10.2.5.1. Replication in prokaryotes

DNA replication in prokaryotes

Initiation.
Elongation (formation of new strands).
- Synthesis of the leading strand.
- Synthesis of the delayed strand.
Termination.

Initiation

The replication begins a sequence of nucleotides in the DNA called origin of replication, oriC or initiation point, which acts as an initiation signal. This sequence is different depending on the species, but it has abundant thymine (T) and adenine (A). The T and A are linked by two hydrogen bonds, instead of three, like the C and G, so these bonds will be weaker and easier to break.

The following proteins are involved in the initiation of replication:

Helicasas. They are enzymes that recognize the nucleotide sequence origin of replication and break hydrogen bonds between complementary nitrogenous bases. They are responsible for opening the double helix so that the chains can serve as a mold for the new chains.

Topoisomerases. The unwinding of the double helix creates stresses between the two strands, and the topoisomerases are responsible for cutting the strands to release the supercoiling stresses. Cutting a (the topoisomerases) or both chains (the topoisomerase II or gyrase) of DNA, and when there are no such tensions, ligases the spliced again.

SSB proteins (Single Strand Binding-DNA). They are the stabilizing proteins that bind to each strand of DNA separated by the helicase so that they do not rejoin. Thus, they allow the correct passage of DNA polymerase , preventing complementary strands from joining before the nucleotides of the new strand that is being formed are added.
A helicase works in each direction, so this process is bidirectional. The two replication forks that have been created form the replication bubbles or eyes.

As DNA polymerase needs to have a primer to which nucleotides can be added, an RNA polymerase must first intervene that synthesizes a small fragment of about ten nucleotides of RNA that serves as a primer. To this RNA polymerase it is called primase, and a fragment of RNA that serves as a primer, first.

Replicación del ADN

By LadyofHats translated by Miguelsierra (translate it myself) [Public domain], via Wikimedia Commons

Elongation (formation of new strands)

The DNA polymerases will be responsible for initiating the synthesis of complementary daughter strands.

In each replication fork, the leading strand and delayed grow differently:

Synthesis of the leading strand

This chain is complementary to the chain 3'→5'. After the RNA polymerase has synthesized the first, primer RNA, DNA polymerase III, it begins to synthesize the new strand in the 5'→3' direction. The energy needed for this process is provided by nucleotides, which lose one of their phosphate groups.

This new chain is of continuous growth, since the helicase does not stop.

Synthesis of the delayed strand

In the other complementary strand, the DNA polymerase should read the strand in the 5'→ 3' sense, adding nucleotides to the new strand in the 3'→5' sense, which is not possible.

This new chain is of discontinuous growth, from separated DNA fragments. It is called a delayed chain or strand because its synthesis is slower than that of the leading strand.

Synthesis of this strand begins when RNA primase synthesizes about 40 nucleotides of RNA, the primer RNA, at a point that is about 1000 nucleotides away from the initiation signal.

The DNA polymerase III binds in a 5'→3', about 1000 or 2000 nucleotides of DNA, forming an Okazaki fragment. This process is repeated as the two chains that serve as a mold separate.

By César Benito Jiménez [CC BY-SA 2.5 es or CC BY-SA 2.5 es], via Wikimedia Commons

Afterwards, DNA polymerase I, due to its exonuclease function, eliminates the primer RNAs, and later, due to its polymerase function, fills the gaps occupied by the ribonucleotides with DNA nucleotides.

Finally, DNA-ligase joins the different Okazaki fragments with a phosphodiester bond.

The DNA strands that serve as templates are also called parental DNA.

By César Benito Jiménez [CC BY-SA 2.5 es or CC BY-SA 2.5 es], via Wikimedia Commons

Termination

The elongation is continued until the DNA is completely replicated. As the growth of the chains is bidirectional, one of the new strands has been synthesized continuously and the other discontinuously, using the Okazaki fragments. The two replication forks will join in a place diametrically opposite to the origin of replication of the bacterial chromosome.

