Lesson Overview 7.2 Cell Structure (PART 1)

THINK ABOUT IT At first glance, a factory is a puzzling place, and the sheer diversity of activity can be confusing. However, if you take your time and watch carefully, what might at first seem like chaos begins to make sense. The same is true for the living cell.

Cell Organization What is the role of the cell nucleus?

Cell Organization What is the role of the cell nucleus? The nucleus contains nearly all the cell’s DNA and, with it, the coded instructions for making proteins and other important molecules.

Cell Organization The eukaryotic cell can be divided into two major parts: the nucleus and the cytoplasm. The cytoplasm is the fluid portion of the cell outside the nucleus. Prokaryotic cells have cytoplasm as well, even though they do not have a nucleus.

Cell Organization Many cellular structures act as if they are specialized organs. These structures are known as organelles, literally “little organs.” Understanding what each organelle does helps us to understand the cell as a whole.

Comparing the Cell to a Factory The is much like a living version of a modern factory. The specialized machines and assembly lines of the factory can be compared to the different of the cell. Cells, like factories, and .

The Nucleus In the same way that the controls a large factory, the nucleus is the of the cell. The nucleus contains nearly all the cell’s and, with it, the and other important molecules.

The Nucleus The is surrounded by a composed of two membranes.

The Nucleus The nuclear envelope is dotted with thousands of , which allow material to move into and out of the nucleus.

The Nucleus Like messages, instructions, and blueprints moving in and out of a main office, a steady stream of move through the nuclear pores to and from the rest of the cell.

The Nucleus contain the that is passed from one generation of cells to the next. Most of the time, the threadlike chromosomes are spread throughout the nucleus in the form of —a complex of DNA bound to proteins.

The Nucleus When a cell divides, its and can be seen under a microscope.

The Nucleus Most nuclei also contain a small, dense region known as the . The nucleolus is where the begins.

Organelles That Store, Clean Up, and Support What are the functions of vacuoles, lysosomes, and the cytoskeleton?

Organelles That Store, Clean Up, and Support What are the functions of vacuoles, lysosomes, and the cytoskeleton? Vacuoles . Lysosomes into small molecules that can be used by the rest of the cell. They are also involved in that have outlived their usefulness. The cytoskeleton helps the cell and is also involved in movement.

Vacuoles and Vesicles Many cells contain large, saclike, membrane-enclosed structures called that store materials such as water, salts, proteins, and carbohydrates.

Vacuoles and Vesicles In many plant cells, there is a single filled with liquid. The pressure of the central vacuole in these cells increases their rigidity, making it possible for plants to support heavy structures such as leaves and flowers.

Vacuoles and Vesicles are also found in some unicellular organisms and in some animals.

Vacuoles and Vesicles Nearly all eukaryotic cells contain smaller membrane-enclosed structures called . Vesicles are used to between cell organelles, as well as to and from the cell surface.

Lysosomes are small organelles filled with enzymes that function as the cell’s cleanup crew. Lysosomes perform the vital function of that might otherwise accumulate and clutter up the cell.

Lysosomes One function of lysosomes is the breakdown of into small molecules that can be used by the rest of the cell.

Lysosomes Lysosomes are also involved in that have outlived their usefulness. Biologists once thought that lysosomes were only found in animal cells, but it is now clear that lysosomes are also found in a few specialized types of plant cells as well.

The Cytoskeleton Eukaryotic cells are given their shape and internal organization by a network of protein filaments known as the . Certain parts of the cytoskeleton also help to transport materials between different parts of the cell, much like conveyer belts that carry materials from one part of a factory to another. Microfilaments and microtubules are two of the principal protein filaments that make up the cytoskeleton.

Microfilaments Microfilaments are threadlike structures called actin. They form extensive networks in some cells and produce a that supports the cell. Microfilaments . Microfilament assembly and disassembly is responsible for the that allow cells, such as amoebas, to crawl along surfaces.

Microtubules Microtubules are hollow structures made up of proteins known as . They play critical roles in maintaining cell shape. Microtubules are also important in cell division, where they form a structure known as , which helps to .

Microtubules In animal cells, structures known as are also formed from tubulins. Centrioles are located near the nucleus and . Centrioles are .

Microtubules Microtubules help to build projections from the cell surface, which are known , that enable cells to swim rapidly through liquids. Microtubules are arranged in a “9 + 2” pattern. Small cross-bridges between the microtubules in these organelles use chemical energy to pull on, or slide along, the microtubules, allowing cells to .