Introduction to Histology and Cell Biology

Comprehensive practice flashcards covering histology fundamentals, tissue preparation, staining, microscopy, body fluid compartments, cell membrane architecture, cytoskeleton dynamics, and organelle structures.

What are the six structural levels of organization in the human organism?

Chemical level $\rightarrow$ Cellular level $\rightarrow$ Tissue level $\rightarrow$ Organ level $\rightarrow$ Organ system level $\rightarrow$ Organismal level.

What are the four primary tissue types in the body, and what are their representative subcategories?

1. Epithelial tissue (squamous, cuboidal, columnar); 2. Connective tissue (connective tissue proper, cartilage, bone, blood); 3. Muscle tissue (skeletal, cardiac, smooth); 4. Nervous tissue (neurons and neuroglia).

How does extracellular matrix (ECM) content vary across the four primary tissues?

Epithelial tissue contains a small amount of ECM; Connective tissue has an abundant amount; Muscle tissue has a moderate amount; and Nervous tissue has a very small amount.

What is formalin and what four preservation roles does it serve during tissue fixation?

Formalin is a $37\%$ aqueous solution of formaldehyde. It preserves tissue by: 1) preventing enzymatic degradation, 2) terminating cellular metabolism, 3) killing pathogenic microorganisms, and 4) hardening tissue.

What is the correct sequence of steps involved in preparing paraffin-embedded tissue sections?

Fixation $\rightarrow$ Dehydration $\rightarrow$ Clearing $\rightarrow$ Infiltration (at $52^{\circ}\text{C}-60^{\circ}\text{C}$) $\rightarrow$ Embedding.

How do hematoxylin and eosin (H&E) differ in terms of dye properties, target chemical groups, and resultant colors?

Hematoxylin is a basic dye that reacts with anionic (negatively charged) components—such as nucleic acid phosphate groups, glycosaminoglycan sulfate groups, and protein carboxyl groups—producing a dark blue or violet stain. Eosin is an acidic dye that reacts with cationic (positively charged) groups—such as protein amino groups—producing a red or pink stain.

Which macromolecular structures are specifically stained by the Periodic acid-Schiff (PAS) reaction and the Feulgen reaction?

The Periodic acid-Schiff (PAS) reaction stains carbohydrates and carbohydrate-rich molecules; the Feulgen reaction stains DNA.

In the fluorescent-antibody assays shown, what is the mechanistic difference between a direct and an indirect test?

In a direct fluorescent-antibody test, a fluorescent dye-labeled primary antibody binds directly to the target antigen. In an indirect fluorescent-antibody test, an unlabeled primary antibody binds to the antigen, and a fluorescent dye-labeled secondary antibody (anti-human immunoglobulin) binds to the primary antibody.

What are the fundamental differences in beam path and image generation between Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM)?

TEM passes an electron beam through an ultra-thin tissue section to project a 2-dimensional internal structural image onto a fluorescent viewing screen or CCD detector. SEM scans an electron beam across the surface of a 3-dimensional specimen, detecting scattered electrons to reconstruct a 3-dimensional surface image on a monitor.

What microscopy technique utilizes the setup shown below featuring a laser, photodiode, cantilever, tip, and piezoelectric scanner?

Atomic Force Microscopy (AFM).

How is total body water (TBW) calculated, and how is it partitioned between fluid compartments?

$\text{Total body water} = 0.6 \times \text{Body weight}$. Intracellular fluid (ICF) comprises $66\%$ ($2/3$) of TBW, and extracellular fluid (ECF) comprises $33\%$ ($1/3$) of TBW. ECF is further divided into interstitial fluid ($80\%$ of ECF) and plasma ($20\%$ of ECF).

What are the key morphological distinctions between prokaryotic and eukaryotic cells?

Prokaryotic cells are smaller ($1\,\mu\text{m}$ in diameter, $1/10$ the size and $1/1000$ the volume of human cells), lack a membrane-bound nucleus (DNA is in a nucleoid), lack membranous organelles, and possess a protective cell wall and outer membrane. Eukaryotic cells contain a membrane-bound nucleus, membranous organelles, and a protein cytoskeleton.

What components form the plasma membrane according to the fluid mosaic model?

An amphipathic phospholipid bilayer, interspersed cholesterol molecules, integral (transmembrane) proteins, and peripheral proteins.

