Cytoskeleton
Free online life science study material. Made up of actin filaments or microfilaments, intermediate filaments and microtubules.
Intermediate filaments are absent in plants except for lamins because they have rigid cell wall.
Microfilaments
7nm in diameter, filamentous and smallest among the three.
Mainly involved in muscle contraction, locomotion and cell migration, cytoplasmic streaming, cell attachment to extra cellular matrix, cell cell attachment for tissue formation etc.
Free online life science study material. Made up of actin filaments or microfilaments, intermediate filaments and microtubules.
Intermediate filaments are absent in plants except for lamins because they have rigid cell wall.
Microfilaments
7nm in diameter, filamentous and smallest among the three.
Mainly involved in muscle contraction, locomotion and cell migration, cytoplasmic streaming, cell attachment to extra cellular matrix, cell cell attachment for tissue formation etc.
Actin protein is basic unit of microfilament. It is a globular protein with ATP/ADP binding site. It is U shaped protein. The individual subunits are called G- actin and polymer is called F- actin.
The F actin is a polar structure with pointed and barbed ends.
The initial polymerisation is called nucleation. During nucleation three monomers should fit in right manner to form the filament.
Once three monomers are correctly allighned the subsequent monomers can be added through reversible addition.
At the pointed end there is ADP and at barbed end there is ATP present.For polymerisation hydrolysis of ATP is not required.
It only enhances the rate of asembly.
Actin binding proteins:
The F actin is a polar structure with pointed and barbed ends.
The initial polymerisation is called nucleation. During nucleation three monomers should fit in right manner to form the filament.
Once three monomers are correctly allighned the subsequent monomers can be added through reversible addition.
At the pointed end there is ADP and at barbed end there is ATP present.For polymerisation hydrolysis of ATP is not required.
It only enhances the rate of asembly.
Actin binding proteins:
1. Formin: These are barbed end tracking proteins which nucleate the actin monomers.Also move along growing polymers.
2.Arp 2/3 : Causes branching of actin filament. Branching is important for cell migration and cell movement.
3.Cofilin: This is required for remodeling of existing actin filament. ADP actin gets bound to cofilin so reassembly is prevented.
Profilin:Causes exchange of ADP for ATP.The subunit can no longer bound to cofilin and reassembly can take place
2.Arp 2/3 : Causes branching of actin filament. Branching is important for cell migration and cell movement.
3.Cofilin: This is required for remodeling of existing actin filament. ADP actin gets bound to cofilin so reassembly is prevented.
Profilin:Causes exchange of ADP for ATP.The subunit can no longer bound to cofilin and reassembly can take place
Lysosomal disease
Free online life science study material.
Lysosomal disease:
1. Type II glycogenosis: The lysosomal enzyme alpha- 1,4 glycosidase is defected. This enzyme when present breakdown glycogen.
2.Hunter's Syndrome: Due to accumulation of glycoamino glycans. These are major polysaccharide in extra cellular matrix. It is basically X linked recessive disease in which iduronate 2 sulphatase enzyme gets defected.
3. Hurler's syndrome: Autosomal recessive disorder. Enzyme alpha L idurodinase is defected. it is also glycoamino glycan accumulating disease.
Tay Sach's disease: Beta N acetyl hexoseaminidase A enzyme is defective. The ganglioside gets accumulated.
I cell disease: NAG phosphotransferase enzyme is non functional.
1. Type II glycogenosis: The lysosomal enzyme alpha- 1,4 glycosidase is defected. This enzyme when present breakdown glycogen.
2.Hunter's Syndrome: Due to accumulation of glycoamino glycans. These are major polysaccharide in extra cellular matrix. It is basically X linked recessive disease in which iduronate 2 sulphatase enzyme gets defected.
3. Hurler's syndrome: Autosomal recessive disorder. Enzyme alpha L idurodinase is defected. it is also glycoamino glycan accumulating disease.
Tay Sach's disease: Beta N acetyl hexoseaminidase A enzyme is defective. The ganglioside gets accumulated.
I cell disease: NAG phosphotransferase enzyme is non functional.
Peroxisomes:
These are very small, ubiquitous, variable and single membrane bodies.
These have crystalline core made up of urate oxidase.
In animals the catalase enzyme is present in periphery along with core.
It metabolises hydrogen peroxidase by help of catalase enzyme.
It also detoxicate various harmful substances such as methanol, ethanol, phenol etc.
In animals fatty acid oxidation takes place in it.
Some fats and lipids are also synthesies in peroxisomes.
