2.3.1.1. Spatial isomerism or stereoisomerism

Spatial isomerism or stereoisomerism

The spatial isomerism or stereoisomerism is the existence of molecules with the same molecular formula but different spatial structure, so they have different properties.

Stereoisomerism occurs whenever there is an asymmetric carbon atom.

A carbon is asymmetric when it is attached to four different radicals.

All monosaccharides, except dihydroxyacetone, have asymmetric (chiral) carbons, attached to four different chemical radicals.

The isomers are compounds having the same chemical formula but different structure.

Stereoisomers that have the same chemical properties but different optical activity are called optical isomers. Optical isomers can be:

Enantiomers or enantiomorphs. One stereoisomer is the mirror image of the other, not superimposable.
Diastereoisomers. Those that are not mirror images of the other.

The number of optical isomers (stereoisomers) that a biomolecule has is equal to 2ⁿ, where "n" is the number of asymmetric carbons it has.

By convention, it is considered that belong to the D monosaccharides whose penultimate carbon (asymmetric carbon the farthest away from the functional group) has the group -OH to the right, and if L has left.

Most of the carbohydrates found in nature are of the D form.

For example, the second carbon atom in glyceraldehyde is asymmetric. The isomer with structure L is the non-superimposable mirror image (image in a mirror) of the isomer with structure D. Both are called enantiomers or enantiomorphs.

Two optical isomers are enantiomers or enantiomorphic when they are mirror images of each other. The position of the OHs on all asymmetric carbons varies.

Isomería especular

Placing the aldehyde group at the top and looking at that carbon, two spatial isomers or stereoisomers can be distinguished, which only differ in the spatial position of a radical -OH:

the D -gliceraldehído when the -OH is at the d ight .
the L-glyceraldehyde, when the -OH is at the left.

This rule applies to the rest of the monosaccharides.

When two monosaccharides differ only in the position of the hydroxyl group on a carbon, they are said to be epimers. For example, as we will see, D-erythrose is an epimer at carbon 2 of D-treose.

The epimers are stereoisomers wherein only varies the position of the group -OH of one of the asymmetric carbons.

The presence of asymmetric carbons gives these molecules the property of optical activity (or rotational power). When a beam of polarized light falls on them when they are in aqueous solution, a deviation of the plane of vibration of that beam occurs. They are distinguished:

Right-handed molecules, if they deviate to the right (like clockwise), and are represented by the sign (+). For example, since D-glyceraldehyde is dextrorotatory, it is called D - (+) glyceraldehyde.
Left-handed molecules, if they deviate to the left, and are symbolized by the sign (-).

The right-handed (+) form and the left-handed (-) form are called optical isomers. The angle of deviation of the light they produce is the same, although in the opposite direction. The enantiomorphic structures are thus optical isomers.

Whether a monosaccharide is dextrorotatory or left-handed is completely independent of whether it belongs to the D or L form.

The dihydroxyacetone is the only monosaccharide has no asymmetric carbon atom and, therefore, no optical activity.

The enantiomorphic structures differ from each other in the position of all the -OH radicals of the asymmetric carbons. They are the same substance, with the same properties, except in optical activity.

Optical activity and isomerism

A molecule is capable of deviating the plane of polarization of polarized light if it has at least one asymmetric carbon. Each molecule rotates the plane of polarization to the right or left:

They are said to be dextrogyras or (+) if they deviate the plane of polarization of light in a clockwise direction.
They are said to be left-handed or (-) if they deviate the polarization plane counterclockwise.

The presence of asymmetric carbons also determines that apparently the same molecules, with the same chemical formula, have different properties because their atoms have different spatial arrangements, and these molecules are called isomers.

When one isomer is the mirror image of another, they are said to be enantiomers or enantiomorphs, and they are called:

Form D when the -OH of the asymmetric carbon is to the right.
Form L when the -OH of the asymmetric carbon is on the left.

Fundamental Ideas on Asymmetric Carbon and Spatial Isomerism

An asymmetric carbon is that carbon that is attached to four different radicals to each other.

The existence of asymmetric carbons has an impact: the appearance of stereoisomers.

Stereoisomers differ only in the spatial arrangement of their atoms.

All trioses (except dihydroxyacetone) have an asymmetric carbon.

Asymmetric carbons cause the plane in which polarized light vibrates to rotate.

The optical isomers are those isomers having the same properties and differ only in that the plane of polarized light rotates in different direction.

Stereoisomeric compounds are enantiomers when they differ in the position of all -OH.

Stereoisomeric compounds are epimers when they differ in the position of a single -OH.

