Medical

1. Proteins

3. AMINO ACID STRUCTURE

5. Unique Side Groups
• The side groups on amino acids vary from one amino acid to the next, making
proteins more complex than either carbohydrates or lipids.
• A polysaccharide (starch, for example) may be several thousand units long, but
every unit is a glucose molecule just like all the others.
• A protein, on the other hand, is made up of about 20 different amino acids, each
with a different side group.
• The simplest amino acid, glycine, has a hydrogen atom as its side group.
• A slightly more complex amino acid, alanine, has an extra carbon with three
hydrogen atoms.
• Other amino acids have more complex side groups
• Thus, although all amino acids share a common structure, they differ in size, shape,
electrical charge, and other characteristics because of differences in these side
groups.

6. EXAMPLE

7. • The structure and function of all proteins is related to their
amino acid composition: the number and order of linkages.
folding, intrachain linkages and the interaction with other groups
to induce chemical change.
• the amino acids are linked in chains through peptide bonds
• for a protein to be synthesized requires that all amino acids
needed are available at the point of synthesis.
• if one aa is in short supply, this will limit the process of protein
synthesis - a limiting aa

8. • There are 20 common amino acids required for protein synthesis
and all are essential for metabolism
• 9 are classified as essential or indispensable because the body
cannot make them so they must be supplied through the diet
• The remaining 11 amino acids are classified as nonessential or
dispensable because cells can make them as needed through the
process of transamination.
• Some dispensable amino acids may become indispensable when
metabolic need is great and endogenous synthesis is not
adequate.

9. Note:
The terms essential and nonessential refer to whether or not they must
be supplied by the diet, not to their relative importance: all 20 amino
acids must be available for the body to make proteins.

10. • in early childhood, a number of amino acids, which are not
essential in adults cannot be formed in adequate amounts,
because the demand is high, the pathways for theif formation
are not matured or the rate of endogenous formation is not
adequate(or some combination of these)
• These aa have been identified as being conditionally essential
because of their limited ability of their endogenous formation
relative to the magnitude of the demand (arginine, histidune,
glycine,glutamine etc)
• there may be disease situations during adult life when for one
reason or another, a particular aa or group of aa becomes
conditionally essential

11. Conditionally Essential Amino Acids
• Sometimes a nonessential amino acid becomes essential under
special circumstances. For example, the body normally uses the
essential amino acid phenylalanine to make tyrosine (a
nonessential amino acid).
• But if the diet fails to supply enough phenylalanine, or if the
body cannot make the conversion for some reason (as happens
in the inherited disease phenylketonuria), then tyrosine becomes
conditionally essential

13. PROTEINS
• Cells link amino acids end-to-end in a variety of sequences to form thousands
of different proteins.
• A peptide bond unites each amino acid to the next.
• Condensation reactions connect amino acids, just as they combine
monosaccharides to form disaccharides, and fatty acids with glycerol to form
triglycerides. Two amino acids bonded together form a dipeptide
• By another such reaction, a third amino acid can be added to the chain to
form a tripeptide.
• As additional amino acids join the chain, a polypeptide is formed. Most
proteins are a few dozen to several hundred amino acids long.
• example—insulin

14. Amino Acid Sequences
• If a person could walk along a carbohydrate molecule like starch,
the first stepping stone would be a glucose. The next stepping
stone would also be a glucose, and it would be followed by a
glucose, and yet another glucose.
• But if a person were to walk along a polypeptide chain, each
stepping stone would be one of 20 different amino acids. The
first stepping stone might be the amino acid methionine. The
second might be an alanine. The third might be a glycine, and
the fourth a tryptophan, and so on.

15. • Walking along another polypeptide path, a person might step on a
phenylalanine, then a valine, and a glutamine.
• In other words, amino acid sequences within proteins vary. The amino acids
can act somewhat like the letters in an alphabet. If you had only the letter G,
all you could write would be a string of Gs: G–G–G–G–G–G–G.
• But with 20 different letters available, you could create poems, songs, or
novels.
• Similarly, the 20 amino acids can be linked together in a variety of
sequences— even more than are possible for letters in a word or words in a
sentence. Thus the variety of possible sequences for polypeptide chains is
tremendous.

