1. what are the sources, properties, functions, deficiency

Biochemistry Paper I – Aug 2005 KN 504

1. What are the sources, properties, functions, deficiency manifestation and

RDA of ascorbic acid (E-Feb 12)

Common name: anti scorbutic vitamin.

Chemical name: ascorbic acid.

Structure:

It is similar to hexose sugar. L-ascorbic acid and dehydro-L-ascoric acid are the two

forms of this vitamin, both are interconvertable. Both forms are active and present in

the 15:1 ratio respectively.

Functions of vitamin – C:

Due to reversible oxidation of L-ascorbic acid to dehydroascorbic acid, it is strong

reducing agent, so it involved in major oxidoreduction and hydroxylation reactions.

All of the functions is indirectly due to its reducing property.

The important functions as follows –

It is involved in hydroxylation of amino acids (praline & lysine) in

protocollagen. The hydroxylation is important for cross linkage of collagen

fibers& ultimately strength.

It is involved in tryptophan, tyrosine, cholesterol metabolisms

It is important to keep iron in ferrous form for proper absorption.

It converts methemoglobin to hemoglobin.

It necessary for the formation of TH4.

It protects the other vitamins form oxidation.

It is involved in ETC.

It involved in synthesis of carticosteroids.

It enhances the synthesis of Igs.

Rich sources: Goose berry (amla), citrus fruits, guava, green vegetables, tomatoes,

potato skin, adrenal gland, gonads.

RDA: Adults: 60mgPregnancy & lactation: >60mg

Deficiency syndromes:

The deficiency of vitamin C leads to disease called SCURVY, it is characterized with,

spongy and sore gums, loose teeth, anaemia, swollen joints, fragile blood vessels,

decreased immunity, delayed wound healing, sluggish hormonal function of adrenals

& gonads, haemorrhage, osteoporosis.


2. What is the normal fasting and post prandial blood glucose level?

Explain how normal blood glucose level is maintained. Add a note on the

disruption of hormonal regulation of blood glucose (E-Mar 2002, oct

2003)

The normal FBG = 72 – 110 mg/dL

The normal PPBG = 120 – 140 mg/dL.

18 mg glucose = 1 mMol glucose/Lt.

Blood glucose homeostasis:

Blood glucose is maintained at certain normal range. This normal is for optimal

utilization of glucose by the body. In our body, certain tissues like brain, retina, testes

etc solely dependent on glucose for their energy and they need glucose at certain

concentration. If any alteration in the glucose levels leads to alterations of glucose

utilization, which leads to impairment of cell functions.

Sources of blood glucose:

Dietary starch – which is degraded to glucose in the intestine and absorbed in to

blood.

Gluconeogeneis: glucose is formed form non carbohydrates.

Glycogenolysis: the glycogen present in liver and muscle break down to glucose.

Utilization of glucose:

Glucose is used as main energy source by all cells.

Excess glucose is converted to glycogen in both liver and muscle.

Glucose is utilized for synthesis of non-essential amino acids and fat.

Glucose is utilized for synthesis of aminosugars.

Excretion of glucose:

The kidney is the major organs which regulate the glucose excretion.

Glucose is excreted through urine if blood glucose is more than 180 mg/dL, this is

called as renal threshold level.

The maximum Reabsorption of glucose by renal tubules is 350mg/minute.

In normal healthy persons there is no excretion of glucose in urine.

Blood glucose regulation during fed state:

Following a meal, glucose levels are increased in circulation. The high concentration

of these glucose is regulated via two process –


Action of glucokinase: GK specifically found in liver and is having high Km, it means

which have low affinity to the substrate, but during postprandial, glucose levels are

high and this is enough concentration to bind with enzyme. Hence, immediately after

meals the glucose is acted upon by GK in liver and consumed.

Action of insulin: high concentration of glucose in blood will stimulates the production

of insulin from pancreas. Uptake of glucose by most of extrahepatic tissues except

brain is dependent on insulin.

Blood glucose regulation during fasting:

After meal, about 2.5 hrs the blood glucose levels are regulated to normal range.

After another 3 hrs later the glucose is supplied through glycogenolysis, and there

after gluconeogenesis.

