Cytology and Nucleus Review

A comprehensive set of practice flashcards covering cytology basics, nucleus structure, membranes, cytoskeleton, organelles, inclusions, endocytosis, secretory pathways, and cell death mechanisms.

Name the four basic tissue types in the body.

Epithelia, connective tissue, muscle, and nerve.

What are the main functions of epithelial cells?

Protection, absorption, secretion, excretion, and gas exchange; they cover exterior surfaces and line cavities and form glands.

Describe two key features of connective tissue.

Relatively few cells that are not tightly adherent; vascular with abundant extracellular matrix.

What is the primary role of muscle tissue?

Movement and changes in size/shape of body organs; organized in bundles with actin and myosin in the cytoplasm.

What are the two main cell types in the nervous system?

Neurons and supporting (glial) cells.

List three common features shared by most cells.

Membrane-bound organization, nuclei (zero to many), organelles and inclusions.

What are the three major components of the nucleus?

Nuclear envelope, chromatin, and nucleolus.

Name the parts of the nuclear envelope.

Outer nuclear membrane (continuous with rER), inner nuclear membrane, nuclear pores, and the nuclear lamina.

What is the function of nuclear pores?

Bidirectional gates for traffic between nucleus and cytoplasm; small molecules diffuse; larger proteins with a nuclear localization sequence are transported by energy-dependent mechanisms.

What is the nuclear lamina responsible for?

Gives shape and stability to the nuclear envelope, organizes the interphase nucleus, links chromatin to the envelope, and participates in mitosis.

Differentiate between heterochromatin and euchromatin.

Heterochromatin is electron-dense and transcriptionally inactive; Euchromatin is loosely packed and transcriptionally active.

What is the Barr body?

Inactive X chromosome in females that appears as a small, highly compact heterochromatic region near the nuclear envelope.

Where is the nucleolus located and what is its function?

Usually eccentrically placed in the nucleus; site of rRNA transcription and ribosome assembly.

What are Nucleolar Organizing Regions (NORs)?

Regions of interphase chromosomes that contain genes encoding rRNA and help reorganize the nucleoli after division.

Name the three major RNA types and their roles.

mRNA codes for protein sequences; tRNA transports amino acids to the ribosome; rRNA forms ribosomes.

Describe the two ribosomal subunits.

Large subunit contains 5S, 28S, and 5.8S rRNA with ~49 proteins; small subunit contains 18S rRNA with ~33 proteins.

What does the S in ribosomal RNA subunits refer to?

Svedberg unit, a measure of sedimentation rate during centrifugation.

Where are ribosomes typically located and what are polyribosomes?

Ribosomes are in the cytoplasm as free ribosomes or attached to the outer nuclear membrane and rough ER; polyribosomes are clusters of ribosomes on a single mRNA.

What is the general structure of membranes and the concept of unit membrane?

Membranes are trilaminar with two electron-dense leaflets and a central lucent zone; they are dynamic, asymmetric, and vary in composition.

What are the main components of cell membranes and their roles?

Lipids (phospholipids, cholesterol, glycolipids) provide structure and permeability; proteins perform most membrane functions; carbohydrates are on the outer surface.

What is the glycocalyx?

Carbohydrate-rich layer on the cell surface formed by membrane carbohydrates.

What are lipid rafts?

Specialized membrane domains that organize or segregate signaling molecules and proteins.

List the three cytoskeletal filament systems and their approximate thickness.

Microfilaments ~7 nm, intermediate filaments ~10 nm, microtubules ~25 nm.

Describe microfilaments and actin dynamics.

Actin filaments formed from G-actin assembling into F-actin with a plus and minus end; capable of branching and regulated by actin-binding proteins and myosin motors.

Name some actin-binding proteins and their roles.

Proteins such as cofilin, profilin, gelsolin regulate assembly/disassembly; Arp2/3 promotes branching; cap proteins regulate growth; fimbrin/α-actinin bundle filaments; filamin/spectrin organize networks.

What are intermediate filaments and their primary role?

A diverse group (~10 nm) of cell-type specific filaments providing structural mechanical support; lamins are in the nucleus; keratins in epithelia; vimentin in mesenchymal cells; neurofilaments in neurons.

