Biochemistry of Proteins: for nurses

1. Mrs. Namita Batra Guin
Associate Professor
BIOCHEMISTRY OF PROTEINS:
For Nurses

2. ● Essential structural components of a cell.
● Most abundant and functionally diverse molecules
● All proteins are polymers of small units called
amino acids.
● Amino acids are also called as building blocks of
proteins.

3. AMINO ACIDS
● Proteins are polymers of amino acids with each amino acid
residue joined to its neighbour by a specific covalent bond.
● Proteins can be broken down to its constituent amino acids. So
amino acids are called as hydrolysed product of proteins.
▪ Amino acids are organic acids in which one H is replaced by
NH3 usually at α carbon (next to COOH group)
▪ All amino acids have in common
▪ central α carbon to which COOH & H & NH2 are attached
▪ α carbon is also attached to a side chain called R group which is different
for each amino acid
▪ N and C terminals

4. BIOLOGICAL SIGNIFICANCE OF
AMINO ACIDS
● Important dietary source of Nitrogen
● Used for Protein biosynthesis.
● Glucogenic amino acids serve as source of
energy.
● Glycine is precursor of creatine, heme, bile acids
and purines.
● Aromatic amino acids are the precursors of thyroid
hormones, catecholamines and melanin.
● Aspartate and glutamine are used in the
biosynthesis of purines and pyrimidines.

5. Classificatio
n of AA
structure
aliphatic
aromatic
Hetero-
cyclic
Optical
activity
D & L
isomers
Non
active
R polarity
Polar
non
fate
glucogeni
c
ketogeni
c
mixed
value
essential
Non-
Semi-

6. Classification of AMINO ACIDS
● Aliphatic Amino acids: It is further grouped as:
simple, branched, hydroxy and sulphur-containing
amino acids.
● Simple: Have either hydrogen or a methyl group
in aliphatic side chain. e.g. glycine, alanine.
● Branched: Have aliphatic side chain which is
branched. e.g. valine, Leucine.
● Hydroxy: have hydroxyl group. E.g. Serine,
Threonine.
● Sulfur containing: It includes cysteine and
methionine.

7. Classification of AMINO ACIDS
● Aromatic amino acids: has presence of aromatic
side chains. Phenylalanine, tyrosine and
tryptophan possess aromatic ring.
● Heterocyclic Amino acids: It includes other
types of rings also. e.g. tryptophan, Histidine.

8. OPTICAL ACTIVITY
▪ All amino acids are Optically active and show D & L
Isomers as they contain an asymmetric α carbon
except “glycine” which is non optically active
▪ D-amino acids : with their NH2 to the right of α carbon
▪ L-amino acids : with their NH2 to the left of α carbon
▪ All of the amino acids in our body are of the L-amino
acids

9. Classification of AMINO ACIDS
● Polar amino acids: the R group of these amino
acids is more soluble in water, because they
contain functional groups that form hydrogen
bonds with water. E.g. Serine, Threonine,
cysteine, Asparagine etc.
● Non-polar amino acids: AA with non-polar side
chain neither release protons nor participates in
hydrogen/ ionic bond formation. these amino acids
are: glycine, alanine, valine, leucine etc.

10. METABOLIC FATE
1. Ketogenic amino acids: Give rise to ketone bodies and fats
in the catabolic way
Ex. Leucine
1. Glucogenic amino acid
Give rise to carbohydrates …
Ex. glycine, serine ,….
1. Mixed amino acids
Part will enter the fatty acid metabolic pathway .. The other into
glucose pathway
Ex. Lysine , tryptophan ,….

11. NUTRITIONAL VALUE
1. Essential amino acids
Cant be synthesized in the body so must be taken in the diet
Ex. Valine , leucine , isoleucine ,…..
2. Non essential amino acids
Can be synthesized in the body
Ex. Glycine , alanine , aspartic ,…..
▪ Arginine and Histidine are called semi-essential because they are
synthesized in the body in a rate enough for adults but not for
growing individuals

14. Classification of AMINO ACIDS
● Acidic amino acids: have one among group and
more than one carboxyl group. e.g. aspartic acid
and glutamic acid.
● Basic amino acids: these amino acids have one
carboxylic group with more than one amino group
or a heterocyclic group. E.g. Lysine, arginine and
histidine.
● Imino Acid: contain both imino (-NH-) and
carboxyl functional group differing in bonding to
the nitrogen.

15. PROPERTIES OF AMINO
ACIDS
1. Optical activity
2. Amphoteric property
In solution, amino acids act as both acid and alkali d.t
the presence of acidic group (COOH-) and basic group
(-NH2)
3. Isoelectric point (zwitter ion state)
It’s the pH at which the protein carries equal +ve and –
ve charges
At this point
▪ Proteins and enzymes loose their function
▪ Their viscosity in solution becomes maximal
▪ Their solubility becomes minimal (easily precipitated)

16. General properties
● Formation of a peptide bond: two amino acids
molecules can be covalently joined through a
substituted amino linkage termed a peptide bond.
● Isomerism: All naturally occurring amino acids
except glycine have atleast one asymmetric
carbon atom and are optically active. They have
L-configuration.

17. PROTEINS
● Natural polymers essential for growth and
maintenance of life.
● Contains nitrogen, oxygen, carbon and hydrogen.
● Most abundant biological macromolecules occurring
in all cells and all parts of cells.
● All proteins are constructed from same set of 20
amino acids covalently linked in characteristic linear
sequence.
● Several amino acids are linked together to form
polypeptides and proteins. Each polypeptide has a
free α- amino group on the left hand side of the
peptide chain. (N-terminal) and it also has a free α-

18. BIOLOGICAL SIGNIFICANCE OF PROTEINS
● Structural Proteins: Some proteins like: collagens, keratins
etc form an essential part of bone, cartilage, hair and nails
respectively.
● Enzymes: Some proteins lasts as enzymes e.g. pepsin.
● Hormones: e.g. Insulin: helps in regulating metabolic
processes with in the body.
● Transporters: Hemoglobin, ceruloplasmin serve as carrier
for the transport of certain substances within the body.
● Receptors: act as receptors and play important role in signal
transduction.

