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Transcript
Chapter 3: Cells The smallest part of you All organisms are made of cells. Every cell on earth falls into one of two basic categories: • • A eukaryotic cell • has a central control structure called a nucleus which contains the cell’s DNA. • eukaryotes A prokaryotic cell • • does not have a nucleus; its DNA simply resides in the middle of the cell prokaryotes Prokaryotic cells are structurally simple but extremely diverse in type. • Prokaryotes include two major domains of life: the bacteria and archaea • They are characterized by tremendous metabolic diversity. Prokaryotes are all single-celled organisms, and only form simple colonies. None form large multicellular organisms with tissues and organs. Eukaryotic cells have compartments with specialized functions. Eukaryotic cells have organelles. Endosymbiosis Theory Developed to explain the presence of two organelles in eukaryotes, chloroplasts in plants and algae, and mitochondria in plants and animals. Humans, deep down, may be part bacteria. How can that be? Eukaryotes are single-celled or multicellular organisms whose cells have a nucleus that contain linear strands of genetic material. The cells also commonly have organelles throughout their cytoplasm, which may have originated evolutionarily through endosymbiosis or invagination, or both. The nucleus is the cell’s genetic control center. The nucleus—the largest and most prominent organelle in most eukaryotic cells. The nucleus has two primary functions: • genetic control center • storehouse for hereditary information a Chromatin mass of long, thin fibers consisting of DNA with some proteins attached an Nucleolus area near the center of the nucleus where subunits of the ribosomes are assembled Ribosomes factories. The are like little nucleus is usually the largest and most prominent organelle in the eukaryotic cell. It directs most cellular activities by controlling which molecules are produced and in what quantity. The nucleus is the storehouse for hereditary information. Cytoplasm and cytoskeleton form the cell’s internal environment, provide its physical support, and can generate movement. Cytoskeleton: Three Chief Purposes Cilia and Flagellum The inner scaffolding of the cell, which is made from proteins, is the cytoskeleton. It consists of three types of protein fibers: microtubules, intermediate filaments, and microfilaments It gives animal cells shape and support. It gives cells some ability to control their movement. It serves as a series of tracks on which organelles and molecules are guided across and around the inside of the cell. Mitochondria are the cell’s energy converters • Mitochondria consume most of the oxygen we use, and produce most of the energy we use. Inner membrane is folded to provide surface area for chemical reactions. Endosymbiosis Mitochondria may have existed as separate single-celled, bacteria-like organisms billions of years ago. Mitochondria DNA! have their own We all have more DNA from one parent than the other. Who is the bigger contributor: mom or dad? Why? THIS IS HOW WE DO IT Can cells change their composition to adapt to their environment? Why did the researchers use multiple cats from each litter? What was the purpose of counting the capillaries? Why do you think the fat cells in the cats exposed to cold shrank so much? What change in the study would increase your confidence in the conclusions? Take-home message 3.16 • Form follows function in an organism’s cells and reflects their environment. • When cells must perform intensive heat production, they significantly increase the number and size of their mitochondria. Take-home message 3.16 • They also increase the blood supply to the tissue and make use of existing stores of energy. 3.17 Lysosomes are the cell’s garbage disposals Lysosomes round, membrane-enclosed, acid-filled vesicles that function as garbage disposals Why is Tay-Sachs disease like a strike by trash collectors? 50 different enzymes necessary Malfunctions sometimes occur. Genetic disorder Take-home message 3.17 Lysosomes are round, membrane-enclosed, acid-filled vesicles that function as a cell’s garbage disposal. They are filled with about 50 different digestive enzymes and enable a cell to dismantle macromolecules, including disease-causing bacteria. 3.18 In the Endoplasmic reticulum, cells build proteins and disarm toxins Rough Endoplasmic Reticulum The Smooth Endoplasmic Reticulum Critical Responsibilities of the Smooth ER Q How can long-term use of one drug increase your resistance to another, different drug that you have never encountered? Take-home message 3.18 The production and modification of biological molecules within eukaryotic cells occurs in a system of organelles called the endomembrane system, which includes, among other organelles, the rough and smooth endoplasmic reticulum. Take-home message 3.18 In rough ER, proteins that will be shipped elsewhere in the body are folded and packaged. In the smooth ER, lipids and carbohydrates are synthesized and alcohol, antibiotics, and other drugs are detoxified. 3.19 The Golgi apparatus processes products for delivery throughout the body 3.19 Golgi apparatus: Where the cell processes products for delivery throughout the body Take-home message 3.19 The Golgi apparatus—another organelle within the endomembrane system—processes molecules synthesized within a cell and packages those that are destined for use elsewhere in the body. 3.20 The cell wall provides additional protection and support for plant cells Take-home message 3.20 The cell wall is an organelle found in plants (and some other non-animal organisms). It is made primarily from the carbohydrate cellulose and it surrounds the plasma membrane of a plant cell. Take-home message 3.20 The cell wall confers tremendous structural strength on plant cells, gives plants increased water resistance, and provides some protection from insects and other animals that might eat them. In plants, plasmodesmata connect cells and enable communication and transport between them. 3.21 Vacuoles are multipurpose storage sacs for cells The central vacuole can play an important role in five different areas of plant life: • • • • • Nutrient storage Waste management Predator deterrence Sexual reproduction Physical support Take-home message 3.21 In plants, vacuoles can occupy most of the interior space of the cell. Vacuoles also appear in some other eukaryotic species. They function as storage space and play a role in nutrition, waste management, predator deterrence, reproduction, and physical support. 3.22 Chloroplasts are the plant cell’s power plant The stroma and interconnected little flattened sacs called thylakoids Endosymbiosis Theory Revisited Chloroplasts resemble photosynthetic bacteria. Circular DNA Dual outer membrane Take-home message 3.22 The chloroplast is the organelle in plants and algae that is the site of photosynthesis—the conversion of light energy into chemical energy, with oxygen as a by-product. Chloroplasts may have originally been bacteria that were engulfed by a predatory cell by endosymbiosis.