Cells: What are the Building Blocks of Life?

What is the cellular nature of life?

• Cells were discovered using microscopes.• Microscopes have changed considerably in the

past 400 years.

Robert Hooke

• In 1662, he observed boxes in cork and named them “cells” after small, plain rooms occupied by monks.

Anton van Leeuwenhoek

• Creates his own microscope.• In 1675, he reported viewing “animalcules”.

Cell Theory• Organisms are

composed of one or more cells.

• Cells arise from preexisting cells.

• Cells are the fundamental units of life.

Where do cells come from?

• Louis Pasteur found microbes grow in broth exposed to air.

• No microbial growth with prevention of air entry.

• Refutes theory of spontaneous generation.

Viruses

• Viruses are acellular.– Consist of:

• nucleic acids and

• protein coat.

• Considered nonliving.

Viruses

• Dependent on other organisms to:– Reproduce– Obtain raw materials– Obtain energy

• Viruses use host cell machinery to produce proteins.

Different types of cells

Liver cell (magnified 3,048 times)

Human sperm cell (magnified 1,380 times)Retinal cells (magnified 720 times)

Blood cell (magnified 4,445 times)

What are the major kinds of cells?

• Two types:– Prokaryotic cells

• Have few internal parts• Simple cells

– Eukaryotic cells• Possess organelles• Complex cells

Prokaryotic cells• No nucleus• Possess

– single circular chromosome• Contains hereditary material

– ribosomes• Site protein synthesis

– cytosol• Interior fluid compartment

– cell membrane• Surrounds cell• Regulates internal & external

environment

Prokaryotic cells

• Possess– Cell wall– Capsule

• Helps cell withstand hostile environment

– Flagella, pili or microvilli

• Include– single-celled organisms

• Protista

– multicellular organisms• Plants • Animals

Eukaryotic cells

Nucleus

• Largest organelle.• Surrounded by nuclear envelope.

– porous double membrane • Contains chromosomes (hereditary material).

Nucleolus

• Found in nucleus.• Ribosomes are assembled here.

Endoplasmic Reticulum (ER)

• Extensive membranous structure.

• Formed by membrane emerging from nuclear envelope.

• Two types:– Rough ER– Smooth ER

Rough Endoplasmic Reticulum

• Ribosomes are found on the outside.

• Site of protein synthesis.

Smooth Endoplasmic Reticulum

• Site of lipid and carbohydrate synthesis.

Golgi Complex

• Receives transport vesicles from the smooth endoplasmic reticulum.

• Cellular products are modified, packaged and prepared for their final destination.

Golgi Complex

• Following modification, products may be released from the cell via exocytosis.

Lysosomes• Lysosomes arise from

Golgi complex. • May fuse with food

vesicles.– Lysosomal enzymes

digest proteins, carbohydrates and lipids.

• Process cellular debris and worn-out organelles.