This presentation discusses proteins and their functions. It defines proteins as nitrogenous compounds made of amino acids. Proteins perform many crucial functions in the body including growth, enzyme production, transport, defense, and maintenance of acid-base balance. The presentation covers protein structure, classification, sources, digestion and absorption. It emphasizes the importance of consuming complete proteins from both plant and animal sources to meet nutritional needs. Recommended daily intakes vary by age, gender and physiological state. Maintaining positive nitrogen balance is also discussed.

1. NUTRITION AND HEALTH
GROUP TWO PRESENTAION
PROTEINS

2. group memebers
• JOSHUA .W.NYAKEMWE
• CAROLYNE NKATHA THURANIRA
• DAMARIS CHEROTICH CHEBORET
• JOAN PAMBA
• CYNTHIA NAFULA
• COLLINS KIPKIRUI
• JOSEPHAT MUTUA KIMANI
• COLLINS KIPCHIRCHIR

3. What are proteins?
• Proteins are a class of nitrogenous
compounds which have larger molecule
compound of one or more twisted and folded
chains of amino acids.
• Proteins contain carbon, hydrogen, oxygen,
nitrogen and Sulphur.
• They are the most versatile macromolecules
in living systems which serve crucial
functions in all biological processes such as
metabolism, movement, defense, cellular
communication and molecular recognition

4. Functions of proteins
1. promoting growth and maintenance of body tissues
• Proteins are used to form new tissues and repair the worn out ones.
2. formation of essential compounds in the body
• Proteins are precursors of enzymes, hormones and antibodies.
• all enzymes are proteins and are essential catalysts in digestion and
metabolic processes in the tissues.
• Hormones regulate all the activities of the body. examples are thyroxine,
growth hormones and insulin.
• Proteins form anti bodies and special white blood cells which defend the
body against infections.
3. Regulatory functions
Hemoglobin, a protein ion complex ensures smooth running of the respiratory
cycle by being the vital oxygen carrier in the red blood cells.
• Plasma proteins in blood contribute to osmotic pressure and thus exert an
important influence on the exchange of water between tissue cells and the
surrounding fluids and on the water balance of the body as whole.

5. Functions of proteins
• Maintenance of body neutrality
• Proteins are amphoteric and their presence prevents their accumulation
of too much acid and base which could interfere with the normal
functioning of the body.
• Transport proteins
• Due to their amphoteric nature, proteins are ideal carriers of nutrients
across cell membranes.
• Proteins as lipoproteins transport triglycerides, cholesterol,
phospholipids and fat soluble vitamins across the cell wall.
• Special functions of amino acids
• Tryptophan serves as a precursor for the B-vitamin niacin and serotonin,
a neurotransmitter
• Glycine, is used in the synthesis of porphyrin nucleus nucleus of
hemoglobin. It is also a constituent of the bile acids. It combines with
many toxic substances to form harmless products, which are excreted.

6. Functions of proteins
• Histidine is used in the synthesis of histamine used as a vasodilator
in the circulatory system.
• Phenylalanine is a precursor of tyrosine and together they lead to
the formation of thyroxine and epinephrine.
• Tyrosine is also the precursor of skin and hair pigment.
• Milk formation
• human milk contains about 1.2 per cent protein.
• Energy supply
• 12% of body energy is supplied by products of protein metabolism
• Each gram of food protein yields four calories to the body.

7. Classification of proteins
• Classification by composition
• Proteins are divided into three:
• 1. simple proteins
• They are made up amino acids only, hence on hydrolysis, they
yield only amino acids. Examples are: human plasma albumins,
globulins, Trypsin, chymotrypsin, pepsin, insulin, soya bean
trypsin inhibitor and ribonuclease.
• 2. conjugated proteins
• Contain non-protein part (prosthetic group) attached to the
protein component linked by a covalent bond and hydrophobic
interactions.
• On hydrolysis they yield amino acids and non-protein
compounds .
• classified into subclasses depending on the prosthetic group.

