Cell OrganellesSection 3.2: Cytoskeleton and Nucleus

A Mitochondrion

Objectives

• SWBAT describe the internal structure of eukaryotic cells.

• SWBAT visualize the structures and functions of organelles in plant and animal cells.

Vocabulary – Section 3.2• Cytoskeleton (microtubules, intermediate filaments, microfilaments) • Nucleus• Rough endoplasmic reticulum (rough ER)• Smooth endoplasmic reticulum (smooth ER)• Ribosome • Golgi apparatus• Vesicle• Mitochondrion (mitochondria is plural)• Vacuole• Lysosome• Centriole• Cell wall • Chloroplast

Animal Cell

Plant Cell

Cellular Structure

• Eukaryotic cell organization:– Surrounded by a protective membrane.– Containing membrane bound organelles, which

perform specific cellular processes, divide certain molecules into compartments, and help to regulate the timing of key events.

– Organelles and molecules are anchored to specific sites in the cell – based on the cell’s type.

Cellular Structure• Each eukaryotic cell has a cytoskeleton. – Network of proteins that is constantly changing

to meet the cell’s needs.– the proteins form long threads which

“crisscross” the entire cell holding organelles in place.

If the cell membrane were “evaporated,” the cell would maintain shape through the cytoskeleton (for a short time).

Cytoskeleton

Cytoskeleton photo: 750X magnification

Cytoskeleton

• Cytoskeleton is made up of three main types of fibers: – Microtubules – long hollow tubes giving cell its

shape and acting as tracks for organelle movements.

– Intermediate filaments – smaller than microtubules giving cell strength.

– Microfilaments – tiny threads which enable cells to move and divide (during mitosis and meiosis).

Microtuble Network

Microfilament Bundles

The Nucleus

• The storehouse for DNA (deoxyribonucleic acid) in your cells.

• DNA contains the genes – which are instructions – for making proteins.

• The Nucleus must:– Protect the DNA and– Make the DNA available for use at the proper

time (DNA transcription).

Cell Nucleus

The Nucleus

• The nucleus protects the cell’s DNA from molecules that might damage it.

• At the same time, the nucleus makes the DNA available to the many proteins that are involved in turning genes on and off.

• The nucleus is composed of the cell’s DNA enclosed in a nuclear envelope (a double membrane).

The Nucleus

• The nuclear envelope is pierced with pores (nuclear pores) which allow large molecules to pass between the nucleus and cytoplasm.– RNA passes through the nuclear envelope

between the nucleus and cytoplasm. • The nucleolus is also found in the nuclear

envelope. – Its main purpose is producing the “subunits (the

parts)” from which ribosomes are assembled.