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The Law

Belief - VI

Our Cellular Biology - V

We have discussed earlier that cells archive their genetic information in their DNA, which serves as a master set of instructions for building proteins. It is an amazing system made enormously complex by many levels of control, on-off switches, feedback, and fine-tuning. Segments of DNA are transcribed onto RNA and this RNA is then translated into proteins. The resulting proteins then fold into their three-dimensional configurations, combine with other proteins, or are decorated with sugars or fats to create finely-crafted tools for carrying out specific cellular functions. Proteins are involved in almost all of the processes going on inside your body: they break down food to power your muscles, send signals through your brain that control the body, and transport nutrients through your blood. Many proteins act as enzymes, meaning they catalyze (speed up) chemical reactions that wouldn't take place otherwise. But other proteins power muscle contractions, or act as chemical messages inside the body, or hundreds of other things.Protein functions range from structural supports, motors to catalysts of bio-chemical reactions and monitors of cell's internal and external environments. Some of the examples of functions of protein are:

• Amylase starts the process of breaking down starch from food into forms the body can use.
• Alcohol dehydrogenase transforms alcohol from beer/wine/liquor into a non-toxic form that the body uses for food.
• Hemoglobin carries oxygen in our blood.
• Fibrin forms a scab to protect cuts as they heal.
• Collagen gives structure and support to our skin, tendons, and even bones.
• Actin is one of the major proteins in our muscles.
• Growth Hormone helps regulate the growth of children into adults.
• Potassium Channels help send signals through the brain and other nerve cells.
• Insulin regulates the amount of sugar in the blood and is used to treat diabetes.

Protein folding

Note: Protein Folding: Even though proteins are just a long chain of amino acids, they don't like to stay stretched out in a straight line. The protein folds up to make a compact blob, but as it does, it keeps some amino acids near the center of the blob, and others outside; and it keeps some pairs of amino acids close together and others far apart. Every kind of protein folds up into a very specific shape -- the same shape every time. Most proteins do this all by themselves, although some need extra help to fold into the right shape. The unique shape of a particular protein is the most stable state it can adopt. Picture a ball at the top of a hill -- the ball will always roll down to the bottom. If you try to put the ball back on top it will still roll down to the bottom of the hill because that is where it is most stable.

This folded structure specifies the function of the protein. For example, a protein that breaks down glucose so the cell can use the energy stored in the sugar, will have a shape that recognizes the glucose and binds to it (like a lock and key).

Every step in the protein production pathways can be adjusted up or down as the cell's needs dictate. The ability to carefully regulate transcription, translation, protein folding, and protein function is a feature that makes cells such resilient and versatile life-forms.

The genetic information stored in DNA is a living archive of instructions that cells use to accomplish the functions of life. Inside each cell, catalysts seek out the appropriate information from this archive and use it to build new proteins. Although all of the cells, that make up a multi-cellular organism,contains identical genetic information, functionally different cells within the organism use different sets of catalysts to express only specific portions of those instructions to accomplish the functions of life.

When cell divides, it creates one copy of genetic information - in the form of DNA molecules - for each of the two daughter cells. The accuracy of these copies determines the health and inherent features of the daughter cells. This process is called DNA replication.This process occurs in all living organisms and is the basis for biological inheritance. 

Attached is a 3 min You Tube video on DNA replication simplified.

The first step in DNA replication is unzipping the double helix of the DNA molecule. This is carried out by an enzyme called helicase.

Note: Helicases are enzymes that bind and may even remodel nucleic acid or nucleic acid protein complexes. There are DNA and RNA helicases. DNA helicases are essential during DNA replication because they separate double-stranded DNA into single strands allowing each strand to be copied

Pictorial presentation of DNA replication

The separation of the two single strands of DNA creates a "Y" shape called a replication fork. The two separated strands will work as the templates for making the new strands of DNA.

One of the new strands is oriented from 3' to 5' direction (towards the replication fork); this is the leading strand. The other strand is oriented from 5' to 3' direction (away from the replication fork); this is the lagging strand. As a result of their different orientation, the two strands are replicated differently. 

We will continue with the DNA replication in the next post.

Namaste

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Prabir