19. BIOLOGICAL SIGNIFICANCE OF PROTEINS
● Storage proteins: Some proteins bind to a
substance for its storage in different tissues in the
body. e.g. Ferritin for the storage of Fe3+.
● Antibodies: Proteins such as 𝛄-globulin, act as
antibodies and provide immunity.

20. ● According to the constituents of their molecule,
proteins are of three types:
● Simple: albumin, globulin, protamines etc.
● Conjugated: Nucleoproteins, glycoproteins,
lipoproteins.
● Derived: primary and secondary.

21. SIMPLE PROTEINS
● Those on complete hydrolysis, yield only amino
acids.
● E.g. Albumin, globulins, prolamines, glutelins,
histones and scleroproteins.
● Albumin: serum, milk, eggs. (soluble in acids,
alkalies and water)
● Globulin: eggs, milk and plasma. (insoluble)
● Prolamines: gliadin of wheat, zein of maize etc.
● Glutelins: glutenin of wheat.
● Histones: globin of haemoglobin.
● Scleroproteins: fibrous proteins. Keratin,
collagen, elastin.

22. CONJUGATED PROTEINS
● Composed of protein molecule joined to a non-
protein group.
● Protein part also known as: apoprotein
● Non protein: prosthetic group.
● Entire molecule possessing both called as
holoenzyme.
● Classification:
● Nucleoproteins: E.g. Ribonucleoproteins of ribosomes
● Chromoproteins: haemoproteins like haemoglobin
● Phosphoproteins: casein of milk. (having phosphoric
acid)
● Lipoproteins: proteins containing sphingolipids etc.
● Metalloproteins: having metal ion. ferritin
● Glycoproteins: have mucopolysachharides as
prosthetic group. Blood plasma.

23. DERIVED PROTEINS
● Derivatives of simple proteins formed by partial
cleavage of peptide bonds.
● Denatured and coagulated proteins- primary
derived proteins.
● Produced by cleavage of peptide bonds-
secondary derived proteins.

24. DERIVED PROTEINS
● Derivatives of simple proteins formed by partial
cleavage of peptide bonds.
● Denatured and coagulated proteins- primary
derived proteins.
● Produced by cleavage of peptide bonds-
secondary derived proteins.
● e.g.

25. STRUCTURE OF PROTEINS
● Primary
● Secondary
● Tertiary
● Quarternary

26. Primary structure
● Refers to the order and sequence of amino acids
in a protein chain.
● Linear sequence of amino acids in a polypeptide
bond.
● Particular function of proteins is dependent upon
primary structure of proteins.

28. SECONDARY STRUCTURE
● Refers to folding and twisting pattern of a
polypeptide chain.
● Long polypeptide chains undergoes folding, then it
is considered as a secondary structure.
● Term secondary structure refers to local
conformation of some part of polypeptide.
● Most common are:
● Alpha –helix: coiled into a regular spiral. Most stable
conformation. It has right hand folding. There are 3.6
amino acids residues per turn of the helix.
● Left handed helix generally does not occur in
proteins.
● Beta- sheets: extended into zigzag pattern. Can be
arranged side by side to form pleats. Hydrogen

29. SECONDARY STRUCTURE

30. SECONDARY STRUCTURE

31. TERTIARY STRUCTURE
● It involves intramolecular folding of polypeptide
chain thereby forming a compact 3-D structure
which has a specific shape.
● Further coiling and folding of secondary structures
takes place. It forms many domains or structural
coils.
● It’s a complete 3-D structure maintained by weak
bonds like: hydrogen, ionic, disulphide etc.

32. QUARTERNARY STRUCTURE
● Multi subunit proteins contain several identical
ans/or different chains, where each one of the
peptide chains is referred as a subunit.
● Protein chains possessing two or more separate
polypeptide chains or subunits.
● The arrangement of these are in 3-dimensional.
● E.g. Haemoglobin consists of four subunits.

34. LEVELS OF PROTEIN
STRUCTURE

35. ● Depending on their overall morphology proteins can be
classified as : globular and fibrous proteins.
● Globular proteins: spherical in shape. Often contain
several types of secondary structures. Small proteins
are soluble in water and are non-contractile but larger
are insoluble and coagulate by heat. E.g. albumen of
eggs, Hb etc.
● Fibrous proteins: polypeptide chains are spirally
bound, assuming shape of fibres. Have high degree of
secondary structure giving them strength and rigidity.
Insoluble in water. Found mostly as structural
components in cells and intercellular tissues. E.g. actin,
myosin and fibrin.

37. FUNCTIONS OF PROTEINS
● Building material of cells and tissues.
● Essential for growth and repair.
● May act as fuel to supply energy.
● Serves as carrier of functionally important
molecules. Like haemoglobin helps in transporting
oxygen.
● Some acts as antibodies.
● Helps in movement of body. Like actin and myosin
are contractile proteins.
● Some may catalyze biological reactions and act
as enzymes.
● Some act as hormones and regulate metabolic
activities of body. e.g. insulin.

38. Deficiency of proteins
● Kawashiorkar: affects infants and children in age
group 1-3 years. C/M: underweight, poor brain
development, loss of appetite, protuding belly,
slender legs and bulging eyes.
● Marasmus: emaciation and wasting in an infant.
C/M: impaired physical growth, retarded mental
development, prominent ribs, dry skin, extreme
leanness and loss of weight.

