Lecture 2: Cytology I

Basic structural and functional unit of any living thing

Definition of a cell

•Explains the relationship between cells and living things:

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 is the cell theroy and what is it composed of (3)

Never form tissues

No nucleus

No organelles (only ribosomes)

Has a cell wall

May have a capsule

Characteristics of a prokaryotic cell

•Unicellular and multicellular organisms

•Form tissues (multicellular organisms)

•Have a nucleus

•Have organelles

Some have cell walls

Characteristics of a Eukaryotic cell

Eukaryotic cells, Have NO cell wall

What types of cells are human cells? Do they have a cell wall?

Human tissues

What do human cells form?

Differentiation

What processes do human cells undergo for Specialization and Diversity?

Interaction between genes and the cellular microenvironment that leads to different genetic expression, structure, and function.

What is cell differentiation?

Different genes are expressed, leading to different structures and specialized functions.

How does genetic expression change in differentiated cells?

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

What happens to a cell’s functions during differentiation?

Specific functions are supported by changes in cell morphology

How is a cell’s specific function supported morphologically?

Great morphological and functional cellular diversity.

What results from cell differentiation in terms of diversity?

1. Zygote (toti potent stem cell)

2. Blastomeres (Progenitor pluripotent stem cells)

3. Cells of all human cells (differentiate into mature cells)

What is the order in which a cell differentiates?

1. Different appearance and structure

2. Functional specialization

Cell differentiation leads to what two main outcomes?

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

What is the Nucleus?

Genetic (hereditary) material (DNA).

What does the nucleus store?

•Growth

•Metabolism

•Protein synthesis

•Cell division

What cell activities does the nucleus coordinate? (4)

•DNA synthesis

•RNAs processing

What molecular machinery is found in the nucleus? (2)

Pore riddled

What is the nuclear envelope of the nucleus?

fluid

What is the nucleoplasm of the nucleus?

DNA + Proteins

What is the chromatin of the nucleus contain? (2)

dense cluster of RNA and proteins + inactive ribosomes

What is the Nucleolus of the Nucleus contain? (3)

Selectively permeable barrier formed by two membranes units with pores

What is the Nuclear Envelope?

Separates nucleoplasm form cytoplasm allowing selective passage of molecules

What is the function of the nuclear envelope?

1. Inner membrane (associated with nuclear lamina)

2 Outer membrane (binds ribosomes)

3. Perinuclear space or cisterna (in between)

What are the components of the nuclear envelope?

They are continuous with the rough endoplasmic reticulum (rER)

How are the outer membrane and perinuclear space connected to the rest of the cell?

Stabilizes the nuclear envelope

What is the function of the nuclear lamina?

Proteins of the nuclear lamina closely associated with the inner membrane.

What forms the meshwork associated with the inner membrane?

Intermediate filament proteins (lamins) bound to membrane proteins and associated with chromatin in nondividing cells.

What proteins make up the nuclear lamina and what are they associated with?

Nuclear pore complexes.

What bridges the inner and outer membranes of the nuclear envelope?

Various nucleoporins (core proteins) arranged with eightfold symmetry around a lumen.

What are nuclear pores made of?

simple diffusion

How do ions and small molecules pass through nuclear pores?

1.Passage of ions and small molecules by simple diffusion

2.Regulate movement of macromolecules between nucleoplasm and cytoplasm

What are the functions of nuclear pores?

GTP hydrolysis by GTPases.

What provides the energy for import and export through nuclear pores?

Viscous fluid containing water, dissolved ions, and a complex mixture of other molecules.

What is nucleoplasm (Karyoplasm) composed of?

Serves as a suspension medium for other nuclear components.

What is the function of nucleoplasm (Karyoplasm)?

1.DNA

2.Associated proteins (histones)

What are the components of Chromatin? (2)

Divided among 46 chromosomes (23 pairs), except in gametes.

How is chromatin organized in human cells?

2 meters long

3.2 billion bp

How long is human DNA and how may base paris?

Structural units of DNA called nucleosomes.

What do histones and DNA form together?

Eight histones: 2 copies each of H2A, H2B, H3, and H4.

What forms the core of a nucleosome?

150 base pairs (bp) of DNA.

How much DNA is wrapped around the nucleosome core?

H1 histone.

Which histone is associated with the DNA at the surface of the nucleosome core?

Linker DNA, 50–80 bp long.

What separates nucleosomes from each other?

They are key to DNA replication and transcription.

Why are nucleosomes important for DNA processes? (2)

•Histone modification

•Histone rearrangement

What processes involving histones occur in nucleosomes? (2)

2 nm thick.

How thick is the DNA double helix?

