3. Structure and regulation of biochemical pathways Part 2

Question 1

What is irreversible inhibition? Give 2 examples:

Answer 1

When certain side chains at the active sites of enzymes are irreversibly modified, ruining the enzymes by destroying their capacity to function as catalysts (Eg. Mercury, arsenic).

Question 2

Give the overall equation for photosynthesis:

Answer 2

Carbon dioxide (6CO2) + Water (12H2O) = Glucose (C6H12O6) + Water (6H2O) + Oxygen (6O2)

Question 3

What is photosynthesis?

Answer 3

Photoautotrophs contain pigments, such as chlorophyll, that capture light energy from the sun and use this energy, together with CO2, as the source of carbon to produce organic molecules.

Question 4

List the photosynthesising organisms:

Answer 4

• Plants
• Algae
• Bacteria called cyanobacteria

Question 5

List the 2 different pigments of chloroplasts that absorb light energy:

Answer 5

• Chlorophylls

- Carotenoids

Question 6

What do chlorophyll pigments absorb and how do they appear?

Answer 6

Absorb mainly the red (which is used more effectively in photosynthesis) and blue-violet wavelength of visible light. The green wavelength of visible light is reflected making leaves appear green.

Question 7

What do carotenoid pigments absorb and how do they appear?

Answer 7

Absorb mainly light in the blue-violet range and appear orange, yellow, or red.

Question 8

Name the worded chemical equation for the light-dependent phase:

Answer 8

Light energy
Water = Hydrogen ions + oxygen gas + ATP
Chlorophyll

Question 9

Describe the light-dependent phase of photosynthesis:

Answer 9

• Occurs inside the grana of the chloroplast, where light energy is absorbed by chlorophyll
• Light energy is converted into chemical energy via an electron transport chain (ATP is produced from ADP)
• The sun splits water molecules into hydrogen ions (H+) which are taken up by hydrogen acceptor molecules NADP to form NADPH2 and oxygen (O2) and creates ATP.
• Only the NADPH2 (H+ ions) and ATP go on to take part in the second stage
• Oxygen is released from the light-dependent reaction as a waste product either into the atmosphere or used for cellular respiration

Question 10

List the inputs and outputs of the light-dependent phase photosynthesis:

Answer 10

Inputs: Water, ADP, NADP+
Outputs: ATP, NADP, O2

Question 11

Name the worded equation of the light-independent phase of photosynthesis:

Answer 11

ATP + Hydrogen ions + Carbon dioxide = Glucose + Water + ADP

Question 12

Describe the light-independent phase (Calvin cycle) of photosynthesis:

Answer 12

• Occurs inside the stroma of the chloroplast, where the end result in the formation of glucose molecules
• The hydrogen ions (H+) from the NADPH2 are combined with CO2 (that diffuses into the chloroplast from the atmosphere or from cellular respiration reactions) to form glucose.
• The ATP produced during the light reaction provides the energy required for this anabolic reaction
• Excess glucose that is formed can be stored in the form of starch in the starch granules of cells

Question 13

List the inputs and outputs of the light-independent phase of photosynthesis:

Answer 13

Inputs: CO2, NADPH, ATP
Outputs: Glucose, H2O, ADP, NADP+

Question 14

List 3 factors which affect the rate of photosynthesis:

Answer 14

• Increasing light intensity
• Increasing temperature and light intensity
• Increasing carbon dioxide levels and light intensity

Question 15

What are the cristae of mitochondria?

Answer 15

The infolding’s of the inner membrane, which is the location of the electron transport chain

Question 16

What is the matrix of mitochondria?

Answer 16

The region enclosed by the inner membrane, which is the location of the Krebs (citric acid) cycle and transition reaction.

Question 17

What is cellular respiration?

Answer 17

The process by which an organism breaks down energy-rich molecules, such as glucose, to release the energy in the useable form of ATP.

Question 18

List the 2 types of cellular respiration:

Answer 18

• Aerobic

- Anaerobic

Question 19

What is fermentation?

Answer 19

The process of anaerobic respiration in yeasts that results in the formation of alcohol.

Question 20

List 3 differences between aerobic and anaerobic respiration:

Answer 20

• Anaerobic respiration does not require oxygen while aerobic respiration does
• Anaerobic respiration releases less energy than aerobic respiration
• Anaerobic respiration is faster than aerobic respiration

Question 21

Describe stage 1 of cellular respiration:

Answer 21

Glycolysis:

• Occurs in the cytosol and requires no oxygen (process is anaerobic)
• Involves the splitting of one glucose molecule (6C) into two pyruvate molecules (3C) and the energy released produces 2 ATP molecules and is used to form 2 NADH molecules (NADH generated from NAD+)
• 2 water molecules released

Question 22

Describe stage 2 of cellular respiration:

Answer 22

The Krebs Cycle:

• If oxygen is present the 2 pyruvate molecules from glycolysis move from the cytosol into the matrix and the Kreb cycle begins.
• As the 2 pyruvate molecules are broken down, 6 CO2 molecules are formed (3 from the breakdown of each pyruvate molecule), and the energy released produces 2 ATP molecules and loads 12 H+ ions and electrons onto NAD and FADH molecules (another type of acceptor molecule) to form 12 energy-carrying molecules (Eg. 8 NADH and 4 FADH2).

Question 23

Describe stage 3 of cellular respiration:

Answer 23

Electron Transport Chain:

• Only stage that uses oxygen
• Takes place in the cristae of the mitochondria, where electron-accepting compounds called cytochromes are embedded.
• During these reactions, electrons donated by the NADH and FADH2 molecules formed during the Krebs cycle (and sometimes Glycolysis), are passed along a series of cytochromes with the 12 H+ ions, released from the molecules, to form 6 water molecules.
• The energy released from the transport of electrons during these electron transport reactions produces 32 or 34 ATP (depending on cell type).

Question 24

What is the overall equation for cellular respiration?

Answer 24

Glucose + 6 Oxygen = 6 Carbon dioxide + 6 Water

Question 25

Describe the structure of the grana in chloroplasts:

Answer 25

• Located in the inner membrane of the chloroplast
• Consists of a stack of thylakoids, where each thylakoid is surrounded by a thylakoid membrane
• Plural of granum is ‘grana’
• Light-dependent reactions of photosynthesis take place in the grana (on the thylakoid membranes)

Question 26

Describe the structure of the stroma in chloroplasts:

Answer 26

• Is the fluid matrix in which the grana are suspended in the chloroplast
• Light independent reactions of photosynthesis take place in the stroma