1 | Clinical Chemistry Finals
CLINICAL CHEMISTRY FINALS Non-polar Uncharged Polar
Chapter 8: Proteins
Glycine (Gly, G)
Alanine (Ala, A)
INTRODUCTION Valine (Val, V)
Serine (Ser, S)
• Proteins are polymers of amino acids. These amino Threonine (Thr, T)
Leucine (Leu, L)
Tyrosine (Tyr, Y)
acids are joined together by peptide bonds. For Isoleucine (Ile, I)
Asparagine N) (Asn,
example, two amino acids are joined together by a Phenylalanine (Phe, F)
Cysteine (Cys, C)
Tryptophan (Trp, W)
peptide bond to form a dipeptide. Methionine (Met, M)
Glutamine (Gln, Q)
• The peptide bond is an amide linkage formed Proline (Pro, P
between the carboxyl group of one amino acid and
the amino group of another. Acidic Basic
(negatively charged) (positively charged)
• The protein formed will have an amino terminus in one
end and a carboxyl terminus in the other end. Histidine (His, H)
Aspartic acid (Asp, D)
Lysine (Lys, K)
• Proteins play many important roles in the body. Most Glutamic acid (Glu, E)
Arginine (Arg, R)
of the enzymes in the body are protein in nature.
• Enzymes act as biological catalysts.
• Proteins like albumin, lipoproteins, hemoglobin, • Of the twenty amino acids, ten are considered
transferrin and ceruloplasmin function for transport essential (nutritionally essential) because they are not
and storage of certain substances. produced in the body.
o Albumin, for example, carries fatty acids, bilirubin, • Thus, a supply of these amino acids must be met by
and other insoluble metabolites in the plasma. intake of food.
o Iron, calcium and copper must be bound to • To easily recall these essential amino acids, just
proteins to prevent their excretion via the kidney. remember this mnemonic: PVT. TIM HALL i.e.,
• Other proteins function for muscle contraction. o Phenylalanine
o Contractile proteins e.g., actin and myosin o Valine
regulate muscle contraction. o Threonine
o Collagen and keratin function for mechanical o Tryptophan
support. The immunoglobulins protect the body o Isoleucine
from invading microorganisms. Many hormones o Methionine
are polypeptides in nature. Examples are insulin, o Histidine
adrenocorticotrophic hormone (ACTH) and thyroid o Arginine
stimulating hormones (TSH). Their receptors on cell o Leucine
membranes of target cells are also made from o Lysine
proteins. Cellular growth and differentiation are • Each amino acid has a characteristic isoelectric point
also controlled by regulatory proteins. (p1). This is the pH at which the amino acid assumes a
net charge of zero i.e., it has a double charge,
AMINO ACIDS positive and negative (i.e., a zwitterions).
• There are twenty primordial amino acids. • Amino acids therefore can act as an acid and as a
base.
• The nature of each amino acid depends on the kind of
side chain present in the molecule. • It is amphoteric (i.e., an ampholyte).
• Thus, there are four major groups of amino acids:
o non-polar or hydrophobic
o uncharged polar STRUCTURAL ORGANIZATION OF PROTEINS
o acidic 1. Primary structure – is the linear sequence of amino
o basic acids in the polypeptide.
2. Secondary structure – involves the winding of the
polypeptide chain.
Prepared by: Joshua S. Manong
, 2 | Clinical Chemistry Finals
3. Tertiary structure – folding of the polypeptide chain & • On the other hand, the secretion of enzyme-rich
elements of secondary structure into a compact 3- pancreatic juice is mediated by the hormone
dimensional shape. pancreozymin or cholecystokinin (CCK).
• CCK is also a potent stimulant for the contraction of
the gallbladder.
• The pancreatic enzymes are activated by
4. Quaternary structure – is the shape or structure that enteropeptidase.
results from the interaction of more than one protein • Trypsinogen is converted to trypsin by the action of
molecule or protein subunits, held together by non- enteropeptidase.
covalent forces such as hydrogen bonds and • The trypsin formed then activates chymotrypsinogen,
electrostatic interactions. Ex. Hemoglobin pro-elastase and pro-carboxypeptidase.
Intestinal Phase
• This phase is mediated by peptidases- produced by
the mucosal cells.
• Aminopeptidases and dipeptidases hydrolyze the
residual peptides.
• The end products of protein digestion are amino acids
and some short peptides (polypeptides).
PROTEIN METABOLISM
• There are three phases of protein metabolism namely
the gastric phase, the pancreatic phase, and the ABSORPTION OF AMINO ACIDS
intestinal phase. • Most of the amino acids in nature are L-amino acids.