8. Conjugated proteins
subclass Prosthetic group examples Type of linkage
Lipoproteins lipids Chylomicrons, very
low density
lipoproteins(VLDL),
low density
lipoproteins(LDL)(bad
cholesterol), high
density
lipoproteins(HDL),lipo
vitellin of egg.
Hydrophobic
interaction
glycoproteins carbohydrates Immunoglobulins of
blood, egg albumin,
covalent
phosphoproteins phosphorus Casein of milk, vitellin
of egg yolk
Covalent
Nucleoproteins Nucleic acids Chromatin,
ribosomes
Non covalent
Hemoproteins/chrom
oproteins
heme Hemoglobin,
myoglobin,
cytochromes
Non-covalent
Flavoproteins Flavin Succinate Covalent

9. Structure of proteins
• The building blocks of proteins are amino acids.
• Each amino acid has a central carbon bound to
four components which include:
1. Hydrogen
2. Nitrogen containing amino group( -NH2)
3. Carboxylic acid group( -COOH)
4. A side chain (R) that is unique for every amino
acid.
• NB: Proteins are the only macromolecules
containing nitrogen as part of their structure

11. Classification of amino acids
• There are 20 amino acids. Based on the nature of their ‘R’ group, they are classified based on
their polarity.
• AMINO ACIDS
hydrophobic amino acids hydrophilic amino acids
( non-polar) (polar)
neutral acidic basic
R=alkyl R= aromatic tyrosine glutamic acid lysine
Glycine phenylalanine serine aspartic acid histidine
Alanine tryptophan threonine argenine
Leucine cysteine
Valine glutamine
Isoleucine asparagine
Methionine
proline

12. Classification of amino acids
Based on essentiality:
1. Non essential amino acids–are amino
acids that are synthesized by the body
hence they are not required in the diet.
2. Essential amino acids- are amino acids
that cannot be synthesized by the body
so they must be obtained from the diet

13. Classification of amino acids
3. Conditionally essential amino acids
• These are the non essential that cannot
be synthesized by the body during
infancy, growth and diseased states and
more of them will now be required in the
diet.

14. Essential amino acids Non essential amino acids
Histidine Alanine
Isoleucine Arginine*
Leucine Asparagine
Lysine Aspartic acid
Methionine Cysteine*
Phenylalanine Glutamic Acid
Threonine Glutamine
Tryptophan Glycine*
Valine Proline*
Serine
Tyrosine*
*Conditionally essential

16. Protein level of organization
• Proteins are structurally complex and
different proteins are produced because there
are 20 types of naturally occurring amino
acids that are combined in unique
sequences.
• Protein level of organization
1. Primary structure
2. Secondary structure
3. Tertiary structure
4. Quaternary structure

21. • Protein structure also influences the
nutritional quality.
• Large fibrous protein structures are more
difficult to digest than smaller proteins
hence not all amino acids are absorbed
and made available for the body hence the
nutritional value is decreased
• Other proteins like keratin are indigestible
hence they have no nutritional value.

22. Protein types and functions
Types Examples Functions
Structural/fibrous
proteins
Actin, myosin, collagen,
elastin, keratin
Give tissues such as bones,
tendons, muscles strength
and texture
Collagen forms the
connective framework of
your muscles, bones,
tendons, skin and cartilage.
Enzymes Amylase, lipase, pepsin,
lactase
Perform steps in metabolic
pathways to allow for
nutrient utilization
Hormones Insulin, glucagon, thyroxin Chemical messengers that
travel in blood and
coordinate processes in the
body

23. Type Examples Functions
Fluid and acid –
base balance
Albumin and
hemoglobin
Maintains
appropriate balance
of fluids in and ph in
different body
compartments
Transport Hemoglobin,
albumin, protein
channels, carrier
proteins
Carry substances
around the body in
the blood or lymph;
help molecules
cross cell
membranes
Defense Collagen, lysozyme,
antibodies
Protect the body
from foreign
pathogens

24. Nitrogen Balance
• Refers to the status of nitrogen metabolism in
the body.
• It is the comparison between the nitrogen
intake and the nitrogen loss through
excretion.
• Proteins are the sole source of nitrogen in the
body.
• It is basically the amount of nitrogen intake in
the form of dietary protein and nitrogen lost or
excreted in the form of urea, uric acid,
creatinine

25. Nitrogen balance contd…
• Nitrogen equilibrium:
o Dietary intake = daily loss through
excretion
• Positive nitrogen balance:
o Dietary intake > daily loss
Growth, pregnancy, recovery from illness
and growth hormones lead to positive
nitrogen balance.

