Cell Biology - lecture 1 - Cell Types and Subcellular Structures

Lecture Overview

• Learning Outcomes:

  • Explain the concept of 'the cell'.

  • Classify different types of cells: prokaryotes, eukaryotes, bacteria, archaea, fungi, plants, animals.

  • Outline the organization of eukaryotic cells and describe major organelles and processes.

Concept of the Cell

• Cell Theory:

  1. All living organisms are made up of one or more cells.

  2. The cell is the basic unit of life.

  3. Cells arise from existing cells by division.

Classification of Cells

Types of Cells

• Prokaryotes:

  • No nucleus.

  • Always single-cellular.

  • Examples include bacteria (eubacteria) and archaea.

  • Archaea: known for thriving in extreme environments.

• Eukaryotes:

  • Have a true nucleus.

  • Can be single-cellular (like protists) or multi-cellular (plants, animals, fungi).

  • Major Groups:

    • Plants (including algae)

    • Animals

    • Fungi (molds, yeasts, mushrooms)

    • Protozoans

Structure of Cells

Eukaryotic Cell Organization

• Plasma Membrane:

  • Composed of a bilayer of phospholipids with embedded proteins.

  • Functions as a barrier, enables communication, and regulates import/export.

  • Dynamic structure with lipid rafts.

  • Allows the development of membrane potentials

• Cytoplasm (Cytosol):

  • Aqueous solution with a defined pH (approx. 7.2) that houses various cellular components.

  • Contains high concentration of proteins, metabolic enzymes, tRNAs, ribosomes, etc.

• Cytoskeleton:

  • Network of protein fibres

  • Composed of actin filaments, intermediate filaments, and microtubules.

  • Functions:

    • Maintenance of shape

    • Cell division

    • Motility

    • Movement of materials within the cell.

Key Organelles

Nucleus

• Structure: Surrounded by a double membrane (nuclear envelope).

• contains nuceloplasm, chromosomal DNA, histones and gene regulatory proteins

• Functions:

  • Houses chromosomal DNA and nucleoplasm

  • Site for RNA synthesis and processing, including splicing.

  • Nucleolus: Site of ribosome synthesis.

Endoplasmic Reticulum (ER)

• network of interconnected membrane vesicles (cisternae), continuous with the outer nuclear membrane

• Rough ER (rER): Synthesis of secreted and transmembrane proteins.

• Smooth ER (sER): Synthesizes lipids and detoxifies, e.g., in liver cells.

Golgi Apparatus

• Structure: Stack of flattened vesicles.

• Function: Modifies proteins destined for secretion and transmembrane proteins.

• cis golgi → trans golgi

Mitochondria

• can make up 25% of the cytoplasm

• Structure: Double membrane with inner folds

• contains circular DNA and ribosomes in matrix

• Functions:

  • Respiration/oxidative phosphorylation.

  • Citric acid cycle (Krebs cycle).

  • Apoptosis and Ca²⁺ storage.

  • Associated with mitochondrial disorders.

Lysosomes

• Function: Degradation of unwanted proteins and organelles.

• Acidic pH (optimal for degradation enzymes).

Peroxisomes

• Functions:

  • Degrade fatty acids and produce precursors for biosynthetic pathways.

  • Detoxify harmful substances like hydrogen peroxide.

  • oxidation produces water

  • the enzyme catalase neutralises H₂O₂ to water and oxygen