Flashcards in Cytology Deck (61):
Organelles and particles (general)
Membranes form barrier between cell and external environment (plasma membrane).
They subdivide the cell into compartments.
These compartments are organelles.
What is there environment/function/
What are they composed of?
What is there size and what do you stain with?
-Membranes allow each type of organelle to maintain novel ionic and enzymatic interior environments.
-Membranes are composed of lipids, proteins, and carbohydrates.
-Membranes are ~7nm and can be seen through an electron microscope when stained with osmium tetroxide.
Membrane Lipids (phospholipids, cholesterol, and glycolipids)
-uncharged hydrophobic tails
-polar hydrophilic heads.
-hydrophobic center acts as an anchor to membrane proteins that can move freely within the lipid bilayer.
Fluid Mosaic Model
-membrane is highly permeable for small, uncharged molecules that cross the membrane by simple diffusion.
-all other molecules require membrane transport proteins to provide them with passage across the membrane.
Structural membrane proteins: integral and peripheral
-Integral membrane proteins have a hydrophobic region which is embedded into the hydrophobic core of the membrane.
-Transmembrane proteins are integral membrane proteins that extend all the way through the membrane.
-Peripheral membrane proteins are not embedded within the lipid bilayer and attach to integral proteins or to the hydrophilic heads of the membrane lipids.
Transport proteins: types and functions
-Channel proteins: form "pores," which allow passage of small molecules across the membrane via passive diffusion. Channels are ion-selective.
-Carrier proteins "drag" other molecules through the membrane by hiding them in a cleft in the protein.
-Pumps use ATP energy to pump ions actively through the membrane.
Some transmembrane proteins bind to specific molecules in the extracellular matrix. This specific binding can result in a conformational change in the transmembrane protein that can serve as a signal that allows the cell to adapt to its environment.
Structural or anchoring proteins
Attach cell to its surroundings. These transmembrane proteins use their cytoplasm domains to link to the elements of the cytoskeleton, and their extracellular domains to link to the extracellular proteins.
Carbohydrates on membrane
Mostly oligosaccharides are attached to the extracellular domains of membrane proteins and lipids to form glycoproteins and glycolipids.
-Large amount of carbohydrates attached to proteins and lipids on the external surface give cell a "fuzzy" coating called the glycocalyx.
Particles and Inclusions
Particles and inclusions are used for synthesis and storage. The two main types are ribosomes and glycogen particles.
3 types in cell?
Ribosomes are RNA/protein particles that catalyze protein synthesis. They bring together mRNA and tRNA to synthesize a polypeptide.
-15-25nm, small subunit and large subunit, each subunit consists of one or more ribosomal RNA (rRNA) and many specialized proteins
-Free ribosomes, mitochondrial ribosomes, Bound to RER. Most cellular proteins are synthesized on free ribosomes. Golgi, lysosomes, secretory granules, and plasma membrane are synthesized by RER ribosomes. 20% of mitochrondial proteins are synthesized by mitochondrial ribosomes, the rest are from free ribosomes.
-Polysomes are a string of ribosomes connected to mRNA during protein synthesis.
Storage form of polysaccharides
Smooth Endoplasmic reticulum
-does not have ribosomes and has more tubular appearance that the rough ER.
-Lipid and steroid metabolism. Phospholipids of the cell's membrane are produced in SER, so SER is involved in membrane synthesis and recycling. SER is prominent in steroid-secreting cells.
-Detoxification of noxious substances. Well developed in liver cells and contains enzymes that can modify and detoxify such toxins as carcinogens and pesticides.
-Involved in glycogen metabolism
-speacialized form of SER found in muscle tissue.
-involved in storage and transport of Ca++, which regulates the contractions of muscle cells.
Rough Endoplasmic Reticulum
-has ribosomes bound to its surface.
-formed mostly of cisternae.
-prominent in cells specialized for protein secretion, so it is the principal site of synthesis of proteins destined for export out of the cell.
-Proteins from the Golgi, lysosomes, secretory granules, and the plasma membrane are synthesized in the RER.
Golgi Apparatus (series of stacked, flattened, membrane-limited cisternae that is polarized, and tubular extensions)
-receives proteins synthesized in the RER.
-side receiving vesicles from the RER is cis Golgi.
-medial Golgi, forms the middle cisternae
-mature proteins are transported from the trans Golgi
Posttranslational modification of Golgi
-add or remove sugar residues, sulfate or phosphate groups.
-early stages in cis Golgi, intermediate steps in medial Golgi, and final modifications are made in the trans Golgi.
Sorting and packaging of proteins into transport vesicles by Golgi.
What are the three destinations?
