Mitochondria Structure

Mitochondria Structure

• Mitochondria have an inner and outer membrane, with an intermembrane space between them.
• The outer membrane contains proteins known as porins, which allow movement of ions into and out of the mitochondrion. Enzymes involved in the elongation of fatty acids and the oxidation of adrenaline can also be found on the outer membrane.
• The space within the inner membrane of the mitochondrion is known as the matrix, which contains the enzymes of the Krebs(TCA) and fatty acid cycles, alongside DNA, RNA, ribosomes and calcium granules.
• The inner membrane contains a variety of enzymes. It contains ATP synthase, which generates ATP in the matrix, and transport proteins that regulate the movement of metabolites into and out of the matrix.
• The inner membrane is arranged into cristae to increase the surface area available for energy production via oxidative phosphorylation.

Functions

The mitochondrion is the site of ATP synthesis for the cell. Therefore, the number of mitochondria found in a cell is a good indicator of the cell’s rate of metabolic activity; cells that are very metabolically active, such as hepatocytes, will have many mitochondria.

Mitochondria also have a role in helping maintain the intracellular environment. They

• store caspases responsible for triggering
• They can store calcium contributing to calcium homeostasis transiently.

In brown adipose tissue, mitochondria have an alternative function of heat production using the electron transport chain. The main job of mitochondria is to perform cellular respiration. This means it takes in nutrients from the cell, breaks it down, and turns it into energy. This energy is then, in turn, used by the cell to carry out various functions.

Structure of Chloroplasts

• Chloroplasts found in higher plants are generally biconvex or planoconvex shaped.
• Chloroplasts can be found in the cells of the mesophyll in plant leaves.
• In different plants, chloroplasts have different shapes, and they vary from spheroid, filamentous saucer-shaped, discoid or ovoid-shaped.
• They are vesicular and have a colourless center.
• Some chloroplasts are in the shape of a club, they have a thin middle zone, and the ends are filled with chlorophyll.
• In algae, a single colossal chloroplast is seen that appears as a network, a spiral band or a stellate plate.
• The size of the chloroplast varies from species to species, and it is constant for a given cell type.
• In higher plants, the average size of the chloroplast is 4-6 µ in diameter and 1-3 µ in thickness.

Functions

• Absorption of light energy and conversion of it into biological energy.
• Production of NAPDH2 and evolution of oxygen through the process of photosys of water.
• Production of ATP by photophosphorylation. NADPH2 and ATP are the assimilatory powers of photosynthesis. Transfer of CO2 obtained from the air to 5 carbon sugar in the stream during the dark reaction.
• Breaking of 6-carbon atom compound into two molecules of phosphoglyceric acid by the utilization of assimilatory powers.
• Conversion of PGA into different sugars and store as stratch. The chloroplast is very important as it is the cooking place for all the green plants. All heterotrophs also depend on plasts for this food.
• In plants all the cells participate in plant immune response as they lack specialized immune cells.
• The chloroplasts with the nucleus and cell membrane and ER are the key organelles of pathogen defense.
• The most important function of chloroplast is to make food by the process of photosynthesis.
• Food is prepared in the form of sugars. During the process of photosynthesis sugar and oxygen are made using light energy, water, and carbon dioxide.
• Light reactions takes place on the membranes of the thylakoids.
• Chloroplasts, like the mitochondria use the potential energy of the H+ ions or the hydrogen ion gradient to generate energy in the form of ATP.
• The dark reactions also known as the Calvin cycle takes place in the stroma of chloroplast.
• Production of NADPH2 molecules and oxygen as a result of photolysis of water.
• By the utilization of assimilatory powers the 6-carbon atom is broken into two molecules of phosphoglyceric acid.

