Secondly, in order to talk about cells and genes, there are two theories, cellular and genetic. For the first part, we shall talk about nature of cells, types, nature of organelles and function, and cell cloning.
Discovery of Cell
The cell was first discovered by a British scientist Robert Hooke in 1665 while observing a multitude of tiny pores on very thin slices of bottle cork through compound microscope and he named “cells”, meaning ‘a small room’ like monks lived in. (With regard to the nature of cells, translators use the term thraphung.)
But he was unable to observe and find details of those pores such as the nature, structure and function of those pores. (Fig. 6) More details of cell theory started developing from 1830s. German botanist Matthais Schleiden understood that all plants are composed of cells and German veterinary Theodor Schwann discovered that all organisms are made up of cells. Due to these findings, biology started developing gradually.
Nature of Cell
Cell is the basic unit of living organisms that are aggregates of all the essential characteristics of life yet it is not the basic unit of things because cell itself is made up of diverse molecules and atoms.
Cells have characteristics of life such that they can reproduce offspring, respond to change in environment, breathing in and out, transformation of intake of nutrients from outside into energy, waste disposal, homeostasis, growth and reproduction. From the standpoint of cellular theory, all cells arise only by division of a previously existing cell and all living organisms are composed of basic unit of cell.
Types of Cell
Secondly, there are two different types of cell, prokaryote and eukaryote.
Firstly, prokaryotes are comparatively smaller in shape than eukaryotes and less complex and simple. It does not have nucleus, have less number of chromosomes and unicellular.
Prokaryotes are of two main groups: archaebacteria and bacteria. Bacteria are amongst the earliest organisms on the earth and they takes birth and grow on land, sea and ponds, salt water and acid soup. They have three different shapes such as spherical, rod shaped and spiral.
Archaebacteria live in the environment such as hot volcanoes, salt water and deoxygenated swamp. Archaebacteria are recognized as living things only around 1990.
Secondly, eukaryotes are composed of membrane covering nucleus and aggregate of different kinds of organelles. There are two kinds: Plant cell and animal cell. Plant cells are those cells that compose plant leaf, root, flower and stem while animal cells are those that compose all the inside of physical body such as skeleton, muscles, blood, skin, nerves and so on.
Plant cell and animal cell have differences such that former has cell wall and chlorophyll while later do not have those. Former are rectangular while later are spherical although the differences in shape is not the primary difference. Former depend on Sun light to generate its nutrient to survive while later it cannot function in that manner but draws nutrients by depending on other living organisms. For example, human body cells cannot make up glucose and so have to take up the nutrients from food items such as wheat, barley and beans and others.
Organelles and their functions
In general, we cannot see from our naked eyes the body cells as its too small yet they are not something which is not composed of something rather they are composed of subtle things. They are called organelles of cell. Each organelle has its separate shapes and functions. Few important organelles amongst are: Gene embedded nucleus, energy producing mitochondria; waste breaking lysosome, and protein synthesizer cytoskeleton.
Nucleus is centered in a cell and there lie chromosomes, DNA, genes and so on. These are formed step by step as DNA is formed from the aggregates of genes and these are spiraled to form chromosomes and they function in encoding most of the cells and body messages.
When cells perform protein synthesis, messenger RNA performs transcription of information in the DNA that is in nucleus and then carries the information and messages onto protein-making RNA through the pores of nucleus. This process is called transcription. Then RNA synthesizes protein according to the information carried on by the messenger. This process is called translation.
Unlike other organelles of cell, mitochondria have uncommon DNA and gene and so it can perform transcription and reproduce by itself. And although eukaryotes only have mitochondria and not the prokaryotes, the later can equally produce energy.
Both the parent cells have mitochondria yet we receive it from mother. This organelle is highly important that most of the energy need for our body is generated by it. Like digestive system, this organelle carries nutrients to cell and break up into pieces to change it into energy form.
