CELL AND BASIC HISTO

Question 1

Collection and processing of material for histological evaluation

Question 2

Basic and special staining methods, principles and results

Question 3

Histochemical methods, principles and applicationI

Question 4

Immunohistochemical methods, principles and application

Question 5

Structural organization of the cell, overview of cell components

Question 6

Cell membrane - structure and function

Question 7

Cell surface specializations

Question 8

Membranous cell organelles - structure and function

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Answer 8

Basic cell characteristics: Cell theory

• Cell is the smallest structural and functional unit of the organism able to live by itself
• Cells are made from other cells by cell division (proliferation), a cell an only arise from a pre exsistsing cell
  
  • “omis cellula e cellula”= all cells come from cells
• All cells have similar structure, contain organells with identical or similar functions

Basic types of cells:

• Prokaryotic: bacteria
  
  • Single cell organism
  • Asextual reproduction: usually binary fission
  • Morphologiccly without membrane bound nucleus called nucleoid
  • DNA is 1 circular double stranded molecule (w/o histone binding)
• Eukaryotic: protozoa, plant, fungi, animals
  
  • Complex structure
  • Nucelus is separted from cytoplasm by membrane
  • DNA organized into chromosomes
  • Mitosis/meiosis is the mechanism of division
  • In multi cellular organism, may undergow difffrientation/ specilization

Cell structure: General

• Cell can be divided into 2 major components
  
  • Cell nucleus
  • Cytoplasm: part of the cell outslide the ncl
    
    • Contains organells (membranous and non-membranous)
    • In a cytoplasmic martix: basic liquid substance – (cytosol)
    • Cell inclusions (deposits)

Organells in cell

• Described as:
  
  • Membrnous- contain plasma membrane that seperate the internal enviorment of the organell from the cytoplasm
  • Nonmembranous

Plasma (cell) membrane

• A lipid bilayer that forms the cell boundary as well as the boundaries of many organelles within the cell;
• Functions of the plasma membrane:
  
  • Separates the cell from its surroundings
  • Regulates the intracellular environment
  • Selective permeability
  • Cell recognition
  • Cell adhesion
  • Cell-cell signaling and regulatory function

Membranous organells include:

Nucelus

Rough-surfaced endoplasmic reticulum (rER)

• System of interconected tubules and cisterns
• a region of endoplasmic reticulum associated with ribosomes and the site of protein synthesis and modification of newly synthesized proteins;
• Cells with highly developed proteosynthetic activity: more basophillic
  
  • Basic staining agents due to righ RNA content in cytoplasm
  • Hepatocytes: synthesis blood plasma cells
  • Fibroblasts: synthesis fibers and ground substance of ECM
  • Plasma membrane: aynthesysis antibodies
  • Nerve cells: synthesis neurotransmitters and receptors
  • Serous cells of endocrine glands: form waterly secretions with high protien content

***Hepatocytes display an eosinophilic cytoplasm, reflecting numerous mitochondria and sER, and basophilic stippling due to large amounts of rough endoplasmic reticulum and free ribosomes.

Smooth-surfaced endoplasmic reticulum (sER)

• System of interconnected tubules not assosiated with ribosome
• Functions of smooth endoplasmic reticulum:
  
  • Lipid and steroid synthesis
  • Detoxification – neutralization of toxic substances (oxidation, conjugation, methylation)
  • In muscles sarcoplasmic reticulum – storage of calcium ions
• Cytoplasm in region of sER may exhibit distinct eosinophilia
• Cells with relativly large amount of sER
  
  • Hepatocytes: epithlial cells of liver
    
    • in assoaiation of glycogen coversion and storage, lipis and cholesterol synthesis and detox function
  • Interstinal endocrine cells of leydig in testies and adrenal cortex
    
    • synthesis steroid hormoens
  • Skeletal and cardiac muscle- calcium storage

Golgi apparatus

• Membranous organelle responsible for modifying, sorting, and packaging proteins and lipids for intracellular or extracellular transport
• Composed of multiple flattened cisterns/vesicles
  
  • Stack of flattened membrane sheets often adjacent to one side of nucleus
  • Vesicles are expanded at the end and secretion vesicles are seperated from them
  • Cis-region: entry face:
    
    • For recieving vesicles, in the direction of RER
  • Trans face/ exit face:
    
    • For seperation of vesicles containing modified protiens
• Vesicles – round shape, light stained
• Granules – round vesicles with a dense content

Lysosomes

• Oval-shaped organelles having a size of 0,05-0,5μm
• Responsible for intracellular digestion, storage site for unesseary substances
  
  • Small organelles containing digestive enzymes that are formed from endosomes by targeted delivery of unique lysosomal membrane proteins and lysosomal enzymes;
• High concentration of protons, pH 4,5-5,0
  
