Intro to histo & cytology I

cell structure, cellular differentiation, nuclear organization, mitosis, meiosis, stem cells, and histology preparation and staining techniques.

What is the primary purpose of fixation in histology tissue preparation?

Fixation cross-links proteins and inactivates degradative enzymes to preserve cell and tissue structure.

What occurs during the dehydration step of tissue preparation?

The tissue is transferred through a series of increasingly concentrated alcohol solutions, ending in $100\%$, which removes all water.

What is the process of clearing in histological tissue preparation?

Alcohol is removed from tissue using organic solvents in which both alcohol and paraffin are miscible.

How is tissue infiltration accomplished during histological preparation?

The tissue is placed in melted paraffin until it becomes completely infiltrated with this substance.

What is involved in the embedding step of histological preparation?

The paraffin-infiltrated tissue is placed in a small mold with melted paraffin and allowed to harden.

What instrument is used to slice trimmed paraffin blocks into thin tissue sections?

A microtome.

Why are stains or dyes necessary when examining tissue under a microscope?

Unstained tissues and cells are difficult to examine, so dyes make cells, tissues, and their components easier to distinguish by reacting with chemical components.

What net electrical charge do cellular components have if they stain well with basic dyes?

Net negative charges (anionic).

What term describes cell and tissue components that have an affinity for basic dyes?

Basophilic.

What net electrical charge do cellular components have if they stain well with acidic dyes?

Net positive charges (cationic).

What term describes cell and tissue components that have an affinity for acidic dyes?

Acidophilic.

Which four basic dyes are specifically named in the histology transcript?

Hematoxylin, Toluidine blue, Alcian blue, and Methylene blue.

Which three acidic dyes are specifically named in the histology transcript?

Eosin, Orange G, and Acid fuchsin.

What is the most common acid-basic dye combination used in histology?

Hematoxylin & Eosin (H&E).

What color do basophilic structures stain when using Hematoxylin?

Purple.

Which cellular structures stain purple with Hematoxylin due to their acidic composition?

Nucleic acids (DNA in the nucleus) and glycosaminoglycans.

What color do acidophilic structures stain when using Eosin?

Pink.

Which cellular components stain pink with Eosin due to their basic components?

Mitochondria, secretory granules, and collagen.

What color do carbohydrate-rich cellular components stain in the Periodic acid – Schiff (PAS) reaction?

Dark purple or magenta.

Which cell type is identified as PAS-positive due to carbohydrate-rich secretory granules?

Goblet cells.

What type of dye is Sudan black, and what structure does it stain?

It is a lipid-soluble dye that stains cell and tissue structures rich in lipids black.

Which specific cell type is given as an example of staining black with Sudan black?

Adipose cells.

What is the approximate resolution limit of an electron microscope provided in the text?

Around $3\,nm$.

What maximum magnification level can an electron microscope achieve according to the transcript?

Up to $400,000\times$.

What structural detail does an electron microscope reveal that light microscopes cannot?

The ultrastructure of the cell, including organelles.

What is the basic definition of a cell?

The basic structural and functional unit of any living thing.

What are the three statements that comprise the Cell Theory?

1. All living things are made of one or more cells. 2. All cells come from existing cells. 3. Cells are the basic building blocks of life.

What are the structural features of prokaryotic cells?

Unicellular organisms that never form tissues, have no nucleus, no organelles, only ribosomes, a cell wall, and a capsule.

What are the defining characteristics of eukaryotic cells?

Unicellular and multicellular organisms that form tissues (in multicellular organisms), have a nucleus, have organelles, and some have a cell wall.

What are the major characteristics of human cells?

They are eukaryotic cells with no cell wall, form human tissues, undergo differentiation, specialization, and diversity, and have a nucleus and organelles.

In a mature ovarian follicle, what cells surround the oocyte?

Follicular cells and theca interna and externa cells.

Cell differentiation results from the interaction between which two factors?

Genes and the cellular microenvironment.

What are the two main outcomes of cell differentiation?

1. Different appearance and structure, and 2. Functional specialization.

What type of stem cell is formed directly by the zygote and blastomeres?

