biology branches and the main characters of prokaryotic and eukaryotic cells

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Dentistry- college - first class
Medical biology- Lec.1
Lecturer –Dr. Hanan S.
Introduction
Biology is the study of living things , it includes the cellular basis of living
things, energy metabolism that underlies the activities of life, the genetic bases
for inheritance in organisms , study of evolutionary relationships among
organisms and the diversity of life on earth. It considers the biology of
microorganisms, fungi , plants, and animals etc.
During the medical biology coarse pupils will study the basis of cell and the
main characters of eukaryotic and prokaryotic cells their structure ,
morphology, nutrition , reproduction and the nature of host relationships with
other groups of organisms in closed environment, also the pupils will taken an
idea on other biology branches as fellow :
Below there are an important branches dealing with them during the
coarse of medical biology in dentistry college:
1- Microbiology: a study of microscopic organisms and their interaction
with other living things like bacteria , virus etc.
2- Cell biology : a branch of biology deals with the study of cells from
morphological, structural, functional and biochemistry points of views.
3 -Parasitology : study of parasites organism and parasitism.
4 - Histology : study of cells and tissue structure .
5 - Genetic : study of genes and heredity.
The microscope
Microscope ( from the Greek , micro , small and scope to look or see ) is an
instrument used to examine the objects that are too small for naked eyes . There are
many types of microscopes , the most common and first to be invented is the optical
microscope which uses the light to image the sample ( fig.)
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The other two major types were :
Compound light microscope - A
Several types of light microscope are commonly used in the Lab.
field microscope – The bright - 1
The ordinary microscope is called bright –field microscope because it forms
a dark image against a brighter background , it is consist of two series of lenses
objective and ocular lenses which function together to resolve the image (fig.) .With
this microscope , specimens are render visible because of the differences in contrast
between them and surrounding medium ,dyes can be used to stain cells or their
organelles increase their contrast so, they can be easily seen in this microscope . This
microscope generally employ a 4x , 10x , 40x , 100x power objective lenses with a 10x
power ocular lens , thus magnifying the specimens 40 , 100 , 400 , 1000 times .
Fig. : The bright –field microscope
field microscope – Dark - 2
It is an ordinary microscope to which a special condenser is attached , the
condenser serves to intensify illumination of the examined specimen through narrow
area , this creates a " dark field" that contrasts against the high light edge of the
specimens .This technique has been useful for observing organisms such as
Treponema palladium a spirochetes which is less than 0.2 µm in diameter .
contrast microscope - Phase - 3
It is an ordinary microscope in which modified objective lenses and condensers are
used to permit direct examination of living cells without fixation or staining, this
microscope takes advantage of the fact that light waves passing through
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transparent objects such as cells emerge in different phases depending on the
properties of the materials through which they pass .
microscope Fluorescence - 4
The fluorescence microscope is used to visualize specimens that fluoresce ,
which is the ability to absorb short wavelengths of light (ultraviolet) and give
off light at a longer wavelength (visible) .
The principle use of this microscope is a diagnostic technique called the
fluorescent –antibody (FA) for example Ab. to bacteria Legionella are chemically
labeled with a flurochrome and then added to microscope slide containing a
clinical specimen , if the specimen contains Legionella, the fluorescent- Ab. will
bind to Ags., on the surface of the bacterium , causing it to fluoresce when
exposed to ultraviolet light .
The Electron microscope - B
The high resolving power of the electron microscope has enabled scientists
to observe the minute details structures of prokaryote and eukaryote cells .The
superior resolution of the electron microscope is due to the fact that electrons have
a much shorter wavelength than photons of wavelength .
There are two types of electron microscope :
) Transmission electron microscope (TEM - 1
It is a first to be developed by employs a beam of electrons projected from an
electron gun directed and focused by an electromagnetic condenser lens on a thin
specimen , as the electron strike the specimen they are differentially scattered by a
number and mass of atoms in the specimens , some electron pass through the
specimen , gathered and focused by an electromagnetic objective lens . TEM can
resolve particles 0.001µm apart , viruses with diameter 0.01 -0.2 µm can be easily
resolved .
ning electron microscope (SEM) Scan - 2
SEM is generally has a lower resolving power than TEM , however , it is
particularly useful for providing three –dimensional images of the surface of
microscope objects , it can resolve features as small as 5nm.The interaction of
electrons with the specimens results in release of different forms of radiation eg.
secondary electrons from the surface of the material , which can be captured by
an appropriate detector , amplified and then imaged on television screen .
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Fig. scanning electron microscope photo
Cell theory concept
All organisms consist of small cells, typically too small to be seen by a naked
eye, but big enough for an optical microscope . The cell is defined as a mass of
protoplasm surrounded by a thin membrane and having one or more nuclei at
least during a stage of its development . The term "cell" was first introduced by
the English scientist , Robert Hooke, in 1665 while he cut a slice of cork and
examined under a simple microscope, he observed several honey comb like
structures in the cork he gave the term cell (L. cella = compartment or small
room) for each compartment. A few years later, Antoine Van Leeuwenhoek was
the first examine a drop of pond water under the microscope, he observed many
tiny , motile organisms he called them "animalcules" meaning little animals.
