U4 Aos 2 Notes (1).docx

KEY FOOD MOLECULES Proteins: formation of dipeptides and polypeptides as condensation polymers of 2-amino acids; primary (including peptide links), secondary, tertiary and quaternary structure and bonding; distinction between essential and non-essential amino acids as dietary components.  Amino acids are monomers that make up different proteins.  A monomer is a single unit, which joins with other monomers to form a polymer. There are 20 different amino acids that make up all proteins in the human body.  Every amino acid has an amino functional group (-NH2 ), a carboxyl group (-COOH) and a hydrogen atom attached to a central carbon.  The central carbon of an amino acid is called the alpha-carbon.  The general formula of an amino acid is H2N-CH(R)-COOH.  R depicts the side chain that differentiates 2-amino acids from one another.  The amino acids that make up the general structure and formula are known as 2-amino acids.  2-amino acids are also known as alpha-amino acids.  The side chain or R group can be non-polar or polar and proton donators or acceptors.  9 of the twenty 2-amino acids are called essential amino acids.  The other 11 2-amino acids are non-essential amino acids.  Essential amino acids must be provided directly through the proteins humans consume.  The human body only has the capacity to produce the other 11 2-amino acids.  The human body cannot store essential amino acids.  A balanced intake of these essential amino acids must be consumed daily.  Condensation polymerisation reactions involve the formation of a polymer.  An amide group (-CONH-) forms when a carboxyl group reacts with an amino group.  When two amino acids react, an amide group called peptide link/bond/group forms that links the molecules together.  Peptides are molecules made from amino acids.  When to amino acid molecules react, a dipeptide is formed.  There are two possible products of a dipeptide, which are differ by structure.  A polymer made from several amino acids is known as a polypeptide.  The protein's primary structure involves the number, type and sequence of the amino acid units in a protein.  In the primary structure only covalent bonds are responsible for joining the monomer units together.  Coiling and pleating the sections of a protein molecule produce a secondary level of structure in a protein.  Hydrogen bonds between the -NH group in a peptide link form at regular intervals.  These hydrogen bonds create regions in which the molecule can form two different segments.  The secondary structure of the protein refer to these segments.  The hydrogen bonds make a molecule coil into the shape of an alpha-helix, the same shape as a spring.  Hydrogen bonds that can form between peptide bonds to produce regions where two or more parts of the polypeptide chains line up parallel to each other .  This repeated structure of the backbone of the protein chain allows these hydrogen bonds to form at regular intervals, stabilising the protein structure.  This type of secondary structure is known at the beta-pleated sheet.  The overall three-dimensional shape a protein molecule adopts is called the protein's tertiary structure.  This structure is produced via the three-dimensional folding of the protein molecule's secondary structure.  The protein can twist backs over itself to create a unique shape.

             

The unique shape of the protein is responsible for its function. The side chains of the amino acid unit in a polypeptide chain affects the tertiary structure of the molecule. There are five bond types important in chain folding. These bond types link two parts of a polypeptide chain together. Hydrogen bonds require -O-H, -N-H or -C=O in the side chain of the polypeptide. Dipole-dipole interactions require any polar group as a side chain. Ionic interactions requires an R group that contains -NH3+ and another R group that contains -COO-. Covalent cross-links require cysteine side groups that react to form a disulfide (-S-S-) bridge. Dispersion forces require any non-polar group as a side chain. Due to these different types of bonds, a great variety of protein shapes exist. Some proteins which contain two or more polypeptides may interact with mono-protein molecules to produce a larger unit. This unit is known at the quaternary structure. Dispersion forces between non-polar R groups cause the attractions between the chains. Dipole-dipole attractions, hydrogen bonds, ionic interactions and disulfide bonds involving R groups may also occur.

