MANIL KANADE

20131005

1)What are differences between Smooth and Rough endoplasmic reticulum? How can you separate smooth and rough ER? What are microsomes?

Rough E R (RER) is involved in some protein production, protein folding, quality control and despatch. It is called ‘rough’ because it is studded with ribosomes. Smooth E R (SER) is associated with the production and metabolism of fats and steroid hormones. It is ‘smooth’ because it is not studded with ribosomes and is associated with smooth slippery fats. Rough and Smooth Regions of ER Can Be Separated by Centrifugation. A small particle in the cytoplasm of a cell, typically consisting of fragmented endoplasmic reticulum to which ribosomes are attached.

2)What is difference in the synthesis of proteins synthesized by free and bound ribosomes?

A free ribosome is one just floating in the cytoplasm, the proteins it makes are free to go wherever within the cell. A bound ribosome is one attached to the (rough) endoplasmic reticulum, the proteins made sttay in the ER and usually get trapped in a vesicle for transport.

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3)What is the difference between ion channel and pump, transporters, carriers? Explain the Sodium potassium channel in detail.

Ion channels: Ion channels are passive transporters (does not require energy). They are pores in the plasma membrane that open and close and allow the passage of ions through the membrane.

Protein pumps: Pumps are primary active transporters, i.e, they require external energy for transportation and they move molecules against the gradient (concentration or electric)

Carriers: Carriers are the secondary transporters that use the gradients created by pumps to transport other molecules.

Transporter: A membrane transport protein (or simply transporter) is a membrane protein involved in the movement of ions, small molecules, or macromolecules, such as another protein across a biological membrane.

Potassium channels are designed to allow the flow of potassium ions across the membrane, but to block the flow of other ions--in particular, sodium ions. These channels are typically composed of two parts: the filter, which selects and allows potassium but not sodium to pass, and the gate, which opens and closes the channel based on environmental signals.. It is comprised of four identical protein molecules that span the width of the membrane, forming a selective pore down the center. Potassium ions, shown in green, flow freely through it, at rates of up to one hundred million ions per second. But it is also remarkably selective--it allows only one sodium ion to pass for every ten thousand potassium ions.

4)What is role of cholesterol in plasma membrane in terms of regulating transition temperature?

The ratio of saturated and unsaturated fatty acids determines the fluidity in the membrane at cold temperatures. Cholesterol functions as a buffer, preventing lower temperatures from inhibiting fluidity and preventing higher temperatures from increasing fluidity.

5)With help of any transmembrane receptor explain how a protein helps in intracellular signalling in cells?

Cells have proteins called receptors that bind to signaling molecules and initiate a physiological response. Different receptors are specific for different molecules. Receptors are generally transmembrane proteins, which bind to signaling molecules outside the cell and subsequently transmit the signal through a sequence of molecular switches to internal signaling pathways.

6)Explain the role of various machinery which helps in transportation and fusion of a vesicles?

The transport of cargo in eukaryotic cells is mediated by the movement of membranous vesicles that pinch off from one membrane and fuse with another. An essential part of this process is the interaction between SNARE (solubleNSF attachment protein receptors) proteins from the vesicle (v-SNARE) and target (t-SNARE) membranes. The resulting SNARE complexes are parallel four-helix coiled-coil structures with melting temperatures between 70 and 90 °C, and it is likely that, at least in part, the free energy of SNARE complex formation drives bilayer fusion. Regulating the assembly and disassembly of SNARE complexes is thus an important aspect of vesicular transport.

7)In plant cells, how microtubules play an indirect role in maintaining cell shape through their influence on the formation of the cell wall?

The cell wall in plants is composed of Cellulose. There are 2 layers of the cell wall, primary and secondary. It has been seen that microtubules influence the direction of cellulose deposition. These cells have oriented bands or rings of microtubules located just under the plasma membrane; these microtubules are transverse to the direction of elongation but parallel to many of the cellulose micro fibrils in the primary cell wall of the elongating cell. This in turn decides the rigidity and shape of the cell.

8)How does microtubules helps in maintaining internal organisation of a cell?

Microtubules help in maintaining cell shape, anchoring the cell organelles, movement of cell organelles and it provides a pathway for the motor proteins to carry the vesicles.

9)What is the importance of cytoskeleton structures like Microtubules and Actin having polarity?

The motor proteins travelling on the microtubules and actin use the polarity (+ and – ends) as a reference for the direction in which they are moving. Different motor proteins move in different directions. Ex: most kinesins move toward the + end of the microtubule, but kinesin-14 moves towards the – end of the microtubule.

10)Does prokaryote also have cytoskeleton like structure? If they have what are they and how do they help them?

The prokaryotic cytoskeleton is the collective name for all structural filaments in prokaryotes. It was once thought that prokaryotic cells did not possess cytoskeletons, but advances in visualization technology and structure determination led to the discovery of filaments in these cells in the early 1990s. Not only have analogues for all major cytoskeletal proteins in eukaryotes been found in prokaryotes, cytoskeletal proteins with no known eukaryotic homologues have also been discovered. Cytoskeletal elements play essential roles in cell division, protection, shape determination, and polarity determination in various prokaryotes.

MANIL KANADE

20131005