华中农业大学微生物学第二章文稿演示

The Prokaryotic Cell
1. Their genetic material (DNA) is not enclosed within a membrane and they lack other membrane – bounded organelles
2. Their DNA is not associated with histidine
Concepts
• Prokaryotes are small and simple in structure when compared with eukaryotes , yet they often have characteristic shape and size.
• Prokaryotic genetic material is located in an area called the nucleoid and is not enclosed by a membrane.
• The prokaryotic cell wall almost always has peptidoglycan and is chemically and morphologically complex.
2.1 Overview of Cell Structure
A procaryotic cell A eucaryotic cell
Gram-positive Cell Wall
The Gram-positive cell wall has a peptidoglycan layer that is relatively thick (ca. 40 nm) and comprises approximately 90% of the cell wall. The cell walls of most Gram-positive eubacteria also have teichoic acids.
3. Their cell wall almost always contain the complex polysaccharide peptidoglycan
4. They are very small!!
Schematic diagram of a bacterial cell
Size: Most bacteria fall within a range from 0.2 to 2.0
• Almost all prokaryotes have cell walls.
Schematic diagram of bacterial cell walls
Gram+
Gram-
Bacteria can be divided into two major groups, called gram-positive and gram-negative. The original distinction between gram-positive and gram-negative was based on a special staining procedure, the Gram stain
Microorganisms in general are very small and are completely invisible to the naked eye.
size comparison of microorganisms
Meters
Visibility scale Relative size of Microbes
Naked eye
Fra Baidu bibliotek
Eukaryotes
Light microscope
Electron microscope
Prokaryotes Viruses
Surface area and volume relationships in cells
a cell increases in size, its surface area – to – volume ratio decreases
华中农业大学微生物学第二章文稿演示
Chapter Outline
2.1 Overview of the structure of microbial cells 2.2 Procaryotic cell wall 2.3 Cytoplasmic membrane 2.4 Cellular genetic information 2.5 Cytoplasmic matrix – Ribosome and Inclusions 2.6 Components external to the cell wall 2.7 Bacterial endospores 2.8 Comparison of the prokaryotic and eukaryotic cell
um in diameter and from 2 to 8 um in length
A cyanobacterium 8 x 50 um
A rod-shaped prokaryote is typically about 1-5 micrometers (μm) long and about 1 μm wide
Shape: Bacteria have a few basic shapes
spherical coccus Rod-shaped bacillus
spirallum
2.2 Prokaryotic Cell Wall Cell Wall
• The cell wall of the bacterial cell is a complex, semi-rigid structure that is responsible for the characteristic shape of the cell. The cell wall surrounds the underlying, fragile plasma (cytoplasmic) membrane and protects it and internal parts of the cell from adverse changes in the surrounding environment.