Cytology lectures 1, 2

Vocabulary flashcards reviewing cellular structure, membrane dynamics, organelle function, vesicle transport mechanisms, and associated pathology from the lecture material.

Cytology

The study of the structure and function of cells, serving as a diagnostic method to analyze cellular morphology and identify diseases such as cancer.

Fluid Mosaic Model

A structural model of the cell membrane characterized by the fluid lateral movement of phospholipids and proteins in a pattern created by scattered protein molecules.

Glycocalyx

A cell coat made of a thick mixture of glycolipids and glycoproteins located on the extracellular surface of cells, serving functions in protection and cell recognition.

ABC Transporters

A ubiquitous superfamily of integral membrane proteins responsible for the ATP-powered translocation of substrates across cell membranes, such as MultiDrug Resistance protein 1.

Signal Peptide

A sequence of $5\text{--}30$ amino acids on a newly translated protein that binds to the Signal Recognition Peptide to direct the polypeptide into the lumen of the rough endoplasmic reticulum.

Sarcoplasmic Reticulum

A specialized smooth endoplasmic reticulum found in striated muscle cells that functions specifically in the storage of calcium ions.

Flippase

An enzyme present in the smooth endoplasmic reticulum that translocates newly synthesized lipid molecules to the opposite layer of the membrane bilayer.

Cisternal Maturation Model

The accepted model of Golgi transport which states that Golgi cisternae are transient structures that mature and alter their enzyme composition over time while cargo remains inside.

Vesicular Transport Model

A model of Golgi transport proposing that cisternae are stable compartments with fixed enzymes, and cargo is transported sequentially between them via budding vesicles.

KDEL Sequence

A four-amino-acid signal sequence ($\text{Lys-Asp-Glu-Leu}$) that targets proteins in the Golgi for recognition by KDEL receptors to return them to the rough endoplasmic reticulum.

COP II

A coat protein complex that coats transport vesicles mediating anterograde transport from the rough endoplasmic reticulum to the Golgi apparatus.

COP I

A coat protein complex that coats vesicles mediating retrograde transport from the Golgi apparatus back to the rough endoplasmic reticulum.

Mannose 6-Phosphate

A specific carbohydrate marker attached to lytic enzymes in the Golgi apparatus to direct their packaging into vesicles destined for lysosomes.

Constitutive Secretion

A continuous pathway of exocytosis using coated vesicles that releases secretory products immediately without depending on specific extracellular stimuli.

Regulated Secretion

A secretory pathway in which products are stored in clathrin-like coated vesicles near the plasma membrane and only released upon receiving a specific extracellular signal.

Autophagy

A form of endocytosis where a cell consumes and degrades its own internal components via lysosomes to retrieve nutrients, energy, or structural building blocks during stress.

Lysosomes

Acidic membrane-bound organelles containing over $50$ lytic enzymes active at $\text{pH } 5.0$, responsible for intracellular digestion, degradation, and macromolecular recycling. Their acidic level is mantained by a proton pump on the membrane. It contains a glycocalyx.

Peroxisomes

Membrane-enclosed organelles containing catalase (representing $40\%$ of their total enzymes) that oxidize fatty and amino acids and convert toxic hydrogen peroxide into water and oxygen.

Lysosomal Storage Disorders

Lysosomal storage disorders (LSDs) are a group of genetic diseases (49) that derive from an abnormal accumulation of some substances in the lysosome. These happens because of mutation in the production of certain enzymes and life expectancy drops to 15 years and affects development, organs and often causes dementia. Therapeutic strategies for LSDs: enzyme replacement therapy, transplantation of bone marrow containing normal genes from an unaffected person, chaperone therapy to assist in the folding of the mutated enzyme and improved their stability, and gene transfer therapies to deliver the correct copy of the mutated gene.

Minimal requirements for a cell

Genetic material, a cytoplasm, ribosomes and a plasma membrane that envelopes it all.

Phospholipids

The phospholipids have hydrophilic polar head and two hydrocarbon hydrophobic tails, which can have different lengths because they’re fatty acids. The glycerol linked to phosphate group and then, at the very head of the phospholipids, to choline (hepatocytes, which is the most abundant), serine (neurons), ethanolamine (neurons and cardiomyocytes) or inositol (adipocytes and immune cells).

Phosphoglycerides are the most abundant type of phospholipids, sphingolipids are contained in some membranes as additions with the amino-alcohol sphingosine. Sphingomyelin is very abundant in nervous cells.

Factors that impact the plasma membrane’s fluidity

The length of the fatty acids (the longer the worse) and same goes for the number of proteins. Unsaturated fatty acids have easier fluidity, and cholesterol is very fluid at high temperatures and not so at low ones. Cholesterol renders the membrane less deformable and decreases permeability, it also prevents crystallisation of fatty chains of phospholipids.

Different types of endocytosis

Endocytosis can happen receptor-mediated, pinocytosis, phagocytosis and autophagy. Receptor-mediated endocytosis happens when the folding evolves after a specific binding causes the process to happen, that triggers the formation of the vesicle. Pinocytosis is engulfing tiny soluble molecules, mainly liquid components non-specifically chosen. Phagocytosis is an engulfment of particulate molecules or bacteria and it happens through actin cytoskeleton. The autophagy is a specific self-eating endocytosis, it is usually a survival eating mechanisms used often in cancer to get “building blocks” or energy.