Histo Mod 1

Comprehensive Question and Answer flashcards covering Cytology lecture content including cell division, nucleus, organelle structure/function, and plasma membrane mechanics.

What is the basic structural and functional unit of any living thing?

The cell

What are the three core principles of 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.

Which classification of cells is unicellular, never forms tissues, lacks a nucleus, and lacks membrane-bound organelles?

Prokaryotic cells

What is the only type of organelle present in prokaryotic cells?

Ribosomes

What outer protective structures can prokaryotic cells possess outside their plasma membrane?

Cell wall and capsule

Do human cells possess a cell wall?

No

What process involves the interaction between genes and the cellular microenvironment leading to specialized structure and function?

Cell differentiation

What are the two main outcomes of cell differentiation?

1. Different appearance and structure 2. Functional specialization

When a cell undergoes differentiation, what happens to its basic cell functions?

All basic functions are maintained while one or more specific functions become more important.

In the cell differentiation hierarchy, what developmental potential does a zygote have?

Totipotent stem cell

What membrane-bound, highly specialized organelle serves as the information processing and administrative center of a eukaryotic cell?

The nucleus

What are three major cellular activities coordinated by the nucleus?

Growth, metabolism, protein synthesis, and cell division

What molecular machinery processes are housed inside the nucleus?

DNA synthesis and RNAs processing

What are the four main components of the nucleus?

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

What selectively permeable barrier separates the nucleoplasm from the cytoplasm?

Nuclear envelope

Which membrane of the nuclear envelope is associated with the nuclear lamina?

Inner membrane

Which membrane of the nuclear envelope binds ribosomes on its cytosolic surface?

Outer membrane

What is the fluid-filled space located between the inner and outer membranes of the nuclear envelope?

Perinuclear space (or cisterna)

With which organelle are the outer nuclear membrane and perinuclear space continuous?

Rough endoplasmic reticulum (rER)

What protein meshwork stabilizes the nuclear envelope and closely associates with the inner membrane?

Nuclear lamina

Which intermediate filament proteins constitute the nuclear lamina?

Lamins

What protein complexes bridge the inner and outer nuclear membranes and exhibit eightfold symmetry around a central lumen?

Nuclear pore complexes (composed of nucleoporins)

By what process do ions and small molecules pass through nuclear pores?

Simple diffusion

What process provides energy for the regulated import and export of macromolecules across nuclear pores?

GTP hydrolysis by GTPases

What is another term for nucleoplasm?

Karyoplasm

What is the primary function of the nucleoplasm?

It acts as a suspension medium for other nuclear components.

What two key molecular components constitute chromatin?

DNA and associated proteins (histones)

How many total chromosomes and chromosome pairs are present in normal human somatic cells?

46 chromosomes (23 pairs)

What is the length and base-pair count of DNA in a single human somatic cell nucleus?

$2\,\text{meters}$ long and $3.2 \times 10^9\,\text{bp}$ (3.2 billion base pairs)

What basic structural unit of DNA is formed by histones and wrapped DNA?

Nucleosome

Which histone proteins form the octamer core of a nucleosome?

Two copies each of H2A, H2B, H3, and H4

How many base pairs of DNA are wrapped around the core histone octamer of a nucleosome?

$$150\,\text{bp}$$

Which histone protein associates with the wrapped DNA at the surface of the nucleosome core?

H1 histone

What is the length of linker DNA that separates adjacent nucleosomes?

$$50\text{ to }80\,\text{bp}$$

What are the structural thicknesses of bare DNA double helix and a nucleosome chain, respectively?

Bare DNA is $2\,\text{nm}$ thick; nucleosome chain is $10\,\text{nm}$ thick.

What are the thicknesses of packed nucleosome fibers and coiled DNA loops?

Packed nucleosome fibers are $30\,\text{nm}$ thick; coiled loops are $300\,\text{nm}$ thick.

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

Condensins

Which type of interphase chromatin is transcriptionally active and appears as slightly basophilic light areas under light microscopy?

Euchromatin

How does euchromatin appear under transmission electron microscopy (TEM)?

Dispersed fine granules

Which type of interphase chromatin is transcriptionally inactive and forms intensely basophilic clumps under light microscopy?

Heterochromatin

Where inside the nucleus is most heterochromatin typically concentrated?

Near the nuclear lamina

Which type of chromatin predominates in cells with little or no metabolic activity?

Heterochromatin

What is the chromosome complement of human somatic cells?

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

What is the chromosome complement of human gametes?

Haploid ($n$): 22 autosomes and 1 sex chromosome

Which sex chromosome can be present in a human oocyte?

Only an X chromosome

Which highly basophilic nuclear region is prominent in protein-synthesizing cells?

Nucleolus

What is the primary function of the nucleolus?

Ribosome production (transcription of rRNA and assembly of ribosomal subunits)

In the nucleolus, what component is contained within the Fibrillar Centers (FC)?

DNA

In the nucleolus, what process occurs in the Fibrillar Material (F) region?

Accumulation of rRNA transcripts

What structural components are found in the Granular Material (G) region of the nucleolus?

Small and large ribosomal subunits being assembled

What are the four sequential phases of the cell cycle?

G1, S, G2, and Mitosis

Which phase of the cell cycle is typically the longest, most variable, and involves cellular size recovery and protein/RNA synthesis?

G1 phase

What three major replication/duplication processes begin during the S phase of the cell cycle?

DNA replication, histone synthesis, and centrosome duplication

What occurs during the G2 phase of the cell cycle?

Accumulation of proteins required for mitosis and general preparation for cell division

What term refers to the quiescent state of the cell cycle where differentiation occurs and cell cycle progression is suspended?