What is the structural role of cholesterol in the plasma membrane bilayer?

Cholesterol is an amphipathic steroid molecule containing a rigid planar steroid ring that inserts between phospholipids to provide mechanical strength and rigidity to the bilayer.

What are the five primary functional categories of integral membrane proteins?

1. Channels, pumps, and carriers; 2. Receptors; 3. Linker or anchor proteins; 4. Enzymes; 5. Structural proteins.

What structural and functional features distinguish heterochromatin from euchromatin?

Heterochromatin is tightly coiled, densely staining, and transcriptionally inactive. Euchromatin is loosely packed, lightly staining, and contains transcriptionally active DNA sequences coding for genes.

What is the nucleolus and what is its primary biological function?

The nucleolus is a non-membranous region of the nucleus surrounding transcriptionally active DNA that codes for ribosomal RNA (rRNA); its primary function is ribosome production and assembly.

What are the three classes of cytoskeletal filaments, their diameters, and their primary protein subunits?

1. Microfilaments (actin filaments): $7\,\text{nm}$, composed of globular G-actin polymerized into filamentous F-actin; 2. Intermediate filaments: $8-12\,\text{nm}$ (or $10\,\text{nm}$), composed of fibrous proteins like keratins, vimentin, desmin, neurofilaments, or lamins; 3. Microtubules: $25\,\text{nm}$, hollow tubes composed of $\alpha$- and $\beta$-tubulin heterodimers.

In microtubule-based intracellular transport, which motor protein transports cargo toward the minus end and which toward the plus end?

Dynein moves toward the minus ($-\text{end}$) of the microtubule, whereas kinesin moves toward the plus ($+\text{end}$).

What nucleotide and cofactor requirements govern the polymerization of microtubules versus actin microfilaments?

Microtubule assembly requires GTP and $\text{Mg}^{2+}$. Actin filament assembly requires ATP, $\text{K}^{+}$, and $\text{Mg}^{2+}$.

How does the assembly and dynamic nature of intermediate filaments differ from microfilaments and microtubules?

Intermediate filaments assemble by pairing two helical monomers into a coiled-coil dimer, then pairing two dimers into a staggered tetramer that packs into insoluble cables. Unlike actin filaments and microtubules, intermediate filaments do not assemble and disassemble dynamically within the cell (they have a fixed assembly).

Match Intermediate Filament Classes I through V to their tissue distribution and protein names.

Class I and II: Acidic and basic cytokeratins (epithelial cells); Class III: Vimentin (mesenchymal cells/fibroblasts/lens), Desmin (muscle cells), GFA protein (glial cells/astrocytes); Class IV: Neurofilament proteins NF-L, NF-M, NF-H (central and peripheral nerves); Class V: Nuclear lamins A, B, C (all cell types).

What are the subunits of the eukaryotic $80\text{S}$ ribosome, and what does a Svedberg unit ($\text{S}$) measure?

The eukaryotic ribosome consists of a $60\text{S}$ large subunit and a $40\text{S}$ small subunit. A Svedberg unit ($\text{S}$) equals $10^{-13}\,\text{s}$ and measures the sedimentation rate of a macromolecule during centrifugation.

What are the primary functional differences between rough endoplasmic reticulum (rER) and smooth endoplasmic reticulum (sER)?

The rER is studded with ribosomes and is responsible for synthesizing, folding, and packaging proteins destined for membranes, lysosomes, or secretion. The sER lacks ribosomes and functions in lipid, phospholipid, and steroid synthesis, intracellular $\text{Ca}^{2+}$ storage, and detoxification of toxins.

Which coat proteins mediate anterograde transport from the ER to the Golgi, and which mediate retrograde transport back to the ER?

Anterograde transport (ER to cis-Golgi) is mediated by COP-II coat proteins; retrograde transport (cis-Golgi to ER) is mediated by COP-I coat proteins.

What are the three destinations for transport vesicles budding from the trans-Golgi network (TGN)?

1. Secretion outside the cell via exocytosis (clathrin-coated secretory vesicles); 2. Insertion into the cell membrane as integral or peripheral proteins (non-clathrin-coated vesicles); 3. Delivery to lysosomes (clathrin-coated vesicles tagged with mannose-6-phosphate receptors).

What is the internal pH of a lysosome and what are its three major degradation mechanisms?

