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#animal cells

23 public questions tagged with this topic.

Animal Tissue Culture 2

Cryopreservation of animal cells commonly uses:

Cryopreservation of mammalian cells routinely employs dimethyl sulfoxide as penetrating cryoprotectant at 5-10% concentration. DMSO is small amphipathic molecule freely crossing lipid bilayer, replacing intracellular water and disrupting hydrogen bonding network required for ice lattice formation. During controlled slow cooling at -1°C per minute achieved using isopropanol containers like Mr. Frosty or programmable freezers, extracellular ice forms first creating osmotic gradient that draws water out of cells dehydrating them. DMSO lowers freezing point, promotes vitrification where residual intracellular water transitions to amorphous glass rather than sharp damaging crystals that would shear membranes, organelles and chromosomes. DMSO also stabilizes proteins through preferential exclusion. At ambient temperature DMSO exhibits cytotoxicity and can trigger differentiation of hematopoietic lines, so after thawing rapid dilution in large volume medium reduces concentration below 1%. Glycerol penetrates slower favoring insect and embryonic stem cells, while ethanol and formaldehyde are lethal and unsuitable. DMSO thus became standard in ATCC and cell bank protocols.

Ref: Freshney Ch.22 Cryopreservation DMSO prevents intracellular ice; Mazur Science 1984 kinetics of water loss and vitrification by DMSO.

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Animal Tissue Culture 2

Which biosafety level is required for routine animal cell culture?

Routine animal cell culture including work with established human lines like HeLa, HEK293, and CHO must be performed at Biosafety Level 2 according to international guidelines. Even well-characterized lines may harbor endogenous retroviruses, latent herpesviruses such as Epstein-Barr virus, human cytomegalovirus, or adventitious agents introduced via bovine serum or mycoplasma contamination. Furthermore, cell line cross-contamination, as historically documented for HeLa overgrowth, poses risks. BSL-2 provides appropriate containment without impairing workflow: access restricted to trained personnel, use of Class II BSC for trypsinization, media changes, pipetting that generates aerosols, mandatory PPE including gloves and lab gowns, biosafety training records, biohazard labels on incubators, and decontamination of liquid waste with bleach or autoclaving. BSL-1 is limited to defined non-pathogenic organisms such as E. coli K-12, while BSL-3 and BSL-4 are reserved for agents causing serious airborne disease like Mycobacterium tuberculosis or Ebola. Therefore BSL-2 represents standard for mammalian cell culture. Certification of cabinets annually and training logs documented in laboratory biosafety manual reinforce adherence. This knowledge strengthens laboratory safety, protocol reproducibility, and regulatory compliance critical for translational research and clinical applications, ensuring reliable data and workforce protection.

Ref: NIH Guidelines for Research Involving Recombinant DNA, Appendix G-II-BSL2; ATCC BSL-2 for animal cell lines. https://www.cdc.gov/labs/BMBL.html

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Animal Tissue Culture 1

Which gas concentration is optimal for most animal cell cultures?

Carbon dioxide role in culture extends beyond waste gas to essential physicochemical regulator and metabolic substrate. Dissolution follows Henry's law concentration equals partial pressure times solubility coefficient 0.03 mM per mmHg at 37°C, so at 5 percent CO2 incubator partial pressure about 38 mmHg dissolved CO2 approximately 1.2 mM. Hydration reaction CO2 plus water forms carbonic acid catalyzed by zinc metalloenzyme carbonic anhydrase II intracellularly with turnover 10^6 per second, spontaneous dissociation to bicarbonate plus proton. Ratio bicarbonate to dissolved CO2 determines pH via Henderson-Hasselbalch. Lowering gas phase to 1 percent raises pH to 8.0 precipitating calcium phosphate as hydroxyapatite needles toxic, increasing intracellular pH impairing endosomal trafficking that requires acidic pH 5 to 6 for ligand release. Raising to 21 percent acidifies to 6.9 causing caspase activation. Empirically 5 percent CO2 approximates alveolar air gas tension matching mammals where arterial pCO2 40 mmHg, supporting physiological partial oxygen 140 mmHg when combined with humidity reducing oxygen fraction.

Ref: Freshney CO2 5% optimal bicarbonate Henry's law dissolved CO2; Lodish MBoC pyrimidine carbamoyl phosphate CO2 metabolic substrate.

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Basics of Cell Biology

What is the role of centrioles in animal cells?

Centrioles are cylindrical non-membranous organelles formed of nine triplet microtubule blades arranged radially around central symmetry, each triplet composed of A, B, C complete and partial tubules, approximate dimensions 200 nanometer diameter and 500 nanometer length, embedded in pericentriolar material comprising pericentrin, CEP192, and gamma-tubulin ring complexes that nucleate microtubule asters. Duplication begins at G1 to S transition via master kinase PLK4 recruitment to mother centriole, SAS-6 cartwheel assembly providing nine-fold symmetry template, STIL and CPAP elongating procentriole in orthogonal orientation. During late G2 and early mitosis, centrosomes separate driven by kinesin-5 Eg5 and dynein, forming bipolar spindle poles that nucleate dynamic microtubules capturing kinetochores via Ndc80 complex attachment, ensuring accurate segregation of sister chromatids to daughter cells preventing aneuploidy and chromosomal instability. In interphase, mother centriole templates basal body anchoring primary cilium axoneme containing 9+0 microtubules for Hedgehog signaling and motile cilia 9+2 for mucus clearance. They do not produce proteins, lipids, or ATP; synthesis belongs to ribosomes, ER, and mitochondria respectively.

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17: Centrosomes, Centrioles, and Spindle Formation.

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Membrane Transportation

Which ion has the highest intracellular concentration in most animal cells?

