<span>A photon of UV light causes mutations in the double-stranded DNA via a photochemical reaction. The product of such photochemical reaction in DNA is a cyclobutane pyrimidine dimer. Dimers may be repaired by mechanisms of photoreactivation or nucleotide excision repair (NER), but if the repair doesn’t occur dimers are mutagenic.
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UV light is absorbed by a double bond in pyrimidine bases (thymine and cytosine in DNA). The bond is opened and UV-modified base can now react with neighbouring molecules. If neighbouring molecule is another pyrimidine base, the UV-modified base forms direct covalent bonds with it. A cyclic ring (cyclobutane), not normally found in DNA, is formed (links the two pyrimidines). Next step is forming a single bond between two carbon atoms on the rings.The product of this reaction is a 6-4 molecule pyrimidine-pyrimidone which is more mutagenic than cyclobutane pyrimidine dimers.</span>
<span>C.) Development occurs as individuals progress through stages.</span>
The phase in the cardiac cycle when the mitral valve is closed and the aortic valve is open is the systolic ejection phase (Option D). It is the second phase of the ventricular systole.
The cardiac cycle is a sequence of contraction and relaxation of the atria and ventricles to pump blood throughout the body.
This cycle (cardiac cycle) can be divided into two major periods: diastole and systole.
The diastole is when the heart relaxes and refills with blood, while the systole is when the heart contracts and pumps blood.
The systolic ejection phase is the second phase of the ventricular systole where blood is pumped from the ventricle.
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skeletal system is a bone that we are having in all human bodies like skeletal in our head it protects our brain. like that the skeletal system defines
Neurotransmitters can affect postsynaptic cells by causing molecular changes in the cells.
The term "chemical messengers of the body" is frequently used to describe neurotransmitters. The nervous system uses these molecules to send information between neurons or from neurons to muscles. A neurotransmitter influences a neuron in one of three ways: excitatory, inhibitory or modulatory.
When a stimulus is potent enough, the chemical messenger neurotransmitter is transferred into the nerve impulse. If it is powerful enough, it will reach the postsynaptic cell and affect the structure of the neuron. And when signal transduction happens, everything mentioned above is completed.
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