26. • Negative nitrogen balance:
Dietary intake < daily loss
Occurs due to chronic or acute illness, protein
deficiency, starvation, and hormones.
• Recommended dietary allowance (RDA) is
determined using Nitrogen Balance.
• The RDA is basically the amount of protein a
person should consume in their diet to balance the
amount of protein used by the body.

27. Dietary sources of proteins
• There are two categories of sources of
proteins which include :
• Plant sources and animal sources
• Plant based sources:
• Include green vegetables e.g. kales and
broccoli
• Legumes e.g. beans, peas, lentils
• Whole grains e.g. rice, oatmeal
• Nuts and seed e.g. peanuts, almonds
• tofu

28. • Animal based sources
• White meat e.g. chicken, turkey
• Fish especially salmon, trout,
mackerel,herring
• Pork
• Red meat from cows, bison and deer
• Mutton
• Dairy products such as cheese, milk
• Poultry products such as eggs

30. Protein Quality
• The nutritional value or quality of
structurally different proteins varies
depending on;
1. Amino acid composition
2. Ratio of essential amino acids
3. Susceptibility to hydrolysis during
digestion
4. Source and the effects of processing
5. Digestibility

31. Protein quality
• Complete protein/ first class proteins
• Contains all the 9 essential amino acids in the required
proportion.
• Animal based sources of proteins fall under this category. For
example; casein of milk.
• Incomplete protein
• They lack one essential amino acid.
• They cannot promote body growth in children; but may be able
to maintain body growth in adults.
• Protein from pulses are deficient in methionine while proteins of
cereals lack in lysine. If both of them are combined in diet,
adequate growth may be obtained.

32. Poor proteins
• They lack in many essential amino acids
and a diet based on these proteins will not
even sustain the original body weight.
• Zein from corn lacks tryptophan and
lysine.

33. • Complementary proteins
• Some plant based foods when consumed
together contain all the 9 essential amino
acids at adequate levels

34. Measurement of protein quality
There are several methods used to determine the protein quality in a diet
1. Biological value
2. Net Protein Utilization (NPU)
3. Protein Efficiency Ratio
Biological Value(BV)
It is the percentage of the absorbed nitrogen (N) retained by the body.
The nitrogen content of the food eaten by the animal and the nitrogen
content of the urine and faeces are determined.
It is calculated using the formula
BV= N retained by the body (dietary N- (Urinary N + faecal N) * 100
N absorbed(dietary N – fecal N)
The quality of protein is directly related to its BV. The BV increses with
increase in the percentage of nitrogen absorbed being retained.
The BV of milk is 84, brown rice 73 and whole wheat 65.

35. Net protein utilization(NPU)
• NPU is digestibility of protein multiplied by its BV.
Protein efficiency Ratio(PER)
• PER =weight gain in g
• protein fed in g
• It is not based on output and intake of food protein residues,
therefore it is less accurate than BV and NPU.
• The PER of milk is reported to be 3 and that of rice is 2.2
• chemical score
• It is based on comparison of amino acid composition of the food
protein with the amino acid of a reference protein such as milk, egg
or FAO reference protein (1973)
• The amino acid score is the concentration of the limiting amino acid
per gram in the food / food mixture as a percentage of the same
amino acids per gram in the acid of the reference protein.
• Formula; mg of limiting amino acid /g of test protein*100
• mg of the same amino acid / g of reference protein

36. Recommended dietary allowance
• The requirement of the body for protein as determined by nitrogen
balance studies is between 0.5 to 0.6/kg of body weight in adults,
when the source of protein supplies the amino acids in the
proportion needed by the body.
• During infancy, pregnancy and lactation there is an increased need
of protein for growth.
• Persons suffering from burns or wasting diseases such as
tuberculosis and rheumatic fever also need additional protein for
regeneration of wasted tissues.
• Also if there is excess loss of blood due to excessive menstruation,
hemorrhages or blood donation, more protein is needed in the diet.
• the recommended dietary intake of proteins are presented in table
below;