-occurs mainly in the trans Golgi.
-Most proteins coming from the Golgi apparatus bear specific signal sequences, which direct them to their destination.
1. Secretory vesicles
3. Constitutive pathway
-maturation process in which secretory proteins are retained within the vesicle. Mature secretory vesicles eventually fuse with the plasma membrane to release the secretory product into the extracellular space in response to a certain signal.
-example: pancreatic acinar cells
-produced by the Golgi
-involved in digesting the material taken up from outside the cell and degradation of senescent organelles.
-low pH and hydrolytic enzymes.
--mannose-6-phosphate is the principal sorting signal.
I-cell disease (mucolipidosis)
-type of lysosomal storage diseases
-Mutation of one of the enzymes of mannose-6-phosphate and lysosomal proteins are secreted into the intercellular space.
3 classes of Lysosomes
Primary lysosomes- have not yet received substrates for digestion.
Secondary lysosomes-fusion of primary lysosomes with their target.
Lipofuscin granules (residual bodies)- senescent lysosomes with indigestible material
Proteins in the trans Golgi, which are not destined for either lysosomes or secretory granules are sorted into small vesicles, which are transported directly to the plasma membrane, where the vesicle fuses with the plasma membrane.
-Integral membrane proteins and proteins that are secreted continuously into the extracellular space (collagen) reach the plasma membrane by this route.
Size and function?
-Small (0.5 microns), membrane-bound organelles containing oxidative enzymes, particularly catalase.
-oxidize long chain fatty acids and converse ethanol to acetaldehyde.
-oxidative enzymes produce hydrogen peroxide as a product of oxidation reaction and catalase is important in degrading H2O2.
Congenital disease which is caused by mutations in the proteins that are responsible for the proper transport of peroxisomal enzymes from the cytoplasm, where they are synthesized on free ribosomes, to peroxisomes.
-Peroxisomes lack the necessary enzymes and do not functions properly. Affects brain development through the improper formation of the myelin sheath (lipid)
-caused by disruptions in oxidation of very long chain fatty acids.
-an inherited X-linked disorder that results in progressive brain damage, failure of the adrenal glands, and eventually death.
-symptoms are caused by the accumulation of lipid in the brain and adrenals.
Function and size?
-Involved in the production of ATP through the oxidation of pyruvate and fatty acids.
-has their own separate genome, posses two membranes, and increase their number by division
-Size: 1-5 microns, shapes include spheres, rods, elongated filaments, and even spirals
Outer mitochondrial membrane
-contacts the cytoplasm on the outer side and intermembrane space on the inner side.
-contains numerous pores (anion channels), which allow passage of small molecules (5,000 dalton), ions, and metabolites.
Inner mitochondrial membrane
-Thinner than the outer membrane and highly folded cristae, which project into the matrix and greatly increase inner membrane surface.
-in steroid-producing cells the cristae may have tubulovesicular appearance. The inner membrane contains many of the enzymes involved in energy production.
-pH and ionic composition is similar to cytoplasm
-protein composition is unique in containing enzymes that use ATP generated in the inner membrane space.
-Cytochrome C is located here and is an important factor in initiating apoptosis
-enclosed within the inner mitochondrial membrane and contains soluble enzymes (Krebs cycle, DNA transcription)
-contains mitochondrial DNA, mitochrondial ribosomes, rRNA, mRNA, and tRNA.
-contains electron-dense granules that store Ca++ so mitochondria also regulate concentration of certain ions in the cytoplasm, the role they share with SER.
-mutations in both nuclear and mitochondrial genes
-mitochrondial diseases my presen in young adulthood and manifest with proximal muscle weakness, sometimes affecting the extraocular muscles involved in eye movements.
-the weakness may be accompanied by other neurological symptoms lactic acidosis, and cardiomyopathy
Size and functions
-Large (5-10 microns)
-surrounded by double membrane called the nuclear envelope
-membrane-limited organelle that contains the genome in eukaryotic cells in the form of DNA bound to proteins, which is known as the chromatin.
-contains machinery for DNA replication and RNA transcription and processing and one or more nucleoli.
-two membranes, perinuclear space between them, nuclear lamina, and nuclear pores.
Outer nuclear membrane
-resembles the membrane of the RER and is continuous with the latter.
-ribosomes are commonly attached to the cytoplasmic surface of the outer nuclear membrane in a manner identical to the rest of the RER.
Continuous with the lumen of the RER
Inner nuclear membrane
-distinct from the endoplasmic reticulum in its ability to bind chromatin and lamins.
