11.2.1. Gene or point mutation

Gene or point mutation

The gene mutations are those that alter the sequence of nucleotides of a single gene, so also called point. They can be produced by:

Base pair substitution: For example, instead of a thymine nucleotide there is a cytosine nucleotide.
Loss of nucleotides.
Insertion of new nucleotides.
Nucleotide inversion.
Translocation of complementary nucleotide pairs.

See page for author [Public domain], via Wikimedia Commons

Substitution of bases

They are produced when one nitrogen base changes in one position for another (it is the nitrogenous bases that distinguish the nucleotides of a chain). They account for about 20% of gene mutations. They can be of two types:

Transitions When a puric base is substituted for another puric one (adenine for guanine and vice versa) or a pyrimidine for another pyrimidine (cytosine for thymine and vice versa).

Mutaciones génicas: transición y transversión

By Sara (Own work) [CC BY-SA 3.0], via Wikimedia Commons

Transversions. When a puric base is substituted for another pyrimidine, or vice versa.

These mutations only alter one triplet, and since the genetic code is degenerate, it may be that the new triplet encodes the same amino acid and that this mutation is silent and does not affect the individual. If the mutation creates a stop triplet it will generate a shorter protein. If it affects the stop codon, the synthesized protein will be longer, until another stop codon appears. If the mutation creates an amino acid other than the active center of the enzyme, the function of the protein will also be altered. If that protein improved the original, the individual would have an advantage over the rest of the population and could transmit it to their offspring.

Gene mutation affecting the pattern of lecture

The gene mutations affecting the reading frame are produced by insertions or deletions of nucleotides, but never three or multiples of three. They originate amino acid sequences different from the original ones or a termination codon, which prevents the protein from fulfilling its function.

When a nucleotide is added or lost, all the triplets change, which is why it is said that they cause a shift in the reading frame, creating a completely different protein.

These gene mutations are transmitted to all descendant cells of the cell in which the mutation occurred. If the mutation affects an intronic or other nonessential region of DNA, it would be a silent mutation. But if it is produced in an exonic (coding) region, the sequence of the gene will be altered, which will translate a different sequence of amino acids of a protein.

If the new amino acid is similar to the substituted one, it may be that the functionality of the protein is maintained, but if they are very different or affect the active center of the protein, the new protein will not have its biological function.

The effects of these mutations can be different:

Harmful, yet compatible with life, such as:
- Pituitary dwarfism: produced by a growth hormone mutation.
- Sickle cell anemia: a mutation in hemoglobin that causes it to lose its ability to carry oxygen.
- Albinism: they cannot synthesize melanin because a mutation prevents an enzyme from synthesizing it.

By The original uploader was Muntuwandi at English Wikipedia (Transferred from en.wikipedia to Commons.) [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

Beneficial. It is rare, but it may be that the new protein has better properties and can perform its function better, so that the individuals that have it will have adaptive advantages over the rest of the species, and natural selection will make this one prevail over the original, causing evolution.
Lethal. They cause the death of the organism that suffers it. For example, in mutations produced during embryonic development that cause many of the natural abortions.

The accumulation of mutations that occur throughout the life of an organism is related to the aging of its cells, and the appearance of certain types of cancer.

Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU)

Aragon. July 2020, question 8.

8. According to an article published in February 2020 in the journal Genome Biology and Evolution, a group of scientists has discovered in the remains of mammoths found on Wrangel Island, that these animals accumulated a high number of mutations, responsible for numerous diseases, some of them serious. Answer the following questions: (2 marks)

a) Define mutation. What consequences do they usually have for the individual? (0.4 points)
b) Briefly explain the types of point (or gene) mutations that you are aware of (0.8 points)
c) Suppose a mutation occurs in the DNA of a cell, what impact will it have on the transcribed mRNA? What about the protein encoded by the affected gene? Explain the answer (0.4 points)
d) Is there a difference if the mutation occurs in a somatic cell or in a germ cell? Reason for the answer. (0.4 points)

Aragon. June 2006, option A. Issue 1.

Short development topic (3 points): Gene or point mutations.

Cantabria, July 2019, option 1, question 4.

Explain why a DNA mutation consisting of a base substitution may have no apparent phenotypic effects. (Substitution: change from one base to a different one)

Fundamental ideas about gene or point mutations

The gene or point mutations can be of two types:

Base substitution mutations. A nucleotide with a nitrogenous base is exchanged for another with a different nitrogenous base, which causes the alteration of a single triplet of the gene. As the genetic code is degenerate, there are different triplets that can encode the same amino acid, so it is possible that the substitution of bases does not imply a change in the encoded amino acid. If this is not the case, one amino acid will be substituted for another or protein synthesis will be interrupted, so the synthesized protein will be different.
Nucleotide insertion or deletion (loss) mutations. When a nucleotide is inserted or lost, there is a change in the reading pattern, so that all the triplets that follow the site of the mutation are altered.

