Lecture 15- Chemical Basis of Life 6 PDF

The Chemical Basis of Life-6 ORGANIC MOLECULES: 3. Lipids and Nucleic Acids 1  Recap: Protein Structure… Primary Assembly STRUCTURE PROCESS Secondary...

The Chemical Basis of Life-6 ORGANIC MOLECULES: 3. Lipids and Nucleic Acids 1  Recap: Protein Structure… Primary Assembly STRUCTURE PROCESS Secondary Folding Tertiary Packing Quaternary Interaction 2  Lesson outcomes Discuss the different types of lipids Discuss nucleic acids 3 Lipids: Fats & Oils 4  Characteristics of Lipids Diverse group of organic compounds includes fats, oils, phospholipids, and cholesterol (steroids) composed of Carbon, Hydrogen, and Oxygen ratio of H:O greater than 2:1 building blocks are fatty acids and glycerol 5  Lipids Lipids are composed of C, H, O long hydrocarbon chains Do not form polymers larger molecules made of smaller subunits fat 6  Biological functions of Lipids Different kinds of lipids have different functions.. fats & oils - energy storage Fat – thermal insulation waxes & oils - Protective coatings and water barriers phospholipids - Structural and recognition components of cell membranes carotenoids - Accessories for acquisition of light in photosynthetic organisms Steroids & modified fatty acids - play a regulatory function as hormones and vitamins myelin – lipid coating around nerves = electrical insulation 7  Lipids Lipids are non-polar hydrocarbons = composed mainly of hydrogen and carbon insoluble in water Fats – solid at room temperature (20◦C) Oils – liquids at room temperature (20◦C) Fats & oils are triglycerides = 3 glycerides Triglyceride = 1 glycerol + 3 fatty acids Glycerol = a small molecule with 3 OH groups Fatty acid = long non-polar hydrocarbon chain and a polar carboxyl (COOH) group The fatty acids may be saturated or unsaturated. 8  Fatty Acid Structure Carboxyl group (COOH) forms the acid. “R” group is a hydrocarbon chain. 9 Fatty acid 10 Glycerol 11  Building Fats Triacylglycerol/triglyceride: 3 fatty acids linked to glycerol ester linkage = between OH & COOH formed by dehydration synthesis 12  Please note….. The three fatty acids of a triglyceride do not have to be identical They often differ markedly from one another 13  Triglyceride molecules non-polar Therefore, not soluble in water They clump together when placed in water 14 Note the clump formed 15  Saturated/Unsaturated fatty acids Saturated fatty acids = all bonds between C atoms in hydrocarbon chains are single bonds i.e. All bonds are saturated with H atoms Unsaturated fatty acids = hydrocarbon chains contain 1 or more double bonds 16  Animal triglycerides – usually long-chain saturated fatty acids tightly packed together. – are solid at room temperature Plant, vegetable, fish oils – usually short- chain unsaturated fatty acids, poorly pack together - are liquid at room temperature 17 18 19 20  Please note…. If a given fatty acid has more than one double bond: it is said to be polyunsaturated Double bonds prevent fat molecules from aligning closely with one another Hence they are liquid at room temperature (have low melting points) 21  Unsaturated Saturated No double bonds between carbon atoms; fatty acid chains fit close together Double bonds present between carbon atoms; fatty acid chains do not fit close together 22  Phospholipids Glycerol + 2 fatty acids + PO4 The phosphate has –ve electric charge= hydrophilic (“loves” water) Fatty acid tails = hydrophobic (“hates” water) Hydrophilic heads attracted to H2O Hydrophobic tails “hide” from H2O Phospholipids form cell membranes 23 24  At an oil-water interface, phospholipid molecules will orient so that their polar (hydrophilic) heads are in the polar medium, water, and their nonpolar (hydrophobic) tails are in the nonpolar medium 25 26  Steroids They are signal molecules Some are important part of the membranes Testosterone & estrogen: regulate sexual development in vertebrates 27  Cholesterol: Synthesized in the liver Part of structure in some membranes Starting material for making testosterone & other steroid hormones 28 Examples of steroids 29  From Cholesterol Sex Hormones What a big difference a few atoms can make! sex hormone is nearly always synonymous with sex steroid. 30  Nucleic Acids (DNA and RNA) Another class of Carbon-based molecules with unique properties Nucleic acids are polymers responsible for storage, transmission, and use of genetic information There are two types: - DNA (deoxyribonucleic acid) - RNA (ribonucleic acid) 31 31  Nucleic Acids (DNA and RNA) Composed of monomers called nucleotides consisting of: a pentose sugar (5 C) a phosphate-group (P with oxygen atoms) a nitrogen-containing base 32 32 Nucleotides vs Nucleosides Nucleotides consist of 3 components: a) Pentose sugar, b) Phosphate group, and c) Nitrogen-containing base. Nucleoside: comprises 2 items: a) Pentose sugar, and b) Nitrogenous base. Nucleic Acid Structures Reflect Their Functions RNA contains the sugar ribose. DNA contains the sugar deoxyribose. Nucleic Acid Structures Reflect Their Functions Nucleotides are linked by phosphodiester linkages. Phosphate groups link carbon 3′ in one sugar to carbon 5′ in another sugar. Nucleic acids grow in the 5′-to-3′ direction. Linking Nucleotides Together Linkages: A nucleotide consists of three components: a Nitrogen-containing base, a Pentose sugar (ribose in RNA), and one to three Phosphate groups Rest of polymer Phosphate Formation of the linkage Base between nucleotides The numbering of always occurs by adding ribose carbons is the the 5'-phosphate end of the basis for identification new nucleotide to the 3'-OH of 5' and 3' ends of end of the nucleic acid. DNA and RNA strands. Ribose 39 39  Differences between DNA and RNA DNA RNA The bases are: The bases are: Adenine Adenine Purines Purines Guanine Guanine Cytosine Cytosine Pyrimidines Prymidines Uracil Thymine The pentose sugar is The pentose sugar is Ribose. Deoxyribose. RNA is single stranded. DNA is double stranded. RNA does not have There is base-pairing in DNA. base-pairing. 40 RNA Molecule 3 end RNA (single-stranded) In RNA, the bases are attached to the ribose. The bases are Adenine (A) and Guanine (G) = [the purines]; and Cytosine (C) and Uracil (U) = the [pyrimidines]. 5 end DNA Molecule DNA (double-stranded) 5 end In DNA, the bases are 3 end attached to deoxyribose. Bases are: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T) (instead of uracil). DNA is double-stranded. Hydrogen bonds between purines and 3 end pyrimidines hold the two strands of DNA together. 5 end  In summary …chemical basis of life All elements are made up of unique atoms What makes different elements differ? There is finite # of known elements (see Periodic Table) Only some are essential for life - which ones? Elements make compounds through bonding of atoms The chemicals of “life” are the same in ALL living things See summary at end of Chapter 3 & 4 Next Origin of life 43 Q: Fats and Carbohydrates Fats rich in energy more than carbs Carbs used to provide energy to the cell Fats can provide energy when carbs are depleted 44 Why is starch digestible while cellulose is NOT?  Answer Both starches and cellulose are made of glucose molecules,..but the difference between them is that starch is a branched polymer, while cellulose is a linear polymer. This difference makes starch more digestible than cellulose.  Proteins Fibrous proteins covered in non-polar amino acids Do not dissolve into the aqueous solution Thank you Questions Comments 51