L3 - The Host II

Proteasome

A complex that degrades and recycles damaged or unneeded proteins within a cell, playing a critical role in maintaining cellular homeostasis.

3 cellular homeostasis methods

• Unfolded protein response

• Proteasome

• Autophagy

Chaperone proteins

Proteins that assist in the proper folding and assembly of other proteins, preventing misfolding and aggregation.

ER Stress Response Cascade

1. Shut-down of protein translation

2. Degradation of mRNA

3. Protein degradation

4. ER Expansion

What mediates the shutdown of protein translation?

PERK

What mediates the degradation of mRNA?

IRE1

What mediates protein degradation?

Xbp1

What mediates ER expansion?

ATF6

Ubiquitination

Process that tags proteins for degradation by the proteasome, allowing for the selective removal of damaged or misfolded proteins.

Ubiquitin-proteasome pathway

A complex of 3 proteins which together contitute a ubiquitin ligase that recognises a protein destined for degradation and facilitates its transfer to the proteasome for breakdown.

Polyubiquitination

Process of attaching multiple ubiquitin molecules to a target protein, signalling it for degradation by the proteasome.

Immunoproteasome

A specialised proteasome used to process proteins for antigen presentation

Endocytosis

Process to bring extracellular material into the cell

Ways endocytosis is utilised

• Recycling membrane molecules

• Eukaryotic cell feeding

• Digestion

• Degradation of foreign microbes

Main methods of endocytosis

• Pinocytosis

• Phagocytosis

• Receptor-mediated endocytosis

Pinocytosis

The process by which a cell engulfs liquid or small particles from the extracellular environment, often referred to as "cell drinking."

Phagocytosis

The process by which a cell engulfs large particles, such as bacteria or dead cells, often called "cell eating."

Receptor-mediated endocytosis

A specialised process where cells internalise substances by binding them to specific receptors on the cell surface, allowing for selective uptake.

Clathrin

A protein that plays a key role in receptor-mediated endocytosis by forming a coat around vesicles, assisting in the internalisation of membrane-bound receptors and their ligands.

GTPase dynamin

A GTPase enzyme that is crucial for membrane fission during endocytosis, facilitating the detachment of vesicles from the plasma membrane.

Lysosome

An organelle that contains digestive enzymes to break down waste materials and cellular debris within the cell.

3 Classes of lysosomes

• Early

• Late

• Recycling

How viruses enter the cell

Viruses act as a ligand & bind to a cell surface receptor to promote the accumulation of clathrin & endocytosis

Low Density Lipoprotein

Generates cholesterol and binds to a receptor to facilitate its uptake into cells.

Autophagy

Second degradation pathway in lysosomes where the cell degrades its own constituents & recycles them

Autophagasome

A double-membraned structure formed during autophagy, which engulfs cellular components for degradation in lysosomes.