39. General Properties of Proteins
● Large size: They form colloidal solutions and do
not diffuse through cell membrane.
● Amphoteric nature: amino group is basic while
carboxyl group is acidic. Because of which
proteins add to the buffering capacity of the cell.
● Reactive group on the side chains of their amino
acids, helps them in binding to inorganic ions like:
nucleic acid, phospholipid etc.
● Denaturation: extreme temperature or pH disturbs
the bonds resulting in loss of functional activity
and its native structure.

40. PROTEIN DENATURATION
● Soluble in water due to their organised structure.
● Looses its native structure and gets precipitated
on heating or adding a strong acid.
● On denaturation, protein looses its biological
activity.
● Under ideal conditions denaturation may be
reversible, however most of the proteins, once
denatured remain disordered.
● Denatured proteins are insoluble and precipitate
from the solution.

41. PRECIPITATION OF PROTEINS
• Protein Precipitation is the process in which protein is separated
from any extra contaminants that may be mixed with it.
• Methods of protein precipitation are:
• Salting out: Precipitation can be done by addition of salt
solution. NaCl and (NH4)2SO4 are usually used for the
purpose. Precipitation of protein is due to neutralisation of the
charges as well as dehydration of the molecule. Protein
which has been precipitated remains native and can be
redissolved when put back.
• Precipitation by other reagents: Since proteins are
insoluble in organic solvents. Proteins can also be
precipitated with the addition of some non aqueous solvents
like: alcohol, acetone etc. Proteins get precipitated due to
dehydration of the molecule.

42. PRECIPITATION OF PROTEINS
• By heavy metals: Most commonly used metals as
proteins precipitants include metal salts such as
lead acetate, mercuric chloride, barium chloride,
zinc sulphate etc. They get precipitated due to
adsorption of metallic cations by the negatively
charged colloidal particles of the proteins.
• By alkaloid reagents precipitation by alkaloid
reagent is due to the formation of an insoluble salt
between the anion of the reagent and the positively
charged protein particles.

43. PRECIPITATION OF PROTEINS
• By heating: By heating protein gets coagulated.
This is referred to as heat coagulation.

44. PLASMA PROTEIN
● Major proteins in plasma: albumin, globulins and
fibrinogens.
● All proteins are synthesised in liver except gamma
globulin.
● Total plasma protein concentration: 6.3-8.0 g/dl.
● Albumin- 3.7-5.3g/dl
● Globulins- 1.8-3.7 g/dl

45. FUNCTIONS OF PLASMA PROTEINS
• Protein Nutrition: Plasma proteins act as a source of protein for the
tissues, whenever the need arises.
• Osmotic Pressure and water balance: Plasma proteins exert an
osmotic pressure of about 25 mm of Hg and therefore play an important
role in maintaining a proper water balance between the tissues and
blood. Plasma albumin is mainly responsible for this function due to its
low molecular weight and quantitative dominance over other proteins.
• Buffering action: Plasma proteins help in maintaining the pH of the
body by acting as ampholytes. At normal blood pH they act as acids and
accept cations.
• Transport of Lipids: One of the most important functions of plasma
proteins us to transport lipids and lipid soluble substances in the body.
Fatty acids and bilirubin are transported mainly by albumin, whereas
cholesterol and phospholipids are carried by the lipoproteins present in
β-globulins also transport fat soluble vitamins (A, D, K and E)

46. FUNCTIONS OF PLASMA PROTEINS
• Transport of other substances: In addition to lipids, plasma
proteins also transport several metals and other substances α2-
Globulins transport copper (Ceruloplasmin), bound hemoglobin
(haptoglobin) and thyroxine (glycoprotein) and non-heme iron is
transported by transferrin present in β-globulin fraction. Calcium,
Magnesium, some drugs and dyes and several cations and anions are
transported by plasma albumin.
• Blood Coagulation: Prothrombin present in α2-globulin fraction
and fibrinogen, participate in the blood clotting process.
• Antioxidants: Presence of sulfhydryl (-SH) groups helps in this
property.
• Protein reserve: in case of nutritional depletion

