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Biology Chapter 5

by: Alexis Elston

Biology Chapter 5 BSC 114

Alexis Elston
GPA 4.0

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Complete coverage for chapter 5 from book and class powerpoint
Principles Of Biology I
Daryl W. Lam
Class Notes
Biology, week5, notes
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This 8 page Class Notes was uploaded by Alexis Elston on Friday September 23, 2016. The Class Notes belongs to BSC 114 at University of Alabama - Tuscaloosa taught by Daryl W. Lam in Fall 2016. Since its upload, it has received 6 views. For similar materials see Principles Of Biology I in Biology at University of Alabama - Tuscaloosa.


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Date Created: 09/23/16
Chapter 5 The Structure and Function of Large Biological Molecules  Within Cells, small organic molecules are often joined together to form larger molecules, called  Macromolecules o All living organisms are made up of four classes of macromolecules  Carbohydrates:  Monosaccharides, disaccharides, and polysaccharides   Lipids  Fats, phospholipids, sterols, etc.  Proteins  Amino acid polymers  Nucleic Acids  Nucleotide polymers  Polymers: long molecule consisting of many similar building blocks called monomers o Proteins and nucleic acids consist only of polymers  Carbohydrates consist of monomers, dimers, and polymers o Synthesis and Break down of Polymers  Dehydration reactions (dehydration synthesis)  Monomers use this reaction to form larger polymers o Covalent bonding of two molecules to each other through loss of a  water molecule  One molecule provides (­OH) and other provides a (H)  To make a polymer the dehydration reaction is repeated as  monomers are added one by one  Hydrolysis:   Biopolymers are disassembled to monomers through the revers of the  dehydration reaction o Bonds are broken by the addition of water molecules o Hydrogen from the water bonds to one monomer and the hydroxyl  group bonds to thee adjacent monomer  Carbohydrates: serve as fuel and building material o Include sugars and the polymers of sugars  The simplest carbohydrates are monosaccharides, or single sugars  Have molecular formulas that are usually multiples of 2H O o Glucose (C6H 12)6is the most common monosaccharide  Have a hydroxyl group bonded to each carbon except one, which is double  bonded to an oxygen to form a carbonyl group  Classified by  o Location of carbonyl group   Aldose: carbonyl group at end of carbon skeleton  Ketose: carbonyl group within carbon skeleton o Number of carbons in the carbon skeleton  Trioses – 3 carbon sugars  Pentose – 5 carbon sugars  Hexoses – 6 carbon sugars  Many monosaccharides form ring structures in aqueous solutions o ie: glucose  Monosaccharides serve as a major fuel for cells o In cellular respiration, cells extract the energy stored in glucose  molecules  Monosaccharides serve as raw material for synthesis of other types of small  organic molecules o Including amino acids and fatty acids Chapter 5  Monosaccharides not immediately used are incorporated as monomers into  disaccharides and polysaccharides  Disaccharide is formed when dehydration reaction joins two monosaccharides  Covalent bond is called a glycosidic linkage  Most common disaccharide is sucrose  Polysaccharides are sugar polymers composed of many sugar building blocks  Polymers of monosaccharides o Typically consist of a few hundred to several thousand  monosaccharides linked together  Two types o Storage polysaccharides  Starch in plants  Consists entirely of glucose monomers  Plants store surplus starch as granules, with  chloroplasts and other plastids  Simplest form of starch is amylose o 1­4 linkage, unbranched  Complex form is amylopectin o 1­6 linkage, branched  Glycogen in animals  More branched in structure than starch  Humans and other vertebrates store glycogen mainly  in liver and muscle cells  Hydrolysis of glycogen in these cells release glucose  when the demand for sugar increases o Structural polysaccharides  Serve as building material for structures protecting cells or  whole organisms  Cellulose is a major component of the tough walls that enclose plant cells  Fiber o Enzymes that digest starch by hydrolyzing  alpha linkages can’t hydrolyze beta linkages in cellulose o Some microbes and herbivores use enzymes  to digest cellulose  Like starch, cellulose is a polymer of glucose, but the  glycosidic linkages differ  The difference is based on two ring forms for  glucose: o Alpha in starch  Helical, branched  OH lies on same side o Beta in cellulose  Straight, unbranched  