IndicatorspH indicator is a dye that appears in different colours in its protonated and deprotonated forms.

-Often organic dye

-Different indicators change colour over different pH ranges - Effective indicators change colour rapidly at the equivalence point to an end-point colour

e.g :- Litmus papers –Phenolphthalein

Hln(aq) ↔ (H+) +( In-)

- For litmus :-

Red(in acidic medium), Blue(in basic medium)

Ka= [H+] [In-]/[HIn] Rearrange:

[Hln]\[ln]=[H+]\ka

-The colour of indicator depends on pH or [H+] and Ka

-When pH=pKa, the two colours have equal Concentrations.

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Buffers II

Biological buffer system in the body

Note: In this sheet I rearranged some ideas that Dr. Diala mentioned in the lecture to achieve higher understanding .

We have different types of buffers systems in our body, each one of them work in a different place whether intracellular or extracellular.

Buffer systems in the body:

The bicarbonate – carbonic acid buffer system (the most important one extracellularly)

The hemoglobin buffer system in RBCs The phosphate buffer system in all types of cells The protein buffer system of cells and plasma

They all act as the first line defense to maintain PH of the body.

If there’s certain problems regarding the capacity of the buffer and it’s not performing its function properly, then we should move to the second line of defense-the respiratory mechanism:It affects the rate of inhalation and exhalation, how much oxygen is taken in and the amount of carbon dioxide released.There’s the third line of defense that is associated with renal mechanism (kidneys) - process of absorption and reabsorption for the components within the buffer system.

Bicarbonate-carbonic acid buffer system:

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From outside air:

1. We breathe (inhale) → take in oxygen which then goes to the lungs, where gas exchange takes place.

2. Oxygen then travels to the blood, which is loaded byHemoglobin in RBC and distributed to the cells in thebody.

3. It then travels to the active cells where there’s oxygenConsumption and releases carbon dioxide, thereforeCO2 leaves the cell and diffuses to the cell membraneand returns back to the blood.** Actually the synthesis of H2CO3 doesn’t take place inthe blood now; it has to go to the RBC specifically as it has a specific enzyme needed to form H2CO3.

4. After H2CO3 forms in the RBC and released in the blood it dissociate forming the components ofbicarbonate-carbonic acid buffer system.The reactions that occur in this system:

1- CO2(g) released as a waste product from metabolic reactions.It surrounded by an aqueous environment therefore it dissolved in H2O producing CO2 in the aqueous state:

CO2 (g) CO2 (aq)

2- Then CO2(aq) interact with H20 to form H2CO3(aq)

CO2 (aq) + H2O (I) H2CO3 (aq)

3- H2CO3 is considered to be as one of the main components of the buffer system in the blood,So it dissolved to release a proton and the conjugate base:

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H2CO3 (aq) H+ (aq) + HCO3- (aq)

4- So the net equation is :

CO2 (g) + H2O (l) H+ (aq) + HCO3 - (aq)

Calculations about this buffer system:

First we put the net equation CO2 (g) + H2O (l) H+ (aq) + HCO3 - (aq)

pKa of H2CO3 is 6.1, and the pH of the blood is 7.4 we suppose to calculate the ration between the conjugate base

( HCO3- ) to the acid (CO2) ?

According to Henderson equation :PH = pKa + log(conjugate base)/(acid)

7.4 = 6.1 + log [HCO3-]/[CO2]

1.3 = log[HCO3-]/[CO2]

[HCO3[/]-CO2 = ]20 so according to this number we can say that most of the dissolved CO2

is present as HCO3 . -

The normal values (physiologically):pH = 7.4

pCO2= 40 mm Hg (~ 1.2 mM)

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]HCO3 = [-25 mM.

What happens when the pH of the blood drops?

When pH decrease that means the acidity increases and the protons H+ increase also,

So when this happens, the buffer system resist the drop in pH by the following steps:

1 -HCO3- interacts with the H+ to give H2CO3

H+ (aq) +HCO3- (aq) H2CO3 (aq)

2 -Then H2CO3 broke down to give its components CO2 and H2O

H2CO3 (aq) CO2 (aq) + H2O (I)

3 -the produced CO2 leave the body by exhalation CO2 (aq) CO2 (g) exhaled by the lungs.

What happens when the pH of the blood increases?

if the pH increases that means a lot of OH- , and it called Alkalosis.