The DNA polymerase I remove the last primer, and the fragments are joined by DNA ligase. Thus, two strands of DNA are obtained, without RNA, and identical to the parental DNA molecules.

Animation: DNA replication.

Animation: The replication process.

Fundamental insights on DNA replication in prokaryotes

DNA replication in prokaryotes

Initiation.
- It begins in the DNA sequence called the origin of replication.
- Enzymes involved:
  - Helicases.
  - Topoisomerases.
  - Stabilizing proteins SSB.
- Bidirectional replication. Replication forks are formed.
- The RNA polymerase (primase) synthesized a 10 nucleotide RNA which serve as primer (PRIMER).
Elongation (formation of new strands).
- Synthesis of the leading strand.
  - It is complementary to the chain 3'→5'.
  - The DNA polymerase III, begins to synthesize the new chain in the 5'→ 3', after the RNA polymerase is synthesized first, RNA primer.
  - Continuous growth.
- Synthesis of the delayed strand.
  - Discontinuous growth, slower than the leading chain.
  - The primase synthesizes RNA primer, and the DNA polimesa III nucleotide added in the 5'→3' forming an Okazaki fragment.
  - The DNA polymerase I removes the RNA primer and complete the gaps with nucleotides of DNA.
  - The DNA ligase joins a phosphodiester bond different Okazaki fragments.
Termination.
- The RNA polymerase I removes the last primer and the fragments are joined by DNA ligase.

