5/12/2015. Cell Size. Relative Rate of Reaction

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1 Cell Makeup Chapter 4 The Cell: The Fundamental Unit of Life We previously talked about the cell membrane The cytoplasm is everything inside the membrane, except the nucleus Includes Cytosol = liquid portion Organelles (NOTE ERROR IN STUDY GUIDE) Lecture 3: Organelles Cells are small, but molecules for their chemical reactions are much smaller Utah Genetics Glucose is 10 8 times smaller than a bacterium Reactants needed for metabolism are present in low concentrations Low concentration means reactants don t collide often (Don t draw this in your study guide) Concentration gets lower as cells get bigger What happens to chemical reaction rate in cells as cells get bigger? (Draw this one in your study guide) Relative Rate of Reaction Why prokaryotic cells stay small Eukaryotic cells have found a way around this: membrane-bound bound organelles Serve to concentrate reactants in appropriate compartments Improve cell efficiency 1

2 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) 1 µm 2 µm Volume increases faster than surface area (x 3 vs x 2 ) 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 Organelles Often categorized by presence/absence of membrane(s) Non-membranous Cytoskeleton Cellular extensions Microvilli Cilia Flagella Ribosomes Membranous Mitochondria Endoplasmic reticulum Golgi aparatus Lysosomes Peroxisomes Nucleus Organelles We will consider the organelles contribution to the production and management of protein Non-membranous Cytoskeleton Cellular extensions Microvilli Cilia Flagella Ribosomes Membranous Mitochondria Endoplasmic reticulum Golgi aparatus Lysosomes 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! 2

3 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, = binds to free ribosome mrna Final destination of protein Bound for export, membrane, or membrane- bound organelle = mrna/ribosome complex associates with endoplasmic reticulum Collection of membranous tubes and envelopes 2 forms Endoplasmic Reticulum Smooth endoplasmic reticulum (ser) Site of lipid synthesis, detoxification Abundant in liver, kidney, endocrine glands 3

4 Proteins enter rer through pore Portion of rer pinches off to encapsulate protein in a transport vesicle Rough Endoplasmic Reticulum Rough Endoplasmic Reticulum Some vesicles stay in cytoplasm Others migrate to the Golgi apparatus Cis face = Receiving face Transport vesicle Proteins are modified and/or combined in the Golgi, encapsulated and transported to 1. Secretory vesicles Proteins for discharge from cell Trans face = Shipping face Vesicles bound for elsewhere Proteins are modified and/or combined in the Golgi, encapsulated and transported to 2. Cell membrane components Example: glycoproteins Proteins are modified and/or combined in the Golgi, encapsulated and transported to 3. Lysosomes Cytosolically-active active vesicles 4

5 Contain more than 50 enzymes ph of ~4.5 Lysosomes Break down almost any biomolecule Cell s garbage disposal Can fuse with other membrane-defined structures and release contents Lysosome storage diseases (>30) Example: Tay-Sachs disease Originate in rer Peroxisomes Involved in lipid catabolism, modification Produce oxidative enzymes, hydrogen peroxide Detoxifies substances in kidney by means of peroxidation Site of ATP synthesis powerhouse of cell Features: Mitochondria Double membrane (inner and outer) 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 Internal protein network of cells Stabilize cell s 3-dimensional shape Guide vesicles Cytoskeleton 5

6 Formed from tubulin subunits 1. Component of cytoskeleton cell shape, anchor organelles 2. Intracellular transport with motor proteins 3. Move chromosomes during cell division 4. Cilia, flagella Intermediate Filaments >60 different kinds Resist stretching Functions: 1. Strength 2. Stabilize organelle position 3. Transport Microfilaments Made of actin subunits Associated with cell movement, changes in cell shape 6

7 Comparison of Cytoskeletal Proteins Thick Filaments ~15nm diameter Microfilaments = 3-6nm in diameter Example: myosin in muscle Interacts with actin for movement Cilia Whip-like Cellular Extensions Move substances in one direction across stationary cells Example: trachea Flagella Cellular Extensions Substantially longer than cilia Only example in human body: sperm Microvilli Cellular Extensions Very small, highly numerous Increase absorptive surface area Example: small intestine Genetic library Nucleus Contains all instructions needed to build cell s proteins Dictates types, amounts of proteins to be made Responds to extracellular signals 7