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What is a cell?

Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. Cells also contain the body’s hereditary material and can make copies of themselves.

Cells have many parts, each with a different function. Some of these parts, called organelles, are specialized structures that perform certain tasks within the cell. Human cells contain the following major parts, listed in alphabetical order:

Cytoplasm (illustration)
Within cells, the cytoplasm is made up of a jelly-like fluid (called the cytosol) and other structures that surround the nucleus.
Cytoskeleton
The cytoskeleton is a network of long fibers that make up the cell’s structural framework. The cytoskeleton has several critical functions, including determining cell shape, participating in cell division, and allowing cells to move. It also provides a track-like system that directs the movement of organelles and other substances within cells.
Mitochondria (illustration)
Mitochondria are complex organelles that convert energy from food into a form that the cell can use. They have their own genetic material, separate from the DNA in the nucleus, and can make copies of themselves.
Nucleus (illustration)
The nucleus serves as the cell’s command center, sending directions to the cell to grow, mature, divide, or die. It also houses DNA (deoxyribonucleic acid), the cell’s hereditary material. The nucleus is surrounded by a membrane called the nuclear envelope, which protects the DNA and separates the nucleus from the rest of the cell.
Plasma membrane (illustration)
The plasma membrane is the outer lining of the cell. It separates the cell from its environment and allows materials to enter and leave the cell.

Source : https://ghr.nlm.nih.gov/primer/basics/cell

Atelier “Anglais scientifique” – DNA

Introduction

The genetic information carried in the molecule called DNA determines every inherited physical characteristic of every living thing. DNA—more formally known as deoxyribonucleic acid—is found inside almost every cell. It controls how the cell replicates and functions, and what traits are inherited from previous generations. DNA determines traits that can be seen—such as eye color in animals—as well as traits that are not visible, such as blood type. DNA is also found in some viruses (see virus).

DNA molecules consist of two strands of biochemical compounds called nucleotides linked together by chemical bonds (see molecule). Nucleotides are composed of three molecules: a phosphate, a sugar, and a nitrogen-containing base. In DNA, the sugar is deoxyribose, and the base is either adenine, guanine, cytosine, or thymine (see biochemistry, “DNA Carries Heredity”). Adenine and guanine (symbolized for convenience as A and G, respectively) are classified as purines; cytosine (C) and thymine (T) are pyrimidines.

Within each strand the nucleotides are connected to each other by covalent bonds linking the phosphate of one nucleotide with the sugar of the next (see inorganic chemistry). This forms a chain from which the bases protrude. The bases of one strand are linked to bases of the second strand by hydrogen bonds. This base pairing is very specific—because of their structures, adenine can only pair with thymine, and cytosine can only pair with guanine. Thus joined, the ladder-shaped DNA strands are coiled around each other, forming a spiral, or double helix. This configuration makes the DNA molecule very stable.

Within the cell, DNA and various proteins are organized into dense units called chromosomes. In prokaryotes—organisms such as bacteria whose cells lack a true nucleus—these float freely in the cell’s cytoplasm. In eukaryotes, chromosomes are located within the nucleus, though some DNA is found also in mitochondria and in chloroplasts (see genetics; living things, “Simple and Complex Cells”).

The History of DNA

DNA was first discovered in 1869, but its role in genetics was not clear until the 1940s. In 1953, scientists James Watson, Francis Crick, Maurice Wilkins, and Rosalind Franklin determined the double-helix structure of DNA, as well as its method of replication. Their work earned a Nobel prize in 1962 (see Franklin, Rosalind).

Source : Encyclopedia Britanica

The Discovery of the Molecular Structure of DNA – The Double Helix.
Source : http://www.nobelprize.org

Play the DNA – The Double Helix Game