21/07/2015

1

151.232 NUTRITION AND

METABOLISM

Protein (part 1)

Dr Cath Conlon

c.conlon@massey.ac.nz

IFNHH, 2015

1

Learning objectives

Describe the chemical structure of proteins.

Describe the structure of amino acids, and explain how their sequence in proteins affects the proteins' shapes.

Define what an essential, non-essential and conditionally essential amino acid is.

3

Learning objectives

Discuss the processes of protein digestion and absorption. Describe protein synthesis.

Briefly discuss the function and roles proteins play in the human body.

Discuss protein requirements and how requirements are estimated.

4

What are Proteins?

Essential organic compounds made of smaller building blocks called amino acids

Form vital structural and working substances in all cells of the body

70kg man contains about 11kg (16%) of proteins (nearly found as skeletal muscle)

Unlike fats and carbohydrate, the body does not maintain an energy storage form

Found in a range of animal and plant foods

5

A chemists perspective

Proteins contain the same atoms as CHO & lipids

Carbon (C)

Oxygen (O)

But also contain nitrogen (N)

These nitrogen atoms give the name amino (nitrogen containing) to amino acids the links in the chain of proteins

21/07/2015

2

Amino Acids

7

Amino Acids 20 different aa

Sequence of aa in each protein which determines its unique shape & function

Side groups (r group) vary from one aa to the next making proteins more complex than CHO or lipids

aa share common structure but differ in size, shape, electrical charge and other characteristics due to diff in

side groups

8

Examples:

Alanine Glycine Phenylalanine Aspartic acid

Simplest aa

with hydrogen

side group

More complex side groups

Not Essential Amino Acids Essential amino acids (also called indispensable amino

acids)

9 aas that the body cannot make at all or in sufficient quantities

Must be obtained from food

Non-essential amino acids (also called dispensable amino acids)

The body can synthesise itself

Conditionally essential amino acids

Become essential under certain physiologic conditions

10 You need to be able to give examples

More than half of the aa are non essential meaning the body can synthesise them for itself. Proteins in foods often

deliver these non essential aa but its not essential that they

do.

The body is able to make all the non-essential aa given nitrogen form the amino group and fragments from CHO

and lipids to form the rest of the structure

9 essential aa that must be supplied by the diet

12

21/07/2015

3

Phenylketonuria

Example of a conditionally essential aa is tyrosine

- essential in PKU

Autosomal recessive disorder inherited error of metabolism

Phenylalaine normally converted to Tyrosine which enters Krebs cycle

PKU results in elevated blood levels of phenylalaine

13

PKU; treatment and prevention

Tyrosine must be supplied by diet

Phenylalanine intake must be carefully restricted; THIS AMINO ACID IS STILL IMPORTANT FOR GROWTH,

ETC.

All infants are tested for PKU at birth

14

Transamination

Transfer of the amine group from an essential amino acid to a different acid group and R group

The acid groups and R groups can donated by amino acids or they can be made from the breakdown products of CHO

and lipids

This is also the process by which we make non essential aa

15

Proteins Cells link aa end to end in a variety of sequences to

form 1000s of diff proteins

Linked by peptide bonds

Condensation

reaction

Proteins Polypeptide eg insulin small protein 51 aa which

consists of 2 polypeptide chains linked by disulphide bridges which always involve aa cysteine (r group contains sulphur)

Primary structure of a protein

It is the sequence of amino acids that makes each protein different from the next

Huge variety of polypeptide chains (more complex than CHO or lipids)

Dipeptide = 2 amino acids

Tripeptide = 3 amino acids

Polypeptide = many amino acids

Most proteins have many 100 amino acids

18

21/07/2015

4

Protein structure

4 levels

Primary: sequence of AAs which are linked together

Secondary: conformations of the polypeptide

backbone

Tertiary: folding secondary structures into a compact

globular protein

Quaternary: arrangement of subunits into a single

functional protein

20

Protein shape and function

21

22 (Bu, 2009)

ApoE protein is involved in the transportation of cholesterol and other lipids.

There are 3 isoforms which are genetically determined depending on whether you have arginine or cysteine at positions 112 and 158.

These single AA differences alter the proteins structure and conformation and influence how cholesterol is dealt with.

People carry ApoE4 are at higher risk of CVD

Protein Function is Altered by

Denaturation

Uncoiling of protein that changes its ability to function

If proteins are subject to heat, acid or other conditions that affect their stability they

become denatured

Examples

Food: hardening of an egg when it is

cooked, curdling of milk when acid is

added.

In stomach: acid denatures proteins aids digestion and kills pathogens

24

What Happens

to the Protein You Eat?

