introduction to biology

Biology is the scientific study of life, Biologists ask questions such as

How does a single cell develop into an organism?

How does the human mind work?

How do living things interact in communities?

different levels of biological organizations 

as we all may know we can study life at different level, however, different levels of biological organizations are as follow;

The biosphere, Ecosystems, Communities, Populations, Organisms, Tissues, Cells, Organelles, molecules, atoms.

figure 1. Levels of Biological Organization

cell

The cell is life’s fundamental unit of structure and function. Some organisms, such as amoebas and most bacteria, are single cells. Other organisms, including plants and animals, are multicellular. Instead of a single cell performing all the functions of life, a multicellular organism has a division of labor among specialized cells. A human body consists of trillions of microscopic cells of many different kinds, such as muscle cells and nerve cells, which are organized into the various specialized tissues.

All cells, Are enclosed by a membrane and Use DNA/RNA as their genetic information.

Eukaryotic cell

A eukaryotic cell has membrane-enclosed organelles, the largest of which is usually the nucleus which contains the cell’s DNA. The other organelles are located in the cytoplasm, the entire region between the nucleus and outer membrane of the cell.

Prokaryotic cells

a prokaryotic cell is simpler and usually smaller, and does not contain a nucleus or other membrane-enclosed organelles. In a prokaryotic cell, the DNA is not separated from the rest of the cell by enclosure in a membrane-bounded nucleus.

figure 2. Eukaryotic and prokaryotic cells

Heritable information of DNA keeps our life going

  • Chromosomes contain most of a cell’s genetic material in the form of DNA (deoxyribonucleic acid). Each chromosome has one long DNA molecule with hundreds or thousands of gene, DNA is the substance of genes. Genes encode information for building proteins.
  • Genes are the units of inheritance that transmit information from parents to offspring.
  • The ability of cells to divide is the basis of all reproduction, growth, and repair of multicellular organisms. DNA controls the development and maintenance of organisms.

figure 3. chromosome, DNA, Genes

DNA structure

Each DNA molecule is made up of two long chains arranged in a double helix. Each link of a chain is one of four kinds of chemical building blocks called nucleotides and nicknamed A (Adenine), G (Guanine), C (Cytosine) and T (Thymine). Historically, On February 28, 1953, Cambridge University scientists James D. Watson and Francis H.C. Crick announce that they have determined the double-helix structure of DNA, the molecule containing human genes.

figure 4. DNA double helix and single strand structure

Figure 5. Watson and Crick, double helix DNA model

DNA function

Genes control protein production indirectly. DNA is transcribed into RNA then translated into a protein and Gene expression is the process of converting information from gene to cellular product.

figure 6. DNA transcription and translation

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