• There are at least five transport systems for amino
Gastric Phase
acids to affect their absorption in the small intestine.
• Digestion of proteins begins in the stomach where the
• The transport across the mucosal cell membrane
enzyme pepsin is secreted by the chief cells as a
usually involves the glutamyl cycle or the Meister
proenzyme or zymogen (the inactive form).
cycle.
• Pepsinogen is activated by gastric acidity (HCl
• Some proteins, however, as absorbed without being
secreted by the parietal cells) and by auto-activation,
digested first.
i.e, pepsin itself stimulates its own activation.
• Immunoglobulin A (IgA), for example, is absorbed
• Gastrin is the hormone that stimulates the secreation
intact in newborns.
of both pepsinogen and HCl. This is produced by the
antrum (distal end of the stomach) during ingestion of • Certain allergens also find their way to the blood
food. without being digested.
• After absorption, the amino acids are brought to the
Pancreatic Phase liver via the portal circulation.
• Once the chyme reaches the duodenum, the exocrine • The amino acids are used to build up many nitrogen-
pancreas releases the protcolytic enzymes trypsin, containing metabolites such as heme (porphyrin),
chymotrypsin, elastase, and carboxypeptidase in choline (in phospholipids), glycosamine (in many
their zymogen forms. glycosaminoglycans), nucleotides, proteins, biogenic
• The first three are endopeptidases while amines (catecholamines and neurotransmitters),
carboxypeptidase is an exopeptidase. carnitine and creatine phosphate.
• Endopeptidases cleave proteins in their internal sites
while carboxypeptidases cleave one amino acid from PROTEIN MEASUREMENT
the carboxyl-terminus of the polypeptide. • Total Protein= 60-70 g/L (SI units) or 6.0-7.8 g/dL
• The hormone secretin stimulates the pancreas to (conventional units).
produce a protein-free electrolyte solution rich in o Albumin- (32-45 g/L)
bicarbonates. o Globulin (23- 35 g/L)
• It is produced by the duodenum in response to chyme. o Fibrinogen (2-4 g/L)
• Bicarbonates are needed to neutralize the acidity of • Plasma proteins regulate the distribution of fluids
the chyme. between the blood and the tissue through their osmotic
effect.
Prepared by: Joshua S. Manong
CLINICAL CHEMISTRY FINALS Non-polar Uncharged Polar
Chapter 8: Proteins
Glycine (Gly, G)
Alanine (Ala, A)
INTRODUCTION Valine (Val, V)
Serine (Ser, S)
• Proteins are polymers of amino acids. These amino Threonine (Thr, T)
Leucine (Leu, L)
Tyrosine (Tyr, Y)
acids are joined together by peptide bonds. For Isoleucine (Ile, I)
Asparagine N) (Asn,
example, two amino acids are joined together by a Phenylalanine (Phe, F)
Cysteine (Cys, C)
Tryptophan (Trp, W)
peptide bond to form a dipeptide. Methionine (Met, M)
Glutamine (Gln, Q)
• The peptide bond is an amide linkage formed Proline (Pro, P
between the carboxyl group of one amino acid and
the amino group of another. Acidic Basic
(negatively charged) (positively charged)
• The protein formed will have an amino terminus in one
end and a carboxyl terminus in the other end. Histidine (His, H)
Aspartic acid (Asp, D)
Lysine (Lys, K)
• Proteins play many important roles in the body. Most Glutamic acid (Glu, E)
Arginine (Arg, R)
of the enzymes in the body are protein in nature.
• Enzymes act as biological catalysts.
• Proteins like albumin, lipoproteins, hemoglobin, • Of the twenty amino acids, ten are considered
transferrin and ceruloplasmin function for transport essential (nutritionally essential) because they are not
and storage of certain substances. produced in the body.
o Albumin, for example, carries fatty acids, bilirubin, • Thus, a supply of these amino acids must be met by
and other insoluble metabolites in the plasma. intake of food.
o Iron, calcium and copper must be bound to • To easily recall these essential amino acids, just
proteins to prevent their excretion via the kidney. remember this mnemonic: PVT. TIM HALL i.e.,
• Other proteins function for muscle contraction. o Phenylalanine
o Contractile proteins e.g., actin and myosin o Valine
regulate muscle contraction. o Threonine
o Collagen and keratin function for mechanical o Tryptophan
support. The immunoglobulins protect the body o Isoleucine
from invading microorganisms. Many hormones o Methionine
are polypeptides in nature. Examples are insulin, o Histidine
adrenocorticotrophic hormone (ACTH) and thyroid o Arginine
stimulating hormones (TSH). Their receptors on cell o Leucine
membranes of target cells are also made from o Lysine
proteins. Cellular growth and differentiation are • Each amino acid has a characteristic isoelectric point
also controlled by regulatory proteins. (p1). This is the pH at which the amino acid assumes a
net charge of zero i.e., it has a double charge,
AMINO ACIDS positive and negative (i.e., a zwitterions).