What are the main features and organizing center of microtubules?

Polarity with plus and minus ends; assembled from α/β tubulin dimers; organized by the microtubule organizing center (MTOC) in the centrosome, which contains γ-tubulin ring and centrioles.

What are the three types of microtubules in the mitotic spindle?

Polar MTs (pushed poles apart), kinetochore MTs (attach to kinetochores at centromeres), astral MTs (radiate from centrosome and position poles.

Explain cytokinesis.

Division of the cytoplasm by a contractile actin-myosin II ring that forms a cleavage furrow and splits the cell.

What are the two major components of the endoplasmic reticulum and their functions?

Rough ER bears ribosomes and modifies newly synthesized proteins; Smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage.

What is the Golgi apparatus and its functional polarity?

Modifies, sorts, concentrates, and packages proteins; has cis (receiving) and trans (shipping) faces with the trans Golgi network for final sorting.

Describe the four Golgi compartments proteins pass through.

From the cis compartment to medial, then trans, and finally the trans Golgi network for sorting to lysosomes, plasma membrane, or secretion.

What are mitochondria and their key features?

Double-membrane organelles with an outer membrane containing porins, an intermembrane space, an inner membrane with cristae and ATP synthase, and a matrix containing enzymes of the Krebs cycle and mtDNA.

What roles do mitochondria play beyond ATP production?

Apoptosis initiation through cytochrome c release; contain their own DNA and ribosomes; can be abundant in energy-demanding cells; brown fat mitochondria show uncoupled respiration.

What is the composition and function of the inner mitochondrial membrane?

High protein concentration with cristae, ATP synthase complexes, and cardiolipin; sites of the electron transport chain for ATP production.

What are lysosomes and how are they targeted to lysosomes?

Membrane-bound organelles with acid hydrolases; acidic pH maintained by proton pumps; lysosomal enzymes are targeted via mannose-6-phosphate tagging.

What are peroxisomes and their main functions?

Beta-oxidation of fatty acids; detoxification of toxins; contain catalase and urate oxidase; important for plasmalogen synthesis in nerves.

What are proteasomes and their function?

Protein complexes that degrade misfolded or damaged polypeptides and regulate protein turnover.

Describe clathrin-coated and COP vesicles.

Clathrin-coated vesicles mediate trafficking from the TGN to lysosomes or secretory granules and receptor-mediated endocytosis; COPI mediates retrograde transport from Golgi to ER; COPII mediates anterograde transport from ER to Golgi.

What are caveolae and their role?

Small lipid raft–derived invaginations rich in caveolin involved in clathrin-independent endocytosis and transcytosis.

What are endosomes and phagosomes?

Endosomes are vesicles from endocytosis that mature as they traffic; phagosomes form during phagocytosis and fuse with lysosomes to degrade ingested material.

What are the two main secretory pathways to exocytosis?

Constitutive secretion, delivering contents continuously; regulated secretion, which is Ca2+-dependent and requires a signal.

What are inclusions and provide examples?

Inactive storied products such as glycogen, lipid droplets, pigments (lipofuscin, hemosiderin, melanin), and sometimes crystals.

What is lipofuscin and its significance?

Yellow-brown residual pigment from lysosomal digestion; accumulates with age and may contribute to aging and related diseases.

What is hemosiderin and how is it detected?

Aggregates of ferritin indicating iron storage; detectable by Prussian blue staining.

What is melanin and where is it found?

Pigment found in keratinocytes and pigmented cells of the retina and brain; synthesis discussed in integumentary system.

Compare necrosis and apoptosis.

Necrosis is cell and tissue damage with swelling and inflammation; apoptosis is programmed cell death with cell shrinkage and phagocytosis without inflammation.

What are caspases?

Proteases that execute apoptosis; activated from inactive procaspases in response to pro-apoptotic signals.

Why does apoptosis occur during development?

To regulate neuron numbers and spacing, shape developing structures, and remove unneeded tissues (eg, mammary tissue, interdigital spaces).

Why is apoptosis important in adults?

Maintains tissue homeostasis and eliminates harmful or infected cells; helps shape organs and respond to cellular stress.