Lecture 4 Cell Organells II

Question 1

Organelles involved in cellular digestion

Answer 1

Lysosomes
Proteasomes
Peroxisomes

Question 2

Lysosomes

Answer 2

• Tiny usually ranging from 50-500 nanometers

• Lysosome enzymes: special enzymes inside lysosomes that break down molecules

• Acidic pH (5.0)

Question 3

What are the three types of lysosomes, and what are their roles in cellular processes?

Answer 3

Primary lysosomes - responsible for storing enzymes

Secondary lysosomes - involved in digesting materials

Tertiary lysosomes - contain undigested waste

Question 4

In which cells are lysosomes found

Answer 4

in all cells expect RED BLOOD CELLS

Question 5

How is the lysomal membrane protected

Answer 5

Protected by its specific structure which includes components like cholesterol and lyso-bisphosphatic acid

Additionally carbohydrate molecules coat the internal face

Question 6

Proteasomes

Labelling for degradation is done with?

Most common proteasome?

Answer 6

•Protein complexes that degrade defective/no longer needed proteins by proteolysis (using proteases)

• Labeling for degradation is done with ubiquitin (you be quitin)

• The most common proteasome in mammals is the one in the cytosol, with a sedimentation rate of 26S, composed of one proteolytic subunit (20S) and two regulatory subunits (19S)

Question 7

Peroxisomes

Answer 7

Small organelles in cells
500-1500 nanometers

Semi autonomous organelles, capable of self-replication by fission (asymmetric division) when necessary
eg. Excess of fatty acids

unusually diverse organelles - may contain different sets of enzymes in different cell types of a single organism.

Question 8

Peroxisome roles

Answer 8

• Beta oxidation of fatty acids with more than 18 carbons

• Decomposition of hydrogen peroxide

• synthesis of lipids

Question 9

Cytoskeleton components

Answer 9

• assembled by polarisation of small subunits

• weak links lead to rapid reorganisation

• Actin and tubulin are polarized.

Question 10

actin-associated proteins

Answer 10

involved in the formation, assembly, stabilization, depolymerization and connection to the membrane.

Question 11

Microfilaments (actin) size

Answer 11

the thinnest filaments of the cytoskeleton (Φ=6-7nm)

Question 12

Microfilaments (actin) organisation

Answer 12

Networks in the cytoplasm of all cells

Bundles in the axis of intestinal microvilli

Bands in the structure of sterocilia

Myofibrils in muscle cells

Question 13

Microfilaments (actin)
Roles

Answer 13

• Structural: maintains cell shape, provides mechanical resistance, supports other components

• Dynamic: cell movement, muscle contraction, formation of contractile rings

Question 14

Intermediar filaments

Answer 14

• intermediate size between actin filaments and microtubules (Φ=10nm);

• They are not polarized, being the most stable components of the cytoskeleton

• keratin filaments (in epithelial cells)

• vimentin filaments (in the mesenchymal cell)

• desmin filaments (in muscle fibers)

• neurofilaments (in neurons)

• nuclear laminae (inside the nucleus, on the inner face of the nuclear envelope).

Question 15

Microtubules

Answer 15

Cylindrical formation = 25 nm

Polarised structure one end -
One end +

Question 16

Microtubules roles

Answer 16

Structural
• membrane specializations (cilia, flagellum)
• The centrosome.

Dynamic:
• intracellular guidance/transport of organelles;
• transport of synaptic vesicles along axons; • formation of division spindle fibers;
• movement of chromosomes during division.

Question 17

Centrosome

Answer 17

• The microtubule organizing center
• Anchored to the nuclear envelope
• Composed of 2 perpendicular centrioles
• It binds to the “-“ end of microtubules.