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Download Chapter 4 The Cell: The Fundamental Unit of Life
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5/12/2015 Cell Makeup Chapter 4 • We previously talked about the cell membrane • The cytoplasm is everything inside the membrane, except the nucleus The Cell: The Fundamental Unit of Life • Includes… • Cytosol = liquid portion • Organelles (NOTE ERROR IN STUDY GUIDE) Lecture 3: Organelles Cell Size • Cell Size Glucose is 108 times smaller than a bacterium Cells are small, but molecules for their chemical reactions are much smaller • Reactants needed for metabolism are present in low concentrations Utah Genetics • Low concentration means reactants don’t collide often • (Don’t draw this in your study guide) Cell Size Cell Size Concentration gets lower as cells get bigger • Why prokaryotic cells stay small • What happens to chemical reaction rate in cells as cells get bigger? • Eukaryotic cells have found a way around this: membrane--bound organelles membrane (Draw this one in your study guide) Relative Rate of Reaction • • Serve to concentrate reactants in appropriate compartments • Improve cell efficiency Cell Size 1 5/12/2015 Cell Size • Cell Size This means eukaryotic cells can be larger than prokaryotic cells • Still, being small has some advantages • Solutes taken into cells through membrane • Consider 2 cubes (even though most cells are spherical)… 2 µm 1 µm Cell Size • Volume increases faster than surface area • • • Organelles (x3 vs • Often categorized by presence/absence of membrane(s) • Non--membranous Non x2) So as cells get bigger, the proportion of surface area decreases Keeps cells small • Cells need surface area to absorb solutes • Less surface area = fewer reactions • Mitochondria • Cellular extensions • Endoplasmic reticulum Organelles We will consider the organelles’ contribution to the production and management of protein • Non--membranous Non • Membranous • Cytoskeleton • • Cellular extensions • • Mitochondria Membranous Cytoskeleton • • • • • Microvilli • Cilia • Golgi aparatus • Flagella • Lysosomes Ribosomes • Peroxisomes • Nucleus Ribosomes • Site of protein synthesis • Abundant in cells that produce a lot of protein • Example: human liver cells have on average 13 million ribosomes in each cell! Endoplasmic reticulum • Microvilli • Cilia • Golgi aparatus • Flagella • Lysosomes Ribosomes • Peroxisomes • Nucleus 2 5/12/2015 Ribosomes • Made from rRNA (2 units) • Polypeptide chain constructed using information provided by mRNA Ribosomes • Many ribosomes can read the same strand of mRNA at once mRNA • Contains information for… • Amino acid sequence • Final destination of protein mRNA • Final destination of protein • Bound for cytosol cytosol,, = binds to free ribosome mRNA • Final destination of protein • Bound for export, membrane, or membranemembranebound organelle = mRNA/ribosome complex associates with endoplasmic reticulum Endoplasmic Reticulum • Collection of membranous tubes and envelopes • 2 forms • Smooth endoplasmic reticulum (sER (sER)) • Site of lipid synthesis, detoxification • Abundant in liver, kidney, endocrine glands 3 5/12/2015 Rough Endoplasmic Reticulum • • Rough Endoplasmic Reticulum Proteins enter rER • Some vesicles stay in cytoplasm through pore • Others migrate to the Golgi apparatus Portion of rER pinches off to encapsulate protein in a transport vesicle Golgi Apparatus Golgi Apparatus • Cis face = Receiving face Transport vesicle Proteins are modified and/or combined in the Golgi, encapsulated and transported to… 1. Secretory vesicles • Trans face = Shipping face Vesicles bound for elsewhere Golgi Apparatus • Proteins are modified and/or combined in the Golgi, encapsulated and transported to… 2. Cell membrane components • Example: glycoproteins Proteins for discharge from cell Golgi Apparatus • Proteins are modified and/or combined in the Golgi, encapsulated and transported to… 3. Lysosomes • Cytosolically--active vesicles Cytosolically 4 5/12/2015 Lysosomes • Contain more than 50 enzymes • pH of ~4.5 • Break down almost any biomolecule • Cell’s “garbage disposal” • Can fuse with other membranemembrane-defined structures and release contents • Lysosome storage diseases (>30) • Example: TayTay-Sachs disease Peroxisomes Mitochondria • Originate in rER • Site of ATP synthesis – “powerhouse of cell” • Involved in lipid catabolism, modification • Features: • Produce oxidative enzymes, hydrogen peroxide • Double membrane (inner and outer) • Detoxifies substances in kidney by means of peroxidation • Carry own DNA, make some of their own protein • Only cellular site to use molecular oxygen Mitochondria • Provide energy = most abundant in cells that need a lot of energy • Examples: muscle cells, sperm Cytoskeleton • Internal protein network of cells • Stabilize cell’s 33-dimensional shape • Guide vesicles 5 5/12/2015 Microtubules • Microtubules Formed from tubulin subunits 2. Intracellular transport with motor proteins 1. Component of cytoskeleton – cell shape, anchor organelles Microtubules Microtubules 3. Move chromosomes during cell division 4. Cilia, flagella Intermediate Filaments Microfilaments • >60 different kinds • Made of actin subunits • Resist stretching • • Functions: Associated with cell movement, changes in cell shape 1. Strength 2. Stabilize organelle position 3. Transport 6 5/12/2015 Comparison of Cytoskeletal Proteins Thick Filaments • ~15nm diameter • Example: myosin in muscle • Interacts with actin for movement • Microfilaments = 33-6nm in diameter Cellular Extensions • Cilia Cellular Extensions • Flagella • Whip--like Whip • Substantially longer than cilia • Move substances in one direction across stationary cells • Only example in human body: sperm • Example: trachea Cellular Extensions • Microvilli • Very small, highly numerous • Increase absorptive surface area • Example: small intestine Nucleus • Genetic library • Contains all instructions needed to build cell’s proteins • Dictates types, amounts of proteins to be made • Responds to extracellular signals 7