16. Protein Shapes
• Polypeptide chains twist into a variety of complex, tangled shapes, depending on
their amino acid sequences.
• The unique side group of each amino acid gives it characteristics that attract it to,
or repel it from, the surrounding fluids and other amino acids.
• Some amino acid side groups carry electrical charges that are attracted to water
molecules (they are hydrophilic).
• Other side groups are neutral and are repelled by water (they are hydrophobic).
• As amino acids are strung together to make a polypeptide, the chain folds so that
its charged hydrophilic side groups are on the outer surface near water; the neutral
hydrophobic groups tuck themselves inside, away from water.
• The intricate, coiled shape the polypeptide finally assumes gives it maximum
stability.

17. Protein Functions
• The extraordinary and unique shapes of proteins enable them to
perform their various tasks in the body. Some form hollow balls that
can carry and store materials within them, and some, such as those
of tendons, are more than ten times as long as they are wide,
forming strong, rodlike structures. Some polypeptides are functioning
proteins as they are; others need to associate with other
polypeptides to form larger working complexes. Some proteins
require minerals to activate them. One molecule of hemoglobin—the
large, globular protein molecule that, by the billions, packs the red
blood cells and carries oxygen—is made of four associated
polypeptide chains, each holding the mineral iron (

18. Structure of haemoglobin

29. Protein Digestion
• Proteins are crushed and moistened in the mouth.
• In the Stomach there is partial breakdown (hydrolysis) of proteins.
Hydrochloric acid uncoils (denatures) each protein’s tangled strands
so that digestive enzymes can attack the peptide bonds.
• The hydrochloric acid also converts the inactive form of the enzyme
pepsinogen to its active form, pepsin. Pepsin cleaves(splits)
proteins—large polypeptides—into smaller polypeptides and some
amino acids.

30. In the Small Intestine
• Pancreatic and intestinal proteases hydrolyze polypeptides further
into short peptide chains, tripeptides, dipeptides, and amino acids.
• Peptidase enzymes on the membrane surfaces of the intestinal cells
such as trypsin and chymotrypsin split most of the dipeptides and
tripeptides into single amino acids.
• Protein digestibility is 90% to 99% for animal proteins, over 90% for
soy and legumes and 70% to 90% for other plant proteins

31. Protein Absorption
• A number of specific carriers transport amino acids (and some
dipeptides and tripeptides) into the intestinal cells.
• Once inside the intestinal cells, amino acids may be used for energy or
to synthesize needed compounds.
• Those not used by the intestinal cells are transported across the cell
membrane into the surrounding fluid where they enter the capillaries on
their way to the liver

32. Protein metabolism
The liver acts as a clearing house for the amino acids it receives;
• The liver retains amino acids to make liver cells, nonessential
amino acids, and plasma proteins such as heparin, prothrombin
and albumin
• It regulates the release of amino acids into the bloodstream and
removes excess amino acids from the circulation
• It synthesizes specific enzymes to degrade excess amino acids

33. Cont.
• It removes the nitrogen from amino acids so that they can be
burned for energy
• It converts certain amino acids to glucose if necessary
• It forms urea from the nitrogenous waste of protein when
protein and calories are consumed in excess of need
• It converts protein to fatty acids that form triglycerides for
storage n adipose tissue

34. SUMMARY
• Before proteins taken in the diet can be utilized, they have to be
broken down to the constituent aa through digestion
• the catalytic breaking of the peptide bond is achieved through
enzymes, which act initially in the acid environment of the
stomach and the process is completed in the alkaline
environment of the small intestine
• The products for digestion are presented for absorption as
individual aa, dipeptides, or small oligo peptides.
• absorption takes place in the small intestine as an energy-
dependent process through specific transporters.

35. Proteins in the body – Protein synthesis
• protein synthesis is an intracellular event and the amount and patterns
of protein being formed in a cell at any point in time are determined by
the factors that control genomic expression, the translation of the
message, and the control of the synthetic machinery on ribosomes
• The instructions for making every protein in a person’s body are
transmitted by way of the genetic information received at conception.
• This body of knowledge, which is filed in the DNA (deoxyribonucleic
acid) within the nucleus of every cell, never leaves the nucleus.

36. • protein degradation is also an intracellular event
• in normal adults, about 4g protein/kg body weight are
synthesized each; about 300g protein/day in men and 250g
protein/day in women.
• in newborn infants, the rate is about 12 g protein/kg, falling to
about 6g/kg by 1 yea of age.

