Describe the structure of a DNA molecule. What molecules form the “backbone’? What molecules form the ‘steps’?

What molecules form the "backbone'?. A sugar-phosphate backbone (alternating grey-dark grey) joins together nucleotides in a DNA sequence. The sugar-phosphate backbone forms the structural framework of nucleic acids, including DNA and RNA. This backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.

What molecules form the ‘steps’?. The four nitrogen bases that are found in DNA are Adenine, cytosine, guanine, and thymine. The two molecules that make up the sides of the ladder or the side portion of a DNA molecule are Sugars and phosphates. The molecules that meet across the middle, forming the steps of the “ladder'” are known as Nitrogen bases.

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

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