Proteins - KSUfac.ksu.edu.sa/sites/default/files/4._proteins.pdf• Chemical composition • Proteins are complex organic compounds with C, H, O and N • These nitrogen atoms give

Proteins

Proteins

• In this section we will discuss…

• Introduction

• Chemical composition of proteins

• Classification of proteins

• Protein quality

• Calorie value and RDA

• Functions

• Digestion, absorption and metabolism

• Malnutrition of proteins

Proteins

• Protein word comes from Greek meaning primary / having 1st place

• These are organic substances that upon digestion yield unit-building blocks the amino acids

• All most every species has their characteristic protein shared with no other

• Proteins are larger molecules compared to carbohydrates and fats

Proteins

• Chemical composition

• Proteins are complex organic compounds with C, H, O and N

• These nitrogen atoms give the name amino (nitrogen containing)

• Amino acids are building blocks of proteins joined together by peptide bond

• Peptide bond is formed when COOH group of one molecule joins with NH2 group of another releasing water (dehydration)

Proteins


• Amino acids

• Different classifications

• Based on structure

• Based on polarity

• Based on metabolic fate

• Based on nutrition

Proteins


• Amino acids

• Based on structure (nature of the side chain i.e. R

group)

Proteins


• Amino acids

• Based polarity (charge of R group)

• Acidic amino acids

• Basic amino acids

• Neutral amino acids

Proteins


• Amino acids

• Based on metabolic fate

• Ketogenic – gives ketone bodies

• Glucogenic – gives glucose

• Mixed amino acids

Proteins


• Amino acids

• Based on nutrition

• Essential – must be supplied from food

• Non essential – body can synthesize

• Semi essential – adults can synthesize not by children

Proteins


• Based on composition

1. Simple proteins

• Upon hydrolysis give only a.a

2. Conjugated proteins

• Simple proteins combined with non-protein material (CHO, metal, P,…)

3. Derived proteins

• Derived from simple or conjugated proteins by physical or chemical modifications

Proteins


Proteins

• Classification of proteins – nutritional aspect

• From nutritional point of view proteins are 2 types

1. Complete proteins (high quality proteins)

• Contain all the essential amino acids

• Generally animal source – egg, meat…

2. Incomplete proteins (low quality proteins)

• Deficient in one or more essential a.a

• Generally plant source – pulses, beans.

Proteins


• Protein quality

• Changes with type of protein

• Egg and milk proteins are taken as reference proteins

• Depending on the need of the body each essential amino acid is given rank

• Depending on proportionality pattern of amino acids proteins quality is measured

• Proteins containing amino acids mostly needed by human body are of top quality

Proteins

• Protein quality determination, indices

• Principle of nitrogen balance

• Used to determine protein requirement

Proteins


• Biological value

• Index of protein quality that reflects the percentage of absorbed nitrogen from dietary nitrogen retained by the body

• More BV means good quality protein

• Tested in controlled conditions

Proteins


• Net protein utilization

• NPU is index that takes into account the relative digestibility of proteins

• If essential amino acids are packed in a indigestible protein, they are not available

• NPU = BV x digestibility

• In most cases NPU = BV as most proteins are digestible 90 % or more

Proteins


• Protein efficiency ratio

• Calculated as change in body weight relative to the amount of protein intake

• Controlled conditions needed to calculate

• Not a very precise method

• But offers technical feasibility to do the test

• Egg has PER 3.8

Proteins

• Protein quality determination, indices• Protein digestibility corrected amino acid score

(PDCASS)

• measures protein quality based on human essential amino acid requirements and our ability to digest it

• Test protein is compared to standard a.a profile and score is given (0-1)

• Test score 1 indicates that the protein after corrected for digestibility gives essential a.a as per requirements

Proteins


• Amino acid score

• It is a score based on chemical analysis of protein

• Not a biological test

• Compares the content of essential a.a with that found in reference protein

• Aids in identifying limiting a.a in a food

• Helpful in dietary planning

• Helpful in developing new foods

Proteins


• Amino acid score

• Limiting amino acids - supplementation

Proteins

• Calorie value

• In human body 4 cal/g

• RDA

• Expressed requirement in terms of body weight

• Generally 1gm/kg body weight

• Changes according to age and life style

• Sedentary work

• Moderate work

• Hard work

Proteins

• Functions

• Different classes and functions

Proteins

• Digestion

• Proteins are large complex molecules

• A series of enzymes needed to breakdown in to amino acids to absorb

• Digestion In Mouth

• Mainly mechanical breakdown due to mastication

• Food particles mix with saliva and passed on to the stomach in semi solid form

Proteins

• Digestion – in Stomach

• Enzymes (proteases) involved in protein digestion are stored as inactive proenzymes called zymogens