Nucleosomes, 10 nm thick.

What is formed when DNA wraps around histones?

Fibers of packed nucleosomes, 30 nm thick.

What is the next level of chromatin organization after nucleosomes

Larger loops of coiled DNA, ~300 nm thick.

What comes after the 30 nm fiber in chromatin folding?

Condensins (protein complexes).

What proteins help stabilize many chromatin loops?

Euchromatin and Heterochromatin in an Interphase Nucleus

What are the two main types of chromatin based on condensation?

Transcriptionally active

Is euchromatin transcriptionally active or inactive? **

Slightly basophilic areas

How does euchromatin appear under a light microscope?

Dispersed fine granules

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

Metabolically active cells.

In what type of cells does euchromatin predominate?

Transcriptionally inactive (or less active).

Is heterochromatin transcriptionally active or inactive?***

Intensely basophilic clumps.

How does heterochromatin appear under a light microscope?

Coarse, electron-dense material.

How does heterochromatin appear under a transmission electron microscope (TEM)?

Cells with little or no metabolic activity.

In what type of cells does heterochromatin predominate?

Only during maximum DNA coiling in mitosis and meiosis

When are chromosomes visible?

Diploid (2n).

Are somatic cells diploid or haploid?

22 pairs of autosomes and 1 pair of sex chromosomes.

How many autosomes and sex chromosomes are in somatic cells?

Haploid (n).

Are gametes diploid or haploid?

22 autosomes and 1 sex chromosome.

How many autosomes and sex chromosomes are in gametes?

A highly basophilic chromatin region prominent in protein-synthesizing cells.

What is the nucleolus?

Dense concentration of rRNA.

What is concentrated in the nucleolus?

Ribosome production.

What is the main function of the nucleolus?

Transcription of rRNA

association of rRNAs with ribosomal proteins

assembly of ribosomal subunits.

What processes occur in the nucleolus? (3)

1. Mitosis

2. G1

3. S

4. G2

What are the 4 phases of the cell cycle?

RNA and protein synthesis, and cells recover their size (reduced during mitosis).

What happens during the G1 phase?

DNA replication.

What is the main event of the S phase?

Histone synthesis and the beginning of centrosome duplication.

What other processes occur during the S phase?

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

What happens during the G2 phase?

A quiescent state where the cell cycle is suspended.

What is the G0 phase?

Cellular differentiation; the cell may or may not restart the cell cycle.

What occurs in cells during G0?

All somatic cells.

In which cells does mitosis occur?

A parent cell divides to form two identical daughter cells (clones) with the same DNA.

What happens during mitosis?

1.Prophase

2.Metaphase

3.Anaphase

4.Telophase

How many main phases are there in mitosis?

The nucleolus disappears.

What happens to the nucleolus during prophase?

Chromatin condenses into visible chromosomes.

What happens to chromatin during prophase?

The mitotic spindle forms

What structure forms in prophase?

The nuclear envelope vanishes.

What happens to the nuclear envelope in prophase?

Phosphorylation of lamins and inner nuclear membrane proteins causes the nuclear lamina and nuclear pores to disassemble.

What molecular events lead to nuclear envelope disassembly during prophase?

Chromosomes further condense.

What happens to chromosomes during metaphase?

Kinetochore proteins.

What attaches to the center of chromosomes during metaphase?

Along the equator (metaphase plate) of the cell.

Where do chromosomes align during metaphase?

Sister chromatids separate.

What happens to sister chromatids during anaphase?

They migrate to opposite poles of the cell.

Where do sister chromatids move during anaphase?

Each sister chromatid is now considered a single chromosome

After separation in anaphase, what is the status of each sister chromatid?

To prepare the genetic material to be apportioned between the two future daughter cells.

What is the purpose of anaphase in mitosis?

Two sets of chromosomes, one at each spindle pole, return to an uncondensed state.

What is the status of chromosomes during telophase?

They depolymerize.

What happens to spindle microtubules during telophase?

It reassembles around each set of daughter chromosomes.

What happens to the nuclear envelope during telophase?

Actin and myosin filaments.

Which filaments form a belt at the equator during telophase?

Cytokinesis

What process begins at the end of telophase?

Constriction of the actin-myosin ring forms a cleavage furrow, resulting in two daughter cells.

How is the cell physically divided during cytokinesis?

Undifferentiated cells capable of renewing differentiated cells as needed.

What are stem cells?

Divisions are asymmetric: one daughter remains a stem cell, and the other becomes a progenitor cell committed to differentiation.

What is unique about stem cell divisions?

Frequent mitosis to increase the number of new cells

How often do progenitor cells (amplifying cells) divide?