Transcript Cellula
Please read or listen to this book http://video.google.com/videoplay?docid=6650219631867189375 Characteristics of living organisms • Are highly organized, complex entities • Are composed of 1 or more cells • Contain a blueprint of their characteristics (a genetic program encoded in DNA) • Acquire and use energy • Carry out and control numerous chemical reactions • Grow in size and change in appearance and abilities • Maintain a fairly constant internal environment (homeostasis) • Reproduction • Respond to changes in their environments • May evolve into new types of organisms Six kingdoms of life are recognized Figure 1.6 The development of a scientific theory rests on a five-tiered foundation. The basic tier comprises observations made of natural phenomenon. Observations lead to questioning. Does what we observe fit with our expectations of what should occur? Especially if the answer is no, observations and questions lead to tentative, testable alternative explanations, that is, to hypotheses. Now follows intense testing, conducted ideally by both the framer of the hypothesis and others. Testing may lead to refinement of they hypothesis and an eventual explanation of the hypothesis. Only after extensive testing and widespread acceptance within the community of scientists can an idea in science reach the level of theory. Six elements make up 99% of all living things • • • • • • Carbon Hydrogen Oxygen Nitrogen Phosphorus Sulfur There are four organic macromolecules (or polymers) that are made from simple building blocks (or monomers) • Carbohydrates also known as Polysaccharides (monosaccharides) • Lipids (fatty acids) • Proteins (amino acids) • Nucleic Acids (nucleotides) Carbohydrates (polysaccharides) are built from simple sugars (monosaccharides) Lipids are built from fatty acids Proteins are built from amino acids Nucleic Acids (DNA and RNA) are built from nucleotides Cells and Microscopes • The cell was first named by Robert Hooke in 1665. He remarked that it looked strangely similar to cellula or small rooms which monks inhabited, thus deriving the name. However what Hooke actually saw was the non living cells from a cork (cork) . Hooke's description of these cells was published in Micrographia. The cell walls observed by Hooke gave no indication of the nucleus and other organelles found in most living cells. The first man to witness a live cell under a microscope was Anton Van Leeuwenhoek, who in 1674 described the algae Spirogyra and named the moving organisms animalcules, meaning "little animals". Cell Theory • All organisms are composed of one or more cells. • The cell is the fundamental unit of life. • Cells arise from preexisting cells. Credit for developing Cell Theory (1839-1858) is usually given to three scientists, Theodor Schwann, Matthias Jakob Schleiden, and Rudolf Virchow. Examples of two eukaryotic cells Organelles and their functions • • • • • • • • • • • • • • • Nucleus-control center of the cell Nucleolus-synthesis of ribosomes Endoplasmic recticulum-membrane tunnel system where many proteins and lipids are made Golgi bodies-modification, packaging, and distribution center for proteins Ribosomes-sites of protein synthesis Vesicles-storage and transport of cellular products and raw materials Central vacuole-water, waste and food storage Lysosomes-involved with intracellular digestion Mitochondria-power pack of the cells; site of aerobic respiration; ATP formation Chloroplasts-site of photosynthesis; production of food Centrioles- facilitate division of the genetic material in the nucleus during cell division and organization of the cytoskeleton Cytoskeleton-system of microfilaments, intermediate filaments and microtubules that provide internal cellular structure Plasma membrane-regulates the movement of substances into and out of the cell Flagella & cilia- plasma membrane projections; involved with cell movement Cell wall-provides structural support and protection to the cell Most biologists view viruses as non-living as they are acellular. How do molecules get into and out of cells? • • • • • • Bulk flow Diffusion Osmosis Facilitated diffusion (passive transport) Active transport Endocytosis and Exocytosis Figure 4.17 Osmosis is the net diffusion of water across a selectively permeable membrane. In this illustration, green protein molecules cannot cross the membrane, but blue water molecules can. Water will move in both directions, but there is a net movement from the left compartment of the chamber to the right compartment. The left compartment is said to be hypotonic relative to the right compartment. Conversely, the right compartment is hypertonic relative to the left compartment. Figure 4.19 Membrane transport involves specific transport proteins that are embedded in the phospholipid bilayer. (a) Ion channels must be opened (step 1) before the ion can pass through (step 2). Channels can be opened or closed in response to various kinds of messages received by the cell. (b) In facilitated diffusion, substances enter a protein carrier and change the shape of the protein (step 1). After the solute is moved across the membrane, the protein resumes its original shape (step 2). For both ion channels and facilitated diffusion, substances move from high to low concentration. No energy is needed. Figure 4.20 Active transport moves substances from low to high concentration-against their concentration gradient. In this illustration, sodium (Na+) outside of the cell attaches to the protein (step 1). The protein gets energy when the ATP donates a phosphate to the protein (step 2). This changes the shape of the protein and pushes the sodium across the membrane (step 3). Potassium (K+) from outside the cell binds to the altered protein (step 4) and is expelled into the cell when the protein resumes its original shape (step 5). Figure 10.7 Adenosine triphosphate (ATP) is an important nucleotide in cellular metabolism. When the terminal phosphate on ATP is cleaved leaving ADP and a free phosphate, a small packet of energy is released that can be used by the cell to fuel metabolic processes. Figure 4.21 Cells can transport substances in bulk across their membranes. (a) In endocytosis, the membrane engulfs the substances and the movement is into the cell. (b) In exocytosis, the movement is out of the cell. Figure 12.16 (a) The kidney, which has about a million nephrons. (b) The nephron, which includes a vascular portion (the glomerulus and the peritubular capillaries, in red and blue) and a tubular portion (in gold).