BACTERIA

What are BACTERIA?

-first cells on Earth-are prokaryotic cells

Structures of BACTERIA All cells have 3 main components:

Nucleoid a region where DNA is located

Plasma membrane limits access to the cell’s interior

Cytoplasm a place where all metabolic reactions occur (e.g. protein synthesis, which occurs on the

ribosomes) a gel-like structure composed mainly of

water that contains enzymes, salts, cell components, and organic molecules

Bacteria also often have these features: Cell wall

helps the cell retain its shape made of peptidoglycan

Flagellum plural: flagella responsible for movement

Pili are filamentous proteins that help

cells adhere to a surface or facilitate conjugation

Glycocalyx sometimes called ‘capsule’ a sticky layer composed of proteins or

polysaccharides that surround the cell wall

for protection Plasmid

circles of DNA apart from the nucleoid Ribosome

site for protein synthesis

How do BACTERIA reproduce?

Binary Fission

Prokaryotes reproduce by BINARY FISSION, an asexual process that replicates DNA and distributes it and other cell parts into two daughter cells.

Bacterial Recombination

Binary fission is an effective way for bacteria to reproduce, however it does produce problems. Since the cells produced through this type of reproduction are identical, they are all susceptible to the same types of antibiotics. In order to incorporate some genetic variation, bacteria use a process called recombination.

Bacterial recombination can be accomplished through conjugation, transformation, or transduction.

Conjugation

one bacterium connects itself to another through a protein tube structure called pilus or sex pilus. Genes are transferred from one bacterium to the other through this tube.

sometimes called “bacterial sex”

Transformation

a prokaryote takes up naked DNA without cell-to-cell contact. It occurs when prokaryotes die and pieces of their DNA enter other cells.

Transduction

It is a type of recombination that involves the exchanging of bacterial DNA through bacteriophages.

Where do BACTERIA live?

Bacteria are present in almost every environment, e.g. in the soil, in the air, in animals and plants. They are found all over our bodies e.g. on our skin, in our mouth and in our gut. Most are harmless and are even beneficial.

How do BACTERIA get nutrients?

Nutrition refers to how an organism obtains energy and a carbon source. Phototrophs are species that use light energy, and chemotrophs obtain their energy from chemicals taken from the surrounding environment. An autotroph is an organism that only needs carbon dioxide as its carbon source, and a heterotroph is an organism that requires at least one organic nutrient as a source of carbon for making other organic compounds.

The four major modes of nutrition for prokaryotes are: 

1. Photoautotrophs are photosynthetic organisms that harness light energy to drive the synthesis of organic compounds from carbon dioxide. All photosynthetic prokaryotes use this mode of nutrition.

2. Chemoautotrophs only require carbon dioxide as a carbon source. Instead of using light for energy, they obtain energy by oxidizing inorganic substances. Only certain prokaryotes use this mode of nutrition.

3. Photoheterotrophs may use light to make ATP but must also obtain carbon in organic form. Only certain prokaryotes use this type of nutrition.

4. Chemoheterotrophs consume organic molecules for energy and carbon. Prokaryotes, protists, fungi, animals and some plants use this nutritional mode.

Most bacteria are heterotrophic, living off other organisms. Most of these are saprobes, bacteria that live off dead organic matter. The bacteria that cause disease are heterotrophic parasites. There are also many non-disease-causing bacterial parasites, many of which are helpful to their hosts.

Autotrophic bacteria manufacture their own food by the processes of photosynthesis and chemosynthesis (see autotroph ). The photosynthetic bacteria include the green and purple bacteria and the cyanobacteria . Many of the thermophilic archaebacteria are chemosynthetic autotrophs. 

Gram Positive and Negative Bacteria

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