What makes proteins in a plant cell

DNA in the nucleus is composed of nucleotides, which consist of 3 things: 1 a deoxyribose sugar 2 a nitrogenous base 3 phosphate groups. In a normal double helix of DNA, two strands are held together by associations between their respective nitrogenous bases, such that A always pairs with T, and C always pairs with G. This means that the two strands of DNA are complementary to each other.

They are not identical, but essentially opposites of each other. First, one strand of the DNA, known as the template strand, must undergo a process called "transcription" in the nucleus to create a strand of mRNA.

The sugar in RNA is also a bit different chemically and is called ribose. Once the mRNA is produced, it then exits the nucleus and enters the cytoplasm. In the cytoplasm, this mRNA strand then undergoes the process of "translation". The mRNA must associate with the ribosome, which is the primary component in producing the resulting protein. A complementary tRNA strand then recognizes the code on the mRNA by reading the nitrogenous bases in sets of 3 called a codon , and attaches its corresponding amino acid.

Metabolic activities may be generally distributed throughout the cytoplasm, confined to specific regions, or clearly carried out within the organelles.

Although more research has been directed to the analysis of the chemical composition and activities of the organelles than of the cytoplasm, it is apparent that the cytoplasm is composed in part of cytoskeletal elements and chains of functionally related enzymes surrounded by the cytosol, which includes water, ions, small metabolites, and proteins.

See also: Cytoplasm. The organelles, which are compartments in which certain metabolic activities are localized, are bounded by membranes similar to the plasma membrane. The molecular components phospholipids and proteins of the membranes are subject to rapid turnover. The membranes act as sites for the synthesis or breakdown of materials and frequently, as in mitochondria, are structurally highly specialized for these activities. Therefore, far from being simply selective barriers to the movement of materials, the membranes of the plant cell are dynamic structures that play key roles in metabolism.

Conspicuous among the components of the cytoplasmic matrix are millions of particles, approximately 20 nanometers nm in diameter, known as ribosomes. Each ribosome is composed of a small subunit and a large subunit that are formed separately in the nucleolus from rRNA and proteins and brought together in the cytoplasm.

The ribosomes are the sites of protein synthesis and function in translating the sequence of nucleotides in mRNA into the sequence of amino acids that make up the protein encoded by the mRNA. Translation of the genetic code in the ribosomes also requires tRNA.

Smaller ribosomes are also present in the mitochondria and plastids, where they translate RNA encoded by the DNA that resides in these organelles. In all types of cells, some of the ribosomes in the cytoplasm appear to be free, whereas others are attached to the surface of the membranes of the endoplasmic reticulum or to the outer membrane of the nuclear envelope.

See also: Ribosomes. The endoplasmic reticulum is an architecturally regular structure only in a few types of plant cells. It is a protean highly variable structure, and the manners in which its profiles are associated differ with the stage of development and metabolic activity.

In certain stages, numbers of profiles are seen to be stacked, frequently parallel to the surface of the cell. The profiles may also surround the nucleus or seem to encompass any of several types of organelles. The endoplasmic reticulum may be smooth or rough; that is, the outer surfaces of the membranes may be studded with ribosomes.

Although all plant cells have rough and smooth types of endoplasmic reticulum to synthesize the proteins and lipids necessary to construct many of the membranes of the cell, the rough endoplasmic reticulum is enriched in cells that are specialized for protein synthesis, including the cells of the aleurone layer of cereal seeds, and the smooth endoplasmic reticulum is enriched in cells specialized for lipid production, including oil gland cells and some stigmatic cells. Transitional endoplasmic reticulum, which is intermediate in structure between the smooth and rough endoplasmic reticulum, is rich in cells of the tapetum and the cells of seeds that store lipids in the form of osmotically active lipid bodies.

See also: Endoplasmic reticulum. The Golgi apparatus in many plant cells clearly functions in secretion, but the ubiquitous occurrence of the organelle suggests that it may have other roles in cellular activity. Although many aspects of its function are still obscure, it is apparent that certain materials are sequestered into its cisternae or saccules, synthesized there, or variously combined in the cisternae to form complex secretion products. The secretory products are then separated from the cisternae as membrane-bound vesicles and transported to and through the plasma membrane or to the vacuolar compartment where they remain inside the cell.

