1.1 Aspects of Biochemistry

• Cellular respiration facilitates the breakdown of glucose and the production of ATP for energy.
• What is the difference between saturated and unsaturated fats?

  Saturated fats - Have no carbon to carbon double bonds, are saturated with H+, are solid at room temperature, are usually found in warm-blooded animals. e.g. lard, butter

  
  

  Unsaturated fats - Have carbon to carbon double bonds, are liquid at room temperature, are usually found in cold blooded animals and most plants. e.g.fish oil, soybean oil
• Give the uses of lipids

  1. Protection and cushioning of body organs

  2. Energy storage

  3. Structural Components of Membranes

  4. Chemical messengers (hormones)
• What are nonreducing sugars?

  Non-reducing sugars do not have an OH group attached to the anomeric carbon so they cannot reduce other compounds.
• What are reducing sugars?


  A sugar that can donate an electron to a substance to reduce this substance. A reducing sugar is any sugar that is capable of acting as a reducing agent because it has a free aldehyde group or a free ketone group. All monosaccharides are reducing sugars.
• Compare the different levels of protein structures

  Primary

  
  

  Secondary

  
  

  Tertiary

  
  

  Quatenary
• State the tests for reducing and nonreducing sugars, starch, lipids, and proteins
• Describe the generalised structure of an amino acid, and the formation and breakage of a peptide bond
• Describe the structure of phospholipids and their role in membrane structure and function

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• Describe the relationship between triglycerides and obesity
• Describe the molecular structure of a triglyceride and its role as a source of energy
• Discuss how the molecular structure of starch, glycogen and cellulose relate to their functions in

  living organisms
• Explain the relationship between the structure and function of sucrose
• State the differences between alpha and beta glucose
• Explain the relationship between the structure and function of glucose
• Define Macromolecules

  macromolecules are polymers made up of their individual monomers and formation and breakage

  of bonds
• Discuss how the structure and properties of water relate to the role that water plays as a medium of life.
• outline the molecular

  structure of haemoglobin,

  as an example of a

  globular protein, and of

  collagen, as an example of

  a fibrous protein
• Emulsion Test For Fat & Oils

  Fats do not dissolve in water but they do in alcohol.

  
  

  1.Add ethanol (alcohol) to test substance. Shake or crush in order to dissolve.

  
  

  2.Take another tube containing water, and pour the ethanolic solution (prepared above) into top.

  
  

  A white (milk-like) emulsion indicates the presence of fats or oils. Explanation: Ethanol dissolves lipids. When added to water lipids disperse as tiny particles forming emulsion.
• Biuret test for Proteins

  •Add Biuret solution (sodium hydroxide + small amount of copper sulphate) to the test substance.

  
  

  - THERE IS NO NEED TO HEAT, but the result is not quite instantaneous.

  
  

  A colour change from blue to purple/mauve shows the presence of a protein.

  
  

  Explanation: A coloured complex forms where there are peptide bonds.
• Iodine test for starch


  A colour change from brown to blue-black shows the presence of starch.

  Explanation: Iodine binds to the centre of the helix of amylose to form a starch iodine complex.

  
• Benedict's Test For Non-Reducing Sugars e.g. sucrose

  •Make solution of food to be tested and divide into two equal parts A and B.

  
  

  •Do simple sugar test on part A to make sure no reducing sugar is present.

  
  

  •Add a few drops of Hydrochloric acid (HCl) to part B and boil for a few minutes to break apart sucrose into fructose and glucose.

  
  

  •Add sodium bicarbonate (alkaline) until contents stop fizzing, to neutralize leftover HCl.

  
  

  •Finally add Benedict's solution and heat for 2 mins.

  
  

  •Reddish colour indicates the presence of reducing sugars.

  No colour change when Benedict's solution is first added. Remains blue. Only turns brick red after hydrolysis by HCl to form simple sugars.

  
• Benedict's Test- For simple (reducing) sugars e.g. glucose


  •Add Benedict's solution (alkaline solution of copper sulphate ) to a test solution in a test tube

  
  

  •Heat the tube gently for about 2 minutes in the water bath.

  A colour change from blue to green/yellow to orange to brick red shows the presence of a simple (reducing) sugar.

  
• Haemoglobin vs Collagen

  Transport protein in red blood cells, soluble in water. Structural protein forming between cells, insoluble in water.

  
  

  Transports oxygen around the body. Provides toughness in skin, bones, cartilage, tendons, ligaments and muscles.

  
  

  Four polypeptide chains (2 alpha + 2 beta). Three polypeptide chains (alpha; identical) forming triple helix.

