Unit 1 biology

• Why is (control) used? - as a control - to show effect of x - to show that x does not affect results - to show that only y causes the change - may be used as baseline value to investigate effect of treatments
• Why is a representative sample important? - more reliable mean
• A decrease in temperature decreases the kinetic energy of molecules in a solution. Explain how a decrease in temperature decreases the rate of an enzyme-controlled reaction. MS [2] molecules moving less/slower;reduces chance of collision (between enzyme and substrate)/of enzyme-substrate complexes being formed;
• Recall the uses of ATP. [6] provides energy for - synthesis of macromolecules - muscle contraction - active transport - secretion Phosphate Released: - phosphorylation of molecules - can active other key bio molecules
• What are the 3 aspects to consider when choosing a temperature for an experiment? - sufficient kinetic energy - does not denature proteins - optimum
• What is the general formula for monosaccharides? (CH20)n
• Why are unsaturated lipids liquid at room temperature? The precense of the double bond means that the molecule is able to bend. As a result, the unsaturated fats cannot pack together as tightly, hence it's liquid at room temperature.
• Saturated lipids are found in animals whilst unsaturated lipids are found in plants
• Illustrate the formation of a Dipeptide
• Why do hydrogen bonds form in the secondary structure? The hydrogen in the -NH has a slight positive charge whilst the oxygen in the -C=O has a slight negative charge.
• Proteins can be either globular or fibrous.
• All polysaccharides and some disaccharides are non-reducing sugars
• Contrast DNA and RNA in terms of: - Name - Chain Length - Strand Number - Pentose Sugar - Organic Bases - Chemical Stability - Function
• Describe the structure of RNA (5) 1) single stranded 2) short polynucleotides 3) ribose sugar 4) bases: uracil, guanine, cytosine, adenine 5) less stable
• Explain why, in semi-conservative DNA replication, that DNA polymerase works in different directions (1) The two strands of DNA are antiparallel to each other (2) The alignment / orientation of the nucleotides are arranged differently (3) Enzymes have active sites with a specific shape (4) Only substrates will the complementary shape and orientation will be able to bind to the active site of DNA polymerase
• Illustrate the reaction of ADP + Pi, labelling the enzymes and names of the reaction
• What is the limitation of the lock and key model? Suggested AS of an enzyme is rigidScientists observed inhibitors could bindHence enzymes shape was being altered by binding molecule
• Describe the structure of a cellulose molecule and explain how cellulose is adapted for its function in cells (6 marks) (9 potential points) 1. made from β-glucose; 2. joined by condensation to form glycosidic bond; 3. 1 : 4 link described; 4. “flipping over” of alternate molecules; 5. hydrogen bonds linking long straight chains; 6. cellulose makes cell walls strong; 7. can resist turgor pressure/osmotic pressure; 8. bond difficult to break; 9. resists action of enzymes
• Describe the structure of proteins MS [7] Polymer of amino acids;Joined by peptide bonds;That are formed by condensation;Primary structure is the order of amino acids;Secondary structure is folding of polypeptide chain due to hydrogen bonding;Tertiary structure is 3-D folding due to hydrogen bonding and ionic / disulfidebonds;Quaternary structure is two or more polypeptide chains
• ATP is useful in many biological processes. Explain why (4 marks) 1. Releases energy in small &; easily manageable amounts; 2. Broken down in a one step reaction which makes sure energy is available rapidly 3. Phosphorylates substances to make them more reactive 4. Reformed/made again rapidly
• Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample (5 marks) Lipid Add ethanol/alcohol and shake/mix then pour into/add water; 2. White/milky emulsion Non-reducing sugar 3. Do Benedict’s test and stays blue/negative; 4. Boil with acid then neutralise with alkali; 5. Heat with Benedict’s and becomes red/orange (precipitate); Amylase 6. Add biuret (reagent) and becomes purple/violet/mauve/lilac; 7. Add starch, (leave for a time), test for reducing sugar/absence of starch;
• Haemoglobins are chemically similar molecules found in many different species. Differences in the primary structure of haemoglobin molecules can provide evidence of phylogenetic (evolutionary) relationships between species. Explain how. (5 marks) 1.Mutations change base / nucleotide (sequence); 2.(Causing) change in amino acid sequence; 3.Mutations build up over time; 4.More mutations / more differences (in amino acid/ base / nucleotide sequence / primary structure) between distantly related species; 5. Closely related species have recent common ancestor;
