In this process, known as photosynthesis, the green chlorophyll absorbs energy from sunlight, and this energy is used to convert carbon dioxide and water into carbohydrates. These carbohydrates are then converted, through cellular respiration, into ATP, which is the energy source for all living things.
Chloroplast DNA codes for catalytic proteins called enzymes that are necessary to the photosynthetic process. The mitochondria in an animal cell are also responsible for energy production. Mitochondrial DNA provides instructions for producing enzymes necessary for the process of oxidative phosphorylation.
This process uses oxygen and simple sugars obtained from food to produce ATP. Mitochondrial DNA can be used to trace an individual's ancestral line back to its prehistoric place of origin.
The Structure of a Eukaryotic Cell. At the periphery of the cell is the plasma membrane. In some prokaryotes the plasma membrane folds in to form structures called mesosomes, the function of which is not clearly understood. Outside the plasma membrane of most prokaryotes is a fairly rigid wall which gives the organism its shape.
The walls of bacteria consist of peptidoglycans. Sometimes there is also an outer capsule. Note that the cell wall of prokaryotes differs chemically from the eukaryotic cell wall of plant cells and of protists. Eukaryotic cells contain a membrane-bound nucleus and numerous membrane-enclosed organelles e. Animals, plants, fungi, and protists are all eukaryotes. Eukaryotic cells are more complex than prokaryotic cells and are found in a great many different forms. The nucleus contains most of the genetic material DNA of the cell.
Additional DNA is in the mitochondria and if present chloroplasts. The nuclear DNA is complexed with proteins to form chromatin, which is organized as a number of linear chromosomes. Genetic control of the cell is carried out by the production of RNA in the nucleus the process of transcription and the subsequent transfer of this RNA to a ribosome in the cytoplasm, where protein synthesis the process of translation is directed.
The resulting proteins carry out cell functions. Also located in the nucleus is the nucleolus or nucleoli, organelles in which ribosomes are assembled. The nucleus is bounded by a nuclear envelope, a double membrane perforated with pores and connected to the rough endoplasmic reticulum membrane system.
The cytoskeleton consists of microtubules, intermediate fibers, and microfilaments, which together maintain cell shape, anchor organelles, and cause cell movement.
The microtubules and microfilaments are frequently assembled and disassembled according to cellular needs for movement and maintaining cell shape. Intermediate filaments are more permanent than microtubules and microfilaments. The cell diagrams shown here represent intestinal epithelial cells with fingerlike projections, the microvilli.
The location and appearance of cytoskeletal fibers in different cell types will vary. A ribosome is the site of protein synthesis in the cell. Each ribosome consists of a large subunit and a small subunit, each of which contains rRNA ribosomal RNA and ribosomal proteins.
The amino acids are joined to produce the protein. You may access more information on From Gene to Protein: Translation.
Ribosomes exist free in the cytoplasm and bound to the endoplasmic reticulum ER. Plant cells also include chloroplasts, which are responsible for photosynthesis. Use these classroom resources to examine how cells function with your students. Cells function differently in unicellular and multicellular organisms.
A unicellular organism depends upon just one cell for all of its functions while a multicellular organism has cells specialized to perform different functions that collectively support the organism. Even the most basic parts of a cell can enable complex cellular processes, and multifunctional organelles expand these capabilities to make advanced activities possible for higher life-forms.
Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Image organelles Just as organs are separate body parts that perform certain functions in the human body, organelles are microscopic sub-units that perform specific functions within individual cells.
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Related Resources. Cell Functions. View Collection. Unicellular vs.
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