  
  

  Quaternary Structure

  - Two alpha globins

  - Two beta globins

  - 4 haem groups binds to oxygen

  
  

  Quaternary Structure -Triple helices joined together by covalent bonds to form strong collagen fibres similar to strands in a rope.
• Molecular Structure of Collagen

  PRIMARY STRUCTURE: Unbranched polypeptide chain

  
  

  SECONDARY STRUCTURE: Polypeptide chain tightly wounded together.

  
  

  TERTIARY TRUCTURE: Polypeptide chain twisted into second helix.

  
  

  QUATERNARY STRUCTURE: Three alpha chains(~ 1000 amino acids) of repeated amino acid sequence of Glycine---X---Y

  
  

  X and Y are often proline and hydroxyproline.

  
  

  Glycine has the smallest R-group so doesn't take up much space allowing the helices to wound tightly together by many hydrogen bonds.

  
• Quaternary Structure of Collagen

  •Collagen is a fibrous protein found in the flesh and connective tissue.

  
  

  •Most abundant protein in mammals.

  
  

  •Found mostly in tough tissues like skin, nails, bones, tendons, ligaments and cartilage.

  
  

  •Has great tensile strength and elasticity. Serves a structural purpose.

  
  

  •Made up of 3 identical polypeptide strands of alpha chains, forming a triple helix
• Quaternary Structure of Haemoglobin

  •Haemoglobin is a globular protein found in red blood cells giving its red colour.

  
  

  •Made up of 4 polypeptide chains (globular subunits):

  - 2 alpha chains & 2 beta chains

  
  

  •Haem (heme) group found at centre of each chain. Made of iron (Fe2+) and forms a temporary bond with oxygen.

  
  

  •Serves a transport function of oxygen in blood

  
• Globular proteins VS Fibrous proteins

  Globular proteins are folded into a compact spherical shape. E.g. haemoglobin, enzymes

  These proteins are water soluble

  
  

  Fibrous proteins have elongated structures with polypeptide chains arranged as long strands.

  E.g. collagen, keratin.

  
• Tertiary structure of protein

  Bonds that stabilize protein:

  1. Hydrogen bond between polar R groups.

  2. Ionic bonds between ionized R groups.

  3. Hydrophobic interactions between non-polar R groups.

  4. Disulphide bonds (covalent) between -SH groups.

  
• Secondary structure of protein

  
• Primary structure of protein

  
• Molecular Structure of Proteins Levels of Organization

  1. Primary Structure- Amino acid sequence of the polypeptide chain. Held together by peptide bonds. Also positioning of disulphide bonds.

  
  

  2. Secondary Structure- Polypeptide chains arranged to form alpha helix OR beta plated sheets. Defined by hydrogen bonds between peptide groups.

  
  

  3. Tertiary Structure- Three dimensional (3D) structure. Chains & sheets folded into compact globules. Hydrophobic interactions between chains. Can be either Globular or fibrous.

  
  

  4. Quaternary Structure-Large assembly of two or more protein molecules. Stabilized by non-covalent interactions and disulphide bonds.

  
• Amino acid groups- Alanine

  
• Amino acid groups- Glycine

  
• Forming a Peptide Bond between Two Amino Acids


  Peptide bond[C=O-NH]- forms between two amino acids linking the C of the carboxyl group of one amino acid with the N of the amine group of the other amino acid.

  Water is removed (condensation reaction)

  
• Structure of an Amino acid

  •Amino acids are water-soluble organic molecules. •They are the building blocks of proteins.

  •There are 20 essential amino acids.

  
  

  •Each amino acid contains a carboxyl group (COOH) and an amine group (NH2 ) attached to the central (alpha) carbon atom.

  
  

  R- residual groups (side chains) are variable and they determine the chemical properties of each amino acid.

  
• Importance of Phospholipid Bilayer

  •Provides a partially permeable barrier for cell separating contents of cell from its surroundings

  - Permeable to non-polar molecules

  - Impermeable to ions and large polar molecules

  
  

  •Promotes selective diffusion and active transport of materials

  •Gives cell membrane flexibility/fluidity

  
  

  •Home of integral membrane proteins (used in signaling/active transport)

  
• Phospholipid bilayer structure


  A double layer of phospholipids that makes up plasma and organelle membranes.

  
• The structure of the cell membrane is composed of phospholipids, cholesterol, proteins, and carbohydrates.
• Single layered phospholipid molecule

  Polar heads facing outwards in water, hydrophobic tails facing each other