Totipotent stem cell.

What happens to a cell's basic functions when it undergoes differentiation?

One or more functions become more important, while all other basic functions are maintained.

Why is the nucleus described as the command center of the cell?

It is a membrane-bound, highly specialized organelle that serves as the information processing and administrative center of a eukaryotic cell.

What are the three primary functions of the cell nucleus?

1. Stores genetic (hereditary) material, 2. Coordinates all cell activities, and 3. Contains molecular machinery for DNA synthesis and RNAs processing.

What four specific cell activities are coordinated by the nucleus?

Growth, metabolism, protein synthesis, and cell division.

What are the four main structural components of the nucleus?

1. Nuclear envelope, 2. Nucleoplasm, 3. Chromatin, and 4. Nucleolus.

What physical feature characterizes the nuclear envelope?

It is pore-riddled.

What is the nucleoplasm?

The fluid component of the nucleus.

What two components make up chromatin?

DNA and associated proteins (histones).

What makes up the nucleolus?

A dense cluster of RNA and proteins plus inactive ribosomes.

What is the structure and function of the nuclear envelope?

It is a selectively permeable barrier formed by two membrane units with pores that separates the nucleoplasm from the cytoplasm, allowing selective passage of molecules.

With what structure is the inner membrane of the nuclear envelope associated?

Nuclear lamina.

What binds to the outer membrane of the nuclear envelope?

Ribosomes.

What is the space between the inner and outer membranes of the nuclear envelope called?

Perinuclear space or cisterna.

Which cellular organelle is continuous with the outer membrane and perinuclear space of the nuclear envelope?

Rough endoplasmic reticulum (rER).

What is the function of the nuclear lamina?

It stabilizes the nuclear envelope.

What proteins compose the meshwork of the nuclear lamina?

Intermediate filament proteins called lamins.

How are lamins positioned in nondividing cells?

They are bound to membrane proteins and associated with chromatin.

What structures bridge the inner and outer membranes of the nuclear envelope?

Nuclear pore complexes.

What core proteins form the nuclear pore complex, and what symmetry do they possess?

Nucleoporins, arranged with eightfold symmetry around a lumen.

How do ions and small molecules pass through the nuclear envelope?

By simple diffusion through nuclear pore complexes.

How is the movement of macromolecules between nucleoplasm and cytoplasm regulated?

By nuclear pore complexes using energy provided by GTP hydrolysis by GTPases.

What energy source powers the import and export of macromolecules through nuclear pores?

GTP hydrolysis by GTPases.

What is another name for nucleoplasm?

Karyoplasm.

What is the composition and function of nucleoplasm?

It is a viscous fluid containing water, dissolved ions, and other molecules that acts as a suspension medium for nuclear components.

How is human DNA divided in somatic cells versus gametes?

In somatic cells, it is divided among 46 chromosomes (23 pairs); gametes are an exception.

What is the total length and base pair count of human DNA?

$2\text{ meters}$ long and $3.2\text{ billion bp}$.

What type of proteins are histones?

Basic proteins.

What structural units of DNA are formed by histones and DNA?

Nucleosomes.

What components form the core of a nucleosome?

An octamer core of eight histones: 2 copies each of H2A, H2B, H3, and H4.

How many base pairs of DNA wrap around the histone core in a nucleosome?

$150\text{ bp}$ of DNA.

Where is the H1 histone located in a nucleosome?

It is associated with the wrapped DNA at the surface of the core.

What is the length of linker DNA separating adjacent nucleosomes?

$50\text{ -- }80\text{ bp}$.

Why are nucleosomes described as dynamic structures?

They undergo histone modification and rearrangement, which is key to DNA replication and transcription.

What are the structural stages and thicknesses of chromatin folding?

1. DNA double helix ($2\,nm$ thick), 2. Nucleosomes ($10\,nm$ thick), 3. Fibers of packed nucleosomes ($30\,nm$ thick), 4. Larger loops of coiled DNA ($300\,nm$ thick).

What protein complexes tether larger loops of coiled DNA during chromatin folding?

