Untitled Quiz

Histology Lecture Notes

Main Title: Histology
Subtitle: The Ultrastructure of Cell
Lecturer: Prof. Yeşim Ulutas Uğur M.D.

Cell Structure

Cell Membrane: Essential for cell viability, dynamic structure, organized as a bilayered lipid. Contains two electron-dense (dark) and one electron-lucent (light) layers. Thickness is 8-10 nanometers. Contains embedded integral membrane proteins and attached peripheral membrane proteins. Defined as a modified fluid-mosaic model.
Surface Pits/Projections: Part of the cell membrane, involved in cell junctions and other processes.
Cell Junctions: Structures that connect cells to each other, including anchoring junctions.
Cytosol: The intracellular fluid, containing various dissolved molecules.
Organelles: Membrane-bound compartments within the cell, carrying out specific functions. Includes the Nucleus, mitochondria, ER, Golgi, Vesicles, lysosomes, peroxisomes etc
Vesicles: Small membrane-bound sacs in the cytoplasm.
Golgi Apparatus: Modifies, sorts, and packages proteins for secretion or use within the cell.
Intermediate Filaments: Provide structural support and connect cytoplasm to the extracellular environment.
Microtubules: Form cell shape and structural support. Involved in cellular transport and movement.
Microfilaments: Involved in cell shape, cytoplasmic streaming and movement with actin as a major protein.
Nucleus: Contains the cell's genetic material (DNA). Separated from the cytoplasm.
Nuclear Envelope: Separates the cytoplasm from the nucleoplasm, composed of two membranes, and is a selective barrier.
Peroxisome: Involved in detoxification, contains oxidative enzymes like peroxidases. Participates in fatty acid degradation.
Endoplasmic Reticulum (ER): Network of interconnected membranes, important for protein synthesis and lipid metabolism. Two types: Granular (rough) and smooth.
Granular ER (Rough ER): Synthesizes proteins using attached ribosomes, extensively modifies those that are destined for the extracellular space.
Smooth ER: Involved in lipid metabolism, detoxification, and calcium storage.
Ribosomes: Synthesize proteins. Found attached to the rough ER or free in the cytoplasm.
Mitochondria: Generate ATP (energy). Have an outer and inner membrane with cristae extending into the matrix. Divides and proliferates independently of cell cycle. Contains own DNA, RNA and ribosomes.
Centrioles: Pair of organelles, part of microtubule organizing center (MTOC) important for cell division and formation of cilia and flagella. Made up of microtubule triplets. They help form the mitotic spindle during cell division.

Plasma Membrane Components

Cholesterol: Important component of the cell membrane.
Phospholipids: Major component of the membrane bilayer.
Glycoprotein: Glycoprotein(at the surface forms glycocalyx) form the outer part of glycocalyx along with glycolipids.
Glycolipid: Glycolipid(at the surface forms glycocalyx) form the outer part of glycocalyx along with glycoproteins.
Glycocalyx: Complex carbohydrate coating that covers proteins and lipids on the outer surface of the cell membrane.

Plasma Membrane Transport

Simple Diffusion: Movement of small, uncharged molecules across the membrane without energy.
Channel Proteins: Membrane proteins forming channels for specific ions or molecules to pass.
Carrier/Transporters: Membrane proteins facilitating selective transport of larger or charged molecules.
Endocytosis: Internalization of materials by the cell, including pinocytosis (for fluids) and phagocytosis (for solids/large particles).
Exocytosis: Release of materials from the cell through the plasma membrane.
Transcytosis: Movement of substances across the cells and within the cytoplasm, in both directions.

Types of Integral Membrane Proteins

Receptor: Bind to external signaling molecules.
Linker: Connect the intracellular cytoskeleton to the ECM.
Pump/Transporter: Move ions or molecules against their electrochemical gradient.
Channel: Create hydrophilic pathways for water and specific ions.
Enzyme: Catalyze specific reactions at the membrane surface.
Constitutive Protein: Always present, has constant function.
Endocytosis & exocytosis of materials Transport of materials via vesicles inside the cell.

Endosomes

Early Endosome: Constructed by fusion of plasma membrane-originated vesicles. Located near the plasma membrane, sorts internalized proteins and returns some to the membrane. Inner environment not acidic yet.
Late Endosome: Acidic inner environment. Located near Golgi and nucleus, destined for fusion with lysosomes.

Lysosomes

Derived from endosomal structures.
Contain enzymes for degrading materials.
Lysosome-specific membrane proteins and enzymes are added.
Lysosomes are marked by containing mannose-6-phosphate on their surfaces and receptors inside.

Proteasome

Degrades abnormal proteins and recycles short-lived normal regulatory proteins in the cell.
Requires ubiquitin to target its proteins.
Requires ATP for its activity.

Peroxisomes

Responsible for detoxification.
Contains oxidative enzymes like peroxidases.
Surrounded by a single membrane.
Involved in fatty acid degradation.

Endoplasmic Reticulum (ER) further Detail

Granular (Rough) ER (GER): Studded with ribosomes. Primarily involved in protein synthesis, modification, and folding that are secreted or need further processing in other regions of the cell.
Smooth ER (SER): Lacks ribosomes. Responsible for lipid synthesis, detoxification, and calcium storage.
Cytosolic Ribosomes/Free Ribosomes: Involved in synthesis of proteins destined for the cytosol, mitochondria, peroxisomes or nucleus.

Golgi Apparatus Detail

Polarity: Organelle with distinct cis and trans faces. This polarity directs flow of cargo as it moves through the organelle.
Functions: Sorting, packaging and further modification of proteins.
Cargo transport: Well-developed transport vesicle system.

Mitochondria Detail

Outer Membrane: Contains porins and enzymes.
Inner Membrane: Contains folds called cristae, creating a large surface area for ATP production via oxidative phosphorylation. Impermeable to ions, relying on dedicated transport proteins.
Matrix: Contains enzymes for the citric acid cycle, fatty acid oxidation, and mitochondrial DNA replication and transcription.

Cytoplasm further Detail

Cytoplasmic Matrix: Fluid component of the cytoplasm. Contains macromolecules such as proteins and metabolites. Contains enzymes and functional elements like ribosomes and cytoskeletal elements like intermediate filaments.

Cell Cycle

Chromosomes & DNA replication: The centrioles and basal bodies play a role in cellular division and the formation of the mitotic spindle during cell division. This is essential for cells to divide themselves.

Protein Synthesis

Translation: Occurs in the cytoplasm. Ribosomes read the mRNA sequence to synthesize polypeptides. Special cases exist where proteins are synthesized directly into the ER or require additional modifications using chaperones, etc.

Transport Detail (Including Vesicles and Coatomers)

Anterograde (forward) transport: Movement from the ER to the Golgi. Uses COPII, a type of coatomer.
Retrograde (backward) transport: Movement from the Golgi to the ER. Uses COPI, a type of coatomer.
Cargo movement: Cargo gets separated from the coatomer when reaching its target organelle.

Nucleus Detail

Nuclear Envelope: Double membrane structure surrounding the nucleus.
Nucleoplasm: Cytoplasm within the nuclear membranes.
Nuclear Pore Complex (NPC): Regulates the passage of RNA, ribosomal subunits, etc. through the nuclear membrane to the cytoplasm.

Nucleolus

Structure: Contains rRNA genes. The site for the synthesis of rRNA and the assembly of ribosomes.
Components: Fibrillar center, fibrillar material, granular material

Inclusions

Intracellular structures, remnants of metabolic activities, sometimes around the plasma membrane.
Example: pigment granules (e.g., lipofuscin), glycogen granules, lipid droplets.