Chemical in The Cell Play a Role as Buffer

The Major Body Buffer Systems

Site Buffer System Comment

1. ISF

a. Bicarbonate For metabolic acids

b. Phosphate Not important because concentration too low

c. Protein Not important because concentration too low

2. Blood

a. Bicarbonate Important for metabolic acids

b. Hemoglobin Important for carbon dioxide

c. Plasma protein Minor buffer

d. Phosphate Concentration too low

3. ICF

a. Proteins Important buffer

b. Phosphates Important buffer

4.Urine

a. Phosphate Responsible for most of 'Titratable Acidity'

b. Ammonia Important - formation of NH4+

5. Bone

a. Ca carbonate In prolonged metabolic acidosis

The other buffer systems in the blood are the protein and phosphate buffer systems.

These are the only blood buffer systems capable of buffering respiratory acid-base disturbances as the bicarbonate system is ineffective in buffering changes in H+ produced by itself. The phosphate buffer system is NOT an important blood buffer as its concentration is too lowThe concentration of phosphate in the blood is so low that it is quantitatively unimportant. Phosphates are important buffers intracellularly and in urine where their concentration is higher.

Haemoglobin is an important blood buffer particularly for buffering CO2

Protein buffers in blood include haemoglobin (150g/l) and plasma proteins (70g/l). Buffering is by the imidazole group of the histidine residues which has a pKa of about 6.8. This is suitable for effective buffering at physiological pH. Haemoglobin is quantitatively about 6 times more important then the plasma proteins as it is present in about twice the concentration and contains about three times the number of histidine residues per molecule.

The carbonate and phosphate salts in bone act as a long term supply of buffer especially during prolonged metabolic acidosis. The important role of bone buffers is often omitted from discussions of acid-base physiology.

Bone is the major CO2 reservoir in the body and contains carbonate and bicarbonate equivalent to 5 moles of CO2 out of a total body CO2 store of 6 moles. (Compare this with the basal daily CO2 production of 12 moles/day)

CO2 in bone is in two forms: bicarbonate (HCO3-) and carbonate (CO3-2). The bicarbonate makes up a readily exchangeable pool because it is present in the bone water which makes up the ‘hydration shell’ around each of the hydroxyapatite crystals. The carbonate is present in the crystals and its release requires dissolution of the crystals. This is a much slower process but the amounts of buffer involved are much larger.

How does bone act as a buffer?

Two processes are involved:

• Ionic exchange

• Dissolution of bone crystal

Bone can take up H+ in exchange for Ca++, Na+ and K+ (ionic exchange) or release of HCO3-, CO3- or HPO4-2. In acute metabolic acidosis uptake of H+ by bone in exchange for Na+ and K+ is involved in buffering as this can occur rapidly without any bone breakdown. A part of the so called ‘intracellular buffering’ of acute metabolic disorders may represent some of this acute buffering by bone. In chronic metabolic acidosis, the major buffering mechanism by far is release of calcium carbonate from bone. The mechanism by which this dissolution of bone crystal occurs involves two processes:

• direct physicochemical breakdown of crystals in response to [H+]

• osteoclastic reabsorption of bone.

The involvement of these processes in buffering is independent of parathyroid hormone. Intracellular acidosis in osteoclasts results in a decrease in intracellular Ca++ and this stimulates these cells.

Bone is probably involved in providing some buffering for all acid-base disturbances. Little experimental evidence is available for respiratory disorders. Most research has been concerned with chronic metabolic acidoses as these conditions are associated with significant loss of bone mineral (osteomalacia, osteoporosis). In terms of duration only two types of metabolic acidosis are long-lasting enough to be associated with loss of bone mineral: renal tubular acidosis (RTA) and uraemic acidosis. Bone is an important buffer in these two conditions.

In uraemia, additional factors are more significant in causing the renal osteodystrophy as the loss of bone mineral cannot be explained by the acidosis alone. Changes in vitamin D metabolism, phosphate metabolism and secondary hyperparathyroidism are more important than the acidosis in causing loss of bone mineral in uraemic patients. The loss of bone mineral due to these other factors releases substantial amounts of buffer.

Buffering Capacity

Buffer solution is able to retain almost constant pH when small amount of acid/base is added. Quantitative measure of this resistance to pH changes is called buffer capacity. Buffer capacity can be defined in many ways. You may find it defined as "maximum amount of either strong acid or strong base that can be added before a significant change in the pH will occur". This definition instead of explaining anything - raises a question "what is a significant change?" - sometimes even change of 1 unit doesn't matter too much, sometimes - especially in biological systems - 0.1 unit change is a lot. Buffer capacity can be also defined as quantity of strong acid or base that must be added to change the pH of one liter of solution by one pH unit. Such definition - although have its practical applications - gives different values of buffer capacity for acid addition and for base addition (unless buffer is equimolar and its pH=pKa). This contradicts intuition for a given buffer solution its resistance should be identical regardless of whether acid or base is added. Where n is number of equivalents of added strong base. Note that addition of n moles of acid will change pH by exactly the same value but in opposite direction.

sources :

http://www.chembuddy.com

www.anaesthesiamcq.com

Buffer

The buffer solution is a substance that resist changes in pH when small amounts of acid or base added to them. Acidic buffer solution is something that has pH less than 7. Acidic buffer solution typically made of a weak acid and garammya, frequently sodium salt. Common examples are a mixture of sodium ethanoate and ethanoic acid in solution. In this case, if the solution containing an equal molar concentration of acid and salt, then the mixture will have a pH of 4.76. This is not a problem in terms of concentration, as long as both have the same concentration.

