G protein-coupled receptors and receptor tyrosine kinases are both largely conse
ID: 267257 • Letter: G
Question
G protein-coupled receptors and receptor tyrosine kinases are both largely conserved mechanisms of cell communication. What scientific question is valid to ask when investigating the similarities between these two receptors to understand common mechanisms from which the two may have evolved?
How did phosphorylation first begin as a way of modulating protein activity?
How early in evolution did cells start using ATP-to-ADP conversion for energy to transduce signals?
How has simple diffusion across a membrane remained a signal transduction mechanism?
What factors lead to the ability to use cell energy for dimerization?
Explanation / Answer
Answer1:
Points to know about RTK and GPCR:
Signal transduction and endocytosis are common to RTK and G-Protein coupled receptors.
Signalling from both occurs in endocytosis derived intracellular organelles.
Both span membranes, bind to hormone and are present in eukaryotes.
Scientific question:
What evolutionary similarities can be suggested based on receptor internalization and signal transduction from intracellular organelles in RTK and GPCR following a hormone interaction?
Answer2:
Protein phosphorylation is a reversible reaction and occurs as a post-translational modification, which employs a protein kinase to add phosphate or protein phosphatase to remove phosphate group to/from amino acids. The earliest reported phosphorylated protein was in 1906, a phosphorylated vitellin, but the discovery of phosphorylation activity as a regulatory mechanism happened only in 1955. The work involved activation of glycogen phosphorylase b to glycogen phosphorylase a, which required a protein kinase and ATP.
Answer3:
An exact time period or year cannot be suggested for this question. However, it is believed that as mitochondria formed by nucleus engulfing an aerobic prebiotic organism, oxygen derived organelle shaped. Mitochondria hold in the inner layers mechanism to generate ATP. It has been argued that mitochondrial granules have phosphates and they move towards the inner membrane which is the site of ATP generation. Reversibility of this reaction would have needed a mechanism too. Phosphotransferase system involving phosphoenol pyruvate dependent dihydroxyacetone kinase is another enzyme traced back to have evolved from an ATP-dependent ancestor. This relation also explains the connectivity of phosphate groups to ATP. When a phosphate is removed by breaking the phosphoanhydride bond, ATP is converted to ADP.
Answer 4:
Simple diffusion is the event where molecules pass through the cell membrane, from higher concentration to lower concentration, without the need of any aide/intermediary. The only driving force is diffusion. This is triggered by the uneven concentration of substances on the two sides of the membrane. When cytoplasmic water content drops, external water starts flowing in.
But the process does not involve any receptors, no physical or chemical signals are actually transmitted, nor does any conformational changes take place. Considering the lack of any receptor involvement in active diffusion, it is hard to consider it as a signal transduction mechanism.
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