Chapter 2. Chemicals

Chapter 2. Chemicals Attributes of Living things 1. They are composed of cells. Cells consist of a membrane around the outside, a nucleus containing DNA, and the cytoplasm. 2. Growth 3. Reproduction Sexual reproduction: the offspring vary from the parents Asexual reproduction: the offspring are identical clones 4. Respond to stimuli: for example plants respond to light, water, gravity, touch. 5. Metabolism: all the chemical reactions in an organism. The most critical reactions are respiration and photosynthesis. 6. Movement: for example sperm can swim, whole plants grow in particular directions, or there is cyclosis in cells. 7. Complexity: they are made of molecules and organelles. 8. Adaptation and evolution: populations evolve to become better adapted to their environment. Atoms & Bonds Element : a substance that cannot be broken down by chemical reaction eg carbon, gold. Everything in the universe is made of 92 different elements. Living things contain a maximum of 25 elements. Important biological elements : Carbon Hydrogen C H Calcium Potassium Ca K Oxygen Nitrogen O N Phosphorus P Sulfur S Compound - two or more elements joined by chemical bonds eg salt, water, plastic. Atom - the smallest unit of an element. Particle Proton Neutron Electron Location Nucleus Nucleus Shells Weight Charge 1 dalton (amu) +1 1 dalton (amu) 0 1/2000 dalton (amu) - 1 Atomic number = Number of Protons per atom. Atomic number also equals the number of electrons. Example : Carbon has 6 protons and 6 electrons (Table 2.1). Atomic mass = Number of Protons + Neutrons. Example: carbon 14 has 8 neutrons (14 minus 6 ). Isotopes : atoms of the same element that differ in the number of neutrons. Radioactive atoms : large isotopes that break apart, releasing energy. The energy is either: Alpha particles : weak, cannot penetrate paper. Beta particles : stronger, can penetrate paper but not metal. Gamma rays : very strong, can penetrate metal and harm living things. Radioactive atoms can be used to: a) Track chemicals in the body b) Work out the age of fossils. Accuracy of fossil dating methods c) Track the movement of individual animals (eg butterflies). Isotopes and murder Chemical bonds Chemical bonds only involve electrons. Valence electrons - electrons in the outer shell ( the valence shell ) of an atom. All atoms try to fill their valence shell of electrons. Maximum number of electrons per shell : First shell 2 Second shell 8 Third shell 8 So, for example, oxygen has a total of 8 electrons. Two go in the first shell, and 6 go in the second shell. Molecule: two or more atoms joined by chemical bonds. A) Covalent bonds are very strong. The atoms share electrons. Examples: hydrogen gas H2 , water H2O B) Ionic bonds are also strong. One atom gives electrons to another. Eg. NaCl or Na+ClC) Hydrogen bonds are weak. A hydrogen atom is attracted to a slight negative charge on a different molecule. Hydrogen bonds are important in holding together proteins. Macromolecules : very large molecules, made of hundreds, or thousands, of atoms. Many are polymers : large molecules made of similar, small monomers joined together. Hydrolysis : a chemical reaction that breaks polymers into monomers eg digestion Condensation synthesis : a chemical reaction that joins monomers together by removing water. There are 4 types of macromolecule in living things : carbohydrates, lipids, proteins and nucleic acids. 1). Carbohydrates Carbohydrates contain C , H and O. They are made of simple sugars called monosaccharides, such as glucose (C6H12O6), fructose (C6H12O6) and glyceraldehyde (C3H6O3). Monosaccharides dissolve in water. Disaccharides consist of 2 monosaccharides joined by condensation synthesis such as maltose or brewing sugar ( 2 glucose ) and sucrose or table sugar ( glucose + fructose ). Polysaccharides are made of many monosaccharides such as: starch ( energy storage in plants ) and cellulose ( cell walls in plants ). 2). Lipids Lipids contain C , H , and O. Lipids do not dissolve in water. Lipids can be fats, phospholipids , waxes or steroids. A) Fats (triglycerides). Fats are made of glycerol and 3 fatty acids. They are used for energy storage. Saturated fats : no double bonds (only single bonds); straight molecules ; solids ; found in animals ; eg butter Unsaturated fats : have 1 or more double bonds ; bent molecules ; liquids; in plants ; eg corn oil Trans fats are produced during cooking, and are common in cookies, snacks and fried food. Only unsaturated fat in the diet is healthy. You should try to cut back on the saturated and trans fat, as they increase the risk of heart attack. B) Phospholipids. Phospholipids are made of glycerol, 2 fatty acids and phosphate. Part of the molecule is hydrophobic, part is hydrophilic. Phospholipids make up most of the cell membrane. C) Waxes. Waxes consist of a fatty acid joined to an alcohol. They are used for waterproofing in plants ( and some animals ). 3). Proteins Proteins contain C , H , O and N. They are made of amino acids joined together. There are 20 different amino acids. The order of amino acids in a protein is important. Proteins are found in cell membranes, seeds and as enzymes. Primary structure : the order of amino acids. Secondary structure : the protein folds, and is held by hydrogen bonds. Tertiary structure : covalent or ionic bonds between different side chains of the protein. 4). Nucleic acids Nucleic acids contain C , H , O , N and P. They are made of nucleotides, ( phosphate, sugar and base ) DNA ( Deoxyribonucleic acid ) DNA has deoxyribose as the sugar. It has 4 bases : Adenine Guanine Thymine Cytosine Bases pair up and join with hydrogen bonds to form a double helix (Adenine opposite thymine and guanine opposite cytosine). The code on DNA carries information the cell needs to make proteins ( the primary structure). Closely related species have similar DNA. Humans and primates. Similarly, DNA studies can show if what looks like one species is really two different species. RNA ( ribonucleic acid ) RNA has ribose as the sugar. RNA has 4 bases : with Uracil instead of Thymine. RNA is a single strand. RNA moves from the nucleus of the cell to the cytoplasm to allow the cell to make proteins ( mRNA : messenger RNA ). New RNA drugs could be very useful, for example to prevent blood clots or treat cancer.