-supported by a rigid network of intermediate filaments
-thin, protein-dense layer attached to the inner nuclear membrane
-represents the "skeleton" of the nucleus formed by the specialized intermediate filaments proteins called lamins.
-Lamins, unlike other intermediate filaments, can dissemble. They do this in mitosis and reassemble when mitosis ends.
-Lamin filaments are cross-linked into an orthogonal lettuce, which is attached to the inner nuclear membrane
70-80nm openings in the envelope, which all communication between the cytoplasm and the nucleus.
-protein "spokes" projecting into the lumen of the pore to the central "plug"
-pores allow passage for small (<9nm) particles. The larger particles (proteins, RNA-protein complexes) must be actively transported through the membrane.
-contains DNA associated with roughly an equal mass of various nuclear proteins, such as histones.
-has heterochromatin and euchromatin
-transcriptionally active DNA
-indicated active chromatin, or the chromatin that is stretched out so that the DNA can be read and transcribed.
-prominent in metabolically active cells such as neurons.
-predominates in metabolically inactive cells.
-contains transcriptionally inactive DNA
-stains more intensely that euchromatin
-small area within the nucleus in which ribosomal RNA is processed and assembled into ribosomal subunits.
-part of nucleolus
-contain DNA loops with rRNA genes and transcription factors
Dense fibrillar component (pars fibrosa)
-part of nucleolus
-contains ribosomal genes that are being translated and large amounts of RNA
Granular component (pars granulosa)
-part of nucleolus
-site for ribosome assembly and is made of densely packed clusters of pre-ribosomal particles.
Determines the shape of cells, provides structural support for tits organelles, and plays a major role in cell motility (mitosis and cytokinesis)
-consists of actin filaments, microtubules, and intermediate filaments
Plays an important role in cell movement, cell shape, and organelle transport
-G-actin and F-actin
G-actin and F-actin
-soluble monomeric globular protein
-polymerize into a double-stranded helical filament, called F-actin.
-Polymerization occurs head-to-tail, so the actin filaments have polarity.
-F-actin is a.k.a thin filaments
Actin (thin) filaments
-form a thin sheath beneath the cytoplasm called the cortex.
-cross lined actin filaments resist cell deformation, transmit forces, and restrict the movement of organelles.
-Cortex reinforces the plasma membrane and restricts lateral motion of some integral membrane proteins.
Interacts with actin to generate force and movement.
-myosin is the motor associated with thin filaments.
-present in all cells except erythrocytes
-involved in organelle and vesicle movement sometime over long distances (movement of materials along the axon of a neuron)
-Formation of mitotic spindle and chromosome movement during mitosis and meiosis
-beating of cilia and flagella
-stiff, non-branching, cylindrical polymers made of two polymerized globular proteins, alpha-tubulin and beta-tubulin.
-polymerized side to side and head to tail.
-"plus" end grows faster than the "minus" end.
-"plus" end is on the cell periphery and the "minus" end is usually associated with the microtubule-organizing center/centriole.
Microtubules motor proteins
How they function"
-motors use ATP energy to generate force that moves the motor and materials attached to it along the microtubule.
-Dyneins- group of motor proteins that move towards the minus end of a microtubule. Involved in beating of cilia and flagella
-Kinesins- group of motor proteins that move towards the plus end of a microtubule.
Microtubule (higher order structure)
-higher order structures, include cilia, flagella, centrioles, and microtubules-organizing centers.
-core of cilia and flagella
-9 doublets and a central pair of microtubules
-dynein arms attached to the A-tubule of each of the doublets interacts with the neighboring B-tubule of the next doublet and by "walking" along it causes the bending of the axoneme.
-axoneme generates force for the movement of cilia and flagella
Centriole (basal body)
-base of each cilium or flagellum
-composed of microtubules arranged into 9 triplets without the central pair.
Microtubule-organizing center (MTOC)
-most human cells except neurons and RBC's contain MTOC, which consists of two centrioles
-virtually all cellular microtubules arise from the MTOC
-intermediate in thickness between actin and microtubules
-strong,but flexible polymers that provide mechanical support for cells.
-do not have polarity and there are no motor proteins associated with them
-form bundles between the plasma membrane and the nucleus. Spread tensile forces, maintain cell architecture, and act as a cocoon when cell is damaged.
-anchor ion channel proteins
Classes of intermediate filaments
5. Glial fibrillary acidic protein
1. Form a mesh work of filaments on the inner side of the nuclear envelope, where they form the nuclear lamina and provide structural support for the nucleus.
2. Found principally in epithelial cells
3. Found principally in the fibroblasts of the CT
4. Found in muscle cells.
5. Found in the cup port cells of the nervous system, called glial cells.
6. Found in neurons