Biological Molecules


Biological Molecules

Carbohydrates=used to store and supply energy and can be structured

Proteins=used for transport and structure also, basic components of all hormones, enzymes, antibodies, haemoglobin, ribosomers and more.

Lipids=parts of cell membrane, insulator and minor energy supplu.

Water= important in the formation of many molecules and also metabolic reactions

Nucleic acids = made up of nucletides. These are DNA and RNA

Enzymes=made of proteins they are biological catalyst

All these molecules (apart from water) are carbon based

Carbon - small molecule -forms single/double covalent bonds 

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Types of Bonds

Covalent= strong bonds formed be sharing electrons(carbon forms 4 covalent bonds)

Ionic=occurs between two oppositely charged ions. Ions are formed by the loss or gaoin of electrons.

Hydrogen= form where slightly positive charged part of a molecule meets a slightly charged part of another molecule. The individual bonds are weak but one molecule may had 1000's of H-bonds within it --> can stabilise a large molecule.

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carbohydrates (monosaccharides)

BM found n living organisms.


  • Found in both lving things and non-lingng situations e.g. water and mineral ions


  • Only produce by living things. Contains two or more carbon atoms e.g. carbohydrates, lipids,protein

BM made up of long chain. Carbon-carbon backbone. Because carbon bonds easily with other crabon.

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Properties of monosaccharides

Properties of monosaccharided:

  • simple sugars
  • small molecules
  • low melting point
  • sweet
  • soluble
  • crystalline form

General formula (CH2O)n              n=any number

  • if n=3, troise
  • if n=5, pentose
  • if n=6, hexose
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Isomers: molecules that have the same molecular formula, but different molecular structure

The condensation reaction joins monosaccharides together.

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Some examples:

  • glucose joined to glucose forms maltose
  • glucose joined to fructose forms sucrose

Sucrose is the form used to transport sugars through plants and as an artificial sweetner.

Maltose is the two glucos molecule produced when amylase breaks down starch


Is                                                                                    reducing sugars gain electrons. That's

Loss                                                                               why the Benedict's solution changes colour

Reduction          = OILRIG



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Benedict's Test

The benedict's test shows if a reducing sugar is present and the concentration. It changes colour:

  • No colour change no reducing sugar
  • green there is a very low concentration of reducing sugar
  • yellow there is a low concentration of reducing sugar
  • orange there is a medium concentration of reducing sugar
  • brick red there is a hight concentration of reducing sugar
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Polysaccharides are polymers containing many monosaccharides. They are linked by glycosidic bonds. They are formed by condensation reaction.

Examples: starch and cellulose (in plants) and glycogen (in animals)

Very large molecule, insoluble and used for storage

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Test for starch

Starch easily detectable as changes the colour of the iodine solution from yellow to blue-black. Test carried out at room temp.  

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  • Has a-helical structure (very compact)
  • Two types of starch - Amlose (helix structure) and amylopection (highly branched chains)

Starch stored as starch grains in organele called plastids

Plastids can be green (chloroplasts) or colourless (in potatoes)

Starch is produced from glucos made during photosynthis ad broken down during repiration to provide energy.  

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  • polysaccaride
  • main part of cell wall
  • very strong
  • consists of long chains of beta glucose molecule joined by beta 1-4 glycosidic bonds.
  • chains form rope-like microfbrils which are layered to form a network
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