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Protein

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by

Elaine Farrell

on 6 September 2016

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Transcript of Protein

Protein
Composition of protein
Contains the elements: Carbon Hydrogen Oxygen and Nitrogen
Some amino acids contain Sulphur Phosphorus and Iron
Protein is the only nutrient to contain NITROGEN
Nitrogen is needed for growth
The elements are arranged into units called AMINO ACIDS (aa's)


These amino acids join to form chains (polypeptide chain) which makes up protein molecules

Protein Structure
Classifications
Protein - Junior Cert
Protein
Sources
Animal protein: meat, poultry, fish, eggs, cheese, yoghurt, milk.

Plant protein: Lentils, Beans, Peas, nuts, cereals

Plant protein foods contain:
Less saturated fat
More fibre
Cheaper to produce
Structure
Protein is made of of amino acids joined by peptide links
Functions
Growth and repais of cells
production of hormones, enzymes and antibodies
Production of heat and energy
Classifications
High biological value - mainly animal sources
Low biological value - mainly plant sources
Basic structure of amino acid
C = Carbon
H = Hydrogen
COOH = Carboxyl group (acidic)
NH2 = Amino Group (basic)
R =
Variable
.
C
Glycine
Cysteine
Peptide bonds/links
1. Forms when 2 aas join
2. There is the loss of a water molecule
3. Called a condensation reaction
4. The NH2 group of one aa reacts with the COOH group of another aa
5. The NH2 group loses a Hydrogen atom
6. The COOH group loses an OH group
7. A CONH bond if formed

Stages in a peptide bond
Primary structure
1. The order/ sequence of aa in a polypeptide chain
2. the amino acids bond together, releasing a water molecule, forming peptide links
3. Many different combinations can be made

Alphabet.......
Draw basic chain
Tertiary structure
1. The further folding of the polypeptide chain
2. A 3D structure
3. Can be
F
I
BROUS - Straight/spiral/zigzag -
I
nsoluable in water
not easily denatures
eg collagen
or
GLOBULAR - globe shape - Soluable in water
easily denatured
ge ovalbumin
Secondary structure
1. Further linking of aa's in a polypeptide chain or from 2 different polypeptide chains
2.Gives proteins their shape - often spiral
3. 2 examples:
Disulphide cross-links - 2 sulphurs join eg 2 cysteine aa's EG Insulin
Hydrogen cross-link - The H in one aa and the O in another bond EG Collagen


Diagram x 2
8 essential for adults and 10 for children

Valine
Lysine
Methionine
Trytophan
Histidine (children)
Threonine
Leucine
Isoleucine
Arginine (children)
Phenylalnine

Vincent’s
Lovely
Mother
Took
Him
To
London
In
a
Pram

Essential Amino acids:
1. cannot be made by the body
2. must be obtained from food

AMINO ACID CLASSIFICATION
PROTEIN CLASSIFICATION

Simple
Conjugated
Derived
These proteins are formed due to a chemical or enzymic action on a protein i.e: Rennin acts on caesinogen and makes caesin

Protein + non-protein
Protein + Lipid = lipoprotein (lecithin)
Protein + Phosphate = phosphoproteins (caseinogen)
Animal
Plant
Fibrous
Globular
Collagen
Ovalbumin
Glutenins
Glutenin
Prolamines
Gliadin
Sources
need to know:
List of animal sources
List of plant sources
1 protein found in the main foods
1 food source for each of the main proteins
Properties of protein
Digestion, absorption and utilisation
Value in the diet
High biological value Protein/ 1st class/ complete - Contains all of the essential amino acids
- Usually animal sources (exception: Soya beans)

Low biological value protein/ 2nd class/ incomplete - contains only some of the essential amino acids
- Usually plant sources (exception: Gelatine)
Biological Value of different proteins

When low biological value foods, that lack essential amino acids, are eaten together they can provide all the essential amino acid.
The essential amino acids missing in one food can be made up for by being present in the other food and visa versa.
This complementary value of protein means that vegans can get all the essential amino acids without eating animal food
Example; Bread is lacking Lysine but is high in Methionine. Beans are lacking Methionine but high in Lysine. By eating beans on toast both essential amino acids are included in the meal.

Supplementary Value of Protein

RDA
1gram of protein per kilogram of body weight.
Child 30-50g/day
Teenager 60-80g/day
Adults 50-75g/day
Pregnant or lactating 70-85g/day
Energy Value
1g of protein gives 4kCal energy

RDA Protein & Energy value

Biological Functions of protein
Structural function
Growth & repair of body cells muscles &skin

Physiologically active proteins
Production of hormones, antibodies, enzymes, blood proteins and nucleoproteins
Nutrient
proteins
Provides the body with essential amino acids
Exess protein is used for energy
Result of deficiency: Retarded growth and delayed healing
Result of deficiency Body organs & systems malfunction. Easily infected.

Result of deficiency: Lack of energy

Protein and energy
Main function - growth and repair
If enough carbohydrates and fats are not consumed, protein can be used for energy
1g protein = 4kcal
15% of energy should come from protein
DEAMINATION

1gram of protein per kilogram of body weight.
Child 30-50g/day
Teenager 60-80g/day
Adults 50-75g/day
Pregnant or lactating 70-85g/day
Energy Value
1g of protein gives 4kCal or 17 kJ energy

RDA
Digestion of protein

Amino Acids are absorbed into blood capillaries in the villi of the small intestine.

These capillaries connect into the portal vein which carries the amino acids to the Liver.

From here the Amino Acids will be sent to (a) replace & repair body cells, (b) form new cells, antibodies, hormones, enzymes or (c) be deaminated

Absorption & Assimilation of Amino Acids

The reverse of this is called hydrolysis

Hydrolysis involves the addition of water and enzyme action

This occurs during digestion when proteins are broken down into individual aa,s so that they can be absorbed into the blood
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