Micro Script 5

8/3/2019 Micro Script 5

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SCRIPT 5

This script includes the continuation of Chapter 3, and part of Chapter 4.For your convenience I have prepared a list of Key Points that you

should remember.

Done By: Aya Rihan

: Zeina Hammad


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We start off the lecture where it ended last time with a quick review of

SPORULATION; asexual reproduction in the form of spore formation. Spores

are reproductive structures that are adapted for dispersal and survival in

unfavorable conditions, which is why this type of reproduction is required for

bacteria and fungi. In general eukaryotic cells reproduce either by meiosis or

mitosis.

As for reproduction in prokaryotic cells, a process known as binary fission

splits the parent cell in half to produce two daughter cells. As we all know

however, that before any cell division chromosomes replicate so that each

daughter cell will have diploid number of chromosomes. The length of time it

takes for one bacterial cell to split into two cells is known as the organisms

generation time. Each micro-organism has its owngeneration time whichranges from 15 min 10 hours depending mainly on the type of micro-

organism.

Binary Fission


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Taxonomy: It is the science of classification of living organisms; it includesclassification, nomenclature and identification. Classification is the

arrangement of organisms into taxonomic groups (known as taxa)

Key for remembering the sequence of Taxa:

King David Came Over For GoodSpaghetti

( K for Kingdom, D for Division, C for Class, O for Order, F for Family, G for

Genus, S for Species)

Taxonomic classification of organisms separates them into kingdoms,divisions, classes, orders, families, genera, and species, based on their

characteristics, attributes, properties, and traits.

The science of taxonomy was established on the binomial system of

nomenclature: the first name is the genus, the second name is the specific

epithet, and the two names together are referred to as a species. Ex:

Escherichia coli; Escherichia is the genus, while coli is the specific epithet. The

genus is usually abbreviated with just a single letter (E for Escherichia); a


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single species is abbreviated with sp, while more than one species is

abbreviated with spp.

Organisms are categorized into larger groups based on their similarities and

differences; there are several systems of classifications of which the mostprominent one is the Five-Kingdom System of Classification. Viruses are not

included among those groups because they are acellular organisms.


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The Three-Domain System of Classification is another biological

classification that divides into Archaea,Bacteria, and Eucarya.


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y Relatedness among organisms the degree of diversity among them- isdetermined by analysis of genes that code for small subunit ribosomal

RNA ( 16S). The more similar the gene sequences, the more closely

related are the organisms. The less similar the sequences, the less

related are the organisms. Ribosomes are made up of two subunits , the

larger subunit , 18S, and the smaller subunit, 16S.

KEYPOINTS:

The cell is the fundamental unit of any living organism. It exhibits the basiccharacteristics of life. All living organisms are composed of one or more

cells.

Genes are located along chromosomes. An organisms complete collectionof genes is referred to as its genotype or genome.

Each gene codes for one or more gene products. Most gene products areproteins.

Ribosomes are the sites of protein synthesisMitochondria can be considered power plants or energy factories, for it

is within mitochondria that much energy is produced.

Eukaryotic cells contain a true nucleus, a complex system ofmembranes and membrane-bound organelles, whereas prokaryotic

cells do not.

Eucaryotic cells reproduce either by mitosis or meiosis. Procaryotic cellsreproduce by binary fission the simple division of one cell into two cells.

The length of time it takes for one bacterial cell to split into two cells isreferred to as the organisms generation time.

Most bacteria possess only one chromosome.An organisms physical characteristics are collectively known as the

organsims phenotype. An organisms phenotype is determined by the

organisms genotype.

In the binomial system of nomenclature, the first name is the genus, thesecond name is the specific epithet, and the two names together are referred

to as a species.


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Taxonomic classification of organisms separates them into kingdoms,divisions, classes, orders, families, genera, and species, based on their

characteristics, attributes, properties, and traits.

In the Five-Kingdom System of Classification, microorganisms are found inthe first three kingdomsProcaryotae (bacteria), Protista (algae and protozoa), and Fungi. In the Three-Domain System of Classification,

microorganisms are found in all three domainsArchaea, Bacteria, and

Eucarya.

Relatedness among organisms is determined by analysis of genes that codefor small subunit ribosomal RNA.

