Skip to content
Login Register

#phosphorylation

33 public questions tagged with this topic.

BOTANY

Which type of phosphorylation occurs in the Electron Transport Chain?

Oxidative phosphorylation occurs in the Electron Transport Chain, where ATP is produced using a proton gradient. This follows from latest NCERT 2026-27 principle explaining the concept clearly for NEET students in simple steps as per rationalized syllabus.

Ref: NCERT Biology Textbook - Latest Edition for Academic Session 2026-27 (Botany section, Rationalized Textbook for Class XI and XII), Chapter: Biology - Botany portion (Latest NCERT Textbooks for Academic Session 2026-27 -

View Details
Paracrine Factor

Which enzyme phosphorylates β-catenin, marking it for degradation in the absence of Wnt signaling?

Beta-catenin degradation circuit includes scaffold proteins regulating turnover tightly and rapidly. In absence of Wnt, cytosolic destruction complex assembles Axin dimer, APC tumor suppressor, CK1alpha, GSK3beta. CK1alpha primes Ser45 phosphorylation, then Glycogen synthase kinase 3 phosphorylates Ser33, Ser37, Thr41 creating phosphodegron recognized by beta-TrCP SCF E3 ubiquitin ligase leading to polyubiquitination and proteasomal degradation in proteasome. Protein kinase A phosphorylates other sites increasing activity, JAK and MAP kinase not primary degradative kinases. This constitutive t

Ref: Stamos & Weis, Annual Review Biochemistry 2013: Destruction complex phosphorylates beta-catenin via GSK3 and CK1.

View Details
Membrane Transportation

The regulatory (R) domain of CFTR is phosphorylated by:

Regulatory R domain of CFTR spanning approximately residues 590 to 850 is an intrinsically disordered segment bridging NBD1 and TMD2 containing numerous consensus PKA and PKC phosphorylation sites. Phosphorylation is central to activation. Elevated intracellular cAMP activates protein kinase A which phosphorylates serines including Ser660, Ser737, Ser795, Ser813 and Ser768, neutralizing inhibitory interactions between R domain and NBDs and between NBD1-NBD2 interface. This conformational unblocking permits ATP binding to NBDs, dimer formation, and pore opening. Protein kinase C, Ca2+/calmoduli

Ref: Hwang & Sheppard, Trends Pharmacol Sci 2009, CFTR R domain regulation; Riordan, Annu Rev Biochem 2008.

View Details
Cytoskeleton

How does phosphorylation affect intermediate filaments?

Intermediate filaments are apolar polymers of tetrameric coiled-coil dimers that lack intrinsic nucleotide turnover, so dynamic regulation relies on post-translational modification. Phosphorylation within the N-terminal head domain by mitotic kinases such as Cdk1, Plk1, Aurora B, as well as PKA, PKC and MAP kinases, introduces dense negative charge that disrupts head-to-rod electrostatic interactions essential for filament elongation. The result shifts equilibrium toward soluble tetramers and monomers, enabling mitotic disassembly of vimentin networks and nuclear lamina breakdown at prometapha

Ref: Alberts Ch 16 Cytoskeleton; Lodish Ch 18; IF phosphorylation controls disassembly via head domain serine.

View Details
Protein Sorting and Trafficking

What happens if a mutation prevents phosphorylation of Mannose-6-Phosphate (M6P)?

Targeting soluble acid hydrolases to lysosomes hinges on carbohydrate tag mannose-6-phosphate discovered by fractionation. In cis-Golgi, UDP-GlcNAc:lysosomal enzyme GlcNAc-1-phosphotransferase alpha2 beta2 gamma2 recognizes structural patch including lysine residues clustered in tertiary structure on hydrolases like cathepsin B and adds GlcNAc-phosphate to terminal mannose of high-mannose N-glycans. Uncovering in TGN by NAGPA removes GlcNAc exposing M6P monoester capable of binding M6P receptors. M6P receptors divert enzymes from default secretory flow into clathrin-AP1 and GGA vesicles destin

Ref: Alberts et al., MBC: I-cell disease defective GlcNAc-phosphotransferase causes lysosomal enzyme secretion.