47. Biochemistry For Medics
Separation of Plasma proteins
❑Salting-out methods-three major groups—
fibrinogen, albumin, and globulins—by the
use of varying concentrations of sodium or
ammonium sulfate.
❑Electrophoresis- five major fractions
❑Albumin
❑α1 and α2 globulins
❑β globulins
❑ γ globulins
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48. Biochemistry For Medics
Albumin
❑Albumin (69 kDa) is the major protein of
human plasma (3.4–4.7 g/dL)
❑Makes up approximately 60% of the total
plasma protein.
❑About 40% of albumin is present in the
plasma, and the other 60% is present in the
extracellular space.
❑Half life of albumin is about 20 days.
❑Migrates fastest in electrophoresis at
alkaline pH and precipitates last in salting
out methods
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49. Biochemistry For Medics
Synthesis of Albumin
❑The liver produces about 12 g of albumin
per day
❑Albumin is initially synthesized as a
preproprotein
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50. Biochemistry For Medics
Structure of Albumin
❑Mature human albumin consists of one
polypeptide chain of 585 amino acids and
contains 17 disulfide bonds
❑Has a relatively low molecular mass
❑Has an iso-electric pH of 4.7
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51. Biochemistry For Medics
Functions of Albumin
❑ Colloidal osmotic Pressure-albumin is
responsible for 75–80% of the osmotic
pressure of human plasma due to its low
molecular weight and large concentration
❑It plays a predominant role in maintaining
blood volume and body fluid distribution.
❑Hypoalbuminemia leads to retention of fluid
in the tissue spaces(Edema)
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52. Biochemistry For Medics
Functions of Albumin
Transport function-albumin has an ability to
bind various ligands, thus acts as a transporter
for various molecules. These include- free fatty
acids (FFA),calcium, certain steroid hormones,
bilirubin, copper
❑A variety of drugs, including sulfonamides,
penicillin G, dicoumarol, phenytoin and aspirin,
are also bound to albumin
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53. Biochemistry For Medics
Functions of Albumin
❑Nutritive Function
Albumin serves as a source of amino acids for
tissue protein synthesis to a limited extent,
particularly in nutritional deprivation of amino
acids.
❑ Buffering Function-Among the plasma
proteins, albumin has the maximum buffering
capacity due to its high concentration and the
presence of large number of histidine residues,
which contribute maximally towards
maintenance of acid base balance.
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54. Biochemistry For Medics
Clinical significance of Albumin
❑Blood brain barrier- Albumin- free fatty
acid complex can not cross the blood brain
barrier, hence fatty acids can not be utilized
by the brain.
❑Loosely bound bilirubin to albumin can be
easily replaced by drugs like aspirin
❑In new born if such drugs are given, the
released bilirubin gets deposited in brain
causing Kernicterus.
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55. Biochemistry For Medics
Clinical significance of Albumin
Protein bound calcium
❑ Calcium level is lowered in conditions of
Hypo- Albuminemia
❑ Serum total calcium may be decreased
❑ Ionic calcium remains same
❑Tetany does not occur
❑Calcium is lowered by 0.8 mg/dl for a fall of
1g/dl of albumin
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56. Biochemistry For Medics
Clinical significance of Albumin
Drug interactions—
Two drugs having same affinity for albumin
when administered together, can compete for
available binding sites with consequent
displacement of other drug, resulting in
clinically significant drug interactions.
Example-Phenytoin, dicoumarol interactions
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57. Biochemistry For Medics
Clinical significance of Albumin
Edema- Hypoalbuminemia results in fluid retention
in the tissue spaces
Normal level- 3.5-5 G/dl
Hypoalbuminemia- lowered level is seen in the
following conditions-
❑Cirrhosis of liver
❑Malnutrition
❑Nephrotic syndrome
❑Burns
❑Malabsorption
❑Analbuminemia- congenital disorder
Hyperalbuminemia- In conditions of fluid
depletion(Haemoconcentration)
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58. Biochemistry For Medics
Globulins
❑Globulins are separated by half saturation
with ammonium sulphate
❑By electrophoresis globulins can be
separated in to –
❑α1-globulins
❑α2-globulins
❑β-globulins
❑ Y-globulins
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59. Biochemistry For Medics
Synthesis of Globulins
❑α and β globulins are synthesized in the liver.
❑Y globulins are synthesized in plasma cells
and B-cells of lymphoid tissues (Reticulo-
endothelial system)
❑Synthesis of Y globulins is increased in
chronic infections, chronic liver diseases, auto
immune diseases, leukemias, lymphomas and
various other malignancies.
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60. Biochemistry For Medics
α- Globulins
❑ They are glycoproteins
❑Based on electrophoretic mobility , they are
sub classified in to α1 and α2 globulins
❑α1 globulins
Examples-
❖α1antitrypsin
❖α1-fetoprotein (AFP)
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61. Biochemistry For Medics
α1 globulins
α1-antitrypsin
❑Also called α1-antiprotease
❑It is the major component (> 90%) of the α 1
fraction of human plasma.
❑ It is synthesized by hepatocytes and
macrophages and is the principal serine protease
inhibitor of human plasma.
❑ It inhibits trypsin, elastase, and certain other
proteases by forming complexes with them.
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62. Biochemistry For Medics
Clinical consequences of α1-antitrypsin
deficiency
❑Emphysema- Normally
antitrypsin protects the
lung tissue from
proteases(active
elastase) released from
macrophages
❑Forms a complex with
protease and
inactivates it.
❑In its deficiency, the
active elastase destroys
the lung tissue by
proteolysis.
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63. Biochemistry For Medics
α1
-fetoprotein (AFP)
❑Present in high concentration in fetal blood
during mid pregnancy
❑Normal concentration in healthy adult-
< 1µg/100ml
❑Level increases during pregnancy
❑Clinically considered a tumor marker for the
diagnosis of hepatocellular carcinoma or
teratoblastomas.
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64. Biochemistry For Medics
❑ Clinically important α2-globulins are-
❑ Haptoglobin
❑ Ceruloplasmin
❑ α2- macroglobulins
α2-globulins
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65. Biochemistry For Medics
Haptoglobin-(Hp)
❑It is a plasma glycoprotein that binds
extracorpuscular hemoglobin (Hb) in a tight
noncovalent complex (Hb-Hp).
❑The function of Hp is to prevent loss of free
hemoglobin into the kidney. This conserves
the valuable iron present in hemoglobin,
which would otherwise be lost to the body.
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66. Biochemistry For Medics
Clinical Significance of Haptoglobin
❑Concentration rises in inflammatory conditions
❑Concentration decreases hemolytic anemias
❑The level of haptoglobin falls rapidly in hemolytic
anemias.
❑Free Hp level or Hp binding capacity depicts the
degree of intravascular hemolysis.
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67. Biochemistry For Medics
Ceruloplasmin
❑ Copper containing α2-globulin
❑ Glycoprotein with enzyme activities
❑It has a blue color because of its high
copper content
❑Carries 90% of the copper present in
plasma.
❑Each molecule of ceruloplasmin binds six
atoms of copper very tightly, so that the
copper is not readily exchangeable.
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Ceruloplasmin

