4.4 The Cell Nucleus Section 4.4

Learning Objectives Compare & contrast the structure of prokaryotic cells & eukaryotic cells Relate the structure of the nucleus to its function as the control center of the eukaryotic cell Identify the parts that make up the structure of the nucleus & describe their function Identify organelles produced in the nucleus & their function

Eukaryotic Cells All start life with a nucleus Nucleus = double membrane organelle that contains a eukaryotic cell’s DNA Nucleoplasm = jellylike area inside nucleus Have organelles that are membrane-bound Made of membrane layers Cytosol = the fluid part of the cytoplasm Cytoplasm is technically the cytosol and the organelles of the cell (except for the nucleus

DNA In Eukaryotic Cells DNA is in long threadlike (strings) pieces Not circular like prokaryotic cells have Has genes Genes = areas of DNA that contains instructions for making proteins and RNA molecules

Chromatin = DNA wrapped around histones Histones = proteins that DNA wraps around Chromatin looks like a messy area of string in a microscope Chromosome = coiled DNA pieces visible when a cell is dividing Look like Xs

Nucleus Stores the DNA Is created by the nuclear envelope Nuclear envelope = a double membrane that separates the nucleoplasm from the cytoplasm Nuclear pores = holes or openings in the nuclear envelope Controls what large molecules enter and leave the nucleus

Nucleolus Nucleolus = dense area inside the nucleus where RNA & ribosomes are made Cells can have one or more nucleoli

Ribosomes Made in the nucleolus Made up of a large subunit & a small subunit Can be found in free-floating in the cytoplasm (free ribosomes) or attached to ER membranes (bound ribosomes) Make proteins for the cell Cells can change how many ribosomes they have in order to meet its metabolic needs