Chapter 2: Cytology Flashcards
(221 cards)
1
Q
What are peroxisomes (micro bodies)?
A
Membranous organelles that contain oxidases and catalase enzymes.
2
Q
What is the peroxisomes origin?
A
Membranous Vesicles that bud off from the rER. Their peroxisomes enzymes are synthesized in free ribosomes.
3
Q
What is the number of peroxisomes?
A
More in liver and kidney cells. They increase in response to diet or drugs.
4
Q
Peroxisomes LM
A
Detected by Histochemical method.
5
Q
Peroxisomes EM
A
Small moderate electron density vesicles. Spherical to ovoid, bound by a single membrane.
6
Q
What are the functions of peroxisomes?
A
The oxidases enzyme does beta oxidation of long chains of fatty acids. This produces energy as heat, which is not stored as ATP, and hydrogen peroxide which is a toxic product.
The catalase enzyme, then, would break down the hydrogen peroxide to water and oxygen which protects the cell.
7
Q
Why is oxidases important?
A
They are important in liver cells by oxidizing various organic substances to detoxify alcohol and drugs.
8
Q
What is the result of the lack of peroxisomes?
A
The lack of peroxisomes affects the function of some organs such as the liver.
9
Q
What are ribosomes?
A
Non membranous particles formed of rRNA and Proteins.
10
Q
What is the origin of ribosomes?
A
rRNA is formed in the nucleolus and proteins are formed in the cytoplasm and pass through nuclear pores. Both unite in the nucleolus to form small and large subunits that pass to the cytoplasm again through the nuclear pores. They join each other only during protein synthesis.
11
Q
What type of division do peroxisomes have?
A
Simple division (fission).
12
Q
What is the number of ribosomes?
A
Abundant in protein synthesizing cells such as plasma cells.
13
Q
Ribosomes LM
A
When abundant they cause basophilia of the cytoplasm due to the acidity of phosphate group in RNA. The basophilia may be focal, diffusing, or localized.
14
Q
Ribosomes EM
A
Small electron dense granules. Each is formed of two subunits, small and large, unite by binding to mRNA. The large subunit has a groove in its center to accommodate the polypeptide chain. The ribosomes have two forms:
1. Free: scattered singly or as polyribosome (polysomes) that are linked by mRNA to appear as Rosettes or spiral chains.
2. Attached: bind to the outer surface or rER by large subunits at ribophorins.
15
Q
What are the two forms of ribosomes?
A
- Free: scattered singly or as polyribosome (polysomes) that are linked by mRNA to appear as Rosettes or spiral chains.
- Attached: bind to the outer surface or rER by large subunits at ribophorins.
16
Q
How do ribosomes form the polypeptide chains?
A
mRNA Carries the information for the sequence of amino acids for protein synthesis. tRNA picks up the specific amino acids and transports them to rRNA forming the polypeptide chain that extends down the groove and is injected into the lumen of rER.
17
Q
What are the functions of ribosomes?
A
Ribosomes are factories of protein synthesis.
Free ribosomes: form proteins used within the cell as glycolytic enzymes.
Attached ribosomes form proteins secreted by cells as enzymes and hormones.
18
Q
What is the cytoskeleton?
A
It is a complex network of microtubules , microfilaments, and intermediate filaments together with proteins to link them to each other and to the cell membranes to form a framework called microtrabecular lattice.
19
Q
What is the structure of microtubles?
A
Hollow cylinders of fixed diameter with a wall of 13 parallel protofilaments. Their length varies on the polymerized tubulin molecules directed by microtubular organizing center (MTOC), which has gamma tubulins.
20
Q
What is the diameter of microtubules (MT)?
A
24nm
21
Q
What is the protein unit of microtubules?
A
a and B tubulin.
22
Q
What is the location of microtubules?
A
Radiating from the cytoplasm from MTOC, cilia.
23
Q
Microtubules LM
A
Difficult to be seen except by using immunofluorescent techniques.
24
Q
What are the functions of microtubules?
A
- Determine the cell shape and cell elongation.
- Intracellular transport of organelles, vesicles, and macromolecules.
- Formation of mitotic spindle during cell division.
- Formation of the centrioles, cilia, and flagella.
25
What is the structure of microfilaments?
Fine strands of 2 chains of globular G actin, coiled around each other to form filamentous F actin.