The internal pH is acidic ($\sim 4.5-5.0$), compared to cytoplasmic pH ($7.2$). Its mechanisms are: 1) Heterophagy (fusing with phagosomes to digest extracellular debris/pathogens); 2) Autophagy (digesting old or damaged organelles); 3) Apoptosis (participating in programmed cell death).

What metabolic functions take place inside peroxisomes?

1. $\alpha$- and $\beta$-oxidation of very long chain fatty acids (VLCFA) to acetyl-CoA; 2. Synthesis of plasmalogen; 3. Reactive oxygen species (ROS) detoxification via catalase ($\text{H}_2\text{O}_2 \rightarrow \text{O}_2 + \text{H}_2\text{O}$); 4. Ethanol metabolism ($\text{Ethanol} \rightarrow \text{Acetaldehyde} \rightarrow \text{Acetic acid} \rightarrow \text{Acetyl-CoA} \rightarrow \text{H}_2\text{O} + \text{CO}_2$).

What is the structural organization of mitochondria, and in which mature human cell type are they absent?

Mitochondria consist of a smooth outer membrane, an inner membrane folded into cristae to maximize surface area, an intermembrane space, and an internal matrix. They are absent in mature red blood cells.

What is the structural organization of a centrosome, and during which cell cycle phase do centrioles duplicate?

A centrosome consists of two centrioles (mother and daughter) oriented at right angles to each other, embedded in pericentriolar material (PCM). Centriole duplication occurs during the S-phase, concurrently with DNA replication.

What are the four primary tissue types found in the human body?

Epithelial, connective, muscle, and nervous tissues.

In routine tissue preparation for histology, what is the correct sequence of steps from tissue removal to sectioning?

Fixation, dehydration, clearing, infiltration, and embedding.

What is the primary substance used for histological fixation, and what are its four main functions?

Formalin (a $37\%$ aqueous solution of formaldehyde); it preserves tissue by preventing enzymatic degradation, terminating cellular metabolism, killing pathogenic microorganisms, and hardening the tissue.

In H&E staining, how does hematoxylin interact with cellular components and what color does it produce?

Hematoxylin is a basic dye that reacts with anionic (negatively charged) components, such as the phosphate groups of nucleic acids, producing a dark blue or violet positive stain.

In H&E staining, how does eosin interact with cellular components and what color does it produce?

Eosin is an acidic dye that reacts with cationic (positively charged) components, such as amino groups of proteins, producing a red or pink negative stain.

What specific macromolecule class is detected using the Periodic acid-Schiff (PAS) reaction?

Carbohydrates or carbohydrate-rich molecules.

Which histological staining technique specifically stains DNA?

The Feulgen reaction.

What is the key difference between direct and indirect immunofluorescence tests?

Direct immunofluorescence utilizes fluorophore-labeled antibodies that bind directly to the target antigen; indirect immunofluorescence uses an unlabeled primary antibody against the antigen, followed by a labeled secondary antibody that binds to the primary antibody.

What are the key imaging differences between transmission electron microscopy (TEM) and scanning electron microscopy (SEM)?

TEM passes an electron beam through an ultra-thin tissue section to visualize internal 2D ultrastructure on a fluorescent screen or detector, whereas SEM scans an electron beam across the surface of a 3D specimen to detect scattered electrons and produce a 3D surface view.

Which imaging technology uses a laser reflected off a cantilever with a sharp tip and a piezoelectric scanner to produce high-resolution nanoscale surface topography?

Atomic force microscopy (AFM).

How is total body water (TBW) calculated and divided between body fluid compartments?

$\text{TBW} = 0.6 \times \text{body weight}$, with approximately $66\%$ situated in the intracellular fluid (ICF) and $33\%$ in the extracellular fluid (ECF).

How is the extracellular fluid (ECF) compartment subdivided into interstitial fluid and plasma?

Approximately $80\%$ of ECF is interstitial fluid and $20\%$ is blood plasma.

What are the primary distinguishing features of prokaryotic cells compared to eukaryotic cells?

Prokaryotes are smaller ($1\,\mu\text{m}$ in diameter, $1/10$ the size and $1/1000$ the volume of an average human cell), lack a membrane-bound nucleus (genetic material is in a nucleoid), lack membranous organelles, and possess a cell wall and outer membrane.

What is the amphipathic structure of a membrane phospholipid?

