Biological Molecules



4 main types of Biological Macromolecules:

  • Polysaccharides (carbohydrate) - polymer
  • Protein - polymer
  • Nucleic Acids (DNA/RNA) - polymer
  • Lipids (fats/oils) - not a polymer

Polymer = a long-chained molecule that consists of many smaller & similar subunits known as monomers

Condensation Reaction = a creation of a bond which makes a water molecule

Hydrolysis = a breaking down of a bond using a water molecule

- Monomers are usually joined together and broken down through hydrolysis and condensation reactions

-During condensation and hydrolysis, there is always 1 less water molecule than monomer in the reaction.

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3 main types of carbohydrates:

  • Monosaccharides ('mono' = 1)
  • Disaccharides ('di' = 2)
  • Polysaccharides ('poly' = many)

Monosaccharides are the simplest carbohydrate:

  • they usually have the molecular formula CH20
  • Can be shown using skeletal diagrams (carbon atom is where 2/more lines meet)

Isomer = Different molecules with the same molecular formula (i.e C6H1206 = glucose, fructose, galactose)

- α-glucose and β-glucose are both isomers of each other. The difference is the H and OH bonds on C-1 is switched

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Glycosidic Bond = then bond between 2 monosaccharides to form a disaccharide through a condensation reaction

Making disaccharides:

  • α-glucose + α-glucose = Maltose + water
  • α-glucose + galactose = Lactose + water
  • α-glucose + fructose = sucrose + water

- When writing the molecular formula of these disaccharides, you must consider that water is lost - i.e Maltose = C12H22O11 due to the loss of water in the condensation reaction

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Polysaccharide = a polymer of many monosaccharides which are linked together

Glucose can be bonded togther to make a polysaccharide. It allows energy to be transported to cells around the body. Its properties are:

  • Water soluble = travels easily around the body in the blood
  • Small = enters + exits cells easily
  • Chemically reactive = broken down to provide energy when needed

- It can be made into a polymer if needed - stored as glycogen or starch

Starch = energy storage

Glycogen = energy storage

Cellulose = structure 

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Structure of Starch:

  • Helical chains of α-glucose monomers - compact so more energy can be stored in the cell
  • It is a large molecule - it cant leave the cell through the membrane
  • Stored in the cloroplasts as insoluble starch granules - doesn't affect water potential
  • Can be hydrolysed into α-glucose for respiration

Starch can come in 2 forms:

  • Amylose = unbranced + helical
  • Amylopectin = branched + helical

-Branches mean more ends for the enzymes to hydrolise the glucose from. The more branches, the faster the rate of hydrolysis is.

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Structure of glycogen:

  • Consists entirely of α-glucose monomers
  • Helical & insoluble
  • More branches but shorter chains = hydrolysed faster into α-glucose

The quicker rate of hydrolysis benefits animals as they move so they need more energy, compared to plants. The animals muscles and nervous system need more energy at a faster rate of respiration.

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Structure of Cellulose:

  • Polymers of β-glucose
  • Long, straight and unbranched chains - lots line up in parallel to form microfibres
  • Strong - lots of hydrogen bonding between the microfibres. Each hydrogen bond is weak on its own but m,any together give the polymers strength.

In β-glucose, the OH in C-1 is flipped; therefore for glycosidic bonds to form every 2nd OH moleclue has to flip upside-down. This creates an alternating up-down pattern. 

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Important Lipids:

  • Triglycerides (fats & oils)
  • Phoshoplipids
  • Chloesterol

-Lipids are a major part od macromolecules however they aren't a polymer. The are hydrophobic.

Hydrophobic = don't mix with water

Hydrophillic = mix well with water

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Functions of Triglycerides:

  • Energy storage - densest energy storage molecule
  • Insulation - reduce loss of body heat as they're poor conductors
  • Protection - fat stored around delicate organs

Structure of Triglycerides:

  • Made up of 3 fatty acids and 1 glycerol, with ester bonds between the fatty acid and glycerol
  • Insoluble as they're hydrophobic - no affect on water potential/osmosis
  • Fatty acid tails are energy rich - each C-C and C-H bonds contain energy

alcohol + carboxyl group -> ester group + water

-Animal fats = saturated and solid at room temperature. Saturated fatty acids are packed closely together as they dont have kinks, compared to unsaturated fatty acids.

-Plant/fish fats = usually unsaturated and liquid at room temperature

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Amino Acids

Each amino acids include:

  • an amine group - NH2
  • a carboxyl group - COOH
  • one of 20 side chains - R-Group
  • all attatched to a central Carbon atom along with a Hydrogen atom.

-Amino acids differ only by their R-Group and are all joined together through condensation reactions.

Peptide Bond = the bonds between 2 amino acids

Dipeptide = the molecule formed between 2 amino acids joining together

Polypeptide = when many amino acids are bonded together through peptide bonds

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Structure of Proteins:

  • Polymers - made of many monomers called amino acids.
  • 20 different amino acids which would be included in the polymer - creates a huge variety of combinations (20^n) 

Levels of stucture in proteins:

  • Primary - unique sequence of amino acids forming a polypeptide - held together through Hydrogen bonds. Different proteins have different primary structures
  • Secondary - folding of the polypeptide chain into 2 structures (alpha helix & beta pleated sheet) - held together through hydrogen bonds
  • Tertiary - folding of the polypeptide into its overall 3D shape - held together by hydrogen bonds, ionic bonds and disulfide bridges
  • Quaternary - coming together of 2 more more polypeptide chains - if the protein isn't made up of more than 1, then this process doesn't occur

Disulfide Bridge = 2 sulfur containing R-groups bond together

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