Chapter 4:

Categories of micro-organisms

y Microbiology is the study of microbes that are too small to beseen in the naked eye.

Micro-organisms are divided into:

1) Cellular e.g. bacteria, fungi, archaeons, algae, protozoa etc.

2) Acellular e.g. viruses, viroids, prions

Cellular micro-organisms are further divided into:

y Prokaryotes : bacteria, archaeay Eukaryotes : algae, protozoa, fungiAcellular micro-organisms are not considered to be living

organisms by most scientists , thus we use these terms to

describe them rather than micro-organisms : Viruses,

Viroids, Prions

Acellular microbes = infectious particles


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Viruses:

y Complete virus particles are called Virionsy They are small and simple in structure; 10 300 nm in

diameter cannot be seen in light compound microscope, they

can be seen using an electron microscope.

y Viruses infect humans, animals, plants, fungi, protozoa, algaeand bacterial cells.

y Some viruses are called oncogenic viruses or oncoviruses, theycause specific types of cancer, including lymphomas,

carcinomas and some types of leukemia.y Carcinogenic viruses include: 1) Papiloma Virus which is

responsible for warts and can lead to cervical cancer in

women. 2) Herpes Virus which also leads to cervical cancer in

women as well as throat cancer.

y Viruses can cross-over from one species to another; theyescape either by lyses of the cell or budding. Examples include

the H1N1 virus , also known as the swine flu , which starts byinfecting birds, then passes over to pigs and finally to humans .

Now that weve stated the most important facts about viruses, the

table below describes the main points of Prions and Viroids,

establishing the differences between them.


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Prions ViriodsInfectious agents Infectious agents

Protein particles Pieces of naked RNA; like virusesbut not real viruses.

Abnormal in shape and function

Affects normal proteins when

they come in contact with them;

they lose their structure and

function and become abnormal(

example is when the brain and

spinal cord are affected by prionsand turn into a mushy like

substance in animals and

humans) ; transported from

animals to humans.

Affects plants only

Viruses are said to have five specific properties that distinguish

them from living cells:

y The vast majority posses either DNA or RNA, unlike livingcells that have both.

y They are unable to replicate on their own; they require ahost cell.

y Unlike cells, they do not divide by binary fission, mitosis,or meiosis.

y They lack the genes and enzymes necessary for energyproduction.y They depend on the host cell for protein and nucleic acid

production.


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A typical virion consists of a genome of either DNA or RNA,surrounded by a capsid (a protein coat) , which is

composed of many small protein units called capsomeres.

The nucleic acid and the capsid are referred to as thenucleocaspid.

Some viruses are enveloped viruses composed of an outer envelope

made of lipid and polysaccharide such as AIDS virus, which has a

capsomere and an extra outer envelope. Structures like

Glycoproteins can be found on the envelope whose function is to

help the virus attach itself to certain hosts. Viruses that have no

envelope are called naked viruses.

Viruses are classified depending on the following features:

y Type of genetic material (DNA or RNA)y Shape and size of capsidy Number of capsomerey Presence and absence of envelopey Type of host it infectsy The disease it producesy Their antigenic properties


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Key points:

Microbes can be divided into those that are cellular (bacteria,algae, protozoa, and fungi) and those that are acellular

(viruses, viroids, and prions).

Complete virus particles are called virions.Viruses are not living organismsExcept in extremely rare cases, viruses possess eitherDNA or

RNAnever both

Viruses that cause cancer are known as oncogenic viruses oroncoviruses

Acquired immunodeficiency syndrome (AIDS) is caused by anenveloped, single stranded RNA virus known as humanimmunodeficiency virus (HIV).

Viroids are infectious RNA molecules that cause a variety ofplant diseases

Prions are infectious protein molecules that cause a variety ofanimal and human diseases. The highly publicized mad cowdisease is an example of a prion-caused disease.

By this we end our lecture; we hope that you benefit from it.

Special thanks to our colleagues: Louai Kababji (Loweiiiii) ,

MohammedMalik (bb), Baras Srouji(wlee 3ala 2amtee), Asil Louzi (

baladuna)

O raja2an el tafree3 ma ynbaa3 la Abdul-rahman Al Doori :p


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Micro Script 5

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