| How are mitochondria observed? | LM but ultrastructure is seen by EM |
| How are mitochondria found? | Present in eukaryotes only, transmitted by mother only since sperm contains only the nucleus and their mitochondrion are not transmitted to the zygote. But it is not 100% maternal since its proteins are encoded by either paternal or maternal genetic material. |
| Talk about mitochondrial variation. | Their size shape structural organization number per cells intracellular location vary considerably among species and even among tissues of the same species as well as in the same cell type according to its physiological activity, In general, when mitochondria numbers are low, organelles are large and vice versa. |
| Talk about the presence rate of mitochondria. | certain microorganisms have one mitochondria, others have several thousands of them (liver cells, muscle fibers)
Usually concentrated in metabolically active regions for example epithelia apical pole where much ATP are synthesized (needed for nutrient transport as energy) through plasma membrane and endo and exocytosis. |
| How are mitochondria present in muscle fibers and sperms? | Muscle fibers: aligned in rows parallel to contractile fibrils (actin and myosin)
Spermatozoa: located on basis of flagellum to supply necessary ATP for movement to mediate locomotion of sperm. |
| How is number of mitochondria varying? | number may increase or decrease depending on physiology, for instance, actively dividing cell and mobile cell have more mitochondria than stationary ones or during interphase. cells cultured in O2 absence have fewer mitochondria and become richer in aerobic medium. |
| How do mitochondria proliferate? | By fission of preexisting mitochondria, no assembly of components to form a new one,
mitochondrion divides to form to smaller ones after it has doubled its contents, especially DNA and proteins. Increase in mitochondrial size requires import of proteins and lipids produced by other cell compartments and replication of mitochondrial DNA. |
| Talk about mitochondrial membrane in general | Mitochondria has two membranes having two different surface areas and distinct properties and functions, separated by intermembrane space, each is a lipid bilayer, intermembrane space is usually narrow but may expand during aerobic cell respiration. Mitochondrial matrix is enclosed by these membranes and contains nearly all kinds of organic and inorganic molecules. |
| Talk generally about the function of mitochondria. | Oxidation of organic compounds (into carbon and water) and aerobic cell respiration which leads to the production of ATP (process known as oxidative phosphorylation. |
| Talk about prokaryotic oxidation and cell respiration. | Although they do not have mitochondria, they carry out oxidation of organic compounds and cell respiration by enzymes of cytoplasm and plasma membrane. For instance, ATP synthase in aerobic bacteria are similar to those of mitochondria and are located in the inner face of plasma membrane. |
| Talk about the structure of mitochondria. | 1-4 microm in length, 0.2-1 microm in diameter, however there are mitochondria that are organized as interconnected tubular network (yeast, mammalian cells) or spiral form (sperm) |
| Describe the mitochondrial membrane. | Inner membrane is thicker than outer (60A-80A) and has a greater surface area because it presents inward folds called cristae. Density, shape and orientation of cristae are variable depending on tissue and aerobic activity level (cell respiration rate.) For example: hepatocyte cristae are lamellar, whereas adrenal glands are tubular, protists as well.
Moreover IMM defers from OMM in terms of protein content (outer has 50% proteins whereas inner has 75% in weight) IMM is devoid of cholesterol and has over 100 types of proteins. |
| List some proteins present in OMM. | Those that catalyze oxidation of certain aa, those that elongate FA, and porins or channels (2-3nm in diameter) that are wide enough and highly permeable to cytosolic solutes. Moreover they contain complex channels that import mitochondrial proteins synthesized by free ribosomes. |
| List some proteins present in IMM | ATP synthase, (F0F1 complex) and respiratory chain proteins, proteins needed for control of Ca+ concentration in cytosol which triggers many metabolic processes. It also contains transporters that export ATP to the cytosol and import ADP, and it may have some mitochondrial ribosomes attached to it. |
| What is the respiratory chain? | metabolic chain not physical, composed of four enzymatic complexes, proteins of this chain act in a sequential manner although not covalently bonded. Among them there are proteins such as cytochromes (hemoproteins) and flavoproteins (FAD with proteins) involved in oxidation reduction reactions.