68. Biochemistry For Medics
Ceruloplasmin
❑Normal plasma concentration approximately
30mg/dL
❑ Enzyme activities are Ferroxidase, copper
oxidase and Histaminase.
❑Synthesized in liver in the form of apo
ceruloplasmin, when copper atoms get attached it
becomes Ceruloplasmin.
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69. Biochemistry For Medics
Clinical Significance of Ceruloplasmin
Normal level- 25-50 mg/dl
❑Low levels of ceruloplasmin are found in
Wilson disease (hepatolenticular degeneration),
a disease due to abnormal metabolism of
copper.
❑The amount of ceruloplasmin in plasma is
also decreased in liver diseases, mal nutrition
and nephrotic syndrome.
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70. Biochemistry For Medics
α2- Macroglobulin (AMG)
❑Major component of α2 proteins
❑Comprises 8–10% of the total plasma protein in
humans.
❑Synthesized by hepatocytes and macrophages
❑Inactivates all the proteases and thus is an
important in vivo anticoagulant.
❑Carrier of many growth factors
❑Normal serum level-130-300 mg/dl
❑Concentration is markedly increased in nephrotic
syndrome, since other proteins are lost through
urine in this condition.
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71. Biochemistry For Medics
β Globulins
β Globulins of clinical importance are –
❑ Transferrin
❑ C-reactive protein
❑Haemopexin
❑Complement C1q
❑β Lipoprotein(LDL)
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72. Biochemistry For Medics
Transferrin
❑Transferrin (Tf) is a β 1-globulin
❑It is a glycoprotein and is synthesized in the liver.
❑It plays a central role in the body's metabolism of
iron because it transports iron (2 mol of Fe3+ per
mole of Tf) in the circulation to sites where iron is
required, eg, from the gut to the bone marrow and
other organs.
❑Approximately 200 billion red blood cells (about 20
mL) are catabolized per day, releasing about 25 mg
of iron into the body—most of which is transported
by transferrin.
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73. Biochemistry For Medics
Clinical Significance of Transferrin
❑The concentration of transferrin in plasma is
approximately 300 mg/dL.
❑This amount of transferrin can bind 300 g of iron
per deciliter, so that this represents the total iron-
binding capacity of plasma.
❑However, the protein is normally only one-third
saturated with iron.
❑In iron deficiency anemia, the protein is even less
saturated with iron, whereas in conditions of storage
of excess iron in the body (eg, hemochromatosis) the
saturation with iron is much greater than one-third.
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74. Biochemistry For Medics
Clinical Significance of Transferrin
❑Increased levels are seen in iron deficiency
anemia and in last months of pregnancy
❑ Decreased levels are seen in-
❑Protein energy malnutrition
❑Cirrhosis of liver
❑Nephrotic syndrome
❑ Trauma
❑Acute myocardial infarction
❑Malignancies
❑Wasting diseases
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75. Biochemistry For Medics
C- reactive protein(β Globulin)
❑So named because it reacts with C-
polysaccharide of capsule of pneumococci
❑Synthesized in liver
❑Can stimulate complement activity and
macrophages
❑Acute phase protein- Concentration rises in
inflammatory conditions
❑Clinically important marker to predict the risk
of coronary heart disease
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76. Biochemistry For Medics
Haemopexin(β Globulin)
❑Normal level in adults-0.5 to 1.0 gm/L
❑Synthesized in liver
❑Function is to bind haem formed from
breakdown of Hb and other haemoproteins
❑Low level- found in hemolytic disorders, at birth
and drug induced
❑High level- pregnancy, diabetes mellitus,
malignancies and Duchenne muscular dystrophy
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77. Biochemistry For Medics
Gamma Globulins
❑ They are immunoglobulins with antibody
activity
❑They occupy the gamma region on
electrophoresis
❑Immunoglobulins play a key role in the
defense mechanisms of the body
❑There are five types of immunoglobulins
IgG, IgA, IgM, IgD, and IgE.
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78. Biochemistry For Medics
Different Classes of Immunoglobulins
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79. Biochemistry For Medics
Major functions of immunoglobulinsImmunoglobulin Major Functions
IgG Main antibody in the secondary
response. Opsonizes bacteria, Fixes
complement, neutralizes bacterial
toxins and viruses and crosses the
placenta.
IgA
Secretory IgA prevents attachment of
bacteria and viruses to mucous
membranes. Does not fix complement.
IgM
Produced in the primary response to an
antigen. Fixes complement. Does not
cross the placenta. Antigen receptor on
the surface of B cells.
IgD Uncertain. Found on the surface of
many B cells as well as in serum.
IgE Mediates immediate hypersensitivity
Defends against worm infections. Does
not fix complement.
7/11/2012 79

80. Biochemistry For Medics
Fibrinogen
❑Also called clotting factor1
❑Constitutes 4-6% of total protein
❑Precipitated with 1/5 th saturation with ammonium
sulphate
❑Large asymmetric molecule
❑Imparts maximum viscosity to blood
❑Synthesized in liver
❑Amino terminal end is highly negative due to the presence
of glutamic acid
❑Negative charge contributes to its solubility in plasma and
prevents aggregation due to electrostatic repulsions
between the fibrinogen molecules.
7/11/2012 80

81. Biochemistry For Medics
Transport proteins
Name Compounds transported
Albumin Fatty acids, bilirubin, hormones,
calcium, heavy metals, drugs etc.
Prealbumin-(Transthyretin) Steroid hormones thyroxin, Retinol
Retinol binding protein Retinol (Vitamin A)
Thyroxin binding protein(TBG) Thyroxin
Transcortin(Cortisol binding protein) Cortisol and corticosteroids
Haptoglobin Hemoglobin
Hemopexin Free haem
Transferrin Iron
HDL(High density lipoprotein) Cholesterol (Tissues to liver)
LDL(Low density lipoprotein) Cholesterol(Liver to tissues)
7/11/2012 81

82. ALBUMIN / GLOBULIN RATIO
•The normal A/G ratio is 1.2-2: 1, which amy be altered in
number of conditions like
•Increase in total plasma proteins occurs in dehydration,
due to prolonged diarrhoea, vomiting, Diabetes
insipidus.
•Decrease in total plasma protein is due to
hypoalbuminemia as seen in liver cirrhosis, nephrotic
syndrome, kawashiorkar etc.

