Definition of Plastids: Function, Structure, Characteristics, Types, Classification and Differences with Mitochondria

Definition of Plastids: Function, Structure, Characteristics, Types, Classification and Differences with Mitochondria – What do you mean by plastids? On this occasion, about the knowledge.co.id will discuss it and of course about other things that also cover it. Let's look at the discussion together in the article below to better understand it.

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Definition of Plastids: Function, Structure, Characteristics, Types, Classification and Differences with Mitochondria

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Plastids are cytoplasmic organelles associated with specific metabolic processes of plant cells. Plastids contain photosynthetic pigments for the production of glucose as energy by the process of photosynthesis with the help of sunlight and CO2.

Plastids are the second largest cell organelle bounded by a double unit membrane and can be colored or colorless. Plastids are one of the most dynamic organelles and are able to divide, grow, differentiated into various shapes, relatively large, and filled with a rich fluid of proteins.

Mayer and Schimper were the first to use the term plastid. Plastids are found in plant cells and some algae. Plastids are primarily responsible for the manufacture and storage of several vital chemical substances used by autotrophic eukaryotic cells.

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Plastids function

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  Photosynthesis - This function is carried out by chloroplasts which become units that contain many chlorophyll pigments to then carry out photosynthesis.

• Color Change - That is very closely related to the process of pollination and dispersal of seeds in plants. With the change in color, organisms such as insects will then pollinate.
• Increase Storage of Food Reserves - This one function is played by chromoplasts and also played by leucoplasts. The change of chloroplasts into chromoplasts will result in an increase in the ability of tissues and cells to absorb water-soluble materials such as carbohydrates.
• Food Storage - It is played by chromoplasts in small amounts & leucoplasts such as amyloplast for starch storage, elaioplas for lipids or fat and also for proteinoplas proteins.
• Production of Amino Acids and Proteins - Which functions are played by leucoplasts.
• Where the Light Reaction Occurs, which is Very Important in the Food Formation Process – Which one function occurs in the chloroplast.

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Plastid Structure

All green plastids, in this case each type of plastid is surrounded by two unit membranes; i.e. the outer and inner membranes are 7 nm thick and they are separated by a periplastid space 8–10 nm thick. Unlike mitochondria, the inner membrane of fully developed plastids does not show inward folds; but play an active role during the development of proplastids into mature plastids.

Chloroplasts are completely filled with a fluid called stroma, in which highly organized membranous structures are found they are called grana. In addition to the grana, the stromatic fluid contains a number of enzymes, plastid DNA, RNA, and 70's ribosomes.

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Characteristics of Plastids

• Membrane-enclosed organelles found in plant cells, algae, and many other eukaryotic organisms.
• Location for manufacture and storage of important chemical compounds used by autotrophic eukaryotic cells.
• it often consists of pigments used in photosynthesis, and the type of pigment in the plastid determines the color of the cell. They share a common evolutionary origin and have circular, double-stranded DNA molecules, just like prokaryotic cells.
• is another important energy transduction organelle found only in plants. Shimper coined the name Plastids for the structures responsible for photosynthesis.
• Commonly found in almost all plant body cells, either in the form of colorless plastids or colored plastids or proplastids.
• In fact, photosynthesis transports chemical energy, directly or indirectly, to all other living organisms, Chloroplasts are exclusive organelles because they are able to capture, convert and conserve solar energy in the form of energy chemistry.
• Discovered and named by E. Haeckel, but A. F. W. Schimper was the first to provide a clear definition.

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Types of Plastids

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  Chromoplast

Chromoplast: Chromoplast (Gr. Chroma, color) is a photosynthetically active colored plastid that occurs in plant cells. These plastids produce pigments and store them which are mainly found in leaves, flowers, ripe fruits and even plant roots.

The most common types of chromoplast plastids are as follows:

• Chloroplasts

Chloroplasts (Gr. Chloros, pale green) plastids found in green algae and higher plants. These are the chlorophyll-containing plastids of plant cells that take part in photosynthesis. These plastids contain pigments such as chlorophyll a, chlorophyll b, DNA and RNA.

