Deck 11: The Nucleus

Question 1

The principal difference between eukaryotic and prokaryotic cells is that eukaryotic cells have

A) larger ribosomes.
B) cell walls, whereas prokaryotic cells do not.
C) DNA replication and transcription in the same compartment, whereas prokaryotic cells do not.
D) a nucleus, whereas prokaryotic cells do not.

Answer 1

D

Question 2

The nuclear envelope is continuous with the

A) mitochondrial outer membrane.
B) rough endoplasmic reticulum.
C) Golgi apparatus.
D) plasma membrane.

Answer 2

B

Question 3

The nuclear lamina is built of proteins called

A) lamins.
B) laminins.
C) nucleons.
D) nucleoplasmins.

Answer 3

A

Question 4

Emery-Dreifuss muscular dystrophy and Hutchinson-Gilford progeria are caused by mutations in genes that code for

A) importin or Ran.
B) Polycomb proteins.
C) NF-κB.
D) A-type nuclear lamins or emerin.

Question 5

The filaments of the nuclear lamina are composed of a type of

A) intermediate filament.
B) microtubule.
C) microfilament.
D) thick filament.

Question 6

The nuclear lamina binds to

A) both the inner nuclear envelope membrane and the chromatin.
B) the inner nuclear envelope membrane only.
C) the chromatin only.
D) both the inner and outer nuclear envelope membranes.

Question 7

Lamins are associated with the inner nuclear envelope membrane via

A) GPI anchors on lamins.
B) lipid tails on lamins only.
C) lamin-binding proteins in the nuclear envelope membrane only.
D) lipid tails on lamins and lamin-binding proteins in the nuclear envelope membrane.

Question 8

Nuclear pores are organized with _______ symmetry.

A) sixfold
B) eightfold
C) ninefold
D) tenfold

Question 9

The major pathway for molecules to pass into and out of the nucleus is through

A) gap junctions between the nuclear envelope membranes.
B) porin channels in the nuclear envelope membranes.
C) nuclear pore complexes.
D) diffusion through the membrane bilayers of the nuclear envelope.

Question 10

Small molecules (< 20 kd) enter nuclei by way of

A) passive diffusion through nuclear pore complexes.
B) selective transport through nuclear pore complexes.
C) active transport across the nuclear envelope membranes.
D) passive diffusion across the nuclear envelope membranes.

Question 11

Which of the following is not involved in the transport of RNAs out of the nucleus?

A) Ran
B) Expenditure of chemical energy
C) Small RNAs crossing by passive diffusion
D) Exportins

Question 12

The first nuclear localization signal to be mapped is the signal responsible for the transport of

A) nucleoplasmin.
B) histone H1.
C) lamin B.
D) SV40 T antigen.

Question 13

Nuclear proteins that are stripped of their nuclear localization signal and injected into the cytoplasm of cultured cells will localize

A) to the nucleus.
B) in the cytoplasm.
C) in a ring around the outside of the nuclear envelope.
D) extracellularly.

Question 14

The nuclear localization signal is typically a(n) _______, rich in the amino acids _______.

A) α helix; Pro, Lys, and Arg
B) α helix; Leu, Phe, and Gly
C) short sequence; Lys and Arg
D) short sequence; Pro, Leu, and Gly

Question 15

The nuclear localization signal is recognized by and binds to which protein in the process of nuclear protein import?

A) Ran
B) Importin
C) Exportin
D) The outer fibril protein

Question 16

The directionality of nuclear transport is determined by _______ in the nucleus and _______ in the cytosol.

A) high Ran; low Ran
B) low Ran; high Ran
C) high Ran/GTP; high Ran/GDP
D) high Ran/GDP; high Ran/GTP

Question 17

Export of RNAs from the nucleus occurs primarily by

A) passive diffusion through nuclear pore complexes.
B) cotranscriptional insertion through protein pores of the nuclear envelope membrane.
C) selective transport through nuclear pore complexes.
D) release from the nucleus when it breaks down at mitosis.

Question 18

Which statement about snRNAs is true?

A) They are synthesized in the nucleus and function in the cytoplasm.
B) They are synthesized in the cytoplasm and function in the nucleus.
C) They are synthesized in the nucleus and function in the nucleus without passing into the cytoplasm.
D) They are synthesized in the nucleus, move to the cytoplasm to form functional complexes with proteins, and then return to the nucleus.