26
What is the diameter of microfilaments?
5-7 nm.
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What is the protein subunit of microfilaments?
G actin.
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What is the location of the microfilaments in the cell?
Beneath plasmalemma microvilli.
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Microfilaments LM
Difficult to be seen except by using immunofluorescent techniques.
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What are the functions of microfilaments?
1. Cell shape changes such as endocytosis, exocytosis, and ameboid movements.
2. Intracellular transport of organelles and granules.
3. Cleavage of the cell during cell division.
4. Form microvilli core to keep their shape and change their length by the shortening or elongation.
5. Muscle contraction.
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What is the intermediate filament’s structure?
Filaments formed by polymerization of tetrameric subunits that differ chemically.
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What is the diameter of intermediate filaments?
8-10 nm.
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What is the protein subunit of intermediate filaments?
Various proteins.
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What is the location of intermediate filaments in the cell?
In the cytoplasm, nuclear envelope.
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Intermediate filaments LM
Difficult to be seen except by using immunofluorescent techniques.
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What is the function of intermediate filaments?
Supportive function.
1. Cytokeratin
2. Vimentin
3. Desmin
4. Neurofilaments
5. Glial fibrillar acidic protein (GFAP)
6. Lamins
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Cytokeratin
In cells of epithelial tissue.
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Vimentin
Cells of connective tissue and muscular tissue.
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Desmin
Muscular tissue.
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Neurofilaments
In neurons in nervous tissue.
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Glial fibrillar acidic protein (GFAP)
Glial cells of the nervous tissue.
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Lamins
Nuclear envelop.
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How is cancer chemotherapy is used to arrest cell proliferation in tumors?
By preventing microtubules formation.
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Why is the identification of intermediate filaments proteins by immunocytochemical methods is important for diagnosis and treatment of tumors?
The cell of origin of tumor can be recognized.
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What are centrioles?
Cylindrical structure formed of microtubules (MT).
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Centrioles LM
Appear by iron hematoxylin stain as two dark bodies near the nucleus.
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Centrioles EM
2 cylindrical structures perpendicular to each other. They are surrounded by a matrix of tubulin (centrosome) in non dividing cells. The wall of each cylinder is formed of 9 bundles of MT and each bundle is formed of 3 MT’s (triplets), so the wall of the centriole is 9x3=27 MT’s.
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What are the functions of centrioles?
1. Forming of mitotic spindle during S phase of interphase of the cell cycle. The centrosome duplicates itself. During mitosis, it moves to poles of the cell and become organizing centers (MTOC) for MT of the mitotic spindle.
2. Share in formation of cilla and flagella.
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Cilia definition
Motile processes with microtubular core covered with plasmalemma.
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Cilia origin
Cillia duplicate thousand of time to form the basal body of cillia that migrate to the apical cytoplasm. A shaft grows from the basal body.
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Cillia LM
Hair-like striations.
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Cillia EM
Formed of a Basal body, shaft, and rootlets.
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Basal Body
A centriole formed of 27 microtubules, 9 triplets, embedded in the cytoplasm.
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Shaft (anexome)
Finger like projections form the cell surface covered by plasmalemma.
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Shaft structure
From each triplet, A and B microtubules grow as doublets pushing the cell membrane in front of them.
So the shaft is formed of 9 peripheral doublets and 2 singlet microtubules in the center that are formed by polymerization (20 microtubules).
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Rootlets
Formed by the growth of microtubule C in each triplet of the basal body into the cytoplasm (9 MT).
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Rootlets function
They fix the basal body and shaft to the cytoplasm.
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What are the cillia’s functions?
1. Repeated beating motion by bending of adjacent doublets which results in the movement of secretions or particles in one direction such as respiratory and female genital tracts.
2. Cilia can modify and act as receptors as in rods and cones of retina.
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Flagella
Motile projections from the cell, designed to move the cell itself.
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Flagella structure
They have the same exact structure as the axoneme of the cilium (. 9 peripheral doublets and 2 singlets), but extremely longer. In human, flagella forms the tail of sperm, which helps its movements.
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What happens if the cilia is unable to move?
It results in bacterial infections on top of accumulated secretions causing chronic respiratory infections.
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What happens if the flagella is immotile?
It causes male infertility.
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Microvilli
Finger like projections (shorter than cilia) from cell membrane of some cells.
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Microvilli LM
Apical striated brush border.
