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Intro to cell biology chapter 4

by: Elizabeth Allen

Intro to cell biology chapter 4 Biology 140

Marketplace > Anderson University > Science > Biology 140 > Intro to cell biology chapter 4
Elizabeth Allen
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About this Document

This is an outline for chapter 4.
Intro to cell biology
Professor Smolen
Class Notes
Science, Biology, cellular biology, chapternotes, chapter4




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This 8 page Class Notes was uploaded by Elizabeth Allen on Monday September 26, 2016. The Class Notes belongs to Biology 140 at Anderson University taught by Professor Smolen in Fall 2016. Since its upload, it has received 13 views. For similar materials see Intro to cell biology in Science at Anderson University.

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Date Created: 09/26/16
Chapter 4 Lecture Outline Most of the functions and activities of cells are performed by proteins which are intricately and specifically folded and which can change shape, making them extremely versatile! I. Importance of Proteins/General Protein Functions A. Enzymes Each enzyme catalyzes a specific reaction Names end in “-ase” Recall specifics of enzyme activity (lowers activation energy, forms enzyme-substrate complex, is conserved at the end of the reaction) Examples: protein kinase adds phosphate to a protein molecule, lipase hydrolyzes lipids B. Structural Proteins(provide mechanical support to cells and tissue) Extracellular examples: collagen(cannot be easily stretched) , elastin(can stretch then recoil, your ear is made of elastin) Intracellular examples: tubulin(helps to form micro tubules), actin(helps form structure in muscle cells) , keratin(hard, sclera protein) C. Transport Proteins Carry small molecules or ions Extracellular example: hemoglobin – transports oxygen through bloodstream Examples of plasma membrane proteins that aid in transport: (Stationary) sodium/potassisum pump - actively transports both Na+ and K+ against their gradients across a cell’s plasma membrane sodium ion channel – allows Na+ to move along its gradient across a cell’s plasma membrane NOTE: protein “pumps” actively transport, proteins carriers or channels passively transport, unless otherwise noted D. Motor Proteins Generate movement in cells and tissues Examples: actin and myosin (interact to produce shortening of muscle cell) Kinesin (interacts with microtubules within cell to move organelles) Dynein (allows eukaryotic cilia and flagella to move) E. Storage Proteins Store amino acids or ions Examples: ferritin stores iron in the liver Casein- milk protein, helps to store amino acids in milk, source of nutrition for babies or infants F. Signal Proteins (coordinate functions) Carry extracellular signals from cell to cell (are signal molecules or “ligands”) Examples: hormones and growth factors Insulin- acts as a hormone, allowing cells to use glucose Netrin- attracts growing nerve cells axons to specific locations in the developing spinal cord Nerve Growth Factor- stimulates some types of nerve cells to grow axons G. Receptor Proteins Receive signals (chemical or otherwise) and transmit them to the cell’s response machinery Examples: Rhodopsin (photoreceptor in retina of your eye) receives light energy Acetylcholine Receptor (chemoreceptor in plasma membrane of neuron) receives chemicals Insulin Receptor (chemoreceptor in plasma receptor of insulin- dependent cell) receives chemicals H. Gene Regulatory Proteins Bind to a cell’s DNA to switch genes on or off (control of gene expression) Examples: lactose repressor protein in bacteria – prevents expression of gene that codes for enzymes that break down lactose sugar I. Special Purpose Proteins Variety of proteins with varying other functions intracellularly and extracellularly Examples: antifreeze proteins – prevent blood of animals in cold environments from freezing (lower freezing point of the blood) Green fluorescent protein – allows for bioluminescence in jellyfish Glue-like proteins (glycoproteins) – secreted proteins that allow cells and organisms to stick to other substances/surfaces II. Protein Structure and Function A. Recall: Function is related to structure! B. Shape/Structure of Amino Acids 1. Shape determined by amino acid sequence and amino acid side chains a. Review of amino acid structure: Side chain (variable region) – makes one amino acid different from another Amino Carboxyl group (acts as group (acts as base) acid, also called “carboxylic acid”) b. Varieties of side chains: Polar amino acids- (hydrophilic, and charge distribution) Non-polar amino acids- (Hydrophobic, no charge distribution) c. Polypeptide backbone(dehydration synthesis) Recall peptide bonds d. N-terminus(amino beginning of chain) / C-terminus(carboxyl ending the chain) e. Non-covalent bonds cause folding of the chain (weak interactions, but can stabilize the folding of the chain Electrostatic interactions H-bonds Hydrophobic interactions of side chains with environment f. Protein terminology based on size Dipeptide- 2 amino acids Oligopeptide- 3-20 amino acids in a chain Polypeptide- 21-199 amino acids in a chain Protein- 50-2,000+ amino acids long g. Proteins can also attach to other types of organic molecules Glycoprotein-attached to a carbohydrate. (Sugar groups) Lipoprotein- attached to lipids. 2. Protein folds and importance of folding (Final folded structure> conformation) a. lowest energy state(least amount of useful energy> G) energetically favorable b. denaturation(unfolding a protein) / renaturation(refolding on its own) example: urea c. prions(misfolded proteins) and importance of chaperones(mad cow disease is caused by misfolded proteins) d. varieties of shapes 3. Alpha helix and beta pleated sheet th Alpha helix: H-bonds every 4 amino acid; membrane-bound proteins Beta sheet: segments of polypeptide chain (H-bonding) Example: beta-sheet stacking 4. Levels of Protein Organization a. Primary Structure – amino acid sequence b. Secondary Structure – alpha helix, beta sheet segments within chain c. Tertiary Structure – 3-D shape of entire polypeptide includes repeating primary and secondary structures compact, spherical may be globular or fibrous (linear) d. Quaternary Structure – more than one polypeptide chain may be globular or fibrous e. Protein domains (e.g., binding sites)


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