Regulation of Glucose by Hormones:

The various hormones play significant role in regulation of blood glucose

concentrations, they are as follows –

1. Insulin:

It is 51 amino acid peptide produced form β-cells of pancreas. Insulin is a

hypoglycemic hormone. Insulin lowers the blood glucose by means of following

mechanisms

Insulin stimulates glycolysis, glycogenesis,HMP shunt, fat synthesis.

Insulin suppress gluconeogenesis, glycogenolysis.

2. Glucogaon:

It is produced form α-cells of pancreas, it functions are agonist to the insulin

actions.

It stimulates gluconeogenesis, glycogenolysis.

3. Epinephirne, thyroxine, glucorticoids:

these hormones are hyperglycemic in nature.

They stimulate gluconeogenesis, and glycogenolysis.

Glucocarticoids stimulates protein metabolism.

4. Growth hormone:

It inhibits the glucose utilization by cells.

It stimulates protein synthesis.


3. Write short notes

a. Allosteric enzymes and its feedback regulation (E-Feb 2005)

Allosteric enzymes has two individual sites for binding of substrate and for

modifier/regulator

The binding of regulatory molecule can either enhance the activity of the enzyme

(allosteric activation) or inhibit the activity of the enzyme (allosteric inhibition)

Negative feedback regulation: inhibition of enzyme activity by product is called as

negative feedback regulation. It is necessary to control metabolic pathways for

efficient cellular functions

Positive feedback regulation: it is quite opposite to negative feedback regulation

Eg of allosteric enzymes and their modifiers

S.No Allosteric enzyme Allosteric activator

Allosteric inhibitor

1 ALA synthase Heme

2 Aspartatretranscarbamoylase ATP CTP

3 HMG CoA reductase Cholesterol

4 PFK AMP,F-2,6-P ATP, citrate

5 Acetyl CoA carboxylase Citrate acylCoA

6 Citrate synthase ATP


b. Phospholipids and their clinical importance (SN-Aug 2004)

Phospholipids: they contain esters of fatty acids with glycerol/spingosine,

nitrogenous base, and phosphate group.

Properties and functions of phospholipids:

They are amphipathic in nature.

They are made up of fatty acids, alcohol, carbohydrate and phosphate.

They are structural components of cell membrane.

They are structural components of lipoproteins.

They help in fat absorption in the form of micelle.

They prevent fatty liver.

They help in removal of cholesterol.

They act as hormones.

Types of phospho lipids:

1. glycerophospho lipids: they are made up of fatty acid ester with glycerol,

phosphate, and nitrogenous group as functional group.

e.g.: phosphatidic acid – is the simple and precursor for all glycerophospho lipids.

Lecithin – the functional group is choline.

Cephalin – functional group is ethanolamine.

Phosphotidylinositol – functional group is myoinositol.

Phophatidylserine – functional group is serine.

Dipalmitoyl lecithin – it having two pamitic acids, it serves as surface acitive in

newborn Childs and protect from respiratory distress syndrome.

Cardiolipin - it is made up of two phaophatidic acids linked to central glycerol, it

having antigenic property.

2. Spinophospholipids: they are made up of esters of fatty acids, amino alcohol

namelyspingosine, and carbohydrate.

e.g.:spingomyelin – it is constituent of myelin sheath of axon.


c. Kwashiorkor (SN-apr 2001, aug 2004)

Kwashiorkor: This is due to the malnutrition of proteins, with adequate energy

intake. Kwashiorkor means sickness the older child gets, when the next child is born.

This is the commonest nutritional disorder in many parts of the world. Kwashiorkor is

entirely preventable if children are given a well-balanced diet congaing adequate

amount of protein and the essential amino acids.

The salient features of kwashiorkor is tabulated

kwashiorkor

Age of onset 1-5y

Growth retardation of child

Severe

Attitude Lethargic and apathetic

Appearance Edema on face & limbs

Appetite anorexia

Skin Crazy pavement dermatitis

Hair Sparse, soft & thin

Other Angular stomatitis, cheilosis, watery diarrhea, muscle wasting, Fatty liver

Serum albumin < 2g (hypoalbuminemia)


d. Inhibitors of ETC (SN-Mar 2002, Aug 10)

Barbiturates such as amobarbital inhibit electron transport via Complex I by

blocking the transfer from Fe-S to Q. At sufficient dosage, they are fatal in vivo.