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Microvilli EM
A core of actin filaments ( to maintain its shape) is covered by cell membrane and inserted into the terminal web.
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Microvilli function
Increase surface area for more absorption. Eg. Small intestine.
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Stereocilia
Non motile solid cilia. Not true cilia but long microvilli.
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Stereocilia LM
Hair like processes from free surfaces of some cells.
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Stereocilia EM
Their core have actin filaments (no microtubules).
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Stereocilia function
Help absorption in male genital system. Eg. Epididymis.
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What are cytoplasmic inclusions?
1. Carbohydrates
2. Fats
3. Pigments
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Carbohydrates site
Stores as glycogen granules in liver and muscle cells.
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Carbohydrates LM
H and E: vacuoles dissolve away during heating.
Best’s Carmine stain: red granules
PAS: magenta red granules
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Carbohydrates EM
Single granules or rosette shaped aggregations. Mostly concentrated in areas of cytoplasm rich in sER. Why?
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Fats site
In fat cells: as large globules. In liver cells: small droplets.
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Fats LM
H and E: fat appears vacorkated as it dissolves in preparation.
Sudan III stains: fat appears as orange globule in fat cell.
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Pigments
Colored particles either produced by cells or taken from outside. Pigments are materials that possess color of their own nature.
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What are types of pigments?
Endogenous and exogenous pigments.
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Endogenous pigments
Hemoglobin Hb, melanin, lipofuscin.
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Exogenous pigments
Carbon and dust particles, carotene pigments, tattoo marks.
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Hemoglobin hb
In RBC'S, carries gases (CO2 and O2).
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Melanin
In skin, to give its color and protects from ultraviolet rays.
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Lipofuscin
In cardiac muscle and nerve cells. Waste products which accumulate with age.
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Carbon and Dust particles
Taken by dust cells of the lung.
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Carotene pigments
In Carrots
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Tattoo marks
Dyes injected under the skin taken by phagocytic cells.
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What is a nucleus?
The largest component of all cells except the RBC’s and Platelets because they’re not true cells.
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Nucleus number
Usually there one nucleus present in each cell (mononucleated). Some have two nuclei like liver cells (binucleated). Some have more than two nuclei (multinucleated) like skeletal muscles and osteoclasts.
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What are the positions of the nucleus?
1. Central, basal , essentric, and peripheral
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What are the shapes of the nucleus?
1. Rounded, flat, oval, billowed, multilobed, segmented, and kidney.
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Nucleus stains
Appears basophiric in H and E stained sections due to its content DNA and RNA.
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Nucleus appearance
Pale stained ( vesicular) or darkly stained (condensed).
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Pale stained (vesicular)
In active cells like nerve cells and liver cells.
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Darkly stained (condensed)
In inactive cells like small lymphocytes.
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The structure of the nucleus contains:
Nuclear membrane (envelope), chromatin material,nucleolus, and nuclear sap.
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Nuclear membrane LM
Basophilic line by chromatin on its inner side and ribosomes on its outer side.
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Nuclear membrane EM
Double walled membrane formed of two parallel unit membranes separated by a perinuclear space, interrupted at intervals by nudear pores.
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Outer nuclear membrane
Rough and granular due to attached Polyribosomes. It is continuous with rough endoplasmic reticulum cisternae.
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Inner nuclear membrane
Fibrillar due to attached chromatin threads (peripheral chromatin). It is associated with nuclear Lamins formed mainly of Lamins for stabilization of nuclear envelop.
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Nuclear pore complexes
Circular openings at intervals where inner and outer membranes fuse. They are formed of 30 nucleoporin proteins that form an octagonal ring. Nucleoporin filaments extend into the cytoplasm and nucleus.
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Function of nuclear pores
Transport of proteins to the nucleus and export of RNA and ribosomal subunits to the cytoplasm through transporter protein.
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Chromatin
In non dividing nuclei, chromatin is the chromosomal material in uncoiled state.
It represents the genetic material formed of nucleoproteins:
1. Double stranded DNA + histones
2. No his tone protein.
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What are types of chromatin?
Euchromatin and Heterochromatin.
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What is the difference between Euchromatin and Heterochromatin?