• Zymogens are activated according to need

• Chemical digestion of protein starts in stomach with the help of 3 agents in the gastric secretions

1. Pepsin

2. Hydrochloric acid

3. Renin

Proteins


1. Pepsin

• This is the main enzyme specific to proteins

• Produced as pepsinogn (inactive form) and HCl in gastric juice converts in to pepsin (active from)

• Action of pepsin produces proteoses and peptones (small amino acid chains)

Pepsin

Proteins


2. HCl

• HCl provides the acidic pH required to convert pepsinogen to pepsin

• HCl also aids in denaturation of proteins

• This denaturation and unfolding makes the individual amino acids more available for digestion

Proteins


3. Renin

• Present only during infancy and childhood

• Important for digestion of milk protein

• Renin also produced inactive form prorenin, HCl converts to active enzyme renin

• Renin and Ca++ act on casein of milk to produce curd (yogurt)

Proteins

• Digestion – in small intestine

• Protein digestion begins with acidic medium of stomach and ends with alkaline medium of small intestine

• Enzymes from secretions of pancreas and intestine participate

Pancreatic secretions Intestinal secretions

Trypsin Aminopeptidase

Chymotrypsin Dipeptidase

Carboxypeptidase

Proteins

Digestion – Small intestine – Pancreatic secretions

• Trypsin• Secreted as trypsinogen. By the action of

enterokinase converted in to trypsin

• When food enters duodenum, enterokinase is secreted

• Trypsin acts on large polypeptide chains to produce small chains

• Trypsin also activates chymotripsinogen to chymotripsin and procarboxypeptidase to carboxypeptidase

Proteins

Digestion – Small intestine – Intestinal secretions

• Two proteins are produced• Amino peptidase – produces peptides and free amino

acids

• Dipeptidase – acts on dipeptides and forms free amino acids

• Free amino acids are ready to be absorbed in blood

• No storage of proteins as fats – every day supply needed

Proteins

Digestion – summary

METABOLISM AND ELIMINATION

All essential amino acids must be present to build and

repair the cells as needed. When amino acids are

broken down, the nitrogen-containing amine group is

stripped off.

This process is called deamination.

Deamination produces ammonia, which is released into

the bloodstream by the cells.

The liver picks up the ammonia, converts it to urea, and

returns it to the bloodstream for the kidneys to filter out

and excrete.

The remaining parts are used for energy or are converted

to carbohydrate or fat and stored as glycogen or adipose

tissue.

DIETARY REQUIREMENTS

One’s protein requirement is determined by size, age, sex, and

physical and emotional conditions. A large person has more body

cells to maintain than a small person.

A growing child, a pregnant woman, or a woman who is

breastfeeding needs more protein for each pound of body weight than

the average adult.

Extra proteins are usually required after surgery, severe burns, or

during infections in order to replace lost tissue and to manufacture

antibodies.

In addition, emotional trauma can cause the body to excrete more

nitrogen than it normally does, thus increasing the need for protein

foods.

The RDA (recommended dietary allowance) for protein is

computed for proteins of mixed biologic value at 0.8 g/kg of

body weight for adults, or about 56 g of protein for a 70-kg

individual.

People who exercise strenuously on a regular basis may benefit

from extra protein to maintain muscle mass; a daily intake of

about 1 g/kg has been recommended for athletes.

Women who are pregnant or lactating require up to 30 g/day

in addition to their basal requirements. To support growth,

infants should consume 2 g/kg/day.

DIETARY REQUIREMENTS

Proteins

• Malnutrition - deficiency

• Too much or too little consumption can be problematic for body functions

• Protein energy malnutrion may result in children because of high growth rate

• Kwashiorkor : results from acute deficiency of proteins

• Edema in feet and legs

• Bloated abdomen

• Muscle wasting

• Stunted growth

• Diarrhoea

• Browning of hair

Marasmus, a condition resulting from severe malnutrition,

afflicts very young children who lack both energy and protein

foods as well as vitamins and minerals. The infant with

marasmus appears emaciated but does not have edema. Hair is

dull and dry, and the skin is thin and wrinkled.

Proteins

• Malnutrition – excess intake• Body has limited need of protein

• Too much animal protein intake is also associated with too much fats

• Kidneys have to work over time to remove excess nitrogen

• Excess protein intake also leads to loss of calcium

• Supplements even though not harmful not needed for healthy life

Documents

Proteins - KSUfac.ksu.edu.sa/sites/default/files/4._proteins.pdf• Chemical composition • Proteins are complex organic compounds with C, H, O and N • These nitrogen atoms give