Question 18

Describe the structure and function of the mitochondrion. 

[Click here to toggle visibility of the answers]

College Answer

Most candidates had at least a basic understanding of mitochondral function although some 
detail was required for a pass and many did not provide this. A well labelled diagram was used 
by many candidates and scored marks. Repetition of the same information illustrated on a 
labelled diagram in subsequent text was not required and did not score additional marks. 
It was expected answers would cover basic structure (double membrane structure with cristae 
and enzymes lining the membrane and within the matrix), details of the electron transport 
chain, the citric acid cycle and beta-oxidation of long chain fatty acids and mention the 
maternal origin of DNA. Better Answers provided some information on other functions such as 
production of reactive oxygen species, role in calcium homeostasis and apoptosis, urea cycle, 
haem synthesis and heat production

Discussion

In the short span of time allowed by this MCQ, you'd be lucky to produce something as good as this (from Cellular Organelles by Bittar):

mitochondrion from Tyler, 1995

The most important features of mitochondrial structure are as follows:

  • Two membranes
    • Outer membrane with pores
    • Inner membrane without pores
    • These membranes meet at contact sites (areas where membrane lipids and proteins may be exchanged with other organelles)
  • Two separate compartments
    • Intermembrane space or "outer compartment"
    • Matrix space or inner compartment
  • Organisation of the inner membrane into cristae (a comb of many folds) which increases its surface area
  • Molecular components
    • ATP synthase molecules on the inner surface of the inner membrane 
    • Mitochondrial ribosomes in the inner compartment
    • Mitochondrial DNA in the inner compartment
    • Electron dense-granules in the inner compartment (composed of RNA)

Mitochondrial DNA characteristics include

  • Maternal inheritance from oocyte mitochondrial DNA (paternal contribution is minimal)
  • Mitochondrial DNA is short (16,500 base pairs) and encodes only 8 protein subunits (mainly from the electron transport chain)
  • This DNA is susceptible to mutation (10 times more than nuclear DNA)

Mitochondrial function includes:

  • ATP synthesis functions, including:
    • Citric acid cycle
    • Electron transport chain
    • Beta-oxidation of long chain fatty acids
  • Regulatory and synthetic functions
    • Haem synthesis
    • Calcium ion storage
    • Urea cycle
    • Haem synthesis
    • Steroid synthesis
  • As a byproduct of these functions
    • Heat production
    • CO2 production
    • Production of reactive oxygen species
  • Non-metabolic roles
    • Apoptosis

References

Garlid, Keith D. "Physiology of mitochondria." Cell Physiology Source Book. Academic Press, 2001. 139-151.

McCarron, John G., et al. "From structure to function: mitochondrial morphology, motion and shaping in vascular smooth muscle." Journal of vascular research 50.5 (2013): 357-371.

Zeth, Kornelius. "Structure and evolution of mitochondrial outer membrane proteins of β-barrel topology." Biochimica et Biophysica Acta (BBA)-Bioenergetics 1797.6-7 (2010): 1292-1299.

Sagan, Lynn. "On the origin of mitosing cells." Journal of theoretical biology 14.3 (1967): 225-IN6.

Gray, Michael W., Gertraud Burger, and B. Franz Lang. "Mitochondrial evolution." Science 283.5407 (1999): 1476-1481.

Gray, Michael W., Gertraud Burger, and B. Franz Lang. "The origin and early evolution of mitochondria." Genome biology2.6 (2001): reviews1018-1.

Herrmann, Johannes M., and Jan Riemer. "The intermembrane space of mitochondria." Antioxidants & redox signaling 13.9 (2010): 1341-1358.

Pandey, Alok, et al. "Fe-S Cluster Biogenesis in Isolated Mammalian Mitochondria COORDINATED USE OF PERSULFIDE SULFUR AND IRON AND REQUIREMENTS FOR GTP, NADH, AND ATP." Journal of Biological Chemistry290.1 (2015): 640-657.

Colombini, Marco. "VDAC: the channel at the interface between mitochondria and the cytosol." Molecular and cellular biochemistry 256.1-2 (2004): 107-115.

Cortese, Jorge D., A. Laura Voglino, and Charles R. Hackenbrock. "The ionic strength of the intermembrane space of intact mitochondria is not affected by the pH or volume of the intermembrane space." Biochimica et Biophysica Acta (BBA)-Bioenergetics 1100.2 (1992): 189-197.

Srere, Paul A. "The infrastructure of the mitochondrial matrix." Trends in biochemical sciences 5.5 (1980): 120-121.

Srere, Paul A. "The structure of the mitochondrial inner membrane-matrix compartment." Trends in Biochemical Sciences 7.10 (1982): 375-378.

Andersson, B. S., T. Y. Aw, and DEAN P. Jones. "Mitochondrial transmembrane potential and pH gradient during anoxia." American Journal of Physiology-Cell Physiology 252.4 (1987): C349-C355.