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Skip navigation Biology 2nd Baccalaureate Biology 2nd Bac. 1. Bioelements and biomolecules. Water and mineral salts 1.1. Chemical bonds in biology 1.1.1. Intramolecular bonds 1.1.1.1. Covalent bond 1.1.1.2. Ionic bond 1.1.2. Intermolecular bonds 1.1.2.1. Van der Waals forces 1.1.2.2. Hydrogen bonds 1.2. The chemical basis of life: inorganic and organic components 1.2.1. Primary bioelements 1.2.2. Secondary bioelements 1.2.3. Trace elements 1.3. The immediate principles or biomolecules 1.3.1. Water 1.3.1.1. Chemical structure of water 1.3.1.2. Properties and functions of water 1.3.2. Mineral salts 1.3.2.1. Functions of salts in solution 1.3.2.2. Colloidal solutions and dispersions 1.3.2.3. Properties of colloidal dispersions 1.3.2.4. Diffusion, osmosis and dialysis 1.3.2.4.1. Diffusion 1.3.2.4.2. Osmosis 1.3.2.4.3. Dialysis 1.4. Bibliography 2. Glucides 2.1. Glucid concept 2.2. Classification of carbohydrates 2.3. Monosaccharides 2.3.1. Trioses 2.3.1.1. Spatial isomerism or stereoisomerism 2.3.2. Tetroses 2.3.3. Pentoses 2.3.3.1. Monosaccharide cyclization 2.3.4. Hexoses 2.4. The N-glucosidic and O-glucosidic bonds 2.4.1. Substances derived from monosaccharides 2.5. Disaccharides 2.6. Polysaccharides 2.6.1. Homopolysaccharides 2.6.1.1. Reserve homopolysaccharides 2.6.1.2. Structural homopolysaccharides 2.6.2. Heteropolysaccharides 2.6.3. Heterosides 2.7. General functions of glucides 2.8. Bibliography 3. Lipids 3.1. Lipid concept 3.2. Classification of lipids 3.2.1. Fatty acids 3.2.1.1. Saturated and unsaturated fatty acids 3.2.1.2. Chemical properties of fatty acids 3.2.1.3. Physical properties of fatty acids 3.2.1.4. Fatty Acid Functions 3.2.2. Saponifiable lipids or with fatty acids 3.2.2.1. Simple lipids 3.2.2.1.1. Acylglycerides 3.2.2.1.2. Cerides 3.2.2.2. Complex lipids 3.2.2.2.1. Phospholipids 3.2.2.2.2. Glycolipids 3.2.3. Unsaponifiable lipids or without fatty acids 3.3. Lipid functions 3.4. Bibliography 4. Proteins 4.1. Introduction to proteins 4.2. Amino acids 4.2.1. Classification of amino acids 4.2.2. Properties of amino acids 4.3. The peptide bond 4.4. Protein 4.4.1. Protein structure 4.4.1.1. Primary structure of proteins 4.4.1.2. Secondary structure of proteins 4.4.1.3. Tertiary structure of proteins 4.4.1.4. Quaternary structure of proteins 4.4.2. Protein properties 4.4.3. Classification of proteins 4.4.3.1. Holoproteins 4.4.3.2. Heteroproteins 4.4.4. Protein functions 4.5. Enzymes 4.5.1. Structure of enzymes 4.5.2. The active center of enzymes 4.5.3. General Mechanism of Enzyme Catalysis 4.5.4. Regulation of enzyme activity 4.5.5. Allosteric enzymes 4.5.6. Nomenclature and classification of enzymes 4.6. The vitamins 4.6.1. Fat-soluble vitamins 4.6.2. Water soluble vitamins 4.7. Bibliography 5. Nucleotides and nucleic acids 5.1. The chemical composition of nucleic acids 5.1.1. Components of nucleic acids 5.1.2. Concept, types and functions of nucleic acids 5.1.3. Nucleosides 5.1.4. Nucleotides 5.1.4.1. Nucleotide functions 5.1.5. Nucleic acids 5.2. Deoxyribonucleic acid (DNA) 5.2.1. DNA structure 5.2.1.1. Primary structure of DNA 5.2.1.2. Secondary structure of DNA 5.2.1.3. Tertiary structure of DNA 5.2.1.3.1. Tertiary structure of DNA in prokaryotes 5.2.1.3.2. Tertiary structure of DNA in eukaryotes 5.2.1.4. Quaternary structure of DNA 5.2.2. DNA types 5.2.3. Genetic material: chromatin and chromosomes 5.2.3.1. Karyotype and karyogram 5.3. Ribonucleic acid (RNA) 5.3.1. RNA types 5.3.1.1. Transfer RNA 5.3.1.2. Messenger RNA 5.3.1.3. Ribosomal RNA 5.3.1.4. Nucleolar RNA 5.3.1.5. Small nuclear RNA 5.3.2. Functions of ribonucleic acids 5.4. Bibliography 6. Cell morphology 6.1. Cell concept 6.1.1. Cell history 6.1.2. Cell theory 6.2. Levels of cellular organization 6.2.1. General characteristics of cells 6.2.2. Prokaryotic cells 6.2.2.1. Prokaryotic cell morphology 6.2.2.2. Structure of prokaryotes 6.2.2.2.1. Bacterial capsule 6.2.2.2.2. Bacterial wall 6.2.2.2.3. Plasma membrane 6.2.2.2.4. Cytoplasm-Ribosomes-Inclusions 6.2.2.2.5. Bacterial DNA 6.2.2.2.6. Bacterial