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Lecture 7

BIOB10H3 Lecture Notes - Lecture 7: Virulence-Related Outer Membrane Protein Family, Mitochondrial Matrix, Intermembrane Space

Biological Sciences
Course Code
Aarti Ashok

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Structure & Function
Mitochondria: origin
-Mitochondria arose from aerobic prokaryotes - phagocytosed by eukaryotes
-Mitochondria can divide within the cell - ^u]}Z}v]o(]]}v_
Mitochondria: structure
-Outer membrane (OMM)
-Inner membrane (cristae) Å two are intermembrane space
-Matrix Å GEL LIKE
-2 membranes
-2 aqueous compartments
Mitochondria structure: OMM Æ The outer mitochondrial
-serves as the outer boundary of the organelle
-has ~ 50% protein : 50% lipid ratio
-has a diverse number of proteins that function as enzymes
-several large protein channels t porins
- Not specific & variety of moleciles
-t-pleated sheets
-can allow passage of large number of molecules ((e.g. ATP)
-respond to conditions within the cell Æ E.G. cell stress
Mitochondria structure: IMM
The inner mitochondrial membrane Æ thin folds
-has cristae
-has ~75% protein: 25% lipid ratio
-almost 100 different proteins present and has almost no cholesterol
-is rich in a phospholipid called cardiolipin Æ found in many bacterial membrane
-very impermeable to molecules and has many channels & pumps Æ highly selective
Mitochondria structure: matrix
-gel-like consistency from the high concentration of proteins and DNA
-contains DNA (own genetic material) and ribosomes
-mitochondrial DNA encodes ~ 37 genes in humans
Mitochondrial proteins
-The majority of proteins that function in the mitochondria are encoded by DNA in the cell nucleus
-These proteins are translated on free ribosomes in the cytosol
-They then need to be imported into the mitochondria Æ POST-translational import protein

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Mitochondria are cellular organelles.
What do you need to target proteins to an organelle? SIGNAL
Mitochondrial proteins: signals for import
Matrix proteins:
Signal = u]}Z}v]o^µv_
-at the N-terminus of proteins: composed of several positively charged residues Æ +
IMM proteins (integral membrane proteins):
Contain internal targeting sequences (poorly defined) and stop- transfer sequences
Mitochondria: importing proteins
-For mitochondrial import, proteins need to be in an unfolded state
-helped by chaperone proteins in the cytosol Æ E.G. HSP 70
-Unfolded proteins then bind to membrane receptors on OMM
-Receptors are located close to large protein channels called TOM complexes
TOM = translocase (or transporter) of the outer membrane
-help to move proteins past the OMM into the intermembrane space
Å Fig 8.47
- bound by chaperone to keep it unfold,
then interact with receptor
Post-translational import of IMM proteins
-proteins delivered to the intermembrane space
then interact with the TIM 22 complex
-TIM = translocase (or transporter) of the
inner membrane
-stop transfer sequence then interacts with channel
and is moved laterally into the IMM
Æ fig. Interact with TIM to inner membrane
-several proteins that are involved in energy
production are imported by this pathway
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