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 .
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 1831Robert 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 newcells 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.
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 circularchromosome andthe 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 .
Fig. bacterial cell structure
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.
b- Most of vascular plants could nۥt grow without the symbiotic fungi or mycorrhizae that inhabit onplant 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.
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 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 structure of eukaryotic cell
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