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Lecture 2

lecture 2 macromolecules.docx

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University of Toronto Scarborough
Biological Sciences
Rene Harrison

Lecture 2 Macromolecules  Electrons are required for atoms in each column to achieve stability Either 2 or 8 valence shell (outer shell) electrons  Biochemicals = organic molecules Biochemistry centers around carbon (can bind up to 4 different atoms)  Atoms become molecules because they want complete shells (attach or share with other atoms  There are many types of molecular bonds in biochemistry (covalent bonds and non covalent bonds) Covalent Bonds Electrons pairs are shared between atoms to make molecules and atoms are most stable with a full outer electron shell The number of covalent bonds formed is determined by the number of electrons needed to completely fill the outer shell Example: Water, which is composed of oxygen and two hydrogen atoms. The oxygen already has 6 valence electrons and requires two more to have a full outer shell, in order to do this the two hydrogen atoms share their electrons giving a total of 8 valence electrons in oxygen’s outer shell. Covalent bonds can lead to polar molecules, non-polar molecules or ionized atoms. Polar Molecules Non-polar molecules Ionized Atoms Unequal sharing of the Equal sharing of electrons Atoms, which are strongly molecules Molecules do not have electronegative that it can If the nucleus of one atom electronegative atoms or capture electrons from is more positively charged polar bonds another atom than the nucleus of Hydrocarbons and non (steal the entire electron another atom than that polar and do not fight over pair) atom will attract electrons electrons The atom that gains the more (oxygen atom is electrons becomes an pulling the hydrogen anion and the atom which electrons closer to it) losses the electron This makes that atom becomes the cation relatively electronegative compared to the other (oxygen is more electronegative) = Asymmetric charge distribution Oxygen – partially negative Hydrogen – partially positive Biologically important polar molecules have electronegative atoms (O, N, S and P) 1 Lecture 2 Macromolecules Non – Covalent Bonds Govern interactions between molecules or different parts of a large biological molecule (bonds are typically weaker linkages) There are three types: ionic bonds, hydrogen bonds and hydrophobic interactions Ionic Bonds Hydrogen bonds Hydrophobic interactions Atoms or molecules with Occurs between polar Non-polar molecules are positive ad negative molecules (unequal not charged and cannot charges that attract eacsharing) example: water interact with water other (opposites attractThe partially + H on onThey form aggregates to These bonds are water molecule interacts minimize exposure to responsible for holding with – O on the second polar surrounding macromolecules together water molecule In other words Polar molecules interacthydrophobic molecules with other polar group together to undergo molecules minimum interactions Water is hydrophilic with the polar molecules H bonds hold the nucleic bases together (holds the two strands of the DNA together)  Macromolecules built around carbon Hydrocarbons contain only hydrogen and carbon atoms. The structure may be linear, branches or cyclic Hydrogen are often replaced by function groups Functional groups Hydroxyl O H - makes alcohols H Sulfhydryl O C Carboxyl O O H - makes acids O P O H Phosphate H N Amino O H H Generally function groups have one or more electronegative atoms (N,O,S or P) They make organic molecules more polar and more reactive Many are capable of ionization and may be either + or – in charge 2 Lecture 2 Macromolecules Macromolecules are formed when monomers are joined by condensation reaction (H 2 is removed) Polymers are broken down by hydrolysis (H O is added) 2 There are four types of biological macromolecules: carbohydrate, nucleic acids, lipids, and proteins Carbohydrates Monomer = monosaccharides Stores chemical energy (glucose) Structural function – exoskeleton of insects plant cell wall Attaches to plasma membrane lipids and proteins (glycocalyx - sugary coat which covers the cell and is important for cell recognition for cell identity) General formula = (CH O)n 2 Sugars with five or more carbons convert into closed rig-containing molecules glycosidic linkage – linking sugars together, which forms a covalent bond between carbon 1 of one sugar and the hydroxyl group (OH) of another Most sugars in cell metabolism have 3-7 carbons (energy is stored in the hydrogen atoms and is used in mitochondria) Two glucose molecules come undergo condensation to form maltose (water is removed which causes a glycosidic linkage between the two glucose molecules) there are many forms of carbohydrates, which are identified by the number of monosaccharides used Disaccharide Oligosaccharides Polysaccharides 2 monosaccharides Small chains of sugars Many sugars hooked covalently bond together Attached to lipids and together very large used for energy storage proteins converting them molecules to glycolipids and Example: Glycogen glycoproteins (animal energy stores), starch (plant energy storage), cellulose (structural plant cell walls) and chitin (exoskeletons of invertebrates) 3 Lecture 2 Macromolecules Nucleic Acids Both DNA & RNA are composed of nucleotides (phosphate+sugar+base) the neucleotides connect to form polymers known as polynucleotides the phosphate group (PO -4 is linked to 5’ carbon of sugar the 5 carbon sugar can be ribose or deoxyribose nitrogenous base – nitrogen atoms form part of the rings of the molecules monomers polymerize when OH on sugar of one nucleotide binds convalently to phosphate of next nucleotide in chain nucleotides are joined by sugar-phosphate linkages ester bonds- phosphodiester linkage there are two types of nitrogenous bases: Purines and pyrimidines purines bind to pyrimidines purines consists of Guanin and Adenine pyrimidines consists of cytocine, thymone and uracil (RNA) Guanine can link to cytosine using 3 hydrogen bonds Adenine can link with either thymine (DNA) or uracil (RNA) using 2 H bonds DNA serves as genetic material of all cellular organisms and information stored in DNA used to govern cell activities through formation of RNA messages RNA consists of three types: ribosomal RNA (rRNA), transfer RNA (tRNA), and messenger RNA (mRNA)  important for protein translation Other nucleic acids consist of ATP (adenosine triphosphate, which is an RNA nucleotide). It is a major source of energy for biochemical reactions The energy comes from ATP hydrolysis to create ADP + Pi The release of phosphate releases energy The three phosphates found on ATP are super negative and don’t what to be next to each other (takes a lot of energy to keep them together) an
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