BI203 Lecture 16: The Nucleus - Internal Organization Within the Nucleus

Question 1

Chromosomes & chromatin are ____ randomly distributed throughout the nucleus in interphase cells.

Answer 1

NOT

Question 2

Chromatin becomes highly ____ during mitosis to form the compact metaphase chromosomes.
During interphase, most of the chromatin ____ and is distributed throughout the nucleus.

Answer 2

condensed, decondenses

Question 3

Individual chromosomes occupy distinct ____.

Answer 3

territories

Question 4

In interphase, the chromosomes occupy distinct regions and are organized such that ____ activity of a gene is correlated with its position.

Answer 4

transcriptional

Question 5

DNA replication and transcription take place in ____ regions within the nucleus.

This organization was first suggested in 1885 and confirmed in 1984 by studies of ____ chromosomes in ____ salivary glands.

Each chromosome was found to occupy a discrete region of the nucleus, called a ____ ____.

In situ hybridization with fluorescent probes specific for repeated sequences on individual chromosomes has been used to visualize the location of chromosomes within a nucleus.

Answer 5

clustered, polytene, Drosophilia, chromosome territory

Question 6

Chromatin structure is ____ - It can change in coordination with changes in gene expression.

Answer 6

dynamic

Question 7

Some domains are associated with the nuclear lamina (called ____ ____ or LADs).
The genes within LADs are generally transcriptionally ____.
LADS correspond to heterochromatin.

Answer 7

lamina-associated domains, repressed

Question 8

Heterochromatin is localized to the periphery of the ____, where it anchors the chromatin to the ____ ____ at lamina-associated domains (LADs)

Answer 8

nucleus, nuclear lamina

Question 9

Actively transcribed genes are situated at the periphery of ____ ____ (adjacent to interchromosomal domains).

Answer 9

chromosome territories

Question 10

The nucleolus is also surrounded by heterochromatin (called ____ ____ or NADs).
DNA sequences found in NADs substantially overlap with those in LADs.

Answer 10

nucleolus-associated domains

Question 11

The ____ is also surrounded by heterochromatin (called nucleolus-associated domains or NADs).
DNA sequences found in NADs substantially overlap with those in LADs.

Answer 11

nucleolus

Question 12

____ is localized to the periphery of the nucleus, where it anchors chromatin to the nuclear lamina called lamina-associated domains (LADs).

Answer 12

Heterochromatin

Question 13

____ ____ ____ are situated at the periphery of chromosome territories (adjacent to interchromosomal domains).

Answer 13

active transcribed genes

Question 14

Most nuclear processes occur in distinct ____.

Answer 14

regions

Question 15

DNA replication takes place in large complexes called ____ ____, where replication of multiple DNA molecules takes place.

Answer 15

replication factories

Question 16

Transcription occurs at clustered sites (____ ____) that contain newly synthesized RNA.

Coregulated genes, such as ____ genes from different chromosomes, may be transcribed in the same factory.

Answer 16

transcription factories, immunoglobulin

Question 17

____ ____ are organelles within the nucleus that concentrate proteins and RNAs for specific processes.
They are ____ enclosed by membranes; they are dynamic structures maintained by protein-protein and protein-RNA interactions.

Answer 17

nuclear bodies, NOT

Question 18

The ____ functions in rRNA synthesis and ribosome production.

Answer 18

nucleolus

Question 19

The nucleolus contains ~____ copies of the rRNA gene encoding 18S, 5.8S, & 28S rRNA.

Answer 19

200

Question 20

Actively growing mammal cells have 5 to 10 million ____ that must be synthesized each time the cell divides.

Answer 20

ribosomes

Question 21

The 5.8S, 18S, and 28S rRNAs are transcribed as a single unit in the nucleolus by ____ ____ ____, yielding a 45S pre-rRNA.

Answer 21

RNA polymerase I

Question 22

The 5.8S, 18S, and 28S rRNAs are transcribed as a single unit in the nucleolus by RNA polymerase I, yielding a ____ ribosomal precursor RNA.