appendages 6.2.2.3. Bacteria Physiology 6.2.3. Eukaryotic cells 6.2.3.1. Animal and plant cell 6.2.3.1.1. Animal eukaryotic cell 6.2.3.1.2. Plant eukaryotic cell 6.2.3.2. Cell Evolution: Endosymbiont Theory 6.3. Size, shape and quantity 6.4. The plasma membrane 6.4.1. Chemical composition of the membrane 6.4.2. The structure of the membrane. The fluid mosaic model 6.4.3. Functions of the plasma membrane 6.4.4. Transport across the membrane 6.4.4.1. Small molecule transport 6.4.4.2. Macromolecule transport 6.4.5. Plasma membrane differentiations 6.5. The cell wall of plant cells 6.5.1. Chemical composition of the cell wall 6.5.2. Cell wall structure 6.5.3. Cell wall differentiations 6.5.4. Cell wall functions 6.6. Extracellular matrix or glucocalyx 6.7. Cytosol or hyaloplasm 6.8. The cytoskeleton 6.8.1. Microfilaments or actin filaments 6.8.2. Intermediate filaments 6.8.3. Microtubules 6.9. Cell membrane and organelle systems 6.9.1. Membrane systems 6.9.1.1. The endoplasmic reticulum 6.9.1.2. Golgi apparatus 6.9.2. Cell organelles 6.9.2.1. Lysosomes 6.9.2.2. Peroxisomes 6.9.2.3. Vacuoles 6.9.2.4. Mitochondria 6.9.2.4.1. Functions of the mitochondria 6.9.2.5. Plastids 6.9.2.5.1. Chloroplasts 6.9.2.6. Ribosomes 6.9.2.7. Centrosome 6.9.2.8. Cilia and flagella 6.10. Cell motility 6.11. The cell nucleus 6.11.1. Characteristics of the cell nucleus 6.11.2. The interphase nucleus 6.11.3. The mitotic nucleus or nucleus in division 6.12. Bibliography 7. Metabolism 7.1. Metabolism 7.1.1. Energetic Aspects of Cellular Chemical Reactions 7.2. Catabolism 7.2.1. Catabolism and obtaining energy 7.2.2. Carbohydrate catabolism 7.2.2.1. Glycolysis 7.2.2.2. Cellular respiration 7.2.2.2.1. Oxidative decarboxylation 7.2.2.2.2. Krebs cycle 7.2.2.2.3. Electron transport chain 7.2.2.2.4. Energy balance of cellular respiration 7.2.2.3. Fermentations 7.2.2.3.1. Alcoholic or ethyl fermentation 7.2.2.3.2. Lactic fermentation 7.2.2.3.3. Other types of fermentations 7.3. Anabolism 7.3.1. Autotrophic anabolism 7.3.2. Photosynthesis 7.3.2.1. Photochemical or light phase 7.3.2.1.1. Photosystems 7.3.2.1.2. Photophosphorylation 7.3.2.1.2.1. Non cyclic photophosphorylation 7.3.2.1.2.2. Cyclic photophosphorylation 7.3.2.2. Biosynthetic or dark phase 7.3.2.3. Factors influencing photosynthesis 7.3.2.4. Products of photosynthesis 7.3.3. Chemosynthesis 7.4. Bibliography 8. Cell reproduction 8.1. The cell cycle 8.1.1. Interphase 8.1.2. Cellular division 8.2. Cellular division 8.2.1. Mitosis 8.2.1.1. Prophase 8.2.1.2. Metaphase 8.2.1.3. Anaphase 8.2.1.4. Telophase 8.2.1.5. Cytokinesis 8.2.1.6. More on mitosis 8.2.2. Meiosis 8.2.2.1. Meiosis I 8.2.2.2. Meiosis II 8.2.3. Meiosis and sexual reproduction 8.2.4. Meiosis and life cycle 8.2.5. Biological importance of meiosis 8.3. Differences and similarities between mitosis and meiosis 8.4. Bibliography 9. Classical genetics 9.1. Genetics basics 9.2. Mendelian genetics 9.2.1. The method 9.2.2. Mendel's Laws 9.2.2.1. Mendel's first law or principle of uniformity in the first generation 9.2.2.2. Mendel's second law or principle of segregation 9.2.2.2.1. Backcross and test crossover 9.2.2.3. Mendel's third law or principle of independent combination 9.3. Gene interaction 9.3.1. Gene interaction between allelic genes 9.3.2. Gene interaction between non-allelic genes that influence for the same trait 9.4. Chromosomal theory of heredity 9.5. Ligation and recombination 9.6. Complex mendelism 9.6.1. Multiple allelism 9.6.1.1. Lethal genes 9.6.2. Pleiotropy 9.6.3. Expressiveness and genetic penetrance 9.7. Sex-linked inheritance 9.7.1. Y-linked inheritance 9.7.2. X-linked inheritance 9.8. Heredity influenced by sex 9.9. Bibliography 10. Molecular genetics 10.1. DNA as hereditary material 10.2. DNA replication 10.2.1. The need for DNA replication 10.2.2. First hypotheses about DNA duplication 10.2.3. Meselson and Stahl experiment 10.2.4. The sense of growth of the new strands 10.2.5. Mechanism of DNA replication 10.2.5.1. Replication in prokaryotes 10.2.5.2. Replication in eukaryotes 10.2.6. Error correction 10.2.7. Enzymes