Table of contents

Intro

This article puts Archaea and Bacteria into some context, shows their scientific nomenclature and points out the general aspects of bacterial structure (giving special attention to the bacterial cell wall and to the differences between Gram-positive and Gram-negative bacteria), replication and metabolism.

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Note: Drawings are not to scale.

Archaea and Bacteria are microorganisms that share a common ancestor. An evolutionary process of more than 3 billion years gave rise to organisms that today we group into three domains:

• Archaea,
• Bacteria,
• Eukarya (includes animals, fungi, plants and protozoa).

Archaea and Bacteria are prokaryotes.

Eukarya are eukaryotes.

Prokaryote organism:

• unicellular
• the genome is a DNA (deoxyribonucleic acid) usually single molecule
• the genome is haploid (with a single set of chromosomes)
• the genome occupies an area of the cytoplasm called nucleoid ‒ there is no nuclear membrane involving the genome
• it has no other membranous organelles such as mitochondria, Golgi bodies and endoplasmic reticulum
• ribosomes are 70S ribosomes (subunit 50S + subunit 30S)
• the cytoplasmic membrane usually doesn’t contain sterols
• it usually has a cell wall
• it reproduces through asexual reproduction only