Dentistry- college - first class
Medical biology- Lec.1
Lecturer – Dr. Hanan S.
Medical biology
Introduction
Biology: is the study of life, it has many aspects and specializations
within this broad field has relationship with human life, health,
environment, education, economic , agricultural etc.
During the medical biology coarse pupils will taken an idea on cell
theory origin and study the main characters of eukaryotic and prokaryotic
cells their structure ,morphology , nutrition and reproduction and the
nature of host relationships with other groups of organisms in closed
environment, also the pupils will taken an idea on cell biology, parasitology
genetic and histology in eukaryotic cells.
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 and parasitism.
4 - Histology : study of cells and tissue structure .
5 - Genetic : study of genes and heredity .
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Cell theory concept
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".
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 .In
1957 cells were classified into prokaryote and eukaryotic cells ,differing
fundamentally in their cell structure.
Eukaryotes (eu: true, karyon : nucleus) cells are having well developed or
true nucleus, multiple chromosome and more complex structurally than
prokaryotes . Prokaryotes (pro :primitive or before , karyon :nucleus) are the
most primitive nucleus and cells from morphological point of view.
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It is a cell which has minimum of internal organization , not possesses
membrane bound organelles and the cytoplasm lack the endoplasmic reticulum,
Golgi apparatus, mitochondria, lysosomes etc. The genetic material is present in a
region of the cells lacks a bounding membrane to separate it from the surrounding
cytoplasm, this region called "nucleoid". The amount of DNA is relatively small
and not associated with histones , the nucleolus is absent. There is no mitotic or
meiotic division ,instead it multiply by simple binary fission, the prokaryotic cell
contain a single circular chromosome and the respiratory system associated with
its plasma membrane . Cells possess ribosome which are non- membranous
particles that function as a site for protein synthesis, some prokaryotes have
motility organelles called flagella (single flagellum) fig. Prokaryotes include all
bacteria and blue – green algae .
Figure: the structure of a typical prokaryotic cell
Fig. bacterial cell structure
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KINGDOM
Kingdom is the highest category in the classification of organisms
created by Carolos Linnaeus around 1750 .Linnaeus recognized two
kingdoms plants and animals, then in 1959 Robert Whittaker devised a five
kingdom system that maintained kingdoms planate and animalia but added
kingdoms protista , fungi and monera.
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.1).
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 but never starch.
7- Fungi can play an important roles by:
a- breaking down organic material , they continue the cycle of
nutrients through ecosystems.
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b- Most of vascular plants could n‫ۥ‬t 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 (fig. 2) others producing bubbles in bread.
d- Some fungi causes number of diseases in other higher organisms.
Fig.1: the mycelium and yeast cells
Fig. 2: mushroom
Kingdom of Protista
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.
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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, as shown in figure below.
5- They show mitosis , meiosis in simplest type of sexual reproduction
Fig. Amoeba, Paramecium, Euglena
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
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plant products vital human include wood and wood products ,
fibers , drugs , oil , pigments etc .
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 different sex cells , These
cells are fuse to from a new diploid individual called zygote.
Fig. the
of eukaryotic
cell
Figure:
thestructure
structure
of a typical
eukaryotic cell
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