Chapter 12: Genetic Code and Transcription

Question 1

True or False. The code is unambiguous – each triplet specifies only a single amino acid

Answer 1

True

Question 2

Enables the production of synthetic mRNAs.

Answer 2

Polynucleotide phosphorylase

Question 3

Type of RNA that is composed of only one type of ribonucleotides.

Answer 3

RNA Homopolymers

Question 4

Type of RNA with two or more different ribonucleoside diphosphates added in combination to form the synthetic mRNA.

Answer 4

RNA Heteropolymers

Question 5

Almost all amino acids are specified by two, three, or four different codons.

Answer 5

Degeneracy

Question 6

The first two letters of a codon coding for one amino acid are the same, with only the third differing.

Answer 6

Wobble hypothesis

Question 7

Either U or C is often present in the second position of triplets that specify what type of amino acids, including valine and alanine, among others.

Answer 7

hydrophobic amino acids

Question 8

A codon with either G or C in the second position always specifies what kind of amino acid?

Answer 8

hydrophilic amino acids

Question 9

Significance of an “ordered” code?

Answer 9

It buffers the potential effect of mutation on protein function.

Question 10

When the chemical constitution of genes and their encoded proteins, the linear sequence of triplet codons corresponds precisely with the linear sequence of amino acids in each protein. This phenomenon is called?

Answer 10

Colinearity

Question 11

True or False. Codon UGA, normally specifying termination, encodes tryptophan during translation in yeast and human mitochondria.

Answer 11

True

Question 12

True or False. In human mitochondria, AUA, which normally specifies isoleucine, directs the internal insertion of methionine.

Answer 12

True

Question 13

There may be several points of initiation in one mRNA thus, creating several different reading frames within the same mRNA, and specifying more than one polypeptide. These mRNAs are called?

Answer 13

Overlapping genes

Question 14

The process by which RNA molecules are synthesized on a DNA template.

Answer 14

Transcription

Question 15

The enzyme that catalyzes the synthesis of RNA molecule has the same general substrate requirements as does DNA polymerase, the major exception being that the substrate nucleotides contain the ribose rather than the deoxyribose form of the sugar.

Answer 15

RNA polymerase

Question 16

The active form of the RNA polymerase is made of subunits alpha, beta, beta prime, and sigma.

Answer 16

holoenzyme

Question 17

Which subunits provide the catalytic basis and active site for transcription in RNA polymerase?

Answer 17

beta and beta prime

Question 18

What molecule serves as the substrate for the RNA polymerase?

Answer 18

nucleoside trisphosphate (NTPs)

Question 19

RNA polymerase converts nucleoside triphosphate

to what molecule as it is being added to the growing mRNA.

Answer 19

nucleoside monophosphate

Question 20

Nucleotides are linked during synthesis by what kind of bond?

Answer 20

3′-to-5′ phosphodiester bonds

Question 21

Which DNA is being transcribed during transcription?

Answer 21

template strand

Question 22

The DNA strand that is not involved in the transcription

Answer 22

Partner strand

Question 23

The site of this initial binding is established when the RNA polymerase sigma subunit recognizes specific DNA sequences called what?

Answer 23

Promoters

Question 24

Point in the DNA sequence at which transcription actually begins.

Answer 24

Transcription Start Site

Question 25

These sequences are similar (homologous) in different genes of the same organism or in one or more genes of related organisms. They usually exist as promoter sequences or as telomere sequences.

Answer 25

Consensus Sequences

Question 26

This bacterial promoter is located 10 nucleotides (Pribnow Box) upstream from the site of initial transcription.

Answer 26

TATAAT sequence

Question 27

This bacterial promoter is located 35 nucleotides upstream (the −35 region).

Answer 27

TTGACA sequence

Question 28

Promoter sequence in eukaryotes.

Answer 28

TATA box

Question 29

The insertion of the first 5′-ribonucleoside triphosphate, which is complementary to the first nucleotide at the start site of the DNA template strand.

Answer 29

Initiation

Question 30

Subsequent ribonucleotide complements are inserted and linked by phosphodiester bonds as RNA polymerization proceeds. This process is called?

Answer 30

Elongation

Question 31

The unique sequence of nucleotides in the termination region causes the newly formed transcript to fold back on itself, forming what is called?

Answer 31

hairpin secondary structure

Question 32

A large hexameric protein that physically interacts with the growing RNA transcript and serves as termination region.

Answer 32

termination factor, R (rho)

Question 33

A large mRNA is produced that encodes more than one protein. Products of genes transcribed in this fashion are usually all needed by the cell at the same time, so this is an efficient way to transcribe and subsequently translate the needed genetic information.

Answer 33

Polycistronic mRNA (found in bacteria)

Question 34

What type of mRNA is occurring in eukaryotes?

