Shelf Review 2024-2025

Fluid Mosaic Model Of Cellular Membranes

• The hydrophilic (polar) residues of the component molecules are arranged to maximize their contact with water.
• Cholesterol reduces the fluidity of the membrane.

Iron Transport

• Defects in iron transport result from a mutation preventing clustering in a coated pit.
• Receptor-mediated endocytosis internalizes substances at the plasma membrane in a coated vesicle.
• A number of viruses hijack receptor-mediated endocytosis by binding to plasma membrane proteins to enter cells.

Botulism

• Botulism results from the cleavage of synaptobrevin, which is necessary for the fusion of the synaptic vesicle membrane with the plasma membrane at the neuromuscular junction.

Transcriptional Activity In The Nucleus

• Euchromatin is the major site of transcriptional activity in the nucleus for messenger RNA (mRNA).
• In euchromatin, the chromatin is less tightly packed, which allows transcription to occur.
• Heterochromatin is more tightly packed in the form of nucleosomes.
• Ribosomal RNA transcribed at region A of the image.

Transport Of Large Proteins Into The Nucleus

• Transport of large proteins into the nucleus occurs by nuclear pores and involves binding of these proteins to importins.
• Proteins larger than about 50-65 kDa usually require binding to importins to enter the nucleus through the nuclear pore.
• Exportins are needed for proteins to exit from the nucleus through the nuclear pore.

Cell Cycle Stages

• Cells in tissue culture that are actively growing, dividing every six hours, and have completed duplication of their DNA but have not yet entered into division are in the G2-phase.

Apoptosis

• During apoptosis, the release of cytochrome C activates caspase enzymes in the cytoplasm.

Rhabdomyolysis

• In rhabdomyolysis, necrosis and breakage of the plasma membrane of the cells is consistent with the presence of myoglobin and increased concentrations of other muscle cytoplasmic proteins in the blood.

Mitochondria

• Tissue with extremely large numbers and sizes of mitochondria need large amounts of ATP production.
• Porins are characteristic of the outer membrane of mitochondria, mediate translocation of ions and metabolites into mitochondria, and are characteristic of prokaryotes such as bacteria.
• Cardiolipin is primarily found in the inner mitochondrial membrane, helps regulate or is important for the electron transport chain enzymes, ATP synthesis, and signaling activities.
• ATP synthetase is in the inner mitochondrial membrane in the F1-particles on the cristae and is required for ATP synthesis.

Endoplasmic Reticulum

• The smooth endoplasmic reticulum becomes more abundant in the liver cells of a patient that takes large amounts of barbiturates (sleeping tablets) and is important for the detoxification of the drug.
• The liver plays a key role in detoxification via P450 enzymes in the smooth ER.
• The smooth ER is also important for glycogen synthesis/degradation and lipid synthesis/degradation and is found in large amounts in steroid-secreting cells.
• The rough endoplasmic reticulum (rER) synthesizes proteins for export, including secretion, membrane, and lysosomal proteins.
• Synthesis of all proteins in the cell is initialized on free ribosomes and polysomes in the cytoplasm.
• In the case of proteins for export, the polysomes attach to rough endoplasmic reticulum by binding of signal recognition particle to signal recognition particle receptor on the rER.
• The nascent polypeptide will enter into the rER by a channel called translocon.

COPII Function

• Blocking COPII (coatomer II) function will affect anterograde transport of proteins from the RER to the Golgi complex.
• COPI is required for the retrograde transport from the Golgi Apparatus back to the rER; COPI and COPII are coating proteins on coated vesicles.
• Clathrin is involved in receptor-mediated endocytosis.

Golgi Apparatus

• The major function of the Golgi apparatus is packaging and modification of proteins for export.
• Proteins for export are made on the rER, destined to be secreted as secretory products, destined to be plasma membrane proteins, or destined to be packaged as lysosomal and endosomal proteins.
• These proteins are modified by glycosylation and sulfation and packaged in the Golgi.

