Microbiology 1st Lecture PDF

## Microbiology, 1st Lecture **Microorganism:** A microscopic living organism, which may be single-celled or multicellular. **Microbiology:** The study of microorganisms, a subject that began with the discovery of microorganisms in 1674 by Antonie van Leeuwenhoek using a microscope of his own desi...

## Microbiology, 1st Lecture **Microorganism:** A microscopic living organism, which may be single-celled or multicellular. **Microbiology:** The study of microorganisms, a subject that began with the discovery of microorganisms in 1674 by Antonie van Leeuwenhoek using a microscope of his own design. **Germs:** Many people think of microorganisms mainly in terms of "germs". Some germs cause disease, but others are beneficial to humans and the environment. **Microorganisms** are present in high populations in soil and in varying numbers in the air we breathe, the water we drink, and the food we eat. They are on our skin and in our noses, throats, mouths, intestinal tracts, and other bodily cavities. ### Classification of living things * Scientists have found and described approximately 1.75 million species on Earth, with new species being discovered everyday. * Living things are divided into three groups called kingdoms based on their genetic similarity. ### The three groups are: 1. **Archaea** - very ancient prokaryotic microbes. The archaea exhibit many differences from bacteria. - Different cell membrane structure - Cell wall present, but not composed of peptidoglycan. - First amino acid in proteins is not methionine like in other bacteria and eukaryotes. - DNA contains histone-like proteins similar to eukaryotes (true bacteria have no histone proteins) - Live in only extreme environments (groups include extreme halophiles, extreme thermoacidophiles, and methanogens). 2. **Eubacteria** - more advanced prokaryotic microbes. 3. **Eukaryota** - All life from with eukaryotic cells including plants and animals. * The Eukaryota domain is divided into several groups called Kingdoms: * **Kingdom Protista** * **Kingdom Fungi** * **Kingdom Plantae** * **Kingdom Animalia** ### Viruses * While some believe viruses are living entities, others refuted this idea. * **Arguments supporting that viruses are alive:** * The chemical composition of viral units is similar to that of many living bodies, for example, gene plastids and mitochondria. * Every virus has its own characteristic genotype and phenotypic characteristics (morphological characteristics). The new generation units always carry the phenotypic and genotypic characteristics of the original generation. * Viral chemistry, morphology, and activities were found to be susceptible to many factors which affect other living organisms, such as radiation, pH, temperature, and many chemicals. * Viruses have the ability to catalyze the production of chemical compounds inside the host cells. * Viruses are susceptible to mutations like other living organisms when exposed to shocks, such as heat shocks or chemical shocks. * Viruses infect cells, producing specific symptoms which appear again when viral particles are isolated from the diseased organism and transferred to healthy ones. * Viruses, like other living organisms, can multiply, producing new units like the original viruses in large numbers. * **The third logic opinion is that viruses can be considered as a border of life where they are between living organisms and nonliving bodies.** ### The Cell - The cell is the basic unit of life. - It can be divided into two major categories: **Prokaryotic cells** and **Eukaryotic cells**. **Prokaryotic cells** * Bacteria * Archaea **Eukaryotic cells** * Protista * Fungi * Plants * Animals **A heterotrophic organism that lives in detritus and parasitic places.** ### Difference between prokaryotic and eukaryotic cells | Feature | Prokaryotic cells | Eukaryotic cells | |---|---|---| | Cell Size | Typically 1-5 um | Typically 10-100 um | | Example | Bacteria, archaea | Animal cells and plant cells | | Genetic material | Free in cytoplasm, single circular chromosome or nucleoid | Contained within a membrane-bound nucleus, multiple chromosomes generally in pairs | | Internal Feature | membrane-bound organelles absent | several membrane-bound organelles present including mitochondria, Golgi body, endoplasmic reticulum, and (in plants and alga) chloroplasts | | Ribosomes | smaller (70S), free in cytoplasm | larger (80S), free in cytoplasm or attached to membrane | | Respiratory enzymes | Bound to plasma membrane | Located in mitochondria | | Cell wall | Usually based on peptidoglycan | When present, based on cellulose or chitin |