The nucleus consists of the nuclear envelope, nucleolus, chromatin, and nucleoplasm.

Nuclear Envelope

Structure -two unit membranes with a fluid-filled space
                -nuclear pores present
                -outer membrane may be continuous with endoplasmic
                  reticulum

Function -selectively permeable to control movement in or out
               -contains nuclear contents

Chromatin

Structure -composed of long thin strands of DNA

Function -contains instructions that control cell metabolism and heredity

Nucleolus

Structure -non-membraneous matrix of RNA (ribonucleic acid)
                 and protein

Function - instructions in DNA are copied here
               - works with ribosomes in the synthesis of protein