respiratory chain performs cell respiration by oxidizing the coenzymes that are reduced during glycolysis, Krebs cycle, beta-oxidation. Cell respiration generates a proton gradient during the transfer of electrons from coenzymes to O2. |
| Talk about the mechanism of respiratory chain. | collaborates with ATP synthase complex in order to produce ATP, ATP synthase is a globular protein composed of several subunits located in inner face of IMM and coupled to integral proteins forming a channel. |
| What does the difference in composition of IMM and OMM explain? | Great difference of their respective permeabilities and functions, actually IMM has restricted permeability whereas OMM is permeable to a wide variety of substances (because of presence of porins) |
| Where are mitochondrial membrane lipids produced? | By enzymes of RER membrane and then exported to OMM and IMM (not through vesicles). However certain lipids are produced or modified by mitochondrion itself since OMM contains enzymes of fatty acid metabolism. |
| Talk about the mitochondrial matrix. | Has a gel-like consistency since it has a high protein concentration, there are several circular DNA molecules, ribosomes (differ from cytoplasmic) tRNA and enzymes necessary for gene expression, it also contains enzymes that catalyze oxidation of organic compounds, Krebs cycle and beta-oxidation ones. |
| Talk about protein synthesis in mitochondria. | DNA carries genes that encode 13 proteins in mammals, all other proteins are encoded by nuclear genes and synthesized by free ribosomes, after translation these proteins are sent to the mitochondria precisely through one of the 4 different subcompartments which are: Matrix, IMM OMM and intermembrane space. |
| Talk about import of protein mechanism. | Proteins are post-translationally imported towards the mitochondria. It is possible due to the presence of a certain address code whose named presequence or targeting sequence, located near N-terminus of polypeptide chains and contains a number of positively charged presequence and mediates with the help of chaperons HSP proteins, translocation towards the mitochondria through the TOM and TIM (translocases) complexes present in OMM and IMM respectively, they are multisubunit channels specialized in import to mitochondrion, presequence is removed after delivery by proteases of mitochondria. |
| Talk about the oxidation function of mitochondria. | They extract energy from organic components and store it temporarily in form of electrochemical energy that is a proton gradient across IMM which is utilized by ATP synthase for ATP synthesis.
Oxidation reaction: organic compound--->H2O + CO2 + energy by metabolic reactions (Krebs and beta oxidation cylces) and aerobic cell respiration coupled to oxidative phosphorylation (ATP synthesis). |
| What is oxidation? | Loss of electrons and protons which are transferred from oxidized organic molecules to specific coenzymes (NAD, FAD) Then electrons and protons are transferred through respiratory chain proteins and finally accepted by O2 to produce H2O. |
| What is oxidative phosphorylation? | As electrons move into the mitochondria, proton gradient is generated by going outside of it which triggers the ATP synthase, since energy is used to turn ADP into ATP as an energy source. |
| How does the mitochondria act in the oxidation manner when in anaerobic medium? | Cell respiration is replaced by fermentation of organic compounds (because electrons cannot be accepted by the O2 which is absent.) which produces incomplete oxidized compounds (lactic acid, ethanol...) |
| Talk about carbohydrate oxidation in mitochondria. | Polysaccharides are first digested into monosaccharides in digestive tract. Glucose mainly in transported to the cell which starts oxidation in cytosol and terminated in the mitochondria, oxidation is in two steps: glycoslysis and Krebs cycle AKA tricarboxylic acid cycle and cytric acid cycle. first one occurs in cytosol while others occur in mitochondrial matrix. |
| Talk about glycolysis. | 10 reaction series catalyzed by different enzymes, may be endergonic or exogonic. Final outcome has positive energy (secretion), covert glucose into 2 glyceraldehyde which are then converted into pyruvic acid (3C) |
| Talk about Krebs cycle. | series of 8 reactions, takes place in mitochondrial matrix aerobic, pyruvate is converted first into acetyl (CH3-CO-) by decarboxylation (removal of CO2) and reduction of NAD+ into NADH, H+ for each results in reaction between acetyl and CoA making acetyl CoA which leads finally to production of CO2 and transfer of all electrons into CoA. (NAD and FAD) and produce a small amount of GTP |
| How do all organic compounds oxidation pathways intersect? | All of them intersect at acetyl CoA which is oxidized by Krebs cycle which is involved in oxidation of 500 metabolites. |
| Talk about fatty acid oxidation. | They are oxidized in mitochondria as well as peroxisomes by cyclic metabolic reaction called beta-oxidation in matrix of mitochonria.20 carbon atoms are oxidized into 10 acetyl CoA in 9 cycles, and then enter TCA cycle to produce more energy. |
| What happens to reduced coenzymes? | NADH H+ and FADH2 are reoxidized by respiratory chain that transfers electrons and protons to oxygen and producing water and proton gradient. Function of mitochondrion is same for animal and plants |