Chloroplast function

Chloroplasts perform the following important functions:

• Chloroplasts receive light energy and convert it into biological energy;
• They produce NADPH2 and ATP (Adenosine Tri-Phosphate) by photo-phosphorylation;
• They help make food (carbohydrates) through the process of photosynthesis. In this case, glucose is produced using sunlight, CO2, and H2O;
• Chloroplast DNA and RNA synthesize proteins with the help of enzymes;
• They fight disease as part of the cell's immune system;
• They store energy for cells;
• They make amino acids for cells;

Chloroplast plastids:

• Plant cells contain many chloroplast plastids which are evenly distributed throughout the cytoplasm. Generally, they are found concentrated near the cell wall or nucleus.
• In higher plants, chloroplast plastids are generally round or disc-shaped. The chloroplasts of some algae are in the form of stellate plates or spiral bands.
• The size of chloroplast plastids varies from 4μm-6μm with a thickness of 1 μm-3 μm. The number of chloroplasts varies from cell to cell.
• Chlamydomonas (algae) often contain a single, large chloroplast plastid whereas in higher plants there are usually 30-40 chloroplasts per cell. Generally, chloroplasts develop from proplastids.
• Proplasts are small membrane-bound structures seen in meristematic cells. In the presence of sunlight, proplasts develop into normal chloroplast plastids.
• Plastids that have chlorophyll can carry out photosynthesis and are called chloroplasts.
• Plastids can also accumulate products such as starch and can produce fatty acids and terpenes, which can be used to produce energy and as raw materials for the synthesis of other molecules.
• All plastids originate from proplastids, which are present in the meristematic regions of plants.

Chloroplast structure of plastids

Chloroplast plastids contain the following structures:

membrane unit: Each chloroplast is bounded by two membrane units, namely the outer and inner membranes. Each membrane is trilaminar with a thickness of 50-60 Å and consists of lipoproteins. In between the two membranes, a space is present which is known as the periplastidal space which is 100 to 300 Å in diameter.

Stroma: It is a transparent, clear and homogeneous colloid-like liquid in the inner membrane. Also known as matrix containing the following substances:

• 50% chloroplast protein;
• fat lumps;
• starch grains;
• Osmiophilic Granules;
• pyrinoids;
• Enzyme;
• Vitamins E and K;
• 70-s ribosomes;
• DNA;
• RNAs;
• Various types of ions;

Thylakoids: The membrane structure in chloroplast plastids is organized into flattened sacs, which are known as thylakoids. They are embedded in the water matrix. In higher plants, thylakoids are arranged in piles, such as piles of coins. Each thylakoid is 100-300 Å wide. Thylakoids make sites for the light dependent reactions of photosynthesis. The space within the thylakoid contains the following components:

• Photosynthetic pigments (Chlorophyll a and b, yellow to red carotenoids),
• lipids;
• Enzyme;

grana: Stalked thylakoids are grana. The granum (singular) is the functional unit of the chloroplast. The size of the ganaum can range from 0.3-2.7 µm. The number of thylakoids in a granum can vary from 50 to 100. Each chloroplast usually contains 40-60 grana in its matrix.

Stroma Lamalae: The grana are interconnected by a network of tubules, known as the stromal lamellae or intergranal frets.

Quantosome: Thylakoids are made up of smaller spherical objects called quantosomes. Each quantosome consists of about 250-300 chlorophyll molecules and several carotenoid particles capable of carrying out the Hill reaction of photosynthesis.

Pheoplast:

Brown plastids containing the pigment fucoxanthin. Fucoxanthin is a carotenoid pigment that absorbs light and transfers energy to chlorophyll a. This type of pigment is found in diatoms, brown algae, and dinoflagellates, etc.

Rhodoplast:

These are red colored plastids that contain the pigment phycoerythrin and they are found in red algae.