Protein digestion

Proteins in foods do not become body proteins!

They supply aa from which the body makes its own proteins

Food containing protein

Long polypeptide strands

Shorter strands

Shorter strands

Tripeptides

Dipeptides

Amino acids

21/07/2015

5

Simplified version of digesting protein

Protein

Digestion in

the GI Tract

Protein digestion and absorption in the small

intestine

1. brush-border membrane peptidases

2. brush-border membrane

amino acid transporters

3. brush-border membrane

di- and tripeptide

transporters

4. intracellular peptidases

5.basolateral-membrane

amino acid carriers

6. basolateral membrane di-

and tripeptide carriers

Protein absorption

Intracellular peptidases digest absorbed di- and tripeptides. (90% or more appear in the portal blood as free amino acids).

Absorption of amino acids and peptides is developmentally regulated and is influenced by diet, hormones and growth factors.

A high protein diet - upregulation of peptide and most amino acid transport. Short term fasting increases absorption rates, but long term fasting decreases amino acid transport with little change in peptide absorption.

Absorbed amino acids (especially glutamine, glutamate, and aspartate) are the major respiratory fuels for the small intestine. 10% of the absorbed amino acids are used for protein synthesis within the enterocyte.

Protein myths

You can ingest enzymes and they will work

Consuming amino acid supplements will be beneficial saves the body having to break down proteins

Whole proteins better as the body dismantles and absorbs aa at optimal rates

Protein synthesis

In adults 4g/kg body weight of protein is synthesised each day

In infants 12g/kg of body weight falls to 6g/kg by 1 year

In adults in steady state protein synthesis is matched by an equivalent rate of protein degradation protein balance

In infancy, childhood & pregnancy protein synthesis exceeds protein degradation (positive protein balance). Accounts for the deposition of tissues accompanying growth

35

21/07/2015

6

Protein Synthesis Protein Synthesis

Protein Synthesis Body contains about 30,000 different kinds of proteins. Each human being is unique because of the small

differences in the bodys proteins. These differences are determined by the amino acid

sequence of proteins which in turn are determined by genes.

Process we have just described - how cells synthesize proteins according to the genetic information provided by the DNA in the nucleus of each cell.

This information dictates the order in which amino acids must be linked together to form a given protein.

Sequencing errors occasionally occur sometimes with significant consequences eg sicke cell anaemia.

Sequencing errors Functions of proteins

Functional diversity

Cell membrane structure & function Enzymes Hormones & other chemical messengers Immune functions Fluid balance Acid-base balance Transport Source of energy & glucose

41

21/07/2015

7

Structural & maintenance

Provide building materials for growth and maintenance

Collagen

Bone & Skin

Keratin

Hair & nails

Motor proteins

Muscles

42

Enzymes

43

Hormones

Chemical messengers that are made in one part of the body but act on cells in another part

44

Immune function Lymphocytes produce antibody proteins that fight

antigens that invade the body

Provide immunity

45

Fluid balance Proteins help maintain volume & composition of body fluid

Acid-Base balance Act as buffers to help maintain acid-base balance of body fluids

Fluid Balance

Plasma proteins attract water - oedema can result when get plasma proteins entering interstitial spaces faster than can

be cleared by lymphatic system.

Protein related causes include excessive protein losses eg kidney disease or large wounds, inadequate synthesis or

inadequate intake or inadequate levels plasma proteins.

Transport Proteins

21/07/2015

8

Blood clotting There are 13 blood clotting proteins (coagulation factor)

found in the blood. If one factor is missing or present at low

levels, this causes hemophilia and other blood clotting

problems and a proper clot will not form.

48

Source of energy & glucose

Proteins provide some fuel for the bodys energy needs

Body will use protein if insufficient energy or glucose provided by the diet

49

50

Body composition Formation of enzymes

Other functions:

Energy

Hair, nails, bones

Synthesis

Transport Blood clotting

Homeostasis:-

Hormones

Acid-base balance

Immunity

Summary of uses of protein

Uses of protein

Protein metabolism protein turnover and aa pool

Proteins continually being made and broken down protein turnover

When protein break down free aa which mix with aa from dietary protein forms the aa pool within cells and circulating blood

Rate of protein degradation and protein intake may vary BUT pattern of aa within the pool is constant

Regardless of source pool of aa used to make body proteins or other N containing compounds or stripped of

N & used for energy (or stored as fat)

Nitrogen balance

Because all protein contains 16% nitrogen by weight a simple chemical analysis of nitrogen can be used as a means of calculating how much protein the nitrogen has come from

To convert nitrogen values to protein values multiply by 6.25 (100/16)

