Lecture 3: Cytology II

Cellular compartment between nuclear envelope and cell membrane

What is the cytoplasm?

Enzymes, oxygen, carbon dioxide, ions, substrates, metabolites, waste products

What does the cytosol contain?

•Plasma membrane

•RER

•SER

•Golgi apparatus

•Lysosomes

•Mitochondria

•Peroxisomes

What organelles are MEMBRANOUS! *** (7)

•Microtubules

•Filaments

•Centrioles

•Ribosomes

Proteasomes

Which organelles are NON-MEMBRANOUS!!! (5)***

Two subunits (small 40S and large 60S)

What are ribosomes composed of?

Highly folded rRNA chain and 30+ proteins

What does the small ribosomal subunit (40S) contain?

Three rRNA molecules and about 50 proteins

What does the large ribosomal subunit (60S) contain?

When the two subunits are assembled

When is a ribosome considered active?

As cytoplasmic basophilia (purple)

How do ribosomes appear under a light microscope?

Many ribosomes bound to a single mRNA during protein synthesis

What are polyribosomes

A convoluted membranous network in the cytoplasm that extends from the nucleus

What is the endoplasmic reticulum (ER)

Interconnected channels of the ER

What are cisternae in the ER?

ER membrane surface is 30 x the plasma membrane

How does the ER membrane surface compare to the plasma membrane? ***

Lipid and protein synthesis

What are the major metabolic activities of the ER?

Rough ER and Smooth ER

What are the two types of ER?

Lipid synthesis and carbohydrate metabolism

What is the function of smooth ER in synthesis?

Synthesizes proteins for secretion, incorporation into the plasma membrane, and as lysosomal enzymes

What is the function of rough ER in synthesis?

Moves molecules through cisternal space from one part of the cell to another, sequestered from the cytoplasm

What is the transport function of the ER?

Stores newly synthesized molecules

What is the storage role of the ER?

Detoxifies drugs and alcohol

What detoxification role does smooth ER perform?

Flat cisternae

What shape do rough ER membranes form?

Outer nuclear membrane

What is rough ER continuous with?

Proteins for plasma membrane, membranous organelles, and secretion (by exocytosis)

What types of proteins are synthesized in rough ER? (3)

Glycosylation, post-translational modification, and multichain protein assembly

What additional processes occur in rough ER besides protein synthesis? (3)

Tubular or sac-like cisternae with no ribosomes

What shape do smooth ER membranes form?

Cellular specialization

What determines smooth ER functions?

Synthesis of phospholipids and steroids for plasma membrane; steroid hormones in specialized cells like Leydig and adrenal cortex cells

What is the smooth ER's role in synthesis?

Detoxification of harmful molecules (e.g., alcohol, barbiturates) and calcium sequestration/release in muscle cells (sarcoplasmic reticulum)

What are other key functions of smooth ER? (2)

Cytoplasmic basophilia (purple staining)

How do cells with well-developed rough ER appear under light microscopy?

Negative image (pale zone corresponds to sER. sER does not stain with H&E)

How do cells with well-developed smooth ER appear under light microscopy?

Close to the cell nucleus

Where is the Golgi apparatus located in the cell?

Membranous vesicular/flattened saccules

What is the structure of the Golgi apparatus?

Cis face (receiving), middle face, trans face (shipping)

What are the three functional regions of the Golgi apparatus?

Post-translational modification of RER proteins; packaging and distribution of proteins

What are the main functions of the Golgi apparatus? (2)

Golgi zone (Light Microscopy)

Golgi does not stain well with H&E

How does the Golgi apparatus stain in light microscopy?

Addition of mannose-6-phosphate to lysosomal enzymes; N-linked oligosaccharides trimmed and other sugars added

What occurs at the cis face of the Golgi apparatus?

1. Glycosylation on –OH groups of certain lipids

as well as O-linked serine and threonine residues

2. Further modification of N-linked oligosaccharides on proteins

3. Sorting of glycoproteins and glycolipids into specific vesicles

What occurs in the medial Golgi?

1.Addition of sialic acid as terminal sugar to some oligosaccharides

2.Sulfatation of tyrosine and some sugars

3.Separation and sorting of vesicles with different destinations

What occurs at the trans face of the Golgi apparatus?

Spherical

What is the shape of lysosomes?

Uniform granular content with more than 40 hydrolytic enzymes

What is the content of lysosomes?

