AQA A level Biology Topic 1 - Biological molecules notes (A* achieved)

AQA AS Biology notes Topic 1 – Biological molecules
Topic 1 – Biological molecules
Table of Content

1.1 Monomers and polymers..............................................................2
1.2 Carbohydrates..............................................................................2
1.3 Lipids............................................................................................5
1.4 Proteins structures.......................................................................6
1.4.1 General properties of proteins................................................................................................................................................6
1.4.2 Many proteins are enzymes....................................................................................................................................................7


1.5 Nucleic acids are important information-carrying molecules.......12
1.5.1 Structure of DNA and RNA....................................................................................................................................................13
1.5.2 DNA replication.....................................................................................................................................................................13


1.6 ATP.............................................................................................15
1.7 Water.........................................................................................17
1.8 Inorganic ions.............................................................................18




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, AQA AS Biology notes Topic 1 – Biological molecules

1.1 Monomers and polymers
Monomers: small single repeating unit in a polymer
Polymers: Molecule made up of many monomers joined together
Condensation reaction: Loss of a water molecule to form a bond that links subunits between two
molecules when a new monomer is attached to a polymer eg polypeptide -> amino acids
Hydrolysis reaction: Addition of water molecule to break a bond that links subunits between two
molecules


1.2 Carbohydrates
Saccharides: A sugar, which is a basic monomer unit in carbohydrate

Monosaccharides
 A single, sweet-tasting and soluble monomer
 Eg glucose, fructose, galactose
General formula of monosaccharides: (CH2O)n

Isomers: same molecular formula but differently atom arrangement
Isomers of glucose:




Condensation reaction Hydrolysis reaction
 When monosaccharides join, condensation
reaction occurs where a molecule of water is
removed and form glycosidic bond between 2
hydroxyl groups that produces maltose




Disaccharides
 Compounds made of 2 monosaccharides that are joined together by a glycosidic bond
 General formula of disaccharides: C12H22O11
 glucose + glucose = maltose + water (Go grandma)
 glucose + fructose = sucrose + water (Go father son)
 glucose + galactose = lactose + water (Go good luck)


Polysaccharides
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, AQA AS Biology notes Topic 1 – Biological molecules
 Polymers formed by joining many monosaccharides together by glycosidic bonds by condensation
reaction
 Eg starch, cellulose, glycogen
Starch
Function: energy storage in plant cells
Structure
 Polymers made of helical α-glucose joined by
glycosidic bonds by condensation reaction
 Contain carbon, hydrogen & oxygen
 Glucoses same way up (OH groups are pointing
inwards)
 No H-bonds between molecules, no microfibres/fibrils




Unbranched chains (amylose)
 Wound into a tight coil – makes molecules compact – good for storage


Branched chains (amylopectin)
 Has many ends which can be hydrolysed simultaneously by enzymes to release glucose monomers
rapidly

How is the structure of starch is related to its function?
1. Insoluble – doesn’t affect water potential so no osmotic effect
2. Large – doesn’t’ diffuse out of cells / can't leave cell
3. Helical - compact – lots can be stored in small space
4. Branched form – can be rapidly hydrolysed into glucose that is easily transported for respiration to
provide energy

Cellulose
Function: provide strength & structural support to plant cell walls
Structure
 Polymers made of beta glucose joined by glycosidic
bonds by condensation reaction
 Contain carbon, hydrogen, oxygen
 Position of hydrogen and hydroxyl groups on carbon
atom 1 inverted
 Made of beta glucose – form long, straight, parallel,
unbranched chain
 Parallel strands are cross-linked by
many hydrogen bond to form
microfibrils – provide strength &
rigidity to cell wall

How is the structure of cellulose is related to its function?
1. Made of beta glucose joined by glycosidic bonds by condensation reaction – form long, straight,
parallel, unbranched chain
2. Parallel strands are cross-linked by many hydrogen bond that are difficult to break to form
microfibrils – provide strength & rigidity to cell wall

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