Carbohydrates: formation of disaccharides from monosaccharides, and of complex carbohydrates (specifically starch and cellulose) as condensation polymers of monosaccharides; glycosidic links; storage of excess glucose in the body as glycogen; comparison of glucose, fructose, sucrose and the artificial sweetener aspartame with reference to their structures and energy content .  Carbohydrates consist of carbon, hydrogen and oxygen.  Carbohydrates usually have the general formula Cx(H2O)y, where x and y are whole numbers.  Monosaccharides are the smallest carbohydrates.  Two monosaccharides react to form a disaccharide.  To form a disaccharide a condensation reaction between the hydroxyl groups on neighbouring molecules occur.  The bond formed between the two monosaccharides is known as an ether or a glycosidic link. GLYCOSIDIC PREFERRED.  In this condensation reaction, a water molecule forms as the by-product.  A by product is something produced in a usually industrial or biological process in addition to the principal product

        

Reactions between monosaccharides can produce a polymer, a polysaccharide. A polysaccharide can contain thousands of glucose units. Glycogen is a polysaccharide formed from the polymerisation of glucose. Glycogen is a polymer of glucose. Glycogen forms from the excess glucose and is stored in the liver or muscle tissue. Glucose, fructose and galactose are monosaccharides. Glucose, fructose and galactose are isomers of the composition C6H12O6. Glucose is found in fruit juices. Fructose is found in fruit juices and honey.

   

Galactose is not found naturally in its free form. Small carbohydrates are called sugars because of their sweet taste. Aspartame is an artificial sweetener and also known as food additive 951. The energy content of aspartame is almost the same as sugar but is used in lower proportions because of its greater sweetness.

Fats and oils (triglycerides): common structural features including ester links; distinction between fats and oils with reference to melting points; explanation of different melting points of triglycerides with reference to the structures of their fatty acid tails and the strength of intermolecular forces; chemical structures of saturated and unsaturated (monounsaturated and polyunsaturated) fatty acids; distinction between essential and nonessential fatty acids; and structural differences between omega-3 fatty acids and omega-6 fatty acids.  Fats and oils are a major energy source in your diet.  Animals use fats to store energy,  Fats and oils belong to the class of biological molecules known as lipids.  Lipids are insoluble in water but soluble in non-polar solvents.  Therefore lipids are non-polar.  Fats and oils contain large non-polar molecules known as triglycerides.                  

At room temperature fats are solids. At room temperature oils are liquids. The melting point of an oil would be equal to or under 20 degrees Celsius? Fats have higher melting points than oils. Triglycerides are made through condensation reactions between a glycerol molecule and three fatty acid molecule. Glycerol is also known as propane-1,2,3-triol. Glycerol is a small molecule with three functional groups. Fatty acids have a carboxyl functional group attached to a long unbranched hydrocarbon chain. A condensation reaction can occur between a molecule with a carboxyl group and a molecule with a hydroxyl group. This reactions forms an ester functional group and a water molecule. The condensation of fatty acid, containing a carboxyl group and a glycerol molecule, containing a hydroxyl group form an ester link and produce a triglyceride. Saturated fatty acids only have carbon-carbon single bonds. Unsaturated fatty acids have one or more carbon-carbon double bonds. Omega-3 fatty acids are unsaturated fatty acids with a double bond on the third last carbon atom in the hydrocarbon chain. Omega-6 fatty acids are unsaturated fatty acid with a double bond on the sixth last carbon atom in the hydrocarbon chain. The most significant intermolecular forces between fatty acid molecules are dispersion forces, Saturated fatty acids pack together more closely than unsaturated fatty acids. Saturated fatty acids can form stronger intermolecular forces than unsaturated fatty acids.

    

Therefore, saturated fatty acids have higher melting points and are more likely to be solids at room temperature, than unsaturated fatty acids. Monounsaturated fatty acids contain one carbon-carbon bond in their hydrocarbon chain. Polyunsaturated fatty acids contain more than one carbon-carbon double bond in their hydrocarbon chain. Essential fatty acids are fatty acids the human body require but do not produce. Non-essential fatty acids are fatty acids the human body can produce so do not have to be included in the human diet.