An example for alkalosis is: High altitudes, not deep breath , and the rate of respiration increases. As with hyperventilation, more carbon dioxide is expired from the lungs, ultimately lowering the H+ level in blood and raising the pH, therefore less H2CO3 to be produced.

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so when this happens the buffer system resists the increase in pH by the following steps :

1- When a base enter the body such as (NaOH), it interact with H2CO3 to produce salt and water:

NaOH + H2CO3 NaHCO3 + H2O2-Here the acid (H2CO3) is consumed, so it

should be replaced to keep the concentration within the range so the buffer can work, and this happen by react CO2 and H2O and produce H2CO3. CO2+ H2O H2CO3

] CO2 [decrease and respiration decrease to reduce the rate of CO2 consumption and this happen to keep the ratio

20

[HCO3] / [CO2] = 25 mM/ 1.25 m M = 20. the buffer range = 6.1 +- 1 = 5.1 – 7.1

Now we will start talking about the buffer system and their relationship with the respiratory and renal systems: (slide 8)

For the first step which is the production of H2CO3 from H2O and CO2 , its related to the rate of respiration because it related to CO2, If I had small amount of H2CO3 then I decrease the respiratory rate to get more CO2 to produce H2CO3 and vice versa. H20 + CO2 H2CO3

The second step is when the H2CO3 formed, it will be broken to give H+ and HCO3 . -

H2CO3 HCO3- + H + HCO3- interacts with the renal system by the reapsorbtion process.

Protein buffers system:

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It is related to the proteins and proteins formed from amino acids.

The proteins such as glycine consist of carboxyl group (COO-) – acidic and amino group (NH3+) – alkaline.The acidic and basic amino acids can’t act as buffers because they either have very low or high pKa values compared to the pH of the blood, such as glycine.

Except for Histidine,it can act as a buffer, because it hasNonsharing electrons which can accept H+ and release it. It’s the only amino acid that has pKa value close to that PH of the blood. (pka = 7.3)

histidine.

Albumin is a blood protein with 16 histidine sequences in one mole of protein. And those histidine amino acids they either loose or gain H+ depending on the medium of the buffer system, And it account for 95% of non-carbonate buffering action in plasma.So any protein that contain histidine can work as a buffer. Also hemoglobin contain histidine and can act as a buffer.

Phosphate buffer system:

Phosphate anions and proteins are important buffers that maintain a constant pH of ICF (Intracellular and tubular fluids of kidney).

They are related to the phosphoric acid/phosphates group.

Phosphoric acid (H3PO4) is a strong acid and it can’t act as a buffer.

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The (H2PO4-) which is the phosphoric acid derivative will act as a buffer.

Also, there are groups that contain phosphate in its structure such as ATP and Glucose-6-phosphate, they can act as a buffer.

** glucose-6-phosphate : glucose molecule attached to it a phosphate group on carbon number 6.

And BPG (bisphosphoglycerate) is a molecule that contains two phosphate groups that found in RBCs, this molecule can act as a buffer, too.

The main reason that make the phosphate compounds act as a buffer is their pka which is (pka = 7.1 – 7.2).

Hemoglobin buffer system:

It is the major intracellular buffer of the blood.

Hemoglobin is a protein that also consists of histidine amino acids. It has (38 histidine molecule/mole of Hb).

It can be protonated and deprotonated according to thesituation, It’s specially found in RBCs.

This system`s idea is the same as protein buffer system that is related to (histidine).

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Also, Hemoglobin buffer system interacts with the bicarbonate buffer system.

Slide 12 :all the buffers work together and this slide show how they work together and interact with each other in a hepatic cell (liver cell) and RBC and this is just an example:

1) CO2 is produced by metabolic reactions in the cell as a Waste product. Then, CO2 gas dissolves in aqueous

solution and converts to CO2(aq) .

2) Then from the hepatic cell CO2 diffuses through the membrane into the blood dissolving CO2 into the water to form H2CO3 in the presence of carbonic anhydras enzyme in the RBC.

** carbonic anhydrase: an enzyme that catalyze the Production of H2CO3 which found in the cytosol of RBC.

3) the H2CO3 that produced in the previous step will Broke up: H2CO3 → H+ + HCO3

4) H+ is going to interact with the histidine in the Hemoglobin (Hb)

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5) HCO3- the main component of the buffer system has to Go back to the blood. But this molecule is charged and If it left the cell like that the charge of the cell will be affected, so it should be replaced with Cl ion to balance the electrical potential of the cell.