Antimycin A and dimercaprolinhibit the respiratory chain at Complex III.

The classic poisons H2S, carbon monoxide and cyanide inhibit Complex IV and

can therefore totally arrest respiration.

Malonate is a competitive inhibitor of Complex II.


e. Diagnostic value of isoenzymes

The enzymes with similar function and physically distinct from each other are called

as isoenzymes are the products of different genes are known as trueisoenzyes.eg:

salivary and pancreatic amylase

The characteristic features of Iso-enzymes are tissue specific and differ in affinity to

the substrate. Hence study of isoenzymes is useful to understand diseases of

different organs.

Identification techniques for isoenzymes: electrophoresis, heat stability, inhibitors,

substrate specificity, cofactor, compartmentalization, use of specific antibodies

Diagnostic important isoenzymes:

Lactaedehydrogense (LDH):

LDL catalyses the conversion of pyruvate to lactate and vice versa. LDL is

concentrated in RBC cell; therefore minor haemolysis causes the false value. Normal

values ranges from 100-200 U/L.

Differential diagnosis of LDH: the elevation of LDH is seen in haemolytic anaemia,

hepatocellular damage, muscular dystrophy, cancer etc.

It has 5 tissue specific isoenzymes.

LDH is tetramer made up of two H(heart) bands and two M(muscle) bands. Both of

these are same molecular wt. and with minor amino acid variations.

With two different polypeptide chains therefore 5 combinations of H and M are

possible, namely H4, H3M, H2M2, M3H, M4. The tissue specificity and diagnostic

importance of these 5 isoenzymes is as follows

H4 form found in heart, which is useful for diagnosing heart disease

M4 form found in muscle, hence it is useful in diagnosing muscle diseases

Creatine kinase (CK)

It catalysis the synthesis of creatine phosphate from creatine and ATP. Normal blood

ranges from 15-100 IU/L. it is made up of 2 polypeptides namely M & B. therefore 3

combinations of isoenzymes are possible. They are MM found in skeletal muscle,

MB found in heart and BB found in brain

CK subform is highly elevated in muscular dystrophies, acute cerebrovascular

injuries. It is most reliable factor in diagnosing AMI

Alkaline phosphatase (ALP)


It is nonspecific enzyme which hydrolyses alphaic, aromatic and heterocyclic

compunds at pH 9-10 in the presence of Mn and Mg. ALP produced by osteoblasts

for the calcification process. Normal serum levels are 40-125 u/L. moderate increase

seen in hepatic diseases, and very high levels are seen in extraheptic obstruction or

intrahepatic obstructions, and very high levels are seen in bone diseases.

ALP has nearly 6 types of Iso-enzymes

Alpha 1 ALP: it is about 10% total ALP,and is increased in obstructive

jaundice

Alpha 2 ALP: it is about 20 % of total ALP

Alpha 2 heat stable ALP: it is abount 1 % of total ALP. It is heat stable above

65oC

Pre beta ALP: it is about 50% of total ALP. It is elevated in bone diseases

Gamma ALP: it is about 10%, it is increased in ulcerative colitis

Leucocyte ALP: it is increased in lymphomas and decreased

inchroicmeloidleukemia


f. Basal Metabolic Rate (BMR) (SN-feb 07, Aug 08)

Definition: The energy required by a awaken individual during physical, emotional

and digestive rest.

It is the minimum amount of energy required to perform vital functions such as

circulation, respiration, working of heart etc.

Measurement of BMR: subject should be awake, and complete physical and mental

rest, and done during post absorptive state in comfortable surroundings

Instrument: benedict‟s and Roth apparatus or Douglas bag method

Procedure for benedict Roth method: the O2 consumed is recorded for 2-6 min

under basal conditions

The standard calorific value for 1 Lt of O2 consumed = 4.825 cal

Heat produced in 6 min = 4.825 X A

Heat produce in 1 Hr = 4.825 AX 10

Units: BMR expressed as calories per Sq. meter of body surface area per hour i.e.