Vitamins: inability of humans to synthesise most vitamins (except Vitamin D) making them essential dietary requirements; comparison of structural features of Vitamin C (illustrative of a water-soluble vitamin) and Vitamin D (illustrative of a fat-soluble vitamin) that determine their solubility in water or oil.  Vitamins are organic compounds that are required in the diet for the body to function properly.  Vitamins help prevent specific diseases.  Vitamins do not share a common structure.  Vitamins are either fat-soluble or water-soluble.  Water-soluble vitamins are usually in the aqueous environment of the blood.  The body does not store water-soluble vitamins.  Fat-soluble vitamins store in fatty tissues for a long time.  Fat-soluble vitamins form dispersion forces with the lipids in fatty tissue.  Humans cannot synthesise vitamins except for biotin and vitamin D.  Biotin can be manufactured in the intestines.  Vitamin D is synthesised in the skin after exposure to radiation.  The solubility differences of vitamins relate to how many functional groups in a molecule can form hydrogen bonds with water.  The higher number of groups that can form hydrogen bonds with water, the higher its solubility with water.  Fat-soluble vitamins are insoluble with water because most of their molecules are non-polar.  Vitamin D is a fat-soluble vitamin.  Vitamin C is a water-soluble vitamin.  The following table compares Vitamins C and D: 

METABOLISM OF FOOD IN THE HUMAN BODY

Metabolism of food as a source of energy and raw materials: general principles of metabolism of food involving enzyme-catalysed chemical reactions with reference to the breakdown of large biomolecules in food by hydrolytic reactions to produce smaller molecules, and the subsequent synthesis of large biologically important molecules by condensation reactions of smaller molecules.  Food supplies nutrients for the human body.  Nutrients are large biomolecules that the body uses to:  Provide energy  Regulate growth  Maintain and repair body tissue  Proteins, triglycerides (fats and oils), carbohydrates, minerals, vitamins and water are all nutrients.  Macronutrients are components of food bodily functions require in large amounts. Eg. Proteins.  During metabolism, macronutrients are generally insoluble in water excluding smaller molecules.  These small molecules can be transported throughout the body in the blood.  Metabolism refers to the chemical processes that occur within living cell or organism that are necessary for the maintenance of life.  Metabolism involves the breakdown of substances, usually nutrients from food.  The breakdown of these substances yields energy for vital processes.  Metabolism also involves the synthesis of larger molecules necessary for life from smaller molecules.  Metabolism is all the chemical reactions that occur within a living organism to maintain life.  In the digestive system, the metabolism of food begins.  Food breaks down into smaller molecules in a process called digestion.  Digestion involves the breakdown of a large number of separate enzymes into different components of the food.  Enzymes are highly specific biological catalysts.  Enzymes catalyse the hydrolysis of nutrients in the body.  The human body reduces compounds to smaller soluble molecules that form the building blocks for new substances.  Hydrolysis consists of hydrolytic reactions where large molecules split by their reaction with water molecules.  Condensation reactions involve joining smaller molecules to form a large molecule and a by-product (usually water).  Condensation and hydrolysis reactions are reversible.  Condensation and hydrolysis can be seen as the opposite of one another.  Enzymes are critical for hydrolysis and condensation to occur in biological systems.  Condensation reactions tend to be endothermic, as they would require energy to form larger molecules.  Hydrolytic reactions tend to be exothermic, as they would release energy when bonds break to form smaller molecules. 

Enzymes as protein catalysts: active site; modelling of process by which enzymes control specific biochemical reactions (lock-and-key and induced fit models); consequences of variation in enzymesubstrate interaction (lock-and- mechanism) due to the behaviour of a particular optical isomer; explanation of effects of changes in pH (formation of zwitterions and denaturation), increased temperature (denaturation) and decreased temperature (reduction in activity) on enzyme activity with

reference to structure and bonding; action of enzymes in narrow pH ranges; and use of reaction rates to measure enzyme activity.  Enzymes are proteins that catalyse biochemical reaction by providing an alternative pathway with a lower activation energy.  Enzymes a highly specific in that an enzyme may only catalyse on specific reaction or a reaction consisting of a particular bond or functional group.  Enzyme molecules have uniquely shaped active sites that interact with specific reactant molecules called substrates.  Reacting with substrates weakens of breaks the bond of the reactant molecules.  The catalytic activity of an enzyme is highly specific an depends on its overall 3-D structure.  Since enzymes are proteins, their tertiary and quaternary structure dictate the enzyme’s overall 3-D structure.  The particular part of an enzyme molecule that interact with the reactants is the active site of the molecule.  Enzyme molecules have uniquely shaped active sites that interact with specific reactant molecules called substrates.  Reacting with substrates weakens of breaks the bond of the reactant molecules.  Substrates are the reactant molecules that bind to the active sites.     