Euchromatin:
1. Extended (uncoiled) chromatin.
2. Contains active genes.
3. Predominates metabolically in active cells as protein forming cell.
4. LM: fine thread, pale basophilic (vesicular) nucleus with clear nucleolus.
5. Appears as electron lucent.
Heterochromatin:
1. Coiled inactive chromatin.
2. Contains inactive genes.
3. Predominates in metabolically in inactive cells Eg. Small lymphocytes.
LM: Coarse clumps, dark basophilic (condensed) nucleus with unclear nucleolus.
EM: appears as electron dense.
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Site of Heterochromatin
1. Peripheral chromatin
2. Chromatin islands
3. Nucleolus-associated chromatin
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Peripheral chromatin
Attached to the inner surface of nuclear membrane.
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Chromatin islands
Aggregated clumps scattered in the nuclear sap.
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Nucleolus-associated chromatin
Condensed around the nucleolus.
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What are the functions of chromatin?
1. Carries genetic information
2. Formation of RNA (mRNA, rRNA, tRNA)
3. Directs and controls protein synthesis.
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What happens in chromosomal alterations?
They are associated with tumors and genetic disorders.
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Nucleolus LM
- Round, deeply basophilia, rich in nucleus acids.
- Surrounded by chromatin.
- Usually one or two per nucleus.
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Nucleolus EM
Spongy area not limited by membrane.
Has dark and light areas.
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Dark areas:
1. Pars amorpha (nucleolar organizer)
2. Pars fibrosa (fibrillar component)
3. Pars granulosa ( granular component)
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Pars amorpha
Filaments of DNA, which are parts of chromosomes carrying the genes encoding rRNA.
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Pars fibrosa (fibrillar component)
Strands of newly formed rRNA.
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Pars granulosa (granular component)
Granules of mature rRNA.
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What is nucleolonema?
Both pars granulosa and fibrosa.
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Light areas
Formed of nuclear sap.
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What are the functions of the nucleolus?
Formation of ribosomal RNA and ribosomal subunits (rRNA + proteins), which pass through nuclear pores to the cytoplasm.
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Where is large nucleoli found?
They are found in rapidly growing malignant cells.
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What is a nuclear sap?
A colloidal solution that fills the space between chromatin material and the nucleolus.
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What are the constituents of nuclear sap?
1. Nuclear proteins
2. Enzymes
3. Sugars
4. Calcium
5. Potassium
6. Phosphorus ions
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What is the function of nuclear saps?
They provide a medium of transport of RNA through nuclear pores to cytoplasm for protein synthesis.
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What are the functions of the nucleus?
1. Carries all genetic materials and hereditary factors.
2. Controls all the cell functions including protein synthesis.
3. Responsible for formation of RNA.
4. Directs cell division.
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What are glycoproteins?
Proteins linked to carbohydrate group. (Oligosaccharide group.
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True or false Glycoproteins contain more protein and less carbohydrates.
True, they contain 95% of protein and 5% of carbohydrates.
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Where is the oligosaccharide deficient?
In uronic acid or repeating disaccharides.
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What are the 8 monosaccharides commonly found in oligosaccharides?
1. Glucose
2. Galactose
3. Mannose
4. Xylose
5. Fucose
6. NANA
7. N acetyglucosamine
8. N acetygalactosamine
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Site of Glycoproteins
Mucous, cell membrane, and blood.
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Percentage of carbohydrates
1% collagen
4% immunoglobulins
50% mucin
80% ABO group antigens
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Proteoglycan protein content
95%
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Glycoprotein protein content
5%
133
Proteoglycan carbohydrate content
5%
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Glycoprotein carbohydrate content
5%
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Proteoglycan type of carbohydrate
GAGs
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Glycoprotein type of carbohydrates
Oligosaccharides chain with No:
Uronic acid or repeated disaccharides
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Examples of Proteoglycans
1. Proteoglycans in CT
2. Cornea
3. Sclera
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Examples of glycoproteins
Immunoglobulins, collagen, and mucin.
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The cell
Basic structural and functional unit of the living body.
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The cell functions
1. Absorption.
2. Respiration.
3. Secretion.
4. Excretion.
5. Sensation.
6. Conduction.
7. Contraction.
8. Movement.
9. Growth.
10. Reproduction.
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Cell size
Varies from 4 micrometers (as granular cells of cerebellum) to 150 micrometers (as ovum).
