Biology Assignment: Krebs Cycle, ETC, and Photosynthesis Comparison

This biology assignment provides an overview of cellular respiration, focusing on the Krebs cycle (also known as the citric acid cycle or TCA cycle) and the electron transport chain (ETC). The assignment explains the Krebs cycle as a series of chemical reactions that produce ATP, NADH, and FADH2, with CO2 as a byproduct, and how these products are utilized in the ETC to generate energy. The ETC is described as a process occurring inside the mitochondria, where NADH and FADH2 are used to generate ATP through oxidative phosphorylation, and a comparison is drawn between the ETC and photosynthesis, highlighting the electrochemical gradient across membranes and proton pumping. The assignment also touches on the light-dependent phases of photosynthesis, detailing ATP formation in the thylakoid membrane, the role of water and NADP+, and the similarities and differences between these processes. References to relevant research papers are included to support the discussion.

Running head: ASSIGNMENT ON BIOLOGY
Assignment on Biology
Name of the student
Name of the University
Author Note

1ASSIGNMENT ON BIOLOGY
Question 2.
Krebs cycle is also referred to as citric acid cycle due to production of citric acid in this
cycle and also known as TCA cycle or tricarboxylic acid cycle as in this cycle 3 unit of
carboxylic acid is formed. TCA cycle is a cascade of chemical reaction that occurs during the
aerobic metabolism. Therefore,TCA can be defined as metabolism that occurs in the presence of
oxygen. TCA cycle is associated with the release of energy by the oxidative reaction from the
primary food elements that is carbohydrate, fat and protein. In this cycle acetate, in the form of
Acetyl CoA and water is used and as a result NAD+ is reduced to NADH. Along with this, CO2
is produced as byproduct of this cycle. The NADH that is produced from this cycle, is
transported to the electron transport reaction in order to produce energy that can be used as
chemical energy. In TCA cycle, primarily 2 molecules of ATP are produced. In addition to this,
the product that are formed in the TCA cycle are transferred to the electron transport chain of
mitochondria. In the mitochondria, each of the NADH and FADH2 that are produced during
TCA cycle are burnt and 2.5 ATP and 1.5 ATP are formed respectively. In the TCA cycle there
are three steps where NADH are produced and in only one step FADH2 is produced. Ultimately
from 3 units of NADH and 1 unit of FADH2 can produce 9 units of ATP inside the electron
transport chain (Akram 2014).
Question 3.
Electron transport chain or ETC takes place inside the mitochondria. In case of
eukaryotic cells, the NADH and FADH2 that is generated from the TCA cycle are
phosphorylated in the presence of oxygen and produces ATP. In case of plant cells, this process
is continued inside the thylakoid membrane.

2ASSIGNMENT ON BIOLOGY
Photosynthesis
In case of light dependent phases of photosynthesis, ATP is formed in photosynthesis in the
presence of lights. The whole process takes place inside the thylakoid membrane. In this process,
electrons are formed from the water which are excited by the presence of light. Inside the
thylakoid membrane there is /only one proton pump that is responsible for the production of
proton motif force during the transportation of the electron inside the thylakoid. During the light
dependent phosphorylation NADP+ acts as a terminal electron acceptor. In this process, water is
used as the initiator of the reaction (Xu et al. 2017).
ET Cycle
In case of oxidative phosphorylation during ET cycle, the process is continued inside the inner
mitochondrial membrane and FADDH2 and NADH supplies the high energy electrons for this
process. Inside the inner membrane of the mitochondria, there are 3 proton pumps that help to
generate the proton motif forces. In the fourth step of cellular respiration ,that is the ET cycle,
Oxygen acts as a terminal electron acceptor and it produces a water molecule when it combines
with the protons.
When it comes to similarities between the above-mentioned processes, in both the
processes, an electrochemical gradient is created across the membrane that helps in pumping of
proton from low to high concentration (Aerts andMorais2017).

3ASSIGNMENT ON BIOLOGY
References
Aerts, L. and Morais, V.A., 2017. Electron Transport Chain. In Parkinson's Disease (pp. 41-75).
Akram, M., 2014. Citric acid cycle and role of its intermediates in metabolism. Cell biochemistry
and biophysics, 68(3), pp.475-478.
Xu, Y., Fei, J., Li, G., Yuan, T., Li, Y., Wang, C., Li, X. and Li, J., 2017. Enhanced
Photophosphorylation of a Chloroplast‐Entrapping Long‐Lived Photoacid. AngewandteChemie
International Edition, 56(42), pp.12903-12907.