The shape of the substrate molecule must match the shape of the active site. The lock-and-key model explains the significance of the 3-D shape of an enzyme. The following image describes this model.

   

Optical isomers are organic molecules which contain a carbon that bonds to four different substituents that can have two superimposable mirror images called enantiomers. These carbon atoms are described as being chiral centres, as depicted by the following image. Enantiomers differ by how they interact with - plane polarised light - other chiral molecules. May substrates have more than one chiral centre. This allows enzymes to distinguish between enantiomers of a chiral substrate. Enzymes are sensitive to changes in the environment including temperature and pH. Since the lock-and-key model, it has been learnt that enzymes have flexible structures. The binding of a substrate can modify the shape of an enzyme’s active site. The induced fit model depicts this finding as portrayed in the following image. Coenzymes are additional non-protein molecules require in order to function. Vitamins often make up coenzymes. Coenzymes can acts as carriers of electrons or groups of atoms in biochemical pathways. The enzyme activity is a quantity that measures the rate of conversion of a substrate into a product by an enzyme. Enzyme activity is the amount of substrate that converts in to products per unit time. Enzyme activities relies on the quantity of the active enzyme present and reaction conditions. Enzymes only work effectively within a narrow pH range. The pH at which the enzyme activity is the greatest is known as the enzyme’s optimum pH.



2-amino acids can form zwitterions.



A zwitterion has both a negative and positive charge within the molecule.



At a high pH, the -NH3+ group if the zwitterion can act as an acid to become a -NH2 group.

 

         



At a low pH, the -COO- group can act as base to become a -COOH- group.



The charge of a zwitterion depends on the pH of the solution.



At a low pH a zwitterion is a cation.



At an intermediate pH a zwitterion is an uncharged molecule.



At a high pH a zwitterion is an anion



Some r groups of amino acids can be affected by changing the pH.



The temperature affects enzyme activity.



The temperature at which enzyme activity is the greatest is called the enzyme's optimum temperature.



Enzymes in human cells usually have an optimum temperature of 37 degrees Celsius.



Increasing the temperature over the optimum temperature leads to an increase in kinetic energy.



This increase in kinetic energy disrupts the structure of the enzyme.



This changes the 3-D structure which means the active site cannot effectively catalyse the reaction, decreasing the rate of reaction.



If the temperature is below the optimum temperature the enzyme and substrate have lower kinetic energies, decreasing the rate of reaction.



Denaturation is when an enzyme undergoes a change in its three-dimensional shape so that it cannot catalyse reactions.



Denaturation is what occurs to an enzyme when it experiences a temperature above its optimum temperature.



If the temperature drop below the optimum temperature the enzyme and substrate have lower kinetic energies, decreasing the rate of reaction or allowing a reduction in activity.

The distinction between denaturation of a protein and hydrolysis of its primary structure. 

Denaturation is when an enzyme undergoes a change in its three-dimensional shape so that it cannot catalyse reactions.



This change in protein structure is sometimes irreversible.



Denaturation can also be a result of a change in pH as this affects the 3-D shape of the enzyme.



Denaturation does not influence the primary structure of an enzyme.



The primary structure of an enzyme breaks down during hydrolysis.



