TOPIC 1 MARK SCHEME SHIT Flashcards
Describe how mRNA is produced in the nucleus of a cell (7)
- Helicase
- Breaks hydrogen bonds
- Only one DNA strand acts as template
- RNA nucleotides attracted to exposed bases
- according to base pairing rule
- RNA polymerase joins nucleotides together
- pre-mRNA spliced to remove introns
Describe the structure of proteins (7)
- Polymer of amino acids
- Joined by peptide bonds
- Formed by condensation
- Primary structure is order of amino acids
- Secondary structure is folding of polypeptide chain due to hydrogen bonding
- Tertiary structure is 3D folding due to hydrogen bonding and ionic/disulphide bonds
- Quaternary structure is two or more polypeptide chains
Starch vs cellulose: explain structural difference
Position of hydrogen and hydroxyl groups on carbon atom 1 inverted
Explain how cellulose molecules are adapted for their function in plant cells (3)
- Long and straight chains
- Become linked together by many hydrogen bonds to form microfibrils
- Provide strength to cell wall
Lipid test (2 marks)
- Dissolve in alcohol then add water
- White emulsion shows presence of lipid
Describe the chemical reactions involved in the conversion of polymers to monomers and vice versa. Give two named example of polymers and their associated monomers. (5)
- A condensation reaction joins monomers together AND forms a chemical bond AND releases water
- A hydrolysis reaction breaks a chemical bond between monomers AND requires water
- Starch & alpha glucose (example)
- Cellulose & beta glucose (another example)
- 1-4 glycosidic bond (example of bond)
REJECT TRIGLYCERIDES & ESTER BOND
What is a monomer?
smaller/repeating unit
molecule from which larger molecules/polymers are made
Why can new nucleotides only be added in 5’ to 3’ direction? (4)
- DNA polymerase
- is specific
- complementary to 5’ end
- 5’ end different shape to 3’ end
3 differences between prokaryotic & eukaryotic DNA
- Prokaryotic DNA is circular/non-linear
- Prokaryotic DNA not associated with proteins/histones
- Prokaryotic DNA has no introns
Describe the structure of a cellulose molecule and explain how cellulose is adapted for its function in cells (9)
- made from beta glucose
- joined by condensation
- 1-4 glycosidic bonds
- “flipping over” of alternate molecules
- H bonds linking chains
- cellulose makes cell walls strong
- can resist turgor pressure
- bond difficult to break
- resists digestion
2 properties of water important in the cytoplasm + explanation
- Polar molecule = universal solvent
- Universal solvent = metabolic reactions occur faster in solution
Explain why maltase only breaks down maltose & allows this reaction to take place at normal body temperature (5)
- Tertiary structure means
- active site complementary to maltose
- description of induced fit model
- Enzyme is a catalyst
- by forming enzyme-substrate complexes
Describe competitive and non-competitive inhibition of an enzyme (5)
- Inhibitors prevent formation of ES complex
COMPETITIVE - Inhibitor similar shape to substrate
- Binds to active site
- Can be overcome by adding more substrate
NON-COMPETITIVE - Inhibitor binds to allosteric site
- Changes shape of active site
- Cannot be overcome by adding more substrate
Why is a colorimeter good for measuring quantity of reducing sugars? (2)
Quantitative
Standardises results
More cristae advantage?
More enzymes for ATP production/oxidative phosphorylation/for electron transport chain
Give 5 ways in which ATP is a suitable energy source for cells to use
- Release relatively small amount of energy/little energy lost as heat
- Immediate source of energy
- Phosphorylates other compounds, making them more reactive
- Can be rapidly re-synthesised
- Isn’t lost from/doesn’t leave cells
Give 2 ways in which the properties of ATP make it a suitable source of energy in biological processes
- Energy released in small/suitable amounts
- Soluble
Explain why it is necessary for humans to synthesise more than their body mass of ATP each day (2)
- ATP is an immediate energy source
- ATP only releases a small amount of energy each time
What are the component molecules of ATP?
Adenine
Ribose
Three phosphates
Explain why H bonds are important in cellulose molecules (2)
- Holds chains/cellulose molecules together/forms cross links between chains/forms microfibrils, providing strength/rigidity
- H bonds strong in large numbers
“Making energy” is BANNED - what should you say instead?
RELEASING energy/making ATP/energy from ATP
Describe the induced fit model of enzyme action and how an enzyme acts as a catalyst (3)
- Substrate binds to the active site
- Active site changes shape slightly so it is COMPLEMENTARY to the substrate
- Reduces activation energy
Give 3 features of DNA & explain how each one is important in the semi-conservative replication of DNA
- weak/easily broken H bonds between bases allow two strands to separate
- 2 strands so both can act as templates
- complementary base pairing allows accurate replication
Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule (2)
- Condensation
- (Between) phosphate AND deoxyribose
- (Catalysed by) DNA polymerase
Explain 5 properties that make water important for organisms (5)
- a METABOLITE IN condensation/hydrolysis/photosynthesis/respiration
- a solvent SO (metabolic) reactions can occur / allowing transport of substances
- high SHC SO buffers changes in temperature
- high latent heat of vaporisation SO provides a cooling effect (through evaporation)
- cohesion (between water molecules) SO supports columns of water (in plants)
- cohesion (between water molecules) SO produces surface tension supporting (small) organisms
Describe how an ATP molecule is formed from its component molecules (4)
1 and 2. Adenine, ribose/pentose, THREE phosphates
3. Condensation
4. ATP synthase
