SABS Molecular Biology

Cell Structure and Function

  • Levels of Organization

    • Non-living Levels: Atom (element) and molecule (compounds)

    • Living Levels: Cells, tissues, organs, organ systems, organism

8 Main Characteristics of Organisms

  • Made of cells

  • Require energy (food)

  • Reproduce

  • Maintain homeostasis

  • Organized

  • Respond to the environment

  • Grow and develop

  • Exchange materials with surroundings

Molecules of Life

  • Living Matter Composition:

    • 75-80% by weight is water, inorganic ions, and small organic molecules.

    • Water accounts for about 75% of a cell’s volume, acting as a solvent and medium for cellular processes.

  • Amino Acids:

    • Only L-forms are incorporated into proteins.

    • Only D-forms of glucose can be metabolized.

  • Adenosine Triphosphate (ATP):

    • Stores readily available energy in two chemical bonds; formed by ADP and Pi through photosynthesis or breakdown of sugars and fats in cells.

Eukaryotic Cell Cycle and Cell Theory

  • Cell Theory:

    • All living things are made of cells.

    • Cells are the basic unit of structure and function.

    • Cells arise from pre-existing cells.

  • Cell Size:

    • Plant Cell > Animal Cell > Bacteria

    • Cells must divide when their surface area is insufficient for waste removal and nutrient intake.

    • Cells within an organism are generally similar in size.

  • Cell Specialization:

    • Specialization occurs through differentiation via gene expression.

Prokaryotic Cells (Bacteria/Archaea)

  • No membrane-bound nucleus (DNA in nucleoid region).

  • Organelles are not membrane-bound.

Organelles Overview

  • Plasma Membrane:

    • Double layer of phospholipids and proteins.

    • Selectively permeable; allows some molecules (water, CO2) to pass freely.

    • Characteristics include:

      • Fluid mosaic model

      • Phospholipids: Hydrophilic heads, hydrophobic tails which interact with water.

      • Membrane proteins include channels, receptors, glycoproteins, and enzymes.

  • Cytoplasm:

    • Viscous fluid containing organelles, composed of cytosol, interconnected filaments, and storage substances.

  • Cytoskeleton:

    • Comprises microfilaments, microtubules, and intermediate filaments.

    • Function includes mechanical support, anchoring organelles, and substance movement.

  • Cilia and Flagella:

    • Motility structures:

      • Cilia: Short, moving substances outside cells.

      • Flagella: Whip-like, found on sperm cells.

  • Nucleus:

    • Control center enclosed by a double membrane (nuclear envelope), containing chromosomes and nucleolus.

  • Endoplasmic Reticulum (ER):

    • Rough ER: Ribosome-studded, manufactures and modifies proteins.

    • Smooth ER: No ribosomes, involved in lipid and carbohydrate synthesis.

  • Golgi Apparatus:

    • Synthesis and packaging station for proteins and other molecules.

    • Modifies proteins and facilitates transport.

  • Lysosomes:

    • Contain digestive enzymes for cellular renewal, breakdown of old cell parts, and digestion of invaders.

  • Mitochondria:

    • Energy-releasing organelles with their own DNA; involved in cellular respiration, producing ATP.

  • Chloroplasts:

    • Involved in photosynthesis (found in plant cells).

Genetic Diseases and Cell Function

  • ER Dysfunction: Associated with Parkinson’s Disease.

  • Golgi Dysfunction: Leads to skeletal abnormalities due to failure in protein transport.

DNA and RNA Structure

  • Nucleic Acids:

    • DNA and RNA are polymers of nucleotides with nitrogen bases and sugar-phosphate backbones.

    • Always written in the 5’ to 3’ direction.

    • Chargaff’s Rule: A=T, G=C; specificity due to hydrogen bonding.

DNA Replication and Repair

  • DNA Replication:

    • Semi-conservative model; antiparallel replication with complementary base pairing.

  • DNA Repair Mechanisms:

    • Mismatch repair, base-excision repair, and nucleotide-excision repair.

Link of Genetic Mutations to Oral Health

  • Conditions such as Ataxia-Telangiectasia and Bloom Syndrome affect dental health negatively.

  • Disorders lead to enamel hypoplasia and increased susceptibility to oral diseases.

Gene Expression and Regulation

  • Differential Gene Expression Control:

    • Cells differentiate during development; responses to stimuli lead to specialized functions.

    • Gene transcription is key in determining cell function.

Signaling Pathways**

  • Cell Communication:

    • Direct contact (via gap junctions) and indirect communication (via chemical signals).

  • Types of Signaling:

    • Endocrine, paracrine, and autocrine signaling, crucial in maintaining homeostasis and mediating development.

Gene Activity Control**

  • Signaling Pathways:

    • Activate or inhibit transcription, influencing cell fate decisions such as survival, differentiation, and proliferation.

    • TGFβ and cytokine receptor signaling play roles in immune responses and cellular functions.

Osteoclast-Osteoblast Coupling Theory**

  • Factors like TGF-β influence bone formation and resorption balance affecting oral health and pathologies.

Protein Structure**

  • Levels of Structure:

    • Primary: Linear sequence.

    • Secondary: Local structures (helices, sheets).

    • Tertiary: 3D shape.

    • Quaternary: Multi-chain complexes.

Amelogenesis Imperfecta**

  • Disorder of Tooth Development:

    • Genetic conditions leading to defective enamel formation, influenced by cellular signaling pathways.