The cytoskeleton and how to study cells

Question 1

What are the roles of the cytoskeleton?

Answer 1

• Provides strength
• Controls cell shape
• Transport system
• Cell division
• Connect cells in tissues
• Allows cell movement

Question 2

What is the diameter of an actin filament?

Answer 2

5-9 nm

Question 3

what is the main function of actin filaments?

Answer 3

strength - help support the plasma membranes of cells as they are thin and highly flexible

Question 4

what is another function of actin filaments?

Answer 4

movement and shape - highly dynamic and can grow, shrink and branch to respond to changes in the environment

Question 5

from what end do actin filaments grow and shrink?

Answer 5

they grow from the plus end and shrink from the minus end

Question 6

what is the diameter of a microtubule?

Answer 6

25 nm (larger than actin)

Question 7

what is the structure of microtubules?

Answer 7

rigid hollow cylinders

Question 8

where are the minus ends of microtubules located?

Answer 8

the Microtubule Organising Centre (MTOC) also known as the centrosome

Question 9

where is the MTOC located?

Answer 9

near the nucleus

Question 10

where do plus ends on microtubules grow towards?

Answer 10

the plasma membrane

Question 11

from what end do microtubules grow and shrink from?

Answer 11

they grow and shrink from the plus end

Question 12

how do microtubules grow?

Answer 12

monomers of the protein tubulin are added to the plus end and when fully grown it is capped for stability

Question 13

how do microtubules shrink?

Answer 13

the cap is removed and tubulin dissociates from the plus end

Question 14

what is the role of intermidiate filaments?

Answer 14

• Provide mechanical strength to the cell and connect cells together in tissues
• Also form the nuclear lamina, just beneath the nuclear membrane that helps anchor chromosomes and the nuclear pore complex.

Question 15

what is the diameter of intermediate filaments?

Answer 15

8-12 nm

Question 16

what are intermediate filaments mostly made of?

Answer 16

keratin

Question 17

How is the cytoskeleton dynamic?

Answer 17

• actin filaments are constantly contracting and extending pushing the plasma membrane so the cell can sense it’s environment
• microtubules remodel to allow the cell to send organelles to new parts of the cell during division

Question 18

how are microtubules involved with flagellum?

Answer 18

• Multiple microtubules are arranged down the length of the flagella or cilia as doublets
• Along the length of these microtubule doublets are motor proteins called dynein
• The doublets can be crosslinked with a protein called nexin
• Nexin prevents motor proteins from moving which bends the microtubules

Question 19

how do microscopes magnify light coming through a biological sample?

Answer 19

using lenses

Question 20

how is light focused in a microscope?

Answer 20

collector lens onto a mirror

Question 21

what focuses light on the specimen in a microscope?

Answer 21

condenser lens

Question 22

what lenses magnify the light from the specimen?

Answer 22

objective and projection

Question 23

what is the last receiver of focused light in a microscope?

Answer 23

the detector

Question 24

what is the limit to what you can visualise using a standard light microscope?

Answer 24

200 nm

Question 25

what is the most commonly used stain in histology?

Answer 25

Hematoxylin & Eosin stain

Question 26

what colour and which organelles does Hematoxylin & Eosin stain?

Answer 26

- Hematoxylin (purple) stains acidic structures such as the nucleus - Eosin (pink) stains basic structures such as the cytoplasm and cell walls

Question 27

what colour and which organelles does Azan trichrome stain?

Answer 27

- Nuclei are stained bright red - collagen, basement membrane and mucin are stained blue - muscle and red blood cells are stained orange to red

Question 28

what is the Azan trichrome stain used for?

Answer 28

staining connective tissue and epithelium

Question 29

what are the differences between light and electron microscopes?

Answer 29

- electron microscopes use electrons instead of light - electron microscopes have electromagnetic lenses rather than optical - electron microscopes can visualise smaller objects - electron microscopes can't produce colour

Question 30

what is fluorescence microscopy?

Answer 30

a type of light microscopy that only uses part of the light spectrum and relies on fluorophores to emit light when stimulated

Question 31

what protein was used to help visualise cells better?

Answer 31

Green Fluorescent Protein (GFP)

Question 32

What other protein was isolated from coral?

Answer 32

Red Fluorescent Protein (RFP)

Question 33

What are the limitations of using fluorescence proteins?

Answer 33

- Photobleaching: destruction of the fluorescent protein by high intensity laser light. - Phototoxicity: Toxicity caused by high-intensity laser light (mainly due to free radical formation). - Overexpression: Tagged genes are often expressed at very high levels in order to produce a good signal. Excess protein may be handled by the cell differently to normal levels of protein. - Protein folding: Fluorescent proteins may affect the folding of the fusion protein and therefore affect its function. - Cellular distribution: The large fluorescent proteins may alter the cellular distribution of the tagged proteins. This is especially important for membrane proteins.