37. Protein turnover
• This is a continuous process that occurs within each cell as
proteins are broken down from normal wear and tear and
replenished.
• Body proteins vary in their rate of turnover. For example, red
blood cells are replaced every 60 to 90 days, GI cells are replaced
every 2 to 3 days, and enzymes use in the digestion of food are
continuously replenished.

38. Metabolic pool
• When proteins break down, they free amino acids to join the
general circulation.
• These amino acids mix with amino acids from dietary protein to
form an “amino acid pool” within the cells and circulating blood.
• The rate of protein degradation and the amount of protein intake
may vary, but the pattern of amino acids within the pool remains
fairly constant.

39. Nitrogen balance
• This reflects the state of balance between protein breakdown
and protein synthesis.
• In healthy adults, protein synthesis balances with degradation,
and protein intake from food balances with nitrogen excretion in
the urine, feces, and sweat.
• When nitrogen intake equals nitrogen output, the person is in
nitrogen equilibrium, or zero nitrogen balance.

40. • If the body synthesizes more than it degrades and adds protein, nitrogen
status becomes positive.
■ Nitrogen status is positive in growing infants and children, pregnant women,
and people recovering from protein deficiency or illness; their nitrogen intake
exceeds their nitrogen output. They are retaining protein in new tissues as they
add blood, bone, skin, and muscle cells to their bodies.
If the body degrades more than it synthesizes and loses protein, nitrogen status
becomes negative.■
Nitrogen status is negative in people who are starving or suffering other severe
stresses such as burns, injuries, infections, and fever; their nitrogen output
exceeds their nitrogen intake. During these times, the body loses nitrogen as it
breaks down muscle and other body proteins for energy.

41. Calculating nitrogen Balance
• Calculate nitrogen intake by measuring protein intake(in grams)
over a 24-hour period and divide by 6.25 because protein is 16%
nitrogen
• Calculate nitrogen excretion by analyzing a 24-hour urine sample
for the amount (grams) of urinary urea nitrogen it contains, add
a coefficient of 4 to this number to account for the estimated
daily nitrogen loss in feces, hair, nails and skin
• Subtract grams of nitrogen excretion from grams of nitrogen
intake to reveal the state of nitrogen balance

42. Calculating nitrogen balance
• When nitrogen intake=nitrogen excretion, this is a state of
equilibrium (healthy adults)
• When protein synthesis exceeds protein breakdown(e.g during
growth, pregnancy, or recovery from injury), nitrogen balance is
positive
• A negative nitrogen balance indicates that protein catabolism is
occurring at a faster rate than protein synthesis, which occurs
during starvation or the catabolic phase after injury.

43. Study question
• Mary is a 25-year old woman who was admitted to the hospital
with multiple fractures and traumatic injuries from a car
accident. A nutritional intake study indicated a 24-hour protein
intake of 64g. A 24-hour urinary urea nitrogen collection result
was 19.8g
• Calculate her nitrogen balance and interpret the results.

45. Functions of proteins
Protein is the major structural and functional component of every
living cell
Every tissue and fluid in the body except bile and urine contain some
protein
1. As Building Materials for Growth and Maintenance- From the
moment of conception, proteins form the building blocks of
muscles, blood, and skin. Also form tendons, membranes, organs
and bones
For example, to build a bone or a tooth, cells first lay down a matrix of
the protein collagen and then fill it with crystals of calcium,
phosphorus, magnesium, fluoride, and other minerals.

46. • Collagen also provides the material of ligaments and tendons
and the strengthening glue between the cells of the artery walls
that enables the arteries to withstand the pressure of the blood
surging through them with each heartbeat.
• Also made of collagen are scars that knit the separated parts of
torn tissues together.

47. • For replacing dead or damaged cells e.g skin cells. Muscle cells,
nails, cells of the GI tract etc.

48. Roles of proteins
3. As Regulators of Fluid Balance - Proteins help to maintain the
body’s fluid balance – proteins help to regulate fluid balance
because they attract water , which creates osmotic pressure.
Circulating proteins such as albumin, maintain proper balance
of fluid among the intravascular, intracellular, and interstitial
compartments of the body.

49. Roles of proteins
4. As Acid-Base Regulators –because amino acids contain both an
acid(COOH) and a base(NH₂), they can act as either acids or
bases depending on the pH of the surrounding fluid. The ability
to buffer or neutralize excess acids and bases enables proteins
to maintain normal blood pH, which protects body proteins
from being denatured.