View Details
Protein Sorting and Trafficking

In which Golgi compartment does phosphorylation of lysosomal enzymes occur?

Soluble acid hydrolases acquire mannose-6-phosphate marker for lysosomal delivery through selective two-step modification restricted to Golgi apparatus, discovered by Kornfeld laboratory. Newly synthesized hydrolases enter ER, receive high-mannose N-glycans, fold with calnexin cycle, then travel to cis-Golgi network. There UDP-GlcNAc:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase alpha2 beta2 gamma2 hexamer encoded by GNPTAB and GNPTG recognizes conformational patch on hydrolases and transfers GlcNAc-1-phosphate to C6 hydroxyl of select mannose residues forming phosphodiester interm

Ref: Lodish et al., MCB, Chapter 14 Figure 14-21 Formation of M6P residues in cis-Golgi by phosphotransferase.

View Details
Cell Cycle Regulation

What happens if the Rb protein is mutated and cannot be phosphorylated?

Retinoblastoma protein Rb functions as central gatekeeper integrating mitogenic signaling with E2F transcription program controlling G1/S restriction point. In quiescent or early G1 cells, Rb exists in hypophosphorylated state, binding E2F1, E2F2, E2F3 through pocket domains A and B, simultaneously recruiting histone deacetylases, SWI/SNF chromatin remodelers, and Polycomb complexes to repress promoters of cyclin E, cyclin A, thymidine kinase, dihydrofolate reductase, and DNA polymerase subunits. Mitogens induce cyclin D-CDK4/6 synthesis downstream of Ras-MAPK and PI3K pathways, which initiate

Ref: Weinberg, Biology of Cancer, 2nd ed., Chapter 8: Rb Pathway. NCBI Bookshelf: Cell Cycle Control.

View Details
Cell Cycle Regulation

In normal conditions, phosphorylation of Rb by Cyclin D-CDK4 leads to:

Retinoblastoma tumor suppressor Rb forms central brake of G1 progression. Hypophosphorylated form present in quiescent G0 and early G1 binds E2F transcription factor family E2F1-3 together with DP1/2 dimer partners and recruits chromatin repressors histone deacetylase HDAC1/2, Suv39h1 H3K9 methyltransferase, BRG1/BRM SWI/SNF subunits and DNMT1 to promoters, maintaining hypoacetylated closed chromatin silencing S-phase genes. Cyclin D-CDK4/6 complexes activated by mitogens phosphorylate Rb at C-terminal residues such as Ser780 Ser795 partially weakening binding to LXCXE motif proteins and permi

Ref: Weinberg, Retinoblastoma Gene and Cell Cycle Control, Cell 1995; Giacinti & Giordano, RB Regulatory Pathway: Mechanisms of Rb Phosphorylation, Oncogene 2006.

View Details
Cell Cycle Regulation

Which kinase phosphorylates Chk1 in response to replication stress?

Replication stress exposes extended single-stranded DNA regions coated by replication protein A, forming a key signaling platform. ATR kinase, recruited via ATRIP-interacting domain to RPA-ssDNA, is the principal sensor of this structure. At stalled forks, factors TopBP1, Claspin, Timeless-Tipin and Rad9-Rad1-Hus1 clamp augment ATR activation through direct binding and allosteric stimulation. Once activated, ATR directly phosphorylates checkpoint kinase Chk1 on serine residues 317 and 345 within its C-terminal regulatory domain. This modification relieves autoinhibition, enabling Chk1 catalyti

Ref: Cimprich & Cortez, ATR role in replication checkpoint, Nat Rev Mol Cell Biol 2008; NCBI Bookshelf, Replication Stress Response.

View Details