Structure And Function Of Cell Organelles Notes
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Ways to study cells
-immuno cytochemistry -labelled antibodies are used to identify proteins and glycoproteins
-insitu hybridisation - localisation of a strand of DNA or RNA using a labelled complementary
-electron microscopy-resolution of 0.1nm- show structures within organelles, membrane, viruses, macromolecules- dna and protein Structure and function of cell organelles The ultrastructure of organelles can be seen through electron microscopy- the proteins of organelles can be labelled using immunocytochemistry where the antibodies can be labelled with fluorescent markers so they can be seen Nucleus Functions: gene replication and repair
-gene transcription- production of mRNA for protein synthesis in the cytoplasm
-ribosome production by the nucleolus Nuclear envelope
-Electron microscopy- double membrane separated by narrow space -50nm (perinulear cisterna) TEM
-Internal membrane of nucleus has protein structure called 'fibrous lamina'- made up of three lamina proteins
-Function of the nuclear lamina: spatially organises the nuclear pore, this stabilizes the nuclear envelope. Non dividing cells, chromosomes are associated with fibrous lamina
-Poly ribosomes attached to the outermembrane, nuclear envelope part of RER.
-sites when inner and outermembrane of nclear envelope fuse, there are gaps 'nuclear pores'- this controlled pathway between nucleus and cytoplasm- nuclear pores are composed of an octagonal pore complex, which consists of 8 large proteins organised around a hole
-ions and molecules with diameter up to 9nm pass freely through nuclear pore- mRNA, proteins and steroid hormones, molecular complexes more than 9nm are transported actively Chromatin
-chromosomes in non dividing cells are attached to the inner membrane of the nuclear envelope and are found in different states of uncoiling- degree of coiling varies with cell activity, more transcriptionally active the cell the less coiled the chromatin which allows more DNA surface available for transcription
-identified by basic stains- hematoxylin and methylene blue
-Two types of chromatin- Heterochromatin and euchromatin
-each nucleosome- 166bp of DNA wound around histone, octamer of H2A,H2B,H3,H4 and H1 is bound to DNA
-Heterochromatin- chromatin is densely coiled and appears as coarse granules known as chromocentres- two types of heterochromatin- constitutative- sections of DNA in eukaryotes that consist of highly repetivie sequences of DNA bases, found in the centromere and telomere- these sections are transcriptionally inactive- facultative chromatin- under specific signalling cues the
chromatin looses its condensed structure and becomes transcriptionally active - one X chromosome in females is selected early in development
-euchromatine- chromatin is less densely coiled, widely dispered and fills the majority of the nucleus-transcriptionally active
-coiled strands of DNA bound to histones (protein)- structural unit is nucleosome (DNA wrapped around histones), nucleosome is coiled on its axis to form solenoid and hoops.
-Chromatin is studied using phytohaemogluttin which stimulates mitosis and colchine which inhibits mitosis Nucleolus
-electron dense structure as seen by the electron microscope as it is rich in rRNA
-spherical structure, rich in rRNA and protein.
-basophilic when stained with hematoxylin
-lightly stained sections consist of nuclear organiser DNA- code for rRNA, darker stained sections are either pars fibrosa (densely packed ribonucleoprotein, contains a large amount of primary transcripts of Rrna genes), pars granulosa- densely staining maturing ribosomes
-during the early stages of embryonic development when proliferation is taking place, the nucleolus is very large as cells are actively producing a large amount of proteins Nuclear matrix Fills space between chromatin and nucleoli in nucleus. Mostly has proteins, metabolites, ions Cytoplasm
-compoased of matrix (cytosol) which are embedded with organelles, cytoskeleton and deposits of carbohydrates, lipids and pigments Plasma membrane
-membrane made of phospholipids bilayer-hydrophobic tails and hydrophilic head, cholesterol breaks up structure and makes it more fluid, proteins
-7.5 to 10nm thickness, visible only in electron microscope
-has intergral and peripheral proteins
-function selective barrier that regulates passage of certain materials into and out of cell plays important role in cell recognition mass transfer occurs at the lipids, endocytosis and exocytosis Mitachondria
-spherical organelles, 0.5 micrometers wide that can be up to 10 micrometer long
-under electron microscope- outer and inner mitochondrial membrane--mitochondrial membranes have a large number of protein molecules
- inner mitochondrial membrane folds to have cristae. -cristae are flat and shelf like, they increase the surface area- contains enzymes and other components of oxidative phosphorylation and electron transport systems. The number of cristae is releted to the energy activity of the cell
-Between the outer and inner membrane in the intermembrane space
-inner mitochondrial membrane enclose the matrix, rich in protein and contain circular DNAdouble stranded DNA synthesised within the mitochondria and duplication is independent of nuclear DNA, also contains 3 types of RNA- mRNA, tRNA and Rrna
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