This pages gives outline details of the content of the topic together with essential questions and student skills and applications. Helpful for revision.

2.1 Molecules to metabolism

Carbon based compounds

• Molecular biology explains biological processes in terms of the chemicals involved.
• The is a diversity of Carbon based compounds in living things because carbon atoms can form four covalent bonds.
   e.g. carbohydrates, lipids, proteins & nucleic acids.
• All the enzyme-catalysed reactions in a cell make up its metabolism. There are two types:
  • Anabolism: forming macromolecules from monomers by condensation.
  • Catabolism: breaking complex macromolecules into simpler molecules by hydrolysis.
• Some biological compounds can be synthesized ouside of living things: e.g. urea.

Drawing molecules

• Draw diagrams of:
  • αD-glucose & βD-glucose,
  • D-ribose,
  • a fatty acid
  • an amino acid with generalised R-group.
• Identification of biochemicals from diagrams to include:
  • monosaccharides
  • disaccharides,
  • lipids (triglycerides, phospholipids and steroids)
  • amino acids
  • polypeptides and peptide bonds.
• Knowledge of the Benedicts reagent test for reducing sugars and iodine to test for starch.

2.2 Water

• Hydrogen bonds form between polar water molecules.
• This force give water special properties, e.g. cohesiveness, adhesiveness, thermal
  and solvent properties.
• Glucose, amino acids and salts are hydrophilic while cholesterol and fats are hydrophobic.
• Compare the thermal properties of water with those of methane and explain how this affects its use a as a coolant in sweat.
• Compare the solubility of glucose, amino acids, cholesterol, fats, oxygen and sodium chloride in water and link this to the way they are transported.
• Explain benefits of water properties to living organisms (Transparency and density not required.)
• Evaluate how significant hydrogen bonding is in the properties of water.

2.3 Carbohydrates & Lipids

• Condensation reactions link Monosaccharide monomers together to
  form disaccharides (Sucrose, lactose and maltose) and polysaccharides.(cellulose starch and glycogen)
• Fatty acids can be saturated, monounsaturated or polyunsaturated.
  and cis or trans isomers if they are unsaturated. (molecule names not required)
• Three fatty acids and one glycerol molecules can form a Triglycerides by condensation reactions.
• How the structure of cellulose and starch (amylose & amylopectin) in plants and glycogen in humans relates to function.
• For long-term energy storage in humans
  lipids are better than carbohydrates.
• Potatoes have been genetically modified to reduce the level of amylose to
  produce a more effective adhesive.
• Evaluate the conflicting evidence for health risks of trans fats and saturated fatty acids and evaluate the methods used
• Abiliy to use molecular visualization software like jmol to compare cellulose, starch and glycogen.
• Ability to work out a BMI using a nomogram or by calculation

2.4 Proteins

• Amino acids are linked together by condensation reactions to form a di-peptides and polypeptides.
• Genes and mRNA strands code for 20 different amino acids which are built into polypeptides on ribosomes.
• Amino acids can be linked together in any sequence (coded for by genes) giving a huge range of possible polypeptides.
• A protein may be a single polypeptide or more than one polypeptide joined together.
• The three-dimensional shape of a protein is determined by the sequence of amino acids.
• Living organisms synthesize many different proteins with a wide range of functions (not structure)
  e.g. Rubisco, insulin, immunoglobulins, rhodopsin, collagen & spider silk.
• Every individual has a unique proteome.
• Proteomics and the production of proteins by cells cultured in fermenters
  offer many opportunities for the food, pharmaceutical and other industries
  (a utilisation)
• Ability to draw molecular diagrams of peptide bond formation.

2.5 Enzymes

• The role of the active site where specific substrates bind.
• The effect of the motion of molecules and the collision of substrates with the active site.
• The effect of Temperature, pH and substrate concentration on the rate of activity of enzymes. (including denaturing)
• Enzymes (often immobilized) are extensively used in industry for the production of items including Lactose-free milk, fruit juice and washing powder.

2.6 Structure of DNA and RNA

• DNA and RNA are polymers each made of nucleotides.
• A DNA nucleotide is made from phosphate, deoxyribose (pentose sugar), and nucleotide bases (T, A,G,C)
• RNA nucleotides are made from phosphate, ribose (pentose sugar) and nucleotide bases (U, A, G, C)
• Base pairing is "complementary"
• DNA is a double helix made of two strands of nucleotides linked by hydrogen bonding RNA is a single strand of nucleotides.
• Students should be able to draw simple diagrams of DNA and RNA nucleotides - using simple shapes (not chemical symbols)
• Students should learn to draw two antiparallel strands of DNA showing base pairing, A 'ladder' structure is enough, and details of purines / pyrimidines are not required

2.7 DNA Replication

• DNA replication
• Complementary base pairing leads to the semi-conservative replication of DNA.
• The enzyme helicase unwinds the double helix and breaks hydrogen bonds which hold the two DNA strands together.
• DNA polymerase (generalised name) links DNA nucleotides together to form a new strand DNA,using the pre-existing strand as a template.
• Transcription is the synthesis of mRNA by RNA polymerase using the DNA base sequence as a template
• Translation is the synthesis of polypeptides on ribosomes.
• The amino acid sequence of polypeptides is determined by mRNA according to the genetic code.
• Three bases of mRNA is called a codon and corresponds to one amino acid in the polypeptide.
• Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA.

2.8 Respiration

• Cell respiration definition,"the controlled release of energy from organic compounds to produce ATP"
• ATP produced is a source of energy ready for immediate use in the cell.
• Anaerobic cell respiration gives a small yield of ATP from glucose compared to aerobic respiration whose yield is large.
• Aerobic cell respiration also requires oxygen.
• Substrates (e.g. glucose) and final waste products (e.g. water, CO2, lactate, ethanol) should be known.
• Anaerobic cell respiration in yeasts is used to produce ethanol and carbon dioxide in baking.
• In the human body anaerobic respiration is used to maximize the power of muscle contractions & produces lactate.
• Know how to use simple respirometers to measure the rate of respiration.
  • to know that an alkali is used to absorb CO₂ produced in respirometers, so that reductions in gas volume are due to oxygen use.
  • To keep the temperature constant, so that gas volumes don't change through expansion / contraction of gas.

2.9 Photosynthesis

• Photosynthesis uses light energy to produce carbon compounds in cells.
• Visible light ranges from violet (400nm) the shortest wavelength to red (700nm) the longest.
  (Students are not expected to recall the wavelengths of other colours.)
• Absorption specrum shows - red and blue light absorbed most and green light least (it is reflected).
• Photolysis of water produces oxygen
  (and also ATP & NADPH)
• Energy ( from photolysis) is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
• Limiting factors of photosynthesis can be; Temperature, light intensity and carbon dioxide concentration.