Genetics Chapter 8 part 2

Question 1

[…] transcripts are more stable than bacterial and archaeal transcripts. Eukaryotic genes have [..], which are not found in most bacterial and archaeal genes. In eukaryotes, transcription and translation are separated in […] and […].
These features are all related to […] modification of eukaryotic transcripts.

Answer 1

Eukaryotic; introns; time; location; posttranscriptional

Question 2

The initial eukaryotic gene m R N A is called the […], whereas the fully processed m R N A is called the […]; modifications include: […], […], […].

Answer 2

pre-mRNA; mature mRNA; 5′ capping; 3′ polyadenylation; Intron splicing

Question 3

After the first 20 to 30 nucleotides of mRNA have been synthesized, a special enzyme, […], adds a guanine to the 5′ end of the pre-mRNA. Additional enzyme action […] the newly added guanine and may also methylate adjacent nucleotides of the transcript. The addition of the guanine to the mRNA and subsequent methylation is called […].

Answer 3

guanylyl transferase; methylates; 5′ capping

Question 4

Functions of the 5’ Cap: Protection of mRNA from […]. Facilitating […] of mRNA out of the nucleus. Facilitating subsequent […]. Enhancing […] by orienting the ribosome on the mRNA.

Answer 4

degradation; transport; intron splicing; translation efficiency

Question 5

Termination of transcription by […] is not fully understood. The 3′ end of the mature mRNA is created by […] that removes a section of the 3′ message from pre-mRNA and replaces it with a string of […]. This is thought to be associated with the subsequent […].

Answer 5

R N A pol II; enzyme action; adenines; termination of transcription

Question 6

[…] and […] specificity factor (C P S F) binds near the polyadenylation signal sequence—[…] —which is downstream of the stop codon.

Answer 6

Cleavage; polyadenylation; 5′-A A U A A A-3′

Question 7

The pre-mRNA is cleaved 15 to 30 nucleotides downstream of the […].
The […] releases a fragment of the mRNA, this fragment is later degraded.

Answer 7

polyadenylation signal sequence; cleavage

Question 8

The 3′ end of the cut pre-mRNA undergoes […] addition of 20 to 200 adenines by PAP. After addition of the first 10 adenines, molecules of […] join the poly-A tail and increase the rate of addition of adenines.

Answer 8

enzymatic; Poly-A-Binding protein II

Question 9

Functions of Polyadenylation: Facilitating transport of mature mRNA across the […] to the cytoplasm. Protecting the mRNA from […]. Enhancing translation by enabling the […] of mRNA

Answer 9

nuclear membrane; degradation; ribosomal recognition

Question 10

Polyadenylation and transcription termination are connected by the activity of a specialized […]. After 3′ cleavage and polyadenylation, the resulting residual transcript (uncapped) is still attached to […]. The specialized RNase rapidly digests the residual transcript like a […] aimed at the residual mRNA attached to RNA pol II. RNase catches up to RNA pol II and triggers […] with RNA pol II releasing from the DNA.

Answer 10

RNase; RNA pol II; “torpedo”; termination

Question 11

[…] become part of mature mRNA and encode protein segments while introns are intervening segments that are removed from pre-mRNA. Introns are common in […] genes, rare in bacterial genes and occasionally found in archaeal genes. Pre-mRNA transcript introns are the most common type of intron and are removed by a […] complex. Other types of introns are removed by either […] or a different […] process

Answer 11

Exons; eukaryotic; spliceosome; self-splicing; enzymatic

Question 12

Intron splicing requires great precision to remove […] accurately. Errors in intron removal would lead to incorrect […].
[..] and […] shared the 1993 Nobel Prize for their codiscovery of “split genes”.

Answer 12

intron nucleotides; protein sequences; Roberts; Sharp

Question 13

The presence of intron sequences can be demonstrated by a technique called […]. DNA encoding a gene is [..], denatured, and hybridized to mature mRNA from the same gene. Regions of the DNA where introns are present have no […] region within the mRNA, and thus loop out visibly

Answer 13

R-looping; isolated; complementary

Question 14

Specific short sequences define the […] between introns and exons. The 5′ splice site is at the 5′ […] and contains a consensus sequence with a nearly invariant GU […] at the 5′-most end of the intron. The 3′ splice site at the opposite end of the intron has an […] consensus with a pyrimidine-rich region and a nearly invariant AG at the 3′-most end

Answer 14

junctions; splice site; dinucleotide; 11-nucleotide

Question 15

A third consensus region, called the […], is 20 to 40 nucleotides upstream of the 3′ splice site. It is […] and contains an invariant adenine called the branch point adenine near the 3′ end. Mutation analysis shows that all three consensus sequences are critical for accurate [….].

Answer 15

branch site; pyrimidine-rich; splicing

Question 16

Introns are removed from the pre-mRNA by an […] complex called the spliceosome. The 5′ splice site is cleaved first and a […] is formed when the 5′ intron end binds to the branch point adenine. Then the 3′ splice site is cleaved and the exon ends are […] together.

Answer 16

snRNA-protein; lariat intron structure; ligated together

Question 17

The spliceosome is a large complex made of multiple […] (s n R N P s; U1, U2, and U4 through U6). The composition is dynamic, changing through the steps of […]. […] snRNPs come and go as particular splicing reaction steps are carried out

Answer 17

small nuclear ribonucleoproteins; splicing; Spliceosome

Question 18

[…] appear to be removed one by one, but not necessarily in order
The three steps of pre-mRNA processing are tightly […] The […] (C T D) of RNA polymerase II functions as an assembly platform and regulator of pre-mRNA processing machinery.

