Cell Metabolism: ATP Production, Cycles, and Photosynthesis

This essay provides a comprehensive overview of cell metabolism, focusing on the central role of adenosine triphosphate (ATP) as the primary energy carrier in cellular processes. It details the generation of ATP through various mechanisms, including fermentation, aerobic respiration, and chemiosmosis in plant cells. The essay explores metabolic pathways, distinguishing between catabolic and anabolic pathways and their regulation to maintain cellular homeostasis. It further examines the significance of the Krebs cycle (tricarboxylic acid cycle) and the Calvin cycle in ATP generation and energy transfer. Additionally, the essay discusses oxidative phosphorylation in mitochondria and photosynthesis in chloroplasts, highlighting their roles in energy production and the conversion of light energy into usable forms. The essay concludes by emphasizing the interrelationship of these processes and the importance of ATP for the growth and reproduction of living organisms, referencing relevant books and online resources.

CELL METABOLISM

TABLE OF CONTENTS
TOPIC: Cell Metabolism ................................................................................................................1
Overview......................................................................................................................................1
Generation of adenosine triphosphate (ATP) in metabolism.......................................................2
Metabolic pathway.......................................................................................................................2
Ways metabolic pathways are regulated......................................................................................3
Significance of the cycle in generating ATP..............................................................................4
Role of the Calvin cycle...............................................................................................................6
Oxidative phosphorylation in the mitochondrion........................................................................7
Photosynthesis in the chloroplast.................................................................................................9
REFERENCES..............................................................................................................................12

TOPIC: Cell Metabolism
Overview
This essay is based on contribution and complete impact of Adenosine/Nucleoside
triphosphate (ATP) in the cellular processes. It is going to describe about role of Krebs cycle,
Calvin cycle, metabolic pathway, oxidative phosphorylation and photosynthesis process. This is
an organic chemical which is defined as the major carrier of energy for all living organisms.
Primarily it is referred as the molecular unit of currency and gives energy to conduct several
processes in cells. The major composition includes 3 triphosphate groups including alpha, beta
and gamma, 5 carbon sugar ribose and nitrogenous base adenine. When the gamma and beta
bonds get broken then it releases energy which is useful in performing several mechanisms and
cellular responses (Kowal, Yegutkin and Novak,2015).
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Illustration 1: Adenosine triphosphate
(Source: Adenosine triphosphate, 2019)

Generation of adenosine triphosphate (ATP) in metabolism
Herein the generation of ATP in the animal cell takes place when the molecules such as
proteins, carbohydrates etc. gets break down into chemical energy. This chemical energy
supports in formation of molecules of ATP. This leads to transportation of chemical energy via
ATP molecules and has consists of processes like fermentation, aerobic respiration etc. In
simpler words, whenever the cell requires an amount of energy, the beta-gamma phosphate bond
gets broken into form ATP. However, in the plan cell, the chemiosmosis is the actual process for
ATP formation where hydrogen ion gradient is formed. This gradient is the resultant between
transfer of hydrogen ions into the mitochondria and chloroplast through a semi permeable
membrane. The excess hydrogen ions or protons releases energy which is utilised by enzymes to
combine ADP and phosphate ions to form ATP.
Metabolic pathway
There is a need to understand the metabolism and its elements to know the pathways and
formations. This is defined as the collective action plan where the chemical reactions takes place
within a cell in carrying out the pathways for living in wholesome and complete manner. The
metabolic pathways are the inter connected and inter dependent chemical reactions within the
cells. Here the metabolites includes reactants, products and intermediates formed during such
reaction. There are two types of metabolic pathways such as catabolic and anabolic types.
Additionally, these pathways help in assessing the internal balance through monitoring of
homoeostasis. The catabolic pathway is the process of breaking up of larger molecules into
smaller particles through releasing energy in the form of ATP synthesis.
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Illustration 2: Metabolic pathways
(Source: Overview of metabolism, 2019)

