Molecular biology
Molecular biology is a field of study that focuses on investigating biological activity at a molecular level
Molecular Biology includes…
elucidating the structure and function of chemical substances and determining their interactions as parts of living processes
Biological processes are regulated by
by enzymes, whose expression is controlled by gene activation (DNA)
changes in activity
Changes in activity are typically determined by signalling molecules (either endogenous or exogenous in origin)
organic compounds
An organic compound is a compound that contains carbon and is found in living things
organic compound exceptions
Exceptions include carbides (e.g. CaC2), carbonates (CO32–), oxides of carbon (CO, CO2) and cyanides (CN–)
carbon
- Carbon forms the basis of organic life due to its ability to form large and complex molecules via covalent bonding
- Carbon atoms can form four covalent bonds, with bonds between carbon atoms being particularly stable (catenation)
Main Classes of Carbon Compounds
carbohydrates, lipids, nucleic acids, proteins
Carbohydrates
- Most abundant organic compound found in nature, composed primarily of C,H and O atoms in a common ratio – (CH2O)n
- Principally function as a source of energy (and as a short-term energy storage option)
- Also important as a recognition molecule (e.g. glycoproteins) and as a structural component (part of DNA / RNA)
Lipids
- Non-polar, hydrophobic molecules which may come in a variety of forms (simple, complex or derived)
- Lipids serve as a major component of cell membranes (phospholipids and cholesterol)
- They may be utilised as a long-term energy storage molecule (fats and oils)
- Also may function as a signalling molecule (steroids)
Nucleic Acids
- Genetic material of all cells and determines the inherited features of an organism
- DNA functions as a master code for protein assembly, while RNA plays an active role in the manufacturing of proteins
Proteins
- Make over 50% of the dry weight of cells; are composed of C, H, O and N atoms (some may include S)
- Major regulatory molecules involved in catalysis (all enzymes are proteins)
- May also function as structural molecules or play a role in cellular signalling (transduction pathways)
macromolecules may commonly be comprised of…
smaller, recurring subunits called monomers
what contains monomers?
Carbohydrates, nucleic acids and proteins are all comprised of monomeric subunits that join together to form larger polymers
what doesn’t contain monomers?
Lipids do not contain recurring monomers, however certain types may be composed of distinct subunits (e.g. triglycerides)
carbohydrate structure
Carbohydrates are composed of monomers called monosaccharides (‘single sugar unit’)
- Monosaccharides are the building blocks of disaccharides (two sugar units) and polysaccharides (many sugar units)
- Most monosaccharides form ring structures and can exist in different 3D configurations (stereoisomers)
- structure of complex carbohydrates may vary depending on the composition of monomeric subunits
lipid structure
Lipids exist as many different classes that vary in structure and hence do not contain a common recurring monomer
- However several types of lipids (triglycerides, phospholipids, waxes) contain fatty acid chains as part of their overall structure
- Fatty acids are long chains of hydrocarbons that may or may not contain double bonds (unsaturated vs saturated)
protein structure
Proteins are composed of monomers called amino acids, which join together to form polypeptide chains
- Each amino acid consists of a central carbon connected to an amine group (NH2) and an opposing carboxyl group (COOH)
- A variable group (denoted ‘R’) gives different amino acids different properties (e.g. may be polar or non-polar, etc.)
nucleic acid structure
Nucleic acids are composed of monomers called nucleotides, which join together to form polynucleotide chains
- Each nucleotide consists of 3 components – a pentose sugar, a phosphate group and a nitrogenous base
- The type of sugar and composition of bases differs between DNA and RNA
Glucose monomer combinations
Glucose monomers can be combined to form a variety of different polymers – including glycogen, cellulose and starch
lipid classes
Lipids can be roughly organised into one of three main classes:
- Simple (neutral) lipids – Esters of fatty acids and alcohol (e.g. triglycerides and waxes)
- Compound lipids – Esters of fatty acids, alcohol and additional groups (e.g. phospholipids and glycolipids)
- Derived lipids – Substances derived from simple or compound lipids (e.g. steroids and carotenoids)
how do amino acids join?
Amino acids join together by peptide bonds which form between the amine and carboxyl groups of adjacent amino acids
- The fusion of two amino acids creates a dipeptide, with further additions resulting in the formation of a polypeptide chain
- The subsequent folding of the chain depends on the order of amino acids in a sequence (based on chemical properties)
how do nucleotides form?
Nucleotides form bonds between the pentose sugar and phosphate group to form long polynucleotide chains
- In DNA, two complementary chains will pair up via hydrogen bonding between nitrogenous bases to form double strands
- This double stranded molecule may then twist to form a double helical arrangement
vitalism
Vitalism was a doctrine that dictated that organic molecules could only be synthesised by living systems
- It was believed that living things possessed a certain “vital force” needed to make organic molecules
- Hence organic compounds were thought to possess a non-physical element lacking from inorganic molecules
