On February 21, 1953, Francis Crick and James Watson discovered the structure of deoxyribonucleic acid (DNA) using unacknowledged photographs and research by their colleague Rosalind Franklin. They had considered many other candidates for the structure, including single and triple strand helices before deciphering the structure. Franklin’s x-ray crystallography (image below)
would provide the missing essential clue they needed to decipher the structure. They would publish a paper that same year describing their discovery, but the significance of the discovery was largely overlooked by the general public for over a year. Today it stands as one of the most remarkable milestones in the history of science.
The word deoxyribonucleic is a compound word formed around the main root word ribose, which arrived in English in 1892 via the German word Ribose which was itself borrowed from the English word of 1880 arabinose, a sugar derived from gum arabic. The word nucleic comes from the Latin word nucleus meaning a kernel around 1700, from the Latin diminutive nucula meaning a little nut. It did not take the meaning of a central characteristic or attribute until 1762. It wasn’t applied to cellular structures for another 70 years around 1862. The -oxy- root comes from the Ancient Greek word οξυς (oxys) meaning sharp or pointed (sharing the earlier common root word that gave the Latin word acer with the same meaning and ultimately the English word acid). The de- prefix is a Latin preposition meaning down from, off or away from, used mainly in English compound words as a privative, meaning that something lacks something.
me when someone credits James Watson and Francis Crick for the discovery of the double helical structure of DNA like they didn’t steal the credit from Rosalind Franklin because they were angry that a woman was better at science than the two of them combined
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now You can not find more power.
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What is the difference between V / D 9 D?
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Other strategies will grow and restore us.
Then the formation of the damage required
that our language be different.
I beseech thee.
G-protein-coupled receptors (GPCRs) are the largest and most diverse group of membrane receptors in eukaryotes.
single polypeptide chain comprising of seven transmembrane α-helices
extracellular N-terminal domain of varying length,
intracellular C-terminal domain.
length of the extracellular N terminus and the location of the agonist binding domain determines family.
The long, third cytoplasmic loop couples to the G-protein
Usually particular receptor subtypes couple selectively with particular G-proteins
For small molecules, such as noradrenaline, the ligand-binding domain of class A receptors is buried in the cleft between the α-helical segments within the membrane. Peptide ligands bind more superficially to the extracellular loops
G protein system
GPCRs interact with G proteins in the plasma membrane when an external signaling molecule binds to a GPCR, causes a conformational change in the GPCR.
G-proteins comprise a family of membrane-resident proteins whose function is to recognise activated GPCRs and pass on the message to the effector systems that generate a cellular response.
G proteins are specialized proteins with the ability to bind the nucleotides guanosine triphosphate (GTP) and guanosine diphosphate (GDP).
The G proteins that associate with GPCRs are heterotrimeric, (alpha beta and gamma subunits)
alpha and gamma are attached to the plasma membrane by lipid anchors
Trimer in resting state
activated alpha monomer and beta/gamma dimer
Guanine nucleotides bind to the α subunit, which has enzymic activity,catalysing the conversion of GTP to GDP. The β and γ subunits remain together as a βγ complex. All three subunits are anchored to the membrane through a fatty acid chain, coupled to the G-protein through a reaction known as prenylation.
G-proteins are freely diffusible so a single pool of G-protein in a cell can interact with several different receptors and effectors
When GPCR is activated by an agonist, a conformational change causes it to acquire high affinity for αβγ (G protein)
bound GDP dissociates and is replaced with GTP, which in turn causes dissociation of the G-protein trimer, releasing α-GTP and βγ subunits - the ‘active’ forms of the G-protein
which diffuse in the membrane and can associate with various enzymes and ion channels
Signalling is terminated on hydrolysis of GTP to GDP through the GTPase activity of the α subunit.
resulting α–GDP dissociates from the effector, and reunites with βγ
Attachment of the α subunit to an effector molecule increases its GTPase activity
GTP hydrolysis is termination –> activation of the effector tends to be self-limiting
Second messenger targets for G proteins
Adenylyl cyclase (responsible for cAMP formation)
Phospholipase C (inositol phosphate and diacylglycerol (DAG) formation)
Ion channels, particularly calcium and potassium channels
Rho A/Rho kinase (system controlling the activity of many signalling pathways for cell growth and proliferation, smooth muscle contraction, etc.)
Mitogen-activated protein kinase (MAP kinase) system controlling cell functions eg division.