• There are twenty primordial amino acids. • Amino acids therefore can act as an acid and as a
base.
• The nature of each amino acid depends on the kind of
side chain present in the molecule. • It is amphoteric (i.e., an ampholyte).
• Thus, there are four major groups of amino acids:
o non-polar or hydrophobic
o uncharged polar STRUCTURAL ORGANIZATION OF PROTEINS
o acidic 1. Primary structure – is the linear sequence of amino
o basic acids in the polypeptide.
2. Secondary structure – involves the winding of the
polypeptide chain.
Prepared by: Joshua S. Manong
, 2 | Clinical Chemistry Finals
3. Tertiary structure – folding of the polypeptide chain & • On the other hand, the secretion of enzyme-rich
elements of secondary structure into a compact 3- pancreatic juice is mediated by the hormone
dimensional shape. pancreozymin or cholecystokinin (CCK).
• CCK is also a potent stimulant for the contraction of
the gallbladder.
• The pancreatic enzymes are activated by
4. Quaternary structure – is the shape or structure that enteropeptidase.
results from the interaction of more than one protein • Trypsinogen is converted to trypsin by the action of
molecule or protein subunits, held together by non- enteropeptidase.
covalent forces such as hydrogen bonds and • The trypsin formed then activates chymotrypsinogen,
electrostatic interactions. Ex. Hemoglobin pro-elastase and pro-carboxypeptidase.
Intestinal Phase
• This phase is mediated by peptidases- produced by
the mucosal cells.
• Aminopeptidases and dipeptidases hydrolyze the
residual peptides.
• The end products of protein digestion are amino acids
and some short peptides (polypeptides).
PROTEIN METABOLISM
• There are three phases of protein metabolism namely
the gastric phase, the pancreatic phase, and the ABSORPTION OF AMINO ACIDS
intestinal phase. • Most of the amino acids in nature are L-amino acids.
• There are at least five transport systems for amino
Gastric Phase
acids to affect their absorption in the small intestine.
• Digestion of proteins begins in the stomach where the
• The transport across the mucosal cell membrane
enzyme pepsin is secreted by the chief cells as a
usually involves the glutamyl cycle or the Meister
proenzyme or zymogen (the inactive form).
cycle.
• Pepsinogen is activated by gastric acidity (HCl
• Some proteins, however, as absorbed without being
secreted by the parietal cells) and by auto-activation,
digested first.
i.e, pepsin itself stimulates its own activation.
• Immunoglobulin A (IgA), for example, is absorbed
• Gastrin is the hormone that stimulates the secreation
intact in newborns.
of both pepsinogen and HCl. This is produced by the
antrum (distal end of the stomach) during ingestion of • Certain allergens also find their way to the blood
food. without being digested.
• After absorption, the amino acids are brought to the
Pancreatic Phase liver via the portal circulation.
• Once the chyme reaches the duodenum, the exocrine • The amino acids are used to build up many nitrogen-
pancreas releases the protcolytic enzymes trypsin, containing metabolites such as heme (porphyrin),
chymotrypsin, elastase, and carboxypeptidase in choline (in phospholipids), glycosamine (in many
their zymogen forms. glycosaminoglycans), nucleotides, proteins, biogenic
• The first three are endopeptidases while amines (catecholamines and neurotransmitters),
carboxypeptidase is an exopeptidase. carnitine and creatine phosphate.
• Endopeptidases cleave proteins in their internal sites
while carboxypeptidases cleave one amino acid from PROTEIN MEASUREMENT
the carboxyl-terminus of the polypeptide. • Total Protein= 60-70 g/L (SI units) or 6.0-7.8 g/dL
• The hormone secretin stimulates the pancreas to (conventional units).
produce a protein-free electrolyte solution rich in o Albumin- (32-45 g/L)
bicarbonates. o Globulin (23- 35 g/L)
• It is produced by the duodenum in response to chyme. o Fibrinogen (2-4 g/L)
• Bicarbonates are needed to neutralize the acidity of • Plasma proteins regulate the distribution of fluids
the chyme. between the blood and the tissue through their osmotic
effect.
Prepared by: Joshua S. Manong
