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Biology Chapter 7 Cells Section 7.2: Plasma Membrane Plasma Membrane • Survival of a cell depends on its ability to maintain the proper condition within itself • Function of plasma membrane– Allow needed supplies into the cell • ie. Sugar, lipids, amino acids etc – If too much is let in, it must also be able to remove it • This is called “Homeostasis” – Maintaining the cells internal environment Homeostasis continued • Selective permeability– One way cells maintain homeostasis – Plasma membrane allows some molecules in but keeps other molecules out • Think of your screens on your windows at home… Structure of plasma membrane • Recall that lipids are “fats” and are insoluble in water (don’t dissolve) • Plasma membrane is made of a phospholipid bilayer (two layers) – Phospholipids are fats with phosphate groups attached to them – Made of fatty acid tails (water insoluble) and phosphate groups heads (water soluble) Phospholipid bilayer Phospholipid bilayer • The polar (water soluble) heads face out • The non-polar (water insoluble) tails face in • This allows water soluble materials to move through membrane but molecules that are not soluble don’t pass through • This model of the plasma membrane if called the “Fluid Mosaic” model Fluid Mosaic Model • The phospholipids flow like water (fluid) • The proteins move throughout the phospholipids like boats. – They make up the “Mosaic” Other components of membrane • cholesterol- stabilizes the phospholipids • Transport proteins- allow larger substances to move through the membrane • Other proteins help cells identify one another – This is important in disease control 7.3 Eukaryotic Cell Structure • Eukaryotic cells have many small structures inside them that each play a vital role in the survival of the cell. They are called organelles. • Cell wall- Rigid structure located outside the plasma membrane. – Provides support – Found in plant cells but not animal cells Organelles • Nucleus- control center of the cell – Contains DNA which makes up chromosomes • Is the blueprint of the cell – Chromatin- strands of DNA that make up chromosomes – Nucleolus- makes ribosomes • Ribosomes- site of protein synthesis • Cytoplasm- clear liquid that fills up the cell Organelles • Endoplasmic reticulum (ER)- site of chemical and cellular reactions. – Has many folds giving it much surface area for reactions to take place – Ribosomes attached to ER make it “rough” ER – Without ribosomes attached, it is “smooth” ER Organelles • Golgi apparatus- flat tubular membrane used to package and store proteins – Acts like the shipping dept. of a business • Vacuoles- used for temporary storage – Often store food, enzymes or waste products • Plant cells have very large water vacuoles compared to animal cells Organelles • Lysosomes- have digestive enzymes in them. – They eliminate worn out organelles or bacteria that need to be removed from the cell • The membrane around the lysosome protects the cell from the digestive enzymes inside • Chloroplasts- found in plant cells – Site of photosynthesis – Contain chlorophyll • Traps light energy so plant can make food Organelles • Mitochondria- powerhouse of the cell – Site of cellular respiration – Produce ATP – Has many folds to increase surface area for chemical reaction • ie sugar + Oxygen = carbon dioxide + water + ATP • Cytoskeleton- made of rods and filaments that give structural support to the cell Other structures • Microtubules- thin, hollow tubes made of protein • Microfilaments- thin solid protein fibers • Make up cytoskeleton and also found in flagella and cillia • Flagella- long hair-like projections used for locomotion in some cells • Cilia- shorter hairs used for locomotion Animal cell