52

Nitrogen balance

Nitrogen balance is a measure of the relationship between the amount of nitrogen taken into the body and the amount

excreted in urine, faeces and skin

+ve bal Nitrogen intake > nitrogen loss

-ve bal Nitrogen loss > nitrogen intake

Equilibrium Nitrogen intake = nitrogen loss

53

21/07/2015

9

Nutritional importance of proteins

Nutritional values determined by its primary structure (ie amino acid composition)

Tertiary structure can influence protein digestibility

Globular proteins are generally more easily digested than filamentous proteins such as collagen, elastin and keratin

54

151.232 NUTRITION AND

METABOLISM

Protein (part 2)

Dr Cath Conlon

c.conlon@massey.ac.nz

2015

55

Learning objectives

List factors that affect the quality of dietary protein. Define a complete protein.

Describe the health consequences of ingesting inadequate or excess protein.

Describe marasmus and kwashiorkor. Discuss how the two conditions can be distinguished, and the

ways they overlap.

List the factors that are considered in establishing recommended protein intakes.

56

Protein quality and amino acid profile

Protein quality

Kind of amino acids contains

Proportion in which they are present

Amino acid profile relative proportions in which essential amino acids are present in the protein

57

Are we generally worried about protein intakes in

NZ?

Types of protein

Complete or high biological value (high quality)

Contain all essential amino acids in proportions capable of promoting growth

Incomplete or low biological value (low quality)

Proteins that lack or have limited amounts of one or more essential amino acids, incapable of promoting growth (if sole proteins in diet)

58

Limiting amino acid

Some proteins that contain all the essential aas but relatively small amounts of one aa. These proteins have sufficient aa to promote repair of body tissues but not enough to promote growth

aa that present in smallest amount required for growth is called limiting amino acid

Legumes methionine

Cereal protein - lysine

59

21/07/2015

10

Animal vs Plant

Animal derived protein from meat, fish, poultry, eggs and dairy

Generally provide high-quality protein

Have high digestibility (90-99%)

Plant derived protein from vegetables, nuts, seeds, gains and legumes

Often tend to be limiting in 1 or more essential aa

Generally less digestible

60

Complementary proteins

61

Evaluation of proteins

Several biological measures and chemical measures are used to evaluate protein quality.

Biological Value (BV)

Net Protein Utilisation (NPU)

Protein Efficiency Ratio (PER)

Chemical (amino acid) Score

62

Requirements for protein

Varies with age & physiological state

Based on quantity of aa required to support optimum health

Definition: requirement is the intake needed to prevent loss of body protein and to allow for adequate deposition or production of protein during growth, pregnancy or lactation FAO/WHO/UNU

67

What is the composition of protein that

we need?

As close as possible to aa ratios found in human proteins

Good sources of complete proteins animal sources

68

Requirements for protein

21/07/2015

11

AMDR = acceptable macronutrient ranges for

macronutrients to reduce chronic disease

Protein = 15% to 25% energy

Many diets for weight loss recommend up to 30%

70

How much protein do we eat in NZ?

Usual daily median

intake (g)

1997 2008/9

RDI (g/day)

Males 105 102 64

Females 71 71 46

71

NNS 2008/9

72

PROTEIN SOURCES IN NZ DIET . NNS 1997 Age 15+

beef and veal

milk

bread

poultry

fish/seafood

bread based dishes

pork

potatoes and kumara

sausages

cheese

vegetables

grains and pasta

14% [f = 12% m = 15%]

10% [f = 11% m = 9%]

11% [f = 11% m = 10%]

7% [f = 8% m = 7%]

7% [f = 7% m = 7%]

5% [f = 4% m = 6%]

5% [f = 5% m = 5%]

4% [f = 4% m = 4%]

4% [f = 3% m = 4%]

4%

4%

3% 73

PROTEIN SOURCES IN NZ DIET . NNS 2008/9 Age 15+

bread

poultry

milk

beef and veal

grains and pasta

bread based dishes

fish/seafood

pork

vegetables

potatoes and kumara

sausages

cheese

11.1% [f = 10.7% m = 11.4%]

8.8% [f = 8.8% m = 8.8%]

8.8% [f = 9.4% m = 8.1%]

7.8% [f = 7.3% m = 8.2%]

6.8% [f = 6.6% m = 7.1%]

6.6% [f = 5.4% m = 7.8%]

6.0% [f = 6.3 % m = 5.6%]

4.5% [f = 3.9% m = 5.2%]

4.3% [f = 5.0% m = 3.5%]

3.2%

3.1%

3.1 % 74

PROTEIN SOURCES IN NZ DIET . CNS02* Age 5-14

beef and veal

milk

bread

poultry

fish/seafood

bread based dishes

potatoes and kumara

Sausages/processed meats

grains and pasta

8% [f = 8% m = 9%]