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Cell shape
1. Rounded.
2. Oval.
3. Flat.
4. Stellate.
5. Polygonal.
6. Cubical.
7. Columnar.
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The cell structure
Animal cell is formed of 2 basic components:
1. Cytoplasm.
2. Nucleus.
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Why is the cytoplasm formed of?
1. Cytosine.
2. Organelles.
3. Inclusions.
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Cytosol
Fluid containing:
1. Carbohydrates.
2. Proteins.
3. Lipids.
4. Minerals.
5. Ions.
6. Salts.
7. RNA.
8. Metabolites.
9. CO2.
10. O2.
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Organelles
1. Living.
2. Permanent.
3. Essential.
4. Active.
5. Vital functions.
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Inclusions
1. Non living.
2. Temporary.
3. Usually non essential.
4. Inert.
5. Result from cell activity.
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Cytoplasmic organelles are classified according to?
Presence or absence of limiting membranes.
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Membranous organelles
1. Covered by membrane.
2. Contain enzymes.
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Non membranous organelles
1. Uncovered by membrane.
2. No enzymes.
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Membranous organelles
1. Plasma membrane.
2. Mitochondria.
3. Endoplasmic reticulum.
4. Golgi apparatus.
5. Lysosomes.
6. Peroxisomes.
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Non membranous organelles
1. Ribosomes.
2. Cytoskeleton:
- Microtubles:
* Centrioles.
* Cilia.
* Flagella.
Filaments:
* Thin and intermediate filaments.
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Plasma membrane
Limiting membrane that envelops all the cells.
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Plasma membrane LM
1. Difficult to be seen because it is very thin (7.5-10).
2. Demonstrated by silver Ag or PAS.
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Plasma membrane EM
1.Two dark layers separated by an intermediate light layer so it’s called trilaminar or unit membrane.
2. Fuzzy material found on the outer surface of plasmalemma only, which represents the cell coat (glycocalyx).
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Molecular structure of plasma membrane
1. Lipids.
2. Proteins.
3. Carbohydrates.
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Lipids
1. Phospholipid molecules.
2. Cholesterol molecules.
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Phospholipid molecules structure
Arranged in two layers (Lipid bilayer). Phospholipid head directed outwards (aqueous solution) and tails directed inwards.
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Phospholipid molecules functions
1. Permeable to certain substances (selectively permeable) and impermeable to ions and polar substances to perform a barrier between internal and external environment of the cells.
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Cholesterol molecules
Present among hydrophobic fatty acids.
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Cholesterol molecules functions
1. Restrict movement of phospholipid molecules thus stabilize cell membrane.
2. Modulate fluidity of the membrane, preventing it from being too fluid to too rigid.
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Proteins
About 50% of total membrane mass and present in two forms:
1. Peripheral proteins.
2. Integral proteins (transmembrane proteins).
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Peripheral proteins
1. Small molecules, loosely attached to both surfaces of the cell membrane.
2. A non continuous layer outside the lipid bilayer.
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Integral proteins
1. Embedded in the lipid bilayer.
2. Two types:
- Channel proteins fro transported of ions and water.
- Carrier proteins for transport of small polar molecules such as glucose and ions such as Na K pump.
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Integral proteins functions
Specific transport of ions and polar molecules.
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Carbohydrates
External surface:
1. Glycoproteins: oligosaccharides linked to protein molecules.
2. Glycolipids: oligosaccharides linked to phospholipid molecules.
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Cell coat glycocalyx is formed of?
Molecules of glycoproteins and glycolipids.
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Glycocalyx site
External surface of cell membrane.
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Glycocalyx includes
Receptors for drugs, hormones, viruses, and bacteria.
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Glycocalyx functions
1. Adhesion.
2. Identification (receptor).
3. Protection.
4. Cell immunity.
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Functions of the cell membrane
1. Endocytosis.
2. Exocytosis.
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Endocytosis
Bulk movement of substances into the call by forming vesicles. It includes 3 types:
1. Phagocytosis.
2. Pinocytosis.
3. Receptor mediated endocytosis.
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Phagocytosis
1. Pseudopedia extend from the cell to surround the particle such as a bacterium.
2. The membranes of these extensions meet and fuse enclosing the bacterium in an intercellular vacuole called phagosome.
3. The phagosome then fuses with lysosomes to digest its contents.
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Example of phagocytosis
WBC engulfing bacteria.
