RESPIRATION HW 1
Assigned September 26, 2024
NAME: JOEL BARNETT
CLASS: 6A-1
Due Oct. 2, 2024
Answer each of the following questions on the paper, creating space as needed, OR complete on a
new document. Remember to save as a pdf before uploading to Canvas.
1. ATP is described as having a universal role as the energy currency in all living organisms.
Explain why it is described in this way. [4]
ATP has a universal role in being the energy currency of all organisms because it is present in
all living organisms, serving as an intermediate molecule in exergonic and endergonic
reactions. This is because of its quick and easy release of high chemical potential energy
derived from the three phosphates groups present. Additionally, ATP is recyclable because it
reacts reversibly as ATP can dephosphorylate to ADP and inorganic phosphate (releasing
energy) after which ADP can then be phosphorylated in the presence of inorganic phosphate
(storing energy). This is advantageous in high energy reactions in the cells of living
organisms.
2. Describe what happens to the pyruvate so that the Krebs Cycle can take place. [4]
A single pyruvate molecule undergoes oxidative decarboxylation in a process known as the
link reaction which is catalyzed by an enzyme known as pyruvate dehydrogenase. This takes
place in the matrix of the mitochondrion. Firstly, the pyruvate loses a CO2 molecule via
decarboxylation. Next, it is oxidised by dehydrogenation to lose two hydrogen ions to NAD
to form reduced NAD. The acetyl remainder of pyruvate combines with a coenzyme A, to
form a compound called acetyl CoA which moves on to the Kreb Cycle. The link reaction
happens twice for every glucose molecule as two pyruvate molecules are made per glucose
molecule.
3. Outline the roles of NAD and FAD in aerobic respiration. [4]
NAD and FAD are coenzymes that either act as H+ acceptors or donors during aerobic
respiration. In glycolysis, NAD oxidises triose phosphates to pyruvic acid by accepting
hydrogen ions from them. In the link reaction, it assists in the catabolism of pyruvic acid
(oxidises it) by accepting hydrogen ions from it. In the Kreb Cycle, it catalyses the oxidation
of a six-carbon compound(citrate) to a four-carbon compound by accepting hydrogen ions
while FAD oxidises the four-carbon compound via the acceptance of hydrogen ions. In
oxidative phosphorylation, Both NADH and FADH become oxidised (via the enzyme
dehydrogenase), losing H+ ions as well as electrons which are used to generate an
electrochemical gradient by providing the energy for hydrogen ions to be pumped from the
matrix of the mitochondrion to the intermembrane space. As that gradient dissipates across
the channel protein ATP synthase, ATP is synthesized from ADP and inorganic phosphate.
4. Describe three ways in which the structure of the mitochondrion is adapted for oxidative
phosphorylation. [6]
The inner membrane of the mitochondrion allows for electrons to be transported between
its faces on an electron transport chain, which provides the energy for H+ ions to be pumped
from the matrix to the intermembrane space forming an electrochemical gradient. Next, the
inner membrane contains protein molecules that act as channels (called ATP synthases/
ATPases) allowing for the movement of H+ ions from the intermembrane space to the
matrix, down a conc. gradient. These ATPases use the dissipation of this electrochemical
gradient to synthesize ATP from ADP and inorganic phosphate. Lastly, the inner membrane is
folded into a structure called cristae, increasing the surface area of the inner membrane. The
larger the surface area of the inner membrane, the more ATPase molecules and electron
transport carriers it can accommodate, thus the more ATP is formed.
5. Figure 1 is a flow chart which represents a part of the glycolysis pathway.
(i) In which part of the cell does the process of glycolysis occur? [1]
Cytoplasm
(ii) State what is occurring at EACH of the stages labelled 1, 2, 3 and 4 in Figure 1. [4]
1. Phosphorylation of Glucose by ATP
2. Isomerization of Glucose-6-phosphate to fructose-6-phosphate
3. Phosphorylation of Fructose-6-phosphate to Fructose-1,6-bisphosphate
4. Lysis of the fructose-1,6-bisphosphate into 2 carbon sugar phosphates
(dihydroxyacetone phosphate and Glyceraldehyde-3-phosphate).
(iii) Suggest the significance of the pathway shown in Figure 1. [2]
The significance of the pathway known as glycolysis is the catabolism of the complex
molecule, glucose(sugar) into a simpler molecule, pyruvate(acid,) as well as
producing chemical energy in the form of 4 ATP with a net of 2 ATP.