Vakifahmetoglu-Norberg, Helin, Amanda Tomie Ouchida, and Erik Norberg. "The role of mitochondria in metabolism and cell death." Biochemical and biophysical research communications482.3 (2017): 426-431.

Starkov, Anatoly A. "The role of mitochondria in reactive oxygen species metabolism and signaling." Annals of the New York Academy of Sciences 1147.1 (2008): 37-52.

Lane, Nick. "Hot mitochondria?." PLoS biology 16.1 (2018): e2005113.

Rolfe, D. F., and Guy C. Brown. "Cellular energy utilization and molecular origin of standard metabolic rate in mammals." Physiological reviews 77.3 (1997): 731-758.

Challoner, David R. "Respiration in myocardium." Nature217.5123 (1968): 78.

Jastroch, Martin, et al. "Mitochondrial proton and electron leaks." Essays in biochemistry 47 (2010): 53-67.

Brand, Martin D., et al. "The causes and functions of mitochondrial proton leak." Biochimica et Biophysica Acta (BBA)-Bioenergetics 1187.2 (1994): 132-139.

Cannon, Barbara, and Jan Nedergaard. "Studies of thermogenesis and mitochondrial function in adipose tissues." Adipose Tissue Protocols. Humana Press, 2008. 109-121.

Himms-Hagen, Jean. "Cellular thermogenesis." Annual Review of Physiology 38.1 (1976): 315-351.

Prusiner, S. T. A. N. L. E. Y., and M. A. R. T. I. N. Poe. "Thermodynamic considerations of mammalian heat production." Brown adipose tissue (1970): 263-282.

Chrétien, Dominique, et al. "Mitochondria are physiologically maintained at close to 50 C." PLoS biology 16.1 (2018): e2003992.

Clarke, Andrew, and Hans‐Otto Pörtner. "Temperature, metabolic power and the evolution of endothermy." Biological Reviews 85.4 (2010): 703-727.

Church, Stanley. "Heat loss and the body temperatures of flying insects. I. Heat loss by evaporation of water from the body." J. Exp. Biol.(in the. 1959.

Murphy, Michael P. "How mitochondria produce reactive oxygen species." Biochemical journal 417.1 (2009): 1-13.

Ito, Kikukatsu. "Isolation of two distinct cold-inducible cDNAs encoding plant uncoupling proteins from the spadix of skunk cabbage (Symplocarpus foetidus)." Plant Science 149.2 (1999): 167-173.

Andreyev, A. Yu, Yu E. Kushnareva, and A. A. Starkov. "Mitochondrial metabolism of reactive oxygen species." Biochemistry (Moscow) 70.2 (2005): 200-214.

Wang, Chunxin, and Richard J. Youle. "The role of mitochondria in apoptosis." Annual review of genetics 43 (2009): 95-118.

Vandecasteele, Grégoire, György Szabadkai, and Rosario Rizzuto. "Mitochondrial calcium homeostasis: mechanisms and molecules." IUBMB life 52.3‐5 (2001): 213-219.

Roux, Etienne, Jean-Pierre Mazat, and Marko Marhl. "Role of mitochondria in calcium homeostasis and contraction of smooth muscle cells." Mitochondria: Structure, Functions and Dysfunctions. Edited by Svensson OL. Hauppauge NY: Nova Publisher (2009).

Mesmin, Bruno. "Mitochondrial lipid transport and biosynthesis: A complex balance." J Cell Biol 214.1 (2016): 9-11.

Steenbergen, Rineke, et al. "Disruption of the phosphatidylserine decarboxylase gene in mice causes embryonic lethality and mitochondrial defects." Journal of Biological Chemistry 280.48 (2005): 40032-40040.

Rimington, C., and B. E. Tooth. "Role of mitochondria in the in vitro formation of protoporphyrin and haem." The Journal of Biochemistry 49.6 (1961): 456-467.

Chung, Jacky, Caiyong Chen, and Barry H. Paw. "Heme metabolism and erythropoiesis." Current opinion in hematology 19.3 (2012): 156.

Drysdale, Jim, et al. "Mitochondrial ferritin: a new player in iron metabolism." Blood Cells, Molecules, and Diseases 29.3 (2002): 376-383.

Lim, Sangbin, Anusha Angajala, and Ming Tan. "Diverse roles of mitochondria in immune responses: Novel insights into immuno-metabolism." Frontiers in immunology 9 (2018): 1605.

Stewart, James B., and Patrick F. Chinnery. "The dynamics of mitochondrial DNA heteroplasmy: implications for human health and disease." Nature Reviews Genetics 16.9 (2015): 530.

Fox, Thomas D. "Mitochondrial protein synthesis, import, and assembly." Genetics 192.4 (2012): 1203-1234.