83. NITROGEN BALANCE
● It refers to the comparison of nitrogen intake to
nitrogen excretion.
● It indicates the protein status of the body.
● Positive nitrogen balance: When nitrogen intake
exceeds that of its excretion. It mean Protein is added
in the body. Generally seen in growing children,
pregnant women and people recovering from protein
deficiency.
● Negative nitrogen balance: When nitrogen excretion
exceeds nitrogen intake. Generally seen in conditions
like starvation on weight loss diets, during fever,
severe illness or infections.
● Nitrogen equilibrium: When intake is equal to nitrogen
excretion, nitrogen balance is zero like in healthy
individuals. there is no net gain or loss of the body

84. NITROGEN FIXATION
● Converts atmospheric Nitrogen to a biologically
useful form.
● It is done by few strains of bacteria called as
diazotrophs such as cyanobacteria.
● They produce enzyme nitrogenase, which
catalyses the reduction of N2 to NH3.
● This enzyme is not present in human beings.

85. NITROGEN ASSIMILATION
● Nitrogen (as NH3) is incorporated into alpha-
ketoglutarate to produce glutamate.
● Once it is assimilated as glutamate, it can be used
in the biosynthesis of other amino acids by
transamination in human beings.

86. PROTEIN METABOLISM
● Proteins breaks down into amino acids, which
undergoes many changes leading to formation of
acetyl-CoA. This goes through the TCA cycle.
● Owing to the structure of amino acids, their
metabolic pathway differs.
● On basis of fate of amino acids they are classified
as glucogenic, ketogenic and both.

87. Catabolism of amino group occurs in 4 stages
⦿ Transamination
⦿ Oxidative Deamination
⦿ Ammonia Transport
⦿ Urea Cycle

88. Transamination
⦿ The transfer of an amino (-NH2) group from an
amino acid to a ketoacid, with the formation of
a new amino acid & a new keto acid.
⦿ Catalysed by a group of enzymes called
transaminases (aminotransferases)
⦿ Pyridoxalphosphate (PLP)– Co-factor.
⦿ Liver, Kidney, Heart, Brain - adequate amount
of these enzymes.

90. Salient features of transamination
⦿ All transaminases require PLP.
⦿ No free NH3 liberated, only the transfer of
amino group.
⦿ Transamination is reversible.
⦿ There are multiple transaminase enzymes
which vary in substrate specificity.
⦿ AST & ALT make a significant contribution for
transamination.

91. ⦿ Transamination is important for redistribution
of amino groups & production of non-
essential amino acids.
⦿ It diverts excess amino acids towards the
energy generation.
⦿ Amino acids undergo transamination to
finally concentrate nitrogen in glutamate.

92. ⦿ Glutamate undergoes oxidative
deamination to liberate free NH3 for urea
synthesis.
⦿ All amino acids except, lysine, threonine,
proline & hydroxyproline participate in
transamination.
⦿ It involves both anabolism & catabolism,
since – reversible.

93. AA1 + α- KG ketoacid1 + Glutamate
Alanine + α- KG Pyruvate + Glutamate
Aspartate + α- KG Oxaloacetetae +Glutamate

94. Glutamate-collecting point

95. Transamination

96. ● After ingestion of protein-rich meal, glutamate levels
are elevated. The breakdown reaction then occurs.
Therefore, deamination depends on concentration of
glutamate, alpha-ketoglutarate, ammonia etc.
● Role of Glutamate:
● Serves as gateway between free ammonia and amino
group.
● Involved in both synthesis and degradation.
● Only amino acid capable of undergoing rapid oxidative
deamination.
● Collects nitrogen from other amino acids by
transamination.
● Oxaloacetate and glutamate undergo transamination to
aspartate and alpha-ketoglutarate.
● Aspartate enters urea cycle.
● NADH formed during deamination passes through ECT
and oxidative phosphorylation to yield ATP

97. Fate of amino acids
● Proteins are degraded to their constituent aminoacids
in G.I. tract by the action of various enzymes.
● Free amino acid is transported into epithelial cells of
small intestine from where they enter blood capillaries
and travel to liver.
● In liver, the amino acids are catabolised, alpha amino
group is removed from amino acid from two
processes: Transamination and deamination.
● Transamination: transfer of alpha amino group from
amino acid to keto-acid resulting in formation of new
amino acid and keto acid. Amino transferase catalyses
the reaction. (Transaminases). Most important
transaminases are GOT and GPT.

98. Fate of amino acids
● Amino acid first reacts with coenzyme pyridoxal-5-
phosphate(PLP) and forms a Stiff’s base. Coenzyme
becomes protonated and is subsequently hydrolysed
to release the alpha-keto acid of corresponding amino
acid while retaining alpha- amino group.
● PLP gets laminated and converted to pyridoxamine-5-
phosphate. Thereafter, alpha-keto acid combines with
the coenzyme bound amino group which in turn
releases the keto acid as new amino acid and
regenerates coenzyme.
● Alpha-ketoglutarate accepts the amino acids and gets
converted to glutamate.

99. ● Deamination: it removes amino group from alpha
amino acid as ammonia leaving alpha keto acid.
Catalysed by the enzyme amino oxidase in liver,
kidney and several other tissues.
● It is elimination of amino group from amino acid with
ammonia formation.
● Oxidative deamination: An amino acid is converted
into corresponding kept acid by removal of amine
functional group as ammonia. The amine functional
group is replaced by ketone group. The ammonia
eventually goes into urea cycle.
● Oxidative deamination occurs primarily on glutamic
acid as it is the end product of many transamination
reactions.

