cytoskeleton

Question 1

cytoskeleton only occurs in which cell?

Answer 1

eukaryotic cell

Question 2

functions of cytoskeleton ?

Answer 2

mechanical support, motility and maintainence of shape.

Question 3

what is the cytoskeleton composed of?

Answer 3

minute ,fibrous and tubular proteinous structure which forms the structural framework of the cell

Question 4

where are microtubules found?

Answer 4

microtubules occur in cytoplasmic matrix ,mitotic apparatus ,cilia , flagella , centrioles and basal body. prokaryotic cell lacks microtubules

Question 5

explain the structure of microtubules?

Answer 5

they are hollow , unbranched cylindrical filaments , with a diameter of 25nm and hollow core of 15nm. the boundary is made up of 13 parallel protofilaments. the protofilaments are made up sub units of alpha and beta tubulin protein. assembly and disassembly of microtubules require GTP and Ca^2+.

Question 6

what kind of protein is tubulin?

Answer 6

non - contractile protein

Question 7

what are the functions of microtubules?

Answer 7

1) the help in astal rays and spindle formation
2) they help in the anaphasic movement of chromosomes
3) they give cell a shape, rigidity , form and cell motility
4) cytoskeleton of cilia and flagella is made up of microtubules
5) they help in the intercellular transportation of nutrients and inorganic ions
6) they determine the positioning of the future cell plate

Question 8

explain the structure of microfilaments?

Answer 8

its solid , unbranched , rod like fibrils of indefinite length. they are mainly composed of globular protein actin and filamenteous protein myosin .they form an extensive network in the cytoplasm and thy may be associated with plasma membrane.

Question 9

functions of microfilaments?

Answer 9

1) they represent the contracttile system of the cell and help in cytoplasmic streaming and amoeboid movement
2) supports the plasma membrane
3) help in the formation of pseudopodia
4) help in the formation of cleavage furrow during cell division

Question 10

what is intermediate filament?

Answer 10

non contractile hollow cylinder of acidic protein

Question 11

functions of intermediate filament ?

Answer 11

1) formation of a basket around the nucleus

2) formations of scaffolds for chromatin

Question 12

what are centrosomes?

Answer 12

it is an organelle present in almost all eukaryotic cells except in high plant cells. it contains two cylindrical structure called centrioles, they are perpendicular two each other and are called diplosomes. they are clouded by amorphous pericentriolar material called centrosphere or kinoplasm

Question 13

structure of centrioles?

Answer 13

1) it is made up of a whorl of 9evenly spaced fibrils made up of tubulin protein.it is absent in the centre, therefore this arrangement is called 9+0
2) each fibril is made up of 3 sub fibres, thus it is called triplet fibril consisting of 3sub fibres A, B, C
3) triplet fibrils are interconnected by proteinaceous C-A linkers
4) the centre of the centriole has a rod-shaped proteinaceous called the hub. from the hub 9 proteinaceous fibres are developed towards the peripheral triplet fibrils. they are called radial spokes

5) due to the presence of a hub in peripheral triplet fibrils, the center gives a cartwheel appearance
6) the centriole is membrane-bound but is surrounded by pericentriolar satellites a.k.a massule (microtubule generator or MTG)

Question 14

what are the functions of centrioles?

Answer 14

1) they help in the formation of basal bodies which gives rise to cilia and flagella
2) centrioles form spindle fibres that give rise to spindle apparatus during cell division

Question 15

what are cilia and flagella?

Answer 15

cilia and flagella are hair-like outgrowths of the membrane. cilia are smaller structure responsible for w either moving the fluid around or the cell. on the other hand, flagella are comparatively longer and are responsible for the movement of the cell. they are present in both eukaryotic and prokaryotic cell but are structurally different.

Question 16

explain the structure of cilia and flagella.

Answer 16

1)they are membrane-bound extensions of the plasma membrane. they arise from centriole like basal body present at their bases that anchor and control their movement.

2)their core is called the axoneme that has a number o microtubules running parallel towards the long axis. the axoneme is made up of 9 microtubule doublets
arranged radially at the periphery and a pair of microtubules present singly at the centre such arrangement is known as 9+2

3) the pair of tubules present are connected by a bridge and enclosed by a common sheath called the central sheath
4) the central sheath is connected to the peripheral doublets by radial spokes, therefore there are 9 radial spokes
5) the peripheral doublets are interconnected by linkers made up of nexin protein.

Question 17

differentiate between cilia and flagella.

Answer 17

cilia: 1) number of cilia per cell is usually very large
2) they are small in size
3) they are present throughout or the major part of the cell surface
4) they help in locomotion, feeding, circulation etc.

flagella: 1) the number of flagella per cell is usually 1-4
2) they are longer in size
3) they are present at one end of the cell
4) the help in locomotion