Produced by RER, packaged by Golgi into vacuoles that form lysosomes

How are lysosomal enzymes produced and packaged?

In most leukocytes

Where are lysosomes abundant?

Active lysosomes

What are heterolysosomes?

•Cellular digestion of extracellular material.

•Release of nutrients.

•Autophagy.

Secretion of hydrolytic enzymes

What are the functions of lysosomes? (4)

Visible with light microscope; TEM shows two separate membranes

How are mitochondria observed with microscopes?

Sieve-like with transmembrane proteins called porins

What is the outer mitochondrial membrane like?

Folds (cristae) containing enzymes for oxidative phosphorylation (ATP production)

What is the inner mitochondrial membrane like?

Innermost matrix (enzymes for pyruvate/fatty acid oxidation and Krebs cycle) and intermembrane space

What are the two mitochondrial regions?

ATP synthesis, apoptosis via cytochrome C release, lipid metabolism (β-oxidation of fatty acids in the matrix)

What are the main functions of mitochondria? (3)

Circular DNA, ribosomes, tRNA, and mRNA

What components are found in the mitochondrial matrix? (4)

Some of their own proteins

What can mitochondria synthesize on their own?

binary fission

How do mitochondria divide?

Each daughter cell receives about half of the mitochondria from the parent cell

How do daughter cells inherit mitochondria?

Due to numerous mitochondria with high protein content, which stain with acidic dyes

Why do renal tubule cells show acidophilic cytoplasm under light microscopy?

Mitochondrial ribosomes and mitochondria surrounded by rough ER and polyribosomes

What is seen in mitochondria under electron microscopy?

Spherical, membrane-bound organelles

What is the shape and structure of peroxisomes?

Detoxification and lipid metabolism (complementing smooth ER and mitochondria)

What are the main functions of peroxisomes? (2)

From the ER or by budding from pre-existing peroxisomes

What is the origin of peroxisomes? (2)

By free ribosomes

How are peroxisomal enzymes produced?

Microtubules, microfilaments (actin filaments), intermediate filaments

What are the main components of the cytoskeleton? (3)

Maintains cellular shape, movement of organelles, and cellular movement

What are the main functions of the cytoskeleton? (3)

In the cytoplasm

Where are microtubules found?

Axonemes with a more stable arrangement

What structures do microtubules form in cilia and flagella?

Hollow and rigid tubules

What is the structure of microtubules?

They have variable length

What is notable about the length of microtubules?

Heterodimer of α and β tubulin

What is the protein subunit of microtubules?

At the (+) end (polarized)

Where does microtubule polymerization occur most rapidly?

Microtubule organizing centers

What directs microtubule polymerization?

Continuous cycles of polymerization and depolymerization

What is dynamic instability in microtubules?

GTP

What provides energy for microtubule polymerization?

Dominant microtubule organizing center of most cells, normally close to the nucleus

What is the centrosome?

Two cylindrical centrioles, each with nine microtubule triplets

What are centrosomes organized around?

They duplicate to form two centrosomes, each with one pair of centrioles (Two

centrosomes and four centrioles in total).

What happens to centrosomes during S phase?

Each centrosome divides and migrates to opposite sides of the cell

What happens to centrosomes during mitosis?

Cell motility and contractility

What are the main functions of microfilaments (actin filaments)

Shorter and more flexible

How do microfilaments compare to microtubules?

Monomers add to the (+) end and dissociate from the (-) end

What is the dynamic behavior of microfilaments?

Migration of monomers through the filament during polymerization-depolymerization

What is treadmilling in microfilaments?

ATP hydrolysis

What provides energy for microfilament polymerization?

Stable polymers that provide increased mechanical stability to the cell

What are the characteristics of intermediate filaments?

By different protein subunits depending on the cell type

How are intermediate filaments formed in different cells

epithelial cells

Where are keratin filaments found?

Tonofibrils attaching to junctions of epithelial cells

What structures do keratin filaments form in epithelial cells?

Prevents dehydration, protects against minor abrasions, and produces hard protections like nails

What is the role of keratin in epidermal keratinization? (3)

In most cells derived from embryonic mesenchyme, including muscle cells and astrocytes

Where is vimentin found?

Intermediate filaments of neurons

What are neurofilament proteins?

Family of seven isoforms in the nucleus forming the nuclear lamina just inside the nuclear envelope

What are lamins and where are they found?

Accumulations of metabolites or other substances with little or no metabolic activity; usually transitory and not membrane-bound

What are inclusions in cells?