involved in replication 10.3. Gene concept 10.4. "One gene-one enzyme" theory 10.5. Transcription 10.5.1. Mechanism of transcription 10.5.1.1. Transcription in prokaryotes 10.5.1.2. Eukaryotic transcription 10.6. Translation or protein biosynthesis 10.6.1. The genetic code 10.6.2. Mechanism of translation of RNA to proteins 10.6.2.1. Translation in eukaryotes 10.7. Regulation of gene expression 10.8. Bibliography 11. Genetics and evolution 11.1. Mutations 11.2. Types of mutations 11.2.1. Gene or point mutation 11.2.2. Chromosomal or structural mutation 11.2.3. Mutation at the genomic level 11.3. Causes of mutations 11.4. Evolutionary implications of mutations 11.5. Metabolic implications of mutations 11.6. Bibliography 12. Microbiology and biotechnology 12.1. Microbiology 12.2. Viruses 12.2.1. Viral morphology 12.2.2. Viral physiology 12.2.2.1. Lytic cycle 12.2.2.2. Lysogenic cycle 12.2.2.3. Cycles of viruses of special interest 12.2.2.3.1. Flu virus life cycle 12.2.2.3.2. Life cycle of the AIDS virus 12.3. Other acellular forms 12.3.1. Viroids 12.3.2. Prions 12.4. Biotechnology 12.5. Bibliography 13. Immunology 13.1. Infection concept 13.2. Defense mechanisms against infections 13.2.1. Nonspecific mechanisms 13.2.1.1. Primary barriers: external defenses 13.2.1.2. Secondary barriers: internal defenses 13.2.2. Specific mechanisms 13.3. Immunity and immune system 13.3.1. Components of the immune system 13.3.2. Concept and nature of antigens 13.4. The immune response 13.4.1. Humoral immune response: the antibodies 13.4.1.1. Antibody-producing cells: B lymphocytes 13.4.1.2. Antibodies 13.4.1.2.1. Types of antibodies 13.4.1.2.2. Antigen-antibody reaction 13.4.1.3. Immune memory: primary and secondary responses 13.4.2. Cellular immune response: T lymphocytes 13.5. Types of immunity 13.5.1. Natural immunity 13.5.2. Artificial immunity 13.6. Immune system disorders 13.6.1. Autoimmunity 13.6.2. Hypersensitivity 13.6.3. Immunodeficiency 13.6.4. Transplants and the phenomenon of rejections 13.7. Bibliography « Previous \| Next » 10.2.5.1. Replication in prokaryotes DNA replication in prokaryotes Initiation. Elongation (formation of new strands). Synthesis of the leading strand. Synthesis of the delayed strand. Termination. Initiation The replication begins a sequence of nucleotides in the DNA called origin of replication, oriC or initiation point, which acts as an initiation signal. This sequence is different depending on the species, but it has abundant thymine (T) and adenine (A). The T and A are linked by two hydrogen bonds, instead of three, like the C and G, so these bonds will be weaker and easier to break. The following proteins are involved in the initiation of replication: Helicasas. They are enzymes that recognize the nucleotide sequence origin of replication and break hydrogen bonds between complementary nitrogenous bases. They are responsible for opening the double helix so that the chains can serve as a mold for the new chains. Topoisomerases. The unwinding of the double helix creates stresses between the two strands, and the topoisomerases are responsible for cutting the strands to release the supercoiling stresses. Cutting a (the topoisomerases) or both chains (the topoisomerase II or *gyrase) of DNA, and when there are no such tensions, ligases the* spliced again. SSB proteins (Single Strand Binding-DNA). They are the stabilizing proteins that bind to each strand of DNA separated by the helicase so that they do not rejoin. Thus, they allow the correct passage of DNA polymerase , preventing complementary strands from joining before the nucleotides of the new strand that is being formed are added. A helicase works in each direction, so this process is bidirectional. The two replication forks that have been created form the replication bubbles or eyes. As DNA polymerase needs to have a primer to which nucleotides can be added, an RNA polymerase must first intervene that synthesizes a small fragment of about ten nucleotides of RNA that serves as a primer. To this RNA polymerase it is called primase, and a fragment of