The nucleus
the nucleus is the storage compartment for dna that code for protein synthesis(it carries genetic information
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*general features of the nucleus
the nucleui of different cells vary in shape,size and number:
-shape:the nucleus may be oval,rounded,kidney shaped ,elongated or segmented
number:most cells have one nucleus "mononucleated", some of them have two nuclei"binucleated"
and others have more than 2 nuceui and socalled "multinucleated"
all nucleui have the same components:
1-nuclear envelope
2- nuclear matrix
3-chromatin
4-nucleolus
4-nucleolus
1-the nuclear envelope
-with light microscope
it appears as basophilic line because there are chromatin attached
.to its inner aspect and ribosomes attached to its outer aspect
-with electron microscope:
the nuclear envelope consists of two membranes (outer and inner membranes)they are 8nm thick :
the outer membrane: is continuous with the rough endoplasmic reticulum and is covered by ribosomes.
the inner membrane:has attached peripheral chromatin and it is supported by intermediate filaments called( nuclear lamina).
-separated by a narrow space called (perinuclear space) this space is 25 nm wide .
*the nuclear envelope has 3000-4000 tiny circular openings called (nuclear pores) .a nuclear pore is 80-100nm in diameter .the inner and outer nuclear membranes fuse at the periphery of each nuclear pore.
a nuclear pore is not just an opening in the nuclear envelope but it represents a complex in the following sentence there is a description to this complex
the nuclear pore complex:
it's a short cylindrical channel crossing from the the inside of the nucleus into the cytoplasm this cylinder have two protein rings one of them faces the cytoplasm and so called (cytoplasmic ring) and the other one faces the nucleus and so called the (nuclear ring)
from the cytoplasmic ring there are filaments protrude into the cytoplasm and from the nuclear ring there are also extending filaments but unlike the filaments of the cytoplasmic ring there form a basket like structure which extends into the nucleus.
can you tell me now what the function of the nuclear envelope and why there are nuclear pore complexes?
the answer is very easy the nuclear envelope acts as a wall that surround the nucleus and segregates its content from the cytoplasm and so the nuclear pore complex acts as a doorway which allows exchange of ions and other molecules like histones and ribosomal RNA subunits between the nucleus and the cytoplasm.
the nuclear matrix contains fibrillar structure "nuclear lamina" which supports the nucleus and gives it its specific shape ,this nuclear lamina is attached to inner surface of the nuclear envelope there are fibrous network extending from the nuclear lamina towards the nucleolus to support it.
this nuclear matrix also provides a medium for chromosomal duplication and gene transcription.
this chromatin is formed of DNA ,histones and non-histone proteins(these proteins have a function in organization of the structure and function of the chromatin.
with light microscope:
it appears as a rounded basophilic masses because of the high content of rRNA.
with electron microscope:
it appears as an irregular mass which is not bounded by a membrane
, it contains nuclear sap as the nucleus and this sap forms electron light areas under the electron microscope
,DNA molecules which carry the genes of the rRNA formation it forms a pale stained area inside the nucleolus called the "nuclear organizer regions,
areas contain newly formed rRNA called "pars fibrosa",
areas contain ribosomes subunit called pars granulosa.
a nuclear pore is not just an opening in the nuclear envelope but it represents a complex in the following sentence there is a description to this complex
the nuclear pore complex:
it's a short cylindrical channel crossing from the the inside of the nucleus into the cytoplasm this cylinder have two protein rings one of them faces the cytoplasm and so called (cytoplasmic ring) and the other one faces the nucleus and so called the (nuclear ring)
from the cytoplasmic ring there are filaments protrude into the cytoplasm and from the nuclear ring there are also extending filaments but unlike the filaments of the cytoplasmic ring there form a basket like structure which extends into the nucleus.
can you tell me now what the function of the nuclear envelope and why there are nuclear pore complexes?
the answer is very easy the nuclear envelope acts as a wall that surround the nucleus and segregates its content from the cytoplasm and so the nuclear pore complex acts as a doorway which allows exchange of ions and other molecules like histones and ribosomal RNA subunits between the nucleus and the cytoplasm.
2-the nuclear matrix"nuclear sap":
it's a colloidal solution in which the chromatin is suspended,it contains also proteins,metabolites ,enzymes and minerals.the nuclear matrix contains fibrillar structure "nuclear lamina" which supports the nucleus and gives it its specific shape ,this nuclear lamina is attached to inner surface of the nuclear envelope there are fibrous network extending from the nuclear lamina towards the nucleolus to support it.
this nuclear matrix also provides a medium for chromosomal duplication and gene transcription.
3-chromatin:
it's a basophilic material from which the chromosomes are composed during cell division .this chromatin is formed of DNA ,histones and non-histone proteins(these proteins have a function in organization of the structure and function of the chromatin.
4-the nucleolus:
it's a rounded structure which is very rich in RNA.with light microscope:
it appears as a rounded basophilic masses because of the high content of rRNA.
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| nuleolus with electron microscope |
it appears as an irregular mass which is not bounded by a membrane
, it contains nuclear sap as the nucleus and this sap forms electron light areas under the electron microscope
,DNA molecules which carry the genes of the rRNA formation it forms a pale stained area inside the nucleolus called the "nuclear organizer regions,
areas contain newly formed rRNA called "pars fibrosa",
areas contain ribosomes subunit called pars granulosa.
