1.3 Biochemistry Macromolecules PDF - Biology Lecture Notes

1.3 BIOCHEMISTRY - Macromolecules Macromolecules: large molecules composed of repeating subunits. Four major classes: carbohydrates, proteins, lipids, and nucleic acids  Carbohydrates Carbohydrates are used for energy, building materials and for cell identification and c...

1.3 BIOCHEMISTRY - Macromolecules Macromolecules: large molecules composed of repeating subunits. Four major classes: carbohydrates, proteins, lipids, and nucleic acids  Carbohydrates Carbohydrates are used for energy, building materials and for cell identification and communication. Carbohydrates contain carbon, hydrogen and oxygen in a 1:2:1 ratio. Carbohydrates are classified into 3 groups: 1. Monosaccharides 2. Disaccharides 3. Polysaccharides  Monosaccharides – simple sugars One subunit of carbohydrate Two types i. Aldose » All carbons have HYDROXYL groups attached, with the exception of CARBONYL group found on a terminal carbon  Monosaccharides ii. Ketose » All carbons have HYDROXYL groups attached, with the exception of CARBONYL group found on a central carbon  Monosaccharides - glucose – When dissolved in water, sugars with 5 or more carbons form rings structures – Glucose forms a ring structure due to interaction between two of its functional groups and there are two possible arrangements – alpha and beta glucose – Both forms of glucose along with fructose and galactose are isomers (same chemical formula but different structure  Disaccharides 2 subunits of simple sugars combined A condensation reaction (dehydration synthesis) forms a glycosidic linkage between the two monosaccharides to make a disaccharide For example, maltose is two α glucose molecules linked by an α-1-4 glycosidic linkage Other common disaccharides are sucrose and lactose Disaccharides  Polysaccharides – complex carbohydrates Many subunits (100’s to 1000’s) Hydrophillic but very large so can attract water but not dissolve Four types: starch, glycogen, cellulose, chitin i. Starch Composed of amylose (α1-4 links) and amylopectin (α1-4 links but α1-6 links where it branches) Energy storage for plants  Polysaccharides ii. Glycogen Composed of α1-4 links but α1-6 links where it branches More branched than starch Animal energy storage – stored in liver and muscle cells  Polysaccharides iii. Cellulose » Composed of β1-4 links » Every other glucose subunit becomes inverted to accommodate this link » Not coiled or branched » Used in plant cell walls  Cellulose structure Hydrogen bonds  Polysaccharides iv. Chitin Cellulose-like polymer of N-acetylglucosamine Monomer is a glucose molecule with a nitrogen containing group attached at second C position Used in insects and crustaceans to form hard exoskeleton and also found in fungal cell walls  Lipids Hydrophobic molecules (“water fearing”). They are generally nonpolar and are insoluble in water Includes fats, phospholipids, steroids and waxes A gram of fat stores 9 calories of energy (compared to 4 calories in carbohydrates and proteins) Used for energy storage, cushioning, and insulation Animals convert excess carbohydrates into fat and store the fat as droplets in the cells of adipose (fat) tissue  Fats 1. Fats (e.g. trigylcerides) The backbone is GLYCEROL which has 3 hydroxyls Each FATTY ACID has a terminal carboxylic acid, and is between 14 and 22 carbons Condensation reaction attaches 3 fatty acids to glycerol making ester linkages (esterification)  Saturated Fats Usually come from animals. Used for long-term energy storage, insulation, protection and helps dissolve fat soluble vitamins. NO double bonds between carbon atoms in the fatty acids Solid at room temperature due to the straight chains 🡪 fatty acids are closer together 🡪 more intermolecular forces Diets high in saturated fats can lead to heart disease  Unsaturated Fats Usually comes from plant oils. One or more double bonds between carbon atoms in fatty acids. Double bonds form kinks, producing more space between fatty acids thus reducing the number of intermolecular interactions Liquid at room temperature. Diets high in unsaturated fats can improve your health  Phospholipids Composed of one glycerol, two fatty acids and a highly polar phosphate group. Consider amphipathic because contains polar and non-polar parts Form cellular membranes (phospholipid bilayer). The phospholipid bilayer is virtually impermeable to macromolecules, relatively impermeable to charged ions, and quite permeable to small, lipid soluble molecules. O2 and CO2 diffuse through with very little resistance. The most common phospholipids are phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidylserine Phospholipids  Steroids Hydrophobic molecules Four fused hydrocarbon rings with several functional groups attached Steroids include cholesterol, and some hormones (e.g. cortisol, estrogen, testosterone, progesterone)  Cholesterol Cholesterol is converted, by the body, into bile salts and vitamin D and is also essential for functioning cell membranes Cholesterol that circulates in the blood comes from the food you eat but is also made in the liver A high level of it in the bloodstream is linked to atherosclerosis Cholesterol is carried in your bloodstream as spherical particles called lipoproteins. The two most commonly known lipoproteins are low-density lipoproteins (LDL) and high-density lipoproteins (HDL).  