Endosomes and Lysosomes

• A knock-out mouse model missing mannose-6-phosphate receptor proteins will majorly affect the sorting and trafficking (targeting) of proteins destined for the endosome and lysosome.
• The early endosome is the site of initial sorting of materials brought into the cell by endocytosis and separation of them from vesicle receptor molecules.
• The fusion of the lysosomal vesicle with the late endosome allows for the breakdown of exogenous molecules, such as molecules brought in by pinocytosis or receptor-mediated endocytosis (heterophagy), or old cellular organelles (autophagy).

Zellweger Syndrome

• Zellweger syndrome (ZS) is a genetic disease resulting from defects in the biogenesis of peroxisomes, which play a key role in beta-oxidation of long-chain fatty acids and the detoxification of ethanol.

Cellular Structures

• Microfilaments consist of globular actin molecules linked into a double-stranded helix.
• Microfilaments form the core structures of microvilli and stereocilia, including stereocilia on ear hair cells.
• They also play a key role in types of motility through polymerization/depolymerization processes or by binding to other motor proteins such as myosin.
• A tumor section that stains positive for glial fibrillary acidic protein most likely originated from astrocytes (or any of the CNS glial cells).

Associated Molecules

• Glial fibrillary acidic protein is associated with astrocytes and glial cells.
• Keratin is of epithelial cell origin.
• Desmin is associated with muscle.
• Vimentin is associated with cells of mesenchymal origin.
• Neurofilaments are associated with neurons.
• Lamin is like an inner coat on the inner nuclear membrane.
• Lamin mutations are associated with early aging and some dystrophies.
• A drug that inhibits the motility and locomotion of neuronally-derived cancer cells affects actin.
• Actin is the molecule most typically associated with the movement of whole cells.

Cytomotor Proteins

• Fast axonal transport of vesicles towards the axonal terminal from the neuronal soma can be blocked by the addition of colchicine.
• Kinesin is the cytomotor protein likely involved in this transport.
• Kinesins are cytomotor proteins generally involved in anterograde transport along microtubules (from nucleus toward the plasma membrane).
• Dyneins are cytomotor proteins involved in retrograde transport along microtubules (from plasma membrane towards the nucleus).

Proteasome Function

• The proteasome's function is the proteolysis of cytoplasmic ubiquitin-tagged proteins.

Cilia Defects

• A defect in cilia is frequently associated with chronic respiratory infections, situs inversus, and male infertility.
• Cilia feature a 9 + 2 arrangement of microtubules

Structures On Intestinal Enterocytes

• Microvilli are present in large numbers on the surface of intestinal enterocytes, increasing their surface area for nutrient absorption.

Epithelial Cell Junctions

• Gap junctions provide electrical and metabolic coupling, allowing fluorescent dye attached to a peptide less than 2 nm in diameter to pass between cells.
• The protein claudin can be found in zonula occludens.
• The zonula occludens acts as a permeability barrier at the luminal apical surface of epithelial cells, blocking the diffusion of larger molecules between the cells.

Alport's Disease

• Alport's disease involves a mutation in a gene for a major protein found in the lamina densa region of the basement membrane.
• Collagen type IV is found in large amounts in the lamina densa region of the basal lamina.

Plasma Membrane

• Abundant basal infoldings of the plasma membrane in close proximity to numerous elongated mitochondria are characteristic of cells involved in active ion transport.
• Epithelium where all cells touch the basal lamina, but not all reach the apical or luminal surface, with stereocilia on their surface, is classified as pseudostratified columnar epithelium with stereocilia.
• Transitional epithelium (urothelium) lines the ureter and bladder of the urinary tract.
• Stratified squamous epithelium provides the greatest degree of protection against abrasion and friction in the body.

Simple vs Stratified Epithelial

• Simple epithelia are generally involved more in absorption, secretion, or movement of substances along their surface.
• Stratified epithelia are more often involved in protective functions such as protecting against dehydration, friction, or abrasion.
• Note that these epithelial types and the organs where they are found are classical examples to know.

Modes Of Secretion

• In the mammary gland, the product (milk fat globule) and a portion of the surrounding plasma membrane of the cell are released into the lumen of the duct.
• This is best described as apocrine secretion.
• A compound exocrine-secreting gland is always characterized by a branched duct system.
• Metaplasia is a process in which one type of epithelium changes reversibly to a different type because of chronic stress factors in its environment, such as smoke particles or chronic infection.