50. Roles of proteins
5. As Transporters-Globular proteins move about in the body
fluids, carrying nutrients and other molecules. The protein
hemoglobin carries oxygen from the lungs to the cells. The
lipoproteins transport fats, cholesterol and fat-soluble vitamins
around the body, albumin transports free fatty acids and many
drugs.

51. Illustration of proteins’ specificity and precision.
• When iron enters an intestinal cell after a meal has been digested and
absorbed, it is captured by a protein.
• Before leaving the intestinal cell, iron is attached to another protein
that carries it though the bloodstream to the cells.
• Once iron enters a cell, it is attached to a storage protein that will hold
the iron until it is needed.
• When it is needed, iron is incorporated into proteins in the red blood
cells and muscles that assist in oxygen transport and use.

52. • Some transport proteins reside in cell membranes and act as
“pumps,” picking up compounds on one side of the membrane
and releasing them on the other as needed.
• Each transport protein is specific for a certain compound or
group of related compound

53. Roles of proteins
6. As Antibodies -Proteins also defend the body against disease.
When the body detects these invading antigens, it
manufactures antibodies, giant protein molecules designed
specifically to combat them.

54. Roles of proteins
7. As a Source of Energy and Glucose - Proteins are sacrificed to
provide energy and glucose during times of starvation or
insufficient carbohydrate intake. Proteins provide 4 cal/g.
8. As Enzymes – enzymes are proteins that facilitate specific
chemical reactions in the body without undergoing change
themselves
Enzymes not only break down substances, they also build
substances (such as bone)■ and transform one substance into
another (amino acids into glucose, for example).

55. Roles of proteins
9. Other body secretions and fluids-neurotransmitters such as
acetylcholine, and some hormones such as insulin, thyroxine,
epinephrine etc are made from amino acids, as are breast milk,
mucus, sperm and histamine.
10. Other compounds- amino acids are components of numerous
body compounds such as opsin, the light-sensitive visual
pigment in the eye, and thrombin, a protein necessary for
normal blood clotting

56. Roles of proteins
11. Some amino acids have specific functions within the body. For
instance;
a) Tryptophan is a precursor of the vitamin niacin
b) Tyrosine is the precursor of melanin, the pigment that colors
hair and skin and is incorporated into thyroid hormone

57. Deaminating Amino Acids
• When amino acids are broken down , they are first
deaminated—stripped of their nitrogen-containing amino
groups. Two products result from deamination: one is ammonia
(NH3); the other product is the carbon structure without its
amino group—often a keto acid which could be used for
provision of energy

58. Protein in Foods – Protein Quality
• Two factors influence protein quality:
the protein’s digestibility
its amino acid composition.
 Protein digestibility depends on such factors as the protein’s source
and the other foods eaten with it.
 The digestibility of most animal proteins is high (90 to 99 percent);
 plant proteins are less digestible (70 to 90 percent for most, but over
90 percent for soy and legumes).

59. Amino Acid Composition
• To make proteins, a cell must have all the needed amino acids available
simultaneously.
• The liver can produce any nonessential amino acid that may be in short
supply so that the cells can continue linking amino acids into protein
strands.
• If an essential amino acid is missing, though, a cell must dismantle its own
proteins to obtain it. Therefore, to prevent protein breakdown, dietary
protein must supply at least the nine essential amino acid plus enough
nitrogen-containing amino groups and energy for the synthesis of the
others.

60. High-Quality Proteins
• high-quality protein contains all the essential amino acids in relatively
the same amounts as human beings require; it may or may not contain
all the nonessential amino acids.
• Proteins that are low in an essential amino acid cannot, by themselves,
support protein synthesis.
• Generally, foods derived from animals (meat, fish, poultry, cheese, eggs,
yogurt, and milk) provide high-quality proteins, although gelatin is an
exception (it lacks tryptophan and cannot support growth and health as
a diet’s sole protein).
• Proteins from plants (vegetables, nuts, seeds, grains, and legumes)
have more diverse amino acid patterns and tend to be limiting in one or
more essential amino acids. Some plant proteins (for example, corn
protein) are notoriously low quality.
• A few others (for example, soy protein) are high quality

61. Complementary proteins
• In order to improve the quality of proteins in plant –based
diets*especially for vegetarians* combining plant-protein foods that
have different but complementary amino acid patterns yields
complementary proteins that together contain all the essential amino
acids in quantities sufficient to support health.
• Example: legumes provide plenty of isoleucine (Ile) and lysine (Lys),
but fall short in methionine (Met) and tryptophan (Trp). Grains have
the opposite strengths and weaknesses, making them a perfect
match for legumes.