Cal/sq.m/hr

Body surface area:

A = H025X W0.425X 71.84

Where, A= surface area in cm2, H = height in cm, W = weight in kg

Normal Value: Men - 34-37 k cal/m2/hr

Women - 30-35 k cal/m2/hr

Factors affecting BMR:

1. Age: In old age, BMR is lowered

2. Sex: Males have a higher value

3. Temperature: BMR increases in cold climate

4. Exercise: It increases during exercise

5. Fever: 12% increase during fever

6. Thyroid hormones: BMR is raised in hyperthyroidism.


g. Fatty acid synthesis

Site of synthesis:

Cytosol of all lypogenetic tissues.

Importance:

The excess consumption of carbohydrates and proteins converted to fatty

acids.

Fatty acids are buildingblokes of fats in the form of tryacylglycerols.

Fatty acids are storage form of energy in the form of triacylglaycerols.

Precursor molecule for fatty acid synthesis:

Acetyl Co A is the starting molecule in fatty acid synthesis. Sequential addition of 2

carbon acetyl CoA molecules resulting in the long fatty acid chain.

Reactions:

All the reactions in the fatty acid synthesis are takes place in multifunctional enzyme

called fatty acid synthase complex. It is a dimmer; each monomer consists of 7

enzymes and one acyl carrier protein.

The total reactions are divided into 3 phases.

1. Production of acetyl co A, NADPH.

2. Conversion of acetyl CoA into malonyl CoA.

3. Synthesis of fatty acid chain.

1. Production of acetyl CoA molecules:

The acetyl CoA molecules are synthesized from – Pyruvate oxidation, oxidation of

fatty acids and amino acids etc.

NADPH „s are mainly produced from HMP shunt.

2. Conversion of acetyl CoA to Malonyl CoA:

In the presence of acetyl CoA carboxylase acetyl CoA is converted into Malonyl

CoA.

3. Synthesis of fatty acid chain:


Acetyl co A is bound to Acyl carrier protein of fatty acid synthase complex in the

presence of acetyl CoA ACP transacetylase. Now the enzyme is called Acetyl –S-

ACP.

Acetyl Co A is then shifted to SH group of ketoacyl synthase. Now the enzyme is

called as acetyl S-enzyme.

Malonyl CoA is banded to SH group of ACP component in the presence of malonyl

CoA ACP transacylase. Now the enzyme is called as acylmalonyl enzyme.

Theacylmalonyl enzyme is then decarboxylated and converted to β-ketoacyl –

ACP.

β-ketoacyl – ACP is reduced to β-hydroxyacyl-ACP in thepresence of β-ketoacyl –

ACP reducatase, and NADPH.

Β-hydorxyacyl-ACP is then dehydrated to form Tran‟s delta 2 enoyl ACP in the β-

hydorxyacyl-ACP dehydratase.

Tran‟s delta 2 enoyl ACP is again reduced to acyl-ACP in the enoyl ACP

reductases.

The carbon chain form the ACP is shifted to SH group of ketoacyl synthase.

Up to these reactions is completion of one cycle it means that formation of 4

carbon fatty acid chain.

In next preceding cycle additions of 2 carbon malanylcoa to growing chain is takes

place.

Now the SH group of ACP is free and it again occupied by one more malonyl CoA

and so on.

For the synthesis of palmitoic acid total 8 cyclic reactions are takes place.

Regulation of fatty acid synthesis:

High energy levels induce the fatty acid synthesis.

The hormone like insulin stimulates the synthesis. Whereas glucagon, epinephrine,

norepinephrine suppress the synthesis.


h. Heme degradation (SN-Apr 2001)

After 120 days RBC degraded and heme is released. The iron present in heme is

reutilized and remaining porphyrin ring is catabolized to bilirubin in the liver, which is

an ultimate end product of heme catabolism

Breakdown of HEME/Generation of BILIRUBIN

The prophyrin ring is degraded in microsomes of reticulo endothelial cell of liver,

spleen, and bone

Each day about 6g of Hb is catabolized, from which about 250 mg of bilirubin is

formed

Microsomal heme oxygenase system:

The components present in this system are – heme oxygenase, molecular O2,

NADPH

This enzyme is induced by heme

The alpha methyenyl bridge present between pyrrole rings I and II is cleaved and

liberated as CO2

The ferric iron liberated is become ferrous and it taken up by transferrin

The so formed linear tetrapyrrole is called as BILIVERDIN, which is in green colour

In mammals which is further reduced to BILIVERDIN, which is in red yellow colour by

NADPH dependent biliverdin reductase

Bilirubin is water insoluble and is taken up by albumin and transported to sinusoidal

surface of the liver. One molecule of albumin can bind two mol of bilirubin.