6) the H+ that produced from the dissolution of H2CO3 also can interact with (HPO4-2) to form (H2PO4-) and H+ also unites with HCO3- that left the RBC to produce H2CO3 which will act as a buffer.

and in this way all the buffer systems work together in the body.

carbohydrates

what is the meaning of carbohydrates?

1) compounds that contain carbon, hydrogen, and Oxygen atoms.

2) members of a large class of naturally occurring polyhydroxy ketones and aldehydes.

** polyhydroxy: a compound that contain more than one hydroxyl group (OH)

** polyhydroxyl ketone: ketone molecule with more than one hydroxyl group.

** Polyhydroxyl aldehyde: aldehyde molecule with more than one hydroxyl group.

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** Aldose : an aldehyde sugar (monosaccharide) that contain an aldehyde carbonyl group.

** Ketose : a ketone sugar (monosaccharide) that contain a ketone carbonyl group.

Roles of the carbohydrates:

- it is the major energy source- immune recognition which means: when bacteria

get into the human body, our antibodies will recognize it by looking for a specific area on the bacteria that contain sugar which is related to carbohydrates.

- cell- cell interaction: most of the cells have in their membranes proteins called glycoprotein which help in the interaction between the cells.

- structural component: most prominent in bacteria cells, that this molecules help in the formation of the cells. example: cellulose (a major component of grass and trees).

Carbohydrates are often referred to as saccharides (Sakchoron means sugar in Greek). They are classified as monosaccharides, oligosaccharides and polysaccharides. This categorization is based on the number of sugar units. Mono- and oligo-saccharides are sweet to taste, crystalline in character and water soluble, hence they are known as sugars.

- Monosaccharides are the simplest group of carbohydrates (also referred as simple sugars). The monosaccharides are divided into different categories, based on the functional group and number of carbon atoms.1) Aldoses: When the functional group is an aldehyde, they are known as aldoses e.g. glyceraldehyde, glucose. 2)Ketoses: When the functional group is a ketone group, they are referred to as ketoses e.g. dihydroxyacetone, fructose.

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- Oligosaccharides (oligo means few in Greek) contain monosaccharide molecules which are liberated on hydrolysis. Oligo saccharides are further subdivided based on the number of monosaccharides units present as disaccharides, trisaccharides etc.

- Polysaccharides are polymers of monosaccharide units (usually more than 10 sugar units) with high molecular weight. They are usually tasteless (not a sugar) and form colloids with water (immiscible). Two types are homopolysaccharides and heteropolysaccharides.

- the simplest aldehyde has one carbon atom but there is no sugar composed of one carbon atom or two carbon atoms, so the simplest aldehyde sugar has 3 carbon atoms (glyceraldehyde)

- on the other hand, the simplest ketone has three carbon atoms and the simplest ketone sugar also has three carbon atoms (Dihydroxyacetone)

- most common sugars in the nature are aldoses rather than ketoses.

Nomenclature of the sugars (monosaccharides):

Nomenclature: aldo-or keto + latin number + ose. latin number: mono (1), bi (2), tri (3), tetra(4), penta(5), hexa(6), hepta(7), octa(8), …. etc.

examples :

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1) ketone or aldehyde? aldehyde, so (aldo)2) how many carbon atoms? 3, so (tri)3) + (ose)

the name: (aldotriose)

1) ketone or aldehyde? ketone, so (keto)2) how many carbons? 3, so (tri) 3) + (ose)

the name: (ketotriose)

- A carbon is said to be asymmetric when attached to four different atoms or groups. (chiral center)

- Stereoisomerism is an important character of monosaccharides. Stereoisomers are the compounds that have the same structural formulae (same molecular formula, same connectivity of atoms), but differ in their spatial arrangement. A carbon is said to be asymmetric when attached to four different atoms or groups. The number of asymmetric carbon atoms determines the possible isomers of a given compound which is equal to 2^n. Glucose contains 4 asymmetric carbons, and thus has 16 isomers (search for meso compounds if you want a recall).

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how we can determine L and D sugars?

we look at the OH group on the farthest chiral center from the carbonyl group (the last chiral center usually) , if it was on the right we call it (D) and if it was on the left we call it (L).

note: if we have an aldose (6 carbons) with 4 chiral center, and also we have a ketone ( 6 carbons) it will has 3 chiral center.

(# chiral center in ketone = # chiral center in aldose – 1 ) Only if they have the same number of carbons.

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Done by: Moath Al-awamlehCorrected by: Yara Basem

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