Ionic composition asymmetry between cytosol and extracellular fluid is actively established but reflects passive equilibrium for some ions. Primary determinant is Na+/K+ ATPase, P-type pump undergoing E1 to E2 transitions phosphorylating Asp369 in DKTGT motif, exporting three sodium and importing two potassium per ATP hydrolyzed. This creates extracellular sodium about 145 millimolar versus intracellular about 12 millimolar, and intracellular potassium about 140 millimolar versus extracellular 4 millimolar. Leak potassium channels dominated at rest maintain membrane potential near minus 90 millivolts close to EK. Chloride distribution about 110 millimolar outside versus 4 to 15 millimolar inside largely follows passive Donnan equilibrium set by impermeable anionic proteins and is modulated by K-Cl cotransporters. Calcium kept extremely low at 100 nanomolar cytosolic compared with 1 to 2 millimolar outside by SERCA sequestering into endoplasmic reticulum and PMCA extruding. Comparing abundant monovalents, potassium concentration highest inside cells, essential for enzyme activation, protein synthesis and volume regulation.

Ref: Lodish et al., Molecular Cell Biology, Section: Intracellular Ion Composition - Na+/K+ ATPase and K+ Dominance.

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Membrane Transportation

Which ion has the highest intracellular concentration in most animal cells?

Intracellular ion composition is highly asymmetric relative to extracellular fluid actively maintained using ATP to support excitability volume and enzyme function. In most mammalian cells at rest dominant intracellular cation is potassium one thirty to one forty millimolar inside versus four to five outside ten to thirtyfold gradient while sodium inverse ten to fifteen inside versus one forty five outside chloride four to twenty inside versus one ten outside bicarbonate ten inside versus twenty five outside free calcium extremely low one hundred nanomolar inside versus one point two millimolar outside twelve thousandfold plus magnesium half millimolar free. Asymmetry established primarily by continuous Na+/K+ ATPase exporting three sodium importing two potassium generating chemical and electrical gradients plus NKCC importing K+, chloride and sodium channels like Kir Kir4.1 leaking potassium to set resting potential close to potassium Nernst minus ninety millivolts. High potassium required for sixty S ribosomal peptidyl transferase pyruvate kinase maintaining negative potential counterbalancing anionic proteins buffering pH via K+/H+ exchange preventing apoptosis. Reduction triggers caspase activation and cell shrinkage during apoptosis.

Ref: Lodish et al., Molecular Cell Biology, 8th ed., Chapter 11: Intracellular Ion Composition – High K+.

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Cell Division

The site of the division plane during cytokinesis in animal cells is determined by:

Cytokinesis in animal cells determines placement of furrow such that daughter cells inherit single genome copy and appropriate cytoplasmic volume. Experimental embryology demonstrated furrow forms where central spindle contacts cortex. Mechanistically, anaphase central spindle assembled from overlapping antiparallel interpolar microtubules bundled by PRC1 and centralspindlin component KIF4 recruits centralspindlin heterotetramer consisting of kinesin MKLP1 and RhoGAP MgcRacGAP. Centralspindlin clusters ECT2 RhoGEF, generating zone of active RhoA-GTP precisely at equatorial membrane. RhoA-GTP activates formin mDia1 to polymerize linear actin filaments and ROCK kinase phosphorylating myosin regulatory light chain serine 19 promoting bipolar myosin II assembly in antiparallel bundles contracting ring similarly to muscle. Astral microtubules reaching polar cortex deliver inhibitory cues through Aurora A phosphorylating ECT2 and RacGEF Trio suppressing ectopic contractility at poles. Net result furrow ingresses perpendicular to central spindle axis between chromosome masses. Manipulation shifting spindle relocates furrow accordingly, proving spindle dominance over chromosomes for division site. This circuitry is highly conserved across eukaryotes, integrating growth factor signals, DNA damage surveillance, and developmental cues, and its disruption frequently underlies oncogenesis, providing targets for checkpoint inhibitors and cancer therapeutics.

Ref: Fededa & Gerlich, Current Biology 2012, Division Plane Specification. Alberts 7th ed., Chapter 17.

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Cell Division

Which protein is essential for cytokinesis in animal cells?

Animal cytokinesis culminates mitosis by physically partitioning cytoplasm through contractile ring machinery. Following chromosome segregation, central spindle composed of overlapping antiparallel microtubules bundled by PRC1 and motor KIF4 recruits centralspindlin complex containing kinesin MKLP1 and RhoGAP MgcRacGAP which tethers ECT2 guanine nucleotide exchange factor to equatorial cortex, generating localized accumulation of active RhoA-GTP. RhoA stimulates formin mDia1 to nucleate linear actin filaments and activates ROCK kinase to phosphorylate myosin regulatory light chain at serine 19, promoting assembly of bipolar myosin II filaments into antiparallel array that slides on actin similarly to muscle contraction, decreasing ring diameter. Scaffold proteins anillin, containing actin, myosin, and membrane lipid binding domains, and septins stabilize ring position. Ingression continues until midbody forms with bundled microtubules. ESCRT-III complex comprising CHMP4B, CHMP2A, and VPS4 ATPase executes final membrane abscission. Inhibitors latrunculin or blebbistatin block division producing multinucleated cells, proving actin-myosin dependence. This circuitry is highly conserved across eukaryotes, integrating growth factor signals, DNA damage surveillance, and developmental cues, and its disruption frequently underlies oncogenesis, providing targets for checkpoint inhibitors and cancer therapeutics.

Ref: Glotzer, Science 2005, Cytokinesis Mechanisms. Alberts 7th ed., Chapter 17, Contractile Ring.

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