Hydrolysis of starch in the body: explanation of the ability of all humans to hydrolyse starch but not cellulose, and of differential ability in humans to hydrolyse lactose; glycaemic index (GI) of foods as a ranking of carbohydrates based on the hydrolysis of starches (varying proportions of amylose and amylopectin) to produce glucose in the body.  Starch and glycogen are polysaccharides.  Polysaccharides are what plants and animals use as a way to store energy.  Starch and glycogen are polysaccharides composed of the same monosaccharide, glucose.  During digestion, the polysaccharides hydrolyse into smaller carbohydrates to eventually become glucose.  Amylase and maltase hydrolyse glycosidic links in starch and maltose in the digestive process.  Humans cannot digest cellulose.  Cellulose if hydrolysed by the enzyme cellulase, which is not present in all animals.  Bacteria that live in some animals' guts produce cellulase.  Lactose is a disaccharide that forms when glucose and galactose react.  Lactose is a predominant carbohydrate in the milk of mammals.  Carbohydrate-containing foods are rated on a scale called the glycaemic index (GI).  This scale ranks foods according to their effect on blood sugar levels over a period of time, usually 2 hours.  Therefore it ranks based on how quickly foods release the energy they contain.  High GI foods digest easily and can cause a spike in sugar levels.  Low GI foods are slow to digest and have a smaller effect upon sugar levels.  Low GI foods instead provide energy over a long period of time.

Hydrolysis of fats and oils from foods to produce glycerol and fatty acids; oxidative rancidity with reference to chemical reactions and processes, and the role of antioxidants in slowing rate of oxidative rancidity.  Triglycerides hydrolyse from enzymes during digestion.  When triglycerides hydrolyse to produce glycerol and the fatty acids.

               

     

Digestion of triglycerides occurs in the small intestine where bile emulsifies fat, which then hydrolyses from the enzyme lipase. The glycerol and fatty acids pass into the bloodstream of the liver where triglycerides reform. The triglycerides can store in adipose tissue or it can be oxidised in muscle cells to release energy. Triglycerides can deteriorate over time, especially with unsaturated triglycerides. Unsaturated fats are less stable than saturated fats. Reactions between fats, enzymes, heat, water, oxygen or light can create extra functional groups. The addition of functional groups breaks the molecules with noxious odours or flavours. When the flavour/aroma of a triglyceride becomes spoilt, the triglycerides is described as a rancid. Oxidative rancidity occurs a consequence of the reaction of oxygen with unsaturated fats or fatty acids. Oxidative rancidity produces aldehydes and ketones. The use of antioxidants slow down the deterioration of food. Antioxidants slow down the oxidation of another substance or simply delays it. Antioxidants improve the shelf life of food, usually by reacting with free radicals and restricting their propagation. Some foods contain natural antioxidants. Some foods contain synthetic antioxidants which are added to prolong shelf life. Synthetic antioxidants usually contain hydroxyl groups.

The principles of the action of coenzymes (often derived from vitamins) as organic molecules that bind to the active site of an enzyme during catalysis, thereby changing the surface shape and hence the binding properties of the active site to enable function as intermediate carriers of electrons and/or groups of atoms (no specific cases required). Coenzymes are additional non-protein molecules that enzymes require in order to function. Vitamins often make up coenzymes. Coenzymes interact with the enzyme during catalysis. Coenzymes can acts as carriers of electrons or groups of atoms in biochemical pathways. Before an enzyme binds to a coenzyme, it is inactive. Unlike an enzyme, coenzymes can change as a result of the reaction as it accepts or donates an electron or group of atoms.



ENERGY CONTENT OF FOOD        

The comparison of energy values of carbohydrates, proteins and fats and oils The unit of energy is joule (J). The energy content of food is measured in kJ/g, kJ/100g or kJ mol-1, if the food is a pure substance. For most foods the energy released on combustion is similar to the energy released when the food is oxidised during respiration. Each of the major food nutrients (carbohydrates, proteins and fats and oils), are considered to have a particular heat of combustion. The energy available to the body from a nutrient of food is called its energy value. Energy value and energy content have the same units. The following table compares the heat of combustion and energy value of the three main nutrients: Fats and oils have a high energy value than carbohydrates.

