Cell Biology: Phagocytosis Overview

Cell Transport Mechanisms

• Active movement of substances occurs via vesicle formation, transporting materials from inside to outside the cell.
• Phagocytosis (Cell Eating) involves pseudopodia extending from the cell membrane to engulf solid particles, such as bacteria. This results in the formation of a phagosome which fuses with lysosomes for digestion.
• Pinocytosis (Cell Drinking) is characterized by the formation of pockets in the cell membrane that surround extracellular fluid, leading to the creation of pinocytic vesicles, which also fuse with lysosomes for content digestion.

Significance of Integral Proteins

• Integral proteins at the cell membrane bind specific ligands and interact with other proteins on the cytoplasmic side, forming coated pits that invaginate and pinch off, allowing for the uptake of substances like hormones.

Growth Hormone Deficiency

• Dwarfism can result from a deficiency in growth hormone (GH) or from non-functioning GH receptors on the target cells, despite normal levels of GH.

Mitochondria

• Membranous organelles responsible for cellular respiration and energy production, often referred to as the "powerhouses of the cell."
• Active cells, such as liver cells, can contain up to 1000 mitochondria per cell.
• Mitochondria exhibit a trilaminar membrane appearance under electron microscopy and have distinctive structures, including two membranes surrounding an intermembranous space.

Histology and Cytology

• Histology is the study of microscopic structures of cells, tissues, and organs (Histo = tissue, Logia = study).
• Cytology focuses on cellular structure and function, defining the cell as the basic unit of life.

Types of Organelles

• Membranous Organelles: Include mitochondria, lysosomes, endoplasmic reticulum (rough and smooth), Golgi apparatus, and nucleus.
• Non-Membranous Organelles: Include ribosomes, centrioles, microfilaments, and inclusions. They are considered living, permanent, essential, and have vital functions.

Structure and Function of Cell Membrane

• The cell membrane, also called the plasma membrane, is trilaminar and typically difficult to visualize due to its thinness (8-10 nm).
• Comprised of phospholipid molecules with a hydrophilic (polar, charged) head and hydrophobic (non-polar, uncharged) tails, contributing to selective permeability.
• Proteins may be loosely attached or embedded in the lipid bilayer, with transmembrane proteins extending across.

Mitochondrial Functions

• Mitochondria are essential for energy production, containing oxidative enzymes for ATP synthesis and being capable of self-replication due to their own DNA.
• Mitochondrial dysfunction can lead to conditions like mitochondrial myopathies, affecting energy production and muscle function.

Glycocalyx

• A layer of glycoproteins and glycolipids on the outer surface of the cell membrane, contributing to cell recognition and communication.

Key Processes and Staining

• Mitochondria can be stained with various techniques, including silver and Janus green, aiding in their identification and study.

Review Questions

• Essential for cell vitality: Membranes and organelles are crucial, while inclusions and vacuoles are non-essential.
• Mitochondria function: Primarily responsible for energy production.
• Glycocalyx: Refers to a protective layer on the cell surface composed of glycoproteins and glycolipids.
• Organelles containing DNA: Only mitochondria possess their own DNA.
• Cell membrane's role: Responsible for selective diffusion.
• "Cell drinking" refers to pinocytosis, where the cell engulfs extracellular fluid.

This quiz explores the process of phagocytosis, where substances move from inside to outside a cell through vesicles. The focus is on how cells engulf solid particles, such as bacteria, using pseudopodia and forming vacuoles for digestion. Test your knowledge on this crucial cellular mechanism!