Biological Molecules

Monomers and Polymers

 * Condensation reactions
 * Join monomers together into larger molecules, releasing water
 * Monosaccharides → Disaccharides → Polysaccharides: glycosidic bonds formed
 * Amino acids → Polypeptides: peptide bond
 * Glycerol + fatty acids → Triglycerides: ester bonds

Carbohydrates

 * Made up of monosaccharides (monomers of carbohydrates)
 * Common monosaccharides - glucose, galactose, fructose
 * Disaccharides
 * Formed by condensation reaction of 2 monosaccharides
 * Maltose → Glucose + Glucose
 * Sucrose → Glucose + Fructose
 * Lactose → Glucose + Galactose



Glucose
Two isomers:


 * α-glucose: Carbon atom 1 has hydrogen pointing up, and hydroxyl group pointing down
 * β-glucose: Carbon atom 1 has hydrogen and hydroxyl groups flipped

The acronyms 'ADDUD' and 'BUDUD' can be used to remember which way the -OH groups point. ADDUD - α-glucose, down, down, up, down. BUDUD - β-glucose, up, down, up down.

Polysaccharides

 * Formed by condensation of many monosaccharides
 * Glycogen → condensation of α-glucose
 * Starch → condensation of α-glucose
 * Cellulose → condensation of β-glucose
 * Structure of Glycogen
 * Energy store in animals
 * Highly branched structure, coiled – so compact
 * Unable to diffuse out of cells, so stays where it is needed until energy is required


 * Structure of Cellulose
 * Unbranched, linear chains
 * Used in plant cell wall – provides rigidity to plants219 Three Important Polysaccharides-01.jpg
 * Fibres group together to form microfibrils – hydrogen bonds (strength in large numbers)
 * Structure of Starch
 * Forms granules – unable to move out of cells it is formed in – doesn’t have to diffuse far, so reasonably quick access to energy
 * Branched chains, coiled – compact

Lipids

 * Triglycerides
 * Glycerol + 3 fatty acid tails
 * Form oils, waxes, fats
 * Hydrophobic – do not mix with water




 * Phospholipids
 * Form the cell wall – phospholipid bilayer
 * Phosphate + glycerol + 2 fatty acid tails
 * Polar molecules – phosphate head is hydrophilic (water loving) // fatty acid tails are hydrophobic (water hating)




 * Fatty acids
 * Saturated – all carbon atoms have single bonds – with the maximum number of hydrogens possible
 * Unsaturated
 * Monounsaturated – 1 pair of carbon atoms have a double bond; removes 2 hydrogens, causes a kink in the chain
 * Polyunsaturated – More than 1 pair of carbon atoms have a double bond; removes more than 2 hydrogens, causes many kinks in the chain
 * Have less energy content than unsaturated fatty acids



Proteins

 * Made up of amino acids




 * Amine group: NH2 Carboxyl group: COOH
 * R group – the side chain causing the amino acid to be unique
 * Dipeptides – condensation of two amino acids
 * Polypeptides – condensation of many amino acids


 * Proteins can be made up of multiple polypeptide chains


 * Primary structure: order of amino acids – polypeptide chain


 * Secondary structure: α-helix or β-pleated sheet – formed by hydrogen bonds between R-groups
 * Tertiary structure: further coiling of α-helix / β-pleated sheet – more compact
 * Quaternary structure: linking together of multiple tertiary structure polypeptide chains
 * Hydrogen bonds – hold together the polypeptide chains in quaternary structure
 * Ionic bonds – join together amino acids into polypeptide chain
 * Disulphide bridges – strong bonds between R-groups holding α-helix / β-pleated sheet togetherMain protein structure levels en.svg

Enzymes

 * Lower the activation energy of the reaction it catalyses
 * Lock and Key model of enzyme action
 * Substrate fits perfectly in the enzyme
 * No explanation as to how the enzyme catalyses the reaction
 * Induced Fit model of enzyme action
 * Enzyme active site changes shape slightly to allow the substrate to bind to it
 * Active site puts stresses on the substrate, causing bonds to brake
 * Reaction is catalysed, causing the product(s) to be released
 * Enzymes are only able to have 1 substrate fit it – amylase only catalyses starch hydrolysis


