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Protein Flashcards

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1
Q

Elemental Composition of Proteins

A

C (Carbon)
H (Hydrogen)
O (Oxygen
N (Nitrogen)

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2
Q

Chemical Structure of Protein

A

Each protein molecule contains a number of amino acids
The amino acids are joined together by peptide links or bonds
A number of linked amino acids are called a polypeptide chain

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3
Q

Essential Amino Acids

A

Cannot be manufactured in the body. Must be obtained from food.

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4
Q

Examples of essential amino acids

A

Valine
Lysine
Leucine
Isoleucine

arginine
histidine

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5
Q

Children’s extra essential amino acids

A

arginine
histidine

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6
Q

Non-Essential amino acids

A

Glycine
Cysteine
Alanine
Asparagine

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7
Q

Protein Structure - Primary Structure

A

Primary structure is the sequence/order of the number of amino acids in a chain.
For example, insulin is made up of 51 amino acids arranged in a definite order.

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8
Q

Protein Structure - Secondary Structure

A

In a protein molecule, a polypeptide chain (or two different polypeptide chains) can be interlinked.
This creates a coiled or spiral shape.
These are known as cross-links or bridges and give proteins their properties - for example, the protein gluten is elastic.

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9
Q

Examples of Cross-Links
Disulphide links

A

This link occurs when two sulphurs join together.
The amino acid cysteine contains sulphur.
When two cysteine units, either in the same chain or two different polypeptide chains, are adjacent, a disulphide link may be formed.
Insulin has disulphide links.

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10
Q

Examples of Cross-Links
Hydrogen Bonds

A

Polypeptide chains can also be linked by hydrogen bonds.
The hydrogen in one chain joins with the oxygen in another chain.
Collagen has hydrogen bonds.
Define and tyrosine are capable of forming hydrogen bonds.

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11
Q

Protein Structure - Tertiary Structure

A

Tertiary structure relates to the pattern of folding of the polypeptide chains.
The coiled or spiral shape of the secondary structure may then be folded over to form a globule: a three dimensional organisation of the polypeptide chain held firmly by links.
Tertiary structures may be either fibrous or globular.

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12
Q

Fibrous

A

The polypeptide chain, composed of long, narrow strands of amino acids, is arranged in a straight, spiral or zigzag shape.
Example: Gluten and collagen, which are insoluble (not easily denatured) in water

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13
Q

Globular

A

The polypeptide chain is arranged in a globe shape.
Example: Ovalbumin (egg white) and myoglobin, which are soluble in water (easily denatured)

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14
Q

Classification of Protein
Simple Proteins

A

Animal:
Fibrous (eg: collagen in skin, myosin in muscle)
Globular (eg: albumin in egg, myoglobin in meat)

Plant:
Glutelins (insoluble in water, soluble in acids and alkalis eg: gluten in wheat)

Prolamins (insoluble in water, soluble in alcohol eg: gliadin in wheat)

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15
Q

Classification of Protein
Conjugated Proteins

A

these proteins consist of amino acids and a non-protein molecule:

Lipoproteins (lipid + protein) eg: lecithin in egg yolks
Phosphoprotein (phosphate + protein) eg: caseinogen in milk

