Topic 4 [Biological Molecles]

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Two Types of Compounds:

:

- Contain carbon and hydrogen

- E.g carbohydrates, proteins, lipids, nucleic acids

:

- Do NOT contain carbon

- E.g water, mineral sals

:

> Contains Carbon, C; Hydrogen, H; Oxygen, O;

> The C:H:O ratio is 1:2:1

Types of Carbohydrates by order of complexity (Starting from the simplest):

(Simple Sugars)

- E.g Glucose, Fructose, Galactose

(Complex Sugars)

- E.g Maltose, Sucrose, Lactose

(Polymers)

- E.g Starch, Cellulose, Glycogen

:

Characteristics:

Example: (Glucose)

- Made out of six carbon atoms joined in a ring, twelve hydrogen atoms and six oxygen atoms

- Formula: C6H12O6

:

Two simple sugar molecules (Monosaccharides) joined together to form a complex sugar which is larger.

Characteristics:

Examples:

1. = Glucose + Fructose

> Found in fruits

2. = Glucose + Glucose

> Found in malt sugar

3. = Glucose + Galactose

> Found in milk

: (A polymer)

Many glucose molecules that act as a repeating unit and join together to form a very large molecule.

Characteristics:

Examples:

1.

> Used as a food storage in plants

2.

> Used to build plant cell walls

3.

> Used as a food storage in animals

:

> Contains Carbon, C; Hydrogen, H; Oxygen, O; Nitrogen, N; Sulphur, S (Only in some proteins);

> Made of long chains of smaller molecules () joined end to end.

> Each protein is made of amino acids in a precise order.

Long chains of amino acids and for three-dimensional shapes of proteins. This is determined by the specific sequence of amino acids. The different sequences of amino acids then lead to different shapes of protein molecules.

:

- Different shape of proteins leads to different active sites of different (To bind to different substrates)and binding sites of (To bind to pathogens).

:

- Contains Carbon, C; Hydrogen, H; Oxygen, O;

Characteristics:

> : Solid at room temperature

> : Liquid at

Fats and Oils:

- A fat molecule is made of four smaller molecules joined together:

1.

2. Three molecules of

: (A monomer)

Two Types:

- Always present in nucleus, within genes and chromosomes

- Contains genetic information

- Inside cytoplasm, particularly in ribosomes

- Reads the information from DNA and assembles amino acids into proteins

:

- Contains genetic information inherited from parents

:

1. Made of , each with a series of .

2. The on the two strands are held together by .

3. The twist together into a spiral called the . The structure makes DNA more stable.

4. There are four kinds of bases: A (Adenine), C (Cytosine), G (Guanine), T (Thymine). [There is no need to memorise the names, just remember ACTG]

5. Base A always pairs up with Base T. Base C always pairs up with Base G.

:

- Almost 70% of the body is made up of water (Cytoplasm, blood, tissue fluid etc).

- Contains Hydrogen, H; Oxygen, O;

- Water is NOT an organic compound.

:

- A solution of many different substances in water.

The spaces between our cells are also filled with .

:

Water dissolves most substances needed for , , and .

(Blood, as blood is made out of plasma and plasma is water)

Dissolved substances can be transported around the body.

Water is needed to dissolve and in the alimentary canal, where digestion takes place.

Kidneys remove the waste product, , from the body. Urea is dissolved in water, forming .

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Tests:

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- To test for the presence of reducing sugars (e.g glucose)

Procedure:

1. X amount of Benedict's reagent is added to X amount of the solution that you want to test (Both have equal volumes).

2. Mixture is in a boiling water bath for 2-3 minutes. The optimum temperature for Benedict's reagent is around 60-80ºC.

3. Positive result is an orange/brick-red colour. (Note that brick-red symbolises a higher concentration of reducing sugar). The Benedict's reagent changes from blue, to green, to yellow, to orange, to brick-red.

4. Negative result is when the Benedict's reagent stays the same colour (Blue).

**Note: Iodine solution is actually , and it is safer to write Potassium Iodide rather than Iodine's solution.**

- To test for the presence of starch.

Procedures:

1. Add a few drops of Iodine solution.

2. Gently shake the mixture.

3. Positive result is a deep blue-black colour.

4. Negative result is when the solution stays the same colour (Orange-brown).

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- To test for the presence of proteins.

Procedure:

1. Add a few drops of Biuret reagent.

2. Gently shake the mixture.

3. Positive result is when a mauve/purple colour is formed.

4. Negative result is when the mixture stays the same colour (Blue).

**The Biuret test is never heated as high temperature denatures/changes the shape of proteins.**

(2,6-Dichlorophenolindophenol)

- To test for the presence of vitamin C.

Procedure:

1. X amount of DCPIP reagent is added to X amount of the solution that you want to test (Both have equal volumes).

2. Positive result is when the solution turns colourless.

3. Negative result is when the solution stays the same colour (Blue).

A replacement test for DCPIP could be starch + iodine. The colour change (If vitamin C is present) would be from brown, to dark blue, to colourless.

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- To test for lipids

Procedure:

1. Add ethanol to the solution that you want to test.

2. Gently shake the mixture, then pour it into a test tube filled with an equal volume of distilled water.

3. Positive result is a milky-white emulsion.

Explanation:

Lipids are insoluble in water, but are soluble in ethanol. When ethanol is added to the solution, the lipids dissolve to form a colourless solution. However, when the mixture is added to water, a milky-white emulsion forms. This is because ethanol loves water than it loves lipids, so it binds to water. The lipids then have nothing to bind to, and revert back to being insoluble, therefore a milky-white emulsion occurs.

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