Energy and Proteins

Energy The foods we eat contain energy. We can measure the amount of energy contained in foods. The units we use are Joules (J) or Calories (C). Different biomolecules have different amounts of energy. Fat= 37 kJ g -1 Protein = 17 kJ g -1 Carbohydrates = 17 kJ g -1

Humans need Energy The recommended daily intake for an adult male who engages in a low level of physical activity is 10,500 kJ (2,500 kcal) and for a woman is 8,000kJ (1,900kcal).

HOW CAN YOU MEASURE THE AMOUNT OF ENERGY FOOD HAS? We can measure the amount of energy by using enthalpy of combustion data. We can burn foods and measure how much the energy released raises the temperature of a fixed mass of water. (We do this in a calorimeter. Example: An apple has 420 kJ of energy. If we burned it, the energy released would raise the temperature of 1 kg of water 100 °C.  H = mc  T= 1000g x 4.18 Jg -1 °C -1 x 100 °C  J = 420 kJ

Proteins

Proteins are made of Amino Acids There are 20 amino acids found in your cells. These are called 2 amino acids. All of the aa share a general formula: RCH(NH 2 )COOH

Properties of 2(  )-amino acids AA are colorless, crystalline solids. AA are zwitter ions (dipolar ions) at their isoelectric point. AA have a high melting point. AA are amphoteric. AAs act as a buffer in an aqueous solution.

What is a zwitterion and why would it have a high melting point? A zwitterion is a molecule with dipolar ends (and acid end and a base end). In aqueous solutions, the amine group can accept a proton and the carboxylic end can donate a proton depending on the pH. At the isoelectricpoint (pI), the pH at which at which the positive and negative charges are balanced, the molecule is neutral and will not migrate in an electric field. Amine group Carboxylic acid

Peptide Bonding +

Peptide Backbone The bonds between amino acid bonds are formed in a hydration reaction where the amine group joins with the carboxylic acid forming the peptide bond and a water molecule. The resulting chain features the peptide backbone with the corresponding R group attached. This sequence of amino acids is referred to as the primary structure of the protein.

Secondary structure The manner in which a protein folds itself due to intramolecular hydrogen bonding. Two features are  -helix and the  -sheet Alpha helix with hydrogen bonds shown Beta sheet with hydrogen bonds

Tertiary Structure Is the interaction between the sequence of amino acids that maintains the 3-d shape of the protein. There are 4 main interactions that determine tertiary structure. 1.Disulfide bonding between cysteine groups. 2.Hydrogen bonding between side chains. 3.Salt bridges (electrostatic attractions) between amine groups and carboxyl groups. 4.Hydrophobic and hydrophillic interactions of non-polar and polar AAs and the aqueous interior of the cell.

Quaternary Structure Only occurs in proteins that contain more than one polypeptide chain and is held together by non-covalent bonds (hydrophobic interctions, ionic and hydrogen bonds). Each polypeptide chain is called a subunit. A haemoglobin protein molecule. One of four subunits

Proteins can be analyzed by Electrophoresis and Chromotography Electrophoresis Proteins are applied to a gel. A current is applied to the gel. Negative charges move towards the positive and positive charges move towards the negative while neutral proteins do not move. Chromotography Proteins are dissolved in a mobile phase and then applied to a stationary phase (ex. Paper). AAs with greater solubility in the solvent will travel further up the stationary phase.

Major Functions of Proteins Structure: ex. collagen and keratin Catalysis (enzymes) ex. Lipase and Amylase Hormones (signal proteins) ex. Peptide hormones Antibodies (part of the immune system) Transport ex. haemoglobin Energy- under starvation conditions