRNA molecule

Question 41

Transcription bubble

Answer 41

region of locally unwound DNA that allows for transcription of mRNA

Question 42

upstream

Answer 42

nucleotides preceding the initiation site; in general, sequences toward the 5' end relative to a site on the mRNA