Bio 11/9

What sort of sequence is on a protein destined for the mitochondria?

An amphipathic alpha helix presequence (aka transit sequence) at N terminus. Positively charged on one side, hydrophobic on other.

Mitochondrial Import: What does the presequence first do?

Recruites chaperones of HSP70, which wrap the backbone of the protein and prevent folding

Mitochondrial Import: HSP70 targets _______ complex to ________

ribosome/mRNA - mitochondrial outer membrane

Mitochondrial Import: Once at outer mitochondrial membrane, what does presequence do?

binds to presequence receptor, which is associate with a translocon (TOM)

Mitochondrial Import: Once ribosome/mRNA complex is at outer mitochondrial membrane, what happens?

translocon of outer membrane (TOM) and translocon of inner membrane (TIM) align

Mitochondrial Import: After translocons are aligned, what happens? And how?

HSP70s are removed from protein (energetically unfavorable reaction). Need to hydrolyze 1 ATP per HSP70.

Mitochondrial Import: After transit sequence (presequence) gets into inner mitochondrial membrane, what happens?

it is cleaved off by transit peptidase

Mitochondrial Import: What happens to the AA chain as it enters the inner mitochondrial membrane?

HSP70s inside the mitochondria wrap it around. Effectively pulling it through the translocon

Mitochondrial Import: Last step in process?

HSP70s inside the mitochondria are removed from protein (again costing, 1ATP/HSP70)

What is the structure of the golgi complex?

Like stacked pancakes called cisternae

What are the three main parts of the golgi complex?

Cis Golgi Network (CGN) closest to ER and nucleus, receives proteins), Medial Golgi Network (MGN), Trans Golgi Network (TGN)

Main function of golgi complex?

add sugars to proteins to be secreted (glycosylation), sort proteins

As opposed to most proteins inside the cell, proteins to be secreted have what attached to them and how?

Covalently attached sugars

Protein sorting enzyme that removes sugars is called…

glycosidase

Protein sorting enzyme that adds sugars is called…

transferase

Protein sorting enzyme that phosphorlylates sugars is called…

kinase

N-Linked glycosylation: where does it happen? sugar attached to what?

ER, asparagine

O-Linked glycosylation: where does it happen? sugar attached to what?

golgi, serine + threonine

Why is glycosylation important?

1. Determines blood type. 2. Has profound implications on protein folding. 3. Glycosylation regulates protein sorting

What are lysosomes? What are the main features?

cellular recycling centers. Contain hydrolytic enzymes, at really low pH (very acidic)

What are hydrolytic enzymes?

they break down almost anything, but only function at low pH (very acidic)

What's at the N terminus of the nRNA sequence for hydrolytic enzyme?

A signal sequence! (so must first be made in the ER)

What sort of event happens to proteins destined to be hydrolytic enzymes in the ER?

A glycolysis event where Mannose-6-Phosphate is attached to the protein

What is the purpose of the Mannose-6-Phosphate on the enzyme?

The Mannose-6-Phosphate(M6P) binds the M6P receptor, which also targets everything to a lysosome

How do the hydrolytic enzymes finally function normally in a lysosome?

The vessicle gets acidified -> M6P no longer binds to the M6P receptor -> the vesicle splits -> enzyme now in lysosome, M6P receptor back to TGN

What kind of bonds held M6P to M6P receptor?

ionic (broke with very low pH).