 * Enzyme concentration – a higher concentration will cause the substrate to be broken down faster. The rate of reaction will plateau as the substrate concentration decreases, as collisions are less likely to occur
 * Substrate concentration – higher concentration of substrate means that the enzymes are more likely to collide with substrate. Increase rate of reaction, to a point. Once all of the enzyme has substrate in active site, reaction cannot continue furtherEnzyme inhibition.png
 * Inhibitor concentration – higher concentration of competitive inhibitors will cause reaction to slow, as more competitive inhibitor blocks active sites Non-competitive inhibitors will have an impact, however it is not based on concentration as they do not block the active site


 * pH – outside of the enzymes optimum pH, the active site denatures quickly. This prevents the reaction from being catalysed
 * Temperature – below the optimum temperature, the reaction slows, as less energy to cause collisions  Above optimum temp – reaction stops – enzymes denatureEnzyme-temperature.pngEnzyme-ph.png

Nucleic Acids

 * Genetic material for living organisms
 * Adenine (purine), Thymine / Uracil (pyramidal), Guanine (purine), Cytosine (pyramidal)Semi conservative replication of DNA (13081032424).jpg
 * Semi-Conservative Replication
 * DNA unzips: DNA Helicase
 * Base pairs move in between the unzipped strands
 * DNA Polymerase used to bind the new bases to the old strands
 * Forms 2 DNA strands, each with 1 old strand and 1 new strand
 * Proof for semi-conservative replication
 * DNA replicated until all Nitrogen is 15N – this is heavier, causing the strand to be lower in solution
 * DNA then replicated 1 generation with 14N – this creates a hybrid DNA, with 50% 15N and 50% 14N
 * DNA replicated 1 further generation in 14N solution – creating DNA with 25% 15N and 75% 14N
 * This is repeated, eventually forming DNA only containing 14N
 * The solution can be centrifuged, DNA containing different Nitrogen isotopes to be identified

ATP – Adenosine Triphosphate



 * Used to transfer energy within cells
 * Made of: Adenine, 3× Phosphate groups, Ribose sugar
 * $$ATP+H_2 O \rightarrow ADP+P_i$$ – condensation on ATP, forming ADP and a phosphate group; breaking the bond releases energy
 * Low activation energy, so it is easy to release energy
 * ATPase – enzyme catalysing hydrolysis of ATP (break down of ATP into ADP)
 * Photophosphorylation
 * Photosynthesis: Plants only, Using light to synthesise ADP → ATP
 * Oxidative Phosphorylation
 * Using respiration to synthesise ADP → ATP; Plants and Animals
 * Substrate-level Phosphorylation
 * When phosphate groups are transferred from donors; plants and animals
 * Uses of ATP
 * Metabolic Processes – provides energy to build up molecules from subunits
 * Movement – energy is required for muscular contraction
 * Active Transport – movement of molecules against a concentration gradient
 * Secretion – ATP is needed to form lysosomes to encase cell products
 * Activation of Molecules – inorganic phosphate released in hydrolysis of ATP can phosphorylate other molecules

Water



 * Essential for all living organisms
 * Polar Molecule
 * Hydrogen bonds between water molecules require lots of energy to break
 * Causes water to have a high surface tension
 * Solvent
 * As water is polar, other polar molecules are able to dissolve in it
 * Ionic compounds are surrounded by water molecules when dissolved
 * Allows gases to be dissolved – CO2, O2, NH3…
 * High Specific Heat Capacity
 * A lot of energy is required to increase the temperature by 1° - this is due to the strength of the hydrogen bonds
 * This means that water acts as a buffer, reducing temperature fluctuations
 * High Latent Heat of Vaporisation
 * A lot of energy is required to evaporate water (into steam)
 * Ideal for cooling an organism – sweating (animals) or transpiring (plants)
 * Cohesion between Molecules
 * High surface tension means that column of water is able to be pulled up a vessel (such as a xylem)
 * Metabolite
 * Used in condensation / hydrolysis reactions to break / form bonds

Inorganic Ions

 * Occur in solution in the cytoplasm / bodily fluids
 * Some are in high concentrations, others in low concentrations
 * Each ion has a specific role
 * Iron ions Haemoglobin
 * Sodium ions co-transport of Glucose and Amino Acids
 * Phosphate ions Part of DNA and ATP