L3: Nucleus

Question 1

What is the nucleus?

Answer 1

It is a rounded or elongated structure which is responsible for all the cellular activities and plays an important role in cell division and hereditary.

Question 2

what is the site of the nucleus?

Answer 2

It is found in nearly all cells except RBCs and blood platelets.

Question 3

what is the number of nuclei?

Answer 3

mono: In most of the body cells.

bi: in liver cells and the top cells of the transitional layer of epithelium

multi: in cells like osteoclast and skeletal muscle fibres

Question 4

what is the size of the nucleus?

Answer 4

It may be small, medium-sized, or large. It may reach 25 um like in the ovum and some ganglion cells

Question 5

what is the shape of the nucleus?

Answer 5

it differs according to the type of the cell as it may be rounded, elongated, rod-shaped, bent rod, bilobed, segmented, kidney shaped.

Question 6

what is the position of the nucleus?

Answer 6

it occupies the widest area of the cell and it may be central, eccentric, peripheral, or basal.

Question 7

how does the nucleus appear under LM?

Answer 7

-it appears as a basophilic structure due to its content of nucleic acids.

-appears in two shapes: vesicular (open face) or condensed

Question 8

Describe the vesicular (open face) nucleus

Answer 8

-lightly stained
-its content can be seen
-in highly metabolic cells like liver and nerve cells

Question 9

Describe the condensed nucleus

Answer 9

-Heavily stained
-Its details cant be identified
-in low metabolic cells like small lymphocytes

Question 10

How does the nucleus appear under EM?

Answer 10

consists of 4 parts:-

nucleolus
chromatin
nuclear sap
nuclear membrane

Question 11

what is the nuclear envelope?

Answer 11

It is a double membraned membrane that surrounds the nucleus and separates it from the cytoplasm.

Question 12

how is the nuclear membrane seen under LM?

Answer 12

-It is seen as a monolayer membrane as it is basophilic due to the chromatin associated with it.

Question 13

how is the nuclear membrane seen under EM?

Answer 13

-It is seen as a double membranes membrane that consists of inner and outer layers and is interrupted by nuclear pores.

Question 14

what is the function of the nuclear envelope?

Answer 14

• it separates the nucleus from the cytoplasm
  -it allows the passage of certain substances in and out of the nucleus.

Question 15

what is chromatin?

Answer 15

it is a basophilic material from which chromosomes are formed.

Question 16

what is the structure of chromatin?

Answer 16

it is formed of nucleoprotein

Question 17

what are the types of chromatin?

Answer 17

-extended chromatin and condensed chromatin

Question 18

extended chromatin
(structure-activity-function-LM-EM-distribution)

Answer 18

-Extended parts of chromosomal threads.

-Carries active genes.

-Directs protein synthesis.

-Appears as clear areas (too thin to be seen).

-Could be seen with high magnification and appears as shades of grey.

-Occupies the more central regions of the nucleus.

Question 19

condensed chromatin
(structure-activity-function-LM-EM-distribution)

Answer 19

-Coiled parts of chromosomal threads

-Carries inactive genes

-Doesn’t direct protein synthesis

-Fine or coarse basophilic chromatin granules

-Appears as electron-dense granules

-Peripheral chromatin, Nucleolus associated chromatin. and Chromatin islands.

Question 20

what is the nucleolus?

Answer 20

one or more rounded basophilic bodies present in the interphase nuclei.

Question 21

How is the nucleolus seen under LM?

Answer 21

-its size may reach up to 1um and it is mostly present in protein synthesizing cells.

-not surrounded by a membrane.

-It is basophilic as it contains RNA and chromatin attached to it

Question 22

what is the function of the nucleolus?

Answer 22

1. Synthesis of ribosomal RNA (rRNA).
2. rRNA is conjugated with protein and migrates through the nuclear pores to reach the cytoplasm as ribosome subunits.

Question 23

what are the nuclear changes indicating the death of the cell?

Answer 23

1. Pyknosis: the nucleus becomes homogenous, smaller in size, darker in staining, and eccentric in position.
2. Karyorrhexis: the nucleus is broken into small fragments.
3. Karyolysis: the nucleus dissolves and finally disappears.