1.1 Basic Biochemistry and cell organisation

• What are all substances made from?

  Atoms of elements
• What are molecules made from?

  Two or more atoms
• What defines a molecule as an element?

  Atoms in the molecule are the same
• What defines a molecule as a compound?

  Atoms in the molecule are different
• From what can ions be formed?

  Metals, non-metals, or combinations of elements
• What characterizes positively charged ions?

  They have lost one or more electrons
• Why do positively charged ions have a positive charge?

  More protons than electrons
• Particles with a charge (ions or polar molecules) have different properties from molecules with no charge (non-polar).

  • Ions and polar compounds attract oppositely charged particles and play important roles in the structure of molecules.
  • Non-polar compounds do not dissolve in water but will dissolve in lipids (fats/oils) – they are said to be lipid-soluble.

  Elements in living organisms

  The six most common elements, accounting for 99% of the mass of the human body are shown in the table below.

  
• What characterizes negatively charged ions?

  They have gained one or more electrons
• Why do negatively charged ions have a negative charge?

  More electrons than protons
• What are compounds made from?

  Atoms of two or more elements
• What types of compounds can include metals and non-metals?

  Ionic compounds
• What types of compounds consist only of non-metals?

  Molecular compounds
• What charge can molecules have?

  No charge or a slight charge
• What is a characteristic of non-polar molecules?

  They have no charge
• What is a characteristic of polar molecules?

  They have a slight charge
• What are the differences between ions and molecules?

  • Ions are charged particles
  • Molecules can be neutral or polar
  • Ions can be formed from elements
  • Molecules are formed from atoms
• The remaining 1% of the mass of the human body is made of about 10 other elements, mainly:

  
• Ions

  Most of these key elements are found as inorganic ions.

  
• Because of their polarity, water molecules are attracted to other water molecules and charged particles. This helps charged particles dissolve in water.

  For this reason, water is sometimes referred to as the universal solvent as a large number of substances can dissolve in water.

  
• Water is also important in chemical reactions, as many small organic molecules can be combined with the loss of a water molecule. Condensation reactions and large molecules are often broken down by hydrolysis which requires the addition of a water molecule.

  Significance of water for life on Earth

  In addition to water acting as a solvent and its involvement in biochemical reactions, it also has other properties that make it essential for life on Earth.

  
• Monosaccharides

  Monosaccharides are monomers – single sugars named according to the number of carbon atoms in the molecule. The numbers on the diagrams below show the number given to each carbon atom in the molecules.

  
• What elements do all carbohydrates contain?

  Carbon, hydrogen, and oxygen
• What is the general formula for monosaccharides?

  (CH2O)n or Cn(H2O)n or CnH2nOn
• What does the variable n represent in the monosaccharide formula?

  The number of atoms
• What is the molecular formula for glucose?

  C6H12O6
• What are structural isomers?

  Molecules with the same formula but different arrangements
• Which three sugars are structural isomers of each other?

  Glucose, galactose, and fructose
• What are the molecular formulas for ribose and deoxyribose?

  Ribose: C5H10O5; Deoxyribose: C5H10O4
• Can ribose and deoxyribose be structural isomers?

  No, they have different molecular formulas
• In what forms can monosaccharides exist?

  Straight chain forms or ring forms
• What is the difference between alpha (α) and beta (β) isomerism?

  Position of the OH group on carbon atom 1
• How can you remember the difference between alpha and beta ring forms?

  • ABBA mnemonic:
  • Alpha: OH Below
  • Beta: OH Above
• What are the different isomers of glucose?

  • Glucose
  • Galactose
  • Fructose
• You need to be able to recognise the following hexose sugars.

  Fructose has a central ring of four carbon atoms and one oxygen atom, with a CHX2​OH at carbon atoms 1 and 6.

  Glucose and galactose all have a central ring of five carbon atoms and one oxygen atom, with a CHX2​OH group at carbon atom 6. They can also exist in alpha and beta forms. Use the table below to tell the difference between the different sugars.

  
• What are disaccharides made from?

  Two monosaccharide units
• How are disaccharides formed?

  By a condensation reaction from two monosaccharides
• What is the bond that holds disaccharides together called?

  Glycosidic bond
• What process breaks the glycosidic bond in disaccharides?

  Hydrolysis reaction
• What happens during a hydrolysis reaction?

  Water is inserted to reform OH groups