BIOB10H3 Lecture Notes - Lecture 7: Beta Sheet, Mitochondrial Fission, Mitochondrial Matrix
14 Jun 2018
School
Department
Course
Professor
May 31, 2018
Lecture 7
Mitochondria
• arose from phagocytosis of aerobic prokaryote
• can divide in the cell: “mitochondrial fission”
• For final: study evidence of endosymbiotic theory and mitochondria being a
bacterium
o Mitochondrial DNA is good evidence that it used to be a bacterium
o Cardiolipin is an important component of IMM, it’s also found in the
membrane of most bacteria
• Functions:
o site of aerobic respiration (producing energy requiring oxygen)
o utilizing oxygen to extract energy from macromolecules (primarily glucose)
and converting it to ATP – ATP Production
• we use 2 x 1026 molecules of ATP/day
• ATP- cells energy source: energy is released when ATP is hydrolyzed to ADP
+ Pi
• Many mitochondria in: muscle cells, liver cells, fat cells, plant cells & sperm
• Outer membrane -> intermembrane space -> inner membrane (cristae) -> matrix
Outer Mitochondrial Membrane (OMM)
• 50% protein: 50% lipid
• contain porin proteins – are large channels in cellular membrane act as a pore
to allow passive diffusion. Allows very large molecules through.
o Porin proteins have beta pleated sheets
Inner Mitochondrial Membrane (IMM)
• 75% protein: 25% lipid (lipid = cardiolipin)
• Cristae – many thin folds of IMM to increase the surface area
• Cardiolipin – unique phospholipid – also found in many bacterial membranes
• IMM very impermeable due to cardiolipin: therefore channels & pumps are
required to move things across 100 different proteins Including proteins of the
ETC
Matrix
• gel-like from high protein [ ]
• contains DNA and ribosomes, tRNA
• mitochondrial DNA encodes for 37 genes
• However, mitochondrial function requires 3,000 proteins
find more resources at oneclass.com
find more resources at oneclass.com
o Therefore,
mitochondria function
requires nuclear gene
products, and these
proteins must be
imported (targeted) to
mitochondria
o Protein translocons
are also involved in
an import of proteins
into mitochondria
o Mitochondria proteins
are completely
translated on free
ribosomes in cytosol
Posttranslational uptake of
proteins into Mitochondria
• What is the targeting
sequence of mitochondrial
proteins?
1. Mitochondrial “pre-
sequence”
o at amino terminus of “preprotein”
o several (+)-charged amino acids
o For soluble matrix proteins
2. Internal targeting sequence & stop transfer sequence
o For integral IMM proteins
• To enter mitochondria:
o Protein is first unfolded by HSP 70
o Protein binds to its receptor on OMM that’s located next to a translocon
(TOM) on OMM.
▪ TOM: translocon of outer membrane
• IMM integral proteins:
o directed to TIM22 complex of IMM
▪ TIM: Translocon of inner membrane
o stop transfer sequence embeds protein in the IMM
▪ includes all the proteins of the ETC and the ATP synthase
o Protons in intermembrane space help to push protein through translocon
• Matrix proteins:
o directed to TIM23 complex of IMM
o preprotein moves through TIM because of membrane potential differences
across IMM
o associates with mt-HSP 70 which also helps pull it through to the matrix
Once in matrix:
o associates with HSP 60 that folds preprotein
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
+ pi: many mitochondria in: muscle cells, liver cells, fat cells, plant cells & sperm, outer membrane -> intermembrane space -> inner membrane (cristae) -> matrix. Outer mitochondrial membrane (omm: 50% protein: 50% lipid, contain porin proteins are large channels in cellular membrane act as a pore to allow passive diffusion. Allows very large molecules through: porin proteins have beta pleated sheets. Inner mitochondrial membrane (imm: 75% protein: 25% lipid (lipid = cardiolipin, cristae many thin folds of imm to increase the surface area, cardiolipin unique phospholipid also found in many bacterial membranes. Imm very impermeable due to cardiolipin: therefore channels & pumps are required to move things across 100 different proteins including proteins of the. Once in matrix: associates with hsp 60 that folds preprotein, mitochondrial processing peptidase (mpp); a protease, then cuts off pre- sequence to create mature protein.