G0 phase

What are the four main phases of somatic mitosis?

Prophase, Metaphase, Anaphase, and Telophase

What four main structural changes mark prophase in mitosis?

1. Nucleolus disappears 2. Chromatin condenses into chromosomes 3. Mitotic spindle forms 4. Nuclear envelope vanishes

What biochemical modification triggers the disassembly of the nuclear lamina and inner nuclear membrane proteins during late prophase?

Phosphorylation of lamins and inner nuclear membrane proteins

Where do chromosomes align during metaphase of mitosis?

At the equator (metaphase plate) of the cell

What protein structures attach to chromosome centers to facilitate spindle microtubule attachment during metaphase?

Kinetochore proteins

What major event defines anaphase in mitosis?

Separation of sister chromatids and their migration to opposite poles

What belt-like structure forms at the cell equator during late telophase to induce cytokinesis?

A ring of actin and myosin filaments

How do stem cells maintain their population while generating differentiated progeny?

Through asymmetric division (one daughter cell remains a stem cell, while the other becomes a progenitor cell)

What is another term for progenitor cells along the pathway to terminally differentiated cells?

Transit amplifying cells

How do progenitor cells differ from terminally differentiated cells regarding mitotic activity?

Progenitor cells undergo frequent mitosis; terminally differentiated cells have low or no division potential.

Give an example of a terminally differentiated cell in G0 that can re-enter the cell cycle.

Hepatocyte

In which specific category of cells does meiosis take place?

Germ cells (cells that become sperm or oocytes)

What process occurs during meiotic Prophase I that generates new gene combinations and genetic variability?

Crossover (or DNA recombination) between paired homologous chromosomes

How long does meiotic Prophase I last in human spermatogenesis compared to human oogenesis?

3 weeks in spermatogenesis; arrested for $12+\text{ years}$ in oogenesis.

What structures separate during Anaphase I of meiosis versus Anaphase II?

Homologous chromosomes separate in Anaphase I; sister chromatids separate in Anaphase II.

What is the nuclear and chromosomal composition of cells resulting from Telophase I of meiosis?

Haploid cells ($n$) containing diploid chromosomes (each chromosome retains two sister chromatids)

How many daughter cells are produced at the completion of Meiosis II, and what is their genetic status?

Four non-identical haploid ($n$) daughter cells

What cellular compartment is defined as the region between the nuclear envelope and the plasma membrane?

Cytoplasm

What are the three main components of cytoplasm?

Cytosol, organelles, and inclusions

List four substances dissolved within the cytosol.

Enzymes, oxygen, carbon dioxide, ions, substrates, or metabolite waste products

List seven membranous organelles present in eukaryotic cells.

Plasma membrane, rER, sER, Golgi apparatus, lysosomes, mitochondria, and peroxisomes

List five non-membranous organelles present in eukaryotic cells.

Microtubules, microfilaments, intermediate filaments, centrioles, ribosomes, and proteasomes

What are the Svedberg (S) unit sizes for eukaryotic small and large ribosomal subunits?

Small subunit is 40S; large subunit is 60S

What molecular components make up the eukaryotic 40S small ribosomal subunit?

A highly folded rRNA chain and more than 30 proteins

What molecular components make up the eukaryotic 60S large ribosomal subunit?

Three rRNA molecules and approximately 50 proteins

What visual staining property does high ribosomal density impart to cytoplasm under light microscopy?

Cytoplasmic basophilia (purple hue)

What term describes a cluster of multiple ribosomes attached to a single mRNA strand during translation?

Polyribosome (or polysome)

What are the interconnected membranous channels of the endoplasmic reticulum called?

Cisternae

How much greater is the surface area of the endoplasmic reticulum compared to the cell plasma membrane?

30 times greater

What are the four primary functions of the endoplasmic reticulum?

1. Synthesis 2. Transport 3. Storage 4. Detoxification

Where are proteins synthesized on the rough ER destined to go?

Plasma membrane, membranous organelles, or extracellular secretion by exocytosis

What structural feature gives the rough ER its 'rough' appearance?

Ribosomes attached to its membrane surface

Why does smooth ER appear as a 'negative image' (pale zone) under light microscopy with H&E staining?

Smooth ER lacks ribosomes and does not stain with hematoxylin and eosin (H&E).

What peptide sequence on a growing protein directs the ribosome to the rER membrane?

Initial signal peptide

What cytosolic complex binds to the initial signal peptide during translation targeting to rER?

Signal Recognition Particle (SRP)

What receptor on the rER membrane binds the SRP-ribosome complex?

SRP receptor

What enzyme inside the rER cisterna cleaves the signal sequence from the nascent protein?

Signal peptidase

In which cell types is smooth ER extensively developed for steroid hormone synthesis?

Leydig cells and adrenal cortex cells

In which organ's cells is smooth ER modified for the detoxification of drugs and alcohol?

Liver cells (hepatocytes)

What specialized smooth ER in muscle cells functions in calcium ion storage, sequestration, and release?

Sarcoplasmic reticulum

What are the three functional regions of the Golgi apparatus?

1. Cis face (receiving region) 2. Middle face 3. Trans face (shipping region)

What modification occurs to future lysosomal enzymes within the cis face of the Golgi apparatus?

Addition of mannose-6-phosphate

Where does O-linked glycosylation of serine and threonine residues occur in the Golgi apparatus?

Medial Golgi (middle face)

What terminal sugar is added to some oligosaccharides in the trans face of the Golgi apparatus?

Sialic acid

What sulfatation reactions occur in the trans face of the Golgi apparatus?

Sulfatation of tyrosine residues and certain sugars