Which molecules do not normally cross the nuclear membrane?
B: Nucleotide triphosphates
The correct answer is option C.
The molecules that do not normally cross the nuclear membrane is DNA.
DNA is the genetic material of the cell which resides in the nucleus in a eukaryotic cell. While the prokaryotes do not have a nucleus; therefore, their DNA is found in the nucleoid.
The nuclear envelope is also called the nuclear membrane. It is made up of two lipid bilayer membranes that surround the nucleus in eukaryotic cells. It encases the genetic material.
The two lipid bilayer membranes include
- an inner nuclear membrane, and
- An outer nuclear membrane.
The nuclear envelope contains many nuclear pores through which the flow of material occurs between the nucleus and the cytosol. Since the nuclear envelope is composed of two phospholipid bilayers, therefore, only small and nonpolar molecules can easily cross the membrane while other large molecules can’t pass it easily.
Large molecules can pass the nuclear envelope at specific places, which are called nuclear pore complexes. Smaller particles can diffuse through the nuclear pore complex while larger particles are transported. The nuclear pores can open and close to allow or restrict the passage of particles.
Substances such as solutes, polypeptides, and mRNA can move in and out of the cell through these pores, which are enclosed by proteins. These proteins molecules can create complexes that manage the movement of these substances. As DNA is hydrophilic in nature, therefore, it can’t pass through the cell membrane, which is made of a lipid bilayer.
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