BIOL 20A Tamkun (Week 2 Macromolecules, Proteins & Carbohydrates)
BIOL 20A Tamkun (Week 2 Macromolecules, Proteins & Carbohydrates) BIO 20A
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This 3 page Class Notes was uploaded by Holly Chen on Tuesday October 4, 2016. The Class Notes belongs to BIO 20A at University of California - Santa Cruz taught by John Tamkun in Fall 2016. Since its upload, it has received 7 views.
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Date Created: 10/04/16
Unit 2 - Macromolecules: Proteins & Carbohydrates The Importance of Carbon Chemistry • Organic chemistry - the study of carbon based molecules. While water is most abundant in cells, the rest is carbon-based molecules. • Carbon - the element of life because of it’s diversity and ability to form polymers. • Carbon can make long and complicated molecule rings/branches (silicon comes in next best). • Carbon’s valance of 4 means it’s readily available to make covalent bonds. • Hydrocarbons - a molecule with only hydrogen and carbon atoms. • All bonds are non polar covalent bonds. • Usually hydrophobic (e.g fats and oils). • Diverse, vary in lengths, linear or branch, contains more than one double bonds and rings. • Other elements commonly found in organic molecules - oxygen, nitrogen, sulfur, phosphorus. They are often found in functional groups attached to a hydrocarbon skeleton. Functional groups • Functional groups - a group of atoms usually attached to a carbon skeleton of organic molecules, functionally important and hydrophilic to make organic molecules soluble in water. Macromolecules • Levels of biology (in order of size): • Elements (e.g carbon, nitrogen, oxygen, hydrogen, phosphorus, sulfur) • Molecules (e.g amino acids) • Macromolecules (e.g proteins, lipids) • Macromolecular complexes, membranes, chromosomes • Viruses, bacteria. • Organelles (e.g mitochondria) • Plants and animal cells. • Chemical composition of a typical cell: • 75% water • 5% ions and other smaller molecules • 20% macromolecules (60% protein / 25% nucleic acid / 10% carbohydrate / 5% lipid). • Macromolecules - polymers built from monomers, large molecules essential for life. The abilities of carbon and functional groups allow a huge diversity of organic molecules (10,000+ organic molecules are present in a typical cell). • Polymers of repeating subunits. • These subunits are called monomers. • Examples: amino acids (monomers) form proteins (polymer) or nucleotides (monomer) form nucleic acids (polymer). • Polymer synthesis and breakdown - bonds between monomers are made by a dehydration process (water removed as bonds form), while bonds are broken by a hydrolysis reaction (water added to break bonds). Macromolecules: Proteins • Proteins - large macromolecules, polymers of one or more long chains of amino acids. The chain can range from a few to hundreds of thousands. • Account for more than 50% dry mass of cells. • Almost all living organisms depend on proteins. • Proteins functions: • Structure - provides support (e.g collagen in tendons). • Regulation - controls gene expression and other processes. • Signaling - hormones, growth factors, receptors, coordination of organism’s activities (e.g insulin). • Movement - muscle contraction, chromosome segregation. • Metabolism - enzymes that increases biochemical reaction rates, selective. • Transport - transportation of material (e.g in cells, through membranes, blood stream). • Amino acids - organic molecule containing both amino group and carboxyl group. They are building blocks for proteins. • Classified by chemical properties of their R groups. • 20 occur naturally. • Linked by peptide bonds to form proteins. R- Groups ofAminoAcids • Non polar R groups - side chains of mostly hydrocarbon, hydrophobic. • Polar R groups - groups that are able to participate in hydrogen bonding. Hydrophilic. • Acicid R group (negatively charged) - contains a carboxyl group. • Basic R group (positively charged) - contains an amino group. Hydrophilic. Polypeptides • Polypeptides - an organic polymer consisting of amino acids bonded together in a chain to form a protein. • This is when two amino acids are positioned so carboxyl group is adjacent to the amino group. • Polypeptides have a C terminus (carbonyl end) and N terminus. • The formation of peptide bonds eliminates the amino and carboxyl groups, except at the N- and C- termini (and on R groups). • Peptide bond - a covalent bond resulted from dehydration process and the removal of water. Levels of Protein Structure • Afunctional protein is not a single polypeptide, but one or more polypeptides folding and twisting in a precise way to form a molecule of a distinct shape. • Primary structure - the linear sequence of amino acids, partly dictates the secondary structure. • Secondary structure - small regions of folding of polypeptide backbones because of the polar characteristics of the polypeptide backbone. • α helix: coil, held together by hydrogen bonds. • β sheet: two or more segments of polypeptide chain lying side by side. • Tertiary structure - 3D structure of the protein. This is held together by the interaction between R groups and a disulfide bridge. • Disulfide bridge: resulted from the folding of the protein, bringing two sulfhydryl groups close together. • Quaternary structure - 3D structure of protein complexes (more than 1 polypeptide chain interacting). • Example: collagen, fibrous protein, which is 3 identical helical polypeptides twisting into a large triple helix. • The interaction between side chain R groups and the polypeptide backbone must be intact, if disrupted, the protein denatures and is useless. • Factors that lead to protein denature: heat, temperature, ph, salinity or solvent polarity changes. Macromolecules: Carbohydrates • Carbohydrates - sugars and their polymers. • They function as energy sources (e.g glucose, startch), structural roles (e.g cellulose), and as precursor for other molecules. • Monosaccharides - single sugars (general formula C_nH_2nO_n). • 3 carbon sugar = triose • 5 carbon sugar = pentose • 6 carbon sugar = hexose • Usually nutrients for cells. • Carbon skeleton of sugar serve as raw material for other organic molecules synthesis. • Disaccharide - double sugar (two monosaccharides linked together by glycoside linkage). • Glycoside linkage: covalent bond between two monosaccharides through dehydration process. • Hydrolysis would split it back into 2 monosaccharides. • Example: glucose + fructose = sucrose. • Oligosaccharides - 3+ monosaccharides linked together by glycoside linkage. • Polysaccharides - a macromolecule, 100s-1000s of monosaccharides linked together by glycoside linkage. • Functions include storage of chemical energy (starch in plants), structural roles (cellulose in plants).