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Transcript
Chapter 7 A View of the Cell 7.1 Microscopes Compound light microscopes • Use a series of lenses to magnify objects • Can magnify up to 1500 times • Uses a beam of light Electron Microscopes • • • • Uses a beam of electrons to magnify objects Can magnify up to 500,000 times Specimens must be examined in a vacuum Two types: Scanning electron microscope scans the surface of cells to view the 3 dimensional shape Transmission electron microscopes allow scientists to study structures in a cell 7.1 Cell Theory With the invention of microscopes, scientists were able to conduct more in-depth investigations and created the cell theory, which has 3 basic ideas: • All organisms are composed of one or more cells • The cell is the basic unit of structure and organization of organisms • All cells come from cells that already existed 7.1 Types of cells There are 2 basic types of cells • Prokaryotes Do not have membrane bound organelles Include most single celled organisms • Eukaryotes Have membrane bound organelles Includes most multi celled organisms Have a nucleus, which manages and controls cellular functions Organelles each have a specific function within the cell 7.1 Prokaryotic cells Prokaryotic cells have the following structures: • Cell wall • Plasma membrane • Ribosomes • DNA • Cytoplasm 7.1 Eukaryotic Cells Eukaryotic Cells contain the following structures: • Plasma membrane • Cytoplasm • Chromosomes • Nucleus • Nucleolus • Organelles 7.2 Plasma Membrane The plasma membrane is the flexible boundary between the cell and its environment • It allows nutrients to enter and exit the cells • It allows waste to exit the cell • It is described as being selectively permeable, because it lets some things through but not others It can also change what it allows to pass through at different times 7.2 Plasma Membrane Structure The plasma membrane is made of a phospholipid bilayer, which is composed of 2 layers of phospholipids back to back • Phospholipids are composed of a glycerol backbone, 2 fatty acids chains and a phosphate group The fatty acid tails are non-polar • These are on the inside of the bilayer The phosphate head is polar • This is on the outside of the bilayer 7.2 Fluid Mosaic Model The model of the plasma membrane is called the fluid mosaic model • Fluid because the phospholipids move within the membrane (similar to water waves moving in a lake) • Mosaic because proteins create a pattern on the surface of the bilayer 7.2 Other components Cholesterol • Stabilizes the phospholipids by preventing their fatty acid tails from sticking together • Cholesterol can be harmful in large quantities, but some is necessary for this purpose Transport proteins • Regulate which substances enter and leave the cells 7.3 Cell Structures Eukaryotic Cells are divided into 2 categories: plant cells and animal cells • Animal cell structures include a plasma membrane, ribosomes, a cytoskeleton, an endoplasmic reticulum, a golgi apparatus, lysosomes (some cells), mitochondrion, a nucleus, a nucleolus, and vacuoles (some animal cells) • Plant cells include these items plus a cell wall and chloroplasts 7.3 Cell Parts & Functions I Plasma membrane- flexible cell boundary that is selectively permeable Cell wall- rigid cell boundary outside the plasma membrane that provides additional structural support Nucleus- controls organelle activity and includes directions to make proteins in the DNA, which is in a stringy form called chromatin Nucleolus- inside the nucleus-makes ribosomes 7.3 Cell Parts & Functions II Ribosomes- where cells produce proteins according to the directions in DNA Cytoplasm-clear gelatinous fluid inside a cell-suspends organelles Endoplasmic reticulum (ER)- site of cellular chemical reactions • Rough ER has ribosomes • Smooth ER does not have ribosomes 7.3 Cell Parts & Functions III Golgi Apparatus- modifies proteins by sorting and packaging them and sending them to the correct location Vacuoles- temporary storage of materials (food, enzymes, waste) Lysosomes- contain digestive enzymes that digest extra or worn out organelles, food, and viruses/bacteria • They can fuse with vacuoles to empty their contents 7.3 Cell Parts & Functions IV Chloroplasts- trap light energy and convert it to chemical energy; contain chlorophyll a green pigment that traps light energy Mitochondria- transform energy for the cell Cytoskeleton- a network of rods (microtubules) and filaments (microflaments) inside the plasma membrane that provide structure and maintain the shape of the cell 7.3 Cell Parts & Function V Centrioles- play a role in cell division Cilia- short numerous projections that look like hairs that allow the cell to move Flagella-long projections (1 or 2 per cell) that allow the cell to move Nuclear membrane- separates the cytoplasm from the nucleus 7.3 Animal Cell Plasma membrane lysosome Golgi Apparatus centriole nucleolus mitochondria Endoplasmic reticulum vacuole nucleus cytoplasm ribosomes Nuclear membrane 7.3 Plant Cell Nuclear membrane Cell wall mitochondria cytoplasm nucleus nucleolus ribosomes Endoplasmic reticulum Golgi apparatus Plasma membrane Vacuole chloroplast cytoskeleton