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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 » 2.3.1.1. Spatial isomerism or stereoisomerism Spatial isomerism or stereoisomerism The spatial isomerism or stereoisomerism is the existence of molecules with the same molecular formula but different spatial structure, so they have different properties. Stereoisomerism occurs whenever there is an asymmetric carbon atom. A carbon is asymmetric when it is attached to four different radicals. All monosaccharides, except dihydroxyacetone, have asymmetric (chiral) carbons, attached to four different chemical radicals. The isomers are compounds having the same chemical formula but different structure. Stereoisomers that have the same chemical properties but different optical activity are called optical isomers. Optical isomers can be: Enantiomers or enantiomorphs. One stereoisomer is the mirror image of the other, not superimposable. Diastereoisomers. Those that are not mirror images of the other. The number of optical isomers (stereoisomers) that a biomolecule has is equal to 2ⁿ, where "n" is the number of asymmetric carbons it has. By convention, it is considered that belong to the D monosaccharides whose penultimate carbon (asymmetric carbon the farthest away from the functional group) has the group -OH to the right, and if L has left. Most of the carbohydrates found in nature are of the D form. For example, the second carbon atom in glyceraldehyde is asymmetric. The isomer with structure L is the non-superimposable mirror image (image in a mirror) of the isomer with structure D. Both are called enantiomers or enantiomorphs. Two optical isomers are enantiomers or enantiomorphic when they are mirror images of each other. The position of the OHs on all asymmetric carbons varies. Placing the aldehyde group at the top and looking at that carbon, two spatial isomers or stereoisomers can be distinguished, which only differ in the spatial position of a radical -OH: the D -gliceraldehído when the -OH is at the d ight . the L-glyceraldehyde, when the -OH is at the left. This rule applies to the rest of the monosaccharides. When two monosaccharides differ only in the position of the hydroxyl group on a carbon, they are said to be epimers. For example, as we will see, D-erythrose is an epimer at carbon 2 of D-treose. The epimers are stereoisomers wherein only varies the position of the group -OH of one of the asymmetric carbons. The presence of asymmetric carbons gives these molecules the property of optical activity (or rotational power). When a beam of polarized light falls on them when they are in aqueous solution, a deviation of the plane of vibration of that beam occurs. They are distinguished: Right-handed molecules, if they deviate to the right (like clockwise), and are represented by the sign (+). For example, since D-glyceraldehyde is dextrorotatory, it is called D - (+) glyceraldehyde. Left-handed molecules, if they deviate to the left, and are symbolized by the sign (-). The right-handed (+) form and the left-handed (-) form are called optical isomers. The angle of deviation of the light they produce is the same, although in the opposite direction. The enantiomorphic structures are thus optical isomers. Whether a monosaccharide is dextrorotatory or left-handed is completely independent of whether it belongs to the D or L form. The dihydroxyacetone is the only monosaccharide has no asymmetric carbon atom and, therefore, no optical activity. The enantiomorphic structures differ from each other in the position of all the -OH radicals of the asymmetric carbons. They are the same substance, with the same properties, except in optical activity. Optical activity and isomerism A molecule is capable of deviating the plane of polarization of polarized light if it has at least one asymmetric carbon. Each molecule rotates the plane of polarization to the right or left: They are said to be dextrogyras or (+) if they deviate the plane of polarization of light in a clockwise direction. They are said to be left-handed or (-) if they deviate the polarization plane counterclockwise. The presence of asymmetric carbons also determines that apparently the same molecules, with the same chemical formula, have different properties because their atoms have different spatial arrangements, and these molecules are called isomers. When one isomer is the mirror image of another, they are said to be enantiomers or enantiomorphs, and they are called: Form D when the -OH of the asymmetric carbon is to the right. Form L when the -OH of the asymmetric carbon is on the left. Fundamental Ideas on Asymmetric Carbon and Spatial Isomerism An asymmetric carbon is that carbon that is attached to four different radicals to each other. The existence of asymmetric carbons has an impact: the appearance of stereoisomers. Stereoisomers differ only in the spatial arrangement of their atoms. All trioses (except dihydroxyacetone) have an asymmetric carbon. Asymmetric carbons cause the plane in which polarized light vibrates to rotate. The optical isomers are those isomers having the same properties and differ only in that the plane of polarized light rotates in different direction. Stereoisomeric compounds are enantiomers when they differ in the position of all -OH. Stereoisomeric compounds are epimers when they differ in the position of a single -OH. 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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Spatial isomerism or stereoisomerism