Condensins.

What is euchromatin?

Transcriptionally active chromatin that predominates in metabolically active cells.

How does euchromatin appear under a light microscope and transmission electron microscope (TEM)?

Light microscope: slightly basophilic areas; TEM: dispersed fine granules.

What is heterochromatin?

Transcriptionally inactive (or less active) chromatin that predominates in cells with little or no metabolic activity.

How does heterochromatin appear under a light microscope and TEM?

Light microscope: intensely basophilic clumps; TEM: coarse, electron-dense material.

Where is most heterochromatin located inside the nucleus?

Near the nuclear lamina.

When is maximum coiling of DNA into visible chromosomes present?

Visible during mitosis and meiosis only.

What is the ploidy and chromosome count of human somatic cells?

Diploid ($2n$) with 22 pairs of autosomes and 1 pair of sex chromosomes.

What is the ploidy and chromosome count of human gametes?

Haploid ($n$) with 22 autosomes and 1 sex chromosome.

What sex chromosome is present in human sperm versus oocytes?

Sperm contain either an 'X' or 'Y' chromosome; oocytes contain only an 'X' chromosome.

What is the primary function of the nucleolus?

Ribosome production.

What three steps take place in the nucleolus to produce ribosomes?

1. Transcription of rRNA molecules, 2. Association of rRNAs with ribosomal proteins, and 3. Assembly of ribosomal subunits.

In what type of cells is the nucleolus especially prominent?

Protein-synthesizing cells.

What are the three structural regions of the nucleolus?

Fibrillar Centers (FC), Fibrillar Material (F), and Granular Material (G).

What material is found in the Fibrillar Centers (FC) of the nucleolus?

DNA.

What occurs in the Fibrillar Material (F) region of the nucleolus?

Accumulation of rRNA transcripts.

What takes place in the Granular Material (G) region of the nucleolus?

Assembly of small and large ribosomal subunits.

What are the four phases of the cell cycle?

1. Mitosis, 2. G1, 3. S, and 4. G2.

Which phase of the cell cycle is usually the longest and most variable?

G1 phase.

What major processes take place during the G1 phase?

RNA and protein synthesis occur, and cells recover their size that was reduced during mitosis.

What three key events occur during the S phase of the cell cycle?

1. DNA replication, 2. Histone synthesis, and 3. Beginning of centrosome duplication.

What happens during the G2 phase of the cell cycle?

Accumulation of proteins required for mitosis and general preparation for mitosis.

What is the G0 phase of the cell cycle?

A quiescent state where cellular differentiation occurs and the cell cycle is suspended.

Which specific liver cells in G0 are noted as being able to re-enter the cell cycle?

Hepatocytes.

What type of cells undergo mitosis, and what are the resulting daughter cells?

All somatic cells; results in two identical daughter cells (clones) with the same DNA.

What are the four main phases of mitosis?

1. Prophase, 2. Metaphase, 3. Anaphase, and 4. Telophase.

What four major structural events occur during Prophase of mitosis?

1. Nucleolus disappears, 2. Chromatin condenses into chromosomes, 3. Mitotic spindle forms as centrosomes migrate, and 4. Nuclear envelope vanishes.

What biochemical modification triggers the disassembly of the nuclear lamina and nuclear pores in prophase?

Phosphorylation of lamins and inner nuclear membrane proteins.

What occurs during Metaphase of mitosis?

Chromosomes condense further, kinetochore proteins attach to chromosome centers, the cell becomes more spherical, and chromosomes align at the equator of the cell.

What happens to sister chromatids during Anaphase of mitosis?

Sister chromatids separate and migrate to opposite poles, with each sister chromatid becoming a single chromosome.

What four structural changes occur during Telophase of mitosis?

1. Two sets of chromosomes reach spindle poles, 2. Chromosomes return to uncondensed state, 3. Spindle microtubules depolymerize, and 4. Nuclear envelope reassembles around each set of daughter chromosomes.

How does cytokinesis begin at the end of telophase?

Actin and myosin filaments form a belt at the equator, and constriction of this ring forms a cleavage furrow.