Biology IB HL - 2.1 Molecular Biology

Molecular biology is a field of study that focuses on investigating biological activity at a molecular level

This includes elucidating the structure and function of chemical substances and determining their interactions as parts of living processes

Biological processes are tightly regulated by enzymes, whose expression is controlled by gene activation (DNA)

Changes in activity are typically determined by signalling molecules (either endogenous or exogenous in origin)

An organic compound is a compound that contains carbon

found in living things

Exceptions include carbides (e.g. CaC2), carbonates (CO32–), oxides of carbon (CO, CO2) and cyanides (CN–)

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)

These properties allows carbon to form a wide variety of organic compounds that are chemically stable

carbohydrates

lipids

nucleic acids

proteins

composed primarily of C,H and O atoms

(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)

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)

Genetic material of all cells and determines the inherited features of an organism

DNA functions as a master code for protein assembly

RNA plays an active role in the manufacturing of proteins

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)

Complex macromolecules may commonly be comprised of smaller, recurring subunits called monomers

Lipids do not contain recurring monomers, however certain types may be composed of distinct subunits (e.g. triglycerides)

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)

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)

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 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

Metabolism describes the totality of chemical processes that occur within a living organism in order to maintain life

They provide a source of energy for cellular processes (growth, reproduction, etc.)

They enable the synthesis and assimilation of new materials for use within the cell

Anabolic reactions describe the set of metabolic reactions that build up complex molecules from simpler ones

The synthesis of organic molecules via anabolism typically occurs via condensation reactions

Condensation reactions occur when monomers are covalently joined and water is produced as a by-product

Monosaccharides are joined via glycosidic linkages to form disaccharides and polysaccharides

Amino acids are joined via peptide bonds to make polypeptide chains

Glycerol and fatty acids are joined via an ester linkage to create triglycerides

Nucleotides are joined by phosphodiester bonds to form polynucleotide chains

synthesising new molecules from simpler ones

uses energy to construct new bonds

typically involves reduction reactions

Catabolic reactions describe the set of metabolic reactions that break complex molecules down into simpler molecules

The breakdown of organic molecules via catabolism typically occurs via hydrolysis reactions

Hydrolysis reactions require the consumption of water molecules to break the bonds within the polymer

breaking down complex molecules into simpler ones

releasing energy when bonds are broken

typically involves oxidation reactions

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

organic compounds were thought to possess a non-physical element lacking from inorganic molecules

Vitalism as a theory has since been disproven with the discovery that organic molecules can be artificially synthesised

In 1828, Frederick Woehler heated an inorganic salt (ammonium cyanate) and produced urea

Urea is a waste product of nitrogen metabolism and is eliminated by the kidneys in mammals

The artificial synthesis of urea demonstrates that organic molecules are not fundamentally different to inorganic molecules