  • Maintained by a proton pump
• Content:
  
  • Around 40 acid hydrolases
  • Enzymes labelled with mannose 6-phosphate
  • Azurophilic granules in blood cells
• Cells rich in lysosomes= Cells with high endocytotic and phagocytotic activity:
  
  • Macrophages, neutrophilic granulocytes
  • Hepatocytes
  • Proximal tubule epithelium in the kidney
• The fate of an undigested material in lysosomes:
  
  • Exocytosis
  • Storage – residual bodies
  • Lipofuscin granules
  • Dust cells – alveolar macropahges
  • Siderosomes – macrophages in liver, spleen and the bone marrow
• Microscope
  
  • Visible only after special enzyme histochemical staining

Mitochondria:

• Energy center of cell- chemical enery from nutrients to ATP molecules
• Two-membrane system:
  
  • Outer membrane and inner membrane arranged in numerous folds (cristae)
  • Diameter 0,5-1 μm, length up to 20 μm
• Contains it’s own DNA and ribosomes:
  
  • Circular double stranded DNA molecules, with their own genome, (probably evolved fro bacteria)
  • Maternal inheritance
• Microscope:
  
  • Sometimes observed in favorable situations (e.g., liver or nerve cells) as miniscule, dark dots; visible in living cells stained with vital dyes (e.g., Janus green)
• Organelles that provide most of the energy to the cell by producing adenosine triphosphate (ATP) in the process of oxidative phosphorylation

Peroxisomes

• Small organelles involved in the production and degradation of H2O2 and degradation of fatty acids.
• Organelles of variable shape (0,5-1,2 μm)
• Participate in fatty acid oxidation
• Enzyme catalase decomposes hydrogen peroxide into water and oxygen
• Catalase is important for detoxification of ethanol in liver and kidney

Melanosomes

• Cell organelles (0,2-1,0 μm) containing pigment melanin derived from amino acid tyrosine
• Protection against UV irradiation - pigment cells, melanocytes

Transport vesicles

• Including pinocytotic vesicles, endocytotic vesicles, and coated vesicles—that are involved in both endocytosis and exocytosis and vary in shape and the material that they transport;

Endosomes

• Membrane-bounded compartments interposed within endocytotic pathways that have the major function of sorting proteins delivered to them via endocytotic vesicles and redirecting them to different cellular compartments for their final destination;
• The nonmembranous organelles include:
• • microtubules, which together with actin and intermedi -
• ate filaments form elements of the cytoskeleton and
• continuously elongate (by adding tubulin dimers) and
• shorten (by removing tubulin dimers), a property referred
• to as dynamic instability;
• • filaments, which are also part of the cytoskeleton and can
• be classified into two groups—actin filaments, which are
• flexible chains of actin molecules, and intermediate filaments,
• which are ropelike fibers formed from a variety of
• proteins—both groups providing tensile strength to withstand
• tension and confer resistance to shearing forces;
• • centrioles, or short, paired cylindrical structures found in
• the center of the microtubule-organizing center
• (MTOC) or centrosome and whose derivatives give rise to
• basal bodies of cilia; and
• • ribosomes, structures essential for protein synthesis and
• composed of ribosomal RNA (rRNA) and ribosomal proteins
• (including proteins attached to membranes of the
• rER and proteins free in the cytoplasm).

Question 9

Cell nucleus and non-membranous cell organelles - structure and function

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Answer 9

Basic cell characteristics: Cell theory

• Cell is the smallest structural and functional unit of the organism able to live by itself
• Cells are made from other cells by cell division (proliferation), a cell an only arise from a pre exsistsing cell
  
  • “omis cellula e cellula”= all cells come from cells
• All cells have similar structure, contain organells with identical or similar functions

Basic types of cells:

• Prokaryotic: bacteria
  
  • Single cell organism
  • Asextual reproduction: usually binary fission
  • Morphologiccly without membrane bound nucleus called nucleoid
  • DNA is 1 circular double stranded molecule (w/o histone binding)
• Eukaryotic: protozoa, plant, fungi, animals
  
  • Complex structure
  • Nucelus is separted from cytoplasm by membrane
  • DNA organized into chromosomes
  • Mitosis/meiosis is the mechanism of division
  • In multi cellular organism, may undergow difffrientation/ specilization

Cell structure: General

• Cell can be divided into 2 major components
  
  • Cell nucleus
  • Cytoplasm: part of the cell outslide the ncl
    
    • Contains organells (membranous and non-membranous)
    • In a cytoplasmic martix: basic liquid substance – (cytosol)
    • Cell inclusions (deposits)