100. ● Enzyme involved: glutamate dehydrogenase (located
in mitochondrial matrix).
● Occurs in two steps. Amino acid is dehydrogenated by
amino oxidase to form alpha-amino acid.
● Water molecule is added spontaeneously and
decomposes the alpha amino acid to corresponding
alpha-keto acid with loss of nitrogen in form of NH3
(ammonia)
● This process results in production of NADH2. also
called as oxidative deamination.

101. ● Deamination:

102. Diagnostic significance of
transaminases
● SGOT and SGPT have diagnostic significance.
● Both are present in large amounts in cardiac
muscles and liver respectively.
● Serum levels of both enzymes are raised in heart
as well as liver diseases.
● SGOT is markedly raised in M.I. while SGPT is
raised in liver disorders like hepatitis.

103. NITROGEN EXCRETION AND UREA
CYCLE
● Urea cycle is the process by which ammonia is
converted to urea (which is less toxic, water soluble).
● Steps:
● Ammonia reacts with CO2 and forms carbamoyl-
phosphate. The reaction is catalysed by carbamoyl
phosphate synthetase (CPS). It required N-
acetylglutamate as coenzyme.
● Carbamoyl group is transferred from
carbamoylphosphate to ornithine and forms cirulline.
Catalyzed by transcarbamoylase.
● Citrulline combines with L-aspartate, and forms
argininosuccinate.
● Argininosuccinate gets hydrolysed to arginine and
fumarate.

104. NITROGEN EXCRETION AND UREA
CYCLE
● Fumarate released in this reaction enters
mitochondria where it is converted to oxaloacetate
via citric acid cycle.
● Arginine is hydrolyzed to ornithine and urea.
● Ornithine is transported to mitochondria and
reenters the cycle.
● Formation of urea involves requirement of 3 high
energy phosphate bonds.
● 2ATP molecules are required for the formation of
carbamoyl phosphate.
● 1 ATP is involved in the formation of
argininosuccinate.

106. Control of UREA CYCLE
● N-acetylglutamate acts as activator of enzyme
carbamoylphosphate synthetase.
● Induction of urea cycle enzymes occur with the
delivery of ammonia or amino acids to the liver is
increased.
● Thus a high protein diet or starvation result in
induction of enzymes in urea cycle.

107. Defects in Urea Cycle
● Since ammonia is very toxic, a metabolic disorder
of urea cycle may result in coma and may be fatal.
● Hyperammonemia may be caused due to
inherited deficiencies in urea cycle due to liver
disease.
● A high protein diet taken for four or more days
induces urea cycle enzymes.
● Treatment of hyperammonemia: Low –protein diet
and administration of sodium benzoate and
sodium phenylacetate. These compounds form
adducts with glycine and glutamate.

108. Catabolism of carbon skeleton of
amino acids
● A larger proportion of amino acids are
incorporated into proteins, which are constantly
being synthesized and degraded. Excess of these
dietary amino acids are not simply excreted but
are degraded to common metabolites and are
used as metabolic fuels.
● Carbon skeleton, forms amphibolic intermediates,
which can be converted to either glucose or
ketone bodies.
● Transamination of alanine, glutamate and valine
forms pyruvate, succinyl CoA, alpha-
ketoglutarate. These are intermediates of citric
acid cycle. And can be converted to glucose.
(glucogenic)

109. ● Catabolism of phenylalanine also forms acetyl
CoA and acetoacyl CoA, which are precursors of
ketone bodies. Therefore these are referred as
both glucogenic and ketogenic.
● Lucine is purely ketogenic as end products of
catabolism are acetyl CoA aand acetoacetyl CoA.

110. Conversion of Phenylalanine to
Tyrosine
● Phenylalanine which is not incorporated into proteins is
converted to Tyrosine.
● The reaction is catalyzed by Phenylalanine
hydroxylase.
● CATABOLISM OF TYROSINE
● As tyrosine can be synthesized from phenylalanine,
tyrosine is non-essential amino acid.
● In liver tyrosine is transaminated to p-
hydroxyphenylpyruvate, by tyrosine aminotransferase.
● Copper containing enzyme p-hydroxyphenylpyruvate
oxidase converts hydroxyphenylpyruvate to
homogentisic acid.

111. ● Iron containing enzyme, homogentisic acid
oxidase oxidizes homogentisic acid and
maleylacetoacetate which after undergoing
isomerization forms the end products i.e. fumarate
and acetoacetate.
● Phenylalanine and tyrosine serves as precursors
of various biologically active compounds.

112. URIC ACID FORMATION
● It is the excreted end product of purine catabolism
in primates, birds and some other animals.
● A healhy human being excretes uric acid at a rate
of about 0.6g/24hr.
● In humans AMP and GMP are catabolized into
uric acid.
● Purine nucleotides are degraded by the pathway
in which they loose their phosphate through action
of 5’-nucleotidase, yielding adenosine from AMP.
● Adenosine is deaminated to inosine by adenosine
deaminase and inosine is hydrolysed to
hypoxanthine.

113. ● Hypoxanthine gets successively oxidized to
xanthine and then uric acid by xanthine oxidase.
● GMP catabolism also yields uric acid as end
product.
● It is first hydrolysed to guanosine which is then
cleaved to free guanine.
● Guanine undergoes hydrolytic removal of amino
group and yields xanthine which is then converted
by xanthine oxidase to uric acid.
● If concentration of uric acid increases in blood and
tissues, it leads to disease of joints called Gout.

114. GOUT
● It is a metabolic disorder of purine catabolism,
characterized by increased levels of uric acid in
blood and high level of uric acid secretion in the
urine.
● Due to increased level of uric acid in blood, there
is accumulation of uric acid in joints and soft
tissues.
● The joints become inflammed, painful and arthritic.
● Gout occurs predominantly in males.
● Kidneys are also affected as excess uric acid is
deposited in the kidney tubules.
● Classified as: Primary Gout and secondary Gout.