OH is on opposite sides, and can  bond with hydroxyls of parallel  cellulose molecules  Chitin is structural polysaccharide found in the exoskeletons  of arthropods Chapter 5  Provides structural support for the cell walls of many  fungi  Flexible and strong material  o Can be used as surgical thread  Structure and function of a polysaccharide are determined by  o Its sugar monomers o The positions of its glycosidic linkages  Lipids: o One class of macromolecules that do not form polymers  Unifying feature of lipids is having little or no affinity for water (hydrophobic)  This is because they consist mostly of hydrocarbons, which form nonpolar  covalent bonds o Most biologically important lipids are   Fats: major function is energy storage  Constructed from two types of smaller molecules, glycerol and fatty acids o Glycerol is a three­carbon alcohol with a hydroxyl group attached to  each carbon o Fatty acid consists of a carboxyl group attached to a long hydrocarbon  tail (acid in fatty acid comes from carboxyl group)  Vary in length and in number of locations and double bonds  Saturated: have maximum number of hydrogen atoms o No double bonds o Straight chain o Solid at room temp o Most animal fats are saturated o Contributes to Cardiovascular disease  through plaque deposits in arteries  Unsaturated: have one or more double bonds o Cis double bond causes bending o Oils o Liquid at room temp o Plant fats and fish fats are usually  unsaturated  Trans Fats: hydrogenated vegetable oils are made by  synthetically converting unsaturated fats to saturated  fats o Lengthens shelf life of certain foods o Converts cis (bent) hydrocarbon tails to a  trans (straight) form, resulting in trans fats  Thought to contribute more to  cardiovascular disease than  saturated fats  Synthesized via dehydration reactions between glycerol hydroxyl (­OH) and  fatty acid carboxyl groups (­COOH) o Fat molecules are called triacylglycerol or triglycerides  Fats separate from water because water molecules form hydrogen bonds with  each other and exclude the fats  Phospholipids  Consist of two fatty acids and a phosphate group attached to a glycerol  backbone o Two fatty acid “tails” are hydrophobic o Phosphate group “head” is polar and therefore hydrophilic Chapter 5  When added to water, they self­assemble into a bilayer, with the hydrophobic  tails pointing towards each other o Structure of phospholipids result in bilayer arrangement found in cell  membranes  Major component of cell membranes  Steroids  Lipids characterized by a carbon skeleton consisting of four fused rings  Steroid Cholesterol is a component of animal cell membranes and a precursor  from which other steroids are synthesized o Although essential in animals, high levels in the blood may contribute  to cardiovascular disease  Some steroids are hormones o Estradiol and testosterone produce contrasting feature of female and  male animals  Proteins o Large organic polymers made of amino acid monomers arranged in a linear chain and joined  together by peptide bonds  Account for more than 50% dry weight of most cells  Tens of thousands of different proteins in human body  Responsible for many biological activities  Synthesis of macromolecules and their building blocks  Structural support  Molecular storage  Transport into, out of, and within the cells  Cellular communication  Cellular mobility  Defense (immune systems) o Protein consists of one or more polypeptides  Polypeptide: unbranched polymers built from the same basic set of 20 amino acids  Amino acids: organic molecules possessing both amino and carboxyl functional  groups  o Consist of an alpha carbon bonded to:  Hydrogen  Amino group  Carboxyl group  Side chain symbolized by “R”  Fall into 3 classes: o Nonpolar – will share electrons equally o Polar – electrons will not be shared equally o Electrically charged  Acidic – contain carboxyl groups  Basic – contain amino groups o Carboxyl group of one amino acid is joined to the amino group of  another via dehydration reaction to make polypeptide  Resulting bond is peptide bond  One end of a polypeptide has a free amino group  Other end has a free carboxyl group  o Chain has polarity with amino end (N­terminus) and carboxyl end (C­ terminus)  N­terminus can gain H  to become positively charged  C­terminus can lose H  to become negatively charged o Structure and Function Chapter 5  Functional protein consists of one or more polypeptides twisted, folded, and coiled into a  unique shape  Water soluble proteins tend to be globular with polar and charged groups exposed to the  aqueous environment  Sequence of amino