4. Molecules of life

• Are macromolecules that are composed of monomeric nucleotides

• Form linear polymers of nucleotides which consist of 3 components (base + sugar + phosphate)

• Carrie genetic information or form structures within the cell

• The most common are DNA and RNA

• Universal in living things, found in all cells and viruses

RNA (Ribonucleic Acid) is a single-stranded (no helix form) nucleic acid crucial for life, acting as the intermediate messenger between DNA and proteins.

It uses sugar ribose and the base uracil (U) instead of thymine (T). Its main roles include:

• mRNA: messenger RNA carrying instructions

• rRNA: ribosomal RNA forming the ribosome (protein factory)

• tRNA: transfer RNA bringing amino acids to build the protein chain

Proteins are large, complex biological molecules that perform the majority of the work within cells, essential for the structure, function and regulation of the body’s tissues and organs. They are the fundamental building blocks of life.

Proteins are polymers (long chains) constructed from smaller units called amino acids.

• Amino acids: There are 20 different types of amino acids that combine in diverse sequences to form all proteins. Amino acids are linked together by peptide bonds to form a linear chain called a polypeptide.

• Four levels of structure: The sequence of amino acids dictates how the polypeptide chain will spontaneously fold into a specific, functional three-dimensional shape.

Proteins are defined by a complex three-dimensional shape that is organised into four hierarchical levels of structure. The final, correct shape determines the protein’s biological function.

1. Primary structure: The linear sequence of amino acids joined by peptide bonds.

2. Secondary structure: Folding into stable shapes like α-helix and β-pleated sheet, stabilized by hydrogen bonds in the backbone.

3. Tertiary structure: The overall 3D shape of a single polypeptide chain, determined by interactions between the amino acids side chains (R-groups).

4. Quaternary structure: The arrangement and interaction of multiple polypeptide subunits to form a functional protein complex.

Lipids are a diverse group of essential hydrophobic (water-insoluble) organic molecules, including fats, oils, phospholipids, and steroids.

They are primarily made of fatty acids and glycerol.

Four main functions are:

• Energy storage: storing high amounts of long-term energy as triglycerides (fats).

• Structures: Forming the phospholipid bilayers that makes up all cell membranes.

• Insulation/Protection: Providing thermal insulation and cushioning vital organs.

• Signaling: Acting as hormones (like steroids) to regulate biological processes.

1. non-polar, alphabetic R groups

2. Polar, uncharged R groups

3. Aromatic R groups

4. Positively charged R groups

5. Negatively charged R groups

The rules of base pairing in DNA describe how the nitrogenous bases on opposite strands of the double helix always connect in specific pairs:

• Adenine (A) always pairs with Thymine (T) - using two hydrogen bonds

• Guanine (G) always pairs with Cytosine (C) - using three hydrogen bonds