Cytology I: The Nucleus

Question 1

True or False. The nuclear membrane is not continuous with the rough endoplasmic reticulum of the cytoplasm.

Answer 1

False. It is.

Question 2

Describe the nucleolus.

Answer 2

It is a non membrane bound structure, containing fibrils and granules rich in RNA. It is electron dense in the EM. Basophillic.

Question 3

Where is the site of RNA synthesis and initial ribosomal assembly?

Answer 3

The nucleolus.

Question 4

What are long tangled threads consisting of DNA, some RNA, and associated proteins.

Answer 4

A) Chromatin

B) Chromosones

Question 5

What is euchromatin?

Answer 5

Dispersed, extended chromatin. It is present in the lightly stained regions of the nucleus and contains the potion of the genome actively being transcribed.

Question 6

What is condensed, tightly coiled, regions of chromatin?

Answer 6

Heterochromatin.

Question 7

How does heterochromatin appear in the microscope?

Answer 7

It appears electron dense in the EM and extremely basophilic in the LM.

Question 8

Describe a euchromatic nucleus.

Answer 8

It is transcriptionally and metabolically active. Lot of dispersed chromatin and a large well developed nucleus.

Question 9

Describe a heterochromatic nucleus.

Answer 9

It is transcriptionally and metabolically inactive. It has a lot of condensed, coiled chromatin and a small poorly developed nucleolus.

Question 10

Describe Interphase.

Answer 10

1. Nucleus appears normal.
2. DNA is duplicated in the previous S phase.
3. Copies of chromosomes are attached to centromeres.
4. Two pairs of centrioles are present.

Question 11

In what phase do chromosomes condense into a dark coil?

Answer 11

Prophase.

Question 12

How does Prophase end?

Answer 12

With the disappearance of the the nuclear membrane and nucleolus.

Question 13

In which phase do the chromosomes line up at the equator of the cell?

Answer 13

Metaphase.

Question 14

In what phase are chromosomes the most condensed?

Answer 14

Metaphase.

Question 15

When are chromosomes karyotyped?

Answer 15

Metaphase

Question 16

Where do mitotic spindles attach to the chromosome?

Answer 16

They attach at the kinetochore.

Question 17

What happens in Anaphase?

Answer 17

Sister chromatids split apart at the centromere forming two seperate chromosomes. They are then pulled to opposite poles.

Question 18

When do chromosomes begin to uncoil and no longer be visible?

Answer 18

Telophase

Question 19

How does Telophase end?

Answer 19

The nuclear membrane and nucleolus reform.

Question 20

What is karyotyping?

Answer 20

The visualization of the number and morphology of the chromosomes of an individual.

Question 21

What is the use of colcchicine?

Answer 21

It is added to the medium of dividing cells to block the cells in metaphase.

Question 22

What is a Barr Body?

Answer 22

An inactivated X chromosome (sex chromatin)

Question 23

What happens in G1?

Answer 23

Protein + RNA synthesis. Grow and perform specialized functions.

Question 24

When does DNA synthesis and proteins associated with chromatin form?

Answer 24

S phase

Question 25

What happens in G2?

Answer 25

Synthesis of mitotic apparatus.

Question 26

Which cells move rapidly through the cell cycle?

Answer 26

Constantly dividing labile cells. I.e. embryonic, skin, and bone marrow cells.

Question 27

How do quiescent stable cells in G0 go through the cell cycle?

Answer 27

They can re-enter the cell cycle by an appropriate stimulus. I.e. liver cells

Question 28

What are post mitotic cells?

Answer 28

Those cells which have exited the cycle.

Question 29

What are some examples of post mitotic cells.

Answer 29

Neurons, cardiac, and skeletal muscles.

Question 30

Describe the nuclear membrane.

Answer 30

2 unit membranes with nuclear pores