Large Molecules
- Monomer (-OH) + Monomer (-H) → Polymer + H2O(l)
- Condensation: monomers (e.g. amino acids) join to form polymers (e.g. proteins)
- Glycosidic bond forms when two carbohydrate monomers join together
- Hydrolysis: break down of a polymer; reverse reaction
- Polymers are also called macromolecules (e.g. starch, proteins, triglyceride)
Carbohydrates
- Organic molecules in which C, H and O bind together in the ratio Cx(H2O)y
- Serve as an energy source important for the brain and cellular respiration
- Plants produce carbohydrates by using energy from sunlight
- 6CO2 + 6H2O + energy (from sunlight) → C6H12O6(carbohydrate) + 6O2
- Animals eat plant materials to obtain the produced carbohydrates
- They can then be used in animal metabolism to release energy
- C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
Monosaccharides
| Triose (3 carbons) | Product of respiration and photosynthesis |
| Pentose (5 carbons) - Ribose - Deoxyribose | Found in RNA and DNA nucleic acids |
| Hexose (6 carbons) - Glucose - Fructose - Galactose | Source of energy in respiration Main energy source in brain Found in sweet-tasting fruits |
Disaccharides (two sugar residues)
|
Polysaccharides (many sugar residues)
| Starch (alpha-glucose) | Main storage of carbohydrates - in plants |
| Glycogen (alpha-glucose) | - in humans and animals |
| Cellulose (beta-glucose) | Important component of the plant cell wall |
Starch
- Consists of amylopectin and amylose (both are made of α-glucose)
- Amylopectin is branched via 1,6-glycosidic bonds
- Amylose forms a stiff helical structure via 1,4-glycosidic bonds
- Both are compact molecules → starch can be stored in small space
- The ends are easily broken down to glucose for respiration
- Does not affect water potential as it is insoluble
- Readily hydrolysed by the enzyme amylase found in the gut and saliva
- Major carbohydrate used in plants
- Found as granules (chloroplast)
- Each granule contains amylopectin combined by a larger amount of amylose
- Commonly used sources are corn (maize), wheat, potato, rice
Glycogen
- Branched, storage, polymer of glucose linked via glycosidic bonds
- Found in skeletal muscle and in the liver
- Chains are linked by alpha-1,4-linkage, branches are linked by alpha-1,6-linkages
- Glycogen is broken down to glucose by glycogenolysis (glycogen phosphorylase)
- Major site of daily glucose consumption (75%) is the brain via aerobic pathways
- Most of the remainder is utilized by erythrocytes, skeletal muscle, and heart muscle
- Glucose is obtained from diets or from amino acids and lactate via gluconeogenesis
- Storage of glycogen in liver are considered to be main buffer of blood glucose levels
Cellulose
- Polysaccharide consisting of long beta-glucose chains
- Linked together by hydrogen bonds to form microfibrils
- Structural function is a important component of plant cell walls
- Its tensile strength helps plant cells in osmosis //cell does not burst in dilute solutions
Proteins
Structure
- Proteins are polymers of amino acids
- Proteins are made up by different combinations of 20 amino acids
- They have a general structure:
- The difference between different amino acids is found in the R-group
- When two amino acids join together, they release -H and -OH groups highlighted in red below
- Peptide bond is formed between alpha-carbon and nitrogen
- Condensation reaction
- Primary structure of a protein
- Sequence of amino acids
- Joined together by covalent peptide bonds
- Secondary structure
- Hydrogen bonds between amino acids
- Made of a combination of alpha-helices and beta-pleated sheets
- Proportion of α-helix and β-sheet depends on sequence (primary structure)
- Tertiary structure
- Complex globular shape
- Folding and twisting of polypeptides (H-bond)
- Polypeptides contain many peptide bonds
- Quaternary structure
- Several polypeptide chains //several tertiary structures combined
- Haemoglobin has 4 polypeptide chains
- Collagen has 3 polypeptide chains, twisted around each other
- Globular proteins are soluble and has folded chains
- Fibrous proteins are insoluble and long, thin, twisted chains
- Same amino acid sequence → same shape always
Bonds Found in Proteins
- Hydrogen bonds
- Between R-groups are easily broken, but are numerous
- The more bonds, the stronger the structure
- Disulphide bonds
- Between sulphur-containing amino acid cystine
- Strong bonds found in skin and hair
- Denaturation
- Destruction of tertiary structure, can be done by heat
- Protein structure is lost and cannot reform → dysfunctional
Absorption and Function
- Absorption of proteins in the digestive tract
- Proteins are taken in as food
- They are broken down in the digestive tract into their individual amino acids
- Amino acids are recombined in the body to form different proteins
- Good food sources include beans, milk, cheese, fish, meat
- Several substances are composed of proteins with distinct functions
- Keratin, collagen are main components in hair, muscles, tendons, skin
- Enzyme amylase digests starch
- Haemoglobin transports O2 in the blood stream
- Insulin regulates glucose storage
Lipids
- Easily dissolved in organic solvents but not in water
- Triglycerides (fats and oils)
- Serves as an energy reserve in plant and animal cells
- Consists of 3 fatty acids linked by ester bonds to glycerol
- Excess energy available from food/photosynthesis is stored as triglycerides
- Can be broken down later to yield energy when needed
- Fats and oils contain twice as many energy stored per unit of weight as carbohydrates
- Triglycerides (TG) are also called triacylglycerides (TAG)
- Saturated fatty acids
- -COOH group without double bonds in the carbohydrate chain
- May cause blockage of arteries which can lead to strokes and heart attacks
- High melting point / solid at room temperature (fats) / typical animal fats
- Unsaturated fatty acids
- -COOH group with double bonds in the carbohydrate chain
- Low melting point / liquid at room temperature (oils)
- Found in plants
- Phospholipids
- Formed by replacing one fatty acids in a triglyceride with a phosphate group
- Phosphate is polar / hydrophilic / does mix with H2O
- Fatty acid tails remain non-polar / hydrophobic / insoluble, does not mix with H2O
- Form a ball called a micelle when placed in a polar solution (e.g. water)
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