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Chapter 7- Biology 1A03 notes.docx

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McMaster University
Lovaye Kajiura

Chapter 7: Inside the cell  The cell is the basic unit of structure and function in living organisms.  There are two fundamental cell types: prokaryotic cells and eukaryotic cells. Prokaryotic Cells- Fig. 7.1 A Prokaryotic Cell  Archaea and bacteria  Most prokaryotic cells are relatively small in size compared to eukaryotic cells  The size of prokaryotic cells is probably limited by the distance that molecules must diffuse or be transported inside the cell.  Are structurally simpler in design  Plasma membrane surrounds the cytoplasm, which collectively refers to the contents of the cell.  Have few or no subdivisions delimited by internal membranes  Interestingly, recent research has identified membrane bound organelles or cytoskeletons of protein filaments in a few prokaryotic species.  No membrane bound nucleus  Ribosomes involved in protein synthesis Eukaryotic Cells- Fig. 7.6 Animal and Plant Cells  Fungi, Protists, Plants and Animals  Are relatively larger in size compared to prokaryotic cells  The evolution of large cell size is thought to have made it possible for eukaryotic cells to act as predators; organisms that kill and consume organisms.  Ions and small molecules such as ATP, amino acids and nucleotides cannot diffuse across a large volume quickly.  Numerous organelles  MTOC- Microtubule organization centre Fig. 7.7 The Nucleus is the Eukaryotic Cell’s Information Storage and Retrieval Centre The genetic or hereditary information is encoded in DNA, which is a component of the chromosomes inside the nucleus. The Nucleus  Is surrounded by a nuclear envelope (a double membrane)  Contains chromosomes (chromatin: DNA and histone proteins), which carry the cell’s genetic information.  Contains the nucleolus, which is the side of rRNA synthesis and ribosome assembly. Fig. 7.8 Ribosomes are the Site of Protein Synthesis Eukaryotic ribosomes are similar in structure to bacterial and achaeal ribosomes, though not identical. They are composed of large and small subunits, each of which contains both RNA molecules and proteins. Ribosomes  Some are present in the cytosol (fluid component of the cell’s cytoplasm)  Eukaryotic ribosomes are composed of RNA and protein  Consists of small and large subunits  Are involved in protein synthesis  Some are located outside the cell Fig. 7.9 Rough ER is a Protein Synthesis and Processing Complex Rough ER is a system of membrane-bound sacs and tubules with ribosomes attached. It is continuous with the nuclear envelope. Rough Endoplasmic Reticulum (rough ER)  Consists of a network of membrane- bound tubules and sacs  Has ribosomes studded into the cytoplasmic surface of the membranes, where secreted and transmembrane proteins are manufactured.  Enzymes, which fold and modify proteins, are present inside the rough ER’s lumen.  The interior of the rough ER is called the lumen. Inside the lumen, proteins undergo folding and other types of processing.  Hundreds of thousands of ribosomes are attached to the rough ER  The ribosomes associated with the rough ER are responsible for proteins synthesis that will be inserted into the plasma membrane, secreted to the cell exterior or shipped to an organelle called the lysosome. Fig. 7.10 The Golgi Apparatus Is a Site of Protein Processing, Sorting and Shipping The Golgi Apparatus is a collection of flattened vesicles called cisternae. Golgi Apparatus  Consists of cisternae (flattened, stacked sacs)  The cis face receives products from the rough ER; which pass through before reaching their final destination (through vesicles). Example: insulin  The trans face sends products to their destination (to the vesicles which then sends them outside the cell).  Allows for processing of things  Close to rough ER, smooth ER is farther away Fig. 7.11 Smooth ER is a Lipid- Handling Centre and a Storage Facility Smooth ER is a system of membrane-bound sacs and tubules that lacks ribosomes. Smooth Endoplasmic Reticulum  Lacks ribosomes on the cytoplasmic surface of the membranes  Enzymes are present, which are involved in several functions such as lipid synthesis, detoxification of harmful materials and calcium ion reserves (development of bone).  TEM photos of SER versus GA Fig. 7.12 Peroxisomes are the Site of Fatty Acid Processing Peroxisomes are globular organelles with a single membrane. There is a high level of peroxisomes within the liver. Peroxisomes  Are single-membrane bound organelles (mitochondria= double membrane).  Locations of oxidative reactions  Contain catalase, which is an enzyme that converts hydrogen peroxide into oxygen and water. Fig. 7.13 Lysosomes are Recycling Centres Lysosomes are usually oval or globular and have a single membrane. Lysosomes  Are single-membrane bound organelles  Participate in solid waste processing and the storage of materials  Have an acidic interior  Possess digestive enzymes (acidic hydrolases) to breakdown macromolecules  Digest dead/ exhausted organelles (example: mitochondria)  Recycle and reuse components of organelles Fig. 7.14 Two ways to Deliver Materials to Lysosomes Materials can be transported to lysosomes after phagocytosis or via autophagy. a) Phagocytosis- the plasma membrane detects a smaller cell or food particle and begins to engulf it and becomes a phagosome. It is delivered to a lysosome, which takes it in and begins digesting it. Small molecules from the digested food particles are released into the cytosol. b) Autophagy- a damaged organelle is surrounded by a membrane, the membrane- bound organelle is delivered to the lysosome which begins to engulf it. Small molecules from the digested organelle are recycled into the cytosol.  Arthritis- leaky lysosomes are breaking down lubricating organelles (can’t tell the difference between functioning cells and phagocytes. Fig. 7.15 Receptor- Mediated Endocytosis May Lead to Lysosome Formation Endosomes created by receptor-mediated endocytosis may mature into lysosomes.  Macromolecules outside the cell bind to the membrane proteins that act as receptors  The plasma membrane folds in and pinches off to form a vesicle called an early endosome.  The early endosome undergoes a series of processing steps including activation of proton pumps that lower its pH.  The early endosome matures into a late endosome that receives digestive enzymes from the Golgi apparatus.  The late endosome eventually matures into a functional lysosome. Fig. 7.16 Vacuoles are Storage Centres Vacuoles are variable in size and function, depending on the type of plant. Some contain digestive enzymes and serve as recycling centres; most are large storage containers. Vacuoles  Not in animal cells; no need for chlorophyll or defense against herbivores.  Found in fungi and plants  Occupy a large portion inside the cell  Serves as storage depots for water, ions and proteins  In plant cells, vacuoles may contain pigments or may house noxious substances for chemical defense against herbivores. Fig. 7.17 Mitochondria are Power-Generating Stations Mitochondria are variable in size and shape, but all have a double membrane with sac-like cristae inside. Mitochondria  Sites of ATP production  Possesses two membranes (the inner membrane has folds or cristae, the outer membrane is smooth).  Possess their own mitochondrial DNA, produce their own ribosomes  Greater surface area= mass production of ATP  Are capable of dividing independent of cell division Fig. 7.18 Chloroplasts Are Sugar- Manufacturing Centers Many of the enzymes and other molecules required for photosynthesis are located in membranes inside the chloroplast. These membranes are folded into thylakoids and stacked into grana. Chloroplasts  Have a double membrane (both inner and outer membranes are smooth)  Inner membrane houses thylakoids (flattened sacs stacked in grana)  Grana- increase surface area= generation of energy 
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