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CELL BIOLOGY
PLASMA MEMBRANE
Ultra-structure and composition of Plasma membrane

Q.What is liposome?

Lipoosmes are small spherical shaped nontoxic phopholipid types of artificial vesicles that can be created from cholesterol. It has an aqueous solution core and surrounded by a hydrophobic membrane in the form of lipid bi layer. The hydrophilic solutes get dissolved in the core, so cannot readily pass through the hydrophobic bilayer. So a liposome can be loaded with both hydrophobic and hydrophilic materials and thus can be used as a vehicle for administration of nutrients and pharmaceutical drugs.

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Fluid mosaic model

Transport across membrane

Active and Passive transport

Q. Distinguish between simple and facilitated diffusion.

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Facilitated transport

 

Cell junctions:

 

Tight junctions

 

Gap junctions

Q.What is plasmodesmata?

A narrow thread of cytoplasm that passes through the cell walls of adjacent plant cells and allows communication between them.Important features of plasmodesmata s follows—

(i) Communicating the cell-cell junctions in plants in which channels of cytoplasm lined by cell membranes connect adjacent cells through small pores in the cell walls.

(ii)The channels called Plasmodesmata. provide for the direct exchange of materials between cytosols of adjacent cells.

(iii)Most of the plasmodesmata are found to be restricted in thin areas(the primary pit fields)of the young walls; on the other hand in mature cells with secondary layers, some times occur in large groups only in the pit membrane.

(iv)Plasmodesmata are mainly concerned with the translocation of food, specially in storage tissue like endosperm.

(v)Plasmodesmata are also found in the cell walls of some members of red algae, mosses, liverworts and pteridophytes.

Desmosomes
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CYTOPLASMIC ORGANELLES I
Structure and Functions

 

Endoplasmic Reticulum

Q.What do you mean by N-linked glycosylation

N-linked glycosylation, is the attachment of the sugar molecule oligosaccharide known as glycan to a nitrogen atom (amide nitrogen of asparagine (Asn) residue of a protein), in a process called N-glycosylation. It involves the assembly of an oligosaccharide on a lipid carrier, dolichylpyrophosphate and the transfer of the oligosaccharide to selected asparagine residues of polypeptides that have entered the lumen of the ER. The assembly of the oligosaccharide (LLO) takes place at the ER membrane and requires the activity of several specific glycosyltransferases.

Golgi Apparatus

 

Lysosomes

 

Protein sorting and mechanisms of vesicular transport

Q.What is protein trafficking?

A special type of protein transferring process where golgi apparatus is involved in the sorting and trafficking of proteins produced within a cell. Proteins translated within the rough endoplasmic reticulum are transferred to the Golgi. From there they are modified and packaged into vesicles for distribution. Proteins can be targeted to the inner space of an organelle, different intracellular membranes, plasma membrane, or to exterior of the cell via secretion. This delivery process is carried out based on information contained in the protein itself. Correct sorting is crucial for the cell; errors can lead to diseases.

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CYTOPLASMIC ORGANELLES II : MITOCHONDRIA
Structure

 

Semi-autonomous nature

Q.List out the enzymes (or marker enzymes) present in mitochondria.

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Endosymbiotic hypothesis

 

Mitochondrial Respiratory Chain

Chemiosmotic hypothesis

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PEROXISOMES
Structure and Functions
CENTROSOME
Kinetochore and centromeric DNA
Structure and Functions
CYTOSKELETON
Type

Structure and functions of cytoskeleton

 

Accessory proteins of microfilament & microtubule

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NUCLEUS
Nuclear envelope

Nuclear pore complex, Nucleolus

CHROMATIN
Euchromatin and Heterochromatin

 

Packaging (nucleosome)

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CELL CYCLE
Cell cycle and its regulation

Q.How restriction point in animal cells differs from START point of yeast.

The proliferation of most animal cells is similarly regulated in the G1 phase of the cell cycle. In particular, a decision point in late G1, called the restriction point in animal cells, functions analogously to START in yeasts.

The passage of animal cells through the cell cycle is regulated primarily by the extracellular growth factors that signal cell proliferation, rather than by the availability of nutrients. In the presence of the appropriate growth factors, cells pass the restriction point and enter S phase. Once it has passed through the restriction point, the cell is committed to proceed through S phase and the rest of the cell cycle, even in the absence of further growth factor stimulation.

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Q.What is MPF?

A Cytoplasmic factor that present in hormone treated oocytes is sufficient to trigger the transition from G2 to M in oocytes that had not been exposed to hormone.As because the the entry of oocytes into meiosis is frequently referred to as oocyte maturation, this Cytoplasmic factor was called maturation promoting factor (MPF). MPF is also present in somatic cells, where it induces entry into M phase of the mitotic cycle. Rather than being specific to oocytes. MPF thus appeared to act as a general regulator of the translation from G2 to M.

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CANCER
Concept of oncogenes and tumor suppressor genes with special reference to p53. Retinoblastoma and Ras

 

Process of Proto-oncogene activation

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Q.”p53 is the guardian of the cell”— justify the statement. Q.Point out the importance of p53 in checkpoint control of cell cycle.

(i) In mammalian cells, arrest at the G1 checkpoint is also mediated by the action of an additional protein known as p53 which is phopshorylated by   

    both ATM and CHK2.

(ii) Phosphorylation stabilizes p53, which is otherwise rapidly degraded, resulting in a rapid increase in p53 levels in response to damaged DNA.

(iii) The p53 protein is a transcription factor and its increased expression leads to the induction of the Cip/Kip family Cdk inhibitor p21. The p21

    protein inhibits Cdk2/cyclinE complexes, leading to cell cycle arrest in G1.

(iv) The gene encoding p53 is frequently mutated in human cancers. Loss of p53 function as a result of these mutations prevents G1 arrest in

    response to DNA damage, so the damaged DNA is replicated and passed on to daughter cells instead of being repaired.

(v) This inheritance of damaged DNA results in an increased frequency of mutations and general instability of the cellular genome, which contributes

    to cancer development.

(vi) Mutations in the p53 gene are among the most common genetic alterations in human cancer, illustrating the critical importance of cell cycle

    regulation in the life of multicellular organisms.

CELL SIGNALLING
Cell signalling transduction pathways

 

Types (Classification and Example only)

 

Signalling molecules

 

Receptors : RTK & JAK/STAT

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Q.What is functional importance of RTK?

Receptor tyrosine kinases (RTKs) are the high-affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones. Of the 90 unique tyrosine kinase genes identified in the human genome, 58 encode receptor tyrosine kinase proteins. Receptor tyrosine kinases have been shown not only to be key regulators of normal cellular processes but also to have a critical role in the development and progression of many types of cancer. Mutations in receptor tyrosine kinases lead to activation of a series of signalling cascades which have numerous effects on protein expression. Receptor tyrosine kinases are part of the larger family of protein tyrosine kinases, encompassing the receptor tyrosine kinase proteins which contain a transmembrane domain, as well as the non receptor tyrosine kinases which do not possess transmembrane domains.

Apoptosis

Q.Distinguish between apoptosis and necrosis.

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Honours / Core Course (CC)

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