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16
Q

Sources of Protein - Animal

A

Cheese
Chicken
Meat
Fish
Eggs
Milk

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17
Q

Sources of Protein - Plant

A

Soya beans
TVP good
Nuts
Lentils
Leas
Beans
Cereals

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18
Q

Cheese

A

casein

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19
Q

Meat connective tissue

A

collagen

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20
Q

Meat fibres

A

myosin/albumin/actin

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21
Q

Meat bones

A

gelatine

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22
Q

Fish

A

myosin/collagen/actin

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23
Q

Eggs

A

albumin

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24
Q

Milk

A

lactalbumin/caseinogen

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25
Wheat
gluten
26
Properties of protein
Denaturation Solubility Maillard Reaction Elasticity Gel forming/Gelling Foam Formation
27
The effects of dry and moist heat on protein
Coagulation Colour Change Maillard Reaction Tenderising Overcooking causes proteins to become indigestible
28
The effects of dry and moist heat on protein Coagulation
Proteins set or harden when subjected to dry or moist heat. Eg: Egg proteins solidify upon cooking (boiling/frying)
29
The effects of dry and moist heat on protein Colour Change
Dry and moist heat make proteins change colour. Eg: Myoglobin in meat turns brown (haematin)
30
The effects of dry and moist heat on protein Maillard Reactions
Dry heat causes a browning of food when amino acids and carbohydrates react together Eg: Roast potatoes
31
The effects of dry and moist heat on protein Tenderising
Collagen in meat changes to gelatine, causing the fibres to fall apart and meat to become more digestible Eg: lamb casserole
32
The effects of dry and moist heat on protein Overcooking causes proteins to become indigestible
Prolonged cooking causes proteins to become indigestible. Eg: overcooking meat will make it tough and difficult to digest
33
Biological Functions of Proteins Structural Protein
Production of: Cell membrane, Muscle and skin (and growth and repair)
34
Biological Functions of Proteins Physiologically active proteins
Production of: Hormones Enzymes Antibodies Blood proteins and nucleoproteins
35
Biological Functions of Proteins Nutrient Proteins
Supply the body with essential amino acids Excess protein can be used for energy
36
Deamination
Is using protein as a source of energy Excess protein not required for growth and repair is deaminated in the liver The NH2 group is removed, converted to ammonia and then urea, and is excreted by the kidneys. The COOH group is oxidised to produce heat and energy.
37
Biological value of proteins HBV
HBV proteins contain all essential amino acids They’re known as complete proteins HBV generally comes from animal sources but also from soya beans Eg: Eggs Milk Meat/Fish Soya Beans
38
Biological value of proteins LBV
LBV proteins contain only some of the essential amino acids They’re known as incomplete proteins LBV proteins generally come from plant sources but also from gelatine Eg: Rice Wheat Maize Gelatine
39
Supplementary/Complementary value of protein
Eating two LBV protein foods together can ensure that all the essential amino acids are obtained. This is very important in vegan diets, where no animal protein is eaten. Beans on toast is an example of proteins supplementing or complementing each other. Beans are high in lysine but low in methionine. Bread (wheat) is low in lysine but high in methionine.
40
Energy value of protein
Protein should make up 15% of total energy value of the average diet RDA is based on: Body weight Rate of growth 1g per kg of body weight
41
Protein digestion Organ/Gland: Stomach
Secretion: Gastric juice Enzyme: Rennin, Pepsin Substrate: Caseinogen, Proteins Proteins: Casein, Peptones
42
Protein digestion Organ/Gland: Pancreas
Secretion: Pancreatic juice Enzyme: Trypsin Substrate: Peptones Product: Peptides
43
Protein digestion Organ/Gland: Lleum
Secretion: Intestinal juice Enzyme: Peptidase Substrate: Peptides Product: Amino acids
44
Absorption and Utilisation of amino acids
Amino acids are absorbed through the villi of the small intestine into the bloodstream. The portal vein carries them to the liver. In the liver: They’re used to maintain and repair liver cells They’re sent into the bloodstream to form new cells, repair damaged cells and manufacture hormones, enzymes, antibodies, blood proteins and nucleoproteins. The excess is deaminated to produce heat and energy
45
Formation of peptide bonds
Peptide bonds form when a “H” from the NH2 group of one amino acid and the “OH” from the carboxyl group of another amino acid joins together to form a water molecule forming a peptide link in a condensation reaction
46
Hydrolysis
a reaction that involves the addition of water and enzyme action
47
Condensation reaction
a reaction that results in the loss of a water molecule
48
Draw the structure with a key
H | R——C——COOH | NH2 C- carbon H- hydrogen NH2 - amino group** COOH - carboxyl group** R - variable
49
Properties of protein - Denaturation
Heat causes coagulation. For example upon heating, the albumin in egg hardens/coagulates Culinary application: protein coagulates when eggs are cooked Acids lower the pH. For example, milk souring bacteria changes lactose to lactic acid which causes the caseinogen in milk to coagulate Culinary application: Lactic acid bacteria is added to milk in cheese making Enzymes denature protein. For example, rennin coagulates milk during cheese-making Culinary application: Tenderising salts contain enzymes, which tenderise meats, proteolytic enzymes (papain) tenderise meat by converting collagen to gelatine Mechanical action: Heat produced by friction slightly coagulates egg protein. For example, whisking egg whites causes them to foam. Culinary application: Aeration of sponge cakes, soufflés and meringues
50
Properties of protein - Solubility
Most proteins are insoluble in water, except egg whites in cold water and collagen in hot water Culinary application: Collagen is converted to gelatine in moist heat, which tenderises meat.
51
Properties of protein - Maillard Reaction
The maillard reaction is the browning of food caused by dry heat when amino acids and carbohydrates react together. It’d non-enzymes browning. Culinary application: Browning of fried potatoes amino acid + sugar + dry heat = attractive brown colour and flavour (eg:) roast potato
52
Properties of protein - Elasticity
Elasticity is a property of some proteins — for example gluten Culinary application: gluten in wheat flour allows baked goods to rise
53
Properties of protein - Gell formation
Gelatine is a setting agent that is extracted from the bones of animals. Gelatine can absorb large amounts of water forming a gel. Culinary application: Gelatine is used as a setting agent in soufflés and mousses
54
Denaturation definition
Denaturation id the unfolding of the protein chain, resulting in an irreversible change in shape. Coagulation of protein is an example of denaturation. Denaturation is caused by: Heat Acids Enzymes Mechanical action
55
Causes of Denaturation: Heat
Heat causes coagulation. For example upon heating, the albumin in egg hardens/coagulates Culinary application: protein coagulates when eggs are cooked
56
Causes of Denaturation: Acids
Acids lower the pH. For example, milk souring bacteria changes lactose to lactic acid which causes the caseinogen in milk to coagulate Culinary application: Lactic acid bacteria is added to milk in cheese making
57
Causes of Denaturation: Enzymes
Enzymes denature protein. For example, rennin coagulates milk during cheese-making Culinary application: Tenderising salts contain enzymes, which tenderise meats, proteolytic enzymes (papain) tenderise meat by converting collagen to gelatine
58
Causes of Denaturation: Mechanical Action
Mechanical action: Heat produced by friction slightly coagulates egg protein. For example, whisking egg whites causes them to foam. Culinary application: Aeration of sponge cakes, soufflés and meringues
59
Properties of Protein - Foam Formation
When egg white is whisked, protein chains unfold and air bubbles form. The protein chains entrap air, creating a foam. Whisking also creates heat that begins to set the egg albumin. This is known as a temporary foam. It will collapse after a while unless heated to coagulate and set a permanent foam. Culinary application: Meringues/Sponges
60
Biological Functions of Proteins - Deficiency of Structural Proteins
Delayed growth and healing
61
Biological Functions of Proteins - Deficiency of Physiologically active proteins
Body organs and systems malfunction Easily infected
62
Biological Functions of Proteins - Deficiency in Nutrient Proteins
Lack of energy Kwashiorkor Marasmus

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