Which structure propels the cell

Under certain circumstances, lysosomes perform a more grand and dire function. In the case of damaged or unhealthy cells, lysosomes can be triggered to open up and release their digestive enzymes into the cytoplasm of the cell, killing the cell. Watch this video to learn about the endomembrane system, which includes the rough and smooth ER and the Golgi body as well as lysosomes and vesicles.

What is the primary role of the endomembrane system? In addition to the jobs performed by the endomembrane system, the cell has many other important functions.

Just as you must consume nutrients to provide yourself with energy, so must each of your cells take in nutrients, some of which convert to chemical energy that can be used to power biochemical reactions. Another important function of the cell is detoxification. Humans take in all sorts of toxins from the environment and also produce harmful chemicals as byproducts of cellular processes.

Cells called hepatocytes in the liver detoxify many of these toxins. Mitochondria consist of an outer lipid bilayer membrane as well as an additional inner lipid bilayer membrane Figure. The inner membrane is highly folded into winding structures with a great deal of surface area, called cristae.

It is along this inner membrane that a series of proteins, enzymes, and other molecules perform the biochemical reactions of cellular respiration. These reactions convert energy stored in nutrient molecules such as glucose into adenosine triphosphate ATP , which provides usable cellular energy to the cell.

Cells use ATP constantly, and so the mitochondria are constantly at work. Oxygen molecules are required during cellular respiration, which is why you must constantly breathe it in.

One of the organ systems in the body that uses huge amounts of ATP is the muscular system because ATP is required to sustain muscle contraction. As a result, muscle cells are packed full of mitochondria. Nerve cells also need large quantities of ATP to run their sodium-potassium pumps. Therefore, an individual neuron will be loaded with over a thousand mitochondria. On the other hand, a bone cell, which is not nearly as metabolically-active, might only have a couple hundred mitochondria. Peroxisomes Like lysosomes, a peroxisome is a membrane-bound cellular organelle that contains mostly enzymes Figure.

Peroxisomes perform a couple of different functions, including lipid metabolism and chemical detoxification. In contrast to the digestive enzymes found in lysosomes, the enzymes within peroxisomes serve to transfer hydrogen atoms from various molecules to oxygen, producing hydrogen peroxide H 2 O 2.

In this way, peroxisomes neutralize poisons such as alcohol. In order to appreciate the importance of peroxisomes, it is necessary to understand the concept of reactive oxygen species. Reactive oxygen species ROS such as peroxides and free radicals are the highly reactive products of many normal cellular processes, including the mitochondrial reactions that produce ATP and oxygen metabolism. Some ROS are important for certain cellular functions, such as cell signaling processes and immune responses against foreign substances.

Free radicals are reactive because they contain free unpaired electrons; they can easily oxidize other molecules throughout the cell, causing cellular damage and even cell death. Free radicals are thought to play a role in many destructive processes in the body, from cancer to coronary artery disease.

Peroxisomes, on the other hand, oversee reactions that neutralize free radicals. Peroxisomes produce large amounts of the toxic H 2 O 2 in the process, but peroxisomes contain enzymes that convert H 2 O 2 into water and oxygen. These byproducts are safely released into the cytoplasm. Like miniature sewage treatment plants, peroxisomes neutralize harmful toxins so that they do not wreak havoc in the cells. The liver is the organ primarily responsible for detoxifying the blood before it travels throughout the body, and liver cells contain an exceptionally high number of peroxisomes.

Defense mechanisms such as detoxification within the peroxisome and certain cellular antioxidants serve to neutralize many of these molecules. Some vitamins and other substances, found primarily in fruits and vegetables, have antioxidant properties.

Antioxidants work by being oxidized themselves, halting the destructive reaction cascades initiated by the free radicals. Sometimes though, ROS accumulate beyond the capacity of such defenses. Oxidative stress is the term used to describe damage to cellular components caused by ROS. Due to their characteristic unpaired electrons, ROS can set off chain reactions where they remove electrons from other molecules, which then become oxidized and reactive, and do the same to other molecules, causing a chain reaction.

ROS can cause permanent damage to cellular lipids, proteins, carbohydrates, and nucleic acids. Damaged DNA can lead to genetic mutations and even cancer.

It is noteworthy that these diseases are largely age-related. Many scientists believe that oxidative stress is a major contributor to the aging process.

Cell: The Free Radical Theory The free radical theory on aging was originally proposed in the s, and still remains under debate. Generally speaking, the free radical theory of aging suggests that accumulated cellular damage from oxidative stress contributes to the physiological and anatomical effects of aging. There are two significantly different versions of this theory: one states that the aging process itself is a result of oxidative damage, and the other states that oxidative damage causes age-related disease and disorders.

The latter version of the theory is more widely accepted than the former. However, many lines of evidence suggest that oxidative damage does contribute to the aging process.

Research has shown that reducing oxidative damage can result in a longer lifespan in certain organisms such as yeast, worms, and fruit flies. Conversely, increasing oxidative damage can shorten the lifespan of mice and worms. Interestingly, a manipulation called calorie-restriction moderately restricting the caloric intake has been shown to increase life span in some laboratory animals.

It is believed that this increase is at least in part due to a reduction of oxidative stress. However, a long-term study of primates with calorie-restriction showed no increase in their lifespan. A great deal of additional research will be required to better understand the link between reactive oxygen species and aging. Much like the bony skeleton structurally supports the human body, the cytoskeleton helps the cells to maintain their structural integrity.