115. ● Primary gout is inherited and found mostly in men
of 30years of age but in females onset is post
menopausal.
● Secondary Gout occurs in both males and
females. Hyperuricemia may be because of other
diseases like leukaemia, polycythemia, chronic
renal insufficiency or by use of anti cancer drugs
in treatment of cancer.
● Treatment is by foods rich in nucleotides and
nucleic acid such as liver or glandular products.
● Drug named Allopurinol inhibits the enzyme
Xanthine oxidase and thus helps in the treatment

116. Biosynthesis of proteins
● It is under direct control of DNA.
● Genetic information is first transcribed into mRNA
and is then translated into proteins.
● Unidirectional flow of information is followed by
most of the organisms.
● It is also known as central dogma.
● Flow of information may occur in circular form.

117. ● DNA unwinds
● mRNA copy is made of one of the DNA strands with
the help of RNA polymerase.
● mRNA copy moves out of nucleus into cytoplasm.
● tRNA molecules are activated as their complementary
amino acids are attached to them.
● mRNA copy attaches to the small subunit of the
ribosomes in cytoplasm. 6 of the bases in the mRNA
are exposed in the ribosome.
● tRNA binds complementarily with mRNA via its
anticodon.
● 2nd tRNA binds with next three bases of mRNA, amino
acid joins onto the amino acid of first tRNA via peptide
bond.

118. ● Ribosome moves along. First tRNA leaves the
ribosome.
● Third tRNA brings a third amino acid.
● Eventually a stop codon is reached on the mRNA.
This signals the ribosome to leave the mRNA.
The newly synthesized polypeptide leaves the
ribosome.

119. Role of nucleic acid in protein
biosynthesis.
● Nucleic acids such as DNA and RNA are
molecular repositories of genetic information.
● Segment of RNA and DNA molecule contains
regarding the synthesis of a protein is referred as
gene.
● Each gene has specific nucleotide sequence
which is responsible for amino acid sequence of a
particular protein.
● Nucleic acids play a significant role in biosynthesis
of proteins.

120. Protein Targetting and
Glycosylation
● After synthesis, proteins are directed to particular
locations in the cell.
● In ER, these proteins are further modified in several
ways.
● It involves: removal of signal sequence, folding of
polypeptide, formation of disulphide bonds and
glycosylation of any other proteins forming
glycoproteins.
● In eukaryotic cells, synthesized polypeptides have
signal sequences which are recognized by signal
recognition particles.
● Polypeptides move to ER lumen as they are
synthesized. Inside the ER lumen, they are modified
by various processes and moved to Golgi complex.
● Where they are sorted and sent to lysosomes, plasma

121. NUCLEIC ACIDS
● Macromolecules, occurring in cells in association
with basic proteins such as histones and
protamines.
● NUCLEOTIDES
● Nucleotide has 3 constituents and consists of
phosphoric acid, pentose sugar and nitrogenous
base.
● Sugars: pentose sugars defines the type of
nucleic acid.
● They are ribose and deoxyribose.
● Two classes of Nucleotides are:
● DNA
● RNA

122. ● Nitrogenous base: the base found in nucleotides
are derivative of purines and pyrimidines.
● Purine is a nine-member ring containing 5-carbons
and 4-nitrogen.
● Pyrimidine is a six member ring with 4carbons and
2nitrogen.
● Purines: adenine and guanine
● Pyrimidines: cytosine, uracil and thymine (methyl
uracil).

123. ● NUCLEOSIDES:
● Has two components. i.e. nitrogenous base and
pentose sugar.
● Sugar: deoxyribose and ribose
● Ribonucleosides: adenosine, guanosine, cytidine
and uridine.
● Deoxyribonucleoside: deoxy-adenosine, deoxy-
guanosine etc.

124. BIOLOGICAL SIGNIFICANCE OF
NUCLEIC ACID
● DNA makes copies of it and thus transfers genetic
information from one generation to the next.
(Replication)
● Determines the properties of living cell and
regulates biological information, by controlling
protein synthesis through RNA.

125. PLASMA PROTEINS
● Proteins found in blood plasma are called plasma
proteins.
● Also called blood proteins.
● Total plasma proteins in blood is 7g/dl.

126. TYPES
● ALBUMIN
● Most abundant of plasma proteins
● Accounts nearly 60% of all proteins.
● Responsible for transporting various substances
in the blood such as lipids, steroid hormones.
● Also helps in maintaining water balance and
contribute to osmotic pressure which in simple
terms is pressure exerted by water moving by
osmosis in and out of cells.

127. ● GLOBIN
● 35% of plasma proteins
● Includes enzymes, protein carriers and gamma
globilin or antibodies.
● While most plasma proteins are synthesized in the
liver, gamma globulins are made by lymphocytes
called plasma cells.

128. ● FIBRINOGEN
● Nearly 4% of plasma proteins are fibrinogen.
● The sole function of fibrinogen is to produce clots
to help stop bleeding.

129. FUNCTIONS OF PLASMA
PROTEINS
● Building blocks of all body cells and tissues
including antibodies, hormones and clotting
factors.
● Help in transport of variety of substances
including, hormones, vitamins and drugs etc.
● Controls osmotic pressure between blood and
tissues thus regulate acid-base balance of blood.
● Act as source of energy for muscles and tissues
under starvation conditions.

130. IMPACT OF ABNORMAL PLASMA
PROTEINS
● Low level indicates liver disease or kidney disease
while high level could be a result of dehydration
or congestive heart failure.
● High globulin levels indicate chronic infection, liver
disease or rheumatoid arthritis. Low levels might
mean acute anaemia, liver dysfunction.
● Elevated levels of fibrinogen indicate increased
risk of stroke and may be combined with high
blood pressure that proves fatal.