Section 3: Eukaryotic Cell Structure
Protists, fungi, plants, and animals are eukaryotic and have a nucleus and other organelles that help them function. The nucleus is the cell’s command center and directs the activity of a cell’s organelles. It contains all of a cell’s DNA. A nuclear envelope surrounds the nucleus with thousands of pores that allow materials in and out of the nucleus. Also found in the nucleus is chromatin, which are strands of DNA. Chromosomes are condensed chromatin that contains genetic information that is passed onto offspring. The nucleolus makes ribosomes inside the nucleus, where proteins are assembled according to the DNA directions. The ribosomes use instructions from the nucleus to build proteins. The cytoplasm is the thick fluid outside of the nucleus found throughout the cell. While many prokaryotes and eukaryotes have cell walls, an animal cell does not. A cell wall is a rigid wall outside the plasma membrane that gives a cell its shape and extra support.
Certain organelles are also necessary for a cell’s assembly, transport, and storage. The endoplasmic reticulum is where lipids for the membrane are assembled along with proteins. There are two kinds of endoplasmic reticulum – smooth and rough. The Golgi apparatus is responsible for sorting and packaging proteins and materials into structures called vesicles. The vesicles ship them out, ensuring they reach the right destination. The vacuole is a saclike structure that stores water, food, and enzymes. A single, large vacuole is found in plant cells, increasing their ability to support heavy structures like leaves. Lysosomes remove waste using digestive enzymes. The mitochondria are often called the powerhouse of a cell. It transforms chemical energy from food into useful energy for plant and animal cells. Chloroplasts, found in green plant cells and some protists, capture the sun’s energy and convert it to chemical energy in photosynthesis.
A cell’s structural support, movement, and communication happen in the following organelles. The cytoskeleton is a network of protein filaments that helps the cell keep its shape. It also helps with the movement of protein filaments called microtubules or microfilaments. Centrioles are made of microtubules and help with cell division. They are not present in plant cells. Cilia are short, hair-like projections that wave to move a cell. Flagella are long, whip-like projections that aid in movement.
Identify the parts of the cell below.