A polar, hydrophilic phosphate head group linked to glycerol, attached to two non-polar, hydrophobic fatty acid tails.

What is the role of cholesterol in the cell membrane?

It is an amphipathic steroid molecule that intercalates between phospholipids to provide strength, rigidity, and stability to the lipid bilayer.

What are five major functional classes of integral membrane proteins?

1. Channels / pumps / carriers
2. Receptors
3. Linker / anchor proteins
4. Enzymes
5. Structural proteins

What are the structural distinctions and functional roles of euchromatin versus heterochromatin?

Heterochromatin is highly condensed, dark-staining, and transcriptionally inactive; euchromatin is loosely packed, light-staining, and transcriptionally active, containing sequences that code for genes.

What is the structural definition and primary function of the nucleolus?

It is a non-membranous region of the nucleus surrounding transcriptionally active DNA that codes for ribosomal RNA (rRNA); its primary function is ribosome production and assembly.

What are the three filament classes of the cytoskeleton and their respective diameters?

1. Microfilaments (actin filaments): $7\,\text{nm}$
2. Intermediate filaments: $8\text{--}12\,\text{nm}$ (or $10\,\text{nm}$
3. Microtubules: $25\,\text{nm}$

What protein subunits and biochemical requirements are needed for microtubule assembly?

Microtubules are composed of $\alpha$- and $\beta$-tubulin heterodimers; polymerization originates from the microtubule-organizing center (MTOC) and requires GTP (guanosine triphosphate) and $\text{Mg}^{2+}$.

Which motor proteins move along microtubules, and in which direction does each travel?

Dynein moves retrogradely toward the minus ($-$) end, while kinesin moves anterogradely toward the plus ($+$) end.

What subunits and cofactors are required for actin microfilament assembly?

G-actin (globular actin) monomers polymerize into F-actin (filamentous actin) in a process requiring ATP (adenosine triphosphate), $\text{K}^+$, and $\text{Mg}^{2+}$.

Which specific intermediate filament proteins are assigned to Classes I, II, III, and V?

Class I: Acidic cytokeratins; Class II: Basic cytokeratins; Class III: Vimentin, desmin, and GFA protein; Class V: Nuclear lamins (Lamin A, B, and C).

What is the structural organization of a centrosome?

It comprises two centrioles (mother and daughter) oriented at right angles ($90^\circ$) to each other, embedded in a dense proteinaceous pericentriolar material (PCM).

What are the ribosomal subunits and full sedimentation coefficient of a eukaryotic ribosome?

An $80\text{S}$ ribosome composed of a $60\text{S}$ large subunit and a $40\text{S}$ small subunit.

What are the primary functional differences between the rough and smooth endoplasmic reticulum?

Rough ER has attached ribosomes and synthesizes, folds, and packages proteins; smooth ER lacks ribosomes and synthesizes lipids, phospholipids, and steroids, stores intracellular $\text{Ca}^{2+}$, and detoxifies harmful compounds.

Which coat proteins mediate anterograde versus retrograde vesicular transport between the ER and Golgi apparatus?

COP-II coats vesicles moving in the anterograde direction (ER to cis-Golgi network), whereas COP-I coats vesicles moving in the retrograde direction (Golgi back to ER).

Which receptor and vesicle coat target newly synthesized acid hydrolases from the trans-Golgi network to lysosomes?

Mannose-6-phosphate receptors in clathrin-coated transport vesicles.

What is the internal pH of lysosomes and what classes of enzymes do they house?

An acidic pH of approximately $4.5\text{--}5.0$, containing hydrolytic digestive enzymes including acid phosphatase, nucleases (DNase, RNase), proteases (collagenase, cathepsins), carbohydrate-cleaving enzymes, and lipases (sphingomyelinase).

What are the major metabolic and detoxification functions of peroxisomes?

Alpha- and beta-oxidation of very long chain fatty acids (VLCFA), synthesis of plasmalogen and bile acid intermediates, degradation of hydrogen peroxide ($\text{H}_2\text{O}_2$) into $\text{O}_2 + \text{H}_2\text{O}$ via catalase, and ethanol oxidation.

What are the structural components of a mitochondrion, and which human cells lack mitochondria?

A smooth outer membrane, an intermembrane space, an inner membrane folded into cristae to maximize surface area, and an internal matrix; mature red blood cells (erythrocytes) lack mitochondria.