chapter 11

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

100,000

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

2

Eukaryotic ribosomes leave the nucleus as

40S and 60S ribosomal subunits

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

A-type nuclear lamins or emerin

Ran GAP association with cytoplasmic filaments of the nuclear pore results in the conversion of the nucleotide that is bound to nuclear Ran into

GDP

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

SV40 T antigen

What is the function of karyopherins?

They transport macromolecules into or out of the nucleus.

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

a nucleus, whereas prokaryotic cells do not

mRNA molecules are exported from the nucleus to the cytoplasm via

a recruited protein complex

The mass of the nuclear pore complex is estimated to be

about 30 times that of a ribosome

Which of the following factors contributes to the relative ease of determining how pre-rRNA is processed?

all of the above

Which of the following is a possible intermediate during pre-rRNA processing?

an RNA molecule containing 5.8S + 28S rRNAs

The directionality of nuclear protein import is determined by

an unequal distribution of Ran/GTP

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

base modification within tRNAs catalyzed by snoRNPs

Typically, nuclear localization signals are composed primarily of

basic amino acids

snRNPs that are responsible for pre-mRNA splicing are assembled and stored in

both Cajal bodies and speckles

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

both adjacent and distant

The nuclear lamina binds to

both the inner nuclear envelope membrane and the chromatin.

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

bromodeoxyuridine

Initial steps in the assembly of functional snRNPs occur in the

cytoplasm

Nuclear pores are organized with _______ symmetry.

eightfold

The outer nuclear membrane is contiguous with the

endoplasmic reticulum

Chromatin that contains sequences that are transcribed is called

euchromatin

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

false

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

false

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

false

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

false

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

false

Ribosomes contain one copy each of 5.8S, 18S, and 28S rRNA. The major mechanism ensuring that each is produced in equal molar amounts is the

grouping of the DNA sequences encoding each rRNA into a single rRNA gene

Most snoRNAs function as

guide RNAs

Highly condensed, transcriptionally inactive chromatin is called

heterochromatin

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

importin

Chromosomes are distributed in the nucleus

in distinct territories

The nuclear basket protein complex is a component of the nuclear pore complex found

inside the nucleus

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

intermediate filament

The fibrous proteins underlying the inner nuclear membrane are

lamins

The nuclear lamina is built of proteins called

lamins

Which of the following are not compartments in the nucleus?

lipid droplets

Lamins are associated with the inner nuclear envelope membrane via

lipid tails on lamins and lain-binding proteins in the nuclear envelope membrane

Polycomb proteins promote heterochromatin formation and gene silencing by

methylating lysine 27 of histone 3

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

nuclear pore complexes

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

nucleolar organizing region

The most prominent nuclear body is the

nucleolus

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

passive diffusion through the nuclear pore complexes

An important step in the import of the transcription factor NF- κB into the nucleus is regulated by a

protease

The nucleolus is the site where

ribosomal RNA is transcribed and ribosomes are partially assembled

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

ribosomal subunits

The nuclear envelope is continuous with the

rough endoplasmic reticulum

Export of RNAs from the nucleus occurs primarily by

selective transport through nuclear pore complexes

Protein transport into the nucleus occurs by

selective transport through the nuclear pores.

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

sequences separated by a centromere rarely interact with each other

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

short sequence; Lys and Arg

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

small RNAs crossing by passive diffusion

Cajal bodies are thought to represent sites of

snRNA processing and assembly

Most snoRNAs

splice cleaved rRNAs

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

tandem arrays located five chromosomes

Cleaving of pre-rRNA produces

the 28S, 18S and 5.8S rRNAs

The 5.8S rRNA associates with

the large subunit of the ribosome

Heterochromatin is normally associated with

the nuclear envelope

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

there are a few thousand origins of replication active at any one time, but they are located in a few hundred discrete clusters

Which statement about snRNAs is true?

they are synthesized in the nucleus, move to the cytoplasm to form functional complexes with proteins, and then return to the nucleus

Which of the following processes does not take place in the nucleus?

translation

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

translation and transcription

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

true

Inactive, condensed chromatin is called heterochromatin.

true

Individual chromosomes occupy discrete territories within the nucleus.

true

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

true

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

true

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

true

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

true