Introduction to Cells

Why does this cell look like a fried egg?

• Cells vary greatly in their size and shape.

• A cell’s shape reflects its function.

• Cells can be branched, flat, round, or rectangular.

– The Cell theory has three principles.• All organisms are made of cells.

• All living cells are produced by other living cells.

• The cell is the most basic unit of life.

– All cells share certain characteristics.• All cells are enclosed

by a membrane.• All cells are filled with

cytoplasm.• All cells have DNA.• All cells have ribosomes.

Bacterium(colored SEM; magnification 8800x)

cell membrane

cytoplasm

• There are two cell types: eukaryotic cells and prokaryotic cells.– Eukaryotic cells have a

nucleus.– Eukaryotic cells

have membrane-

bound organelles.

nucleus

cell membrane

organelles

– Prokaryotic cells do not have a nucleus.

– Prokaryotic cells do not have membrane-bound organelles.

nucleus

cell membrane

organelles

cytoplasm

Prokaryotic and Eukaryotic cells

Cytoskeleton

A

B

C

D

Click to animate the image.

•The cytoskeleton helps the cell move, keep its shape, and organize its parts.

• Several organelles are involved in making and processing proteins.– The nucleus stores genetic information.

The Nucleus

A

BC

D

The nucleolus is a structure within the nucleus where ribosomes are made.

– Many processes occur in the endoplasmic reticulum.

There are two types of endoplasmic reticulum

• rough endoplasmic reticulum

• smooth endoplasmic reticulum

• Rough ER has ribosomes and takes part in the production of protein

• Smooth ER lacks ribosomes. Smooth ER makes lipids and breaks down drugs and alcohol.

– Ribosomes link amino acids to form proteins.

– Ribosomes link amino acids to form proteins.– Vesicles are membrane-bound sacs that hold

materials.– Vesicles help maintain homeostasis by storing

and releasing a variety of substances as the cell needs them.

Golgi apparatus

Protein ProcessingMaking and Exporting Proteins

• The ribosomes located on the rough ER make proteins which then cross into the membranes of the ER. The ER membrane then pinches off and forms a vesicle around the proteins.

• Vesicles transport the proteins from the rough ER to the Golgi apparatus, where they are modified by enzymes and repackaged in new vesicles.

• These new vesicles transport the modified proteins to the cell membrane to be released outside the cell.

Lysosomes

• A lysosome is a vesicle produced by the Golgi apparatus that contains enzymes that break down large molecules.

• Lysosomes recycle old or damaged organelles and digest food particles to provide nutrients for the cell.

Mitochondrion

• Mitochondria supply energy

to the cell.

• Mitochondria use energy from organic compounds to make ATP.

• Vacuoles are fluid-filled sacs that hold materials.

Centrioles are tubes found in the centrosomes.

• Centrioles help divide DNA.

• Centrioles form cilia and flagella.

• Plant cells have cell walls and chloroplasts.– A cell wall provides rigid support.

– Chloroplasts convert solar energy to chemical energy.