Furthermore, these pathways takes place in number of reaction steps and uses enzymes in
the form of protein or catalysed. For instance the ATP serves as signal in the cells where burning
of nutrients occurs and storage as well. When excess of ATP molecules are present then the ATP
stores them and do not let it burn or use it immediately. This helps in improved levels of
immunity to perform several activities within the cells. Nevertheless, it also depends upon nature
of enzymes which further divided into simple systems, multi enzyme complex and organized
multi enzyme complex.
Ways metabolic pathways are regulated
Along with, the metabolic pathways are regulated under constant conditions to maintain
the homoeostasis within cells with respect to the changing environments. This regulation is based
on changing environment and interdependency on the enzyme to understand the response to
signals in either forward or backward modes. When the enzyme is added or presented, its
presence might not be shown largely but has effect on the overall flux of the metabolic gateways.
On the basis of enzyme, there are two type of control namely fine and coarse. The fine control is
faster method to regulate the metabolism activities and depends on the internal levels to regulate
the enzyme's activity. On the other hand, the coarse control is the slow process where the
synthesis of proteins takes place and has control of the enzyme's amount.
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Significance of the cycle in generating ATP.
In regard to the same, the rate limiting step is considered at the initial levels and is
reflected by the feedback inhibition. Here the covalent and non covalent regulatory changes are
important to be examined. The covalent changes consist of adding or displacing a chemical bond
whereas the non covalent changes is highlighted due to regulatory movement of van der waals
forces, hydrogen bonds and the electrostatic that are based on interactive regulations to
understand the binding capacity of enzyme. For e.g. The regulation of glycolysis can be carried
out into three key levels such as hexokinase, phosphofructokinase and pyruvate kinase.
Hexokinase is inhibited by the formation of product named Glucose 6-P. Phosphofructokinase is
stopped by formation of citrate and ATP along with hydrogen ions. Lastly, pyruvate kinase has
been reluctant by the ATP, free fatty acids, acetyl CoA and alanine.
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Illustration 3: Metabolic pathways and the entire interconnectivity
(Source: Metabolic pathway map - Biochemical diagram, 2019)

There is a significance of the Krebs cycle (tricarboxylic acid cycle) in generating ATP
which takes place inside of the mitochondria cell. This cycle plays integral part in an indirect
formation of ATP through NADH and FADH2. This is mainly on the basis of connection
between carbohydrate, protein and fat. It uses two pyruvic acid molecules from the glycolysis
process to give NADH, ATP and FADH2 molecules. Here the process has been undertaken into
breakdown of a carbon atom as CO2 and two other carbon atoms into co enzyme. Thus, it is not
one the second stage of the cellular respiration but also helps in transforming the energy into
ATP molecules. In addition to this, the major usage of this cycle is the donation of energy using
electrons and following an electron transport chain. This is followed by promoting the oxidative
phosphorylation which again helps in the generation of electrons or energy.
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Illustration 4: Steps involved in Krebs
Cycle
(Source:Process of Glycolysis and the
Major Steps, 2019)

Role of the Calvin cycle
In regard to the above, another important cycle is the Calvin cycle is the set of chemical
reactions that take place in the chloroplast at the time of photosynthesis. This type of cycle is
light independent because it takes place after the energy has been captured through sunlight.
Calvin cycle is performed role that can use the energy from the sun in the form of tiny energy
factories known as chloroplast. By using the chloroplast the process of photosynthesis has begun.
It converts sun energy into the storable form in order to sugar molecules like glucose.
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Illustration 5: Steps in the Krebbs Cycle pathway
(Source: Kumari,2018)

The primary role of Calvin cycle is in making simple sugars in the presence of water
(H2O) and carbon dioxide (CO2). Here, CO2 is captured in the reaction of cycle after its
discovers. The plants utilise the Calvin cycle for the carbon fixation and also diffuses into the
stroma of chloroplast which combine with five carbon sugar. This cycle is a type of ancient
biochemical pathway in the chloroplast that connect with the CO2 to 5 carbon carbohydrate to
make intermediate 3 carbon carbohydrate. The 3 Phosphoglycerate can use to make complex
carbohydrate (Jez, Lee and Sherp, 2016).
Oxidative phosphorylation in the mitochondrion
Oxidative phosphorylation is defined as the process of formation of ATP molecules by
the transfer of electrons within the mitochondria. It is also known that mitochondria is known as
the powerhouse of the cell. Thus, this process is known as the maximum number of ATP
molecules producer. The presence of NADH and FADH2 molecules let the production of ATP in
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Illustration 6: The Calvin Cycle
(Source : Calvin Cycle, 2019 )

the presence of oxygen from the given complexes like proteins etc. In this process, enzymes are
presented to break up the proteins which are located in the intermembrane space.
There are several steps that are involved and mainly dependent on both chemiosmosis
and electron transport chain. These together takes place to form large number of ATP molecules
as the end result. Subsequently, at the first stage, the delivery of electrons takes place by using
both NADH and FADH2. Next is the electron transfer and proton pumping where motion of
electrons occurs from high to low energy levels. Then the splitting of oxygen takes place to form
water molecule. Henceforth, this process is necessary for the formation of adenosine triphosphate
molecules for utility of several processes smoothly (Bauwe, 2018).
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Illustration 7: Overview: Oxidative Phosphorylation
(Source:Oxidative phosphorylation, 2019)

