6.4.1. Chemical composition of the membrane

Chemical composition of the plasma membrane

The plasma membrane, in general, is made up of lipids, proteins and, to a lesser extent, carbohydrates.

By LadyofHats Mariana Ruiz, traduction Pilar Saenz [Public domain], via Wikimedia Commons

Lipids

They form the structure of the lipid bilayer. They include:

Phospholipids. Structural function. They are the fundamental components of the plasma membrane. They provide great fluidity to the membrane. They are arranged in a bilayer. Due to their amphipathic nature, on both sides they present a hydrophilic zone, the polar heads (glycerin or glycerol in phosphoglycerides), and a hydrophobic zone (fatty acids), which form the apolar tail, which is oriented towards the interior of the layer.

By Jpablo cad (Own work) [CC BY 3.0], via Wikimedia Commons

By Bensaccount [Public domain], via Wikimedia Commons

Glycolipids. They have an amphipathic character. They are involved in recognition and signaling processes between cells. They are very similar to phospholipids, but contain oligosaccharides. In animal cells they are usually derived from sphingolipids, while in plant and prokaryotic cells, glycolipids are derived from phosphoglycerides. They only appear on the outer side of the plasma membrane.
Sterols (among which is cholesterol). It makes the membrane lose flexibility and permeability, making the bilayer more stable. Sterols are present in the plasma membrane of eukaryotic cells, being more abundant in animal cells than in plant cells.

The lipids are not arranged in the same way in each of the two layers, so it has an asymmetrical arrangement .

As we have already said, the membrane is not a static structure, but the phospholipids have a certain movement, which gives the membrane fluidity.

The movements that lipids can perform are:

Rotational: the phospholipid rotates around its major axis. It is very frequent and largely responsible for the other two movements.
Lateral diffusion: it is the most frequent movement, the phospholipids can move laterally within the bilayer.
Flip-flop: flipase enzymes allow one lipid molecule to move to the other monolayer. It is the least frequent movement, because it is very unfavorable energetically.

By A09231315 (Own work) [CC BY-SA 3.0], via Wikimedia Commons

The fluidity of the membrane by having these movements allows it to repair itself (if it breaks), to fuse with any other membrane, or by endocytosis, to form a vesicle from the membrane.

What does the fluidity of the plasma membrane depend on?

The main factors that determine the fluidity of the plasma membrane are:

Temperature: the higher the temperature, the greater the fluidity in the membrane.
Nature of lipids: the presence of unsaturated and short-chain fatty acids makes the membrane more fluid.
Cholesterol. The presence of cholesterol reduces the mobility of phospholipids, thereby reducing the fluidity and permeability of the membrane.

Proteins

They provide the membrane with its specific functions and are characteristic of each species. Like lipids, they also have lateral diffusion movements, which gives the membrane greater fluidity. Most proteins are globular in structure. There are two kinds:

Peripheral or extrinsic. They are found on one side or the other of the lipid bilayer, loosely linked by non-covalent bonds. They are soluble.
Integral or intrinsic. Embedded in the lipid bilayer, they cross the membrane one or more times, poking out on one or both sides (transmembrane proteins); or by means of covalent bonds with a lipid or a carbohydrate of the membrane. Isolating it requires the rupture of the bilayer.

Membrane proteins are involved in the exchange of substances.

Carbohydrates

Located on the outer side of the membrane, they intervene in cell recognition functions. They are attached to lipids or proteins forming glycolipids and glycoproteins.

Carbohydrates constitute the glucocalyx, a secretion membrane in animal cells made up of two layers: one, next to the plasma membrane with an amorphous texture, and the other, external, with a fibrous appearance and variable thickness.

Each face of the plasma membrane has a different chemical composition, which is why it is said that the membranes are asymmetric, being able to distinguish the inner and outer face of the membrane by its composition.

Game: Cell defense: the plasma membrane.

CÉLULA from jusega Serrano Galán

Fundamental ideas about the composition of the plasma membrane

Chemical composition of the plasma membrane:

Lipids:
- Phospholipids.
  - Arranged in bilayer for its amphipathic character.
  - Fundamental component of the membrane.
- Glycolipids.
  - Recognition of signals between cells.
  - They only appear on the outer side of the plasma membrane.
- Sterols
  - It gives stability to the lipid bilayer.
Proteins:
- Two types:
  - Peripheral or extrinsic.
  - Integral or intrinsic.
- They are involved in the exchange of substances.
Carbohydrates.
- On the outer side of the plasma membrane.

