PRELIM IN BIOLOGY

Carlo Jake O. Carballo Elisa A. Menor, Ph.D.

ASSESSMENT 1: What makes ATP essential to the organelles and the cell itself? Pwede ba
ma-low batt ang ATP? Write your answers here.

Cells within the human body depend upon the hydrolysis of 100 to 150 moles of
Adenosine Triphosphate (ATP) per day to ensure proper functioning. As such, ATP is deemed as
the “molecular unit of currency” because it is the compound that is the driving force behind all
living things’ cellular processes.
An article on www.news-medical.net by Susha Cheriyedath, M.Sc. points out the major
functions of ATP in different cellular processes. Cheriyedath states that ATP provides the energy
to transport molecules in and out of the cell in processes which are called endocytosis and
exocytosis respectively. They also contribute to intra and extracellular signaling. When ATP is
released from synapses and axons, purinergic receptors that modulate calcium and cyclic AMP
levels inside the cell are activated. Further, in the process of signal transduction which is how a
physical or chemical signal is transmitted from receptors on the outside of the cell to the inside
of the cell, kinases, which are enzymes that phosphorylate molecules, use ATP as a source of
phosphate groups.
The article also shares that ATP helps in the assembly of cytoskeletal elements to
preserve the structure of the cell. In addition, the hydrolysis of ATP drives three primary
processes to contribute to muscle contraction. The first is through the generation of force against
adjoining actin filaments through the cycling of myosin cross-bridges. The second is the
pumping of calcium ions from the myoplasm across the sarcoplasmic reticulum against their
concentration gradients using active transport. The third function performed by ATP is the active
transport of sodium and potassium ions across the sarcolemma so that calcium ions may be
released when the input is received.
Finally, Cheriyedath shares that ATP is important to the synthesis of DNA and RNA.
ATP is one of four nucleotide-triphosphate monomers that are necessary during RNA synthesis.
DNA synthesis uses a similar mechanism, except in DNA synthesis, the ATP first becomes
transformed by removing an oxygen atom from the sugar to yield deoxyribonucleotide.
For the question about ATP being “low battery,” in its nature, the ATP is supposed to
lose a certain charge/s. Only in this way will it serve its function of being the energy currency of
the cell.
ATP carries energy that comes from the breakdown of food. The energy stored in the
bond of its phosphate groups is measured to about 7.3 kilocalories per mole, which is also
accurate enough to power cellular processes. Bigger energy demand does not mean bigger
energy in the bonds but rather, more ATP production. As stated earlier, ATP loses a phosphate
group to release the energy needed to power these processes. However, when this happens, ATP
becomes Adenosine Diphospate since it has lost one phosphate group. By definition, the prefix
“di” means “two”. Naturally, we would say that ATP cannot become low battery because when it
loses the phosphate group, it is then labeled as ADP. ATP is the “high energy battery” and ADP
is the “used battery.” But this also prompts the cell to recharge the ADP to become ATP again,
making it a cycle of continuous formation and division of ATP.
ACTIVITY:
Look closely at the parts of these organelles. Using your answers to the assignment,
tabulate the parts and functions of each. Please use the succeeding tables.

MITOCHONDRIA
PARTS FUNCTIONS
Outer Membrane It has the protein porin creating channels that
prohibit bigger molecules to enter.
Inner Membrane It serves as a second filter, only letting the
right molecules reach the matrix.
Inter-membrane space It has an important role in the primary
function of mitochondria, which is oxidative
phosphorylation.
Cristae It greatly increases the total surface area of
the inner membrane. It is the site of ATP
production.
Matrix It is where we can find the mitochondria
DNA, ribosomes, and enzymes that help in
the production of ATP.

CHLOROPLAST
PARTS FUNCTIONS
Outer Membrane It also contains porins and is therefore freely
permeable to small molecules.
Inner Membrane It is impermeable to ions and metabolites,
which are therefore able to enter chloroplasts
only via specific membrane transporters.
Stroma It contains metabolic enzymes and multiple
copies of the chloroplast genome
Thylakoid membrane It contains the light-harvesting complex,
including pigments such as chlorophyll, as
well as the electron transport chains used in
photosynthesis.
ASSESSMENT 2:
Go back to the “compartmentalization” concept. Relate that concept to mitochondria and
chloroplast. Based on your tables, I hope that you have realized the fact that the two
organelles have different parts, they are essential to the cell, and they both contribute to
cell’s life and functions despite the differences in their components.

Reflect on the human body as a compartmentalized body. Compare the parts like heart
and lungs to mitochondria and chloroplast. How does compartmentalization apply to the
human body? Write your answer in the space that follows.

The concept of compartmentalization holds the premise of putting the right subjects into
the right units; hence, creating a series of systems that function differently from each other but
cohesively making the whole series work. If we put this idea alongside the structure of
mitochondria and chloroplasts, we can see exactly where compartmentalization occurs.
The easiest way to point how compartmentalization works in these organelles is by
understanding the functions of its structure, and the earliest example would be the function of
their membranes. Both mitochondria and chloroplasts have membranes that serve as filters which
are only permeable to the molecules specifically needed by the organelles. The outer membranes
sieve the molecules trying to enter the organelles, with only smaller molecules being permitted.
Meanwhile, the inner membranes are even more specific because they have transporters that only
carry specific molecules to enter further inside.
To further justify, the fact that these parts hold different functions yet do not overlap is
aligned to compartmentalization. The site of ATP production is only found in the cristae of
mitochondria. In chloroplasts, photosynthesis takes place in both the stroma and the thylakoid
membrane. However, the processes in which photosynthesis undergoes are different from each
other. This exactly encapsulates the idea of compartmentalization: the process for one part is
separate from the other, but both takes place to power the whole system.
This is also similar with the way the human body works. The human body exists as a
being with multiple systems within one compact machine, playing cogs to keep the motor
running. These systems are differentiated for their functions, aptly called respiratory, skeletal,
nervous, digestive, etc. All of these processes take place inside the body, working side-by-side
simultaneously but never overlapping their job descriptions.
If we were to compare the mitochondria and chloroplasts with any organ in the human
body, I think it would best be described by our senses. Of course, humans don’t have
chloroplasts, but plants have both the organelles. In its essence, plants have mitochondria to aid
its cellular processes when sunlight is not available. Photosynthesis needs sunlight to happen and
mitochondria allow the plant to continue photosynthesis without direct sunlight. How does this
relate to our senses?
Most of the time, we rely on our senses to send signals to our brains so we can
distinguish objects within our sensory evaluations. But what happens we lose one? An article
from https://neuroscience.stanford.edu shared that a loss of one sense improves or heightens
another sense. For example, a person who was born blind would have heightened sense of
hearing or touch because the brain then relies on other senses since eyesight is gone. This is very
much like the chloroplasts and mitochondria in the plants. One has adapted to situations that
inhibit the other from functioning fully.