13.1 Mitochondria

Question 1

Mitochondria are surrounded by a () system

Answer 1

double membrane

Question 2

mitochondrial inner and outer membranes are separated by an ()

Answer 2

intermembrane space

Question 3

the mitochondrial intermembrane space has a similar composition to (), in terms of the ions and small molecules present

Answer 3

cytosol

Question 4

what are the major working compartments of the mitochondria?

Answer 4

1. cristae - folds in the inner mitochondrial membrane
2. matrix - interior of the mitochondria

Question 5

what component of cell respiration occurs in the mitochondrial matrix

Answer 5

citric acid cycle/Krebs cycle (breakdown of carbohydrates and fatty acids)

Question 6

the () is the site of oxidative phosphorylation and thus represents the principal site of ATP generation

Answer 6

inner mitochondrial membrane

Question 7

what properties allow the inner mitochondrial membrane to be the principal site of energy generation (ATP)

Answer 7

1. increased surface area by extending into cristae
2. contains a high percentage of proteins (mostly involved in OXPHOS)

Question 8

the outer mitochondrial membrane is highly permeable to small molecules due to the presence of ()

Answer 8

porins

Question 9

mitochondria are strategically placed in locations of (1) in the cell

Answer 9

high energy use

Question 10

how do mitochondria share genetic material among themselves in the cell

Answer 10

mitochondrial fusion

Question 11

() 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

Answer 11

mitochondrial fission

Question 12

what is a hypothesis on why mitochondria have their own genome?

Answer 12

mitochondria are thought to have evolved from bacteria that began living inside larger cells (endosymbiosis)

Question 13

how do human mitochondrial genomes encode for all mRNAs using only 22 tRNAs?

Answer 13

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)

Question 14

what are some special properties of human mitochondrial genome

Answer 14

1. exceptional wobble rule that allows a single tRNA to recognize 4 different codons
2. some codons in the mitochondria specify different animo acids than in the universal code

Question 15

() can prevent transmission of mutations in mitochondrial genomes

Answer 15

mitochondrial replacement therapy

Question 16

how does mitochondrial replacement therapy work

Answer 16

embryos are created that contain nuclear DNA from the intended mother and mitochondria from a donor with normal mitochondrial genes

Question 17

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 ()

Answer 17

competed polypeptides

Question 18

positively charged () target proteins for import to the matrix and inner membrane, driven by the electrochemical gradient

Answer 18

presequences

Question 19

the protein presequences are cleaved by () following protein import into the mitochondria

Answer 19

matrix processing peptidase (MPP)

Question 20

overview of protein import into the mitochondria using presequences:

Answer 20

1. members of the Hsp70 family of chaperones maintain proteins in a partially unfolded states as well as present them to the Tom complex
2. presequences bind to the Tom complex (translocase of the outer membrane) of the mitochondrial surface
3. the proteins are transferred to the Tim23 complex (one of two translocases of the inner membrane or Tim complexes)
4. mitochondrial matrix proteins are translocated into the matrix though Tim23, while inner membrane proteins exit Tim23 laterally

Question 21

what drives the translocation of mitochondrial matrix proteins through the Tim23 complex?

Answer 21

the electrochemical gradient established across the inner mitochondrial membrane during electron transport drives the transport of the (+) charged presequences

Question 22

most inner mitochondrial membrane proteins are multiple pass transmembrane proteins, thus they contain multiple () signals

Answer 22

internal mitochondrial import

Question 23

the () in the intermembrane space recognizes proteins marked by internal mitochondrial import signals and delivers them to the Tim22 complex

Answer 23

Tim9-Tim10 complex

Question 23

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

Answer 23

Tim22 complex

Question 24

inner membrane proteins encoded by the mitochondrial genome are synthesized by ribosomes within the mitochondrial matrix and targeted to the () in the inner membrane

Answer 24

Oxa1 translocsase

Question 25

what are the 2 kinds of mitochondrial outer membrane proteins

Answer 25

1. ⍺-helical transmembrane proteins
2. β-barrel proteins

Question 26

how are β-barrel proteins incorporated into the outer mitochondrial membrane?

Answer 26

1. partially unfolded proteins enter the intermembrane space through the Tom complex
2. these proteins are then recognized by Tim9-Tim10 complexes that bring them to the SAM complex
3. SAM mediates insertion of proteins into outer membrane

Question 27

how do ⍺-helical transmembrane proteins get inserted into the outer mitochondrial membrane?

Answer 27

they are recognized by chaperons that aid in folding, and are then inserted to the outer membrane through the Mim1 membrane protein

Question 28

most mitochondrial lipids are synthesized in the ()

Answer 28

ER

Question 29

mitochondria catalyze the synthesis of the phospholipid ()

Answer 29

cardiolipin

Question 30

how does cardiolipin improve the efficiency the OXPHOS in the inner mitochondrial membrane

Answer 30

it restricts proton flow across the membrane

Question 31

lipid transfer between ER and mitochondria is mediated by () by extracting single phospholipid molecules from ER membrane

Answer 31

phospholipid transfer proteins

Question 32

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

Answer 32

electrochemical gradient

Question 33

what generates the electrochemical gradient across the inner mitochondrial membrane?

Answer 33

proton pumping during OXPHOS

Question 34

why is the export of ATP in exchange for ADP across the inner mitochondrial membrane energetically favored?

Answer 34

ATP has a more negative charge that favors the accumulated positive charge of the intermembrane space

Question 35

what component of the electrochemical gradient in the mitochondria drives the exchange of OH- and phosphate ions needed for ATP synthesis?

Answer 35

higher pH of the matrix means OH- is more concentrated; this encourages the export of OH- in exchange for phosphate ions

Question 36

what component of the electrochemical gradient in the mitochondria drives the import of pyruvate from the cytosol?

Answer 36

pyruvate is imported into the matrix by exchange for OH-, which is driven by high pH and increased [OH-] in the matrix