Biological Molecules

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  • The monomers of carbohydrates
  • Trioses, pentoses and hexoses.
  • Sweet, soluble and crystalline.
  • Simple sugars with one 1 or chain of 3,5 or 6 carbon atoms. 
  • Examples are ribose, glucose and fructose.
  • The formula is Cn(H20)n
  • The are used for energy and biological building blocks.
  • If the OH at the first carbon is below, it is an alpha-glucose.
  • If the OH at the first carbon is above, it is a beta-glucose.


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  • Sugars with 2 rings of 6 carbon atoms, joined by a glycosidic bond.
  • Examples include sucrose, lactose and maltose.
  • Glucose+ glucose= maltose.
  • Glucose+ galactose=lactose.
  • Glucose+ fructose=,sucrose.
  • They are used to sweeten food.
  • Formed by the condensation of 2 monosaccharides, usually hexoses.
  • The reverse of condensation is hydrolisis (di/polysaccharide to monosaccharide).
  • These reactions are controlled by enzymes.
  • The bond formed in condensation is a glycosidic bond.
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  • Macromolecules with many rings of 6 carbon atoms joined by glycosidic bonds.
  • In a glucose there are lots of bonds that release enrgy in the form of ATP.
  • This breakdown is driven by shape-specific enzymes.
  • Only alpha- glucose can be broken down in respiration as only those enzymes are present.
  • Glucose monomers join through condensation and form glycosidic bonds.
  • Amylose molecules form compact, coiled springs due to the way they bond.
  • Large molecules like amylose are not soluble in water.
  • Iodine molecules can get stuck in the coils, meaning it turns yellow to black.


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Polysaccharides- continued:


  • Made from beta-glucose.
  • Long unbranched chains.
  • If present, Schulze's reagent will turn purple.
  • Found in cell walls in plants.
  • Its function is to support cells.


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Polysaccharides- continued:


  • Made from alpha glucose.
  • Amylose is made of long unbranched chains.
  • Amylopectin is made of long branched chains.
  • The branches form when one end of a chain joins to a glucose in another, forming a glycosidic bond.
  • When present, iodine turns from yellow to black.
  • Insoluble in water so does not affect the water potential of cells.
  • Found in the cytoplasm/starch grains in plant cells.
  • Used for energy storage.

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Polysaccharides- continues:


  • Made of alpha glucose.
  • Like starch, but shorter so more branched.
  • Branching means faster breakdown in respiration and more ends which enzymes can start hydrolyisis from.
  • Insoluble in water so does not affect the water potential of the cell. 
  • Reacts with Lugol's reagent to give a brown-blue color. 
  • Found in the muscles/ liver of animals.
  • Used as energy storage.


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  • Provides energy storage.
  • Provides insulation.
  • Found in the cell membrane.
  • Used for waterproofing in birds.
  • The most common type are triglyerides, which are commonly known as fats and oils.
  • Fats are solid at room temperature.
  • Oils are liquid at room temperature.


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  • Made of three fatty acids bonded to a glycerol molecule.
  • When a fatty acid combines with glycerol, it becomes a glyceride, so when all 3 fatty acids are added it becomes a triglyceride.
  • Fatty acids have long tails made of hydrocarbons.
  • Tails contain lots of chemical energy- lots of energy is released when they are broken down.
  • Because of these tails, lipids contain twice as much energy per gram as carbohydrates.
  • The tails are hydrophobic, so make lipids insoluble in water, meaning it doesnt cause water to enter the cell by osmosis.
  • The bundle together as inoluble droplets, with the hydrophobic ends facing inwards, shielded by the glycerol heads.
  • Glycerol is a type of alcohol.
  • They are organic molecules with a -COOH group attached to a hydrocarbon tail. 
  • Non- polar, insoluble in water, soluble in ether, chloroform and ethanol, and are hydrophobic.
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  • 2 fatty acids and a phosphate bonded to a glycerol.
  • One end is soluble in water becuase one of the three fatty acid molecules is replaced by a phosphate which is polar and can therefore dissolve in water.
  • The phosphate group is hydrophilic which makes the head hydrophilic, although the two tails are still hydrophobic.
  • Make up the bilayer in cell membranes.
  • Form a double layer with heads on the outside and tails on the inside.
  • The centre is hydrophobic so water-soluble products cant easily pass through it. It acts as a barrier to these kinds of substances.

