Eukaryotic Cells and Cell OrganellesKEY CONCEPT Eukaryotic cells share many similarities.

Cells have an internal structure.Your skeleton is made of bones that help keep all your body parts in place. Eukaryotic cells have a skeleton, too. It is called the cytoskeleton. The cytoskeleton is a network of protein fibers. They look like a lot of tiny strings that crisscross a cell. The cytoskeleton is the framework of a cell. It gives a cell shape, support, and strength. The cytoskeleton can change as a cell needs to change.

What might a cell look like if it had no cytoskeleton?

Several organelles are involved in making and processing proteins.

Proteins are a very important type of molecule that are used in all life functions. Basic life functions include reproduction, repair, and growth of injured cells or body parts. Life functions also include the regulation of circulation and digestion systems. You need proteins to digest the foods you eat or to move your muscles when you ride a bike. Proteins are at work when your heart beats or your eye blinks. Some hormones such as insulin, which controls your blood sugar levels, are also proteins.

Proteins are very important, and many organelles work together to make them. These organelles include the nucleus, endoplasmic reticulum, ribosomes, the Golgi apparatus, and vesicles. Ribosomes are found in both eukaryotic and prokaryotic cells. However, the other organelles—those surrounded by a membrane—are found only in eukaryotic cells.

Nucleus The nucleus stores and protects the DNA of the cell. DNA contains the genes that are the instructions for making proteins.

Endoplasmic Reticulum (ER) The endoplasmic reticulum (ER) is a network of thin, folded membranes that helps in the production of proteins and other molecules. The membranes are like a maze; they fold back on themselves and have little spaces inside the folds. There are two types of ER, smooth and rough. The rough ER looks bumpy because it has ribosomes attached to it.

SECTION

3.2Student text pages 73–79

The cytoskeleton supports and shapes the cell.

The nucleus stores and protects DNA.

cytoskeleton

See pictures in student text, pgs. 75–79

Visual Connection

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Ribosomes Ribosomes are tiny organelles that link amino acids together to form proteins. They are found on the surface of the ER and floating freely in the cytoplasm.

Golgi apparatus Each Golgi apparatus is a stack of layers of mem-branes. In the Golgi apparatus, proteins are changed, put into packages, and carried to other places in the cell.

Vesicles Vesicles are small sacs. They carry different molecules to where they are needed. Vesicles are generally short-lived and are formed and recycled as needed.

What is the job of the nucleus?

Other organelles have various functions.Some organelles do jobs other than making proteins.

Mitochondria Mitochondria are bean-shaped organelles that produce chemical energy that is usable by a cell. They have two membranes. The inner membrane has lots of folds that form compartments. Mito-chondria also have their own ribosomes and DNA. At one time, mito-chondria may have been independent prokaryotes that were taken in by larger cells.

Vacuoles Vacuoles are sacs of fluids that store materials in a cell. These materials include water, food molecules, ions, and enzymes. Many plant cells have a large central vacuole. When filled with fluid, the central vacuole exerts pressure that can help support the plant.

Lysosomes Lysosomes are organelles that contain enzymes. They protect a cell by attacking incoming bacteria or viruses. They also break down old cell parts.

Centrioles Centrioles are shaped like cylinders. They are made of tiny tubes in a circle. They move when animal cells divide in two. Centrioles help form cilia and flagella, structures that help cells to move or to move liquids past a cell. Centrioles are surrounded by the centrosome. The centrosome is a small region of cytoplasm that organizes proteins into fibers that help cells divide.

Highlight the organelle that produces usable energy for a cell.

The Golgi apparatus modifi es, packages, and transports proteins.

Mitochondria generate usable energy for the cell.

Centrioles are separated during cell division. They help form cilia and fl agella.

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What is the job of the nucleus?

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FOUND IN PLANT CELLS

chloroplast

central vacuole

cell wall

PLANT CELL

FOUND IN BOTH

cytoskeleton

vesicle

nucleus

nucleolus

endoplasmic reticulum (rough)

ribosome

centrosome

endoplasmic reticulum (smooth)

cell membrane

Golgi apparatus

mitochondrion

vacuole

cytoskeleton

vesicle

nucleus

nucleolus

endoplasmic reticulum (rough)

ribosome

centrosome

endoplasmic reticulum (smooth)

cell membrane

Golgi apparatus

mitochondrion

vacuole

SUMMARY OF CELL STRUCTURE

Eukaryotic cells have highly organized structures, including membrane-bound organelles. Plant and animal cells share many of the same types of organelles, but both also have organelles that are unique to their needs.

FOUND IN ANIMAL CELLS

centriole

lysosome

ANIMAL CELL

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Plant cells have cell walls and chloroplasts.Plant cells have two parts that animal cells do not have. Plant cells have cell walls and chloroplasts.

Cell walls The cell wall is a strong, rigid layer that protects, supports, and shapes the plant cell. It surrounds the cell membrane. Some cell walls are very thick, such as those in a tree. When joined with others, they can support a very large plant. Some cell walls are thinner, like those in celery.

Chloroplasts Chloroplasts carry out photosynthesis that stores energy from sunlight as chemical energy for the plant. The chloro- part of the name chloroplast means “green.” Chloroplasts contain chlorophyll, a green pigment, that helps capture energy from sunlight. Like mito-chondria, chloroplasts have two membranes and their own ribosomes and DNA.

Circle the organelle that is similar in structure to mitochondria.

cytoskeleton Golgi apparatus lysosome

nucleus vesicle centriole

endoplasmic reticulum mitochondrion cell wall

ribosome vacuole chloroplast

Choose the correct term from the list for each description.

1. little sacs that carry molecules

2. bumps that link amino acids

3. green organelles for photosynthesis

4. the skeleton of the cell

5. bean-shaped energy supplier

6. holder and protector of DNA

7. What do the nucleus, ER, ribosomes, Golgi apparatus, and vesicles work together to do?

8. How are plant cells different from animals cells?

3.2 Vocabulary Check

Go back and highlight each sentence that has a vocabulary word in bold.

Mark It Up

3.2 The Big Picture

Chloroplasts convert solar energy into chemi-cal energy through photosynthesis.

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