Question 19

By restricting the traffic of proteins and RNA across the nuclear envelope, eukaryotic cells can regulate _______ in unique ways.

A) translation and transcription
B) transcription only
C) translation only
D) endocytosis

Question 20

Which statement describing the chromosome conformation capture (3C) technique for chromosome structural analyses is true?

A) Sequences of DNA that are physically distant from each other are chemically linked together.
B) Most DNA-DNA interactions are between sequences on different chromosomes.
C) Sequences separated by a centromere rarely interact with each other.
D) All of the above

Question 21

Highly condensed, transcriptionally inactive chromatin is called

A) euchromatin.
B) heterochromatin.
C) a chromatin domain.
D) histone-containing chromatin.

Question 22

Heterochromatin is normally associated with

A) ribosomes.
B) the nuclear envelope.
C) only a few specific human chromosomes.
D) mutated chromosomes.

Question 23

Chromatin that contains sequences that are transcribed is called

A) euchromatin.
B) a centromere.
C) heterochromatin.
D) a telomere.

Question 24

Chromatin domains are loops of at least _______ base pairs of DNA.

A) 1000
B) 10,000
C) 100,000
D) 1,000,000

Question 25

Newly replicated DNA is located in a few hundred spots in the nucleus because

A) there are a few hundred origins of replication per nucleus.
B) there are a few thousand origins of replication, but only a few hundred are active at any one time.
C) there are a few thousand origins of replication active at any one time, but they are located in a few hundred discrete clusters.
D) there are so many charges drawing the DNA molecules together.

Question 26

Sites of newly replicated DNA can be detected with antibodies if the DNA is labeled with

A) tritiated thymidine.
B) tritiated uridine.
C) bromodeoxyuridine.
D) bromouridine.

Question 27

The nucleolus is the site where _______ is(are) assembled.

A) ribosomal subunits
B) nuclear pores
C) chromatin
D) the nuclear matrix

Question 28

The region of chromosomes that codes for most of the rRNAs is found in the

A) nucleolus.
B) nucleolar organizing region.
C) ribosomal assembly region.
D) ribosomal organizer region.

Question 29

The 5.8S rRNA associates with

A) Cajal bodies.
B) the large subunit of the ribosome.
C) the small subunit of the ribosome.
D) the interface between the large and small subunits of a functional ribosome.

Question 30

The eukaryotic 45S pre-rRNA transcript codes for the

A) 28S rRNA.
B) 28S and 18S rRNAs.
C) 28S, 18S, and 5.8S rRNAs.
D) 28S, 18S, 5.8S, and 5S rRNAs.

Question 31

Most snoRNAs

A) splice cleaved mRNAs.
B) splice cleaved rRNAs.
C) cleave the 45S rRNA.
D) guide regions of rRNAs to modifying enzymes.

Question 32

Eukaryotic ribosomes leave the nucleus as

A) intact 80S ribosomes.
B) intact 70S ribosomes.
C) 40S and 60S ribosomal subunits.
D) 18S and 28S rRNAs.

Question 33

Cleaving of pre-rRNA produces

A) the 28S rRNA.
B) the 18S rRNA.
C) both 28S and 18S rRNAs.
D) the 28S, 18S, and 5.8S rRNAs.

Question 34

The genes encoding 5.8S, 18S, and 28S ribosome RNA are clustered together in

A) tandem arrays located on one chromosome.
B) tandem arrays interspersed with tandem arrays of genes encoding 5S ribosomal RNA.
C) tandem arrays located on three chromosomes.
D) tandem arrays located on five chromosomes.

Question 35

Which of the following is an example of nucleolar involvement in processing of non-rRNAs?

A) Base modification within tRNAs catalyzed by snoRNPs
B) Storage of pre-mRNA splicing factors
C) Gene silencing
D) Proteasomal proteolysis

Question 36

Polycomb proteins consist of _______ complex(es) and are concentrated in Polycomb bodies within the nucleus.

A) 1
B) 2
C) 3
D) either 2 or 3, depending on cell type

Question 37

Polycomb bodies act on _______ regions of chromatin, silencing gene expression.

A) adjacent
B) distant
C) both adjacent and distant
D) very short

Question 38

Polycomb proteins promote heterochromatin formation and gene silencing by

A) acetylating lysine 27 of histone 3.
B) deacetylating lysine 27 of histone 3.
C) methylating lysine 27 of histone 3.
D) methylating lysine 9 of histone 3.

