Chloroplasts - the cells' photosynthesis factories

Chloroplasts - the cells' photosynthesis factories

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The endosymbiotic theory

The endosymbiont theory was extensively presented by Lynn Margulis in 1970, but is based on earlier work on the origin of chloroplasts by Mereschkowsky (1905) and Schimper (1883). It says that all eukaryotic organisms arose from symbiotic communities of different eubacteria and archaeobacteria. Today it is generally recognized that chloroplasts from cyanobacteria and mitochondria developed from a "primitive" group of purple bacteria (α-Proteobacteria). The group of α-Proteobacteria includes today's symbionts such as the root nodule bacteriaRhizobium as well as obligate intracellular parasites such as Rikettsia a. These small eubacteria were endocytosed by a primitive anaerobic eukaryote (models are the amoeba Entamoebahistolytica or the Diplomonad Giardia lamblia) absorbed but not digested.

Criteria for the endosymbiotic origin of mitochondria and plastids (chloroplasts) are:

  1. The double membrane covering of the cell organelles, the inner membrane showing characteristics of the prokaryotic membrane, the outer eukaryotic properties. This is consistent with the model conceptions of an endocytosis (Figure 2).
  2. Mitochondria and plastids have their own circular DNA as well as their own ribosomes of the prokaryotic 70S type. The genomes encode many genes with a great phylogenetic similarity to genes of the Proteobacteria and Cyanobacteria. In addition, the gene arrangement and genome organization are very similar. For the chloroplasts, this is best seen in the ribosomal protein superoperon, which is a fusion of the S10, spc and a operons (or the str operon of some algae).
  3. The RNA polymerase and protein biosynthesis of the organelles is inhibited by bacteria inhibitors - but not by inhibitors of eukaryotic RNA polymerase and biosynthesis.
  4. rRNA sequence comparisons of the mitochondria showed great similarities with recent endosymbionts, e.g.Ricketsia, Agrobacterium and Rhizobium. rRNA sequence comparisons of the chloroplasts showed great similarities to certain cyanobacteria.

It is controversial that the nucleus of the eukaryotic cells is also a product of such an endosymbiosis. The endosymbiotic origin of the cytoskeleton or the cilia and flagella of eukaryotic cells is also becoming controversial. LynnMargulis also postulated spirochaete-like ancestors for this as early as 1970.

Related Links:

  • Eukaryotes
  • The Gaia Hypothesis (1)
  • The Gaia Hypothesis (2)


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the Chloroplasts (from ancient Greek & # 160 χλωρός chlōrós "Green" and ancient Greek & # 160 πλαστός plastós "Shaped") are organelles of the cells of green algae and higher plants that carry out photosynthesis. In higher plants, chromoplasts, leucoplasts (amyloplasts, elaioplasts), etioplasts and gerontoplasts (collectively referred to as plastids) can emerge from the photosynthetically active chloroplasts through differentiation.

05/11/2021 11:06 AM - New role for ion transport proteins: As LMU biologist Hans-Henning Kunz shows, they are involved in gene regulation in chloroplasts.

Chloroplasts are the plants' photosynthesis factories. They originally come from cyanobacteria that were "hijacked" by a host cell in the course of evolution and absorbed into the cell interior. Because of this history of origin, they are surrounded by a double H & # 252ll membrane and still have their own genome.

Scientists led by Professor Hans-Henning Kunz from the LMU Biozentrum have now shown for the first time that ion transport proteins in the chloroplast membrane are involved in the regulation of these genes and thus play an important role in the control of photosynthesis.

An inner membrane in the chloroplast is the actual place of photosynthesis. However, it is surrounded by the inner membrane which, among other things, houses ion transport proteins that are responsible for regulating the ion balance in the so-called stroma. The stroma is the plasmatic basic substance inside the organelle, in which both the DNA of the chloroplast and its protein factories - the ribosomes - are located. For photosynthesis to proceed correctly, it is essential that the genes in the cell nucleus and in the chloroplasts work in a coordinated manner. “In the model plant Arabidopsis thaliana, we have now been able to demonstrate that the ion balance in the stroma influences this communication,” says Kunz.

