3: Biological molecules

• The role of water

  • reactant for chemical reactions such as hydrolysis
  • key component for cytoplasm in cells, tissue fluids, blood and digestive juices.
  • helps to regulate body temperature as a component of sweat
  • helps to transport dissolved substances around the body
• examples on the role of water

  • digested food products from the small intestine to other parts of the body
  • removal of waste products from body cells to excretory organs role of water
  • reactant for chemical reactions, such as photosynthesis
  • 6CO2 + 6H20 -> (light) C6H1206 + 6O2
  • solvent for many chemical reactions (photosynthesis)
• examples of the role of water 2

  • helps to transport dissolved mineral salts from the root to other parts of the plant through the Xylem vessel
  • helps to transport food substances from the leaves to other parts of the plant through the Phloem vessel
  • Keep plant cells turgid and firm
• Food

  • contains nutrients known as biological molecules
  • such as carbohydrates , fats (lipids) and proteins
• role of food

  • provide energy for vital activities in living organisms
  • supply raw materials to make protoplasm
• Carbohydrates

  • general formula : CnH2m0m
  • ratio of hydrogen atoms to oxygen atoms 2:1
  • Carbohydrates are organic molecules made up of carbon, hydrogen and oxygen
• Types of Carbohydrates

  • monosaccharides or simple sugars. examples: glucose , fructose , galactose
  • disaccharides or double sugars. examples: Maltose, sucrose ,lactose
  • polysaccharides or complex carbohydrates. examples: starch , cellulose , glycogen
• Monosaccharides

  • simplest form of sugars (cannot be further digested)
  • small molecules (pass through the cell membrane and absorbed into cells
  • soluble in water (osmotically active)
  • different arrangement of atoms give sugar molecules different biological chemical properties
• Disaccharides

  • consists of two molecules of monosaccharides, bonded together via a condensation reaction
  • * 1) Glucose + Glucose = Maltose + water
  • *2) Glucose + fructose = sucrose + water
  • *3) Glucose + galactose = Lactose + water
  • Can be split into the two monosacharides using enzymes via hydrolysis
• Polysaccharides

  • complex carbohydrates . made from many monosaccharides molecules joined together
  • they are also storage molecules
  • Starch and Glycogen (poly) are effective storage molecules of glucose (mono) in plant cells and animal cells
• Starch and Glycogen (poly) are effective storage molecules of glucose (mono) in plant cells and animal cells. WHY?

  • insoluble in water, and hence dont change the water potential of cells.
  • Large molecules which cannot diffuse through the cell membranes. and hence will not be lost from the cells
  • can be hydrolysed easily to glucose during tissue respiration and hence, provides an efficient supply of energy to cells.
  • Have compact shapes, therefore occupy less space than individual glucose molecules which make up a starch molecules or a glycogen molecule
• Polysaccharides (starch)

  • function - main form of storage of carbohydrates in plants
  • can be digested to glucose molecules to provide energy for cell activity
  • are found in storage organs of plants (eg. potato tubers)

  
• polysaccharides (Cellulose)

  • function - cellulose cell wall protects plant cells from bursting and damage
  • cannot be digested in our intestines , serves as dietary fibre to prevent constipation.
  • are found in cell walls of plant cells

  
• polysaccharides (Glycogen)

  • function - main form of storage of carbohydrates in mammals
  • can be digested to glucose molecules to provide energy for cells
  • found in the liver and muscles of mammals

  
• Function of carbohydrates

  • substate for respiration to release energy for cellular activities
  • to form supporting structures , such as cell walls in plants (Cellulose)
  • converted into other organic compounds such as amino acids
  • for the formation of nucleic acids (eg. DNA)
  • synthesise lubricants (eg. mucus)
  • synthesis nectar in some flowers of plants to attract insects.
• Fats

  • made up of carbon , hydrogen , oxygen
  • no general formula - the proportion of elements that make up fats are not fixed
  • Ratio of hydrogen atoms to oxygen atoms is higher than in carbohydrates
  • a fat molecule is made up of glycerol and fatty acid molecules in the ratio of 1:3

  
• function of fats

  • insulating material that prevents excessive heat loss in polar bear blubber ect.
  • reduce water loss from skin surface - sebaceous gland secrete
  • sebum (oily substance) to reduce rate of evaporation and heat loss from the skin
  • essential component of protoplasm, especially cell membranes
  • solvent for fat-soluble vitamins and hormones
  • source and storage molecules of energy
• RECAP

  other biological molecules that can be used as storage molecule in humans -> carbohydrates (Glycogen)

  *rather fats or carbohydrates as a storage molecule for energy?

  • ans: fats. fat molecules contains aprox 2 times the amount of calories per g (9 cal) as compared to a carbohydrate molecule (4 cal)
• Proteins

  • organic molecules made up of elements carbon , hydrogen , oxygen , nitrogen. may contain sulfur.
  • Each protein molecule / polypeptide chain is made of smaller basic units called amino acids
  • *an amino acid is made up of: an amino group, carboxylic acid group, side chain ( R group) , hydrogen atom
  • there are 20 different amino acids found in structures of proteins that differ because of different R groups (R side chain)

  
• Amino acids

  • are building blocks of protein
  • amino acids are linked together in a linear manner by peptide bonds that are formed via a condensation reaction to form a polypeptide
  • A protein is made up of one or more polypeptide chains folded together , and most proteins are folded into complex, three-dimensional shapes.

  
• protein function

  • used in the synthesis of new protoplasm
  • used for growth and repair of worn-out body cells
  • used in the synthesis of enzymes and hormones
  • used in the formation of antibodies to combat diseases
• Iodine Test - starch

  1. place 2cm^3 of food samples into the test tube
  2. add a few drops of iodine solution to test tube
  3. If yellowish-brown iodine solution changed into blue-black, Starch is present
  4. If the solution remained yellowish-brown, no starch is present
  5. (application using food) Use mortar and pestle to crush food.
  6. add iodine solution to crushed food directly
• Benedict's test - reducing sugar

  1. place 2cm^3 of food samples into the test tube
  2. place 2cm^3 of Benedict's solution
  3. shake, then place into boiling water bath 2-3 minutes
  4. Green precipitate -> trace amounts
  5. orange precipitate -> moderate amounts
  6. brick-red precipitate -> large amounts
  7. (application) place some of the crushed food into test tube. add 2.0cm^3 of water to dissolve any sugar and proteins. Decant the mixture into a new test tube and use it as the test solution.
• Ethanol Emulsion test - fat

  1. add 2cm^3 of ethanol to food sample in the test tube
  2. shake
  3. add 2cm^3 of water and shake
  4. A cloudy white emulsion is formed if fat is present
  5. (application) Crush food into pieces and transfer into a test tube. add 2cm^3 of ethanol and shake. allow the solid particles to settle and pour the solution into another test tube with 2cm^3 of water.
• Biuret test - proteins

  1. add 2cm^3 of whatever into test tube
  2. add biuret solution drop by drop, shake after every drop.
  3. shake well and rest for 5min
  4. the solution turns violet in color if protein is present.
  5. (application) place some of the crushed food into test tube. add 2.0cm^3 of water to dissolve any sugar and proteins. Decant the mixture into a new test tube and use it as the test solution.
• distilled water = denotated water

  egg white solution = albunim