The bilirubin uptake by the liver is a carrier mediated active process


i. Eicosanoids

Eicosaniods are 20 carbon containing fatty acids. They are derived from 20 carbon

FA namely prostanoic acid. They are also called as group of local hormones.

Precursor for Eicosaniods:

The precursor molecule for ecosaniods is Arachidonic acid.

General structure:

They contain 20 carbon atoms.

They contain cyclopentane ring made up of 8 -12 carbons, and 2 side chains.

One chain end with carboxyl group.

Types of eicosaniods:

They are 4 types of eicosaniods –

1. prostaglndins (PG‟s)

2. Prostacyclins (PGI)

3. thromboxanes (TXA)

4. Leukotrienes (LT‟s)

Synthesis of ecosaniods:

All the tissues are able to synthesized ecosaniods. The Arachidonic acid undergoes

two pathways and produces all the 4 eicosaniods:

1. Cyclooxygenase pathway: in this pathway all the prostaglandins,

prostacyclins and thromboxanes are produced except LT‟s.


2. Liposygenase pathway: in this pathway Arachidonicacid is converted to

various LT‟s.

Functions of prostaglndinsanr related compounds:

1. PG-E, A, I2 – they are powerful vasodilator, hence they used in treatment

of hypertension.

2. PGE1 & E2 – they are induce inflammation due vasodilation of capillaries.

3. PGE2 & F2 – they induce termination of pregnancy and induction of labor.

They used for induction of labour in cattle‟s.

4. PGE2 & histamine, bradikynin – all of combine cause pain and fever.

5. PGE – it inhibit gastric secretion so it is used for gastric ulcers. it stimulates

glycogenesis, inhibits lipolysis, induces calcium mobilization form bone. It

promotes increase GFR rate

6. PGE & PGF– PGE is the bronchodilator whereas PGF is

bronchoconstrictor. PGE 1 & 2 is used in treatment of asthma.

7. PGI2 – inhibit platelet aggregation.

8. PGE 2 & TXA 2 – promote platelet aggregation and cause thrombosis.

9. PGI 2 – vasodilator whereas TXA 2 is vasoconstrictor.

LT’s:

They are synthesized in WBC, lung, heart, spleens. They are called as sow reacting

substances of anaphylaxis. They produce after stimulation of immune response.

They are very active than histamine and cause violent allergic reaction some time it

may leads to death of organism.

They cause contraction of smooth muscles, broncho constriction, vasoconstriction,

clumping of RBC‟s, and stimulate release of lysosomal enzymes.


j. LDL metabolism

Structure of LDL receptor:

LDL receptor also called “apoB, E” receptor, since it is specific for apo B100 and E. It

is look like pits and occurs on the cell surface. These pits are coated with a protein

called Clathrin on the cytosolic side of the cell membrane. The glycoprotein receptor

spans the membrane, the B-100 binding region being at the exposed amino terminal

end.

LDL metabolism: LDL cholesterol after binding to LDL receptors is taken up intact

by endocytosis. The apoprotein and cholesteryl ester are then hydrolysed in the

lysosomes, and cholesterol is Trans located into the cell. The receptors are recycled

to the cell surface. This influx of cholesterol inhibits in a coordinated manner HMG-

CoA synthase, HMG-CoA reductase, and, therefore, cholesterol synthesis;

stimulates ACAT activity; and down-regulates synthesis of the LDL receptor. Thus,

the number of LDL receptors on the cell surface is regulated by the cholesterol

requirement for membranes, steroid hormones, or bile acid synthesis.

LDL receptors is absent is familial hypercholesterolemia, which is characterized by

high plasma cholesterol levels

1. what are the sources, properties, functions, deficiency

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