31. 32. 35. cytoskeleton components+ inclusions

Question 1

What does the cytoskeleton consist of

Answer 1

microtubules, microfilaments, intermediate filaments

these are protein polymers

Question 2

What is the function of the cytoskeleton

Answer 2

help shape and structure of cells
move organelles and vesicles
movement of entire cells, moves chromosomes during mitosis

Question 3

What is the structure of microtubules

Answer 3

highly dynamic in length outer diameter-25nm

nonbranching, elongated hollow tubes made of 13 parallel protofilaments - arranged in a ring

main protein component are heterodimers of alpha and beta tubulin

polarity: + end grows by adding dimers of tublin (polymerization)
- end removal of tublin (depolymerization)

Question 4

How are the microtubules stabilized

Answer 4

Polymerization of tubulins is directed by microtubule
organizing centers (MTOCs)

equilibrium of
polymerization and depolymerization by means of
microtubule-associated proteins (MAP-1 and MAP-2)

Question 5

How does microtubule stability vary

Answer 5

varies greatly depending on location

dynamic stability in cytoplasm such as those in mitotic spindle (short lived)
but those in axonemes which make up cilia are stable

Question 6

Which is the most dominant microtubule organization centre in most cells

Answer 6

centrosomes organized around 2 cylindrical centrioles

Question 7

function of microtubules

Answer 7

maintenance of cell shape

intracellular transport of organelles eg controlled by motor proteins (kinesins and dyneins)

formation of mitotic spindle

basis for formation of centrioles and cilia/flagella

Question 8

Structure of microfilaments

Answer 8

Thinnest filament of cytoskeleton

2 intertwined filaments of F-actin to make helix

main protein component is globular G-actin monomers

+ and - ends where monomers are added or disassociated Elongation via polymerization like microtubules)

Question 9

What is the stability of microfilaments

Answer 9

dynamic (as monomers added rapidly same in microtubules)

cytochalasin block actin polymerization
Phalloidin promotes actin polymerization and stabilizes it

Question 10

where are the general locations of microfilaments

Answer 10

beneath cell membrane
cytoplasmic extensions like microvilli

Question 11

functions of microfilaments

Answer 11

contractile rings of microfilamnets with myosin to produce 2 cells in cytokinesis

transport of organelles

just like motor proteins, myosin proteins move cargo along F-actin

Question 12

Structure of intermediate filaments

Answer 12

outer diameter 10nm

made of different protien subunits: coiled rod like dimers that form antiparallel tetramers which assemble into protofibrils

Question 13

What is the stability like of intermediate filaments

Answer 13

stable

unlike microtubules and microfilaments

Question 14

what are some intermediate filaments found in eukaryotic cells

Answer 14

keratins- forms bundles to attach to certain junctions of epithelial cells. cytokeratins involved in the keratinization of skin

vimentin- found in mesenchymal cells eg macrophages, fibroblasts, chondroblasts

neurofilamnets - like nerve cell body and processes

lamins- present in nucleus forms nuclear lamina

Question 15

What are cytoplasmic inclusions

Answer 15

small particles of insoluble substances suspended in cytosol

Question 16

what is the difference between inclusions and organelles

Answer 16

inclusions have little to no metabolic activity and not enclosed by membrane

Question 17

what are some important inclusions

Answer 17

lipid droplets- lipid filling adipocytes

glycogen granules- in liver, straited muscle cells, cartilage and nerve cells. Can be seen by PAS reaction in LM

pigement deposits- like melanin in skin which are dark brown granules protecting us from UV. lipofuscin wear and tear pigment. THESE ARE ENDOGENOUS PIGMENTS.
EXOGENOUS could include tatoos, age spots etc