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The chemical nature of the cell


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The chemical nature of the cell

  1. 1. 03. The chemical nature of the cell. Ian Anderson (2013) Saint Ignatius College Geelong
  2. 2. Knowledge and skills. Distinguish between organic and inorganic molecules. Describe the roles of biologically important inorganic molecules. Outline the properties of water that are important to life. Describe the basic structures of carbohydrates, lipids, proteins and nucleic acids.
  3. 3. Organic v inorganic molecules.Chemical compounds can be divided into two groups. Organic compounds.  Most carbon containing compounds are organic.  e.g. methane (CH4) and glucose (C6H12O6).  But not all e.g. carbon dioxide(CO2).  Therefore our definition: Compounds that contain both carbon and hydrogen Inorganic compounds.  All other molecules that do not contain both carbon and hydrogen.
  4. 4. Components of cells.The molecules that make up living organisms can be grouped into five classes Water Carbohydrates Lipids Biomacromolecules Proteins Nucleic acids.
  5. 5. Water. H2O = inorganic compound. Most abundant compound in living organisms  Most organisms 70-90% water  Humans – females ~50%; males ~60%; newborn babies ~75% Unique properties of water help explain why it is so important to life:  Molecules stick together (as a result of H bonding)  A good solvent  Heat capacity
  6. 6. Biomacromolecules. Very large organic molecules. All are polymers (except lipids).  Polymers are made up of many smaller building blocks called monomers. (poly = many; mono = single; mer = segments).  The monomers in a polymer are joined by a dehydration (condensation) reaction (where water is released during the reaction). monomer + monomer  polymer + H2O  (Reverse reaction = hydrolysis reaction)
  7. 7. Carbohydrates. Organic compounds. Most abundant organic compounds in nature. Made up of carbon, hydrogen and oxygen. Energy rich – source of energy for all living organisms. Also important in plants as structural material (cellulose). Exoskeleton of insects (chitin)
  8. 8. Carbohydrates. Basic unit of carbohydrates are the simple sugars – monosaccharides (CnH2nOn)  e.g. glucose (C6H12O6). Disaccharides – two monosaccharide sugars joined together (also called simple sugars)  e.g. sucrose Polysaccharides – many simple sugars (monomers) joined together to form long chains (polymer).  Also called complex carbohydrates.  e.g. starch, glycogen, cellulose.
  9. 9. Lipids. General term for fats, oils and waxes.  But also include phospholipids, steroids, glycolipids and carotenoids. Composed of carbon, hydrogen and oxygen, but in different proportions to carbohydrates (less oxygen & often contain other elements such as phosphorus and nitrogen). All lipids are hydrophobic and insoluble in water. Lipids are not polymers.
  10. 10. Types of lipids. Triglycerides (fats & oils).  Known as simple lipids (composed only of C, H & O, but in different proportions to carbohydrates).  Important energy storing molecules.  Fats store twice as much energy as the same weight of carbohydrates.  Made up of a glycerol molecule and three fatty acid molecules.  Fatty acids may be either saturated (no double bonds) or unsaturated (contains double bonds), which is important for determining the fluidity and melting point of the lipid.  Fats (which are solid at room temperature) have many more saturated bonds than oils (which are liquid).
  11. 11. Types of lipids. Triglycerides (fats & oils). Source: Enger et al. (2011)
  12. 12. Types of lipids. Phospholipids.  Known as complex lipids (also composed of C, H & O, but also other elements such as P & N).  Similar in structure to triglycerides, except that one of the three fatty acids attached to glycerol is replaced by a phosphate containing group.  Structure results in a hydrophilic, polar head (soluble in water) and a hydrophobic, non-polar tail (insoluble in water).  Phospholipids are a major component of cell membranes.
  13. 13. Types of lipids. Phospholipids. Source: Campbell et al. (2011) Source: Enger et al. (2011)
  14. 14. Types of lipids. Steroids.  Have a very different structure than other lipids.  Four interlocking rings of carbon.  Still have large number of carbon-hyrogens, and are non- polar.  Important examples include cholesterol, the sex hormones (testosterone, oestrogen and cortisol) and vitamins such as Vitamin D. Waxes.  Important role in both plants and animals for their ability to form a waterproof coating.
  15. 15. Proteins. Large molecules made up of amino acids.  20 naturally occurring amino acids.  Joined together by peptide bonds (as a result of a hydration reaction).  To form a polypeptide. Contain nitrogen, as well as carbon, hydrogen and oxygen (some also contain sulphur, phosphorus and other elements). Proteins are unique to each type of organism.
