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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