Hidup Ala Ulat Bulu

Jean Henri Fabre, seorang ilmuwan dari Perancis pada tahun 1870-an pernah mengadakan percobaan terhadap sekelompok ulat bulu. Fabre mengambil beberapa ulat dan membuat yang paling depan menyentuh ulat yang paling belakang. Ulat tersebut membentuk suatu lingkaran mengelilingi pot bunga. Di tengah pot itu, diletakkan ranting dan pucuk daun muda sebagai makanan ulat-ulat tersebut. 

Setelah beberapa saat, ulat-ulat itu berjalan beriringan mengitari pot yang berisi makanan. Ulat-ulat itu terus berputar dan berputaaar.... Jam demi jam, siang dan malam... Hari demi hari, hingga genaplah satu pekan ulat tersebut mengitari pot bunga.

Setelah berjalan tanpa mengenal lelah, ulat bulu tersebut mati karena kelaparan dan kehausan. Padahal dalam jarak yang sangat mudah dijangkau (tepatnya di tengah pot) tersedia makanan yang sangat lezat kesukaan mereka.

 Dari cerita di atas, banyak diantara kita yang hidup seperti ulat-ulat itu. Kita hidup mengikuti kebiasaan yang sudah berlaku, terus bekerja keras namuuuun kehilangan kesempatan untuk mengetahui bahwa di dekat kita banyak peluang yang bisa memberi kebahagiaan kepada kita. Untuk menghindari hal itu, kalian harus menentukan hidup, tidak asal ikut-ikutan tradisi atau kebiasaan yang sudah ada.

Untuk merancang masa depan, langkah pertama yang harus kalian siapkan adalah tetapkan prestasi terbaik yang kaliann ingin raih selama hidup di muka bumi. Kalian tahu mengapa???? Karena kalian makhluk spesial, jangan sia-siakan hidupmu, sebagaimana kumpulat ulat bulu itu ^^.

 

Enzymes Accelerate Chemical Reactions

In the body, cells must continually carry out a remarkable assortment of chemical reaction, which much proceed at a rate that is fast enough to be useful to the cell. All living things therefore depend on molecules called enzymes that accelerate chemical reactions, and a proccess known as catalysis. The enzymes catalyze chemical reactions by lowering the activation energy barrier. Most enzymes are proteins, although some are composed of RNA. Enzymes vary in degree to which they accelerate reaction rates. Some accelerate a chemical reaction by just several orders of magnitude, while some enhance reaction rates by a remarkable factor of 10¹⁷.

There are several features that are common to all enzymes. An enzyme binds to one or more molecules known as substrates, promotes a chemical reaction in the substrate molecules and then realeases the products of reaction. The enzyme isn’t permanently modified in a proccess, so it’s then able to bind another substrate molecule and perform the reaction again. Enzymes generally catalyze just one type of chemical reaction and are usually highly specific for the types of substrates on which they act. For this reason, cells produce many different types of enzymes, each uniquely designed for a particular chemical task.

A chemical reaction with negative free energy change should occur spontaneously, given enough time. However, in the course of the chemical reaction, the substrates must undergo transient changes in stereochemistry, charge, or covalent stucture before completing the necessary rearrangements to produce the final products. These changes are energetically unfavorable, which means that the first steps in the chemical reaction generally involve a positive free energy change. These are then followed by chemical steps with a negative free energy change of even greater magnitude, resulting in a chemical reaction whose net free energy change, when summed over all the steps is negative.

A consequence of this energetic pathway is that there is a free energy barrier between the initial and final states of the chemical reaction. The transition state, which is the highest point in free energy on the reaction pathway from substrate to product, marks the top of the free energy barrier. This species exists only transiently (for perhaps as little as 10⁻¹⁵ seconds) and is generally different in stereochemistry and charge configuration from either the substrate or the product. It is the energy difference between the ground state and the transition state that constitutes the activation energy.

Without the aid of an enzyme, few substrate molecules at any one time typically have sufficient energy to reach the transition state, and, as a result, the uncatalyzed reaction proceeds slowly. Enzymes achieve their catalytic effects by lowering the activation-energy barrier using several different strategies (Craig, dkk: 2010).

