Topic 1.5-7 Biological molecules Flashcards
Describe the structure of enzymes
Globular proteins
Specific tertiary structure determines shape of acitve site, complementary to specific substrate
Explain the function of enzymes
Biological catalysts for intra (e.g. DNA polymerase) and extra cellular (e.g. digestive enzymes in tears) reactions.
Formation of enzyme-substrate (ES) complexes lowers activation energy of metabolic reactions.
Explain the lock and key hypothesis
The active site of an enzyme is very specific and only one substrate or type of substrate will fit in it, this is called specificity.
- Random movement causes the enzyme and substrate to collide, the substrate enters the active site
- An enzyme-substrate complex forms. Charged groups attract, distorting the substrate and aiding bond breakage or formation
- Products are released from the active site, leaving the enzyme unchanged and ready to accept another substrate molecule
Explain the induced fit hypothesis
Shape of active site is not directly complementary to substrate and is flexible.
Conformational change enables ES complexes to form.
This puts strain on substrate bonds, lowering activation energy.
Name five factors that effect the rate of enzyme-controlled rates of reactions
- Enzyme concentration
- Substrate concentration
- Concentration of inhibitors
- pH
- Temperature
How does substrate concentration affect rate of reaction?
Given that the enzyme conc. is fixed, rate increases proportionally to substrate conc..
Rate levels off when maximum number of ES complexes form at any given time.
How does enzyme concentration effect rate of reaction?
Given that the substrate is in excess, rate increases proportionally to enzyme conc..
Rate levels off when maximum number of ES complexes form at any given time.
How does temperature effect rate of reaction in an enzyme controlled reaction?
Rate increases as kinetic energy increases and peaks at optimum temperature.
Above optimum temperature, ionic and hydrogen bonds in 3o structure break = active site no longer complementary to substrate (denaturation).
How does pH affect rate of reaction in an enzyme controlled reaction?
Enzymes have a norrow optimum pH range.
Outside range, H+/OH- ions interact with hydrogen and ionic bonds in 3o structure = denaturation.
How do enzymes lower activation energy?
- By bringing substances close together in the active site so bonds are easier to form
- By putting strain on bonds in the substrate to break them appart
Why do organisms need enzymes?
Without enzymes biochemical reactions happen to slowly at the temperature at which living things can survive
How do competitve inhibitors work?
Bind to active site since they have similar shape to substrate. Temporarily prevent ES complexes from forming until released.
Increasing substrate concentration decreases their effect.
How do non-competitive inhibitors work?
Bind to allosteric site.
Trigger conformational change of active site.
Increasing substrate conc. has no impact on their effect.
What is end product inhibition?
One of the products of a reaction acts as a competitive or non-competitive inhibitor for an enzyme involved in the pathway. Prevents further formation of products.
Why is it advantageous to calculate initial rate?
Represents maximum rate of reaction before conc. of reactants decreases and end-product inhibition.
Explain the effect of a competitive inhibitor on a rate of reaction against substrate conc. graph
Initially rate of reaction is lower than without the inhibitor, eventually conc. of substrate outcompetes the inhibitor and rate of reaction will be the same as without the inhibitor
Explain the effect of a non-competitive inhibitor on a rate of reaction against substrate conc. graph
Excess substrate conc. has no effect on rate of reaction, so rate of reaction will always be lower than without the inhibitor
Explain the role of nitrate ions in plants
Used to make:
* DNA
* amino acids
* NADP for photosynthesis
* NAD for respitation
Explain the role of calcium ions in plants
Used to make calcium pectate, which adds stability to middle lamella of cell wall (layer that joins adjacent cells)
Explain the role of magnesium ions in plants
Component of chlorophyll, which absorbs light energy for photosynthesis
Explain the role of phosphate ions in plants
Component of:
* ADP and ATP, which are involved in energy release for metabolic reaction
* NADP for photosynthesis
State 5 biologically important properties of water
- Reaches maximum denstiy at 4oC
- High specific heat capacity
- High surface tension
- Acts as a polar solvent
- Incompressible
Why does water have a permanant dipole?
Oxygen is more electronegative than hydrogen, so attracts the electron density in the covalent bonds more strongly.
Forms O δ- (slight negative charge) and H δ+ (slight positive charge)
Describe the intermolecular bonding that between water molecules
Hydrogen bonds form between lone pair on oxygen of one molecule and H δ+ on neighboring molecule.
Why is the high specific heat capacity of water important for organisms?
Acts as a temperature buffer which enables endotherms to resist fluctuations in core temperature to maintain optimum enzyme activity.
Why is water an important solvent for organisms?
Polar universal solvent dissolves and transports charged particles involved in intra and extracellular reactions.
Why is high surface tension of water important for organisms?
Slows water loss due to transpiration in plants.
Water rises unusually high in narrow tubes, lowering demand on root preasure.
Some insects can “skim” across the surface of water.
Why is the incompressible nature of water important for organisms?
Provides turgidity to plant cells.
Provides hydrostatic skeleton for some small animals - e.g. earthworms
Explain why ice floats on water. Why is this important for organisms?
Ice is less dense than water because hydrogen bonds hold water molecules in fixed positions further away from each other.
Insulates water in artic climates so aquatic organisms can survive
