Question

Binding of oxygen shifts hemoglobin into which state?

	a.	D state
	b.	P state
	c.	T state
	d.	R state

When referring to the ATP-using "head" subunit, which muscle protein is this in reference to?

	a.	Tropomyosin
	b.	Myosin
	c.	Troponin
	d.	Actin
	e.	None of the above

Answer 1

R or relaxed state - Hemoglobin undergoes in R or relaxed state when oxygen bins to it and becomes stable.

T or tensed state -  Hemoglobin undergoes inT or tensed state in absence of oxygen and becomes stable.

Option D - R state is right answer.

Myosin has (thick) filament having two parts, a globular head ( heavy meromyosin or HMM) and a tail (light
meromyosin or LMM).

Actin is thin filament made up of two F- actin wound helically to each other. Each‘F - actin is a polymer of monomeric ‘G’ (Globular) actins.

Tropomyosin - Two filaments of another protein, tropomyosin also run close to the ‘F’ actins throughout its length.
Troponin - Troponin is distributed at regular intervals on the tropomyosin. In the resting state a subunit of troponin masks the active binding sites for myosin on the actin filaments.
Using energy from ATP hydrolysis, the myosin head binds to the exposed active sites on actin to form a cross bridge.