These energies are used in our body such as we need energy to work during day time, walking, thinking, breathing in and out during sleep in the night time and so forth. There are three stages of processes in producing energy and that it produces 36 energies in total, i.e., in the 1st stage – 4 energy molecules ADP, at 2nd stage-6 ADP and in the 3rd stage-24 ADP. That is why it is also called storehouse of cell.
Lysosomes are situated in the outer fluid of cell and membrane-bound tiny vesicles. Lysosomes are located in a part of cell called Golgi apparatus that contains acid. They enter inside the stomach of bacteria and viruses entering from outside the cell that are harmful to cell and kill them by releasing acid. Likewise, acids in the lysosomes help in digestion of nutrients such as proteins and fats. Lysosomes break down those mitochondria that become worn-out and useless and make up new storehouse of cell.
All the living cells have thousands of cytoskeleton and their main function is to make protein and when cells are in need of protein, mRNA in nucleus carries information about what type of protein to synthesize from nucleus to cytoskeleton that lies outside the nucleus. There are two parts of cytoskeleton, small and large, such that smaller one reads information carried on by messenger and larger part synthesize proteins from amino acids transferred by the tRNA through continuous chain of amino acids based on information carried by messenger.
Above-mentioned cell organelles are just the representation of organelles and that there are so many other organelles that you can learn from other books.
Cell Division or Cell Duplication
Cell Division has two types, 1. Mitosis and 2. Meiosis. Mitosis involves restoration of damaged cells during infection on bodies through the production of body cells. That is to say that Nucleus and chromosomes of a diploid cell gets separated into two parts at the beginning. Then that cell divides into two cells and forms two new cells. This process is called mitosis. At this stage, replicated and replicating cells have same number of chromosomes. Diploid refers to the chromosomal pair.
Meiosis occurs in the sexually reproducing organisms. Cell division process involves production of four cells of any of reproduction cells or gamete from the diploid cell. There are two processes called the first phase and the second phase of meiosis. In the first phase, two new cells are formed. Their chromosomal numbers are the same as the initial chromosomal numbers of the diploid cell.
In the second phase, the two new cells again undergo division to form four new cells at the end. In male, the news cells formed from meiosis are sperms and egg in female. Initially, these cells are formed from diploid cells and yet they have half the number of chromosomes than the diploid cells. The main factor behind the formation of two new cells in mitosis and four new cells in meiosis is that the two chromatids of the part of chromosome do not undergo division during mitosis while the two chromatids of the part of the chromosome does undergo division during meiosis. More details are shown in the second book of the introductory to biology.
Genetic Theory
Secondly, in order to talk about gene, we have to talk about Mendel and his idea of gene, chromosome theory, DNA theory and gene.
As mentioned in the second chapter, one of the main properties of life is the ability to reproduce. However, organisms have to arise from same type. For example, pine tree will only grow from pine tree and rhinoceros will only be born from rhinoceros. And again, the offspring are more similar to their parents than far off same species organisms. As shown in chapter 2, the nature of passing of traits from one generation to another generation is called descent with modification.
Although many similar traits are passed down from parent to offspring yet there can be so much differences from all round from their parent. This is called variation. The inheritance nature and variation are known to human for thousands of years earlier and that they are used in producing heredity of animals and plants. But the mechanism of these two have been started to understand from the development of genetics in the 20th century.
Mendelian Gene Theory
Mendel brought an experimental and quantitative approach to genetics and also had he established the basic principes of heredity. He was born in 1822 to a German family in Austria. (Fig 14) He studied philosophy, science and mathematics in school and later became a monk in a Christian monastery. He studied mathematics and plant biology and other studies at University of Vienna.
In around 1857, Mendel began breeding garden peas in the abbey garden at the monastery in order to study on inheritance. Mendel chose to work with peas because they are available in many varieties. For example, one variety has purple flowers, while a contrasting variety has white flowers. Geneticists use the term character for a heritable feature, such as flower color, that varies among individuals. Each variant for a character, such as purple or whit color for flowers, is called a trait.