You can change the pH of the buffer by changing the ratio of acid to salt, or by selecting a different acid and one of the salts. The alkaline buffer solution has a pH above 7. The alkaline buffer solution is usually made from a weak base and its salts. Often used as an example is a mixture of ammonia and ammonium chloride solution. If both are in a state of comparable molar ratio, pH of the solution will have a 9:25. Once again, it's not a problem for the concentration you select both the same.

Buffer solution containing something that will remove hydrogen ions or hydroxide ions which you might add - on the contrary will change the pH. Buffer solution of the acidic and alkaline achieve this condition in a different manner. We will take a mixture of sodium ethanoate and ethanoic acid as a typical example of the acidic buffer solution. Ethanoic acid is a weak acid, and the position of equilibrium will be shifted to the left:

Addition of sodium ethanoate in these conditions add to the excess ethanoate ions in significant amounts. Based on Le Chatelier's Principle, the end of the next equilibrium position shifted toward the left.

Therefore, the solution will contain something important:

• Many of ethanoic acid is not ionized;

• Much of the sodium ethanoate ethanoate ions:

• enough hydrogen ions to make the solution become acidic.

Something else (such as water and sodium ions) that are not important in the explanation.

Addition of acid in the acidic buffer solution should eliminate most of the new hydrogen ion opposite pH ill drop by once conspicuous. Of hydrogen ions join ethanoate ion to produce ethanoic acid. Although the reaction is reversible, for ethanoic acid is a weak acid, a large part of the new hydrogen ions is removed through this method.

Since most of the new hydrogen ions is removed, the pH will not change too much - but because the equilibrium involved, the pH will be slightly decreased. Addition of base in the acidic buffer solution

Aqueous solution containing a buffer solution of hydroxide ions and hydroxide ions remove them.

This time the situation is slightly more complicated because there are two processes that can eliminate the hydroxide ions. Removal of hydroxide ions by reaction with acid ethanoate. Most of the acidic substances which hydroxide ions collide with molecules of ethanoic acid. Both will be reacted to form the ethanoate ions and water.

Because most of the hydroxide ion is eliminated, the pH does not change too much. Removal of hydroxide ions by reaction with hydrogen ions. It must be remembered that some of the existing hydrogen ions from ionization aetanoat acid.

Hydroxide ions can be joined to form water. As long as that happens, replace the tip equilibrium. This still happens to most of the hydrogen ion is removed.

Once again, because you have a balance involved, not all of the hydroxide ion is removed - because there are too many. Ionized water formed back into a very small tingat to give some hydrogen ions and hydroxide ion.

The alkaline buffer solution

We will menganbil mixture of ammonia and ammonium chloride as a typical example.

Ammonia is a weak base, and the position of equilibrium will move to the left:

Addition of ammonium chloride was added on condition of excess ammonium ions within a large number. Based on Le Chatelier's Principle, it will cause the tip equilibrium position will shift to the left.

Therefore, the solution will contain a few important things:

• Many of ammonia does not react;

• Many of ammonia from ammonium chloride ion;

• Enough hydrogen ions to produce the alkaline solution.

Other things (like water and chloride ions) are not important in the explanation.

Addition of acid to alkaline buffer solutions

There are two processes that can remove hydrogen ions that you add.

Removal of hydrogen ions by reaction with ammonia is

Most of the basic substance which hydrogen ions collide with a molecule of ammonia. Both will react to form ammonium ions.

Most, but not all, hydrogen ions are omitted. Acidic ammonium ion is a little weak, and therefore will be released back hidrohen ions.

Removal of hydrogen ions through the reaction with hydroxide ions

It must be remembered that the existing beberepa hydroxide ions derived from the reaction between ammonia and water.

Hydrogen ions can react with hydroxide ions to produce water. As long as that happens, replace the end of the hydroxide ion equilibrium. This continues to happen until the majority of hydrogen ions is removed.

Once again, because you have a balance involved, not all the hydrogen ions is removed - just mostly.

Addition of bases in the alkaline buffer solution

Hydroxide ions of alkali removed melali simple reaction with ammonium ions.

Because the ammonia formed is a weak base, ammonia will react with water - and therefore less reversible reaction. This means that, once again, most (but not all of them) hydrogen ions removed from solution.

source : www.chem-is-try.org

Central Dogma of Molecular by Enzyme

Central Dogma is all the information contained in DNA, and then will be used to produce RNA molecules through transcription, and partial information in RNA will be used to produce the protein through a process called translation.

Here is the mechanism of the process:

Transcription

This is the initial step in the process of protein synthesis which will process will be continued to the expression of genetic traits that emerged as the phenotype. And to study the molecular biology of basic steps that we have to know is how the mechanism of protein synthesis can be expressed as a phenotype sehingge.