37. Recommended dietary intake for proteins
Particulars of the
individual
Man(60)kg
Woman (50kg)
Woman, pregnant
Woman, nursing mother
Infants, 0-6 months
Infants 7-12 months
Children 1-3 years
Children, 4-6 years
Children 7-9 years
Boys 10-12 years
Girls 10-12 years
Girls 13-15 years
Boys 16-18 years
Protein g/day
60
50
65
75
22
2.05 g/kg/day
1.65/g/kg/day
30
41
54
57
70
65
78

38. Vegetarian diet
• A vegetarian diet refers to exclusion of meat, fish, sea food and
possibly other animal products such as dairy and eggs.
• Protein sources for vegetarians are cereals, legumes, immature
beans and peas, vegetables, fruits and milk and milk products for
lactovegetarians
• Reducing red meat consumption can lower the risk of heart disease
and eating vegetarian diet lowers the risk of diabetes, high blood
pressure and cancer.
• However, vegetarians run the risk of deficiencies in nutrients such as
1. Vitamin B12- important in maintaining appropriate brain functioning
and blood flow . It can manifest as megaloblastic anemia i.e low red
blood cells count and cells bigger than normal.
2. Zinc. Plays a role in regulating body’s immune system.
3. Deficiency leads to impared immune system, slow wound
healing, hair loss, diarrhea and loss of appetite.
4. Iron because the body absorbs 2 to 3 times more iron from animal
sources than plant sources. Deficiency leads to anemia.

39. Protein digestion
• Mouth
• only mechanical effect of chewing, breaking food into smaller particles
occurs in the mouth
• Stomach
• The enzymatic breakdown of protein begins in the stomach
• Three chemical agents in the gastric secretions initiate this process.
• pepsin
• hydrochloric acid
• renin
• Pepsin; it is released by the chief cells in the stomach wall as the
inactive proenzyme pepsinogen and requires hydrochloric acid to be
transformed into the active enzyme pepsin. It splits the peptide linkages
between amino acids, breaking large polypeptides into successfully
smaller peptides

40. Protein digestion
• Hydrochloric acid; this provides the acid medium needed to convert
pepsinogen to pepsin.
• Rennin ; it acts casein, the major protein in milk, to produce a curd that
slows the passage of food out of the infant’s stomach.
• stomach
• Protein digestion is completed in the small intestine assisted by
enzymes secreted by the pancreas and glands in the intestinal wall.
• They include the following;
• Pancreatic secretions
• 1. trypsin; it is secreted as inactive pepsinogen and activated by the
enzyme enterokinase produced in the walls of the duodenum.
• Trypsin acts on proteins and large polypeptides to yield smaller
polypeptides and dipeptides.
• 2. chymotrypsin is secreted as chymotrypsinogen and activated by the
trypsin already present in the duodenum chymotrypsin continues the
same protein splitting action of trypsin.

41. Protein digestion
• Carboxypeptidase ; attacks the carboxyl end of the peptide chain to
produce smaller peptides and some free amino acids.
• intestinal secretions
• Aminopeptidase; releases amino acids one at a time from the amino(NH2)
end of the peptide chain to produce smaller short-chain peptides and free
amino acids.
• Dipeptidase; breaks any remaining dipeptides into two free amino acids.
• absorption
• Amino acids are absorbed by an energy requiring sodium assisted transport
system and enter the portal of blood for passage to the liver. A few short
chain peptides and smaller intact proteins escape digestion and are
absorbed in that form.
• Most are broken down as they cross the intestinal wall, however, those
protein molecules that pass into the blood intact may play a part in the
development of immunity and protein sensitivity.

42. metabolism
• tissue proteins are built in the cells.
• Each cell, depending on its nature and function,
requires a unique mix of amino acids to build the
specific proteins needed.
• The metabolic activities of protein are
interwoven with those of carbohydrate and fat,
which provide the energy to drive ongoing tissue
growth and repair

43. Protein Denaturation
• Denaturation involves the breaking of
bonds within a protein molecule that are
responsible for the highly ordered
structure of a protein in its natural state.
• Denatured proteins have a looser, more
random structure mostly insoluble.
• Denatured proteins have no nutritional
value.

44. Causes of protein denaturation
1. Change in pH
There are ionizable groups in the individual
amino acids.
High concentration of hydrogen ions (low ph)
will result in more groups being protonated.
The charged groups will tend to move towards
the surface of the proteins and the
uncharged groups tend to move inwards.
This results to denaturation.