Answer 18

Introns; coupled; carboxyl terminal domain

Question 19

Current models suggest that RNA pol II and an array of pre-m R N A processing proteins function as […]. The proteins that carry out capping, intron splicing, and polyadenylation associate with the […] of RNA pol II. Because of this interaction, transcription and […] occur simultaneously.

Answer 19

gene expression machines; CTD; premRNA processing

Question 20

It is common for large […] to express more proteins than there are genes in the genome. For example, human cells produce over 100,000 distinct […] but contain ~22,000 genes. […] transcription-associated mechanisms can explain this

Answer 20

eukaryotic genomes; polypeptides; Three

Question 21

Pre-mRNA can be spliced in […] patterns in different cell types (alternative pre-m R N A splicing). Alternative promoters can initiate […] at distinct +1 start points in different cell types. Alternative localizations of polyadenylation can produce different […] (alternative polyadenylation)

Answer 21

alternative; transcription; mature mRNAs

Question 22

Alternative intron splicing: processing of identical transcripts in different cells can lead to mature m R N A s with different combinations of […] and thus different […]. Approximately 70% of human genes are thought to undergo […]. It is less common in other […] and rare in […].

Answer 22

exons; polypeptides; alternative splicing; animals; plants

Question 23

The human […] gene-related peptide (CT/CGRP) gene exemplifies the process of alternative splicing. The gene contains […] exons with […] alternative polyadenylation sites, one in exon 4 and the other following exon 6. […] cells use the exon 4 polyadenylation site, producing calcitonin. […] cells splice out exon 4 and use the exon 6 polyadenylation site, producing CGRP.

Answer 23

calcitonin/calcitonin; six; two; Thyroid

Question 24

Use of alternative promoters can occur when more than one sequence […] of a gene can initiate transcription. Alternative […] requires more than one polyadenylation signal in a gene. Alternative promoters and alternative polyadenylation are controlled by […] of regulatory proteins in specific cell types

Answer 24

upstream; polyadenylation; variable expression

Question 25

RNAs can contain […] that catalyze their own removal. There are two categories of […] introns: group I and group II. Group I introns were discovered in 1981 in the laboratory of […]. Group I introns are large, self-splicing ribozymes that catalyze their own […] from some mRNAs, and from […] and […] precursors in bacteria, simple eukaryotes, and plants.

Answer 25

introns; self-splicing; Thomas Cech; excision; tRNA; rRNA

Question 26

Group II introns are also self-splicing ribozymes found in transcripts of archaea and bacteria, as well as those of mitochondrial and chloroplast genes in […]. They form very complex […] and their self-splicing takes place in a lariat-like manner

Answer 26

eukaryotes; secondary structures

Question 27

In bacteria, archaea, and eukaryotes, rRNAs are transcribed as […] that are cleaved into smaller molecules by removal of spacer sequences between the rRNA genes. After processing, the rRNAs fold into complex secondary structures and join ribosomal proteins to form the […]. Some chemical modifications of rRNA occur after […] is complete (e.g., methylation)

Answer 27

large precursor molecules; ribosome subunits; transcription

Question 28

Processing of […] is different in bacteria and eukaryotes. All tRNAs have similar […], albeit different nucleotide sequences
Some bacterial tRNAs are produced […] with rRNAs; others are transcribed as part of a large pre-tRNA transcript and then cleaved into […] tRNA molecules
Each eukaryotic tRNA gene is individually […]

Answer 28

tRNA; structure and function; simultaneously; individual; transcribed

Question 29

The number of different t R N A s produced differs among […].
Most produce about 30 to 40 t R N A s, fewer than 61, due to […], a relaxation of “rules” of complementary base pairing at the […] of codons. Some eukaryote genomes do contain all […] possible t R N A genes, one for each codon.

Answer 29

organisms; third-base wobble; third nucleotide; 61

Question 30

Bacterial tRNAs require […] before they can assume their functional role: Many tRNAs are […] from large precursor tRNA transcripts to produce several individual tRNA molecules. […] are trimmed from the 3′ and 5′ ends of the molecule. Certain individual nucleotides are […].

Answer 30

processing; cleaved; Nucleotides; chemically modified

Question 31

t R N A s fold into a precise […] including four double-stranded stems, three of which are capped by single-stranded loops. tRNAs undergo [….] addition of bases, most commonly CCA at the 3′ end. Eukaryotic and archaeal tRNAs undergo […] processing modifications, but eukaryotic pre-tRNAs may also include small introns that are removed

Answer 31

three-dimensional structure; posttranscriptional; similar

Question 32

A second type of RNA editing is […]. This is seen with production of two different […] B proteins from a single gene in human liver and intestinal cells. Base substitution of the mRNA in intestinal cells produces a premature […]. Such premature termination of translation produces a much shorter apolipoprotein B protein in […] compared to liver cells.

Answer 32

base substitution; apolipoprotein; stop codon; intestinal cells

Question 33

In the mid-1980s, RNA editing was uncovered that is responsible for […] of the nucleotide sequence of some mRNAs. In one kind of RNA editing, […] are added with the assistance of a contains a […] which contains a sequence complementary to the mRNA that it edits
Editing may sometimes involve […] of uracils, too

Answer 33

posttranscriptional; uracils; guide RNA (gRNA); deletion