Human Biochemistry IB Chemistry 3 Robinson High School Andrea Carver
Biochemistry is… • The study of the chemical processes occurring in living organisms. • Includes processes involving the flow of both energy and information. • Deals with biomolecules such as proteins, carbohydrates, lipids, and nucleic acids.
Energy: IB Objectives • B.1.1 Calculate the energy value of a food from enthalpy of combustion data.
Energy • Every living cell contains thousands of biological molecules each of which is involved in the interlinked processes of metabolism. • Cellular respiration is the oxidative process by which energy stored in food is made available for use by the cell. O2 Starch Protein Rxns of Respiration CO2 + H2O Glucose Glycogen Fats Energy
Measuring Energy Production • Combustion analysis is used to determine the amount of energy produced from a unit of a particular food. • A bomb calorimeter measures the heat of combustion of a reaction. • Food is burned within the calorimeter, and heat released raises the temperature of a known quantity of water.
Calculation of Energy Release • Formula: q=mc∆T • q= the energy evolved (J) • m= the mass of water (g) • c= the specific heat of water (4.18 J/g•K) • ∆T= the temperature change of water (K) • Example: A 0.78 food sample combusts raising the temperature of 105.10 g water from 15.4°C to 30.6°C. Calculate the energy value of food in kJ/g.
Proteins: IB Objectives • B.2.1 Draw the general formula of 2-amino acids. • B.2.2 Describe the characteristic properties of 2-amino acids. • B.2.3 Describe the condensation reaction of 2-amino acids to form polypeptides. • B.2.4 Describe and explain the primary, secondary (alpha helix and beta pleated sheets), tertiary , and quaternary structure of proteins. • B.2.5 Explain how proteins can be analyzed by chromatography and electrophoresis. • B.2.6 List the major functions of proteins in the body.
Proteins: Function • Structure- Proteins make up many diverse protective, contractile, and supporting structures in the body. • Examples: keratin, collagen, myosin, immunoproteins, hemoglobin, casein, mucoproteins • Tools- Proteins are valuable operators on the molecular level such as enzymes and hormones. • Examples: lactase, insulin
Proteins: Structure • Amino Acids are the building blocks of proteins.
Amino Acids • 2-amino acids- Numbering begins with carbonyl carbon and R group is bound to carbon 2. • Carbon 2 is also bound to H, NH2, and COOH. • R group- defines the amino acid. Amino acids can be classified by the chemical nature of this group (non-polar, polar, basic, acidic). • 20 amino acids occur naturally.
Characteristics of Amino Acids • Crystalline, high melting points, greater solubility in water than in non-polar solvents. • Exist as dipolar ions- contain both positive and negative charges- zwitterions. • Amphoteric- can react as both an acid and a base. • Amino acids can act as buffers.
Isoelectric Point • This is the pH at which the amino acid is electrically neutral (typically when the amino acid is a zwitterion).
Condensation of Amino Acids • Amino acids link together through condensation reactions to form proteins. • Condensation reaction- H2O is eliminated as a new bond is formed. • Forms a peptide bond. • Two amino acids combine to form a dipeptide. • Three amino acids combine to form a tripeptide. • More amino acids combine to form a poly peptide. • The sequence of linked amino acids will determine the nature of the polypeptide=> variety of proteins (millions of possibilities).
Structure of Proteins • Primary Structure-Number and sequence of amino acids in polypeptide chain. • Secondary Structure- Folding of polypeptide chain due to hydrogen bonding between peptide groups. • Tertiary Structure- Further twisting, folding of the chain due to interactions between R-groups (side chains). • Quaternary Structure- Association between more than one polypeptide subunit.
Primary Structure • Forms covalent backbone of molecule. • Held together by peptide bonds. • All other levels of structure determined by primary structure. • What determines primary structure of a protein?
Secondary Structure • Two main types: • Beta pleated sheets • “side by side” polypeptides • Pleated sheets cross-linked • Inter-chain H-bonds • Flexible, but inelastic • Alpha helix • Regular, coiled • Flexible and elastic • Intra-chain H-bonds • H-bonds four AA’s apart
Tertiary Structure • Determines protein’s conformation. • Important for function of enzymes, hormones, etc. • Most stable arrangement accounting for all possible interactions between side chains. • Possible Interactions: • Hydrophobic Interactions • Hydrogen Bonding • Ionic Bonding • Disulfide Bridges
Quaternary Structure • The association of more than one chain in proteins.
