Cell Structure and Function - Cell Biology

Cell Structure and Function - Cell Biology

• Reem Dakhil, M1 Biochemistry (Lebanese University), M2 Physiology, Epigenetics, Differentiation, and Cancer (Université Grenoble Alpes) is presenting this material.

Chapter 1: Cell Biology Birth

• The presentation is about the Cell Doctrine, and definitions

Cell Biology vs Cytology

• Cell Biology: Study of cells and their components structurally and functionally
• Cytology: Study of cells and their components, specifically focusing on their structure.

The Cell Doctrine

• Unit: The cell is the fundamental unit of structure and function in living organisms.
• Division: Cells divide to produce new cells via mitosis and meiosis for continuity and growth.
• Organism: Cells and their products (e.g., tissues, organs) work together to form an organism.
• Life: Cells are the basis of life continuity, from one generation to the next through fertilization and mitosis/meiosis.
• Double-life: Each cell has a life for itself and contributes to the life of the whole organism.

Chapter 2: Molecular Components of Cells

• The presentation focuses on Inorganic and Organic compounds in cells

What atoms and molecules are found in our cells?

• The presentation discusses the atomic level components of cells

Atomic Level

• Most abundant atoms: 96% are Carbon (C), Hydrogen (H), Nitrogen (N), and Oxygen (O).
• 4% are Sodium (Na), Potassium (K), Chlorine (Cl), and Phosphorus (P).
• Very low, trace elements (e.g., Boron (B), Fluorine (F), Manganese (Mn) and others) are also present in small quantities.

Molecular Level

• Organic molecules ("Biomolecules"): Proteins, Carbohydrates, Lipids, and Nucleic acids
• Inorganic molecules: Water, Mineral salts

1. Water:

• Basis of life
• Most abundant
• Electrically neutral
• Extremely polar (partially negative oxygen and partially positive hydrogen)
• Forms hydrogen bonds with other molecules
• Solubilizes salts via ionic bonds.

2. Mineral Salts:

   • Dissolved and ionized in water.
   • Internal/external balance plays a crucial role in membrane permeability, nerve impulses, muscle contraction, and cell division.
   • Metal ions are essential for certain proteins' activity (e.g., muscle contraction, oxygen transfer, intercellular signaling)

3. Organic Compounds:

• Molecules: amino acids, fatty acids, monosaccharides, nucleotides.
• Macromolecules: proteins, polysaccharides, lipids, DNA, and RNA
• Vitamins: needed at low concentrations; some are part of carbohydrates or lipids.

1. Proteins

• Introduction: Most abundant organic molecules with diverse functions determined by their genes and amino acids. Unbranched chain polymers of amino acids.
• Function: Essential for various cellular processes (e.g., morphology, DNA replication, storage, transport, communication, immunity, senses, cell cycle, muscle contraction), but are not energy sources.
• Diverse Chemical Composition: Chemically homogeneous (unbranched chain of amino acids), differing by the number and sequence, resulting in varied 3D structures and functions.
• Amino Acids: Composed of C, H, N, O, and S. Different groups (non-polar, polar uncharged, polar positive, polar negative) with 20 types: 9 are essential (require diet). Only L-stereoisomers form polypeptides.
  • All amino acids are soluble due to amino and carboxyl groups, although the solubility of proteins/peptides is affected by factors like pH and R-group characteristics (zwitterions).

5. Polypeptide

• Peptide Bond Formation: Covalent bonds forming a linear, and unbranched chain of amino acids. The bond is created by ribosomes. Digested through proteases. Made through a nucleophilic attack of NH2 (amino group) of amino acid (n) and COOH (carboxyl group) of amino acid (n-1). Forming an "amide bond" and eliminating water (H2O).
• Backbone: repeating N - Cα - C - units. Polarized by N-terminus (NH2) and C-terminus (COOH).

6. Polypeptide Flexibility

• Extended groups (R, H, =O) outside the peptide backbone plane allow rotation in relation to one another.
• This confers flexibility, enabling 3D conformation and thus, functionality.