acids determines a proteins conformation (3D shape)  Conformation determines its function   Four Levels of Protein Structure:  Primary structure of a protein is its unique sequence of amino acids o Determined by inherited genetic information (DNA)  Secondary structure is the coils and folds in the polypeptide chain o Result from hydrogen bonds between peptide bonds in the backbone o Typical secondary structures are coil (alpha helix) and folded (Beta  pleated sheet)  Tertiary structure is determined by interactions among R groups o Interactions include hydrogen bonds, ionic bonds, van der waals  interactions, hydrophobic interactions between nonpolar amino groups,  and disulfide bridges  Disulfide bridge: strong covalent bonds between the sulfur  atoms of two cysteines  Quaternary structure results when a protein consists of 2 or more polypeptide  chains o Collagen: fibrous protein consisting of three collagen polypeptides  coiled like a rope o Hemoglobin: globular protein consisting of four polypeptides  Two alpha and two beta chains  What determines Protein Structure? o In addition to primary structure, physical and chemical conditions can  affect structure  Alterations in pH, salt concentration, temperature, other  environmental factors cause a protein to unravel  Loss of proteins native structure is called  denaturation o Denatured protein is biologically inactive o Protein folding in the cell:  Most proteins are thought to go through several  conformational states on their way to a stable structure  Diseases such as Alzheimer’s and Parkinson’s  disease are associated with misfolded proteins  Chaperonins are multi­subunit proteins that assist the proper  folding of other proteins  Unfolded polypeptide enters the cylinder from one  end  A cap attachment causes the cylinder to change  shape, creating a hydrophilic environment for folding  Cap comes off, properly folded protein is released  Methods used to predict protein structure: Chapter 5  X­ray crystallography: used to determine the arrangements of atoms within a  crystal o When a beam of X­ray strikes a crystal, the X­rays are scattered into  different directions  Angles and intensities of the scattered beams are used to  produce a 3D picture of the density of electrons within the  crystal o From the electron density map, the mean positions of atoms can be  determined, as well as chemical bonds, their disorder, and other info.  Computer modeling programs use this info to generate 3D  shape of protein and other macromolecules  Nuclear Magnetic Resonance Spectroscopy o Does not require protein crystallization  Bioinformatics o Uses computer programs to predict protein structure from amino acid  sequences Chapter 5 Chapter 5  Nucleic Acids o The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene  Genes are made of deoxyribonucleic acid  DNA is a linear (unbranched) polymer belonging to a class of compounds called nucleic  acids  DNA and RNA  Roles of Nucleic acid:  DNA provides directions for its own replication  DNA directs synthesis of mRNA, a process referred to as transcription  Through mRNA, DNA controls protein synthesis, a process called translation o Structure of Amino acids  Nucleic acids are polymers called polynucleotides   Each polynucleotide is made of monomers called nucleotides o Polynucleotides consist of sugar­phosphate backbones with different  nitrogenous bases  Adjacent nucleotides are linked by covalent bonds called  phosphodiester linkages between carbon 5­bonded phosphate  of one nucleotide sugar and the carbon 3­bonded hydroxyl of  the next  5’ end has the free phosphate group  3’ end has the free hydroxyl group o Each nucleotide monomer consists of   Nitrogenous base  Two families: o Pyrimidines that have a single 6­membered  ring  Cytosine  Thymine  Uracil o Purines: have a 6­membered ring fused to a  5­membered ring  Adenine  Guanine  Pentose sugar  In DNA, pentose sugar is deoxyribose  In RNA, pentose sugar is ribose  Phosphate group  The portion of a nucleotide without the phosphate  group is called a nucleoside  IN CLASS EXAMPLES:   Sickle­Cell Disease o A slight change in primary structure can affect a protein’s secondary, tertiary, and/or  quaternary structure and ability to function  Sickle­cell disease, an inherited blood disorder, results from a single amino acid  substitution in the protein hemoglobin  Abnormal sickle hemoglobin damages the red blood cell membrane  and can cause the cells to become stuck in blood vessels, depriving  downstream tissues of oxygen.  o Chronic and lifelong, reduced life expectancy


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