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Pinocytosis
1. Smaller invaginations of cell membrane and surround extracellular fluid.
2. Pinocytic vesicles then detach off inwardly from the cell membrane.
3. The vesicle usually fuses with lysosomes to digest it’s contents.
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Pinocytosis example
Pinocytosis of colloid in thyroid follicular cell.
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Receptor mediated endocytosis
1. Receptors in the form of integral proteins in cell membrane bind to specific substances and aggregate at the site of binding.
2. Associate with other proteins on the cytoplasmic side called clathrin to form a coated pit.
3. The coated pit invaginates and pinches off forming a coated vesicle.
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Examples of receptor mediated endocytosis
Uptake of protein hormones as GH by the cell.
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Exocytosis
Bulk movement of substances from inside to outside of the cell by forming vesicles.
1. Cytoplasm vesicle fuses with cell membrane.
2. Release of contents into the extracellular space without affecting continuity of cell membrane.
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What can lack of GH receptors at cell membrane if target cells lead to?
Despite having normal level of GH (growth hormone) in blood, lack of GH receptors in cell membranes of target cells leads to some type of dwarfism.
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Mitochondria
Membranous organelles contains enzymes for aerobic respiration and energy production.
Power house of the cell.
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Mitochondria site
Areas of most activity of the cell.
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Mitochondria number
1. More in active cells as liver cells (2000/cell).
2. Increase in number by simple division.
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Mitochondria LM
1. When abundant they cause cytoplasmic acidophilia.
2. Appear as rods or granules.
3. Dark blue with iron hematoxylin and green with Janus green stain.
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Mitochondria EM
1. Oval or rounded membranous vesicles.
2. Surrounded by two unit membranes separated by an inter-membrane space:
- Outer membrane.
- Inner membrane.
- Mitochondrial matrix.
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Mitochondria outer membrane
1. Smooth.
2. Contains transmembrane proteins called porins.
3. Permeable to small molecules.
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Mitochondria: Inner membrane
1. Less permeable (selective).
2. Projects into the matrix forming shelf like folds called cristae.
- Number increases based on energy needs.
- Increase surface area for attachment of elementary particles, which are globular structures connected to the inner membrane by cylindrical stalks.
- Represent a protein complex with ATP synthase activity (forms ATP in oxidative phosphorylation).
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Mitochondria: mitochondrial matrix is composed of?
1. Oxidative enzymes.
2. DNA, mRNA, tRNA, rRNA.
3. Dense granules rich in Ca2+ that act as catalysts for mitochondrial enzymes.
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Mitochondria functions
Responsible for energy production (cell respiration):
1. Mitochondria obtain energy from metabolites present in the cytoplasm by Krebs cycle (citric acid cycle).
2. Most of this energy is stored as ATP molecules by oxidative phosphorylation and some is liberated as heat to maintain body temperature.
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Defect in mitochondrial enzymes leads to?
Failure to produce ATP which is needed fir all vital functions.
Eg. Causes muscular weakness.
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Endoplasmic reticulum
A membranous network that extends from the nucleus to the cell membrane enclosing a series of inter communicating channels and sacs called cristernae.
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Types of endoplasmic reticulum
According to presence or absence of electron dense particles called ribosomes on their surface.
1. Rough endoplasmic reticulum.
2. Smooth endoplasmic reticulum.
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Rough endoplasmic reticulum site
Protein forming cells as plasma cells.
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Smooth endoplasmic reticulum sites
Lipid forming cells as liver cells.
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Rough endoplasmic reticulum LM
Localized or diffused basophilia.
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Smooth endoplasmic reticulum LM
When abundant: acidophilia.
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Rough endoplasmic reticulum EM
1. Parallel flattened cristernae continuous with outer nuclear envelope.
2. Covered with electron dense particles, ribosomes, bound to specific receptors (ribophorins) on membranes by their large subunits.
3. Under the receptors are pores that allow newly synthesized proteins to enter and to be stored in rER cristernae.
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Smooth endoplasmic reticulum EM
1. Anastomosing tubular cristernae of various shapes and sizes continuous with rER.
2. Absence of Ribosomes.
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Rough endoplasmic reticulum Functions
SIIPPP (SIP)
1. Segregation of formed proteins.
2. Initial glycosylation of some proteins by addition of monosaccharides.
3. Intracellular pathway for the formed substances.
4. Protein synthesis by attached polyribosomes.
5. Protection of cytoplasm from hydrolytic enzymes formed inside it.
6. Packing of formed proteins in membranous vesicles that bud off from the cristernae (transfer vesicles) to be delivered to Golgi apparatus.
