Cells


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The molecules of cells

Cytosol : The cytosol is the "soup" within which all the other cell organelles reside and where most of the cellular metabolism occurs. Though mostly water, the cytosol is full of proteins that control cell metabolism including signal transduction pathways, glycolysis, intracellular receptors, and transcription factors.

Cytoplasm : This is a collective term for the cytosol plus the organelles suspended within the cytosol. Plant and animal cell centrosomes play similar roles in cell division, and both include collections of microtubules, but the plant cell centrosome is simpler and does not have centrioles. During animal cell division, the centrioles replicate make new copies and the centrosome divides.

The result is two centrosomes, each with its own pair of centrioles. The two centrosomes move to opposite ends of the nucleus, and from each centrosome, microtubules grow into a "spindle" which is responsible for separating replicated chromosomes into the two daughter cells. There are three microtubules in each group. Microtubules and centrioles are part of the cytoskeleton. In the complete animal cell centrosome, the two centrioles are arranged such that one is perpendicular to the other. Golgi : The Golgi apparatus is a membrane-bound structure with a single membrane.


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It is actually a stack of membrane-bound vesicles that are important in packaging macromolecules for transport elsewhere in the cell. The stack of larger vesicles is surrounded by numerous smaller vesicles containing those packaged macromolecules. The enzymatic or hormonal contents of lysosomes, peroxisomes and secretory vesicles are packaged in membrane-bound vesicles at the periphery of the Golgi apparatus.

Lysosome : Lysosomes contain hydrolytic enzymes necessary for intracellular digestion.

Introduction to Cells: The Grand Cell Tour

They are common in animal cells, but rare in plant cells. Hydrolytic enzymes of plant cells are more often found in the vacuole. Peroxisome : Peroxisomes are membrane-bound packets of oxidative enzymes. In plant cells, peroxisomes play a variety of roles including converting fatty acids to sugar and assisting chloroplasts in photorespiration. In animal cells, peroxisomes protect the cell from its own production of toxic hydrogen peroxide. As an example, white blood cells produce hydrogen peroxide to kill bacteria. The oxidative enzymes in peroxisomes break down the hydrogen peroxide into water and oxygen.

Secretory Vesicle : Cell secretions - e. The secretory vesicles are then transported to the cell surface for release. Cell Membrane : Every cell is enclosed in a membrane, a double layer of phospholipids lipid bilayer.

The exposed heads of the bilayer are "hydrophilic" water loving , meaning that they are compatible with water both within the cytosol and outside of the cell. However, the hidden tails of the phosopholipids are "hydrophobic" water fearing , so the cell membrane acts as a protective barrier to the uncontrolled flow of water.

The membrane is made more complex by the presence of numerous proteins that are crucial to cell activity.

cell | Definition, Types, & Functions | quakecazews.tk

Mitochondria : Mitochondria provide the energy a cell needs to move, divide, produce secretory products, contract - in short, they are the power centers of the cell. They are about the size of bacteria but may have different shapes depending on the cell type. Mitochondria are membrane-bound organelles, and like the nucleus have a double membrane. The outer membrane is fairly smooth.

But the inner membrane is highly convoluted, forming folds cristae when viewed in cross-section. The cristae greatly increase the inner membrane's surface area. It is on these cristae that food sugar is combined with oxygen to produce ATP - the primary energy source for the cell. Vacuole : A vacuole is a membrane-bound sac that plays roles in intracellular digestion and the release of cellular waste products. In animal cells, vacuoles are generally small.

Vacuoles tend to be large in plant cells and play several roles: storing nutrients and waste products, helping increase cell size during growth, and even acting much like lysosomes of animal cells.

Topic rooms within Cell Biology

The plant cell vacuole also regulates turgor pressure in the cell. They are not part of a multicellular organism, which might have whole layers of cells devoted to protecting other cells from the environment, or to creating motion. This single chromosome is usually round. There is no nucleus, or any other internal membranes or organelles.

Plasmids contain non-essential DNA that the cell can live without, and which is not necessarily passed on to offspring.


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  • When a prokaryotic cell is ready to reproduce, it makes a copy of its single chromosome. Then the cell splits in half, apportioning one copy of its chromosome and a random assortment of plasmids to each daughter cell. When scientists began to examine the biochemistry and genetics of prokaryotes in detail, they discovered these two very different groups, who probably have different relationships to eukaryotes and different evolutionary histories!

    Some scientists think that eukaryotes like humans are more closely related to bacteria, since eukaryotes have similar cell membrane chemistry to bacteria. Others think that archaebacteria are more closely related to us eukaryotes, since they use similar proteins to reproduce their chromosomes.

    What are stem cells, and what do they do?

    Still others think that we might be descended from both — that eukaryotic cells might have come into existence when archaebacteria started living inside of a bacterial cell, or vice versa! This would explain how we have important genetic and chemical attributes of both, and why we have multiple internal compartments such as the nucleus, chloroplasts, and mitochondria! Eukaryotic cells are thought to be the most modern major cell type.

    Cells and Microorganisms

    All multicellular organisms, including you, your cat, and your houseplants, are eukaryotes. Eukaryotic cells usually have more than one chromosome, which contains large amounts of genetic information. Eukaryotic cells also have one or more internal membranes, which has led scientists to the conclusion that eukaryotic cells likely evolved when one or more types of prokaryote began living in symbiotic relationships inside of other cells.

    As mentioned above, archaebacteria are a very old form of prokaryotic cells. Key ways in which archaebacteria differ from other bacteria include: Their cell membranes, which are made of a type of lipid not found in either bacteria or eukaryotic cell membranes.

    What are cells?

    Their DNA replication enzymes, which are more similar to those of eukaryotes than those of bacteria, suggesting that bacteria and archae are only distantly related, and archaebacteria may actually be more closely related to us than to modern bacteria. Some archaebacteria have the ability to produce methane, which is a metabolic process not found in any bacteria or any eukaryotes.

    Scientists became very excited in recent years at the discovery of Lokiarchaeota — a type of archaebacteria which shares many genes with eukaryotes that had never before been found in prokaryotic cells! It is now thought that Lokiarchaeota may be our closest living relative in the prokaryotic world. You are most likely familiar with the type of bacteria that can make you sick.

    Indeed, common pathogens like Streptococcus and Staphylococcus are prokaryotic bacterial cells. But there are also many types of helpful bacteria — including those that break down dead waste to turn useless materials into fertile soil, and bacteria that live in our own digestive tract and help us digest food. Plants cells have chloroplast organelles, which contain pigments that absorb photons of light and harvest the energy of those photons. Chloroplasts have the remarkable ability to turn light energy into cellular fuel, and use this energy to take carbon dioxide from the air and turn it into sugars that can be used by living things as fuel or building material.

    In addition to having chloroplasts, plant cells also typically have a cell wall made of a rigid sugars, to enable plant tissues to maintain their upright structures such as leaves, stems, and tree trunks. Plant cells also have the usual eukaryotic organelles including a nucleus, endoplasmic reticulum, and Golgi apparatus. Like all animal cells, it has mitochondria which perform cellular respiration , turning oxygen and sugar into large amounts of ATP to power cellular functions.

    It also has the same organelles as most animal cells: a nucleus, endoplasmic reticulum, Golgi apparatus, etc.. But as part of a multicellular organism, your liver cell also expresses unique genes, which give it unique traits and abilities. Liver cells in particular contain enzymes that break down many toxins, which is what allows the liver to purify your blood and break down dangerous bodily waste.

    The liver cell is an excellent example of how multicellular organisms can be more efficient by having different cell types work together.

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