Category: Lab Notes

Metabolic disorders occur when biochemical pathways responsible for processing nutrients and generating energy become disrupted. These conditions may involve defects in glycolysis, fatty‑acid oxidation, mitochondrial function or endocrine signalling. Their consequences range from mild metabolic imbalance to severe systemic disease, affecting growth, neurological function and long‑term health.

Nutrient deprivation creates metabolic stress that suppresses mTOR, activates AMPK and induces autophagy. These pathways help cells conserve energy, recycle intracellular components and maintain homeostasis during starvation or limited nutrient availability. Prolonged nutrient deprivation influences gene expression, stress signalling and survival mechanisms across diverse cell types.

Hydrolytic enzymes catalyse the breakdown of macromolecules by adding water to chemical bonds. Found in lysosomes, digestive organs and immune cells, they degrade proteins, nucleic acids, lipids and carbohydrates. Their activity maintains cellular homeostasis, supports nutrient acquisition and protects against pathogens, while dysregulation contributes to metabolic and degenerative diseases.

Autophagosomes are double‑membrane vesicles that capture cytoplasmic material for lysosomal degradation. Formed from expanding phagophores and marked by LC3 lipidation, autophagosomes are central to autophagy, enabling cells to recycle nutrients, remove damaged organelles and maintain homeostasis. Their dysfunction contributes to neurodegenerative, metabolic and cancerous diseases.

Limb development is the process that builds vertebrate appendages through coordinated signalling, patterning, and morphogenesis. This article explains the roles of the AER, ZPA, and key molecular pathways.

Vertebral column formation is the process that builds the axial skeleton from somites. This article explains resegmentation, sclerotome differentiation, Hox patterning, and endochondral ossification.

Cdh1 is a major activator of the APC/C complex, responsible for mitotic exit, G1 maintenance and replication licensing. By degrading Cyclin B, Aurora A, Plk1 and Geminin, Cdh1 prevents premature S‑phase entry and maintains genomic stability. Its dysregulation contributes to replication stress, chromosomal instability and cancer development.

Endoreduplication is a specialised cell‑cycle variant in which cells repeatedly replicate their DNA without mitosis, producing polyploid nuclei. Driven by Cyclin E, CDK2, APC/C–Cdh1 and E2F7/8, this process enhances cell size, biosynthetic capacity and stress tolerance in plants, insects and mammalian tissues.

Asymmetric cell division produces daughter cells with different sizes, molecular compositions or developmental fates. Guided by polarity complexes, spindle orientation and unequal segregation of determinants such as Numb and Prospero, this process maintains stem‑cell pools, drives tissue development and prevents uncontrolled proliferation. Its disruption contributes to degenerative disease and cancer.

Cell‑cycle checkpoints act as surveillance systems that monitor DNA integrity, replication completeness and spindle attachment. The G1, G2 and spindle checkpoints prevent cells with damage or misaligned chromosomes from dividing, ensuring accurate genome transmission and protecting against genomic instability and cancer.

Cell‑cycle genes coordinate the progression of G1, S, G2, and M phases through cyclins, CDKs, checkpoints, and replication machinery. Their precise regulation ensures accurate DNA duplication, faithful chromosome segregation, and controlled cell proliferation. Understanding these genes is essential for explaining genomic stability and the molecular basis of cancer.

The G1/S transition is the critical checkpoint where a cell commits to DNA replication. It integrates cyclin–CDK activity, Rb phosphorylation, and E2F activation to ensure accurate S‑phase entry. Proper regulation protects genomic stability and prevents uncontrolled proliferation.

Meroblastic cleavage is a partial embryonic division restricted to the blastodisc of yolk‑rich eggs. It produces a blastoderm that sits atop the yolk and establishes early developmental polarity.

Holoblastic cleavage is a complete embryonic division that produces progressively smaller blastomeres. It occurs in embryos with low to moderate yolk and establishes the foundation for blastula formation and early developmental patterning.

Embryonic cleavage cycles transform a single‑celled zygote into a multicellular embryo through rapid, synchronous divisions. This article explains cleavage patterns, maternal control, and the mid‑blastula transition.