Cell Structure and Diversity

• The lecture discusses cell structure and diversity, focusing on the building blocks of cells.
• The lecture aims to outline the relationship between molecular building blocks and higher order structures in cells.
• It also aims to identify the structures of major types of macromolecules in cells and describe the roles of carbohydrates, lipids, proteins and nucleic acids in cells.

Typical Mammalian Cell Composition

• Water makes up 70% of a typical mammalian cell.
• Proteins comprise 18%.
• Phospholipids and other lipids constitute 5%.
• Polysaccharides account for 2%.
• RNA makes up 1.1%.
• DNA constitutes 0.25%.
• Inorganic ions make up 1% (sodium, potassium, magnesium, calcium, chloride, etc.).
• Miscellaneous small metabolites comprise 3%.

Molecular Organization

• Biological molecules can be organized into higher order structures.
• Building blocks like amino acids and nucleobases form macromolecules.
• Macromolecules such as proteins and nucleic acids assemble into supramolecular structures.
• Supramolecular assemblies like membranes and ribosomes then form organelles.
• Organelles include the nucleus, mitochondria, Golgi apparatus, and endoplasmic reticulum (ER).

Key Concepts of Macromolecules

• Macromolecules are organic biological molecules essential for life.
• They consist of thousands of atoms or more, resulting in a large molecular mass.
• Building blocks, or monomers, join by covalent (chemically strong) bonds.
• Most building blocks form polymeric molecules, but some form non-polymeric molecules.
• Polymerization is the process of linear formation of polymeric molecules.
• A biomolecule is any molecule produced by a living organism.

Types of Macromolecules

• Life relies on four main macromolecules: polysaccharides (complex carbohydrates), nucleic acids (DNA and RNA), proteins, and lipids.
• Polysaccharides, nucleic acids, and proteins are polymeric macromolecules.
• Lipids are non-polymeric macromolecules.
• Polymeric molecules result from the polymerization of building blocks.

Carbohydrates

• There are four levels of carbohydrates: monosaccharides, disaccharides, oligosaccharides, and polysaccharides.
• Monosaccharides are simple carbohydrates (sugars) and the single unit building blocks of carbohydrates.
• Hexose monosaccharides are the building blocks of higher order carbohydrates and have 6 carbons.
• Pentose monosaccharides are part of larger molecules like nucleic acids and have 5 carbons. Deoxyribose is a part of DNA nucleotide and ribose is a part of RNA nucleotide.
• Disaccharides form when two monosaccharides join together (e.g., sucrose, lactose, maltose).
• Oligosaccharides consist of several monosaccharides linked together (3 to approximately 10).
• Polysaccharides consist of many monosaccharides linked together (more than 10).
• Carbohydrates are polymers of monosaccharides.
• Examples of polysaccharides include starch (amylose, amylopectin), glycogen, and cellulose (fiber).
• Recognition: carbohydrates are involved in cell recognition processes, including toxin recognition, invasions, and cell-to-cell recognition.
• Energy: carbohydrates serve as energy storage, such as starch and glycogen.
• Structure: carbohydrates contribute to cell structure, such as cellulose in plants.

Nucleic Acids

• Nucleic acids include deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
• The nucleotide has a phosphate, base, and ribose sugar, which are identical.
• A polynucleotide forms through phosphodiester bonds.
• DNA features thymine (T), adenine (A), cytosine (C), and guanine (G) bases.
• RNA features uracil (U), adenine (A), cytosine (C), and guanine (G) bases.
• Nucleic acids are polymers of nucleotides.
• RNA is a single strand molecule.
• DNA is a double strand molecule.

Proteins

• Proteins are polymers of amino acids.
• The 20 amino acids differ by their 'R' group (side chain).
• Proteins perform functions in the whole organism.
• Proteins are translated from mRNA, which is transcribed from DNA.

Functions of Proteins

• Proteins perform a variety of biological functions.
• Function Example
• Note the following functions do not need to be memorized.*
• Structural - Collagen is a protein in skin and bones
• Regulatory - Insulin is a peptide hormone
• Contractile - Actin and myosin are muscle proteins
• Transport - Hemoglobin carries oxygen and Cytochrome c carries electrons
• Storage - Egg white (albumin) and seed proteins
• Protective - Antibodies (e.g. IgG) are immune proteins
• Catalytic - Hydrolytic in lysosomes and RNA polymerase are enzymes
• Toxic - Botulinum toxin and diphtheria toxin

Lipids

• Lipids are not polymers and are a heterogeneous group of molecules.
• Examples of lipids include triacylglycerols (“fats”), steroids (sterols), phospholipids, glycolipids and fat-soluble vitamins
• They are hydrophobic
• Lipid functions:
  • Structural: cholesterol and phospholipids in the cell membrane.
  • Regulatory: some lipids such as testosterone and estradiol (an estrogen) have regulatory roles.
  • Energy: fats/oils serve as energy storage (triacylglycerol).