This is an extract of our Structure And Function Of Cell Organelles document, which we sell as part of our Organisation of the Body Notes collection written by the top tier of Oxford students.
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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 (perinulear cisterna)
-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
-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. 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
-mitachondrial ribosomes, smaller than cystolic ribosomes enables for protein synthesis to occur in the matrix- but only a small proportion of mitochondrial proteins is produced locally .
-matrix also has Enzyme for the Krebs cycle and for fatty acid beta oxidation found in the matrix
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