The Covalent Bonds Form

An atom whose outer shell isn’t filled is chemically reactive, meaning that it can participate in chemical reaction with other atoms. An atom with an unfilled outer shell can share electrons with another atom. By sharing electrons, the atom can achieve a full outer shell and it will become more stable as a result. This situation is depicted in the figure below for hydrogen and oxygen, which can combine to form a water molecule. 

Hydrogen atom has just one electron in the outer shell instead of the allowed two, while oxygen atom has six electrons in the outer shell instead of the allowed eight. When two hydrogen atoms share their electrons with an oxygen atom, each atom now has a complete outer shell and is therefore more stable. Sharing of electrons between atoms is the basis of covalent bonds, whereby atoms are joined to one another to form molecules. The sharing of one pair of electrons gives rise to a single bond between two atoms and sharing of two pairs of electrons constitutes a double bond. The covalent bonds are typically very stable, which means it takes a substantial amount of energy to break them. The precise amount of energy is needed to break a covalent bond depends on the types of atoms involved and the number of bonds they form with one another. The double bonds generally being stronger than single bonds.

 

The above figure shows that covalent bonds in (A) a water molecule forms when each of two hydrogen atoms share an electron with an oxygen atom. Each hydrogen atom forms a single covalent bond with the oxygen atom. For figure (B) oxygen is commonly found as the molecule O₂, in which two oxygen atoms share electrons. Each shared electron pair represents a single covalet bond. The two atom oxygen atoms therefore form a double covalent bond with one another (Craig, dkk: 2010).

Kandungan Glukosa pada Urin

Urin merupakan salah satu cairan yang mengandung sisa metabolisme yang diekskresikan oleh ginjal. Seperti yang telah dijelaskan sebelumnya urin terbentuk melalui 3 tahap yaitu filtrasi, absorpsi, dan augmentasi. Pada orang sehat, urin mengandung air, ureum, kreatin, dan garam-garaman, sedangkan urin yang tidak sehat, bisa mengandung glukosa, protein, atau darah. Normalnya glukosa tidak ditemukan atau ada tapi dalam jumlah yang sangat kecil di dalam urin. Hal ini dikarenakan di dalam ginjal glukosa mengalami penyerapan kembali (reabsorpsi) oleh tubulus kontortus proksimal. Apabila tingkat glukosa dalam darah melebihi batas gula ginjal (160-180 mg/dl) maka glukosa mulai nampak dalam urin. Keberadaan glukosa dalam urin (glucosuria) merupakan indikasi adanya penyakit, yaitu diabetes mellitus.

Penyakit diabetes mellitus dapat dideteksi lewat uji kandungan glukosa yang terdapat dalam urin. Uji tersebut menggunakan larutan yang disebut reagen benedict. Reagen benedict adalah larutan yang digunakan untuk mengetahui kandungan glukosa dalam suatu cairan. Glukosa mempunyai sifat mereduksi. Apabila reagen benedict diteteskan ke dalam larutan gula maka tembaga alkalis yang terkandung di dalam benedict akan direduksi oleh gula yang mempunyai gugus aldehida dengan membentuk kuprooksida (Cu₂O) yang akan menghasilkan endapan berwarna merah bata yang berada di dasar tabung. Dengan cara seperti itulah maka glukosa yang terkandung di dalam urin dapat terdeteksi dengan  perubahan warna yang terjadi.

Pada gambar di atas menunjukan bahwa urin yang tidak sehat (mengandung glukosa) setelah ditetesi reagen benedict dan dipanaskan di atas api mengalami perubahan warna menjadi merah bata. Sedangkan, urin yang sehat setelah ditetesi benedict warnanya tidak berubah dan tetap berwarna biru.

Agar terhindar dari penyakit diabetes melitus sebaiknya melakukan hal-hal pencegahan seperti berikut ini: 1) selalu memperhatikan porsi makanan agar tetap seimbang (pilih makanan dengan karbohidrat/rendah gula), 2) olahraga secara teratur dan tidak banyak berdiam diri, 3) usahakan berat badan dalam batas normal, dan 4) hindari obat-obatan yang dapat menimbulkan diabetes (Wijayakusuma, 2008).