62. Dietary protein deficiency and protein deficient states
• for the diets consumed by most populations, the intake of protein is adequate, provided that
the overall intake of food is not limited
• hoewever, for some diets in which the density of protein to energy is low, and where the
quality of amino acids is low, there may be situations related to relative inactivity when the
ability to satisfy the protein intake is marginal
• protein deficient states, where the content of protein in the body is reduced, are mst likely to
be the result of:
• an increase in demand(eg in infection or stress)
• an increase in losses(eg with haemorrhage, burns or diarrhoea)
• a failure of the conservation systems (eg with impairment of urea salvage in the colon)

63. Low protein therapeutic diets
• the two clinical sitations in which control of protein intake and
metabolism are of considerable potential improtance include:
• renal failure, the ability to excrete the urea is impaired
• hepatic failure where there is a limitation in the livers ability to
detoxify ammonia through the formation of urea
• in both situations, reduction of the intake or modification of the
metabolism of protein or aa is an important part of treatment

64. Health Effects of Protein
• Protein-Energy malnutrition(Marasmus and Kwarshiorkor)
• Heart disease – animal proteins tend to be rich in saturated fats; not
surprising to find a correlation between animal-protein intake and heart
disease, although no independent effect has been demonstrated.
• On the other hand, substituting soy protein for animal protein lowers blood
cholesterol, especially in those with high blood cholesterol.
• Research suggests that elevated levels of the amino acid homocysteine may
be an independent risk factor for heart disease.
• In contrast, the amino acid arginine may be a protective factor for heart
disease, slowing the progression of atherosclerosis

65. Cancer
• The effects of protein and fats on cancers cannot be easily separated.
Population studies suggest a correlation between high intakes of animal
proteins and some types of cancer (notably, cancer of the colon, breast, kidneys,
pancreas, and prostate). e.g red and processed meats are associated with cancer
of the colon
Weight Control
• Protein-rich foods are often fat-rich foods that contribute to weight gain with its
accompanying health risks.
• Including low calorie protein at each meal may help with weight loss by
providing satiety

66. Health effects of proteins
• Adult Bone Loss (osteoporosis) – when protein intake is high,
calcium excretion increases. Inadequate intakes of protein may also
compromise bone health. Osteoporosis is particularly common in
elderly women and in adolescents with anorexia nervosa
• Kidney disease – a high protein diet does not cause kidney disease
but it does increase the work of the kidney and accelerate kidney
deterioration in people with chronic kidney disease

67. Recommended Intakes of Protein
• The protein RDA for adults is 0.8 grams per kilogram of healthy
body weight per day. For infants and children, the RDA is
slightly higher.
• AMDR is 10% to 35% of total calories

68. How to calculate Recommended Protein Intake
• Convert pounds to kilograms, if necessary
(pounds divided by 2.2 equals kilograms).
• Multiply kilograms by 0.8 to get your RDA
in grams per day.
• (Older teens 14 to 18 years old, multiply by 0.85.)

69. Example:
• Weight 150 lb
• 150 lb 2.2 lb/kg 68 kg (rounded off)
• 68 kg 0.8 g/kg 54 g protein (rounded off)

70. When the RDA Doesn’t Apply
• The RDA is intended for healthy people only.
• Conditions that require tissue repair or growth increase a
persons protein requirement
• Protein restriction is used for people with severe liver disease
and for those who unable to adequately excrete nitrogenous
wastes from protein metabolism due to impaired renal function.

71. Conditions that increase the need for protein
When calorie intake is inadequate and so protein is being used for
energy e.g PEM. Starvation etc
When the body needs to heal itself
• Hypermetabolic conditions such as burns, sepsis
• Skin breakdown
• Multiple fractures

72. Cont.
To replace excessive protein losses
• Peritoneal dialysis
• Protein-losing renal diseases
• Malabsorbtion syndromes such as short bowel syndrome
During periods of normal tissue growth
• pregnancy
• Lactation
• Infancy through adolescence

73. ASSIGNMENT
• Describe the In born errors of aa metabolism(CONDITIONS THAT
ARE DUE TO AA METABOLISM)

74. THANK YOU