Macromolecules

Based on Lucarelli's Essential Chemistry Chapter 12

Macromolecule

An extremely large molecule, with extremely Hugh molar masses

Polymers

Long chain molecules made up of thousands of smaller molecules known as monomers (typically made of only a few atoms). Polymers are also known as plastics.

Uses of polymers

Fabric, proteins, DNA, containers, bags, insulation, cling wrap, traffic cones

Thermoplastics

Recyclable plastics that soften and melt when heated, making them able to be reshaped.

Thermosetting Polymers

Polymers that cannot be melted down and reshaped, decomposing or charring when heated.

Cross linking

When polymer chains are joined to each other by covalent bonds, giving the polymer elastic propertie, though stiffening it if there is a lot present.

Addition polymerisation

The process by which monomers with a double bond are added to each other end to end to form a polymer.

Are polymers pure substances?

No, therefore they have inconsistent physical properties

Low density polyethylene

A form of polyethylene that is polymerised with a side reaction causing it to have side-chains that reduce its packing efficiency and dispersion force strength, causing it to form amorphous/irregular arrangement of its molecules and giving it a lower melting point of around 105-115ºC.

High density polyethylene

A form of polyethylene made up of mostly long, straight chains, which makes its dispersion forces stronger, increasing its density, stiffness, crystallinity and melting point (120-135ºC), and less irregular arrangements of its molecules compared to LDPE.

Why is polytetrafluoroethylene (PFTE/teflon) so unreactive?

Because of the strength of the C-F bonds that make it up

Condensation polymerisation

The joining together of monomers via reactions that produce small molecules such as CO₂ or H₂O to form polymers such as polyesters and polyamides.

How are polyamides (such as nylon) formed?

From the condensation polymerisation of diamines with dicarboxylic acids

How can the strength of nylon be increased?

Extruding melted nylon through small holes helps to align, stretch, and untangle the molecules, creating a stronger and more crystalline structure involving hydrogen bonds.

Proteins

Polymers used by organisms for many purposes. They are made up of long chains of alpha amino acids.

Where do people get alpha amino acids from?

Their food (meat is best)

Dipeptide

A combination of two amino acids, formed via the elimination of water. The dipeptide bond involves the N from the amine group (which loses a H) of one amino acid bonding to the C in the carboxyl group of the other amino acid, which loses its OH (making it a carbonyl group).

Amino acid residue

The part of an amino acid left over after polymerisation (loss of H₂O), which forms part of a polypeptide chain.

How are polypeptide sequences listed?

Starting with its N-terminus and ending at its C-terminus

Primary structure of a protein

The linear sequence of alpha amino acid residues that make it up.

What does a protein’s primary structure affect?

How it folds and curls into its 3D shape, known as its conformation, and how it interacts with other molecules.

Secondary structure of a protein

The regular arrangement of various sections of the protein chain, examples of secondary structures include alpha helices and beta pleated sheets, adjacent chains bonded together forming a corrugated structure.

How are alpha-helices stabilised?

Hydrogen bonds between amide and carbonyl groups separated by 3 residues on the polypeptide chain

How are beta pleated sheets stabilised?

Hydrogen bonds between amide and carbonyl groups in areas where the alpha amino acids have small side chains.

Tertiary structure of a protein

The overall 3D shape of a protein, caused by bonds formed between residue side chains.

What forces can occur between different areas of a polypeptide chain, influencing its tertiary structure?

Ionic bonding, disulfide bridges, dipole-dipole forces, hydrogen bonds, and dispersion forces.

A disulphide bridge is a covalent bond between two oxidised residues of what amino acid?

Cysteine

Protein Data Bank

A free, international, online, public archive of data on the structure of macromolecules that was formed to formalise and standardise how this data is presented and annotated.

Enzyme

A type of protein that act as catalysts, but far more specialised and faster than non-organic catalysts.

Substrate

A reactant catalysed by an enzyme

Active site

The place on an enzyme where weak intermolecular forces hold the substrate in place so that its bonds may be more easily rearranged.

What are some downsides of enzymes compared to inorganic catalysts?

They are vulnerable to changes in temperature and pH that may impact their conformation and thus their catalytic properties.