Similarities

Mitochondria and chloroplast both have:

• A double membrane surrounding the organelles.
• Purportedly prokaryotic origins according to the endosymbiotic theory which suggests that mitochondria and chloroplast were once prokaryotic bacteria engulfed by endocytosis in early eukaryotes.
• Their own circular DNA which codes for certain enzymes required for the chemical reactions that take place in these organelles.
• Their own 70S ribosomes made up of 50S and 30S subunits to translate proteins
• The enzyme ATP synthase which utilizes the energy released from the movement of protons across it (proton-motive force) to phosphorylate ADP to ATP. (Thus, another similarity would be that they both produce ATP)
• Electron transport chains, which are embedded in the inner mitochondrial membrane and thylakoid membrane in mitochondria and chloroplasts respectively.
• Both organelles have chemical cycles in which the initial acceptor is regenerated at the end of the cycle. In mitochondria, the Krebs cycle occurs after which oxaloacetate is regenerated at the end of the reaction. In chloroplasts, the Calvin cycle occurs in which ribulose bisphosphate (RuBP) is regenerated at the end of the reaction.
• convert energy
• have its own DNA
• enclosed by two membranes
• oxygen (O₂) and carbon dioxide (CO₂) are involved in its processes
• both have fluids inside of them.

Differences

• Obvious structural and naming differences that you should be able to figure out from the diagram above.
• Mitochondria are involved in cellular respiration whereas chloroplasts are involved in photosynthesis. Thus, the overall chemical reactions for the processes occurring in them are different and reversed.

– Respiration: C6H12O6+6O2 —> 6CO2+6H2O+ATP

– Photosynthesis: 6CO2+6H2O —>C6H12O6+6O2

• Mitochondria are found in all animal and plant cells. Chloroplasts, however, are found in only specific types of plant cells, such as the palisade mesophyll and spongy mesophyll cells of leaves. These cells are the ones involved in carrying out photosynthesis. Other types of plant cells, such as root cells do not contain chloroplasts.
• Chloroplasts contain pigments such as chlorophyll a, chlorophyll b and carotenoids. Mitochondria do not contain any such pigments.
• The ATP synthase in mitochondria and chloroplast are orientated differently. ATP synthase in mitochondria points into the matrix, with protons flowing from the intermembrane space to the matrix. In chloroplasts however, ATP synthase points towards the stroma, and protons flow from the thylakoid space into the stroma.
• The types of electron acceptors present in mitochondria and chloroplast vary. While mitochondria contain NAD and FAD, chloroplasts contain NADP.
• The sources of energy used to synthesize ATP in mitochondria and chloroplasts are different. In mitochondria, this energy comes from the oxidation of glucose, and is hence termed oxidative phosphorylation. In chloroplast, this energy comes from light, so it is called photophosphorylation.
• Mitochondria function under both light and dark conditions. Chloroplasts, on the other hand, do need light to function.
• Electron transport chains: The final electron acceptor in mitochondria is oxygen, whereas the final electron acceptor in chloroplasts is NADP.
• In mitochondria, the root source of electrons is generally glucose (it could be other substrates depending on what was utilized). In chloroplasts, however, the root source of electrons is the photolysis of water occurring at photosystem II. Water (H2O) is broken down to release 2 protons, 2 electrons and a molecule of oxygen.
• Mitochondria give out carbon dioxide from the decarboxylation (removal of carbon) reactions that occur during the link reaction and Krebs cycle but chloroplasts give out oxygen due to photolysis as explained above.
• Chloroplast Has three compartments(parts): thylakoids (traps sunlight), granum (plural: grana; stacks of thylakoids), stroma (fluid inside the outer membrane, which interacts with the cytoplasm. It surrounds the granum and thylakoids. Mitochondria has two compartments. Crista (cristae) is the compartment formed by the inner and outer membrane of the mitochondria; it is the layer of folds in the mitochondria and is studded with proteins. The other compartment is called matrix; it is the fluid inside the folding (cristae).
• Chloroplast Converts solar/light energy into chemical energy (sugar), while Converts chemical energy (sugar) into another form of chemical energy (ATP), which is simpler and could be used by the cell.
• Chloroplast’s Process is photosynthesis (composed of Light Reactions and Calvin Benson Cycle), whereas Process is cellular respiration (composed of Glycolysis, ETC, and Oxidative Phosphorylation).