Ch. 3 - The Nucleus

Question 1

Nucleus

Answer 1

The command center of the cell
Contains the code for all of a cell’s enzymes and proteins
Stores the genetic information
Largest structure within a cell

Question 2

What are the components of the nucleus?

Answer 2

Nuclear envelope
Chromatin
Nucleolus

Question 3

Chromatin

Answer 3

A mass of DNA and associated proteins

Two types can be distinguished via microscopy, heterochromatin and euchromatin

Question 4

Nucleolus

Answer 4

Specialized subdomain of the nucleus

Contains the genes for pre-rRNA

Question 5

Nuclear envelope

Answer 5

Forms a selectively permeable barrier between nuclear and cytoplasmic components
Two concentric membranes separated by a perinuclear space

Question 6

Perinuclear space

Answer 6

The narrow space between the two concentric membranes of the nuclear envelope
This space and the outer nuclear membrane are continuous with the RER

Question 7

Nuclear lamina

Answer 7

A highly organized meshwork of proteins that is closely associated with the inner nuclear membrane
Stabilizes the nuclear envelope

Question 8

Lamins

Answer 8

Class of intermediate filament proteins that bind to membrane proteins and associate with chromatin in nondividing cells

Question 9

Nuclear pore complexes

Answer 9

Bridge the inner and outer nuclear membranes

Regulate movement of macromolecules between the nucleus and cytoplasm in both directions simultaneously

Question 10

Nucleoporins

Answer 10

Various core proteins of a nuclear pore complex

Eightfold symmetry around the lumen

Question 11

How is heterochromatin visualized with the light microscope? Electron microscope?

Answer 11

Intensely basophilic clumps (light)

Coarse, e- dense material (e-)

Question 12

How is euchromatin visualized with the light microscope? Electron microscope?

Answer 12

Lightly stained basophilic areas (light)

Finely dispersed granular material (e-)

Question 13

Heterochromatin

Answer 13

Highly condensed chromatin
DNA is tightly coiled
Less accessible for transcription

Question 14

Euchromatin

Answer 14

Finely dispersed chromatin
Contains regions of the DNA undergoing active transcription
More prominent in metabolically active cells
Typically more active in protein synthesis

Question 15

Nucleosome

Answer 15

The structural unit of DNA and histones

Has a core of 8 small histones wrapped around DNA of ~150 bp

Question 16

Barr body

Answer 16

A small, dense mass of heterochromatin present in females but not in males
Aka “sex chromatin”
One of the two X chromosomes

Question 17

Chromatid

Answer 17

Each long DNA double helix and its associated proteins

Question 18

Chromosome

Answer 18

Two chromatids held tougher by complexes of cohesin proteins

Question 19

The members of each chromosomal pair are called _______ because, although from different parents, they contain allele of the same genes.

Answer 19

homologous

Question 20

Cells of most tissues (somatic cells) are considered _______ because they contain pairs of chromosomes.

Answer 20

diploid

Question 21

Diploid cell are referred to as _______.

Answer 21

2n

Question 22

Germ cells are _______, with half the diploid number of chromosomes, each pair having been separated during meiosis.

Answer 22

haploid

Question 23

Germ cells

Answer 23

Sperm cells and mature oocytes

Haploid

Question 24

Karotyping

Answer 24

Chromosomal analysis where the condensed chromosomes of one nucleus may be photographed by light microscopy and rearranged to produce a karotype in which stained chromosomal bands can be analyzed

Question 25

What causes the intense basophilia of the nucleolus?

Answer 25

Densely concentrated rRNA that is transcribed, processed, and complexed into ribosomal subunits in the nucleoli

Question 26

Cell cycle

Answer 26

Regular sequence of events that result in new cells

Question 27

What are the four distinct phases of the cell cycle?

Answer 27

1. G1 phase (part of interphase) 2. S phase (part of interphase) 3. G2 phase (part of interphase) 4. M-phase (and cytokinesis)

Question 28

M phase

Answer 28

Cell division that results in clones

Question 29

G1 phase

Answer 29

The time gap between mitosis and DNA replication Cellular content is duplicated, not chromosomes Period of active RNA and protein synthesis Cell volume, reduced in half by mitosis, is returned to normal volume

Question 30

S phase

Answer 30

Synthesis phase The period of DNA synthesis Chromosome duplication Histone synthesis

Question 31

G2 phase

Answer 31

The gap between DNA duplication and the next mitosis Cell grows and prepares for mitosis by accumulating proteins needed Checks for errors

Question 32

What are the phases of M phase?

Answer 32

1. Mitosis 2. Prophase 3. Metaphase 4. Anaphase 5. Telophase

Question 33

G0 phase

Answer 33

Postmitotic cells that stop differentiating and specialize In a state of arrest Stem cells live in this phase

Question 34

Mitogens or Growth factors

Answer 34

Protein signals from the extracellular environment that activate cycling in post mitotic G0 cells Bind to cell surface receptors and trigger a cascade of kinase signaling in the cells

Question 35

Prophase

Answer 35

Nucleolus disappears and chromosomes are visible | At the centromere, kinetochores serve as a site for microtubule attachment