13.1 Mitochondria Flashcards
Mitochondria are surrounded by a () system
double membrane
mitochondrial inner and outer membranes are separated by an ()
intermembrane space
the mitochondrial intermembrane space has a similar composition to (), in terms of the ions and small molecules present
cytosol
what are the major working compartments of the mitochondria?
- cristae - folds in the inner mitochondrial membrane
- matrix - interior of the mitochondria
what component of cell respiration occurs in the mitochondrial matrix
citric acid cycle/Krebs cycle (breakdown of carbohydrates and fatty acids)
the () is the site of oxidative phosphorylation and thus represents the principal site of ATP generation
inner mitochondrial membrane
what properties allow the inner mitochondrial membrane to be the principal site of energy generation (ATP)
- increased surface area by extending into cristae
- contains a high percentage of proteins (mostly involved in OXPHOS)
the outer mitochondrial membrane is highly permeable to small molecules due to the presence of ()
porins
mitochondria are strategically placed in locations of (1) in the cell
high energy use
how do mitochondria share genetic material among themselves in the cell
mitochondrial fusion
() is important in the distribution of mitochondria between daughter cells at cell division, as well as for transport of mitochondria to areas of high energy demand
mitochondrial fission
what is a hypothesis on why mitochondria have their own genome?
mitochondria are thought to have evolved from bacteria that began living inside larger cells (endosymbiosis)
how do human mitochondrial genomes encode for all mRNAs using only 22 tRNAs?
the mitochondrial genetic code has a special “wobble” rule that allows U (uracil) in the tRNA anticodon to pair with any of the bases in the 3rd codon position of mRNA (4 codons can be recognized by a single tRNA)
what are some special properties of human mitochondrial genome
- exceptional wobble rule that allows a single tRNA to recognize 4 different codons
- some codons in the mitochondria specify different animo acids than in the universal code
() can prevent transmission of mutations in mitochondrial genomes
mitochondrial replacement therapy
how does mitochondrial replacement therapy work
embryos are created that contain nuclear DNA from the intended mother and mitochondria from a donor with normal mitochondrial genes
most proteins imported to the mitochondria don’t have signal sequences that trigger their transport to the ER, thus they are transported to the mitochondria as ()
competed polypeptides
positively charged () target proteins for import to the matrix and inner membrane, driven by the electrochemical gradient
presequences
the protein presequences are cleaved by () following protein import into the mitochondria
matrix processing peptidase (MPP)
overview of protein import into the mitochondria using presequences:
- members of the Hsp70 family of chaperones maintain proteins in a partially unfolded states as well as present them to the Tom complex
- presequences bind to the Tom complex (translocase of the outer membrane) of the mitochondrial surface
- the proteins are transferred to the Tim23 complex (one of two translocases of the inner membrane or Tim complexes)
- mitochondrial matrix proteins are translocated into the matrix though Tim23, while inner membrane proteins exit Tim23 laterally
what drives the translocation of mitochondrial matrix proteins through the Tim23 complex?
the electrochemical gradient established across the inner mitochondrial membrane during electron transport drives the transport of the (+) charged presequences
most inner mitochondrial membrane proteins are multiple pass transmembrane proteins, thus they contain multiple () signals
internal mitochondrial import
the () in the intermembrane space recognizes proteins marked by internal mitochondrial import signals and delivers them to the Tim22 complex
Tim9-Tim10 complex
Tim9-Tim10 complex brings multiple pass inner membrane proteins marked with internal mitochondrial import signals to the (), which partially translocates and allows the proteins to exit laterally once transmembrane sequences are encountered
Tim22 complex
inner membrane proteins encoded by the mitochondrial genome are synthesized by ribosomes within the mitochondrial matrix and targeted to the () in the inner membrane
Oxa1 translocsase
what are the 2 kinds of mitochondrial outer membrane proteins
- ⍺-helical transmembrane proteins
- β-barrel proteins
how are β-barrel proteins incorporated into the outer mitochondrial membrane?
- partially unfolded proteins enter the intermembrane space through the Tom complex
- these proteins are then recognized by Tim9-Tim10 complexes that bring them to the SAM complex
- SAM mediates insertion of proteins into outer membrane
how do ⍺-helical transmembrane proteins get inserted into the outer mitochondrial membrane?
they are recognized by chaperons that aid in folding, and are then inserted to the outer membrane through the Mim1 membrane protein
most mitochondrial lipids are synthesized in the ()
ER
mitochondria catalyze the synthesis of the phospholipid ()
cardiolipin
how does cardiolipin improve the efficiency the OXPHOS in the inner mitochondrial membrane
it restricts proton flow across the membrane
lipid transfer between ER and mitochondria is mediated by () by extracting single phospholipid molecules from ER membrane
phospholipid transfer proteins
the energy required for the transport of small molecules into and out of the mitochondria is provided by the () generated by proton pumping across the inner mitochondrial membrane during OXPHOS
electrochemical gradient
what generates the electrochemical gradient across the inner mitochondrial membrane?
proton pumping during OXPHOS
why is the export of ATP in exchange for ADP across the inner mitochondrial membrane energetically favored?
ATP has a more negative charge that favors the accumulated positive charge of the intermembrane space
what component of the electrochemical gradient in the mitochondria drives the exchange of OH- and phosphate ions needed for ATP synthesis?
higher pH of the matrix means OH- is more concentrated; this encourages the export of OH- in exchange for phosphate ions
what component of the electrochemical gradient in the mitochondria drives the import of pyruvate from the cytosol?
pyruvate is imported into the matrix by exchange for OH-, which is driven by high pH and increased [OH-] in the matrix
