Importance of Proteins in Human Structure and Function

This essay discusses the importance of proteins in the structural reform and functional abilities of the human body. It covers the structure of haemoglobin and actin, their role in cellular respiration, cytoanatomy, and more.

Running head: HUMAN STRUCTURE AND FUNCTION
Human Structure and Function
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1HUMAN STRUCTURE AND FUNCTION
Introduction
Anatomy and physiology entail the structural and functional components of human
body. Macromolecules are the essential part and parcel of the human physiological system.
Comprised of carbohydrates, proteins, lipids and nucleic acids, macromolecules form various
structural and chemical components of our body. Each cell in the body is made up of one or
the other kind of macromolecule. The chosen macromolecule is protein, which is widely
acknowledged as the building blocks of life. Proteins are the major components responsible
for forming enzymes and hormones, constructing blood and muscles, transporting various
materials throughout the body (Buenrostro et al, 2013). The following essay tries to establish
the key points addressing the importance of proteins in the structural reform and functional
abilities of human body.
Discussion
Amino acid residues connected with peptide bonds make up proteins (Whitford,
2013). Chosen proteins for this essay are metalloprotein Haemoglobin and multifunctional
globular protein Actin (Whitford, 2013).
Structure
Each protein is quite specific regarding their functions, and the function of each
protein depends solely on their structural configuration. If the protein’s structure changes in
some unfavourable condition, then that protein can no longer function properly. Generally, all
proteins fall under one of the four structural categories, which are as follows:
1) Primary structure: includes sequence of amino acid chains.

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2) Secondary structure: includes α-helix and β-pleated sheets, which are
constructed with the help of hydrogen bonds between the peptide backbones.
3) Tertiary structure: includes different three-dimensional folds in the proteins
due to side-chain interactions.
4) Quaternary structure: includes proteins which are composed of more than one
amino acid.
Red Blood Cells are comprised of protein pigment haemoglobin molecules which are
responsible for its oxygen carrier function. Each RBC consists of about 250 million
haemoglobin molecules. Haemoglobin has a quaternary structure and it is a protein with
multiple subunits (Gleixner et al., 2016). Each subunit is made up of a protein part and a
prosthetic group such as a metal ion or heme group. The porphyrin ring holds the heme group
in place. The ring is made up of four pyrrole rings. This structure mostly contains alpha
helices which are stabilized by hydrogen bonding. Approximately 150 amino acid residues
make up the two alpha and two beta chains (Gleixner, 2016).
The structure of actin can be globular (like in G-actin) or filamentous (in F-actin) or it
can be a multi-domain protein. It possesses the activity of ATP hydrolysing. A glutamate
residue is also found at the active site of the ATP hydrolytic domain. Together with highly
acidic N-terminus and alkaline C-terminus, it also comprises of 374 amino acid residues
(Blanchoin et al., 2014). Tertiary and super secondary structures have been discovered. It is a
highly conserved protein and is involved in many protein-protein interactions. Actins are
responsible for several significant cellular functional properties including maintenance of cell
shape and form, being a regulator of transcription, to most importantly supporting cell
motility. Actin filaments, in conjunction with myosin, form the basis of muscle contraction.

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Cellular respiration
Oxygen from lungs is carried by haemoglobin in blood to cells. It enables the tissues
to perform cellular aerobic respiration cycles. The heme group, consisting of porphyrin ring
and a ferrous atom, reversibly binds one oxygen molecule. In the deoxyhaemoglobin form,
the globin units retain a tense conformation with electrostatic bonds among them.
Conformational changes due to oxygen binding, allow them to attain a relaxed state which
cooperatively binds 500times more oxygen than the deoxy-form (Rummer et al, 2013).
Aerobic organisms like humans, generate 18times more ATPs from glycolysis during aerobic
respiration, with the help of oxygen-utilizing TCA cycle and ETC. Proteins are indirectly
used as energy sources, to run the cellular processes. Thus, haemoglobin only works as a
respiratory gas transport medium and is not associated with the cellular respiratory processes
directly.
Actin filaments, which are major structural components of muscles, are primarily
responsible for muscle contraction and movements. Along with myosin, the globular protein
molecule actin, drives motor functions by utilizing the chemical energy stored in ATP
molecules, (Tang, 2015). Muscle cells produce ATP through the process of aerobic
respiration.
Thus the catabolic pathways do not break down proteins who are not directly involved
in cellular respiration. Glycolysis and TCA cycle, the pathways of respiration, only break
glucose. Digestive enzymes like trypsin and chymotrypsin break down proteins into simpler
forms like peptone or peptides. At last the peptone is broken down into amino acids. Several
amino acids like glutamic acid and aspartic acid produce intermediates for the TCA cycle in
the form of alpha keto glutarate by deamination or transamination reactions (Yang et al,
2014). Thus the by-products of amino acid metabolism enter the cellular respiratory pathway.

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Most importantly, proteins are not the first choice of macromolecules for energy production.
If under any unfavourable circumstances the carbohydrate or lipid storage gets depleted, only
then the cellular processes start relying on proteins for generation of ATP molecules.
Cytoanatomy
Cytoskeleton is made up of microtubules, microfilaments and intermediate filaments.
Microtubule, made up of tubulin units, is the largest type of filament. Microfilaments, made
up of polymers of F-actin filament, are the smallest type of filaments (Blanchoin et al., 2014).
Septins, spectrins are also cytoskeleton proteins present in eukaryotes. Microfilaments have
spiral filamentous structure, made up of globular actin protein molecules, which together with
myosin protein, play a major role in muscle contraction. Plasma membrane is provided with
support and strength by these filaments which thus aid in cellular movement. Due to this
property, actins play a major role in cell division, especially in cytokinesis. Cytoskeletons are
important for maintaining a cell’s shape and organization. During mitosis the actin filaments
help to maintain the cell shape by bearing the tension of centrosome positioning. It is due to
the actin microfilaments that each cell is able to divide properly, without any imparity (Tee et
al, 2015).
Ribosomal RNAs (rRNA) and different proteins make up the cell organelle ribosome.
The structural assembly of the organelle is mainly taken care of by both rRNA and ribosomal
proteins. Eukaryotic ribosome has more than 80 proteins present on the surface and stabilizes
the structure (Bai et al., 2013). Although some of these proteins do not have any role in the
mature ribosome, due to enormous cooperativity of the ribosomal proteins it is quite difficult
to distinguish the function of each protein. Along with their role as house-keeping elements
of the cells, these proteins attend to several functions which are independent of ribosomes.
They possess significant objectivities in immunogenic, tumor-suppressor functions as well

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(Zhou et al, 2015). The essential process of translation accounts for the participation of these
proteins, along with the rRNAs. Different steps of translation require binding of different
ribosomal subunits which are specific for recognizing the core sequences.
Conclusion
Therefore from the above discussion it can be concluded that proteins are the most
diversely significant macromolecules of the human physiological system. The detailed
structure of a haemoglobin molecule and the different forms of actin protein, enable these
macromolecules to perform their roles in cellular processes. Any changes in their structures
lead to severe impairment of the bodily functions. Every protein molecule has a unique
function, such as haemoglobin acts as a transporter for respiratory gases whereas actin entails
cellular structure and motility, as well as muscle contraction and movement. The proteins
involved in translation holds the most importance, since any discrepancy in their function can
lead to unavoidable consequences. Thus, proteins are of incredible importance to the human
body.

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References
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