Organells in cell

• Described as:
  
  • Membrnous- contain plasma membrane that seperate the internal enviorment of the organell from the cytoplasm
  • Nonmembranous

Nucelus

The nonmembranous organelles include:

RIBOSOMES

• General:
  
  • Sturcutre of protien complexes and rRNA
  • Synthesis of proteins
  • Function: translation of mRNA and protein synthesis
• Structure:
  
  • Ribosomes are small electron dense granular particles synthesises in the nucleolus and released to cytoplasm through nuclear pores
  • About 20 x 30 nm in size
  • They determine basophilia of the cytoplasm.
  • Ribosomes consist of two subunits:
    
    • the small subunit reads mRNA, assembles mRNA, tRNA (together with amino acid molecules) and elongation factors at one place,
    • large subunit (has peptidyl-transferase activity) helps to form peptide bonds.
  • Distribution of ribosomes:
    
    • Free or attached to the endoplasmic reticulum (rough ER).
    • Free polyribosomes
      
      • Synthesizes proteins used by cell itself (hemoglobin, actin, myosin, proteins of the intermediate filaments, tubulin, most mitochondrial enzymes).
    • Attached:
      
      • Synthesizes protiens intended for exportation

SYNTHESIS OF PROTEINS

• Gene
  
  • information for the protein synthesis is coded in the structure of DNA
• Transcription
  
  • genetic information is transcribed into nucleotide sequence of RNA (single chain molecule)
• Main types of RNA
  
  • mRNA – coding of proteins (messenger RNA)rRNA – part of ribosomes
  • tRNA – transfers amino acids to the complex of mRNA and ribosomes
• Translation
  
  • Proteins are form by different 20 amino acids
  • Codon (a sequence of three nucleotides) of mRNA determines one amino acid;
  • mRNA is decoded on ribosomes
• Ribosomes producing proteins occur in clusters, are held together by a strand of mRNA into polyribosomes (polysomes).
• Nucleotid sequence of mRNA determines the amino acid sequence of synthesized protein.

CYTOSKELETON

• Cytoplasmic cytoskeleton is a complex network of:
  
  • (1) microfilaments (actin filaments)
  • (2) intermediate filaments
  • (3) microtubules
• Function: determination of the shape of cells, transport of organelles and cytoplasmic vesicles, and also the movement of entire cell.

CENTROSOME, microtubule-organizing center

Microtubules,

which together with actin and intermediate filaments form elements of the cytoskeleton and continuously elongate (by adding tubulin dimers) and shorten (by removing tubulin dimers), a property referred to as dynamic instability;

Filaments, which are also part of the cytoskeleton and can be classified into two groups—actin filaments, which are flexible chains of actin molecules, and intermediate filaments, which are ropelike fibers formed from a variety of proteins—both groups providing tensile strength to withstand tension and confer resistance to shearing forces;

Centrioles, or short, paired cylindrical structures found in the center of the microtubule-organizing center (MTOC) or centrosome and whose derivatives give rise to basal bodies of cilia; and

Ribosomes, structures essential for protein synthesis and composed of ribosomal RNA (rRNA) and ribosomal proteins (including proteins attached to membranes of the rER and proteins free in the cytoplasm).

Question 10

Cytoskeleton - structure, function (and diagnostic application)

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Answer 10

Basic cell characteristics: Cell theory

• Cell is the smallest structural and functional unit of the organism able to live by itself
• Cells are made from other cells by cell division (proliferation), a cell an only arise from a pre exsistsing cell
  
  • “omis cellula e cellula”= all cells come from cells
• All cells have similar structure, contain organells with identical or similar functions

Basic types of cells:

• Prokaryotic: bacteria
  
  • Single cell organism
  • Asextual reproduction: usually binary fission
  • Morphologiccly without membrane bound nucleus called nucleoid
  • DNA is 1 circular double stranded molecule (w/o histone binding)
• Eukaryotic: protozoa, plant, fungi, animals
  
  • Complex structure
  • Nucelus is separted from cytoplasm by membrane
  • DNA organized into chromosomes
  • Mitosis/meiosis is the mechanism of division
  • In multi cellular organism, may undergow difffrientation/ specilization

Cell structure: General

• Cell can be divided into 2 major components
  
  • Cell nucleus
  • Cytoplasm: part of the cell outslide the ncl
    
    • Contains organells (membranous and non-membranous)
    • In a cytoplasmic martix: basic liquid substance – (cytosol)
    • Cell inclusions (deposits)

Organells in cell

• Described as:
  
  • Membrnous- contain plasma membrane that seperate the internal enviorment of the organell from the cytoplasm
  • Nonmembranous

The nonmembranous organelles include:

1- Ribosomes

• Sturcutre of protien complexes and rRNA
• Synthesis of proteins

2- Cytoskeleton

3- Centrosome

CYTOSKELETON

three basic types of fibrous protiens that form a 3D mesh structure

• Cytoplasmic cytoskeleton is a complex network of:
  
  • (1) microfilaments (actin filaments)
  • (2) intermediate filaments
  • (3) microtubules
• Function: determination of the shape of cells, transport of organelles and cytoplasmic vesicles, and also the movement of entire cell.

