Introduction and basic concepts
CARBOHYDRATES (or carbohydrates): these are sugars; they are tertiary compounds (consisting of only three elements: carbon, hydrogen and oxygen). They represent an energy reserve and are the starting point for the production of other organic compounds.
LIPIDS: are commonly called fats and are also reserve substances and are constituents of cellular structures.
PROTEINS: they are made up of amino acids; they contribute to the construction of structures of various organisms, hemoglobin, enzymes, hormones (they regulate the harmonious coordination between the different functions of the organisms), antibodies.
NUCLEIC ACIDS: they consist of a nitrogenous base (cytosine, timid, uracil, adenine and guanine), a sugar and phosphate groups.
THE CELL: the cell membrane has a thickness of 6-7 × 10 -10m; the diameter of a cell is about 15 mm while that of the nucleus is about 5 mm.
The characteristic elements of a cell are:
- Perinuclear membrane: delimits the nucleus;
- Nucleolus: it is a specialized part of the nucleus;
- Mitochondrion: it is the "energy center" of the cell;
- Peroxisomes: they are organelles specialized in oxidation reactions (they release H2O2) and are black in color because they contain a lot of iron;
- Ribosomes: they are contained in the endoplasmic reticulum and synthesize proteins;
- Endoplasmic reticulum: it is rough if it contains ribosomes and smooth if it does not. It has an internal space (lumen) in which the synthesized proteins accumulate;
- Golgi apparatus: consists of bladder systems. The proteins, through this apparatus, reach their destination without errors.
Image taken from www.progettogea.com
A daughter cell is always the same as a mother cell.
The human genome is the whole of the genetic heritage of an individual and consists of forty-six chromosomes (twenty-three pairs) on average consisting of seventy million base pairs, so the whole genome contains (46 × 70 000 000) 3 × 109 base pairs and each pair contributes approximately 6-7 × 10-10 m to the length.
If the DNA of each chromosome is unrolled and the forty-six molecules contained in the nucleus of a somatic cell are aligned, it reaches a length of 2 m (each chromosome is about four cm long). Considering, then, that a man has 10,000 billion cells, the total DNA reaches 20,000 million km (the distance between the sun and the moon is 200 million km)
A single chromosome is a macromolecule with a diameter of approximately 2 × 10-9 m and contains a molecule of DNA; the gene is a portion of the DNA (ie a portion of a chromosome) that contains a "complete and specific information for a certain property. Today" the whole human genome is known, ie the complete succession of the bases in the DNA is known, but only a very few portions of DNA have been given "an" identity: it is necessary to establish which portion of DNA corresponds to a certain property.
There are about thirty thousand genes but one gene can be expressed in different ways so this is indicative.
EXPRESSION: the information contained in a gene leads to the obtaining of a final product (protein synthesis).
TRANSCRIPTION: conversion of the information contained in a gene into a chain of messenger RNA by an enzymatic system; the messenger RNA passes from the nucleus to the cytoplasm in which the ribosomes are contained.
TRANSLATION: ribosomes synthesize the protein which is the product of genetic expression.
ENCODE: means to translate the message.
An enzymatic system, therefore, through the transcription process, converts the information carried by a gene into a chain of messenger RNA and the translation is started.
Replicating DNA means copying the part of DNA of interest to the messenger RNA.
The two main differences between DNA and RNA:
- Ribose is the sugar in RNA, while deoxyribose is in DNA;
- In DNA the nitrogenous bases are: adenine, guanine, thymine and cytosine; while in the RNA the uracil takes the place of the thymine.
Genes usually contain one or more DNA segments within them, which do not code for the protein; these fragments are called introns while the coding segments are called exons.
Exons represent the portion of the gene that can be expressed while introns are not expressed.
Under certain conditions, the gene is expressed without introns, but under other conditions, introns can be transformed into exons and, accordingly, expressed (i.e. they can code for the protein).
Depending on the various introns expressed, there are different protein products: a gene, therefore, can be expressed in different ways.
There is a functional similarity between the various products of the same gene; however, they have a different structure and for this reason they are used in different places.
The genetic information contained in each cell of an organism is the same. For example, the DNA of a liver cell (hepatocyte) and the DNA contained in a muscle cell (myocyte), are the same; to differentiate a hepatocyte from a myocyte is the different expression of the genes contained in the DNA. In general, some genes are expressed in a cell and in another cell, located in another part of the organism, others are expressed.
