VACUOLE

Presented by: Arjama Dhar Roy M.Sc. ; Life Sciences, 1st Semester, CUG; 2014.

§ Topics to be discussed:• What is Vacuole?

• Where is it present?

• How many types of them are there?

• What are their functions?

• Short discussion about their versatility in structure and function.

• Fungal vacuoles have special ATPase system to maintain their Low PH.

• The fate of vacuoles during cell division.

• Where is it present?

Vacuoles are present in large significance in plant cells. Fungal cells and some protists(Paramoecium sp.) and even animal cells also content vacuoles which are small, numerous and functionally less significant than plant cell vacuoles. Bacteria also contain vacuoles[sulfur bacteria beggiatoa].

• What is vacuole?

Vacuoles are membrane bound enclosed compartments which are rich in different types of organic and inorganic Molecules including enzymes and pigments and other metabolic products.

Ø Because vacuoles are present inside a cell and participate in cellular functions, they are cell organelles and membrane

bound- tonoplast.• Basically there are three types of vacuoles:

ü Storage vacuoles [nutrients and pigments and waste product].

ü Contractile vacuoles[osmotic regulation].

ü Vacuoles involved in autophagy.

Ø Functions:• Plant cells have large vacuoles. Occupying the central region

of the cell[approx. 80% of the cell volume].They provide structural support, disposal of waste products, storage of pigments and nutrients, help in growth. Also maintains turgor pressure.

• Animal cells contain numerous small vacuoles those function in storage and transport: exocytosis and endocytosis.

• Some protists and protozoans possess vacuoles for osmoregulation and waste transport.

• Fungi have vacuoles containing low pH that helps in digestion.

• Exocytic Vesicle -ü They transport specific molecules[generally

Proteins or peptides or other molecules with specific Export sequence. Transport happens from inside the Cell to the outside.

• ENDOCYTIC VESICLE:

ü Transport of molecules from outside of the cell to the inside. i) receptor mediated , ii)phagocytosis iii) pinocytosis.

ü Contractile vacuole:

a. Contractile vacuoles are present in Amoeba and Chlmydomonus sp.

b. Contractile vacuoles are involved in transcytosis .

c. Osmotic regulation and waste products are

Transported from inside the

Cell to the outside.

Ø Fungal vacuoles maintain High [H+] in them: V-type ATPase

ü Fungal vacuoles maintain high proton concentrations inside their lumen.

ü For maintaining low PH vacuoles of fungal cells have specialized ATPase[ V-type] to pump H+ ions from cytosol to vacuolar lumen against the expenditure of ATP. Low PH is needed for the optimal activation of enzymes.

• V-type ATPase are also important for vesicular transport of proteins.

• V-ATPase activity is maintained by i) assembly and disassembly of two subunits[V0 and V1], ii)n the transcription and translational level and

• iii) by chloride channels.

Ø Chloride channel dependent regulation: Voltage gated Cl(-) channels are present on tonoplast. They antiport the Cl(-) ions and dissipating the proton gradient; ratio- 2:1.

• V type ATPase translocates H+ ions from the cytosol to the vacuolar lumen and a positive charge generated across the membrane limits the activity of the pump. So Chloride ion pumps transport Cl(-) ions to the lumen also!!

Ø Autophagy mediated by certain vacuoles:

• Autophagy involves transport of cellular organelles to the vacuoles and

their degradation- result of prolonged starvation.

• Overlaps biosynthetic pathway-CVT[ cytoplasm to vacuole targeting]..

• Macroautophagy and microautophagy.

• PMSF treated cells can`t digest cellular

Cargo – formation of intravacuolar

Vesicles[ autophagic bodies] .

• Defective cells in autophagy also can`t

Transport API- vacuolar hydrolase.

Continuation……• Autophagy may be specific[ CVT pathway] or nonspecific.

• Many proteins including CVT9, CVT3. TLG2P are necessary

for CVT pathway- mutation of any of these proteins leads to

accumulation of PrAPI.

• Vac8 mutants are defective in autophagy.

Ø Segregation of Vacuoles During Cell Division:

• During cell division cell organelles are not synthesized de novo

• Dramatic translocation of vacuolar portion is observed during cell cycle in

yeast.

• Actin mutants can`t `segregate vacuoles into daughter cells.

• Myo2P, an unusual molecular motor protein is involved in translocation-

along the actin filaments.

• Vacuolar inheritance depends upon localization of cytoskeletal proteins

towards tonoplast.

ü In brief:• Vacuoles are membrane bound cell organelles.

• They are important in cellular transport, maintenance of pH,

storage of substances, and induction of cell death during

starvation.[Other than apoptosis].

• Segregation of them is dependent upon cellular cytoskeletal

movements[S. cerevisiae]

THANK YOU!