Chapter Two: The Nucleus

Nucleus

Contains DNA and directs the cell’s activities by providing the instructions for protein synthesis. Contains the nuclear envelope, nucleolus, chromatin, and chromosomes

Multinucleate

Large cells that require multiple nuclei

Anucleate

Cells that have no nucleus

Nuclear Envelope

Surrounds the nucleus and consists of two parallel membranes separated by a fluid-filled space

Outer membrane of the Nuclear Envelope

Continuous with the right ER and has ribosomes on its external face

Inner membrane of the Nuclear Envelope

Lined by protein filaments, the nuclear lamina, which maintains the shape of the nucleus

Nuclear Pores

Penetrate the fused regions of the nuclear envelope layers. They allow large molecules to pass in and out of the nucleus

Nucleoplasm

A jellylike fluid enclosed by the nuclear envelope in which chromatin and nucleolus are suspended

Nucleolus

A dark-staining body in the cell nucleus. Contains parts of several different chromosomes and serves as the cell’s “ribosome-producing machine”. Has genes that code for ribosomal RNA and is where subnits of ribosomes are assembled

Nucleotides

Subunits that compose the double helix of DNA. Has distinct bases called thymine, adenine, cytosine, and guanine

Chromatin

Strands in the cell nucleus that consist of DNA and histone proteins

Nucleosome

Each cluster of DNA and histones

Extended chromatin

Nucleosomes have the appearance of beads on a string. Active region of DNA.

Condensed Chromatin

Coiling of the nucleosomes to form a tight helical fiber. Inactive region of DNA.

Chromosome

Contains a single, very large molecule of DNA. Help keep the delicate chromatin strands from tangling and breaking as the chromosomes move.