The biologist had previously observed that chloroplast development is delayed and the plant takes care of it when the genes for two ion transport proteins are switched off. "Our experiments have now shown that helper proteins encoded in the cell nucleus without these ion transporters have difficulty binding their partner RNA in the chloroplast," says Kunz. This hinders so-called RNA maturation, an important intermediate step in the transmission of the information contained in the chloroplast genes to the ribosomes. This defect was particularly pronounced in the RNA from which the ribosomes of the chloroplast are built. "Correspondingly, there are fewer functioning ribosomes, which severely affects protein synthesis in the mutants," says Kunz.

According to the scientists, their new findings can help protect photosynthesis more efficiently in difficult environmental conditions and thus better adapt crops to climate change. "Ion transporters could be an important tool here," says Kunz. “Photosynthesis is very dependent on the biochemical environment in the stroma, and these transporters have a great influence on it. Only when we understand their complex functionality and structure in detail do we have the opportunity to manipulate them and make them usable. "

Chlorophyll and chloroplasts

All of this amazing process takes place within a plant's cells, especially its leaves. Tiny organelles called chloroplasts are where photosynthesis takes place. These chloroplasts contain a green pigment called chlorophyll, which gives plants their distinctive green color. If the leaves of a tree change color, it is because the growing season has ended. The plant has temporarily stopped producing chlorophyll and other pigments in the leaves are becoming visible.

The tree as a living being: chemistry: photosynthesis

The process of photosynthesis takes place mainly in the leaves of the tree and represents one of the most important processes on earth. Chemical reactions between water and carbon dioxide (CO2) new biomass and oxygen (O2) produced. All that is needed is sunlight.

Countless green plants on earth operate this process continuously as soon as the sun rises. In doing so, they can achieve something incredible: The production of mass from nothing. That's not entirely true, of course, but it's still an unending achievement. Plants are the beginning, no matter what, but plants did it. The biomass of all living things including animals and humans only exist because plants once produced the necessary biomass. Our planet is rich in energy such as coal, gas and radioactivity, but without a biomass producer it would be as good as dead. Plants only make life possible by producing oxygen. When plants "invented" photosynthesis through evolution, our atmosphere was absolutely poisonous; no human could have lived there. Over the course of millions of years, however, the percentage of oxygen (currently: approx. 20.1%) continued to rise, which was fatal for many of the primitive creatures of the time, for them oxygen was pure poison. But living beings adapted and from then on almost every form of life was based on O2so do all mammals and we humans.

Caution! What are oil and natural gas made of? These two energy suppliers, which we are absolutely using today, formed millions of years ago. exactly, dead animals and virgin forests. And their mass also came exclusively from plants, as we can see, we owe practically everything to plants. There is a problem here, if we burn these fossil fuels and use the energy, something will be released that the plant there bound an infinitely long time ago. CO2. Today this gas is harmful to our climate and will drastically change all of our lives, we can only hope that we will shut down production and that the plants will be so nice again and pack it nicely and safely. Alternatives such as synthetic biofuels are also made from plant materials. In any case, the process of photosynthesis provides the basis.

So, let's summarize: The plant needs water, CO2 and sunlight, which ultimately turns into oxygen and biomass.

6 C O 2 + 6 H 2 O → h ν C 6 H 12 O 6 + 6 O 2 Δ H 0 = + 2870 k J m o l < displaystyle < begin mathrm <6 CO_ <2> +6 H_ <2> O quad < xrightarrow > C_ <6> H_ <12> O_ <6> +6 O_ <2>> qquad Delta H ^ <0> = + 2870 < frac < mathrm > < mathrm >> end>> Net reaction equation for oxygenic photosynthesis

You can write it like this up here. The parts to the left of the arrow are the starting materials, the parts to the right are the newly formed materials. Take 6 molecules of CO2 and 6 molecules of water, which ultimately turns into 1 molecule of grape sugar (C.6 H12 O6) and 6 molecules of oxygen. Delta H indicates how much energy has to be supplied so that a mole can be formed. In this case, 2870 kiloJoules are required per mole, this energy comes from the sun alone. The only question now is why the plant does this. The plant only tries to feed itself, during photosynthesis biomass, i.e. grape sugar in this case, is formed, the plant cells in turn burn this energy and grow. The oxygen, which is so extremely important for all of us, is just a kind of waste product.