Disorders:
Single enzyme defect includes X-ALD(X- linked adrenoleuco dystrophy). In this, one of the transport protein found in membrane of peroxisome is defective.
This protein is involved in transport of long fatty acid chain inside peroxisome.As a result long fatty acid chain accumulates in cytoplasm.
Another type of disease result from defect in mechanism involved in biosynthesis of peroxisome.Zellweger's syndrome is fatal genetic disease. The defect lies in numerous membrane transporters involved in transport of peroxisomal enzymes inside peroxisomes. So, peroxisomes without enzymes are called empty ghosts.PEX genes are found to be responsible of such disease.
These are very small, ubiquitous, variable and single membrane bodies.
These have crystalline core made up of urate oxidase.
In animals the catalase enzyme is present in periphery along with core.
It metabolises hydrogen peroxidase by help of catalase enzyme.
It also detoxicate various harmful substances such as methanol, ethanol, phenol etc.
In animals fatty acid oxidation takes place in it.
Some fats and lipids are also synthesies in peroxisomes.
Disorders:
Single enzyme defect includes X-ALD(X- linked adrenoleuco dystrophy). In this, one of the transport protein found in membrane of peroxisome is defective.
This protein is involved in transport of long fatty acid chain inside peroxisome.As a result long fatty acid chain accumulates in cytoplasm.
Another type of disease result from defect in mechanism involved in biosynthesis of peroxisome.Zellweger's syndrome is fatal genetic disease. The defect lies in numerous membrane transporters involved in transport of peroxisomal enzymes inside peroxisomes. So, peroxisomes without enzymes are called empty ghosts.PEX genes are found to be responsible of such disease.
Friday, November 7, 2014
Golgi Bodies
Golgi Bodies
Final processing of proteins take place in Golgi bodies.
Lipid synthesis takes place in it.
The mannose-6-Phosphate tagging of N- linked glycosylated protein takes place in Golgi. This tagged glycoprotein is directed to lysosome only.
Sulphation of tyrosine residue of proteins takes place here.
Proteolytic cleavage of certain protein also takes place in it.
Golgi has glycerol based phospholipid (Phosphatidyl choline), the choline group is transferred to ceramides to form sphingiomyelin in Golgi.
The Golgi release carbohydrate during cell plate formation in cell division.
Lysosomes
These are single membrane organelle.
They consist of variety of hydrolytic enzymes and function at acidic pH.
The membrane on the inner side of lysosome has carbohydrate coating which protect it from enzymes present inside it.
Many membrane proteins function as H+ ATPase to pump H+ inside lysosome.
It contains different phosphatase, protease, peptidase, nuclease, lipase etc variety of enzymes for degradation of complex molecules.
When a cell engulf a foreign material by endocytosis it forms early endosomes(fused product of plasma membrane and trans golgi).
When more content is delivered from Golgi to early endosome it becomes late endosome.
The enzymes of endosomes are inactive as they require acidic environment for activation, the acidic environment can be achived by two mechanisms: 1. Late endosome fuse with already existing lysosome or 2. The lumen can be made acidic by H+ATPase pump activity.
Lysosome can be heterophagic: containing extracellular material or autophagic: containing own cell material.
Free life science study material.
Final processing of proteins take place in Golgi bodies.
Lipid synthesis takes place in it.
The mannose-6-Phosphate tagging of N- linked glycosylated protein takes place in Golgi. This tagged glycoprotein is directed to lysosome only.
Sulphation of tyrosine residue of proteins takes place here.
Proteolytic cleavage of certain protein also takes place in it.
Golgi has glycerol based phospholipid (Phosphatidyl choline), the choline group is transferred to ceramides to form sphingiomyelin in Golgi.
The Golgi release carbohydrate during cell plate formation in cell division.
Lysosomes
These are single membrane organelle.
They consist of variety of hydrolytic enzymes and function at acidic pH.
The membrane on the inner side of lysosome has carbohydrate coating which protect it from enzymes present inside it.
Many membrane proteins function as H+ ATPase to pump H+ inside lysosome.
It contains different phosphatase, protease, peptidase, nuclease, lipase etc variety of enzymes for degradation of complex molecules.
When a cell engulf a foreign material by endocytosis it forms early endosomes(fused product of plasma membrane and trans golgi).
When more content is delivered from Golgi to early endosome it becomes late endosome.
The enzymes of endosomes are inactive as they require acidic environment for activation, the acidic environment can be achived by two mechanisms: 1. Late endosome fuse with already existing lysosome or 2. The lumen can be made acidic by H+ATPase pump activity.
Lysosome can be heterophagic: containing extracellular material or autophagic: containing own cell material.
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