• Describe the roles of iron ions, sodium ions and phosphate ions in cells (5 marks) Iron ions 1. Haemoglobin binds/associates with oxygen Sodium ions 2. Co-transport of glucose/amino acids (into cells); 3. (Because) sodium moved out by active transport/Na – K pump; 4. Creates a sodium concentration/diffusion gradient; 5. Affects osmosis/water potential; Phosphate ions 6. Affects osmosis/water potential; 7. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides; 8. Used in/to produce ATP; 9. Phosphorylates other compounds (usually) making them more reactive; 10. Hydrophilic/water soluble part of phospholipid bilayer/membrane;
• Explain five properties that make water important for organisms (5 marks) 1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration; 2. A solvent so (metabolic) reactions can occur 3. High heat capacity so buffers changes in temperature; 4. Large latent heat of vaporisation so provides a cooling effect (through evaporation); 5. Cohesion (between water molecules) so supports columns of water (in plants); 6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;
• Explain how the structure of DNA is related to its functions (6 marks) 1. Sugar-phosphate (backbone) is double stranded into a helix so provides strength & stability (protects bases); 2. Long / large molecule so can store lots of information; 3. Helix / coiled so compact; 4. Base sequence allows information to be stored (protein formation); 5. Double stranded so replication can occur semi-conservatively as existing strands can act as templates via complementary base pairing 6. Weak hydrogen bonds for replication and strand separation OR many hydrogen bonds so stable/strong;
• Describe and explain how the structure of DNA results in accurate replication (4 marks) 1 Two strands therefore semi-conservative replication; 2 base pairing held together by hydrogen bonds 3 hydrogen bonds weak so easily broken, which allows strands to separate; 4 bases exposed and act as a template; 5 A with T, C with G; 6 DNA made has one parent strand and one new strand
• Explain how a mutation can result in the production of a non-functional protein receptor (4 marks) 1. Change in DNA base sequence; 2. Change in amino acid sequence; 3. This alters position of hydrogen/ionic/disulfide bonds; 4. And causes a change in the tertiary structure (of receptor);
• ATP is described as... a nucleotide derivative of adenine with 3 phosphate gorups
• How many amino acids are there and how do they differ from one another? 20 differ only be side ''R'' group
• Recall the function and 3 properties of globular proteins. FunctionalCompactWater solubleMetabolic processes
• Recall function and 2 properties of fibrous proteins. Function: StructuralInsoluble in waterForm long chains
• State the formula for pH pH = -log10[H+]
• Where is glycogen found? found as small granules in the muscles and liver of animals
• Relate the structure of tryglycerides to their properties (4) ➤ source of energy - high ratio of energy storing C-H bonds to C atoms ➤ storage - low mass to energy ratio; much energy in a small volume ➤ insoluble in water - large, non polar molecules dont affect water potential ➤ water source - high ratio of H to O atoms, release water when oxidised
• What control can we carry out for the emulsion test? Repeat with water instead of sample, solution should remain clear.
• Give the properties of glycogen. [4] Insoluble → doesn't affect ψLarge → cannot leave cellsCompact → stored in small spacesHighly branched → larger surface area for enzymes to act on
• When investigating the effect of enzyme concentration on a reaction, what factors must we keep constant? (3) 1. Temperature of the solution 2. pH of the solution 3. Concentration of Substrate
• Explain why maltase can only catalyse the hydrolysis of maltose. [3] Active site of enzyme has specific shapeOnly maltose can bindTo form E-S complex
• Describe competitive and non-competitive inhibition of enzymes. MS [7] 1. Inhibitors reduce binding of enzyme to substrate & prevent the formation of E-S complexes (Competitive inhibition), 2. Inhibitor has a similar shape to substrate; 3. It binds to the active site (of enzyme); 4. Inhibition can be overcome by adding more substrate; (Non-competitive inhibition), 5. Inhibitor binds to a site on enzyme other than active site; 6. This changes the shape of the active site 7. Inhibition cannot be overcome by adding more substrate
• What are micelles? tiny droplets consisting of fatty acids and monoglycerides surrounded by bile salts.