Energy Conversion: Mitochondria and Chloroplasts - Molecular Biology of the Cell - NCBI Bookshelf
Chloroplasts are present in photosynthetic plants and is responsible for other hand, mitochondria also known as the power house of the cell. Mitochondria and chloroplasts likely evolved from engulfed prokaryotes that which then formed an endosymbiotic relationship with the host eukaryote, Eukaryotic cells containing mitochondria then engulfed photosynthetic Learn how ancient collaborations between cells gave eukaryotes an important energy boost. Chloroplast and mitochondria perform vital yet different functions in cells. What are the main differences between an animal and a plant cell?.
You may also know that the reason you need to eat food—such as veggies—is so that you have the energy to do things like play sports, study, walk, and even breathe.
But what exactly happens in your body to turn the food energy stored in broccoli into a form that your body can use? And how does energy end up stored in the broccoli to begin with, anyway? The answers to these questions have a lot to do with two important organelles: Chloroplasts are organelles found in the broccoli's cells, along with those of other plants and algae. They capture light energy and store it as fuel molecules in the plant's tissues.
Mitochondria are found inside of your cells, along with the cells of plants. They convert the energy stored in molecules from the broccoli or other fuel molecules into a form the cell can use. Let's take a closer look at these two very important organelles. Chloroplasts Chloroplasts are found only in plants and photosynthetic algae. Humans and other animals do not have chloroplasts.
The chloroplast's job is to carry out a process called photosynthesis.
In photosynthesis, light energy is collected and used to build sugars from carbon dioxide. The sugars produced in photosynthesis may be used by the plant cell, or may be consumed by animals that eat the plant, such as humans.
The energy contained in these sugars is harvested through a process called cellular respiration, which happens in the mitochondria of both plant and animal cells. Chloroplasts are disc-shaped organelles found in the cytosol of a cell.
Mitochondria and chloroplasts
They have outer and inner membranes with an intermembrane space between them. The membrane of a thylakoid disc contains light-harvesting complexes that include chlorophyll, a pigment that gives plants their green color. Thylakoid discs are hollow, and the space inside a disc is called the thylakoid space or lumen, while the fluid-filled space surrounding the thylakoids is called the stroma.
You can learn more about chloroplasts, chlorophyll, and photosynthesis in the photosynthesis topic section. Mitochondria Mitochondria singular, mitochondrion are often called the powerhouses or energy factories of the cell. Furthermore, it is no surprise that mitochondria are present in both plants and animals, implying major commonalities in regulation, energy production, substrates employed, etc.
This common presence of mitochondria, with similar functions and structure, underscores how close our life forms are. The enslavement process should be equally similar, if not the same. The discovery of kleptoplasty, a functional chloroplast in cells of a non-photosynthetic host [ 24 ] is a remarkable phenomenon [ 24 — 27 ]. It is also found in metazoans, in the sacoglossan sea slugs.
Of equal importance is the longevity of functional kleptoplasts in the host, suggesting again that the common significance of bidirectional communication, and the many commonalities in molecules, exists so that this phenomenon can take place and work.
The dependence on specific algae strongly suggests common bidirectional communication is responsible for this phenomena. Recently, aside from the energy focus, studies have shown that mitochondria function as regulators for signal transduction and liberators of reactive oxygen species ROScommunicating with the endoplasmic reticulum ER to help regulate signals, and inducing stress responses to the rest of the cell, so that they can alter their physiology if needed [ 29 ].
Furthermore they maintain homeostasis and control deoxyribonucleoside triphosphate dNTP pools, which helps with the mitochondrial DNA replication process. It is known that there is a communication between the cytoplasm and the mitochondria for the dNTP pool levels, however, the depth of how much they actually interact is still unclear. Recent research has tried to clarify this process through experimental procedures using both normal cells and transformed cells.
The normal cells have been identified to have a strong correlation between the concentration levels of dNTP in the cytoplasm and the mitochondria, but not for the transformed cells [ 30 ]. Stress signals that are occurring in the mitochondria, such as ATP decline, cause changes in other cellular processes, which can affect the biogenesis of the mitochondrial membranes [ 3132 ].
The calcium transporters involved in the communication processes are directly exposed to ROS, as well as being sensitive to redox regulations. Though some mechanisms are still unclear regarding calcium and the ROS signaling, it is apparent that this communication maintains homeostasis of the cell [ 34 ].
It is surmised that the ER and mitochondria are associated with type 2 diabetes mellitus [ 35 ]. ATP levels in the mitochondria are controlled by the intra-mitochondrial free calcium concentration levels.
Cytochrome C When the mitochondrion undergoes an unexpected change or a stress-related event, it may release the hemeprotein known as cytochrome c. The cytochrome c concentration from inside the mitochondria increases and then is released to their cytosol.
This release of cytochrome c demonstrates that mitochondria are also involved in inducing apoptosis of the cell [ 3738 ]. Bax Family Apoptosis or necrosis causes cytochrome c to redistribute from the intermembrane mitochondrial space to the cytosol space, which leads to depolarization of the inner mitochondrial membrane. When the mitochondrion tries to prevent physiological changes that are occurring, such as apoptotic stress, it signals the release of a protein known as Bcl-xL, which inhibits apoptosis by causing a decrease in the mitochondrial membrane potential.
Thus, Bcl-xL expression is causing osmotic and electrical homeostasis and promoting cell survival [ 38 ].
