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Chapter 6 - Chapter 6 A tour of the Cell Concept 6.2...

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Chapter 6 A tour of the Cell Concept 6.2 Eukaryotic cells have internal membranes that compartmentalize their functions. The major difference between prokaryotes and eukaryotes is the location of their DNA. Most of the DNA in a eukaryotic cell is located in the nucleus. Within a prokaryotic cell, the DNA is found in a region known as the nucleoid, which has no membrane. (Figure6.6) Why compartmental organization? o Provide localized environmental conditions necessary for specific metabolic process. o Sequester reactions, so they may occur without interference from incompatible metabolic processes elsewhere in the cell. (Figure 6.9) Concept 6.3 The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes. The Nucleus Contains the majority of the DNA in a eukaryotic cell. What other organelles contain DNA? o Mitochondria, chloroplast (plant cells) Nucleus is enclosed in a nuclear envelope which separates its contents from the cytoplasm. DNA is organized on chromosomes , which are composed of chromatin , which consists of DNA and proteins. A typical human cell has 46 chromosomes within the nucleus, with the exception of gamete (sex cells), which only have 23. Within the nucleus is the nucleolus , where rRNA, as well as ribosomes are produced and assembled. Directs protein synthesis. Uses instructions within gees (DNA) to synthesize messenger RNA. Exits the nucleus via pore complexes.
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Binds to ribosomes in the cytoplasm which translate the mRNA into a polypeptide (1 degree protein structure). The Nuclear Envelope A double membrane, each a lipid bilayer, facing opposite directions. Perforated by nuclear pores which contain a pore complex. o Functions within the nuclear membrane to regulate entry and exit of proteins, RNAs, and other molecules. Ribosomes Composed of rRNA and protein. Main function is protein synthesis. Number of ribosomes in a cell is directly related to the level of protein synthesis that occurs in that cell. Human pancreatic cells have a several million ribosomes. Why? o Because the pancreas produces insulin, and numerous digestive enzymes. Found in two locations within the cell: o Free ribosomes are suspended in the cytosol. o Bound ribosomes are attached to the outside of the endoplasmic reticulum or the nuclear envelope. Structurally identical and interchangeable. (Figure 6.11) Concept 6.4 The endomembrane system regulates protein traffic and performs metabolic functions in the cell.
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