Topic 2: Molecular biology
This page lists the understandings and skills expected for topic two.
Detailed revison notes, activities and questions can be found on each of the sub-topic pages
- 2.1 Molecules to metabolism.2
- 2.2 Water
- 2.3 Carbohydrates and lipids
- 2.4 Proteins
- 2.5 Enzymes
- 2.6 Structure of DNA and RNA
- 2.7 DNA replication, transcription and translation
- 2.8 Cell respiration
- 2.9 Photosynthesis
2.1 Molecules to metabolism
Carbon based compounds
- Molecular biology is explaining 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.
- Draw diagrams of:
- αD-glucose & βD-glucose,
- a fatty acid
- an amino acid with generalised R-group.
- Identification of biochemicals from diagrams to include:
- lipids (triglycerides, phospholipids and steroids)
- amino acids
- polypeptides and peptide bonds.
- Experience of the Benedicts reagent test for reducing sugars and iodine to test for starch.
- 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
- 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
- Ability to draw molecular diagrams of peptide bond formation.
- 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.
- Advantages of latose-free milk, and ways of producing it, including immobilization in alginate beads.
- Knowledge of possible designs of experiments to test the effect of temperature, pH and substrate concentration on enzyme activity.
- Practical 3: Investigation of a factor affecting enzyme activity.
- The skill of sketching a graph of expected results in enzymes experiments and the ability to explain reasons for their shapes.
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
- 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.
- Awareness that in polymerase chain reaction (PCR) an enzymes called Taq DNA polymerase produces multiple copies of DNA.
- Ability to explain how Meselson and Stahl’s results support for the theory of semi-conservative replication of DNA.
- knowledge that human insulin can be produced in bacteria because of the "universality" of the genetic code. This allows genes to be transferred between species.
- Ability to use a table of the genetic code to deduce which codon(s) corresponds to which amino acid and to deduce the sequence of amino acids coded by a short mRNA or the DNA base sequence for a given mRNA strand
- 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.
- 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.
- Understand that photosynthesis have caused changes to the Earth’s atmosphere, oceans and rock deposition.
- Learn how to draw
- an absorption spectrum for chlorophyll and
- an action spectrum for photosynthesis.
- Design experiments to investigate the effect of limiting factors on photosynthesis.
Ref: control of variables is essential.
- Separate photosynthetic pigments by chromatography. (Practical 4) either by paper chromatography or thin layer chromatography (gives better results)
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