Tour Of Human Cell

Question 1

Lysosomes

Answer 1

• degrade unwanted molecules
• approximately 50 degradative enzymes (acid hydrolyses)
• optimal ph5

Question 2

Peroxisomes

Answer 2

• membrane bound organelle that perform a large number of biochemical reactions
• contain oxidative enzymes, such as catalase
• breakdown of fatty acids
• production of cholesterol and bile

Question 3

Cytoskeleton

Answer 3

• organise cell structure, maintain correct shape of cell, supports fragile plasma memebrane

Question 4

Intermediate filaments

Answer 4

• structural role
• provide mechanical strength
• different intermediate filaments in different cell types
• keratin in skin epithelia cells

Question 5

Microtubules

Answer 5

• polymers of alpha and beta tubulin
• molecular motors: dynein and kinesin
• cell movement, infra cellular transport of organelles, mitotic spindle

Question 6

Microfilaments

Answer 6

• dynamic processes: cell shape change, cell motility,cell structure

Question 7

Tight junctions

Answer 7

• function as gates and fences
• gate: regulation of paracellular permeability
• fence: formation of apical and basolateral intramembrane diffusion barrier

Question 8

How do proteins get it to organelles

Answer 8

-nuclear pores: selective gates for nuclear proteins
- protein translocators: for proteins moving from cytosol into ER, mitochondria, peroxisomes
- transport vesicles: for proteins moving from the ER onwards

Question 9

Post- translation modifications

Answer 9

• phosphorylation, + of phosphate group= alters activity of protein
• acetylation, + acetyl group= histones- regulation of gene expression
• farnesylation, + a farnesyl group= targets protein to cytoplasmic face of plasma membrane
• ubiquitination, + a ubiquitin chain= targets protein for degradation
• glycosylation, + carb group= preprint folding in ER

Question 10

Lysosomal degradation

Answer 10

• Vesicles containing lysosomal enzymes, eg: lipases, nucleases, proteases
• Activated by acidic environment (pH 4.8)
• Lysosomal degradation used for:
• Proteins with a long half life (>20
hours) = autophagy
• Membrane proteins brought into the cell via endocytosis
• Extracellular proteins brought into the cell via receptor-mediated endocytosis
• Pathogenic proteins brought into the cell via phagocytosis

Question 11

Proteasome degradation

Answer 11

Macromolecular complexes
* Takes place in the cytosol at
proteasomes = cylindrical protein
complexes
* Walls formed from protease enzymes - the active site is inside cylinder
* Proteins targeted to proteasome by labelling it with ubiquitin
* Proteasomal degradation used for:
*Proteins that need to be removed quickly/ short half-life (eg cyclins)
*Defective (misfolded proteins)