Answer 22

45S

Question 23

The ____, ____, and ____rRNAs are transcribed as a single unit in the nucleolus by RNA polymerase I, yielding a 45S pre-rRNA.

Answer 23

5.8S, 18S, 28S

Question 24

Transcription of the 5S rRNA takes place outside the nucleolus and is catalyzed by ____ ____ ____.

Answer 24

RNA polymerase III

Question 25

Transcription of the ____ rRNA takes place outside the nucleolus and is catalyzed by RNA polymerase III.

Answer 25

5S

Question 26

Transcription of the 5S rRNA takes place ____ the nucleolus and is catalyzed by RNA polymerase III.

Answer 26

outside

Question 27

Following each cell division, nucleoli become associated with the ____ ____ ____ that contain the 5.8S, 18S, and 28S rRNA genes.

Answer 27

nucleolar organizing regions

Question 28

Transcription of 45S pre-rRNA leads to ____ of small prenucleolar bodies.
In most cells, the initially separate nucleoli then fuse to form a ____ nucleolus.

Answer 28

fusion, single

Question 29

____ ____ - Site of rRNA transcription.

Answer 29

Fibrillar center

Question 30

____ ____ ____ - Site of rRNA processing.

Answer 30

Dense fibrillary component

Question 31

____ ____ - Site of ribosome assembly.

Answer 31

Granular component

Question 32

Size of the ____ depends on the metabolic activity of the cell.

Answer 32

nucleolus

Question 33

Cells actively engaged in translation have larger ____.

Answer 33

nucleoli

Question 34

Nucleoli have ____ regions: fibrillar center, dense fibrillary component, and granular component.

They represent sites of the progressive stages of rRNA transcription, processing, and ribosome assembly.

Answer 34

three

Question 35

Each ____ ____ ____ contains a cluster of tandemly repeated rRNA genes separated by spacer DNA.

The genes are actively transcribed by RNA polymerase I, and their growing RNA chains can be seen in ____ ____.

Answer 35

nucleolar organizing region, electron micrographs

Question 36

____/____ ____ ____ -

Pre-rRNA is processed by a series of cleavages to yield mature rRNA (similar to the action of snRNPs on pre-mRNA).

Answer 36

external/internal transcribed spacers (ETS/ITS)

Question 37

In higher eukaryotes, the primary transcript of rRNA genes is the ____ pre-rRNA.

The pre-rRNA is processed via a series of cleavages, which is similar in all eukaryotes.

Processing of pre-rRNA also includes substantial base modification:
Addition of ____ groups to bases and ribose residues, or the conversion of ____ to ____.

Answer 37

45S, methyl, uridine, pseudouridine

Question 38

Nucleoli have over 300 proteins and 200 ____ ____ ____ (snoRNAs) that function in pre-rRNA processing.

Answer 38

small nucleolar RNAs (snoRNAs)

Question 39

snoRNAs are complexed with proteins, forming ____. They form processing complexes (similar to spliceosomes on the pre-mRNA).

Answer 39

snoRNPs

Question 40

____ families of snoRNAs associate with different proteins, catalyzing either ribose methylation or pseudouridine formation.

Answer 40

Two

Question 41

snoRNAs have sequences complementary to ____ or ____ rRNA, which include the sites of base modification.

Answer 41

18S, 28S

Question 42

Formation of ribosomes requires assembly of the pre-rRNA with ribosomal proteins and ____ rRNA.

Answer 42

5S

Question 43

____ ____ are involved in the assembly of snRNPs and other RNA-protein complexes.

snRNPs assemble and mature inside ___ ___.

Answer 43

Cajal bodies

Question 44

Cajal bodies play a role in the assembly of ____, which replicates the ends of chromosomal DNA.

Cajal bodies promote assembly of the RNA-protein telomerase complex and facilitate its delivery to telomeres.

Answer 44

telomerase

Question 45

Following assembly and maturation in Cajal bodies, snRNPs are then transferred to ____, which contain splicing factors.

____ are recruited to actively transcribed genes where pre-mRNA processing occurs.

Answer 45

speckles