As we read in the last chapter, the actual light reaction takes place in the chloroplasts of the cells. Let's start with the origin, the light. Light is nothing more than a wave or a particle, both states are conceivable for us and they explain many problems. The light particles of the sun (photons) exist as different waves or strengths. One speaks of the wavelength of light. Different wavelengths produce different colors and are of different intensity. The chloroplasts need a wavelength in the range around 450-500nm and in the range around 680nm, the reaction only takes place when this spectrum is available. Normal sunlight delivers all wavelengths anyway, so there are no restrictions.

So now the light photon hits a light-collecting complex in the thycaloids (a granum consists of many thycaloids). This complex is excited by the radiation and one electron of the molecule is put into an energetic state. The electron returns to its original state within a billionth of a second, but the energy it contains can be used (if not, it only generates heat). Now, on the one hand, the water contained is split, H2O becomes oxygen (O) and hydrogen (H). Through a chain of several redox reactions, electrons get to the molecule nicotinamide adenine dinucleotide phosphate (NADP +), this is then reduced to NADP- and immediately reacts with a free hydrogen to form NADPH. At the same time, ADP (adenosine diphosphate) becomes ATP (adenosine triphosphate = universal energy carrier in all living beings) through the charge gradient on the thycaloid membrane. This is called the so-called primary reaction or light reaction, because light is always required here. However, this does not end the photosynthesis process, because the primary products formed (NADPH and ATP) are further converted in the subsequent secondary reaction.

These products and CO2 ultimately the biomass that we all need is formed. The substances are converted in various stages in the so-called Calvin-Benson cycle, ultimately into triose phosphate and then fructose phosphate, from which the substances glucose phosphate, sucrose and starch are then formed again. This turned water into CO2 and light, the oxygen and new biomass that are essential for us.

If this explanation is not precise enough (and I have to apologize, it is not very precise), I would like to name a few books in the sources that deal solely with the subject of photosynthesis. Fortunately, the process of photosynthesis is now very well researched, but there are still gaps in knowledge. In addition, prior knowledge from chemistry and physics is required in order to understand the existing knowledge.

The inner membrane of a mitochondrion is complex compared to the chloroplast. It's covered in crystals created by folding the membrane multiple times to maximize surface area. The mitochondrion uses the large surface area of ​​the inner membrane to carry out many chemical reactions. The chemical reactions include the filtering out of certain molecules and the attachment of other molecules to transport proteins. The transport proteins will carry selected types of molecules into the matrix, where oxygen combines with food molecules to produce energy.

The internal structure of the chloroplast is more complex than that of the Mitochondria. Within the inner membrane, the chloroplast organelle consists of stacks of thylakoid sacs. The stacks of sacks are connected to one another by stroma lamellae. The stromal lamellae hold the thylakoid stacks at certain distances from one another. Chlorophyll covers every pile. The chlorophyll converts sunlight photons, water and carbon dioxide into sugar and oxygen. This chemical process is called photosynthesis. Photosynthesis initiates the formation of adenosine triphosphate in the stroma of the chloroplast. Stroma is a semi-liquid substance that fills the space around the thylakoid stacks and stroma lamellae.

The most important information about chloroplasts at a glance!

    Chloroplasts are found in plant cells and enable the cell to photosynthesize

For most topics about cell organelles, it is worth making a drawing or looking closely at our illustrations. It is often difficult for students to memorize all the complex technical terms and then to understand how everything is interrelated. The drawings help you to internalize the terms on the one hand and on the other hand to better understand what happens in a plant cell or our body.

Take a look at our other articles on cell organelles in order to better understand the relationships and to expand your knowledge for the next exam!

Stage two: dark reactions

The dark phase that takes place in the stroma and in the dark when the molecules that carry energy are present is also called the Calvin cycle or C.3 Cycle. The dark phase uses the ATP and NADPH generated in the light phase to make CC covalent bonds of carbohydrates from carbon dioxide and water, with the chemical ribulose biphosphate or RuBP, a 5-C chemical that traps the carbon dioxide. Six molecules of carbon dioxide enter the cycle, which in turn produces one molecule of glucose or sugar.

Why don't all plant cells contain chloroplasts?

Chloroplasts are important cell structures that give vegetation its characteristic green color. They are responsible for absorbing energy to feed the plant and encourage its growth. They are not present in all plant cells.
What are chloroplasts?

The chloroplasts are specialized organelles that carry out photosynthesis. During photosynthesis, light energy is absorbed by the sun and converted into chemical energy. Light is captured in small pancake-shaped discs called thylakoids, which contain the green pigment chlorophyll. It is then converted into starch for storage in the roots.
Where are chloroplasts found?

