C1 Enzymes and Metabolism, Cell Respiration, Photosynthesis

Enzymes

Biological catalysts made by living organisms. Cause very large increases in the rates of chemical reactions in cells without being used themselves.

Major Chemical Conversions

Happen via a series of reactions catalyzed by different enzymes. The product of one enzyme’s reaction is the substrate for the next enzyme.

Interdependence

When the activity of both being restricted if one is not active enough.

Metabolism

The complex network of interdependent and interacting chemical reactions catalyzed by enzymes that occur in living organisms.

Anabolism

The energy-requiring part of metabolism in which simpler substances are transformed into more complex molecules

Photosynthesis Reactions

Anabolic reactions that produce sugars and other carbon compounds from carbon dioxide and water with light as the energy source.

Catabolism

The energy-releasing part of metabolism where complex molecules are broken down into simpler ones, producing energy.

Cell Respiration Reactions

Catabolic reactions in which glucose or fats are oxidized to release energy, with water and carbon dioxide as waste products.

Active site

Site on surface of an enzyme where catalysis occurs. May only consist of a few amino acids, three dimensional shape, chemical properties that cause substrates to rapidly change into products.

Collision

The meeting of a substrate and active site. The shape and chemical properties of the active site complement those of the substrate, so when close enough and in appropriate orientation the two bind together.

Induced-Fit Binding

The concept of substrate and active site achieving complementarity through mutually induced changes.

Factors Affecting Enzyme Activity

• Temperature

• Substrate-concentration

• pH

Enzymes and Heat Relationship

Enzyme activity increases with heat because collisions between the substrate and the active site are more frequent due to faster molecular motion.

Enzyme Heat Denaturation

At high temps enzymes are denatured because heat causes vibrations which break bonds needed to maintain the structure.

Enzyme-Substrate Concentration Relationship

As substrate concentration increases more and more of the enzymes active sites are occupied.

Enzyme and pH Relationship

Enzymes have an optimum pH where enzyme activity is the fastest. PH 7 is optimum for most enzymes.

Enzyme and pH Denaturation

pH affects the ionization of COOH and NH2 groups, which alters enzyme conformations and can cause permanent denaturation.

Activation Energy

The amount of energy needed to break bonds within the reactant and to reach the transition state. Enzymes reduce this by weakening bonds.

Exothermic Reaction

A chemical reaction that releases energy, usually in the form of heat, as the reactants transform into products.

Endothermic Reaction

A chemical reaction that absorbs energy from its surroundings, usually in the form of heat, resulting in a temperature decrease in the environment as reactants are converted into products.

Properties of ATP

• Chemically stable at neutral pH levels typical of cells

• Soluble in water so ATP can diffuse freely in cytoplasm

• Unable to diffuse through the phospholipid bilayers of membranes

• Can release a quantities of energy that can be used for cellular processes and reactions.

• Can be easily regenerated by adding a third phosphate group to ADP

Converting between ATP and ADP

Energy has to be invested, coming from sources like sunlight, oxidation of food, or a transfer of another phosphate group from other compounds.

Reactions to convert from ATP to ADP and vice versa

ADP → ATP iS a phosphorylation and condensation reaction

ATP → ADP is a hydrolysis reaction

Aerobic Cell Respiration Characteristics

• Uses oxygen

• Can use the substrates sugars and lipids

• Produces 30-32 ATP per glucose (a large yield)

• Waste products are CO2 and H2O

• The reactions occur in the cytoplasm and mitochondria

Aerobic Cell Respiration Reaction

glucose + oxygen → carbon dioxide + water + energy

Anaerobic Cell Respiration Characteristics

• No oxygen

• Uses the substrates glucose and sugars

• Produces only 2 ATP per glucose (a small yield)

• The waste products are lactate (lactic acid)

• Only happens in cytoplasm

Anaerobic Respiration Reaction

glucose → lactate + energy

Respirometers

Devices used to measure the rate of cell respiration.

A sample is put into the apparatus, where it can absorb oxygen from and excrete CO2 into the air around it. It measures the air pressure/volume of the air inside.

Temperature changes affect air pressure so must prevent it from heating up or cooling down.

Photosynthesis

How light energy is transformed into chemical energy when absorbed by pigments (coloured substances such as chlorophyll)

Photosynthesis Formula

Carbon dioxide + water = glucose + oxygen

6CO2 + 6H2O = C6 H12 O6 + 6O2

Requires solar energy

Organisms that photosynthesize

Plants, Algae, Cyanobacteria.

They use some of the oxygen produced in aerobic cellular respiration (ie. roots of plants) But most is excreted into the environment.

In underwater organisms the oxygen emerges as bubbles.

Process of Chromatography

1. Tear leaf into small pieces

2. Grind leaf with pestle and mortar and sharp sand and propanone to extract pigments

3. Transfer sample of extract into watch glass

4. Evaporate until dry with hot air from hair dryer

5. Add a few drops of propanone to dissolve the pigments

6. Transfer drops of the solution to form a concentrated spot 10mm from the end of a strip of chromatography paper

7. Suspend strip in a tube with base dripping into a running solvent

8. Remove the strip from the tube when running solvent has nearly reached the top

9. The pigment in each spot can be identified by its Rf value

Rf = distance moved by spot/distance moved by solvent

Wavelengths of Light

400nm to 700nm reach the earth’s surface and this range is used both in photosynthesis and human vision.

Violet is shortest wavelength and red is the longest. The shorter the wavelength, the more energy a photon of light has.

The absorption spectrum for the 2 most common types of chlorophyll

Chlorophyll absorbed red and blue light the most effectively. Very little green light is absorbed, mostly reflected, making it appear green to us.

Action Spectrum

Similar to Absorption Spectrum with peak in blue and red and trough in green. Some green light is still used in photosynthesis due to accessory pigments.

Limiting factors for rate of photosynthesis

• Temperature

• Light intensity

• Carbon dioxide concentration

Carbon Dioxide Enrichment Experiments

Large-scale studies that expose vegetation to elevated CO2 concentrations under natural conditions. Allows researchers to study the effects of increased CO2 on plants. Help scientists understand how rising atmospheric CO2 levels might impact ecosystems.