Answer:
D. Calcium ions.
Explanation:
Here we are talking about the mechanism of muscle contraction. The most accepted theory of muscle contraction is sliding filament theory. It was given by Huxley and Huxley. During the process actin filaments slides over myosin filament by forming cross bridges. The sequence of events are as follows:
a. An action potential propagates through the motor nerve and reach the nerve endings on the muscle fiber at neuro-muscular junction.
b. Neurotransmitter called acetylcholine is released by the nerve endings.
c. Acetylcholine binds to the receptors on muscle fiber and opens the gated channels which causes flow of Na+ ions into the muscle fiber.
d. This influx of sodium ions initiates an action potential in the muscle fiber which reaches the T- tubules or transverse tubules. Here it causes the sarcoplasmic reticulum to release large amounts of calcium ion.
e. Calcium ions are responsible for initiating the attractive forces between actin and myosin filaments. Cross bridges are formed, actin slides over myosin causing the contraction of muscle.
I don’t even know how to do it!!!
Answer:
Separately in Nucleus and cytoplasm,
Simultaneously in the cytoplasm
Explanation:
In eukaryotes transcription and translation occurs separately in the nucleus and cytoplasm respectively. Transcription occurs inside the membrane bound nucleus and the mRNA transcript is transported to the cytoplasm for translation.
In prokaryotes, because prokaryotic cells lack a membrane bound nucleus, transcription and translation occurs simultaneouslyin the cytoplasm. This means that translation of mRNA begins even while the transcription of the transcript is still active.
