Video4 Tema4

Introduction to Cellular Biology

Overview of the Session

• The session welcomes students to the fourth class on cellular biology, part of the preparatory program for dentistry.

• Previous discussions focused on cellular compartmentalization and the importance of membranes in cell function and health.

Topic Introduction: Cytoskeleton and Cell Junctions

• Today's topic is about the cytoskeleton and cell junctions, emphasizing their roles in cellular communication and dental implications.

Components of the Cytoskeleton

Microfilaments

• Microfilaments are primarily composed of actin, a crucial protein found abundantly in eukaryotic cells.

• Actin exists in two forms: G-actin (monomeric) and F-actin (polymeric), which undergoes polymerization to form filaments.

Functions of Actin

• Actin microfilaments facilitate cellular movement by forming protrusions like lamellipodia (flat extensions) and filopodia (elongated projections).

• These structures enable cell migration, contractility, and overall mobility through dynamic interactions with other proteins.

Microtubules

Structure and Function

• Microtubules are made from tubulin proteins (alpha and beta), forming hollow cylinders essential for intracellular transport.

• They have a diameter of 25 nm with distinct polarity, aiding in vesicle transport within cells.

Role in Mitosis

• During mitosis, microtubules align chromosomes at poles, stabilizing the mitotic spindle structure necessary for cell division.

Intermediate Filaments

Characteristics

• Intermediate filaments vary by cell type; keratins provide mechanical strength in epithelial cells while desmin supports muscle fibers.

Structural Support

• They maintain tissue integrity by providing structural stability without participating directly in transport processes.

Interactions Among Cytoskeletal Elements

Coordination Between Filaments

• All components—actin microfilaments, microtubules, intermediate filaments—work together to maintain cell shape and dynamics through coordinated functions.

Visualization Techniques

Fluorescence Microscopy Insights

• Fluorescent microscopy reveals overlapping distributions of actin microfilaments (red fluorescence) and tubulin microtubules (green fluorescence).

Cellular Dynamics

Importance of Link Proteins

• Link proteins like plectin connect different cytoskeletal elements ensuring functional coordination during cellular remodeling processes.

Cellular Migration Mechanisms

Steps Involved

• Migration involves actin polymerization at leading edges followed by focal adhesion formation using integrins for movement across surfaces.

Cilia and Flagella

Structure Differences

• Primary cilia have a "9 + 2" arrangement allowing mobility while non-motile primary cilia lack central pairs ("9 + 0") serving as sensory receptors.

Movement Mechanism

• Mobile cilia utilize coordinated beating powered by dyneins connecting peripheral pairs to central pairs facilitating movement across surfaces.

Chemotaxis

Definition & Process

• Chemotaxis describes how immune cells migrate towards chemical signals released during infections or inflammation via pseudopod extension driven by actin polymerization.

Understanding Cell Junctions in Epithelial Tissue

Importance of the Cytoskeleton and Adherens Junctions

• The cytoskeleton, particularly microfilaments of actin, is crucial for maintaining adherens junctions during epithelial genesis to preserve cell polarity and prevent detachment.

Desmosomes: Structure and Function

• Desmosomes, also known as maculae or adherent spots, appear darker under a microscope and serve to connect adjacent cells through globins and desmoplakin proteins.

• These proteins traverse cell membranes and involve cadherins; they are essential for maintaining the stability of oral mucosa, keratin in gums, and overall epithelial integrity.

Role of Desmosomes in Oral Health

• The integrity of desmosomes is vital for keeping cells attached; their dysfunction can lead to conditions like blisters due to inflammation when cells detach.

• Disruption in desmosomal connections can result from mechanical trauma (e.g., cuts from food or toothbrushes), affecting healing processes.

Tight Junctions: Structure and Selectivity

• Tight junctions (or "T junctions") are structures that bring cell membranes closer together than adherens junctions or desmosomes, preventing gaps between them.

• Composed of claudins and occludins, tight junctions regulate selective passage of ions, solutes, and water while maintaining cellular polarity.

Gap Junctions: Communication Between Cells

• Gap junctions consist of connexons formed by six connexins each; these channels allow direct communication between adjacent cells.

• In oral tissues, various types of connexins (like 26, 30, 32, 43) play significant roles in synchronizing cellular activities essential for tissue homeostasis.

Clinical Relevance of Cell Junction Integrity

• Proper functioning gap junction connections are critical for coordinating activities among dental epithelial cells; disruptions may lead to hereditary diseases such as keratitis ichthyosis deafness syndrome.

• The importance of gap junction integrity extends beyond local effects; it can influence genetic predispositions to other health issues like dysplasias or neoplasms leading to cancer.

Conclusion

• A bibliography was provided at the end for further reading on the topics discussed today. Students are encouraged to review presentation materials thoroughly for better understanding.