11% [f = 11% m = 11%]

13% [f = 14% m = 13%]

9% [f = 9% m = 9%]

4% [f = 3% m = 5%]

5% [f = 4% m = 6%]

4% [f = 4% m = 4%]

4% [f = 4% m = 5%]

5%

21/07/2015

12

CNS02 results - Protein

Median usual daily intake in NZ children ranges:-

Males 5-6 years 52g; 11-14 years 88g

Females 5-6 years 52g; 11-14 years 66g

NZ children consuming at least double their age specific RDIs

76

Practical advice

Protein in the diet is provided by a wide range of available foods, including lean meat, chicken, seafood, eggs & milk. Bread is also an important source

Choose low & reduced fat options from the meat and milk food groups where possible

If vegetarian, include protein from diverse plant sources (legumes, nuts, breads & cereals). If lacto-ovo vegetarian, also include eggs and milk products

77

Protein deficiency and excess

Can you eat too much protein?

78

Protein energy malnutrition (PEM)

Deficiency syndrome caused by inadequate intake of macronutrients

Characterised by an energy deficit in all macronutrients & many micronutrients

Common in developing countries but can occur in persons of any age in any country

79

PEM

Most lethal form of malnutrition by far

Assoc with >50% of the 10.9 million child deaths each year

Globally children who are poorly nourished suffer up to 160 days of illness each year

Malnutrition magnifies the effects of every disease

WHO

80 81

Poverty and hunger, children aged < 5yrs underweight (%)

WHO statistics, latest available figures since 2000

21/07/2015

13

82

Hunger

In many African languages there are two types of words for hunger.

The first is hunger that goes away (mild), even when it is visible. The other is hunger that you cannot survive (severe).

Examples of hunger words that have become part of the international lexicon are: Kwashiorkor--"the disease that the first child gets when the new child comes" Marasmus--"to waste away"

83

PEM classification & Etiology

There are 3 forms of acute malnutrition:

Marasmus severe weight loss or wasting (dry form)

Kwashiorkor bloated appearance due to water retention (bi-lateral oedema wet form)

Marasmic-kwashiorkor a combination of both wasting and bi-lateral oedema.

Forms depends on balance of non-protein and protein

sources of energy

84

Marasmus

Marasmus is the most common form of acute malnutrition in nutritional emergencies and, in its severe form, can very quickly lead to death if untreated

Characterised by severe wasting of fat and muscle which the body breaks down to make energy.

Skin and bones appearance

A thin old man face

85

Marasmus Dry (thin, desiccated), form of Protein-Energy

Malnutrition

Results from near starvation with deficiency of protein and non protein nutrients.

The marasmic child consumes very little food often because mother is unable to breastfeed

Child is very thin from loss of muscle and body fat.

Marasmus

Energy intake is insufficient for the body's requirements, body draws on its own stores.

Liver glycogen is exhausted within a few hours skeletal muscle protein is then used via gluconeogenesis to maintain adequate plasma glucose.

Triglycerides (fat depots) are broken down into FFAs, to provide some energy for most tissues - not nervous system.

When near starvation is prolonged, fatty acids are incompletely oxidized to ketone bodies, which can be used by the brain

87

21/07/2015

14

Kwashiorkor African word meaning "first child-second child. First child develops PEM when the Second child replaces first child

at the breast

Wet (oedematous, swollen) form of Protein-energy Malnutrition

Characterised by bilateral pitting oedema

Protein deficiency usually

more marked than the

energy deficiency

Children with kwashiorkor tend to be older than those with marasmus -

develop disease after weaning.

89

Kwashiorkor condition resulting from inadequate protein intake

Early symptoms include fatigue, irritability, and lethargy.

As protein deprivation continues, growth failure, loss of muscle mass, generalised swelling (oedema) and decreased immunity.

Large, protuberant belly is common. The incidence of kwashiorkor in

industrialized countries is extremely small.

Typically found in countries where there is drought and famine.

90

Marasmic-Kwashiorkor mix

Combination of the oedema of kwahiorkor and the wasting of maramus

It may be 2 stages of the same condition

Some research indicates that marasmus represents the bodies adaptation to starvation,

while kwashiokor develops when adaptation fails

93

Excess protein

Overconsumption offers no benefits and may contribute to some conditions (?)

Obesity

CVD

Some cancers (e.g. colon, breast, prostrate)

But animal protein also often high in saturated fat effects of each difficult to separate

May also displace fruits, vegetables and grains in diet ( micronutrient defic.)

94 98