Cell Biology: What Makes Molecules Hydrophobic & Hydrophilic?

[uio]

Hi

I'm currently studying cell biology, and I'm reading about the hydrophobic parts of the plasma membrane of the animal cell. But I'm wondering, what exactly makes a molecule hydrophilic or hydrophobic? What is the chemistry behind it, and how can I tell which molecules are which? I know that lipids and certain proteins are hydrophobic, but I can't understand why.

Thanks.

 

[Gokul43201]

When a molecule (or a part of a long molecule) is polar (i.e., it has a significant dipole moment), it can attract a water molecule through a dipole-dipole interaction. That is usually what makes it hydrophilic.