Question

1. Describe the general structure and functions of mitochondria

2. Explain how the processes of fission and fusion affect the number, length, and degree of interconnection of mitochondria

3. Describe the structure/composition and function of the mitochondrial membranes and compartments, listing the components of these membranes/compartments that were discussed in class.

4. Explain the advantage conferred by cristae to mitochondria and describe how you would expect the number of cristae to vary depending on the energetic demands of a cell.

Answer 1

1. Mitochondria is power houses of the living cell: It contain outer membrane and inner membrane. In the inner membrane folded structures called Cristae present. The inner mitochondrial membrane contain Electron Transport Chain Complexes and ATP synthase. The core of the mitochondria comprises Matrix, that comprises ribosomes, several copies of Circular DNA molecules and RNA molecules. The main functions of the mitochondria are: Synthecize ATP, Site for the Krebs cycle, Fatty acid degradation. It is also involved in Apoptosis.

2. Mitochondria continually change shape through the combined actions of fission, fusion, and movement along cytoskeletal tracks. The lengths of mitochondria and the degree to which they form closed networks are determined by the balance between fission and fusion rates. These rates are influenced by metabolic and pathogenic conditions inside mitochondria and by their cellular environment. Fission and fusion are important for growth, for mitochondrial redistribution, and for maintenance of a healthy mitochondrial network. In addition, mitochondrial fission and fusion play prominent roles in disease-related processes such as apoptosis and mitophagy. Three members of the Dynamin family are key components of the fission and fusion machineries. Their functions are controlled by different sets of adaptor proteins on the surface of mitochondria and by a range of regulatory processes.

3. The outer mitochondrial membrane, which encloses the entire organelle, is 60 to 75 Å thick. It contains large numbers of integral membrane proteins called porins. These porins form channels that allow molecules of 5000 daltons or less in molecular weight to freely diffuse from one side of the membrane to the other. The outer membrane also contains enzymes involved in such diverse activities as the elongation of fatty acids, oxidation of epinephrine, and the degradation of tryptophan. The mitochondrial outer membrane can associate with the endoplasmic reticulum (ER) membrane, in a structure called MAM (mitochondria-associated ER-membrane). This is important in the ER-mitochondria calcium signaling and is involved in the transfer of lipids between the ER and mitochondria. Outside the outer membrane there are small (diameter: 60Å) particles named sub-units of Parson. The inner mitochondrial membrane contains proteins with five types of functions: Those that perform the redox reactions of oxidative phosphorylation, ATP synthase, which generates ATP in the matrix, Specific transport proteins that regulate metabolite passage into and out of the matrix, Protein import machinery, Mitochondrial fusion and fission protein

4. As the cristae number increased, the surface area also increased. Due to this it accomodate more number of ATP synthases and intern it synthecise more ATP. So the number of cristae is proportional to the ATP production. If cell requires more ATP, that cell containing mitochondria possess more cristae. Vice versa