RNA that serves as a primer, first. By LadyofHats translated by Miguelsierra (translate it myself) [Public domain], via Wikimedia Commons Elongation (formation of new strands) The DNA polymerases will be responsible for initiating the synthesis of complementary daughter strands. In each replication fork, the leading strand and delayed grow differently: Synthesis of the leading strand This chain is complementary to the chain 3'→5'. After the RNA polymerase has synthesized the first, primer RNA, DNA polymerase III, it begins to synthesize the new strand in the 5'→3' direction. The energy needed for this process is provided by nucleotides, which lose one of their phosphate groups. This new chain is of continuous growth, since the helicase does not stop. Synthesis of the delayed strand In the other complementary strand, the DNA polymerase should read the strand in the 5'→ 3' sense, adding nucleotides to the new strand in the 3'→5' sense, which is not possible. This new chain is of discontinuous growth, from separated DNA fragments. It is called a delayed chain or strand because its synthesis is slower than that of the leading strand. Synthesis of this strand begins when RNA primase synthesizes about 40 nucleotides of RNA, the primer RNA, at a point that is about 1000 nucleotides away from the initiation signal. The DNA polymerase III binds in a 5'→3', about 1000 or 2000 nucleotides of DNA, forming an Okazaki fragment. This process is repeated as the two chains that serve as a mold separate. By César Benito Jiménez [CC BY-SA 2.5 es or CC BY-SA 2.5 es], via Wikimedia Commons Afterwards, DNA polymerase I, due to its exonuclease function, eliminates the primer RNAs, and later, due to its polymerase function, fills the gaps occupied by the ribonucleotides with DNA nucleotides. Finally, DNA-ligase joins the different Okazaki fragments with a phosphodiester bond. The DNA strands that serve as templates are also called parental DNA. By César Benito Jiménez [CC BY-SA 2.5 es or CC BY-SA 2.5 es], via Wikimedia Commons Termination The elongation is continued until the DNA is completely replicated. As the growth of the chains is bidirectional, one of the new strands has been synthesized continuously and the other discontinuously, using the Okazaki fragments. The two replication forks will join in a place diametrically opposite to the origin of replication of the bacterial chromosome. The DNA polymerase I remove the last primer, and the fragments are joined by DNA ligase. Thus, two strands of DNA are obtained, without RNA, and identical to the parental DNA molecules. Animation: DNA replication. Animation: DNA replication. Animation: The replication process. Fundamental insights on DNA replication in prokaryotes DNA replication in prokaryotes Initiation. It begins in the DNA sequence called the origin of replication. Enzymes involved: Helicases. Topoisomerases. Stabilizing proteins SSB. Bidirectional replication. Replication forks are formed. The RNA polymerase (primase) synthesized a 10 nucleotide RNA which serve as primer (PRIMER). Elongation (formation of new strands). Synthesis of the leading strand. It is complementary to the chain 3'→5'. The *DNA polymerase III, begins to synthesize the new chain in the 5'→ 3', after the RNA polymerase* is synthesized first, RNA primer. Continuous growth. Synthesis of the delayed strand. Discontinuous growth, slower than the leading chain. The primase synthesizes RNA primer, and the DNA polimesa III nucleotide added in the 5'→3' forming an Okazaki fragment. The DNA polymerase I removes the RNA primer and complete the gaps with nucleotides of DNA. The DNA ligase joins a phosphodiester bond different Okazaki fragments. Termination. The RNA polymerase I removes the last primer and the fragments are joined by DNA ligase. Licensed under the Creative Commons Attribution Share Alike License 4.0 « Previous \| Next » These pages are semi-automatically translated from the web Biology 2nd Baccalaureate. Biología de 2º de Bachillerato (biologia-geologia.com). 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