Carbon and macromolecules (B1.1.1, B1.1.2,B1.1.3)

• What are covalent bonds and why do they occur?

  Covalent bonds are formed when two atoms share one or more pairs of electrons to achieve a full outer electron shell, stabilizing both atoms. This happens because atoms seek to satisfy the octet rule (having 8 electrons in their valence shell, except for hydrogen, which seeks 2).

  The strength of a covalent bond comes from the electrostatic attraction between the shared electrons and the positively charged nuclei of the bonded atoms, as covalent bonds are the strongest type of bond.

  Stable molecules are formed due to the strong energy required to break covalent bonds.
• How many covalent bonds can a carbon atom form?

  Each carbon can form four covalent bonds. They can be single or double. This is known as tetravalence.
• What is the form of a carbon chain?

  In single covalent bonds, the atoms can rotate but not move further apart. Covalently bonded carbons form a tetrahedral shape-so they cannot be straight, but rather are a zig-zag shape.
• What is the form of a carbon ring?

  Covalently bonded carbons form a tetrahedral shape-so they cannot be straight, but rather are a zig-zag shape. Due to these bond angles, the carbon chains can also form rings. The rings can be made completely of carbon, or contain an atom of another element.
• What is an example of a branched carbon chain?

  One example of a branched chain is isobutane. It contains a main chain with multiple side branches.
• What is an example of an unbranched carbon chain?

  One example of an unbranched chain is Hexane- It contains a continuous linear chain of carbon atoms.
• What is an example of a single carbon ring?

  One example of a single carbon ring is glucose- which is a single-ring structure that is often seen in monosaccharides.
• What is an example of a multiple carbon-ringed structure?

  One example of a multiple ringed structure is cholesterol- it is composed of several fused carbon rings (and is the steroid backbone).
• What are the four classes of carbon compounds (and some facts)?

  Carbohydrates: Function: Provide energy and structural support. Examples: Glucose, starch, cellulose.

  Lipids: Function: Energy storage, insulation, and making up cell membranes. Examples: Triglycerides, phospholipids, steroids.

  Proteins: Function: Catalysts (enzymes), structural components, transport, and signalling. Examples: Haemoglobin, insulin, keratin.

  Nucleic Acids: Function: Store and transmit genetic information. Examples: DNA, RNA.
• What is a functional group?

  Functional groups are specific atoms or clusters of atoms attached to a carbon backbone that determine the reactivity and properties of organic molecules. This occurs due to carbon's ability to form four covalent bonds
• What are the functional groups, and what characteristics do they allow a carbon chain to posses?

  Hydroxyl (—OH)- attaches to carbon, making molecules like alcohols soluble in water.

  Carbonyl (C=O)- groups appear in aldehydes and ketones, influencing reactivity.

  Carboxyl (—COOH)- is a combination of carbonyl and hydroxyl groups and gives organic acids their acidic properties.

  Amino (—NH₂)- attaches to carbon backbones, forming the building blocks of proteins (amino acids).

  Methyl (—CH₃)- binds to carbon, reducing polarity and impacting gene expression when attached to DNA.
• What are macromolecules?


  Macromolecules are molecules composed of a very large number of atoms. The main classes of macromolecule are polysaccharides, polypeptides and nucleic acids, which are all formed by linking subunits together into a chain.
• What is a monomer, a polymer and how are monomers linked to form polymers?

  A monomer is a small, simple molecule that serves as a building block for larger molecules. Examples include glucose, amino acids, and nucleotides. A polymer is a large molecule composed of repeating units of monomers linked together by covalent bonds. Examples include polysaccharides, proteins, and DNA.

  So, subunits are known as monomers, with the chain known as a polymer. The monomers are linked onto the end of a chain through condensation reactions.
• What is a condensation reaction?

  In a condensation reaction, two molecules are linked together. When they link, a smaller molecule, water, is released. This is because a hydroxyl group (-OH) is removed from one molecule being linked, and a hydrogen atom is removed from another molecule being linked, forming water composed of two hydrogens and one oxygen. The release of water allows a bond to be formed to bridge the two molecules.

  Energy is required for a condensation reaction to occur, which is supplied by ATP. This is because the process often involves overcoming activation energy barriers and forming new covalent bonds.
• How is a polysaccharide formed?

  Glucose ( a monosaccharide) is linked to glucose via glycosidic bonds. These linkages are formed via condensation, using hydroxyl groups, and are C-O-C. If two glucose molecules combine they form maltose.

  Cellulose molecules in plants are unbranched chains of beta glucose that contain 15,000 or more individual glucose molecules.

  Glycogen molecules are branched chains of alpha glucose containing up to 60000 individual glucose molecules.

  A disaccharide is two monosaccharides
• How is a polypeptide formed?

  Amino acids are connected via the carboxyl and the amino groups (-COOH) and (-NH2), through what is known as a peptide bond.

  Additional amino acids can join the chain through repeated condensation reactions, forming polypeptides (chains of 50+ amino acids) and eventually folding into functional proteins.
• What is hydrolysis?


  Polymers are deconstructed either so that the monomers within them can be used as a source of energy or to build new polymers.

  This is done via hydrolysis, and this occurs during digestion.

  Hydrolysis reactions are chemical processes in which water molecules are used to break down larger molecules (polymers) into smaller ones (monomers). During this reaction a water molecule is split into a hydrogen ion (H⁺) and a hydroxyl group (OH⁻). These components are added to the bonds within the polymer, breaking it into smaller units.

  Hydrolysis is the reverse of condensation reactions and is essential in digestion, where macromolecules are broken down into their building blocks for absorption.
• How are polysaccharides digested?

  Polysaccharides are broken down into starch, glycogen or cellulose. Within the hydrolysis reaction where water is added, glycosidic bonds between monosaccharides are broken. Each bond cleavage requires one water molecule.

  This may be facilitated by enzymes- starch is broken down into maltose (a disaccharide) by amylase, and maltose is broken down into glucose by maltase.
• How are polypeptides digested?

  Peptide bonds holding the polypeptide together are broken via hydrolysis. The water molecule provides an -OH group to the carboxyl end of one amino acid, and a hydrogen atom (H⁺) to the amino end of another amino acid. Again, these reactions are facilitated by enzymes, proteins are broken into smaller peptides by pepsin (in the stomach) or trypsin (in the small intestine). Peptides are further broken down into individual amino acids by peptidases.
• How are nucleic acids digested?

  Phosphodiester bonds in the sugar-phosphate backbone are hydrolysed, and a water molecule provides both an -OH group to the 3' carbon of one nucleotide and a hydrogen atom (H⁺) to the 5' phosphate group of the adjacent nucleotide. Again, this is facilitated by an enzyme- DNA is broken into smaller fragments by deoxyribonuclease (DNase). RNA is broken into smaller fragments by ribonuclease (RNase). Nucleotides are further broken down into their components (sugar, phosphate, base) by specific enzymes.
• Formation of nucleic acids

  In the formation of the sugar-phosphate backbone, pentoses and phosphates are linked through a condensation reaction, forming a phosphodiester bond and releasing water. The hydroxyl groups bonded to the 5’ carbon-bonded phosphate group of one nucleotide forms a phosphodiester bond with the hydroxyl group bonded to the 3’ carbon of the pentose on another nucleotide.

  Therefore, the backbone is built from 5’ phosphate to 3’ pentose. This directionality has significance for DNA replication and transcription.