Cells

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  1. 1. The ________, or MICROTUBULE ORGANIZING CENTER (MTOC), is an area in the cell where microtubules are produced. Plant and animal cell _________ play similar roles in cell division, and both include collections of microtubules, but the plant cell ________ is simpler and does not have centrioles.
  2. 3. _________ are membrane-bound packets of oxidative enzymes. In plant cells, __________ play a variety of roles including converting fatty acids to sugar and assisting chloroplasts in photorespiration. In animal cells, _________ 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.
  3. 7. The ________ is the "soup" within which all the other cell organelles reside and where most of the cellular metabolism occurs. Though mostly water, the _______ is full of proteins that control cell metabolism including signal transduction pathways, glycolysis, intracellular receptors, and transcription factors.
  4. 9. _________ 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) as seen in the cross-section, above. 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.
  5. 10. The prominent structure in the nucleus is the _________. The __________ produces ribosomes, which move out of the nucleus and take positions on the rough endoplasmic reticulum where they are critical in protein synthesis.
  6. 12. The _____ apparatus is a membrane-bound structure with a single membrane. 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 _______ apparatus.
  7. 13. Cell secretions - e.g. hormones, neurotransmitters - are packaged in ______-______ at the Golgi apparatus. The _______-______ are then transported to the cell surface for release.
  8. 14. (plant cells only): Plant cells have a rigid, protective cell wall made up of polysaccharides. In higher plant cells, that polysaccharide is usually cellulose. The _____-____ provides and maintains the shape of these cells and serves as a protective barrier. Fluid collects in the plant cell vacuole and pushes out against the cell wall. This turgor pressure is responsible for the crispness of fresh vegetables.
  9. 15. The ______ is the most obvious organelle in any eukaryotic cell. It is enclosed in a double membrane and communicates with the surrounding cytosol via numerous nuclear pores. Within the ______ is the DNA responsible for providing the cell with its unique characteristics. The DNA is similar in every cell of the body, but depending on the specific cell type, some genes may be turned on or off - that's why a liver cell is different from a muscle cell, and a muscle cell is different from a fat cell. When a cell is dividing, the nuclear chromatin (DNA and surrounding protein) condenses into chromosomes that are easily seen by microscopy.
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  1. 2. _____-______-_____ appears "pebbled" by electron microscopy due to the presence of numerous ribosomes on its surface. Proteins synthesized on these ribosomes collect in the endoplasmic reticulum for transport throughout the cell.
  2. 4. ________ contain hydrolytic enzymes necessary for intracellular digestion. They are common in animal cells, but rare in plant cells. Hydrolytic enzymes of plant cells are more often found in the vacuole.
  3. 5. A _____ is a membrane-bound sac that plays roles in intracellular digestion and the release of cellular waste products. In animal cells, _______ are generally small. _______ 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. The plant cell vacuole also regulates turgor pressure in the cell. Water collects in cell _______, pressing outward against the cell wall and producing rigidity in the plant. Without sufficient water, turgor pressure drops and the plant wilts.
  4. 6. (animal cells only): Each _______ is a ring of nine groups of fused microtubules. There are three microtubules in each group. Microtubules (and _______) are part of the cytoskeleton. In the complete animal cell centrosome, the two _______ are arranged such that one is perpendicular to the other.
  5. 8. Every ____ is enclosed in a _______, 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 ____. However, the hidden tails of the phosopholipids are "hydrophobic" (water fearing), so the ____-________ acts as a protective barrier to the uncontrolled flow of water. The ________ is made more complex by the presence of numerous proteins that are crucial to cell activity. These proteins include receptors for odors, tastes and hormones, as well as pores responsible for the controlled entry and exit of ions like sodium (Na+) potassium (K+), calcium (Ca++) and chloride (Cl-).
  6. 11. (plant cells only): _______ are specialized organelles found in all higher plant cells. These organelles contain the plant cell's chlorophyll responsible for the plant's green color and the ability to absorb energy from sunlight. This energy is used to convert water plus atmospheric carbon dioxide into metabolizable sugars by the biochemical process of photosynthesis. _________ have a double outer membrane. Within the stroma are other membrane structures - the thylakoids. Thylakoids appear in stacks called "grana" (singular = granum).