Introduction to Cell Biology

• Cell Biology (02-06-08 101) is a lecture introducing the topic of Cell Biology, taught by Dr. Mohamed Elkewedi and Dr. Doaa Fathy

Personal Introduction: Dr. Mohamed Mostafa Hassan

• Dr. Mohamed Mostafa Hassan is a Lecturer at the Biochemistry Department in the Faculty of Pharmacy, Alexandria University
• He obtained a PhD/Doctor rerum naturalium (Dr. rer. nat.) in 2019 from MDC/FUB, Berlin, Germany
• In 2013, he obtained a Master of Biomedical Sciences (MSc) from CMU, Cardiff, UK
• He obtained a Bachelor of Pharmaceutical Sciences in 2010 from Alexandria University, Faculty of Pharmacy, Alexandria (Egypt)

The Science of Biology

• The science of biology involves studying living organisms and their environments
• All living things share seven basic characteristics:
  • Organized
  • Acquire materials and energy
  • Reproduce
  • Grow and develop
  • Homeostatic
  • Respond to stimuli
  • Adapt and evolve

Cell Biology

• Cell biology is a branch of biology studying the different structures and functions of the cell
• It focuses mainly on the cell as the basic unit of life
• It explains the structure and organization of organelles, their physiological properties, metabolic processes, signaling pathways, and life cycle
• This is achieved on both a microscopic and molecular level in prokaryotic and eukaryotic cells

Cell: The Basic Unit of Life

• A cell is the smallest biological, structural, and functional unit of life
• Cells form the building blocks of organisms
• Organisms can be unicellular or multicellular
• Cells cluster up into tissues, tissues into organs, organs into systems, and systems into an organism

Unicellular vs Multicellular

• Unicellular organisms:
  • Made of one cell
  • Single cell performs all life functions (eat, reproduce, rid wastes, move)
  • Example: amoeba, bacteria
• Multicellular organisms
  • Made of more than one cell
  • Specialized cells perform different life functions (i.e., nerve cells)
  • Example: humans

Cell Theory

• As originally postulated by Schwann in 1839, the cell theory had two basic principles:
  • All organisms consist of one or more cells
  • The cell is the basic unit of structure for all organisms
• In 1855, Rudolf Virchow concluded that cells arise only by the division of other pre-existing cells
  • All cells arise only from pre-existing cells

Modern Cell Theory

• Modern Cell Theory details:
  • Cells contain hereditary information in their DNA; this is passed on to new cells through cell division
  • All cells have the same basic chemical composition
  • Energy flow (metabolism and biochemistry) occurs within cells

The Emergence of Modern Cell Biology

• Cytology, biochemistry, and genetics began as separate disciplines but have increasingly merged since about 1925
• Cytological Strand deals with Cellular Structure:
  • Historically, the limited resolving power of the light microscope did not allow seeing details of structures smaller than about 0.2 µm (200 nm), but modern light microscopes (as fluorescence microscope) surpasses that limit
  • A major breakthrough in resolving power came with the development of the electron microscope, which was invented in Germany in 1931 by Max Knoll and Ernst Ruska
  • The electron microscope uses a beam of electrons, rather than visible light, for imaging specimens; it can magnify objects up to 100,000 with a resolving power of less than 1 nm, enabling individuals to view subcellular structures such as membranes, ribosomes, organelles, and DNA and protein molecules
• Biochemical Strand Covers the Chemistry of Biological Structure and Function:
  • Discoveries in biochemistry have revealed how many of the chemical processes in cells are carried out, greatly expanding the knowledge of how cells function
  • Major discoveries in biochemistry were the identification of enzymes as biological catalysts, the discovery of adenosine triphosphate (ATP) as the main carrier of energy in living organisms, and the description of the major metabolic pathways cells use to harness energy and synthesize cellular components
  • Several biochemical techniques that have allowed better understanding of cell structure and function are:
    • Subcellular fractionation
    • Ultracentrifugation
    • Chromatography
    • Electrophoresis
• The Genetic Strand Focuses on Information Flow:
  • The chromosome theory of heredity states that the characteristics of organisms passed down from generation to generation result from the inheritance of chromosomes carrying discrete physical units known as genes.
  • Each gene is a specific sequence of DNA that contains the information to direct the synthesis of one cellular protein
  • DNA is a double helix of complementary strands held together by precise base pairing, allowing the DNA to be accurately duplicated as it is passed down to successive generations.

Characteristics of Living Cells

• Presence of a membrane around the cell restricts entry to certain molecules but allows free passage of water and some gases like oxygen and carbon dioxide.
• The membrane separates the inside space of the cell from the surroundings.
• The energy produced by a cell is conserved in the form of ATP
• A cell has its own genetic information received from its parent cell
• The cell has machinery to carry out transcription, translation, structure, and regulation, where genes lead to mRNA, then proteins, then subunits and enzymes

Cellular Unity

• All cells share a set of common characteristics
• All cells use the same basic building blocks (e.g. DNA, RNA, amino acids, lipids, and carbohydrates)
• Common macromolecules and supramolecular structures and physiology (e.g. lipid bilayers, ribosomes, using ATP as energy)