45. 2. Violent shaking
Agitation denatures proteins
This is evident when whipping egg whites.
Constant churning of milk creates foam
from various proteins which also causes
denaturation of proteins

46. 3. Denaturation by Salts of heavy metals
Since salts are ionic in nature they disrupt
salt bridges in proteins.
The reaction of a heavy metal salt with a
protein usually leads to an insoluble
protein salt complex

47. 4. Denaturation by UV radiation
UV radiation supplies kinetic energy to
protein molecules, causing their atoms to
vibrate more rapidly and disrupting the
relatively weak hydrogen bonding and
dispersion forces of protein molecules

48. 5. Denaturation of proteins by
hydrostatic pressure
Proteins undergo dissociation and unfolding
by pressure mostly because the final
states are more hydrated, have fewer
non-hydrated cavities and therefore,
occupy smaller volumes.

49. 6. Denaturation by heat
Most protein can be denatured by heat
which affects the weak interactions in a
protein (primarily hydrogen bonds) in a
complex manner.

50. Protein deficiency diseases
1. Kwashiorkor
• Caused by severe protein deficiency in addition to other
micronutrients such as folate, iodine, iron, vitamin C.
• Usually occurs in children aged between 6 months and 3 years.
• It is characterized by the following:
1. Subcutaneous fat is preserved
2. Edema is present all over the body
3. Enlarged fatty liver
4. Hair sparse, straight, greyish or reddish
5. Muscular wasting, occasionally present
6. Skin changes- depigmentation of skin all over the body
7. Diarrhea often present
8. Growth retardation
9. Oral lesions present. Eg loss of papillae, a bright reddening of
tongue

51. Marasmus
• Caused by both deficiency of proteins and calories
• Predisposing factors;
 Rapid succession of pregnancies
 Early and often abrupt weaning followed by artificial feeding of infants in
inadequate amounts.
• It is common in infants aged between 1-9 years.
• It is characterized by the following:
1. Weight loss. Below 60% as a percentage of normal
2. Severe muscular wasting
3. Mental and physical growth retardation
4. Loss of skin elasticity
5. Brittle hair
6. Face becomes small and sunken(monkey-like face)
7. The child is irritable and fatigued
8. Diarrhea and anemia may be present

53. Marasmic-Kwashiorkor
• The child has the features of Kwashiorkor
which include Severe edema of the feet
and the legs and lower arms, abdomen
and face. The child also has pale skin and
hair and the child is unhappy.
• The child also exhibits signs of marasmus,
wasting of the muscles of the upper arms,
shoulders and chest so that you can see
the ribs.

55. Effects of protein and protein energy deprivation
on hormones and enzyme production
• Many of the body’s hormones and enzymes are proteins.
Hence any disturbance in protein metabolism lead to
reduced synthesis of hormones and enzymes leading to;
o Delayed puberty and amenorrhea in girls
o Loss of libido and impotence in men
o Marked atrophy of the thyroid gland due to reduced
secretion of thyrotropic hormone
o Diarrhoea due to reduced formation of digestive enzymes
o Marked bradycardia and reduced BMR due to thyroid
deficiency

56. Diseases resulting from excess protein intake
• Gout
• A common disorder of protein metabolism, characterized by
excessive uric acid production, leading to formation of urate crystals
deposited in joints.
• Therefore, it is a form of arthritis characterized by severe pain,
redness and tenderness in joints.
• Amyloidosis
• Amyloid disease is the build-up of amyloid proteins in the heart,
kidney, liver and other organs.
• Amyloid is an abnormal protein that is usually produced in the bone
marrow and can be deposited in any tissue or organ.
• Two main causes of amyloidosis are;
 Amyloid light chain, composed of immunoglobulin light chain
 Amyloid associated, made up of non immunoglobulin protein

57. REFERENCES
• https://www.medicalnewstoday.com/article
s/196279
• https://www.hsph.harvad.edu/nutritions/wh
at-should-you/eat/protein/
• https://medlineplus.gov/ency/article/00246
7.htm
• Nutrition for health fitness and sports,
Melvin H .Williams