Image result for phospholipid

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  • Cholesterol molecules help strengthen the cell membrane by interacting with the phospholipid bilayer.
  • The small size and flattened shape allows cholesterol to fit inbetween the phospholipid molecules in the membrane.
  • They bind to the hydrophobic tails of the phospholipids, causing them to pack more closely together.
  • This helps make the membrane less fluid and more rigid. 

Image result for cholesterolImage result for cholesterol

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  • Amino acids are monomers, proteins are polymers.
  • The monomers (amino acids) are all different.
  • There are around 20 amino acids.
  • Examples are structural proteins, carrier proteins and enzymes.
  • Proteins make antibodies.
  • They contain N, S, C, H and O.
  • Proteins are in muscles (protein fibres overlap as muscles shorten).

Image result for protein chemical structureImage result for amino acid structure

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  • Amino acids are monomers, proteins are polymers.
  • The monomers (amino acids) are all different.
  • There are around 20 amino acids.
  • Examples are structural proteins, carrier proteins and enzymes.
  • Proteins make antibodies.
  • They contain N, S, C, H and O.
  • Proteins are in muscles (protein fibres overlap as muscles shorten).

Image result for protein chemical structureImage result for amino acid structure

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Amino Acids:

  • A dipeptide is formed when 2 amino acids join.
  • A polypeptide is formed when more than two amino acids join together.
  • Proteins are made of one or more polypeptides.
  • All amino acids have the same general structure- a carboxyl group (-COOH) and an amino group (-NH2).
  • The difference between different amino acids in the variable R group.
  • Amino acids are linked by peptide bonds to form di/ polypeptides.
  • A dipeptide is formed by condensation.
  • The reverse reaction adds a water molecule to break the peptide bond and is called hydrolysis. (
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Primary Structure- The sequence of amino acids in a polypeptide chain.

Secondary Structure- Hydrogen bonds form between the amino acids in the chain. This makes it automatically coil into an alpha helix or fold into a beta pleated sheet.

Tertiary Strcuture- The coiled/ folded chain is often coiled/ folded further. More bonds form between different parts of the polypeptide chain. For proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure.

Quaternary Structure- How the polypeptide chains are assmebled if there are more than one. Image result for primary structure of a protein

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Primary Structure- Held together by peptide bonds between amino acids.

Secondary Strcuture- Held together by weak hydrogen bonds that form between nearby amino acids. These bonds create alpha helix chains or beta pleated sheets.

Tertiary Structure- Held together by a few different bonds:

  • Ionic interations- weak attractions between negative and positive charges on different parts of the molecule.
  • Disulphide bonds- whenever two molecules of the of the amino acid cysteine come close together, the sulphur atom in one cysteine bonds to the sulphur in the other, forming a disulphide bond.
  • Hydrophobic and hydrophilic attractions- when hydrophobic groups are close in the protein, they clump together. This means the hydrophilic groups are more likely to be pushed to the outside, affecting how the protein folds up.
  • Hydrogen bonds.

Quaternary Structure- this tends to be determined by the tertiary structure of the individual polypeptide chains being joined together, and can therfore be influenced by all above bonds.

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  • A fibrous protein that forms supportive tissues in animals, so it needs to be strong.
  • Fibrous proteins are tough and rope- shaped.
  • They tend to be found in connective tissues like tendons.
  • Made of three polypeptide chains that are coiled in a tight strong triple helix.
  • The chains are interlinked by strong covalent bonds.
  • Minerals can bind to the triple helix to increase its rigidity.

Image result for collagen structure

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  • Haemoglobin is a globular protein with an iron- containing haem group that binds to oxygen, carrying it around the body.
  • A globular protein is round and compact.
  • They are soluble, so are easily transported in fluids.
  • Its structure is curled up so that hydrophilic side chains are on the outside of the molecule and hydrophobic side chains face inwards.
  • This makes haemoglobin soluble in water, which makes it good for transport in the blood.

Image result for haemoglobin

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  • biological catalysts
  • proteins
  • suited to one specific reaction only
  • affected by PH
  • affected by temperature
  • affected by lack of metal ions (often found in vitamins)
  • able to lower the activation energy barrier of a reaction

Each active site has a particular shape

Each substrate is designed for an enzyme

They fit together like jigsaw pieces

enzymes (

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