Ultra structure of Nucleus sana khan

“Nucleus” is a Latin word meaning Kernel

It is the “CONTROL CENTER” of the cell

It was First cell organelle to be discovered

It is membrane bound organelle found in

eukaryotic cells

Main functions are

- to maintain the integrity of genes

- to control the activities of the cell by regulating

gene expression .

Intorductions

Average diameter of nucleus is 6um, which

occupies around 10% of cell volume

Nuclear Envelope

Nuclear Pores and complex

Nuclear lamina

Chromosomes & Chromatin

Nucleolus

Nucleoplasm

Structure

Also known as perinuclear envelope, nuclear

membrane or karyotheca

Encloses the nucleus and separates the cell's

genetic material from the surrounding cytoplasm

It is a lipid bilayer

Consists two cellular membranes, an inner &

outer membrane, arranged parallel to one another

and separated by 10-50(nm) of space.

The membranes of the nuclear envelope serve as

a barrier that keeps ions, solutes ,and macro-

molecules from passing freely between the

nucleus and cytoplasm.

Nuclear envelope

0uter 0uter MembraneMembrane

6 nm thick

Faces cytoplasm and is continuous at certain sites

with the RER

A loosely arranged mesh of intermediate filaments

(vimentin)

Ribosome stud the cytoplasmic surface of the outer

nuclear membrane

Ribosome synthesize proteins that enter the

perinuclear cisterna (space between two membranes

10-50nm wide)

Faces the nuclear material

Primary site for location of inner nuclear

membrane proteins IMP

Inner membrane proteins – used during formation

of nuclear envelope during mitosis as well as some

role in transcriptional activity.

Outer and inner membranes are fused at the

nuclear pore complex sites

Inner Membrane is supported underneath by

Nuclear lamina.

Inner membraneInner membrane

Network of intermediate filaments, The filament of

the nuclear lamina are approximately 10 nm in

diameter and composed of polypeptides, called

lamins. Composed primarily of lamins A, B1, B2 and

C

Helps in organizing the nuclear envelope and

perinuclear chromatin ,Also plays a role in DNA

elongation phase

Essential during mitotic events where,

Phosphorylation of lamins leads to disassembly, and

dephosphorylation results in reassembly of the

nuclear envelope.

Apoptosis a highly regulated process in which

nuclear lamina is disassembled following proteolytic

activity of caspase protein.

Nuclear laminaNuclear lamina

Nuclear pores are aqueous channels through the

nuclear envelope

Composed of multiple proteins called “nucleoporins.”

Have molecular weight of 125 KD

Nucleus of a cell has 3000 - 4000 pores

Pores are formed by fusion of outer and inner nuclear

membranes

Nuclear Apore complex permits passive movement

across the nuclear envelope via 9-11nm channels

by simple diffusion

Nuclear pores and complex

Allows free passage of water soluble molecules

Most proteins, ribosomal subunits and RNA are

transported via transport factors called

KARYOPHERINS

a) Importins –that mediate movement into the

nucleus

b) Exportins –that mediate movement out of nucleus

Nuclear pore complex is composed of nearly 100

proteins, arranged in eight-fold symmetry around the

margin of the pore.

NUCLEAR PORE

STRUCTURE

Cytoplasmic ring

Nucleoplasmic ring

Middle ring.

Nucleoplasmic side-

Nuclear basket

Cytoplasmic side -

displays fibers

Nucleoplasm is the protoplasm within the nuclear

envelope. Nucleus is filled with a semi-solid granular slightly

acidic ground matrix called as nucleoplasm. The chromatin fibres and nucleolus remain

suspended in the nucleoplasm. Major component of nucleoplasm are

nucleoproteins. Both nucleic acids, RNA and DNA

are present in the nucleoplasm that may occur

either as polymers or monomeric nucleotides. Basic proteins like nucleoprotamines, histones and

acidic proteins (non-histone proteins).

NucleoplasmNucleoplasm

► Chromatin are coiled elongated thread like fibres

visible during the interphase and can readily take

up basic stains like basic fuschin.► During cell division where these chromatin fibres

get thickened to form a ribbon like structure called

“chromosomes”.► chromatin is a nucleoprotein complex composed of

DNA and proteins and very small quantity of RNA.► Chromatin are of 2 types:

Heterochromatin and euchromatin.

Chromatin & Chromatin & chromosomechromosome

Heterochromatin: The deeply stained and highly

condensed region of the chromatin that occurs

around the nucleolus or at the periphery of the

nucleus.

heterochromatin is transcriptionally inactive and

metabolically inert.

Euchromatin is the lightly stained and diffused region

of the chromatin that is transcriptionally active. 

Metaphase chromatin- the chromatin becomes

more and more condensed and compact, making

the chromosome visible with a classic four arm

structure, having a pair of sister chromatids

attached at centromere. Humans have 23 pairs of chromosomes- 22 are

autosomes & 2 sex chromosomes.

Nucleolus is the discrete densely stained

structure found in nucleus

It is a nuclear inclusion that is not surrounded

by a membrane

Present in cells that are actively synthesizing

proteins

Its size depends on metabolic activity of cell

Average size -5.5µm in diameter.

It is generally detectable when the cell is in

interphase

Synthesis of rRNA and its assembly into

ribosome precursors- main function

More than one nucleolus can be present in the

nucleus

Nucleolus

Conclusively cell nucleus is the storehouse of Conclusively cell nucleus is the storehouse of everything what a cell shall do in future, since it everything what a cell shall do in future, since it

handles the gene expression and overall handles the gene expression and overall metabolism of cellmetabolism of cell

thus calledthus called “DIRECTOR OF CELL”“DIRECTOR OF CELL”

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