The document provides information about the structure and function of the nucleus in eukaryotic cells. It discusses that: 1) Most eukaryotic cells contain a single nucleus, though some contain multiple nuclei like muscle and liver cells. The nuclei contain genetic material and can be seen under light microscopes after staining. 2) The nucleus functions to compartmentalize the cell, store and replicate genetic material, and control gene expression and cell metabolism. Cells without a nucleus cannot replicate, grow, or survive for long. 3) The main nuclear structures are the nuclear envelope, nuclear pores, nucleolus, and chromatin. The nuclear envelope separates the nucleus from the cytoplasm, and nuclear pores allow transport between them

1. TEM of red blood cell and platelet.
The nuclei of skeletal muscle cells under light
microscope.
Slime mould fruiting bodies.
The number of nuclei in each macrocyst of amoeba
Dictyostelids are variable.
TEM of a mammalian
tissue culture cell.

2. 2.2.2 Nucleus

3. Objectives
• Understand the structure of nucleus
• Understand the function of nucleus

4. Nucleus
• Nucleus (plural nuclei), originated from Latin word nucleus or
nuculeus, meaning kernel or seed.
• Most eukaryotes have one nucleus, exceptions include:
• No nucleus – mature red blood cell, platelets
• Two or more nuclei – skeletal muscle cells, osteoclast 破骨細胞, hepatocytes
(liver cells 肝細胞), pseudoplasmodium (a crowd of single-celled amoebae of
the groups Acrasiomycota or Dictyosteliida)
After staining, the nuclei are visible
under light microscope.

5. Function of nucleus
• Cell compartmentalization
• Storage and replication of genetic
materials.
• Control centre of genetic
expression and metabolism in the
cells.
• Cell without a nucleus cannot
replicate or grow.
• Artificially enucleated cell (nucleus
removed) cannot live for long.
Maturing RBC still required a nucleus.
Enucleation is used in the cloning process.

6. Primary structure of nucleus
• Main structure:
• Nuclear envelope (nuclear
membrane) 核膜
• Nuclear pore 核孔
• Nucleolus 核仁
• Chromatin 染色质

7. Nuclear envelope and nuclear pores
• Nuclear envelope is a
phospholipid bilayer
membrane barrier that
separates the nucleus from the
cytoplasm in eukaryotes.
• Nuclear pores are pores on the
nuclear envelope that allow
transport of molecules across
the nuclear envelope.

8. Nuclear pore protein complex controls the movement of
molecules across nuclear envelope.
Nuclear pore is not just a pore

9. Quiz
• The structure of the nucleus can be described as
a. enclosed in a cell membrane
b. enclosed in a nuclear envelope
c. composed of cytoplasm
d. composed of cytoplasmic organelles

10. Nucleolus
• from late Latin, diminutive of Latin
nucleus ‘inner part, kernel’
• Largest and most prominent structure of
nucleus.
• Made of proteins, DNA and RNA.
• The site ribosomal RNA synthesis and
ribosome assembly
• Ribosome is a particle containing both
RNA and associate proteins. Ribosome is
the site of protein synthesis.

11. Chromatin
• Primary formed with DNA and protein.
• Chromatin is a “basophil" (acid that like
base components) which can be
stained into a deep-blue or purple
colour with alkaline dyes such as
methylene blue 亚甲蓝.
• When the cell is not dividing, the
chromatin stays as long filament.
• When the cell is dividing, the
chromatin is condensed into
chromosome.

12. Conclusion
• Nucleus stores genetic information and control gene expression.
• Nuclear envelope is a phospholipid bilayer membrane barrier that
separate the nucleus from the cytoplasm.
• Nuclear pore allow movement of molecules across the nuclear
envelope.
• Nucleolus is the major site of ribosomal RNA synthesis.
• Chromatin are condensed DNA strands (with the help of protein) that
are further condensed into chromosome during cell division.

13. Short Quiz
• Draw and label a nucleus. (2 marks)
• Till 9.15am

14. Quiz
• One function of a nucleus in the cell is to
a. digest lipids
b. produce ATP
c. produce secretory vesicles
d. control and coordinate cellular activities

15. Quiz
• In the nucleus, DNA is wrapped within proteins. This structure is
known as
a. chromatin
b. cytoplasmic organelles
c. DNA molecules
d. nucleoli