Leeuwenhoek, was also the first describing various forms of bacteria. In 1831
Robert Brown noticed a spherical body in the cell, he gave it the name "nucleus" .
In 1838, the German botanist Schleiden reported that all plant tissues were
composed of cells and he was considered to be the founder of the cell theory ,then
after one year 1839 ,the German zoologist Schwann extended the finding of
Schleiden to the animal tissues and both proposed the basis of cell theory .
The modern form for the cell theory states that:
?The body of all living organisms is composed of cells, cell products and new
cells are produced by the division of the pre –existing ones".
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Microorganisms and all other living organisms are classified as prokaryotes
or eukaryotes. Prokaryotes and eukaryotes are distinguished on the basis of their
cellular characteristics , for example, prokaryotic cells ( pro : before , karyon :
nucleus ) lack a nucleus and other memorane-bound structures known as
organelles, while eukaryotic cells (eu: true, karyon : nucleus) have both a nucleus
and complex organelles e.g., mitochondria , endoplasmic reticulum , centrioles,
lysosomes, Golgi complexes etc. (Fig. ) .
Fig. the important cellular feature of (a) prokaryotic cell and eukaryotic cells (b)
An essential feature of most living cells (prokaryote and eukaryote) is their
ability to grow in an appropriate environment and to undergo cell division. The
growth of a single cell and its subsequent division is called cell cycle. Prokaryotic
and eukaryotic cells are similar in several ways , both types of cells are enclosed by
cell membranes (plasma membranes), using DNA for their genetic information and
both having non –membranous organelle ribosome for protein synthesis .
Prokaryotes include several kinds of microorganisms, such as bacteria and
cyanobacteria. Eukaryotes include such higher organisms such as animal , plant ,
fungi, protozoa ,etc. Viruses are considered neither prokaryotes nor eukaryotes
because they lack the characteristics of living things, except ability to replicate
which they accomplish only in living cells .
1- Kingdom of Plantae
General characters
1- Multicellular eukaryotic that are photosynthetic autotrophs.
2- Contain chloroplasts with photosynthetic pigments chlorophyll and
carotenoids.
3- Cell walls containing cellulose .
4- Food reserve is starch that is stored in plastids .
5- Aerial parts are coated with a waxy cuticle that help in prevent
desiccation .
6- Gas exchange can t occur across the waxy cuticle so, specialized
openings on the inner surface of the leaf called stomata, allow gas
exchange .
7- Importance of plants : plants are essential in balance of nature and in
people s lives . Green plants those possessing chlorophyll,
manufacture their own food and give off oxygen in process called
photosynthesis, plants are the ultimate source of food and metabolic
energy for nearly all animals in addition to plant products vital
human include wood and wood products , fibers , drugs , oil ,
pigments etc .
2-- Kingdom of Animalia
General characters
1- Animals are multicellular , eukaryotic organisms .
2- Which are heterotrophic, meaning they obtain nutrition by ingesting
other organisms or decomposing organic material.
3- Animal cells are characterized by lack of a rigid cell wall exhibited by
fungi and plants instead , animal cells are held together by
structural proteins such as collagen, all animals are made up of cells
organized into tissues that are specialized for some function.
4- Most animals are diploid, meaning they have two copies of all genetic
information for most of their life cycle. Most animals reproduce
sexually with sex cells , These cells are fuse to from a new diploid
individual called zygote.
3- Kingdom of Fungi
General Characters
1- Fungi are eukaryotic cells , aerobic they need oxygen even in low amounts
to survive .
2- Non –photosynthetic, obtain their nutrients by assimilation they produces
digestive enzymes to predigest food before absorption .
3- The chief components of the cell wall in the majority of fungi is
chitin (polysaccharide).
4- Morphology :-
a-most fungi, thread- like strands (hyphae- collectively mycelium ) which is
composed of branched threads known as hyphae either septated or not ( fig ) .
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b- other fungi single-celled is called yeasts.
c- form spores that can spread by wind , air or soil.
5-Fungus can reproduce asexually, sexually, in each case, the reproductive
cells are known as spores or conidia based on the types of spore
formed.
6- The reserve food material is usually glycogen .
7- Fungi can play an important roles by:
a- breaking down organic material , they continue the cycle of nutrients
through ecosystems.
b- Most of vascular plants could n?t grow without the symbiotic fungi or
mycorrhizae that inhabit on plant roots and supply essential nutrients .
c-Fungi provide numerous drugs such as penicillin and some used as
food like mushroom others producing bubbles in bread.
d- Some fungi causes number of diseases in other higher organisms.
Fig.: the mycelium and yeast cells
a ingdom of Protist K - 4
General characters
1- Protists are eukaryotic cells, grouped into four categories not
necessarily phylogenetic closed related there are :-
a- animal –like (protozoa ) .
b- fungus –like.
c-plant –like (algae).
d- slim molds.
2- They are unicellular, having a well organized nucleus and complex
membranous organelles.
3- They are autotrophic or heterotrophic showing varieties of
metabolic systems.
4- Locomotion via pseudopodia, cilia, flagella ,common example are
Amoeba, Paramecium , Euglena.
5- They show mitosis , meiosis in simplest type of sexual reproduction