i want 30 mutiple choice questions with their model answer below each question that covers different aspects of all information of the following :Objectives

1- Classify types of cytoskeletons

2- Describe the histological structure
of each type).

3- Correlate the functions of these
organelles to their structure.B) Non-Membranous Cell
Organoids

1- Ribosomes and polyribosomes (Discussed before)
2- Microtubules (Centroiles, cilia and flagella).

3- Filaments. CytoskeletonCytoskeleton
(Microtubules ,Microfilaments &
intermediate filaments)Cytoskeleton

The cytoplasmic cytoskeleton is a
network complex of

• 1- Microtubules and

• 2- Microfilament (actin) and

• 3- Intermediate filaments.

General function of cytoskeleton ?

A) Structural--------------

b) Movement.-------------------1- MicrotubuleDefintion : Microtubules are very small
hollow Tubes (25nm diameter & 5 nm
thick), only seen by E.M.EM of
microtubules• It is characterized by rigidity (semiflexible).

• Vary in length & have spiral organization

• Each microtubule consists of 13-rod shaped

structure called Protofilaments arranged

parallel to the long axis of the microtubule.The formation of microtubules:

A-Sites of formation.
B-Mode of formation.

C-Drugs affecting formation.Sites of formation:

- MTOCs act as nucleating sites for
further polymerization & formation
of microtubule.

- The length of microtubule is dynamic.

- (MTOC) or centrosome is an area of
cytoplasm full of tubulin subunits &
other ptns and

- Organized around 2 cylindrical
centrioles.B)- Mode of formation:

1- Subunite : α and β Tubulin (dimers)

2- Longitudinally aligned α and β (dimers)
subunits make up(protofilaments).

3. Each 13 protofilaments arranged to form
the wall of a microtubule.

tubulin Dimers→protofilament→13
protofilaments → M.T• Microtubules show

dynamic instability

(Continous tubulin
polymerization (adding
tubulin subunite) &
depolymerization (lost
tubulin)C-Drugs affecting formation:

-The formation of MT is inhibited by Vinblastin
&vincristine (chemotherapies)…….cell division
will be affected.

• Types of cellular microtubules:

• 1) Unstable form : (mitotic spindle).

• 2) Stable form, (centrioles, cilia & flagella)A) The Centrosome & the Centriole

Defintion:

1- The centrosome is the
microtubule-organizing
center (MTOC) consists of
2 cylindrical centrioles

2- The TEM reveals that the
two centrioles exist at
right angles to one
anotherEach centriole(highly
organized) consists of
9 triplets of
microtubules.

- Each triplet is
composed of 3
microtubulesFunction of centriole:

• At the onset of mitosis, what is happened? (This

part will be discussed later in cell division lecture).Function of Microtubules (MT(

1- intracellular transport of organelles and
vesicles. Examples include:

a- Axoplasmic transport in neurons.

b- Melanin transport in pigment cells,

c- Chromosome movements by the mitotic
spindled- Transport along microtubules is under control of special
motor proteins (kinesin & dynein) which use ATP to move
molecules and vesicles along microtubule.
- Kinesins carry organelles or vesicles away from the
centre of the cell toward cell membrane ; cytoplasmic
dynein carry vesicles in the opposite directionMotor proteins associated with microtubules2- Microfilaments
(Actin )Actin filaments

a- (5–7 nm diameter) , more flexible than
microtubule .

b- Microfilaments composed of globular
subunits (G actin) organized into a
double-stranded helix (F actin)Actin filamentSite of actin filaments:

- Concentrated in

1)-area of cytoplasm under the cell
membrane called (cell cortex) as a
network and 2)-cell extensions (core
of microvilli).

- Pseudopodia: Induce amoeboid movement of the cellFunction of actin filaments

Interaction between actin & myosins MOTORS form the
basis of cell movements:

1- Cytoplasmic streaming .

2- Contractile ring (actin +myosine II)---to produce TWO
cells by cytokinesis during mitosis.

3- Membranous associated (myosin I)+ Actin-----change
cell surface during endocytosis.

4- Interacrion of actin filaments with thicker(16 nm)
myosin filaments are responsible for contractile
movements of muscles3- Intermediate filamentsDefinition : a class of filaments intermediate in
size (8-10 nm) between the microtubule &
microfilaments.

- In comparison with microtubules and actin
filaments, intermediate filaments are much
more stable(not dynamic) provide mechanical
stability to the cell).

- Have various protein components in different cell
types.Structure : All are essentially rod-like rather than
globular proteins that form coiled tetramersWhat are types of intermediate
filaments?1-keratin
(cytokeratin)
filaments…

Bundles of keratin
filaments called
(tonofibrilis).

Site : in epithelial
cells –hair- nail2-Neurofilaments:
Site: in neurons
to support their
long processes3-Desmin: in muscle
cells to connect
myofibrils
together.

- Vimentin: (most
common type)
connective tissues
-muscle cells –4- Lamins:

in nuclear
envelop..Medical application

• Identification of intermediate

filaments ptns by

immunocytochemical methods

This means that we can

recognize the origin of tumors

• So it is imp for diagnosis &

treatment of tumors …