Transcription is the synthesis of RNA molecules in the DNA template. This process occurs in the nucleus of the cell (nucleus) precisely on the chromosomes.

Components involved in the transcription process are: the DNA template comprising the nucleotide bases adenine (A), guanine (G), Thymine (T), Cytosine (S); enzyme RNA polymerase, transcription factors, precursors (ingredients were added as penginduksi).

Results from the synthesis process are the three kinds of RNA, ie mRNA messeger RNA), tRNA (transfer RNA), rRNA (ribosomal RNA).

Before that I will present the first main part of a gene. Gene consisting of: promoter, the structural part (consisting of the genes that encode a trait that will be expressed), and terminator.

While the structure of RNA polymerase: the beta, the beta-prime, alpha, sigma. In the structure of the beta and beta-prime acts as a catalyst in the transcription. Sigma structures to direct the RNA polymerase holoenzim just stick to the promoter. Section called core enzyme consisting of alpha, beta, and beta-prime.

Stages in the transcription process basically consists of three stages, namely:

1. Initiation (escort)

Transcription does not start in any place in the DNA, but in the upstream (upstream) of the promoter gene. One of the most important part of the promoter is a Pribnow box (TATA box). Initiation begins when RNA polymerase holoenzim attached to the promoter. Stages starting from the closed promoter complex formation, the formation of open promoter complex, combining several initial nucleotides, and changes in RNA polymerase conformation because the structure is released from the complex sigma holoenzim.

2. Elongation (elongation)

The next process is the elongation. Here is the elongation elongation nucleotides. After RNA polymerase promoter attached to the enzyme will continue to move along the DNA molecule, unravel and straighten helix. In elongation, the nucleotide added covalently to the 3 'end of newly formed RNA molecule. For example the template DNA nucleotides A, the RNA nucleotides are added is U, and so on. The maximum elongation rate of RNA transcript molecular berrkisar between 30-60 nucleotides per second. Elongation velocity is not constant.

3. Termination (termination)

Termination did not occur in any place. Transcription ends when a specific nucleotide see a STOP codon. Furthermore, irrespective of DNA template RNA to ribosomes.

TRANSLATION

The next stage after transcription is translational. Translation is a translation process that existed at the nucleotide sequence of the mRNA molecule into a series of amino acids that make up a polypeptide or protein.

Required in the translation process are: mRNA, ribosomes, tRNAs, and amino acids.

Before that, I will first explain about the structure of the ribosome. Ribosomes consist of large and small subunits. If both subunits combined to form a monosom. Small subunit contains the peptidyl (P) and aminoacyl (A). While the large subunit contains the Exit (E), P, and A. Both subunits contain one or more rRNA molecules. rRNA is very important to identify bacteria at the level of molecular biology, in prokaryotic and eukaryotic 16 S 18 S.

As with transcription, the translation is also divided into three stages:

1. Initiation

First tRNA binding amino acids, and this led to an activated tRNA or event is called the amino-acylation. Amino-acylation process is catalyzed by the enzyme tRNA synthetase. Then ribosomes experiencing separation into large and small subunits. Selajutnya small subunit attached to the initial codons of mRNA molecules with the attached: 5 '- AGGAGG - 3'. The sequence where the attachment of the small subunit is called Shine-Dalgarno sequence. Small subunit can be attached to the mRNA when IF-3. Complex formation, and IF-3/mRNA-fMet IF-2/tRNA-fMet amino acid called N-formylmethionine, and require a lot of GTP as an energy source. tRNA-fMet and then stick to the small subunit of the P codon opener. Furthermore, large subunit attached to the small subunit. In this process of IF-1 and IF-2 was released and GTP is hydrolysed to GDP, and ready for elongation.

2. Elongation

Differences in the process of transcription, the translation of amino acids lengthen. The step in the process of elongation, the first is the binding of tRNA at the A side in the ribosome. Pemidahan will form a peptide bond.

3. Termination

Translation will be terminated at that time one of the three termination codons (UAA, UGA, UAG) that existed at the mRNA reaches the position A on the ribosome. In E. third coli translational process termination signal is recognized by a protein called a release factor (RF). Posting of RF in termination codons are activated peptidyl transferase enzyme which hydrolyzes the polypeptide DNG tRNA on the P side and causing the empty tRNA had translocated to the E (exit),.

That was the process of transcription and translation mechanisms. The next process is the protein will be expressed by our bodies in shape phenotype.

source : http://biowidhi.wordpress.com

Hello :)

Hello, bloggers! Nice to meet you, all. This is my first posting in my new blog. This is my second blog. You can also look my first blog. Okay, I’ll introduce my self. I’m a student of Chemistry major in English Class 09 Andalas University. This blog I was created because of the assignment from my lecture, Prof. Abdi Dharma, M.Si who teach Bio Chemistry in my class. That my blog will be full about Bio Chemistry. Besides because of the assignment that gave for me, I hope this blog can coming in useful for the others.I also hope that I will meet so many friends here.

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