Question 39

Cajal bodies are thought to represent sites of

A) DNA replication.
B) snRNA processing and assembly.
C) large ribosomal subunit assembly.
D) small ribosomal subunit assembly.

Question 40

In eukaryotic cells, the contents of the nucleus are separated from the cytoplasm by the _______.

Question 41

Entry into the nucleus is limited by the _______ and the _______ complexes.

Question 42

Underlying the nuclear envelope is the _______, a fibrous meshwork composed of proteins called _______.

Question 43

Mutations in the fibrous protein underlying the nuclear envelope can cause premature _______, or progeria.

Question 44

Depending on size, molecules can enter the nucleus by the process of _______ or _______.

Question 45

Receptor-dependent protein transport into the nucleus requires the recognition of a _______ on the cargo protein.

Question 46

Proteins called _______ act as receptors for cargo protein import into the nucleus, and proteins called _______ play the corresponding role in export from the nucleus.

Question 47

A major regulatory protein for nuclear import and export of proteins is the small GTPase _______.

Question 48

Transcriptionally active chromatin, which is called _______, is decondensed, while transcriptionally inactive chromatin, which is called _______, is highly condensed.

Question 49

Individual chromosomes occupy distinct _______ within the nucleus.

Question 50

In addition to replication factories, the nucleus contains a number of discrete structures, maintained by protein-protein and protein-RNA interactions, that are referred to as _______.

Question 51

The most prominent nuclear body, the _______, is the site of ribosome production and rRNA processing and synthesis.

Question 52

In humans, pre-ribosomal RNA consists of a large 45S RNA that contains nucleotide sequences corresponding to _______ different individual rRNAs found within ribosomes.

Question 53

In ribosome assembly, _______ that were synthesized in the cytoplasm are assembled into complexes on pre-ribosomal RNA molecules.

Question 54

Nuclear speckles are nuclear bodies that contain _______ and snRNPs.

Question 55

The nuclear envelope is composed of one nuclear membrane and an underlying nuclear lamina.

Question 56

The nuclear pore complexes provide the only known routes through which molecules can travel between the nucleus and the cytoplasm of interphase cells.

Question 57

The activity of some proteins is regulated by controlling their ability to be imported into the nucleus.

Question 58

All molecules found in the nucleus have been transported there via a process that requires ATP.

Question 59

Small nuclear RNAs are synthesized in the nucleus and function there without ever leaving the nucleus.

Question 60

Messenger RNAs are transported through the nuclear pores as ribonucleoprotein particles.

Question 61

Individual chromosomes occupy discrete territories within the nucleus.

Question 62

Inactive, condensed chromatin is called heterochromatin.

Question 63

Chromatin domains appear to represent discrete functional units that independently regulate gene expression.

Question 64

The nucleolus is the site of rRNA synthesis and processing and of ribosomal subunit assembly.

Question 65

Eukaryotic ribosomal RNAs are synthesized as three transcripts, with sizes of 28S, 18S, and 5.8S.

Question 66

Ribosomal proteins are synthesized in the nucleolus and then assembled onto rRNAs.

Question 67

The eukaryotic large ribosomal subunit contains the 28S, 5.8S, and 5S rRNAs, plus many different proteins.

Question 68

The nuclear envelope consists of what four major components?

Question 69

How does the nuclear envelope differ from the membrane of the endoplasmic reticulum?

Question 70

How does the structure of the outer side of the nuclear pore complex differ from that of the inner side?

Question 71

By what mechanism are most nuclear proteins specifically targeted to the nucleus for import?

Question 72

Nuclear localization signals are usually short sequences rich in which amino acids?

Question 73

What is the function of karyopherins?

Question 74

Give one example of how regulation of nuclear protein import is involved in gene regulation.

Question 75

Within the nucleolus, what functions are associated with the fibrillar center, dense fibrillar component, and granular component?

Question 76

Because of the presence of a nuclear envelope, eukaryotes can perform several functions that prokaryotes cannot. Identify one of these functions.

Question 77

How can fluorescence in situ hybridization be used to show that chromosomes occupy distinct domains of space within the nucleus?

Question 78

How does euchromatin differ from heterochromatin with respect to transcription activity?

Question 79

Why is most heterochromatin bound to the periphery of the nucleus?

Question 80

How have FISH approaches been applied to studying the arrangement of distribution of gene-rich chromosomes relative the nuclear periphery versus the center of the nucleus?