Chloroplasts only occur in those parts of the plant that are capable of photosynthesis. The majority of chloroplasts are found in the leaves of the plant, as these structures have the largest surface area for absorption. The outer part of a plant stem can also contain chloroplasts.
Which cells do not have chloroplasts?

The internal stem cells and underground organs, such as the root system or the tuber, do not contain chloroplasts. Since no sunlight reaches these areas, chloroplasts would be unusable. Fruit and flower cells usually do not contain chloroplasts, since their main task is to reproduce and spread

Molecular factories: the combination between nature and chemistry works

In molecular factories injected into zebrafish embryos, a color reaction occurs when the entrapped enzyme (peroxidase) works. With this, the researchers prove that the combination of synthetic organelles and natural vesicles also works in living organisms. Image: University of Basel

The molecules of life are gathered in cells, the actual factories of biology. The production facilities in the cells are small chambers called organelles in and between which a wide variety of chemical reactions take place.

For medical applications, it would be ideal if molecular factories could be used that behave like artificial cells - for example to produce missing or required molecules and drugs.

A collaboration between the Department of Chemistry at the University of Basel, the Swiss Nanoscience Institute and the NCCR Molecular Systems Engineering made it possible for such molecular factories to be successfully developed.

First, the researchers, under the direction of Prof. Dr. Cornelia Palivan and Prof. Dr. Wolfgang Meier artificial organelles, i.e. demarcated parts of cells. They loaded these soft, biosynthetic capsules with enzymes and inserted membrane proteins into the walls that act like gates.

These gates allow the molecules that are necessary for the enzyme reaction to enter and exit.

Then natural cells were fed the artificial organelles. Upon stimulation, the cells produced natural micrometer-sized vesicles. In addition to the cytoplasm, these have a natural cell membrane, also enclose the artificial organelles inside and can therefore function as a molecular factory.

Zebrafish embryos as an animal model

The molecular factories were built by researchers from the group led by Prof. Dr. Jörg Huwyler from the Department of Pharmaceutical Sciences is injected into zebrafish embryos.

In this animal model, they produced the desired components, which were catalyzed by the enzyme in the artificial organelle. The vitality of the embryo was not affected by the injection.

"This combination of natural vesicles and the small synthetic organelles defines the molecular factory: reactions inside deliver the end product, similar to what is the case in cells," said the two first authors of the study, Dr. Tomaz Einfalt and Dr. Martina Garni.

Inside the molecular factories, several components can be manufactured and put together to form the end product. The biosynthetic vesicles can also transfer components from one cell to another.

Different molecular factories can be combined so that more complex structures with high functionality can be created - a first step towards producing artificial cells in the laboratory or in living organisms.

& # 8211 Prof. Dr. Cornelia G. Palivan, University of Basel, Department of Chemistry, phone +41 61 207 38 39, email: [email protected]
& # 8211 Prof. Dr. Wolfgang P. Meier, University of Basel, Department of Chemistry, phone +41 61 207 38 02, email: [email protected]

Tomaž Einfalt, Martina Garni, Dominik Witzigmann, Sandro Sieber, Niklaus Baltisberger, Jörg Huwyler, Wolfgang Meier, Cornelia G. Palivan
Bioinspired molecular factories with architecture and in vivo functionalities as cell mimics
Advanced Science (2019), doi: 10.1002 / advs.201901923

Structure and function of chloroplast and mitochondria

The thylakoids form stacks, which are referred to as grana, where the light reaction, which is crucial for photosynthesis, takes place. Inside the chloroplast is the stroma, the cytosol of the chloroplast. The stroma also contains the DNA and ribosomes of the chloroplasts

Mitochondria are also known as the powerhouse of the cell. This common name comes from its important function, namely the production of adenosine triphosphate (ATP), the universal energy carrier for all cells. Mitochondria have their own DNA and multiply independently of their mother cell.

Mitochondria are also known as the powerhouse of the cell. This common name comes from its important function, namely the production of adenosine triphosphate (ATP), the universal energy carrier for all cells.

The main function of chloroplasts is photosynthesis. . The sugar (glucose) produced during photosynthesis is first stored in the stroma as a starch grain and later transported on. The chloroplasts are the place for photosynthesis in plants and algae.


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