Cytology Flashcards
Cytoskeleton componets
- Microfilaments
- Intermediate filaments
- Microtubules
Functions of cytoskeleton
-Shaping of cells
-Important in cellular movement
Movement of vesicles and organelles in the cytoplasm
Movement of parts of the cell forming pseudopodia
Movement of the cell as a whole as in spermatozoa
- Supportive internal skeleton to the cell
Microfilaments
Synonym
Actin Filaments
Microfilaments
Size
Thin filaments of 6nm in diameter
Microfilaments
Percentage
Actin constitues 15% of total protein content of non-muscle cell
Microfilaments
Sites
In non-muscle cells: form a sheath under the cell membrane and are also present in cell extensions like pseudopodian and microvilli
In muscle cells: ACtin filaments interdigitate with thick myosin filaments in parallel arrays
Microfilaments
Structure
It is found in the cytoplasm in 2 forms:
G-actin: dispersed in the cytosol, not visible with EM, polymerize together to firm F-actin
F-actin: The filament consists of a double stranded helix. Each strand is a polymer of G-actin
Actin filaments ends
Plus end where molecules are added leading t the elongation of the filament
Minus end where actin molecules are removed leading to shortening of actin filaments
Microfilaments
Functions
-Contraction of muscle cells
-Anchorage and movement of membrane proteins
-Movement of plasma membrane as in endo and exocytosis
-Formation of pseudopodia and microvilli
-Locomotion of cells
Formation of contractile ring during cell divisionn
Intermediate filaments
Size
10 nm
Intermediate filaments
Characteristics
Stable structures with neither a plus or minus end
Keratins
Include tonofilaments
They are found in most epithelia
Desmin
In muscles
Vimentin
In fibroblasts
Neurofilaments
In neurons (axons and dendrites)
Glial filaments
In neuroglial cells
Intermediate filaments
Sites in the cytoplasm
- Keratin
- Desmin
- Vimentin
- Neurofilaments
- Glial filaments
Intermediate filaments
Sities in the nucleus
Lamins
Microtubules
Sites
Cytoplasm of all cells except RBCs
Microtubules
Size
24 nm
Microtubules
Structure
Longitudinally:long, straight, rigid, hollow cylinders
Transverse: fine circles with dense wall and hollow core
Microtubules
Subunits
Tubulin
Is of 2 types: alpha and beta
Tubulin dimers
One dimer is alpha and beta
They are organised into spiral with total number of 13 subunits in each complete turn of the spiralto form 13 linear protofilaments
Microtubules
Types in the cytoplasm
Dispersed microtubules
Organised microtubules as in cilia and centrioles
Microtubules
Functions
-Maintain the shape of the cell because of its rigidity
-Dispersed microtubules are responsible for intracellular transport of organelles and vesicles
-Microtubules provide basis structure for:
Centrioles
Cilia
Flagella
Mitotic spindle
MTOC
Definition, function,examples
Microtubules organising centre is a structure found in eukaryotic cells
It is responsibe for polymerization of tubulin subunits to form microtubules
examples:
- Basal bodies of the cilia
- Centrioles
- Centromeres of the chromosomes
Microtubules associated proteins (MAPs)
definition
They are special proteins that assist in intracellular movement of organelles and vesicles and also prevent depolarization of the mictrotubule
Kinesin
Motor protein
Moves the vesicles towards the plus + end
Cytoplasm dynein
Motor protein
Moves vesicles towards the minus - end
Dynamin
it is a protein that forms cross-bridges between neighbouring microtubules
Axonemal dynein
is a proteins that foms arms of the doublets of the shaft of the cilia and is motor protein responsible for ciliary movement
Functions of centrioles
They form mitotic spindles
They forms basal bodies of cilia and flagella
They form microtubules organising centres (MTOCs)
Cilia sites
Some cells of the respiratory system
Female genital tract (fallopian tube and uterus)
Cilium size
Diameter 0.2 um and length of 7-10 um
Functions of cilia
In trachea, they move to keep the airways clear of mucus and dirt
In the fallopian tube to move the ovum towards the uterus for possible pregnancy
Nucleus stain
By H&E, the nucleus is basophilic because of its contents
By Feulgen stain, DNA is feulgen positive (red) while RNA is feulgen negative
Nucleus structure by EM
Nuclear envelope
Nucleolus
Chromatin
Nucleoplasm or karyoplasm
Nuclear envelope is formed of 2 parallel membranes each is a unit membrane seperated by……..
perinuclear cisternae
Nuclear pore
It is a channel which provide bidirectional communication between nucleoplasm and cytoplasm
Types of heterochromatin
Peripheral chromatin
Nucleolar associated chromatin
Islands of chromatin
Nuleosome
is the basic structural unit of chromatin. DNA is wrapped twice around a core of 8 histones (octamer)
The octamer is formed of 2 molecules of H2A, H2B, H3 and H4
10-11 nm in diameter
Selinoid
Nucelosomes become coiled around an axis with 6 nucleosomes per turn
30 nm
Looped domain of chromatin
Further coiling of the 30 nm forming series of loops
300 nm
Heterochromain and metaphase chromosomes
700 nm
1400 nm
formed during mitosis due to further coiling and condensation
Nucleolus LM
Deepley basophilic due to its content of ribonucleoproteins
Nucleolus EM
Pars amorpha
Pars fibrosa
Pars granulosa
Pars amorpha
Round pale areas formed of tips of chromosomes 13, 14, 15, 21, 22
they are nucleolar organisers responsible for formation of rRNA
Pars fibrosa
Formed of fine electron dense filments of newly formed rRNA
Pars granulosa
dense strands having granular appearance and is the site of formation of ribosomal subunits
Functions of nucleolus
Formation of ribosomes
