Nucleus

General features of nucleiA-Major components

1-nuclear envelope2-Nuclear Sap

3-one to several nucleoli4-Nuclear chromatins

B-nuclear function

1-In heredity(store house for gentic information)

2-Cell division(nucleus regulates the processes of cell division

3-Controlling all cellular function

C-Nuclear Morphology

1-Nuclear size: small,medium,large2-Number per cell: one nuclus,two nuclei

(liver cells,superficial cells of transitional epithelium)&many nuclei (osteoclast cells of bone&skeletal muscle cells

3-shape : round,oval,flattened,rod-shaped,kidney shape,segmented

Nuclear location:basal,central or eccentric

Nuclear Structures

Structures of nucleus

Four components1-nuclear envelope

2-nuclear sap3-nucleolus

4-Nuclear chromatin

1-Nuclear envelope

Dark basophilic membrane which surrounds the nucleus

LM: appears as single dark membranea-Inner fibrillar membrane(rich in chromatin

fibersb-outer granular membrane(rich in ribosomes)

c-nuclear pores(formed nuclear membrane complex which is formed of peripheral spoks&cenral plug this plug diaphragm which regulate the passage of protein from cytoplasm to enter the nucleus

High mag TEM of a nucleolus

Pars fibrosa/granulosa (dense black) and

fibrillar center (arrow)

2-Nuclear Sap

It is acolloidal clear solution,it is formed of

nucleoproteins,enzymes,phosphors,potassium&calciumTwo type of nuclei

1 -open face nucleus: large amount of nuclear sap present in liver cells

2 -condensed nucleus: less amount of nuclear sap(lymphocyte)

Function of nuclear sap1 -provide amedium in which ribonucleic acid(Ri,t&m

RNA)2-Move towards the nuclear pores

3-nucleolus:

basophilic mass formed of RNA&DNA

The nucleolus may enlarge in size in protein forming cells in rapidly growing cancer cells

LM: dark basophilic massFunction of the nucleolus

It forms rRNA&mRNA

4-Chromatin material

basophilic particles&chromosomes are formed during cell division

Structures: are formed mainly of nucleoprotein which is formed of DNA nound to basic protein called histones

Stain:basophilic due to presence of DNA

LM: basophilic granules

There are two type of chromatin

1-Euchromatin(active chromatin2-Heterochromatin(In active)

1-Euchromatin:

Invisible by LMVery lightly with basic stain

Most active chromatinControl protein synthesis

2-Heterochromatin:

inactive chromatinVisible by LM as cours granules

Appears as masses of nucleoprotein called nucleosomes

Stain dark with basic stainThey do not dirct any protein

synthesis

Function of chromatin

1-guides protein synthesis inside the cell

2-stores the genetic information of the individuals

3-DNA chromatin material====rRNA,mRNA,tRNA are formed

TEM of interphase nuclei and a mitotic cell with condensed chromosomes (arrow)

Nuclear pores (arrows) Nuclear pores (en face)

Colorized TEM of nuclear pores (blue) en face

Nucleic Acid

They are the bases of life,control the cellular functions

Two Types of nucleic acid: DNA&RNA

1-DNA= Deoxy-ribonucleic acid

DNA molecules are present in the nuclear chromatin,chromosomes&mitochondria

DNA represent the hereditary substances or genes

DNA molecules consists of two chins forming double helix

There are 4 types of nitrogenous bases in DNA molecules

1-Adenine(A) ,2-Thymine (T),3-Guanine(G),4-cystosine (C)

DNA carries&stores the genetic,information of ech cell

DNA transfers the genetic information by the following 2 processes

a-replication of DNA to to form more DNAb-transcription of DNA to form 3 types of

RNA

2-RNA= Ribonucleic Acid

The same structure to DNA but with some differences

DNA: present in nucleus,mitochondria of cytoplasm

DNA present in the nucleus&cytoplasmDNA: takes blue colour=========

RNA: takes red colour=========Methyl-green-pyronin stain

1-Ribosomal RNA=r-RNA

They are formed in the nucleolus from loops of DNA

Move to the cytoplasma&are known as ribosomes

Present free in cytoplasmFunction: they are the sites for protein

synthesis

2-Messenger RNA=mRNA

Information codes for proteine synthesis are present on DNA

DNA---------------mRNA======which control the processes of protein synthesis

mRNA can direct the synthesis of many identical protein signal which indicate where to begin and where to end translation

3-Transfer RNA=tRNA

t-RNA are formed inside the nucleus from DNA has two arms

a-tRNa==attched to amino acid== called anticodon

DNA is used to produce mRNATranscription

Steps of protein Synthesis in the cell

1-DNA molecule: specific types of protein which share information of hormones&enzymes

2-DNA: have ability to from copies of DNA by replication of DNA

3-DNA :can manufacture three kinds of RNA

a-r-RNA=protein factoriesb-m-RNA=code carries

c-t-RNA=Amino acid transfers

4-m-RNA molecule in the cytoplasm&association with

a-ribosomes(read the secret messages which are present on the mRNA

b-three t-RNA molecules(wanted amino acids from the cytoplasm

c-three amino acids

5-amino acid by tRNA====mRNA&correct aligment

6-amino acids to form apolypeptide7-release polypeptide&dissociation

of ribosomes from messenger RNA====newly synthesized protein

Ribosomes

-composed of rRNA (ribosomal RNA) & protein -may be dispersed randomly throughout the cytoplasm or attached to surface of rough endoplasmic reticulum -often linked together in chains called polyribosomes or polysomes -Primary function to produce proteins

Protein synthesisThe principal organelles involved are The nucleus

+ ribosomesTranscription mRNA molecule cytoplasm

associate

Ribosomal RNA+ associated proteins globular structure

Transfer RNARibosomes +mRNA molecules polyribosomes or polysomes attached to intracytoplasmic

membrane system known as ENDOPLASMIC RETICULUM

+

TRANSLATION mRNA then moves from the nucleus into the

cytoplasm & is used to produce a protein

The life cycle of the cell

Changes which occur in the cell during division(mitosis)&during rest(Interphase)

The cell cycle==mitotic part(two doughter cell)

== Interphase part (resting condition before starting another cell division

Subdivide into 3 three stages

1-G-1 stage(Gap one stage)presynthesis): 46-s-Chromosomes

2-S.2 stage(DNA synthesis)replication of DNA molecules have 46 identical paris of chromatids(92 chromatids

3-G2(post DNA duplication): have 46 D-chromosomes

Types of cells in relation to their cell renewal

Three types of cells in the body1-Non-renewing cells

Cells cannt divide== nerve cells they are not replaced

2-continously renewing cellsThese cells unable to divide:replaced by

doughter cells arising from mother cells called stem cells of the same family

Stem cells

a-unipotential stem cell: one type of the cells ex. Testicular cells

b-multipotential stem cells: bone marrow cells produce different type of cells

3-potential-renewble cellsEx.of these cells are:liver cells&endocrine cells

Nuclear changes during cell necrosis

1-pyknosis:nucleus becomes smaller&deeply stained

2-karyorrhexis:nucleus breks into small fragmentsKaryolisis:the nucleus dissolves&disappears