A theory in science is a remark on what happened
Answer:
The correct answer is a. Helicase unwinds DNA
Explanation:
DNA replication is a process in which DNA make it's own copy. There are several enzymes and factors which access the DNA replication process like helicase, primase, SSB protein, DNA polymerase etc.
The first step in DNA replication is the unwinding of double stranded DNA which is accomplished by an enzyme called Helicase. Helicase opens up the double stranded DNA at replication fork by breaking the hydrogen bond between the nucleotides of complementary strands.
This provides a single stranded template for DNA polymerase to form a new complementary strand. In <em>E. coli </em>Dna B is the primary helicase and in humans the primary helicase is MCM( minichromosome maintenance protein complex).
Human skin pigmentation is the product of two clines produced by natural selection to adjust levels of constitutive pigmentation to levels of UV radiation (UVR). One cline was generated by high UVR near the equator and led to the evolution of dark, photoprotective, eumelanin-rich pigmentation. The other was produced by the requirement for UVB photons to sustain cutaneous photosynthesis of vitamin D3 in low-UVB environments, and resulted in the evolution of depigmented skin. As hominins dispersed outside of the tropics, they experienced different intensities and seasonal mixtures of UVA and UVB. Extreme UVA throughout the year and two equinoctial peaks of UVB prevail within the tropics. Under these conditions, the primary selective pressure was to protect folate by maintaining dark pigmentation. Photolysis of folate and its main serum form of 5-methylhydrofolate is caused by UVR and by reactive oxygen species generated by UVA. Competition for folate between the needs for cell division, DNA repair, and melanogenesis is severe under stressful, high-UVR conditions and is exacerbated by dietary insufficiency. Outside of tropical latitudes, UVB levels are generally low and peak only once during the year. The populations exhibiting maximally depigmented skin are those inhabiting environments with the lowest annual and summer peak levels of UVB. Development of facultative pigmentation (tanning) was important to populations settling between roughly 23° and 46° , where levels of UVB varied strongly according to season. Depigmented and tannable skin evolved numerous times in hominin evolution via independent genetic pathways under positive selection.
<span>folatevitamin DmelanintanningUVB</span>
Answer: The Big Bang Theory is the leading explanation about how the universe began. At its simplest, it says the universe as we know it started with a small singularity, then inflated over the next 13.8 billion years to the cosmos that we know today.
Because current instruments don't allow astronomers to peer back at the universe's birth, much of what we understand about the Big Bang Theory comes from mathematical formulas and models. Astronomers can, however, see the "echo" of the expansion through a phenomenon known as the cosmic microwave background.
Explanation:
I believe st marks because there<span> are no deltas or rivers that would intercept it.</span>
