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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
, 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
2
, 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
3
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