Analysis of Proteins • First, amino acid composition can be determined by hydrolyzing the peptide bonds which link together amino acids in the polypeptide chain. • Specific linkages can be hydrolyzed using certain enzymes. • Then peptides can be separated based on differences in size and charge using the following techniques. • Chromatography • Electrophoresis
Chromatography Amino acids are treated with a locating reagent to colorize them. A small amount of the mixture is placed at the origin. Stationary Phase- does not move (paper) Mobile Phase- travels taking some sample with it (solvent) Movement of peptide fragments determined by size. Rf= distance traveled by amino acid distance traveled by solvent Specific amino acids have characteristic Rf values.
Electrophoresis Separates amino acids based on movement of charged particles. A charge gradient is established on a gel. Proteins migrate based upon charge of side chains present. Proteins settle near their isoelectric points.
Carbohydrates: IB Objectives • B.3.1 Describe the structural features of monosaccharides. • B.3.2 Draw the straight chain and ring structural formulas of glucose and fructose. • B.3.3 Describe the condensation of monosaccharides to form disaccharides and polysaccharides. • B.3.4 List the major functions of carbohydrates in the human body. • B.3.5 Compare the structural properties of starch and cellulose, and explain why humans can digest starch but not cellulose. • B.3.6 State what is meant by the term dietary fiber. • B.3.7 Describe the importance of a diet high in dietary fiber.
Lipids: IB Objectives • B.4.1 Compare the composition of the three types of lipids found in the human body. • B.4.2 Outline the difference between HDL and LDL cholesterol and outline its importance. • B.4.3 Describe the difference in structure between saturated and unsaturated fatty acids. • B.4.4 Compare the structures of the two essential fatty acids, linoleic (omega-6 fatty acid) and linolenic (omega-3 fatty acid) and state their importance. • B.4.5 Define the term iodine number and calculate the number of C=C double bonds in an unsaturated fat/oil using addition reactions. • B.4.6 Describe the condensation of glycerol and three fatty acid molecules to make a triglyceride. • B.4.7 Describe the enzyme catalyzed hydrolysis of triglycerides during digestion. • B.4.8 Explain the higher energy value of fats compared to carbohydrates. • B.4.9 Describe the important roles of lipids in the body and the negative effects that they can have on health.
Lipids: Characteristics • Hydrophobic, insoluble in water • Soluble in non-polar solvents • Contain Carbon, Hydrogen, and Oxygen • Less oxidized than carbohydrates (more H, less O) • Include fats, oils, steroids, and phospholipids • Functions: • Energy Storage • Insulation • Protection of Organs • Absorption of Fat Soluble Vitamins (A,D,E,K) • Structural-Membrane Component • Myelin Sheaths of Axons
Negative Effects of Lipids • Excess lipids are stored in the body as adipose tissue. • Sometimes excess lipids are deposited into the walls of arteries- Atherosclerosis. • Atherosclerosis (aka hardening of the arteries) can lead to hypertension , stroke, and myocardial infarction. • The image shows the aorta of an individual with atherosclerosis.
Cholesterol: Good or Bad? • Cholesterol is insoluble in blood, so it is transported as lipoproteins: HDL and LDL. • LDL- “bad cholesterol” • HDL- “good cholesterol”
Lipid Structure • Three main types: • Triglycerides • Phospholipids • Steroids
Fatty Acids: Saturation • Saturated fatty acids have no double bonds. • Mono-unsaturated fatty acids have one double bond. • Polyunsaturated fatty acids have more than one double bond.
Essential Fatty Acids • Some fatty acids cannot be synthesized by the body and must be obtained from the diet. These are essential fatty acids. Linoleic acid (omega-6) Linolenic acid (omega-3)
Iodine Number • Determination of the number of double bonds in a fatty acid based upon its reactivity with iodine. • Iodine can add to formerly double bonded carbons (addition reaction). • The iodine number is the number of grams of iodine which can react with 100 grams of fat.
Digestion of Fats • Lipases digest fat via hydrolysis reactions.