While the Golgi apparatus is important in the secretion of many proteins, including the fucose-rich mucilage secreted by root cap cells, the digestive enzymes secreted by insectivorous plants, and the wall-degrading enzymes released by the cells in the abscission zone, it is bypassed in the secretion of some proteins, including the prolamin proteins that make up some of the protein vacuoles in the seeds of cereals.

In the majority of plant cells, the Golgi apparatus is responsible for packaging and exporting the hemicelluloses, pectins, and hydroxyproline-rich glycoproteins of the wall that is built up around the cell. See also: Golgi apparatus. The vacuole Fig. In meristematic cells, vacuoles are generally small and are characterized by contents that stain darkly with certain procedures.

The contents of these vacuoles seem to be utilized in the process of development and then are replaced by water. At a certain stage in this process, the vacuoles fuse to form the large central vacuole, and most mature plant cells have large, centrally located vacuoles that make up the greatest part of the total volume of the cell. The cell sap is typically clear, making the vacuole look empty or vacuous.

The increase in volume of this vacuole is important in the growth of the plant cell. Moreover, the presence of water in the vacuole allows plants to have a large open dendritic form with a minimum investment of energy-intensive compounds in order to help the plants acquire light and the necessary nutrients that are dilute in the environment. In plant cells, vacuoles of different sorts are known to have different origins, with the endoplasmic reticulum, the Golgi apparatus, and the plasma membrane being involved.

See also: Vacuole. Vacuoles participate in the homeostasis of the cytosol by acting as large reversible stores of water, protons and other ions, amino acids, and other metabolites. The vacuoles in cells of many seeds function in the storage of proteins, and the vacuoles in the cells of many desert plants function in the storage of water as well as the storage of carbon in the form of organic acids.

In addition, the colors of many flowers and fruits result from the presence of pigments dissolved in the vacuolar fluid. See also: Plant pigment. Another conspicuous feature of many types of plant cells is the presence of large numbers of lipid bodies or spherosomes. They frequently are abundant in cells of embryos or in root or shoot apices and less numerous in more mature plant cells. These bodies are unique in having a structural boundary that is composed of a monolayer instead of a bilayer that is typical of most membranes.

The lipid bodies provide a carbon source for the production of biofuels. See also: Lipid. Mitochondria typically are ellipsoidal bodies bounded by a double-membrane system with the inner membrane projecting into the lumen to form cristae Fig.

In general, there is less extensive development of the cristae in the mitochondria of plant cells than in those of animals. This may reflect the fact that plant cells generally have substantially lower respiratory rates. In the few types of plant cells characterized by relatively high respiratory rates, the extent of the cristae more nearly resembles that in animal cells.

The inner membrane of the mitochondria surrounds the matrix. The mitochondria can often be observed to move incessantly throughout the plant cell. See also: Mitochondria. The mitochondria are the respiratory centers of the cell where the energy released by the combustion of carbohydrates is conserved in the synthesis of ATP from adenosine diphosphate ADP and inorganic phosphate P i.

The conversion of the chemical energy of carbohydrate to the chemical energy of ATP requires a few associated processes. The pyruvate formed during glycolysis, which takes place in the cytosol, is oxidized to carbon dioxide CO 2 in the matrix of the mitochondria in a process known as the Krebs cycle or the citric acid cycle.

The electrons captured in the oxidation process are transported down electron transport chains in the inner membrane. Molecular oxygen is the final receptor for these electrons. See also: Citric acid cycle. Perhaps the most conspicuous and certainly the most studied of the features peculiar to plant cells is the presence of plastids. The plastids are bounded by an envelope consisting of two membranes that touch in regions known as contact sites and an inner membrane system immersed in a viscous gel known as the stroma.

Chlorophylls and other pigments are associated with the inner-membrane system. Plant cells also have additional structures: Structure Function Chloroplast Contains the green pigment, chlorophyll, which absorbs light for photosynthesis, and the enzymes needed for photosynthesis. Cell wall Made from cellulose fibres. Strengthens the cell and supports the plant.

Vacuole Filled with cell sap to help support the cell. Where enzymes and other proteins are made. Contains DNA which carries the genetic code for making enzymes and other proteins used in chemical reactions such as photosynthesis and respiration. Cell membrane. Allows gases and water to diffuse freely into and out of the cell. Mitochondrion plural is mitochondria.

Contains enzymes for the reactions in aerobic respiration in animals, plants and yeast. Where amino acids are joined together to make a protein.