The third chloroplast membrane is arranged in discs called thylakoids. These discs are stacked on top of each other in structures called grana singular granum that look a lot like little stacks of green casino chips. Not that you spend any time in casinos, or gambling, for that matter. Each chloroplast contains many, many grana. The space between the inner chloroplast membrane and the grana is called the stroma.
The space inside the thylakoid discs is called the lumen , or, more specifically, the thylakoid lumen. The work of the chloroplast takes place in the stroma, the lumen, and, most importantly, in the thylakoid membrane itself. Here, the light-capturing green pigment chlorophyll is held in place by membrane proteins. Chlorophyll converts the energy from the sun into electrical energy.
This electrical energy is then passed from one membrane protein to another, providing the power to pump protons from the stroma into the thylakoid lumen.
At this point, ATP and other products produced by the thylakoid membrane proteins are combined with molecules of carbon dioxide CO 2 in the stroma to make glucose. The thylakoids contain the light-harvesting complex , including pigments such as chlorophyll, as well as the electron transport chains used in photosynthesis Figure 2.
These components are organized into three major layers: the primary cell wall, the middle lamella, and the secondary cell wall not pictured. The cell wall surrounds the plasma membrane and provides the cell tensile strength and protection. Plant genetic engineering for biofuel production: towards affordable cellulosic ethanol. Nature Reviews Genetics 9, All rights reserved. The primary cell wall is just outside the plasma membrane. Cellulose is the major component of the primary cell wall.
Cellulose microfibrils are represented as large, green cylinders that lie on top of one another in a crisscross fashion. Among the cellulose microfibrils are pectin molecules, which are depicted as long, thin, orange strands that curve and have some squiggled sections.
The primary cell wall also contains hemicellulose, which is represented by dark-green, thin lines that are straight with some sharp turns, and soluble protein, which is depicted as small blue and green spheres. The middle lamella forms the outermost layer and is depicted as a flat, translucent, blue slab. Many pectin molecules are shown inside the middle lamella.
In this layer, the pectin molecules are represented as light-green strands with some curvature. The middle lamella also contains soluble proteins similar to those in the primary cell wall. Lignin is not shown. The cell wall surrounds the plasma membrane of plant cells and provides tensile strength and protection against mechanical and osmotic stress.
It also allows cells to develop turgor pressure , which is the pressure of the cell contents against the cell wall. Plant cells have high concentrations of molecules dissolved in their cytoplasm, which causes water to come into the cell under normal conditions and makes the cell's central vacuole swell and press against the cell wall.
With a healthy supply of water, turgor pressure keeps a plant from wilting. In drought, a plant may wilt, but its cell walls help maintain the structural integrity of its stems, leaves, and other structures, despite a shrinking, less turgid vacuole.
Plant cell walls are primarily made of cellulose , which is the most abundant macromolecule on Earth. Cellulose fibers are long, linear polymers of hundreds of glucose molecules.
These fibers aggregate into bundles of about 40, which are called microfibrils. Microfibrils are embedded in a hydrated network of other polysaccharides. The cell wall is assembled in place. Precursor components are synthesized inside the cell and then assembled by enzymes associated with the cell membrane Figure 3.
Plant cells additionally possess large, fluid-filled vesicles called vacuoles within their cytoplasm. Vacuoles typically compose about 30 percent of a cell's volume, but they can fill as much as 90 percent of the intracellular space. Plant cells use vacuoles to adjust their size and turgor pressure. Through concerted efforts from the community, greater discoveries definitely will emerge in the future. This Research Topic welcomes all types of articles.
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About this Research Topic Chloroplasts are plant cell organelles that convert light energy into relatively stable chemical energy via the photosynthetic process. Topic Editors.
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