MICROTUBULES

General discription:

• Microtubules are nonbranching and rigid hollow tubes of protein
• that can rapidly disassemble in one location and reassemble in another.
• Create a system of connections within the cell, frequently compared with railroad tracks, along which vesicular movement occurs

Structure:

• Elongated polymeric structures composed of equal parts of α-tubulin and ß-tubulin
  
  • Tubulin= heterodimer consisting of the α- and ß- tubulins
• Consists of 13 circularly arrayed protofilaments
  
  • =elongated columbs consiting of heterodimimers, parallel to the long axsis of the microtubule
• Diameter 24 nm, wall of the microtubule is approximately 5 nm thick

Function and location

• MTs are found in:
  
  • centrioles, mitotic spindle, cilia, flagellum, elongating cell processes, cytoplasm
• MTs are involved in:
  
  • cell elongation and movement,
  • intracellular vesicular transport,
  • movement of chromosomes,
  • maintenance of cell shape
• Protiens:
  
  • MT associated proteins (MAPs)
    
    • regulate polymerization and anchor of MT to organelles
  • Motor proteins: dynein and kinesin
    
    • Microtubules serve as guides for molecular motor proteins.
    • These ATP-driven microtubule-associated motor proteins are attached to moving structures (such as organelles) that ratchet them along a tubular track.
    • Two types of molecular motors have been identified:
      
      • Dyneins
        
        • That move along microtubules toward their minus (-) end (i.e., toward the center of the cell)
      • Kinesins
        
        • That move toward their plus (+) end (i.e., toward the cell periphery).

Microtubule formation

• Heterodimers are added to gamma-tubulin ring in an end-to-end fashion →
  
  • Gamma tubulin rings that form an integral part of the MTOC
  • MTOC - microtubule organizing center, MTs grow from tubulin rings
• Polymerization of tubulin dimers requires the presence of→
  
  • Guanosine triphosphate (GTP) and Mg2
• Each tubulin molecule binds GTP before it is incorporated into the forming microtubule→
  
  • The GTP–tubulin complex is then polymerized, and at some point GTP is hydrolyzed to guanosine diphosphate (GDP). GDP + Pi
• As a result of this polymerization pattern→
  
  • ​Microtubules are polar because all of the dimers have the same orientation.
• Each microtubule possesses a
  
  • Minus (nongrowing) end that corresponds to alfa-tubulin; in the cell, it is usually embedded in the MTOC.
  • The plus (growing) end of microtubules corresponds to beta-tubulin and extends the cell periphery.
• Tubulindimers dissociate from microtubules in the steady state, which adds a pool of free tubulin dimers to the cytoplasm

CENTROSOME, microtubule-organizing center MTOC

General:

• Centrosomes are 2 hollow cylinfricles (centrioles)
  
  • Centrioles represent the focal point around which the MTOC assembles.
• Centrioles are usually found close to the nucleus, often partially surrounded by the Golgi apparatus, and associated with a zone of amorphous, dense pericentriolar material.

Structure: Centrioles

• Visible in the light microscope
• Paired, short, rodlike cytoplasmic cylinders
• Composed of nine sets of microtubular triplets arranged in the fashion of a pinwheel.
  
  • In the triplets, microtubule A is complete (consists of 13 protofilaments),
  • while B and C share 2–3 protofilaments.
• Long axes of the centrioles are at right angles to each other.
• A pair of centrioles is found in non-dividing cell.
  
  • Before cell division each centriole duplicates itself.

The region of the cell containing the centrioles and pericentriolar material is called the microtubule-organizing center or centrosome- FUNCTION

• The MTOC is the region where most microtubules are formed and from which they are then directed to specific destinations within the cell.
• Therefore, the MTOC controls
  
  • the number, polarity, direction, orientation, and organization of microtubules formed during the interphase of the cell cycle.
• During mitosis, duplicated MTOCs serve as mitotic spindle poles. Development of the MTOC itself depends solely on the presence of centrioles. When centrioles are missing, the MTOCs disappear, and formation of microtubules is severely impaired.

Question 11

Structure of intercellular junctions

Question 12

Cell division - mitosis and meiosis

Cell cycle and its regulation, cell death – apoptosis