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Smooth endoplasmic reticulum functions
1. Phospholipid molecules synthesis that constitutes cell membranes.
2. Steroid hormones synthesis as cortisone and testosterone.
3. Breakdown of glycogen to glucose in liver cells.
4. Detoxification of drugs, alcohols, and hormones in liver cells.
5. Calcium ions (Ca++) release (pump) in muscle contraction.
6. Acts as an intracellular pathway.
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Golgi apparatus
A membranous organelle, concerned with secretion.
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Golgi apparatus site
Well developed in secretory cells.
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Golgi apparatus LM
1. Does not appear in H and E stain.
2. In protein forming cells, it can be seen as a pale unstained area near the nucleus called “negative Golgi images”.
3. With silver stain (Ag) it can be demonstrated as a network of brown granules and fibrils
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Golgi apparatus site
1. Apical: between the nucleus and upper pole of secretory cells.
2. Peripheral: completely surrounds the nucleus as in nerve cells.
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Golgi apparatus EM
1. Interconnected parallel flat curved membranous saccules 3 -10 arranged above each other forming stacks.
2. Each saccule has a narrow lumen with expanded ends.
3. Filled with low electron dense material.
4. Each stack has 2 faces:
- Entry (Cis) face: receives transfer vesicles from carrying proteins.
- Exit (Trans) face: vesicles that bud off from this face are either:
* Secretory vesicles: discharge their contents by exocytosis.
* Lysosomes.
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Golgi apparatus functions
1. Packing, concentration, and storage of proteins received from rER.
2. Chemical modification of proteins and lipids by addition of carbohydrates.
3. Formation of secretory vesicles and lysosomes.
4. Discharge of secretory products as hormones in secretory vesicles.
5. Renewal and maintenance of cell membrane by providing it with integral proteins from membrane of secretory vesicles.
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Lysosomes
A membranous organelle contains hydrolytic enzymes such as protease and sulfatase. Responsible for Intracytoplasmic digestion.
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Lysosomes origin
A lysosome is a secretory vesicle that arises from Golgi apparatus containing hydrolytic enzymes.
The hydrolytic enzymes are synthesized in rER then carried via transfer vesicle to Golgi apparatus to come out in lysosomes.
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Lysosomes number
Abundant in phagocytic cells (macrophages and neutrophils.
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Lysosomes LM
1. Not detected by H and E stain. Histochemical stains are used to detect the hydrolytic (lysosomal) enzymes.
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Lysosomes EM
1. Primary lysosomes.
2. Secondary lysosomes.
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Primary lysosomes
Newly released lysosomes from G.A. appear by EM as homogenous (moderate electron dense) vesicles.
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Secondary lysosomes
Lysosomes with variable contents, so appear by EM as different heterogenous vesicles.
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Types of lysosomes
1. Heterolysosomes.
2. Multivesicular body.
3. Autolysosome.
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Heterolysosome
Formed by the fusion of a primary lysosome with a phagosome to digest solid particles as bacteria or viruses.
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Multivesicular body
Formed by the fusion of the primary lysosome with a pinocytic vesicle to digest fluid particles.
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Autolysosomes
Formed by the fusion of primary lysosomes with autophagic vesicles containing destroyed endogenous substrate as mitochondria.
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Fate of secondary lysosomes
The digested material diffuses to the cytoplasm through lysosomal membrane while undigested material is retained within vesicles called residual bodies.
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Residual body
1. Discharge the undigested material by exocytosis (cytostool).
2. Accumulate over the years in long lived cells such as cardiac muscle and nerve cells as lipofuscin granules (age pigments).
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Functions of the lysosomes
1. Digest nutrients and phagocytosed bacteria and viruses.
2. Maintain cell health by removal of excess or non functional organelles.
3. Postmortem autolysis by digestion of cell after death due to lysosomal rupture.
4. Fertilization by helping the head of the sperm penetrate the ovum.
5. Activation of thyroid hormone by breaking bond between hormone and protein.
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Lack of lysosomes results in?
Lack of lysosomes as sulfatases results in intracellular accumulation of sulfates compounds which interfere with normal functions of nerve cells.