    

 

                 

 

Fats and oils contain less oxygen atoms than carbohydrates do. Carbon atoms in carbohydrate molecules have a higher degree of oxidation. Thus, fats and oils have greater potential for oxidation and release more energy on combustion. After the digestion of food, the heat of combustion is often greater than the energy value. This can be due to: - incomplete absorption of nutrients by the body subsequent to digestion. - incomplete oxidation of nutrients including proteins and insoluble fibre. - heat loss as not all energy released by the oxidation of glucose is available for use in cells. The energy value of a food can be calculated using data for the available energy of the various components of the food and the percentages of each component of the food. The energy value can be calculated by following these steps: - multiply each percentage of the nutrient by the available energy per gram, - divide by 100 to find the energy value in kJ/g.

Glucose as the primary energy source, including a balanced thermochemical equation for cellular respiration. Glucose is a monosaccharide. Glucose is one of the simplest carbohydrates. All monosaccharides are white, crystalline solids with a sweet formula. All monosaccharides have the formula C6H12O6. Molecules of monosaccharides contain a number of polar hydroxyl groups. Therefore, monosaccharides are highly soluble in water. Glucose is in all living things. Glucose is the primary energy source for the cells of plants and animals.. Glucose is used to obtain energy by a process known as cellular respiration. The two types of cellular respiration are aerobic respiration and anaerobic respiration. Aerobic respiration requires oxygen and is the main source of energy for the human body. Glucose is oxidised to carbon dioxide and water. The overall equation for aerobic respiration is: Anaerobic respiration does not require oxygen and yields less energy. Anaerobic respiration can occur in muscles during prolonged and vigorous exercise, when the supply of oxygen is limited. The overall equation for anaerobic respiration is: The reactions that occur in both aerobic and anaerobic respiration is exothermic. Anaerobic respiration is a faster process than aerobic respiration.

The principles of calorimetry; solution and bomb calorimetry, including determination of calibration factor and consideration of the effects of heat loss; and analysis of temperature-time graphs obtained from solution calorimetry. Calorimetry is the experimental method of measuring heat energy that is released or absorbed by a chemical reaction or physical process. When an exothermic chemical reaction occurs underneath a container of water, some of the heat released via combustion transfers to the water.



                         

The heat energy that transfers to a volume of water can be calculated by measuring the: - initial temperature of the water. - highest temperature of the water. - volume of water. The following formula calculates the energy that has been transferred to the water: q=mCdeltaT A calorimeter is an instrument that measures energy changes in a reaction. A calorimeter is made up of an insulated container of water in which the reaction occurs. A calorimeter also has a stirrer and thermometer to measure the temperature change during the reaction. A lid is also necessary for a calorimeter for the insulation. A solution calorimeter is an insulated container that holds a known volume of water and in which a reaction in solution or neutralisation carries out. A bomb calorimeter is an insulated container in which a sealed, oxygen-filled reaction vessel is surrounded by a known volume of water. Combustion reactions occur in the reaction vessel of a bomb calorimeter and the heat from the reaction transfers to the surrounding water. A more accurate method to determine the temperature change is to plot a temperature-time graph. Temperature is the vertical axis and is measured in degrees Celsius. Time is the horizontal axis and is measured in seconds. Heat losses that can occur in a calorimeter can lead to inaccurate results. If the insulation around a calorimeter is insufficient, missing, or there is no lid, heat will be lost, lowering the calculated deltaT. To prevent in accurate results, it is essential to determine how much energy will change the temperature by 1 degrees Celsius for the particular calorimeter in use. Calibration involves adding a known quantity of heat energy from an electrical source or from a chemical source. The energy needed is known as the calibration factor of the calorimeter. A calibrated calorimeter knowns the calibration factor. A calorimeter can be calibrated with an electric heater. The electrical heater releases a known quantity and measures the resultant rise in temperature of the water in the calorimeter. The following formulas can be used to calculate the energy released when an electric current passes through the heater. For the chemical calibration of a bomb calorimeter, using the combustion of benzoic acid, the calibration factor is calculated using the equation: When a reaction occurs in a calibrated calorimeter, the energy released by the reaction is determined using the equation: The energy content of food can be determined using the equation: The enthalpy of combustion of pure nutrients can be determined using a calibrated bomb calorimeter. Enthalpy of combustion in a bomb calorimeter is determined using the equation: