Chloroplast may occur in

Chloroplast gene expression is primarily regulated at the post-transcriptional level, where a variety of complex mechanism have evolved to govern the interaction between the chloroplast and nuclear genomes. These rely on different nuclear-encoded proteins that act on chloroplast mRNAs, including RNA polymerase subunits, RNA stability factors and translational activators. Such control mechanisms must be viewed in the light of the evolutionary heritage of the chloroplast, as an independent unicellular organism. Although some features of prokaryotic gene expression still occur in chloroplasts, their multiple genetic mechanisms for synthesizing RNA and protein are new, and appear to have arisen to provide flexibility of responding to the developmental or environmental state of the plant. • Previous article in issue • Next article in issue

What are Chloroplasts? What is the chloroplast definition? A chloroplast is an organelle in plant cells that allows them to produce energy. An organelle is a membrane-bound structure within a cell that has a specific function (if a person were a cell, their "organelles" would be their organs). Cellular energy, or ATP (adenosine triphosphate), is a molecule that cells use for energy; chloroplasts produce these. Chloroplasts are a type of plastid, which are organelles involved in food creation and storage. Their function varies depending upon the pigments they carry or their color. Chloroplasts contain the green pigment chlorophyll. The other two types of Chloroplast Description Chloroplasts have a double-membrane and contain stacks of grana. They are green in color and are found in the mesophyll of plant leaves, which is why plants and their leaves appear green. They can come in various shapes and sizes depending upon the type of plant or algae and what structure of that organism they are found in. Chloroplasts give leaves their bright green color. Parts of a Chloroplast A chloroplast has five main parts: • Outer membrane: This holds everything together and is semi-permeable, so it only allows select molecules to pass through. • Inner membrane: The inner membrane allows for even more specificity and direction of molecules passing in and out of the chloroplast. It surrounds the stroma and thylakoid structures. • Stroma: The • Thylakoids: These are small discs that contain lu...

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Encyclopaedia Britannica/UIG/Getty Images Plant chloroplasts are commonly found in guard Chloroplast structures include: • Membrane Envelope: contains inner and outer • Intermembrane Space:space between the outer membrane and inner membrane. • Thylakoid System:internal membrane system consisting of flattened sac-like membrane structures called thylakoids that serve as the sites of conversion of light energy to chemical energy. • Thylakoid Lumen: compartment within each thylakoid. • Grana (singular granum): densely layered stacks of thylakoid sacs (10 to 20) that serve as the sites of conversion of light energy to chemical energy. • Stroma: dense fluid within the chloroplast that lies inside the envelope but outside the thylakoid membrane. This is the site of conversion of carbon dioxide to • Chlorophyll:a green photosynthetic pigment within the chloroplast grana that absorbs light energy. Robert Markus/Science Photo Library/Getty Images Inphotosynthesis, the sun's solar energy is converted to chemical energy. The chemical energy is stored in the form of The light reaction stagetakes place in the presence of light and occurs within the chloroplast grana. The primary pigment used to convert light energy into chemical energy is chlorophyll a. Other pigments involved in light absorption include chlorophyll b, xanthophyll, and carotene. In the light reaction stage, sunlight is converted to The dark reaction stageis also known as the carbon fixation stage or the Chloroplast Func...

As it turns out, the atoms of carbon in your body were once part of carbon dioxide ( CO 2 \text _2 CO 2 ​ start text, C, O, end text, start subscript, 2, end subscript ) molecules in the air. Carbon atoms end up in you, and in other life forms, thanks to the second stage of photosynthesis, known as the Calvin cycle (or the light-independent reactions). In plants, carbon dioxide ( CO 2 \text_2 CO 2 ​ start text, C, O, end text, start subscript, 2, end subscript ) enters the interior of a leaf via pores called stomata and diffuses into the stroma of the chloroplast—the site of the Calvin cycle reactions, where sugar is synthesized. These reactions are also called the light-independent reactions because they are not directly driven by light. In the Calvin cycle, carbon atoms from CO 2 \text _2 CO 2 ​ start text, C, O, end text, start subscript, 2, end subscript are fixed (incorporated into organic molecules) and used to build three-carbon sugars. This process is fueled by, and dependent on, ATP and NADPH from the light reactions. Unlike the light reactions, which take place in the thylakoid membrane, the reactions of the Calvin cycle take place in the stroma (the inner space of chloroplasts). 3 CO 2 \text _2 CO 2 ​ start text, C, O, end text, start subscript, 2, end subscript molecules combine with three molecules of the five-carbon acceptor molecule (RuBP), yielding three molecules of an unstable six-carbon compound that splits to form six molecules of a three-carbon compoun...