Photosynthesis in the chloroplast
Another process is the photosynthesis which takes place in the plants and has been
considered as the lifeline for the entire earth and living organisms. This process takes place in the
chloroplasts which are the organelles of plant cell. These absorb sunlight and with the help of
carbon dioxide and water, it helps in the production of food. The chloroplasts have chlorophyll
that is the photosynthetic pigment and helps in capturing the sunlight from the sun and fixes it on
the ground and store it. This later gets utilised and converted it into ATP and NADPH molecules
which again helps in making water and carbon dioxide.
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Illustration 8: Overview of oxidative phosphorylation where the electron transport chain
forms a proton gradient across the inner mitochondrial membrane, which drives the synthesis
of ATP via chemiosmosis
(Source: Oxidative phosphorylation, 2019)
Illustration 9: Basic equation of photosynthesis
(Source:Photosynthesis, 2019)

With respect to the above, there are two stages of this photosynthesis process and is
mainly divided into light and dark reactions. In the first stage called as light stage, the breakdown
of water molecules into oxygen takes place. Next in the second stage whioch is also refered as
dark reaction or Calvin cycle is useful in creating sugars from the carbon dioxide. Both the
stages are connected with the presence of the energy carrier called as adenosine triphosphate and
nicotinamide adenine dinucleotide phosphate ion.
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Illustration 10: Structure of chloroplast
(Source: Photosynthesis, 2019)

It has been summarised that adenosine triphosphate is one of the basic essentials that is
required to conduct several processes and also assist in storing the energy levels of living
organisms. Here the significance of glycolysis, Krebs cycle and Calvin cycle has been
significantly explained in relation to the role of ATP molecule to understand its participation on
daily basis. Moreover, the inter relationship of formation of ATP molecules and the mechanism
pathways has been illustrated. Lastly, it also shed light on the role of mitochondria and
chloroplast to highlight the need of such currency units for the growth and reproduction of living
organisms.
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Illustration 11: Flow diagram of photosynthesis
(Source:Photosynthesis, 2019)

REFERENCES
Books and Journals
Bauwe, H., 2018. Photorespiration–Damage Repair Pathway of the Calvin–Benson
Cycle. Annual Plant Reviews online. pp.293-342.
Jez, J.M., Lee, S.G. and Sherp, A.M., 2016. The next green movement: plant biology for the
environment and sustainability. Science.353(6305). pp.1241-1244.
Kowal, J.M., Yegutkin, G.G. and Novak, I., 2015. ATP release, generation and hydrolysis in
exocrine pancreatic duct cells. Purinergic signalling.11(4). pp.533-550.
Online
Adenosine triphosphate. 2019.[Online]. Available through:<http://hyperphysics.phy-
astr.gsu.edu/hbase/Biology/atp.html>.
Calvin Cycle. 2019.[Online]. Available through:< https://s3-us-west-2.amazonaws.com/courses-
images/wp content/uploads/sites/198/2016/11/23225302/7-2-2.jpeg
Kumari, A., 2018. Citric Acid Cycle. [Online]. Available
through:<https://www.google.com/search?
q=adenosine+triphosphate&oq=adenosine+triphosphate&aqs=chrome..69i57j69i60l2.271
j0j4&sourceid=chrome&ie=UTF-8
Metabolic pathway map - Biochemical diagram. 2019.[Online]. Available
through:<https://www.conceptdraw.com/examples/methabolic-diagram>.
Overview of metabolism. 2019.[Online]. Available
through:<https://www.khanacademy.org/science/high-school-biology/hs-energy-and-
transport/hs-introduction-to-metabolism/a/overview-of-metabolism>.
Oxidative phosphorylation. 2019. [Online]. Available through:<
https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/
oxidative-phosphorylation/a/oxidative-phosphorylation-etc>.
Process of Glycolysis and the Major Steps. 2019.[Online]. Available
through:<http://www.rajeshbihani.com/raj/381/>.
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