Blue-green Chromoplast :

This type of plastid contains the following pigments such as phycocyanin, phycoerythrin, chlorophyll a and carotenoids. They are found in blue-green algae.

• Leucoplast

This type of plastid has no color pigment. They store food ingredients like carbohydrates, fats, and proteins. They are found in sex cells and in areas of the plant that do not receive light. They may be rod-like or ball-shaped and of many types:

Amyloplast: It is a double signed plastid which can carry out various biological pathways. These plastids synthesize and store starch via polymerization of glucose in the endosperm, tuber and cotyledons. Sometimes amyloplasts can turn into chloroplasts.

Elaioplast: is one type of non-pigmented leucoplast plastids which store lipids, oils, and they occur in seeds.

Proteinoplast: This plastid was identified in 1960. It is also known as proteoplas, aleuronaplast, and aleuroplast. This type of plastid stores proteins. They are found in the seeds of many peanut plants, nuts, beans, etc.

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Plastids and Mitochondria Similarities

• Both mitochondria and plastids are double membrane bound organelles.
• Both mitochondria and plastids in their outer membrane have porin proteins that make the outer layer more permeable.
• Both mitochondria and plasmids have some of their own DNA for protein synthesis so they are referred to as semi-autonomous cell organelles.

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Difference between Plastids and Mitochondria

• The difference between plastids and mitochondria is that plastids are found in plant cells and mitochondria are found in both plants and animals.
• Mitochondria are a type of organelle in which the biochemical processes of respiration and energy production occur. Plastids are double membrane organelles found only in plants and algae where the production and storage of chemicals takes place within the cell.
• Mitochondria: Mitochondria lack pigment. Plastids are many plastids that contain pigments.
• Mitochondria are found in plant and animal cells. Plastids are found only in plant cells and algae.
• The inner mitochondrial membrane contains folds known as cristae. Plastids no folds are found in the plastid inner membrane.
• Mitochondria: A completely separate space found within the matrix. Plastid: Plasmids lack separate spaces within the matrix.
• Mitochondria are mainly involved in energy production through cellular respiration. Plastids are mainly involved in the production and storage of food in cells.
• The type of mitochondrial structure can vary based on the needs of the cell. Plastids: Leucoplasts, chromoplasts, and chloroplasts are the three types of plastids.
• Mitochondria have their own DNA within the organelle. Plastids: Only chloroplasts have their own DNA.

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Plastids Classification

On the basis of the presence or absence of pigment, and the phase of development, plastids have been classified into proplastids, leucoplasts, and chromoplasts.

• Proplastid

The minor vesicular structures present in meristematic cells are called proplastids. These plastids are colorless and immature. When the cell matures into another cell type, depending on the organ and the presence or absence of light, the proplastids undergo change and develop into colorless leucoplasts or colored chromoplast plastids together with chloroplasts green.

Proplastids are constantly dividing and rearranging and provide them for cells that are differentiating into various types.

• Leucoplast

Colorless plastids present in the storage parenchyma and other colorless tissues are called leucoplasts. Most of these plastids behave as storage organelles. Based on the type of chemical they store, these plastids are further divided into amyloplasts.

If such leucoplasts are exposed to sunlight they will be transformed into colored plastids, which are suggesting that this plastid has reassembled all the genetic potential to develop and perform photosynthesis.

• Chromoplast

All plastids that contain some colored pigments are grouped together under a chromoplast, where those that are green are known as chloroplasts. Depending on the main pigment present in the plastids, they are further divided into Rhodoplasts which are rich in red pigment, i.e. phycoerythrin.

Phaeoplasts and Xanthoplasts have yellow pigments, namely xanthophylls, carotenoids. Along with the above pigments, phycocyanin and other pigments are also present in other colored plastids.

• Additional plastids

Such colored plastids, apart from chloroplasts, are commonly found in certain classes of plants and plant organs that contain floral parts. Although the floral parts are derived from the same type of proplastid, it produces different pigments in the petals. The exact method of differentiation is unknown for different plants to make different colored petals and it is genetically coded.

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