Chapter 3 Biological Molecules

• Explain the structure of water

  Water is polar. This is because it has two hydrogen atoms covalently bonded to one oxygen atom. The oxygen is more electronegative than the hydrogen atoms therefore it has a slightly negative charge while the oxygen atoms have a slightly positive charge.

  Because of the partial dipole water is able to form hydrogen bonds between the slightly negatively charged oxygen atom and the slightly positively charged hydrogen atom.

  
• What are the properties of water?

  -Solvent

  -Transport medium (eg, glucose)

  -High specific heat capacity

  -Hugh latent heat of vaporisation

  -Ice is less dense than water
• Why does water have a High specific heat capacity?


  The hydrogen bonds between the water molecules can absorb a lot of energy. Therefore, water does not experience rapid temperature changes as a lot of energy is needed for it to heat up.

  This makes water a good habitat.
• Why does water have a High latent heat of evaporation?

  A lot of energy is required to break the hydrogen bonds between the water molecules, therefore a lot of energy is used up when water evaporates.

  Water provides a cooling effect for mammals as when sweat evaporates, it cools the surface of the skin.
• Why is water cohesive?

  The polarity of water forms hydrogen bonds between neighbouring molecules of water. This creates a continuous column of water allowing it to transport substances.
• Why is water a good solvent?

  The polarity of water causes the slightly negatively charged oxygen atom to be attracted to the positive ions and the slightly positively charged hydrogen atom to be attracted to the negative ions. This dissolves the ions as they become surrounded by the water molecules.
• Why is ice less dense than water?

  As a solid, the water molecules are further apart and form an open lattice structure which allows ice to float.

  This is useful because ice is able to form an insulating layer over the top of the water, so the water below does not freeze. This maintain habitats for organisms.
• Draw the alpha glucose molecule

  Alpha glucose

  
• Draw the Beta Glucose molecule

  Beta glucose

  
• Draw the structure of ribose

  Ribose

  
• What type of monosaccharide is glucose?

  Hexose monosaccharide
• What type of monosaccharide is ribose?

  Pentose monosaccharide
• What elements are carbohydrates composed of?

  Carbon, hydrogen and oxygen.
• How is a disaccharide formed?

  When two monosaccharides join together via glycosidic bonds. During a condensation reaction, the hydrogen atom of one monosaccharide bonds to the hydroxyl group (-OH) on another forming a 1,4 glycosidic bond and releasing a molecule of water in the process.
• What is a condensation reaction?


  When two molecules join to form a larger molecule whilst also releasing water in the process.
• What is hydrolysis?


  Breaking down a large molecule into smaller molecules through the addition of water.
• What monosaccharides is the disaccharide lactose made from?

  Galactose and Glucose
• What monosaccharides is the disaccharide Sucrose made from?

  Glucose and Fructose
• What monosaccharides is the disaccharide maltose made from?

  Glucose and glucose
• What is a disaccharide?


  When two monosaccharides join together by glycosidic bonds.
• What is a polysaccharide?

  When more than two monosaccharides join together by glycosidic bonds.
• What are monosaccharides? 


  Monomers which are used as a primary energy source for fuelling cellular metabolism.
• Explain the structure of starch

  Starch is composed of two polysaccharides of alpha glucose molecules known as amylose and amylopectin.
• Explain the structure of amylose

  Made up of long unbranched chains of alpha glucose molecules joined together by 1-4 glycosidic bonds. Coils are induced by the glycosidic bonds.
• Explain the structure of amylopectin

  Made up of long, branched chains of alpha glucose molecules joined together by 1-6 glycosidic bonds every 23-30 glucose units with the rest is connected by 1-4 glycosidic bonds.
• Why is amylopectins structure useful?

  Because it means glucose can be released quickly.
• Why is amyloses structure useful?

  Because the coils make the structure compact, meaning it is useful for storage as more are able to pack together into small spaces.
• What is the function of starch?

  Plants store excess glucose as starch as an energy storage molecule.
• Why is starch good for storage?

  Because starch is insoluble in water, so water is unable to enter the cells by osmosis.
• What is the structure of Glycogen?

  Large insoluble molecule composed of highly branched chains of alpha glucose molecules
• What is the function of Glycogen?

  Energy storage molecule in animals, where excess glucose is stored as glycogen.
• Why is Glycogens structure useful?

  Branches mean that the stored glucose can be released quickly. It is also compact allowing more to be stored.
• Explain the structure of Cellulone

  A large insoluble molecule composed of beta glucose 1-4 glycosidic bonds in straight chains. The cellulose chains are held together by hydrogen bonds that form strong fibres known as microfibrils.
• What is the function of cellulose?

  Provides structural support for plant cells and is freely permeable to solutes and solvents.
• Why is Celluloses structure useful?

  The strong microfibrils allows cellulose to provide the structural support.
• Why is glucoses structure useful?

  Soluble so it can be easily transported
• What are the three important properties of starch and glycogen?

  Compact

  Free ends allow glucose to be added or removed easily

  Insoluble
• Explain the structure of a triglyceride


  Three fatty acids attached to a glycerol molecule by an ester bond.
• What are the fatty acid tails composed of?

  Hydrocarbons which makes the tails hydrophobic and insoluble in water.
• What is the basic structure of a fatty acid?

  Fatty acid