Compare and Contrast: Chloroplasts and Mitochondria | Owlcation
Even though Bcl-xL acts as an anti-apoptotic gene, there is also a pro-apoptotic molecule, BAX that will help promote cell death. Its presence is a direct result of signaling between the mitochondrion and the cytosol.
When a death signal is communicated to the cell, the activation of BAX can occur, causing an override of Bcl-xL or interleukin IL -3 leading to apoptosis of the stressed cell [ 39 ]. Bcl-2 is also a member of BAX family that can migrate from the cytosol to the mitochondria, inducing apoptosis [ 40 ]. BAX activity can be inhibited if there is pro-survival of the Bcl-2 proteins. The pro-survival of the Bcl-2 family proteins is key to the BAX being retro-translocated, and if this is inhibited, BAX will build up in the mitochondria and lead to apoptosis [ 40 ].
Conversely, when you have an active oxidative phosphorylation system operating through Complexes I—V, then the superoxide formation is minimized. Mitochondrial oxidants are generally known to be harmful when a leakage occurs. Recently, these oxidants were shown to function as signaling molecules, stimulating communication between the cytosol and mitochondria.
An increase in the release of H from the mitochondria causes the metabolic escalation of a kinase known as JNK1, which causes the inhibition of metabolic enzymes, such as glycogen synthase, leading to regulation of the metabolic pathways [ 42 ]. Normal ROS production not only helps maintain cellular metabolism, but also has been found to help the mitochondria monitor innate immune responses.
The generation of ROS is enhanced when the mitochondria are under apoptotic stress or cellular damage. By acting as a sensing organelle for innate immune responses, such as antiviral signaling and facilitating antibacterial immunity, the mitochondria can accumulate ROS, causing immune activation [ 4344 ].
In this regard, the activation state of this organelle can be ascertained by its conformation. Mitochondrial conformational changes associated with activation, via altering shaping proteins or when retinoic acid-inducible gene I-like helicase RLH is activated, will exhibit an elongated shape. The mitochondria will most likely take an asymmetrical shape as well, and can also fragment if there are pro-apoptotic factors involved [ 38 ].
These shape changes appear to be important in their functional dynamics since they are associated with neurodegeneration, the lifespan of a cell, and also cell death. Conformational change occurs in white blood cells, endothelial cells, microglia and invertebrate immunocytes, following stimulation and is indicative of energy usage [ 4546 ]. In general, immune cells have fewer mitochondria compared to other cells, however the conformational shape changes in mitochondria may allow it to accumulate in cellular processes requiring ATP, and in their absence, degeneration may occur [ 444748 ].
Two organelles that are known to have a specific organization are the endoplasmic reticulum ER and the mitochondria. The research literature documents that these two organelles closely communicate in a bidirectional manner to promote regulation of physiological processes, e. There are still many signaling cascades that can be explored between the ER and the mitochondria that may also lead to insights into disease origin [ 49 ]. Nuclear Communication Not only does the mitochondria help regulate homeostasis, but it has many transcription factors and specific cofactors that regulate its biogenesis.
Though these functions are newer findings, a more recent study has found that the mitochondrion can send messages that change nuclear gene expressions, therefore altering nuclear control [ 52 ].
Through retrograde signaling, communication from the mitochondria to the nucleus provides the status of metabolic and respiratory conditions, along with the genetic instability of the mitochondria.
The mitochondrial genome mtDNA plays a key role in the retrograde signaling when there is a lower amount of mtDNA, which causes it to not function properly due to a reduced membrane potential.
Mitochondria, Chloroplasts in Animal and Plant Cells: Significance of Conformational Matching
This decrease in mtDNA levels is associated with various conditions like diabetes, neurodegenerative disorders, cancer and aging [ 53 ].
Chaperones play a key role in regulating the proteins that are encoded by the mitochondria DNA and nuclear mitochondrial proteins by being involved in the process of their synthesis, transportation and folding [ 54 ]. When stressed, the mitochondria and molecular chaperones will exhibit a specific response to alleviate the situation.
These chaperones are encoded by nuclear DNA, demonstrating a potent communication mechanism [ 54 ]. Conclusions The bidirectional communication that occurs between the mitochondria and the rest of the cell has a functional capacity for promoting a positive environment for the cell through primarily calcium and ATP monitoring and sophisticated internal regulatory processes.
Situations such as cellular stress can affect the fidelity of the communication, which leads to changes and therefore to mitochondrial dysfunction. Even more important is the fact that mitochondria originated from bacteria, which are similar to chloroplasts, demonstrating this enslavement of both is based on common signaling pathways. These similarities are especially noted in the fact that functioning chloroplasts occur in animals.
Since these enslaved organelles are really alien to their host cells, one can surmise that this communication becomes faulty with aging, and may manifest itself in many mitochondrial associated disorders, e. This dynamic immediate relationship is manifest in the fact that mitochondria can alter their ATP producing capacity at times that demand it to do so, producing lesser amounts of ATP [ 2 ]. In all probability, this last phenomenon may be, in part, responsible for the development of chronic conditions.
Footnotes Conflict of interests All authors certify that there is no conflict of interests. Stefano GB, Kream R. Psychiatric disorders involving mitochondrial processes. Eolutionary perspective on modulation of energy metabolism in Mytilus edulis.
Oxidative stress mediated mitochondrial and vascular lesions as markers in the pathogenesis of Alzheimer disease. Oxidative stress in the brain: International Journal of Diabetes Research. Concerted dysregulation of 5 major classes of blood leukocyte genes in diabetic ZDF rats: