Organisation of genetic material

Organisation of genetic material

Eukaryotic cells with nuclei measuring only a few micrometres may contain nearly 2 metres of DNA, coiled multiple times.

Biology

Keywords

genetic material, DNA, deoxyribonucleic acid, double helix, chromosome, adenine, thymine, cytosine, guanine, reproduction, purine, pyrimidine, hydrogen bond, histone protein, nucleosome, human, biochemistry, biology

Related items

Scenes

Fine structure of chromosomes

  • DNA
  • sugar-phosphate backbone
  • nucleobases
  • sugar (deoxyribose)
  • phosphate
  • adenine
  • thymine
  • cytosine
  • guanine
  • beads-on-a-string structure
  • histone core (8 histone protein molecules)
  • H1 histone
  • coil structure
  • loop structure
  • protein skeleton
  • chromosome

Structure of DNA

  • sugar-phosphate backbone - A chain of alternating sugar (deoxyribose) and phosphate molecules.
  • nucleobases - DNA contains 4 types of nucleobases: adenine, thymine, guanine and cytosine. Adenine and guanine are larger purine bases, while thymine and cytosine are smaller pyrimidines.
  • sugar (deoxyribose) - DNA contains a five-atom sugar molecule called deoxyribose. Hence the name deoxyribonucleic acid.
  • phosphate - They are found between deoxyribose molecules.
  • adenine - Adenine and guanine are purines. Adenine attaches to thymine by two hydrogen bonds.
  • thymine - Thymine and cytosine are pyrimidines.
  • cytosine - Cytosine and thymine are pyrimidines.
  • guanine - Guanine and adenine are purines. Guanine attaches to cytosine by three hydrogen bonds.

Narration

DNA molecules are double helix-shaped molecules in which nucleobases are attached to a sugar-phosphate backbone. The order of the nucleobases encodes the amino acid sequence of proteins. Thus DNA determines the characteristics of living organisms.

In the sugar-phosphate backbone, deoxyribose and phosphate alternate. The nucleobases are classified into two types: purines and pyrimidines. Adenine and guanine are purines, thymine and cytosine are pyrimidines. According to the rule of base pairing, there must be a thymine opposite an adenine and a cytosine opposite a guanine, that is, a larger purine is always paired with a smaller pyrimidine. Nucleobases are attached by hydrogen bonds. Adenine is bound to thymine by two hydrogen bonds, and guanine is bound to cytosine by three.

Eucaryotic cells with nuclei measuring only a few micrometres may contain several metres of DNA, which has to be packaged and organised in order to fit into the tiny nucleus without tangling, and to ensure that it can be divided appropriately during cell division.

The DNA molecule is wrapped onto clusters of histone proteine molecules to create nucleosomes. Eight histone molecules make up the core, with the DNA coiled around it twice. DNA is attached to the core by H1 histones. These histone cores form a structure similar to beads on a string.

This beads-on-a-string structure coils into a spiral-like solenoid structure with six nucleosomes in one section.

In the next stage of packaging, parts of the coil attach to a protein skeleton and form a characteristic loop structure.

The loop structure coils again to form the chromosome.

Human cells have 46 of these, with a total of nearly 2 metres of DNA. That is, each of the microscopic chromosomes contains 4 cm of DNA on average.

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Animal and plant cells, cellular organelles

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DNA

Carrier of genetic information in cells.

Meiosis

Our gametes are haploid cells produced from diploid cells by meiosis, a special type of cell division.

Mitosis

Mitosis is the process by which a eukaryotic cell divides into two cells and the number of chromosomes remains unchanged.

Purine (C₅H₄N₄)

A heterocyclic aromatic organic compound, its derivatives include guanine and adenine.

Pyrimidine (C₄H₄N₂)

A heterocyclic organic compound, its derivatives are thymine, cytosine and uracil.

2-deoxy-beta-D-ribose (C₅H₁₀O₄)

A component of DNA, it contains one less hydroxyl group than β-D-ribose.

Levels of biological organisation

This animation presents levels of biological organisation from the level of the individual organism to the level of cells.

Paramecium caudatum

Common ciliated eucaryotic unicellular organisms widespread in freshwaters.

Radioactivity

The process of the decay of unstable nuclei is called radioactivity.

Tardigrade

Tardigrades can survive in extreme environments, they can even stay alive in outer space.

Amoeba proteus

Widespread heterotrophic unicellular organisms with constantly changing shapes

Structure of proteins

The structure and arrangement of polypeptide chains affects the spatial structure of proteins.

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