Ch 5: Food and Humans 🔋

• Functions of food:

  • provides energy for supporting daily activities
  • keeps us warm
  • provides raw materials for growth and repair of body tissues
• Seven types of food substances: carbohydrates, lipids, proteins, minerals, vitamins, dietary fiber, water
• Carbohydrates can be classified into three groups: monosaccharides, disaccharides and polysaccharides.
• Monosaccharides are the simplest form of carbohydrates.

  Disaccharides consist of two monosaccharides joined together.

  Polysaccharides consist of many monosaccharides joined together.
• Disaccharides and polysaccharides are formed by joining monosaccharide molecules in a reaction called condensation. Condensation is a chemical reaction in which two molecules combine with a loss of a water molecule.

  Disaccharides and polysaccharides are broken down into monosaccharides in a reaction called hydrolysis. During hydrolysis, a water molecule is added.

  
• Glucose, fructose and galactose are monosaccharides.

  Maltose, sucrose and lactose are disaccharides.

  Maltose is composed of two glucose molecules, sucrose is composed of a glucose and a fructose molecule, and lactose is composed of a glucose and a galactose molecule.

  Monosaccharides and disaccharides are called sugars. They taste sweet and are soluble in water. All monosaccharides and disaccharides except sucrose are reducing sugars. They can be detected using Benedict's test.
• Glucose and fructose can be found in fruits and honey.

  Maltose can be found in germinating barley.

  Galactose and lactose can be found in milk and dairy products.

  Sucrose can be found in sugar products.
• Polysaccharides are very large molecules. They do not taste sweet and are insoluble in water. Examples of polysaccharides include starch, glycogen and cellulose. They are all made of glucose molecules.

  Starch is the storage form of carbohydrates in plants.

  Glycogen is the storage form of carbohydrates in animals. (It is stored in the liver and muscles.)

  Cellulose is a major component of plant cell walls.
• Functions of carbohydrates:

  • As a main energy source
  • Monosaccharides are broken down to release energy (for example, glucose in respiration)
  • Disaccharides and starch are broken down into monosaccharides to release energy.
  • As energy reserves
  • Excess carbohydrates are converted into glycogen in the liver or muscles and stored as energy reserves. Glycogen is broken down into glucose to release energy when needed.
  • As a source of dietary fibre
  • Cellulose cannot be digested in our body.
• What are the tests used for carbohydrates?

  Benedict's test and glucose test paper
• How is glucose tested using glucose test paper?

  By dipping the test end of the glucose test paper into the food sample and observing color change
• What indicates the presence of glucose when using glucose test paper?


  A change in the color of the test end
• What is the procedure for testing reducing sugars using Benedict's test?


  Add an equal volume of Benedict's solution to the food sample and boil for 5 minutes
• What does a brick-red precipitate indicate in Benedict's test?


  The presence of reducing sugars
• What happens if excess Benedict's solution is added during the test for reducing sugars?


  The amount of precipitate formed is proportional to the amount of reducing sugars present
• How is starch tested using the iodine test?


  Add iodine solution to the food sample and observe the color change
• What color change indicates the presence of starch in the iodine test?


  From brown to blue-black
• What are the steps involved in the Benedict's test for reducing sugars?


  1. Add an equal volume of Benedict's solution to the food sample.
  2. Boil the mixture in a water bath for 5 minutes.
  3. Observe for a brick-red precipitate to indicate the presence of reducing sugars.
• What are the steps involved in the iodine test for starch?


  1. Add iodine solution to the food sample.
  2. Observe for a color change from brown to blue-black to indicate the presence of starch.
• Monosaccharides and disaccharides (except sucrose) lose electrons readily to other substances. They are called reducing sugars because they cause other substances to be reduced.
• Triglycerides are the commonest type of lipids. They are formed from one glycerol and three fatty acids by condensation. They can be broken down by hydrolysis.

  
• Triglycerides that are solid at room temperature are commonly called fats. They mainly come from animals.

  Triglycerides that are liquid at room temperature are commonly called oils. They mainly come from plants.
• What is one of the primary functions of lipids in the body?


  As energy reserves
• Where are lipids stored in the body?


  In adipose tissues
• What are the two locations where adipose tissues can be found?


  Under the skin as subcutaneous fat and around internal organs
• How can lipids be utilized when energy is needed?


  They can be broken down to provide energy
• What role does fat stored in adipose tissues play for internal organs?


  It acts as a shock absorber to protect the internal organs
• What is another function of subcutaneous fat?


  It acts as a heat insulator
• How does subcutaneous fat help the body?


  It reduces heat loss from the body
• Which vitamins are lipid-soluble and associated with lipids?


  Vitamins A, D, E, and K
• What is one of the roles of lipids in relation to vitamins?


  They assist in the absorption, transport, and storage of lipid-soluble vitamins
• What is one of the functions of lipids in hormone production?


  They are involved in producing hormones
• What structural role do lipids play in cell membranes?


  They are a component of cell membranes as phospholipids
• Functions of lipids

  • As energy reserves
  • As a shock absorber
  • As a heat insulator
  • Absorption, transport and storage of lipid-soluble vitamins
  • Component of cell membrane (phospholipids)
  • Production of hormones
• Test for lipids: Grease spot test

  A translucent spot remains on the filter paper that dissolves when immersed in an organic solvent.
• Amino acids are the basic building blocks of proteins. Each amino acid has an amino group, a carboxyl group, and a side chain. There are many different amino acids and each has a different side chain.

  Two amino acids can join together into a dipeptide by condensation. The link between the two amino acids is called a peptide bond. A dipeptide can be broken down by hydrolysis.
• What is formed when amino acids are added to a dipeptide?


  A polypeptide
• How many polypeptides does haemoglobin consist of?


  Four polypeptides
• What determines the final shape of a protein?


  The amino acid sequences of a polypeptide
• What is the relationship between amino acid sequences and protein function?


  • Unique amino acid sequences lead to unique protein shapes
  • Unique shapes allow proteins to perform different functions