Waxes E.g. bees wax, paraffin, cutin Consists of ALCOHOL or CARBON RINGS with an ester linkage to a FATTY ACID They are hydrophobic and very non-polar Act as waterproof coatings on various plant and animal parts Proteins - Overview – A polymer that has many subunits folded into a 3D structure that specifies its function – Most complex and diverse group of molecules in living systems and are involved in almost everything cells do – Examples include enzymes, immunoglobulins, hemoglobin, keratin, fibrin Types of proteins and their function  Amino Acids Proteins (polypeptides) are made of amino acids (monomer) There are 20 different amino acid, 8 of which are essential meaning they cannot be made in human cells and must be obtained in the diet The 20 amino acids differ in the R...when dissolved in water at a groups (side chains) they contain pH of 7, the ‘carboxyl’ donates These side chains can make the an H+ ion to the ‘amino amino acid polar (hydrophilic), non-polar (hydrophobic), or charged (acidic/basic) Nonpolar Amino Acids Polar Amino Acids Charged Amino Acids  Protein Structure The bonds that hold amino acids together are called peptide bonds Peptide bonds are formed by a condensation reaction A polypeptide are greater than 50 amino acids in length which then folds into a 3D shape Only after folding is the protein functional  Protein Structure Also called the conformation Depends on the amino acids it contains, and the interaction between those amino acids  Primary Structure The unique sequence of amino acids in the polypeptide is determined by the nucleotide sequence of a particular gene In a protein with ‘X’ number of amino acids, number of possibilities is 20x  Secondary Structure The folding and coiling of the polypeptide chain as it grows. Formed by hydrogen bonds between oxygen atoms of a carboxyl group and hydrogen atoms of the same amino acid backbone Two types ▪ α helix – tight coil produced by H-bonds every 4 peptide bonds repeated ▪ β pleated sheets – H-bonds formed between parallel stretches of a polypeptide  Tertiary Structure The polypeptide chain undergoes additional folding due to side chain (R-group) interactions. Interactions between side chains include hydrogen bonds, hydrophobic interactions and disulfide bridges Disulfide bridges are bonds that form when the –SH groups of two cysteine amino acids line up and react to form a S-S covalent bond – Strong bond that stabilizes the shape of the protein Tertiary Structure  Quaternary Structure Two or more polypeptide chains come together, such as in collagen and haemoglobin.  Protein Prosthetic Groups Many proteins require non-protein components called prosthetic groups to function e.g. Hemoglobin is composed of four polypeptides chains that each have a heme group which is a ring that contains a single Fe+2 ion. The heme group binds oxygen  Denaturation Temperature and pH changes can cause a protein to unravel (denature). Due to a disruption hydrogen bonds, etc A denatured protein is unable to carry out its biological function A denatured protein can return to its original shape if removed from the extreme environment provided its primary sequence was not destroyed  Nucleic Acids Composed of nucleotides Nucleotides consist of a nitrogenous base, a five-carbon sugar and a phosphate group. The nitrogenous bases are: adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U). DNA and RNA are nucleotide polymers and serve as the assembly instructions for all proteins in living organisms. ATP and GTP are nucleotides that are involved in cell metabolism along with nucleotide coenzymes (NAD+, NADP+ and FAD). Nucleotides Phosphodiester linkage (made of a link between phosphate group and hydroxyl group at adjacent sugar’s carbon 3) Sugars  Nitrogenous Bases Pyrimidines Purines  DNA – nucleotide polymer In DNA, A connects with T with 2 hydrogen bonds, and G connects with C with 3 hydrogen bonds. The two strands are antiparallel (one strand is upside down compared to the other).