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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 » 6.4.1. Chemical composition of the membrane Chemical composition of the plasma membrane The plasma membrane, in general, is made up of lipids, proteins and, to a lesser extent, carbohydrates. By LadyofHats Mariana Ruiz, traduction Pilar Saenz [Public domain], via Wikimedia Commons Lipids They form the structure of the lipid bilayer. They include: Phospholipids. Structural function. They are the fundamental components of the plasma membrane. They provide great fluidity to the membrane. They are arranged in a bilayer. Due to their amphipathic nature, on both sides they present a hydrophilic zone, the polar heads (glycerin or glycerol in phosphoglycerides), and a hydrophobic zone (fatty acids), which form the apolar tail, which is oriented towards the interior of the layer. By Jpablo cad (Own work) [CC BY 3.0], via Wikimedia Commons By Bensaccount [Public domain], via Wikimedia Commons Glycolipids. They have an amphipathic character. They are involved in recognition and signaling processes between cells. They are very similar to phospholipids, but contain oligosaccharides. In animal cells they are usually derived from sphingolipids, while in plant and prokaryotic cells, glycolipids are derived from phosphoglycerides. They only appear on the outer side of the plasma membrane. Sterols (among which is cholesterol). It makes the membrane lose flexibility and permeability, making the bilayer more stable. Sterols are present in the plasma membrane of eukaryotic cells, being more abundant in animal cells than in plant cells. The lipids are not arranged in the same way in each of the two layers, so it has an asymmetrical arrangement . As we have already said, the membrane is not a static structure, but the phospholipids have a certain movement, which gives the membrane fluidity. The movements that lipids can perform are: Rotational: the phospholipid rotates around its major axis. It is very frequent and largely responsible for the other two movements. Lateral diffusion: it is the most frequent movement, the phospholipids can move laterally within the bilayer. Flip-flop: flipase enzymes allow one lipid molecule to move to the other monolayer. It is the least frequent movement, because it is very unfavorable energetically. By A09231315 (Own work) [CC BY-SA 3.0], via Wikimedia Commons The fluidity of the membrane by having these movements allows it to repair itself (if it breaks), to fuse with any other membrane, or by endocytosis, to form a vesicle from the membrane. What does the fluidity of the plasma membrane depend on? The main factors that determine the fluidity of the plasma membrane are: Temperature: the higher the temperature, the greater the fluidity in the membrane. Nature of lipids: the presence of unsaturated and short-chain fatty acids makes the membrane more fluid. Cholesterol. The presence of cholesterol reduces the mobility of phospholipids, thereby reducing the fluidity and permeability of the membrane. Proteins They provide the membrane with its specific functions and are characteristic of each species. Like lipids, they also have lateral diffusion movements, which gives the membrane greater fluidity. Most proteins are globular in structure. There are two kinds: Peripheral or extrinsic. They are found on one side or the other of the lipid bilayer, loosely linked by non-covalent bonds. They are soluble. Integral or intrinsic. Embedded in the lipid bilayer, they cross the membrane one or more times, poking out on one or both sides (transmembrane proteins); or by means of covalent bonds with a lipid or a carbohydrate of the membrane. Isolating it requires the rupture of the bilayer. Membrane proteins are involved in the exchange of substances. Carbohydrates Located on the outer side of the membrane, they intervene in cell recognition functions. They are attached to lipids or proteins forming glycolipids and glycoproteins. Carbohydrates constitute the glucocalyx, a secretion membrane in animal cells made up of two layers: one, next to the plasma membrane with an amorphous texture, and the other, external, with a fibrous appearance and variable thickness. Each face of the plasma membrane has a different chemical composition, which is why it is said that the membranes are asymmetric, being able to distinguish the inner and outer face of the membrane by its composition. Game: Cell defense: the plasma membrane. CÉLULA from jusega Serrano Galán Fundamental ideas about the composition of the plasma membrane Chemical composition of the plasma membrane: Lipids: Phospholipids. Arranged in bilayer for its amphipathic character. Fundamental component of the membrane. Glycolipids. Recognition of signals between cells. They only appear on the outer side of the plasma membrane. Sterols It gives stability to the lipid bilayer. Proteins: Two types: Peripheral or extrinsic. Integral or intrinsic. They are involved in the exchange of substances. Carbohydrates. On the outer side of the plasma membrane. 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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Chemical composition of the plasma membrane

Lipids

Proteins

Carbohydrates