The cytoskeleton is a group of fibrous proteins that provide structural support for cells, but this is only one of the functions of the cytoskeleton. Cytoskeletal components are also critical for cell motility, cell reproduction, and transportation of substances within the cell.

Mitochondrion plural: mitochondria —organelle where aerobic respiration occurs. The mitochondrion is the result of an endosymbiotic event in which one bacterium began living inside another, with benefits for both.

Nucleus—organelle which contains chromosomes, surrounded by a double membrane. The nucleus helps keep the chromosomes organized and separated from the rest of the cell.

Organelle—a membrane-bound compartment inside a cell which has a particular function. Examples include the nucleus, mitochondrion, Golgi apparatus, and central vacuole. Peroxisome—a vesicle which contains hydrogen peroxide, which is used to destroy worn-out cell parts or invading bacteria or viruses.

Plasma membrane—a structure made of phospholipids with embedded proteins which forms the boundary between the inside and outside of a cell; plasma membranes also make up the boundaries of organelles.

Plasmodesmata—a series of connections in the cell walls between adjacent plant cells, through which cytoplasm and other substances can move. Plastid—a class of organelles found only in plants. Examples include chloroplasts, chromoplasts, and amyloplasts. Prokaryotic—refers to cells which do not contain membrane-bound organelles such as a nucleus. Prokaryotic cells are commonly called bacteria. Receptor protein—a protein embedded in the membrane of a cell to which hormone molecules may attach.

Recognition protein—protein molecule embedded in the plasma membrane of a cell which allows the immune system to determine that the cell is part of the body, so that it is not attacked.

Ribosome—non-membranous structure where proteins are constructed. In eukaryotic cells, most ribosomes are on the rough ER. Ribosomes are made of RNA and proteins. Rough ER—endoplasmic reticulum with ribosomes attached; it appears rough under a microscope.

Smooth ER—endoplasmic reticulum without attached ribosomes; it appears smooth under a microscope. Smooth ER is a location for synthesis of lipid and other molecules. Stroma—fluid-filled area between the inner membrane and thylakoid membrane of a chloroplast.

Surface-to-volume ratio—the numerical ratio between the surface area of an object especially a cell and its volume; surface-to-volume ratio is the limiting factor on the size of cells. Thylakoid membrane—innermost membrane of the chloroplast where some of the reactions of photosynthesis take place. We will learn how to stain bacteria so you may observe these spores. Cilia - short, hairlike, motile cellular extensions that occur on the surfaces of certain cells; ex.

Flagella - in humans, the single, long, hairlike cellular extension that occurs in sperm cells; beat in waves prokaryotic flagella rotate! Cell Wall. Animal cells - no cell wall! Plant cells - made of cellulose. Fungi - in most made of cellulose; some made of chitin polysaccharide containing nitrogen - similar to exoskeletons of insects and cellulose. Algae - made of cellulose. Protozoans - no cell wall! Glycocalyx - A glycocalyx may exist outside the plasma membrane; composed of carbohydrate chains from glycoproteins in cell membrane.

Cytoskeleton not found in prokaryotes. Structure in eukaryotic cells:. Function - sites of protein synthesis where amino acids are assembled into polypeptides. We will not discuss these organelles in detail, since the focus of this class will be on prokaryotes.

Structure - 4 to 8 flattened, membrane-bound sacs loosely stacked on top of one another surrounded by vesicles; looks like a stack of pancakes.

Process: transport vesicles from the r. Structure - membrane-bound sacs that could be pinched off pieces of golgi complex, E. Some specialized vesicles:. Lysosomes - contain enzymes for breaking down proteins, lipids, etc. Function - break down energy containing organic molecules ex.

Functions - give the cell shape support , anchor the organelles, transport substances through the cell, involved in cell division. Structure - paired cylindrical structures composed of protein filaments. Function - during cell division, organize a microtubule network, called spindle fibers; spindle fibers are responsible for moving the chromosomes around in the cell during division.

Definition - the net movement of particles from a greater concentration to a lower concentration down a concentration gradient to distribute the particles uniformly; it's a passive process - molecules move by their own kinetic energy - requires no energy expenditure by the cell no ATP ; molecules will diffuse freely until an equilibrium is reached equal distribution on both sides. Simple Diffusion through the Cell Membrane - The lipid interior of the cell membrane is a barrier to simple diffusion; most polar molecules polar molecules get "stuck" in the nonpolar fatty acid tails.

Osmosis - a special case of diffusion; the movement of water across a semipermeable membrane - water moves from a high water concentration to a low water concentration or from a low solute concentration to a high solute concentration ; water moves across cellular membranes through pores in channel proteins or through momentary openings in the membrane. Note: The above examples describe the environment that the cell is in i.

You can also talk about the cell in relation to its environment i. You have to make this distinction!! The cells in our bodies try to maintain the isotonic condition so that they are not in danger of lysing or crenating.

Facilitated Diffusion - Again, only small, nonpolar molecules readily diffuse across the cell membrane.

Small, polar molecules, like water, and some ions can diffuse through channel proteins. Special selective carrier proteins are located in the membrane to transport molecules like glucose. In facilitated diffusion, carrier proteins move molecules from a high concentration to a low concentration like in simple diffusion; it is believed that changes in the shape of the carrier protein allow it to envelop and then release the transported substance.