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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 » 11.2.1. Gene or point mutation Gene or point mutation The gene mutations are those that alter the sequence of nucleotides of a single gene, so also called point. They can be produced by: Base pair substitution: For example, instead of a thymine nucleotide there is a cytosine nucleotide. Loss of nucleotides. Insertion of new nucleotides. Nucleotide inversion. Translocation of complementary nucleotide pairs. See page for author [Public domain], via Wikimedia Commons Substitution of bases They are produced when one nitrogen base changes in one position for another (it is the nitrogenous bases that distinguish the nucleotides of a chain). They account for about 20% of gene mutations. They can be of two types: Transitions When a puric base is substituted for another puric one (adenine for guanine and vice versa) or a pyrimidine for another pyrimidine (cytosine for thymine and vice versa). By Sara (Own work) [CC BY-SA 3.0], via Wikimedia Commons Transversions. When a puric base is substituted for another pyrimidine, or vice versa. These mutations only alter one triplet, and since the genetic code is degenerate, it may be that the new triplet encodes the same amino acid and that this mutation is *silent* and does not affect the individual. If the mutation creates a stop triplet it will generate a shorter protein. If it affects the stop codon, the synthesized protein will be longer, until another stop codon appears. If the mutation creates an amino acid other than the active center of the enzyme, the function of the protein will also be altered. If that protein improved the original, the individual would have an advantage over the rest of the population and could transmit it to their offspring. Gene mutation affecting the pattern of lecture The gene mutations affecting the reading frame are produced by insertions or deletions of nucleotides, but never three or multiples of three. They originate amino acid sequences different from the original ones or a termination codon, which prevents the protein from fulfilling its function. When a nucleotide is added or lost, all the triplets change, which is why it is said that they cause a shift in the reading frame, creating a completely different protein. These gene mutations are transmitted to all descendant cells of the cell in which the mutation occurred. If the mutation affects an intronic or other nonessential region of DNA, it would be a silent mutation. But if it is produced in an exonic (coding) region, the sequence of the gene will be altered, which will translate a different sequence of amino acids of a protein. If the new amino acid is similar to the substituted one, it may be that the functionality of the protein is maintained, but if they are very different or affect the active center of the protein, the new protein will not have its biological function. The effects of these mutations can be different: Harmful, yet compatible with life, such as: Pituitary dwarfism: produced by a growth hormone mutation. Sickle cell anemia: a mutation in hemoglobin that causes it to lose its ability to carry oxygen. Albinism: they cannot synthesize melanin because a mutation prevents an enzyme from synthesizing it. By The original uploader was Muntuwandi at English Wikipedia (Transferred from en.wikipedia to Commons.) [GFDL or CC-BY-SA-3.0], via Wikimedia Commons Beneficial. It is rare, but it may be that the new protein has better properties and can perform its function better, so that the individuals that have it will have adaptive advantages over the rest of the species, and natural selection will make this one prevail over the original, causing evolution. Lethal. They cause the death of the organism that suffers it. For example, in mutations produced during embryonic development that cause many of the natural abortions. The accumulation of mutations that occur throughout the life of an organism is related to the aging of its cells, and the appearance of certain types of cancer. Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU) Aragon. July 2020, question 8. 8. According to an article published in February 2020 in the journal Genome Biology and Evolution, a group of scientists has discovered in the remains of mammoths found on Wrangel Island, that these animals accumulated a high number of mutations, responsible for numerous diseases, some of them serious. Answer the following questions: (2 marks) a) Define mutation. What consequences do they usually have for the individual? (0.4 points) b) Briefly explain the types of point (or gene) mutations that you are aware of (0.8 points) c) Suppose a mutation occurs in the DNA of a cell, what impact will it have on the transcribed mRNA? What about the protein encoded by the affected gene? Explain the answer (0.4 points) d) Is there a difference if the mutation occurs in a somatic cell or in a germ cell? Reason for the answer. (0.4 points) Aragon. June 2006, option A. Issue 1. Short development topic (3 points): Gene or point mutations. Cantabria, July 2019, option 1, question 4. Explain why a DNA mutation consisting of a base substitution may have no apparent phenotypic effects. (Substitution: change from one base to a different one) Fundamental ideas about gene or point mutations The gene or point mutations can be of two types: Base substitution mutations. A nucleotide with a nitrogenous base is exchanged for another with a different nitrogenous base, which causes the alteration of a single triplet of the gene. As the genetic code is degenerate, there are different triplets that can encode the same amino acid, so it is possible that the substitution of bases does not imply a change in the encoded amino acid. If this is not the case, one amino acid will be substituted for another or protein synthesis will be interrupted, so the synthesized protein will be different. Nucleotide insertion or deletion (loss) mutations. When a nucleotide is inserted or lost, there is a change in the reading pattern, so that all the triplets that follow the site of the mutation are altered. 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). You can make any suggestion, question, comment, ..., in our forum 2º Bachillerato Biología - Foro de biologia-geologia.com
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Gene or point mutation

Substitution of bases

Gene mutation affecting the pattern of lecture