Answer 34

Monocistronic mRNA

Question 35

Alteration of the primary RNA transcript to produce mature eukaryotic mRNA. The initial processing step involves the addition of a 5′ cap and a 3′ tail to most transcripts destined to become mRNAs.

Answer 35

RNA processing

Question 36

Such RNA molecules are of variable but large size and are complexed with proteins, forming heterogeneous nuclear ribonucleoprotein particles (hnRNPs). Immature RNA transcript.

Answer 36

Pre-RNA

Question 37

Pre-RNA is part of a group of molecules found only in the nucleus referred to as?

Answer 37

Heterogeneous nuclear RNA (hnRNA)

Question 38

Initiation of transcription of eukaryotic genes requires that the compact chromatin fiber, characterized by nucleosome coiling, must be uncoiled and the DNA made accessible to RNA polymerase and other regulatory proteins. This tran sition is referred to as?

Answer 38

Chromatin Remodeling

Question 39

Responsible for the transcription of a wide range of genes in eukaryotes

Answer 39

RNA polymerase II (RNAP II)

Question 40

Determines where RNAP II binds to the DNA and where it begins copying the DNA into RNA.

Answer 40

Core-promoter (TATA box in eukaryotes)

Question 41

o Located about 30 nucleotide pairs upstream (−30) from the start point of transcription. It is the cis-acting core-promoter element in Eukaryotic genes.

Answer 41

TATA Box (or the Goldberg-Hogness box)

Question 42

Facilitate RNAP II binding and, therefore, the initiation of transcription.

Answer 42

Trans-acting factors (transcription factors)

Question 43

This category of transcription factors is absolutely required for all RNAP II-mediated transcription.

Answer 43

General transcription factors (GTFs)

Question 44

What general transcription factor (GTFs) is involved with human RNAP II binding?

Answer 44

TFIID (binds to TATA box)

Question 45

Once the initial binding of TFIID to DNA occurs, the other general transcription factors, along with RNAP II, bind sequentially to TFIID, forming what structure?

Answer 45

Pre-initiation complex

Question 46

These molecules influence the efficiency or the rate of RNAP II transcription initiation.

Answer 46

Transcriptional activators and repressors

Question 47

Posttranscriptional modification of eukaryotic RNA transcripts destined to become mRNAs occurs at the 5′-end of these molecules, where a molecule cap is added. What molecule is being described?

Answer 47

7-methylguanosine (7-mG)

Question 48

What posttranscriptional molecule is added after the 3′-end of the initial transcript is cleaved enzymatically at a position some 10 to 35 ribonucleotides from a highly conserved AAUAAA sequence?

Answer 48

poly-A tail

Question 49

Nucleotide sequences that are not expressed in the amino acid sequence of the proteins they encode. These internal DNA sequences are represented in initial RNA transcripts, but they are removed before the mature mRNA is translated.

Answer 49

Intervening sequences (introns)

Question 50

Part of pre-RNA that are retained and expressed.

Answer 50

Exons

Question 51

These genes appear to be deprived of introns.

Answer 51

Genes coding for histones and interferon

Question 52

True or False. In bacterial tRNA, a specific endonuclease recognizes the intron termini and excises the intervening sequences. Then RNA ligase seals the exon ends to complete each splicing.

Answer 52

True

Question 53

Represented by introns that are part of the primary transcript of rRNAs, require no additional components for intron excision; the intron itself is the source of the enzymatic activity necessary for removal.

Answer 53

Group I introns

Question 54

Type of RNAs that are capable of catalytic activity

Answer 54

Ribozymes

Question 55

Primary RNA and tRNA transcript in mitochondria and chloroplasts where self-excision is also the case.

Answer 55

Group II introns

Question 56

Mediates the splicing reactions in nuclear-derived pre-RNA.

Answer 56

Spliceosome

Question 57

5’ end of the intron in nuclear-derived pre-RNA

Answer 57

Donor sequence

Question 58

3’ end of the intron in nuclear-derived pre-RNA

Answer 58

Acceptor sequence

Question 59

Loop of intron produced after spliceosome mediated splicing.

Answer 59

Lariat

Question 60

Produced by a group of similar but nonidentical mRNAs resulting from a gene spliced in more than one way.

Answer 60

Isoforms

Question 61

The nucleotide sequence of a pre-mRNA is actually changed prior to translation. This process is called?

Answer 61

RNA editing

Question 62

An RNA editing process whereby nucleotides are added to or subtracted from the total number of bases.

Answer 62

Insertion/Deletion Editing

Question 63

This molecule directs the insertion/deletion editing in Trypanosoma mitochondrial RNA.

Answer 63

guide RNA (gRNA)

Question 64

In this editing method, identities of individual nucleotide bases are altered. This is also used in some nuclear-derived eukaryotic RNAs and is prevalent in mitochondrial and chloroplast RNAs transcribed in plants.

Answer 64

Substitution Editing