  16. 16. Proteins. Amino acids (the monomers of proteins).  All amino acids share a common structure  Amino group.  Carboxyl group.  Central α (alpha) carbon, and a  R group (also called the side chain).  Only the R group differs between amino acids.
  17. 17. Protein structure. Proteins are very complex, with four levels of complexity used to describe them.  Primary.  Secondary.  Tertiary.  Quaternary.
  18. 18. Protein structure. Primary structure.  The sequence of amino acids in the polypeptide chain.  The polypeptide chain is the result of dehydration reactions between the carboxyl group of one amino acid and the amino group of another, resulting in peptide bonds.  The amino acid sequence determines what three- dimensional shape the protein will have.  The specific sequence of amino acids in a polypeptide is controlled by the genetic information of the organism. Source: Enger et al. (2011)
  19. 19. Protein structure. Secondary structure.  Hydrogen bonding between the amino groups and the carboxyl groups in a polypeptide can result in  α-helices (coils)  β-pleated sheets (folds), or  random coils (no distinct pattern). Source: Enger et al. (2011)
  20. 20. Protein structure. Tertiary structure.  The overall three-dimensional shape of the protein.  A polypeptide chain can contain one or more combinations of α-helices and β–pleated sheets, causing the chain to twist, bend and loop.  The result is interactions between the various side chains (R groups) of the amino acids, incl  Hydrogen bonding, ionic bonding, covalent bonding (e.g. disulphide bridges between two cysteine side chains), hydrophobic interactions, etc.  Chaperone proteins (found in cells) help proteins fold into their normal shape.
  21. 21. Protein structure. Tertiary structure. Interactions between the side chains in the tertiary structure of a protein. Source: Campbell et al. (2011) Tertiary structure of a protein. Source: Enger et al. (2011)
  22. 22. Protein structure. Quaternary structure.  Two or more polypeptide chains, each with their own tertiary structure, joined together as one functional macomolecule.  e.g. Haemoglobin (4 polypeptide chains), insulin (2 polypeptide chains), immunoglobulins (4 polypeptide chains). Source: Enger et al. (2011)
  23. 23. Proteins. Two major types of proteins.  Fibrous proteins  The secondary structure (either α-helices or β-pleated sheets) forms the dominant structure of the protein (i.e. generally only have primary and secondary structure).  Are insoluble in water.  Play a structural or supportive role in the body.  e.g. keratin, collagen, silk, muscle and ciliary proteins.  Globular proteins  Are soluble in water.  All have tertiary and some have quaternary structure .  e.g. enzymes and hormones.
  24. 24. Proteins. Proteins have any different functions, incl.  Structural Collagen  e.g. collagen, keratin, etc.  Regulatory  Enzymes e.g. pepsin, catalase, etc.  Hormones e.g. insulin, glucagon, etc.  Carrier molecules (transport)  e.g. Haemoglobin. Source: Reece et al. (2011)
  25. 25. Nucleic acids. The genetic material of all life. Made up of long chains of monomer units called nucleotides. Two types  Deoxyribonucleic acid (DNA)  Ribonucleic acid (RNA). (We look at these in more detail later, so just an introductory look for now.)
  26. 26. Nucleic acids. Each nucleotide (the monomer) is made up of three parts  a sugar  a phosphate group, and  a nitrogenous base. Source: Walpole et al. (2011)
  27. 27. Nucleic acids - DNA. Double stranded and helical shape (double helix).  Sugar and phosphate groups form the backbone of the ladder, while the bases form the steps.  The two strands are attached by hydrogen bonds between their bases. Sugar = deoxyribose. Nitrogenous bases =  Adenine (A), cytosine (C), guanine (G) and thymine (T).
  28. 28. Nucleic acids - DNA. Source: Raven et al. (2011)
  29. 29. Nucleic acids - RNA. Single stranded. Sugar = ribose. Nitrogenous bases = Adenine (A), cytosine (C), guanine (G) and uracil (U). Three types.  Messenger RNA (mRNA)  Transfer RNA (tRNA)  Ribosomal RNA (rRNA)
  30. 30. Nucleic acids - RNA. Source: Raven et al. (2011)
  31. 31. Other important compounds. Vitamins  Organic compounds required by animals in very small (trace) amounts for normal functioning.  Essential for many chemical reactions  e.g. Vitamin C are components of co-enzymes. Minerals  Inorganic ions required by both animal and plant cells.  Play a role in metabolic process of cells.