Answer:
Cells are sometimes referred to as "life's atoms" because there the basic units of life. All cells are surrounded by a structure called the cell membrane — which, serves as a clear boundary between the cell's internal and external environments.
Answer: Substances that are protein based cannot cross the lipid cell membrane, but can exert their effect by binding to the proteins based receptors present on the lipid bilayer.
Explanation:
Hormones such as calcitonin , Parathyroid hormone and pituatry horomones are proteins and water soluble.They cannot cross lipid bilayer but can bind to ligand binding protein receptors.
These receptors are protein macromolecules that are specific in nature for specific hormones.
After binding to the receptors, these hormone-recpetor complexes activate second messengers and regulate the downstream effects.
<span>Organisms all possess DNA as their genetic material. What differentiates them (and their DNA) is the sequence of base-pairs within the DNA. The base-pairs are actually specific sequences of nucleotides (i.e. adenine , thymine, guanine and cytosine, labelled A, T, G, and C respectively) which encode genes. In other words, the DNA in each organism is made of these bases, but their sequences differ from organism to organism.</span>
