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Protein Flashcards

1
Q

Primary Structure of Protein

A

The primary structure refers to the sequence/order and the number of amino acids in a chain.
For example insulin has 51 amino acids arranged in a definite order.

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2
Q

Secondary Structure

A

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

An example of a Cross-Link would be a disulphide link.
This link occurs when two sulphur units 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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3
Q

Cross-Link Example

A

An example of a Cross-Link would be a disulphide link.
This link occurs when two sulphur units 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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4
Q

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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5
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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6
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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7
Q

Deamination

A

Deamination is using excess protein as a source of energy.
Excess protein not needed for growth and repair is deaminated in the liver.
The NH2 is removed, converted to ammonia then urea and is excreted by the kidneys as a waste product in urine.
The COOH group is oxidised to produce heat and energy.

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8
Q

Classification of protein - simple

A

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

Plant
Glutelins: insoluble in water, soluble in acids and alkalis (Eg:) glutenin in wheat
Prolamins: insoluble in water, soluble in alcohol (Eg:) gliadin in wheat, zein in maize

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9
Q

Classification of proteins - conjugated proteins

A

These proteins consist of amino acids and a non protein molecule.
Examples include:
Lipoproteins (Eg:) lecithin in eggs
Phosphoproteins (Eg:) caseinogen in milk

Lipid + protein
Phosphate + protein

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10
Q

Sources of protein
Animal

A

Cheese
Chicken
Meat
Fish
Eggs
Milk

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11
Q

Sources of protein
Plant

A

Soya beans
TVP food
Nuts
Lentils
Peas
Beans
Cereals

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12
Q

Cheese

A

Caesin

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13
Q

Meat connective tissue

A

Collagen

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14
Q

Meat fibres

A

Myosin/ actin/ albumin

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15
Q

Meat bones

A

Gelatin

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16
Q

Eggs

A

Albumin

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17
Q

Fish

A

Myosin/ collagen / actin

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18
Q

Milk

A

Lactalbumin
Caseinogen

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19
Q

Wheat

A

Gluten

20
Q

Properties of protein

A

Denaturation
Solubility
Maillard reaction
Elasticity
Gel formation/forming
Foam formation

21
Q

Denaturation

A

The unfolding of the protein chain, resulting in an irreversible change in shape
Coagulation is an example of denaturation

22
Q

Denaturation - heat

A

Heat causes coagulation, upon heating the ablumin in egg gardens/coagulates.
Egg white coagulates at 60°C
Egg yolk coagulates at 68°C

Culinary application
Protein coagulates when eggs are cooked (Eg:) boiled, scrambled, fried
Moist heat (boiling) changes collagen to gelatine. This tenderises meat.

23
Q

Denaturation - Acids

A

Acids lower the pH. For example milk souring bacteria change lactose to lactic acid which causes caseinogen in milk to coagulate

Culinary Application
Lactic acid bacteria is added to milk in cheese making

24
Q

Denaturation - Enzymes

A

Enzymes denature protein. For example rennin coagulates milk during cheese making

Culinary Application

proteolytic enzymes (Eg:) Papin tenderise meat by converting collagen to gelatine

25
Q

Denaturation - Mechanical Action

A

Heat produced by friction slightly coagulates egg protein. For example whisking egg white causes them to foam

Culinary Application
Aeration of sponge cakes, soufflés, meringues

26
Q

Solubility

A

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

27
Q

Maillard Reaction

A

Maillard reaction is the browning of food caused by dry heat when amino acids and carbohydrates react together.
It is non-enzymic browning.

Culinary Application
Browning of fried potatoes, brown crusts on bread

28
Q

Elasticity

A

Elasticity is a property of some proteins — for example gluten

Culinary Application
Gluten in wheat allows baked goods to rise

29
Q

Gel formation/Gelling

A

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

30
Q

Foam formation

A

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 whole, unless heated to coagulate and set as a permanent foam

Culinary Application
Meringues/ sponges

31
Q

Biological functions of proteins
Structural

A

Production and growth and repair of:
Cell membranes
Muscle and skin

Deficiency: delayed healing/growth

32
Q

Biological functions of protein
Physiologically active

A

Production of
Hormones
Enzymes
Antibodies
Blood proteins
Nucleoproteins

Deficiency: body organs and systems malfunction, easily infected

33
Q

Biological functions of protein
Nutrient

A

Supply the body with essential amino acids
Excess protein can be used for energy

Deficiency: lack of energy, kwashiorkor marasmus

34
Q

Biological value of proteins
HBV

A

HBV proteins contain all essential amino acids
They are also known as complete proteins
HBV proteins generally come from animal sources, but also from soya beans

HBV foods:
Eggs
Milk
Meat/fish
Soya beans

35
Q

Biological value of proteins
LBV

A

LBV proteins contain only some of the essential amino acids
They are also known as incomplete proteins
LBV proteins generally come from plant sources but also from gelatine

LBV foods:
Rice
Wheat
Maize
Gelatine

36
Q

Effects of dry and moist heat on protein

A

Coagulation
Colour change
Maillard reaction (fry)
Tenderising (moist)
Overcooking - indigestible

COMCT

37
Q

Effects of dry and moist heat on protein
Coagulation

A

Proteins set or harden when subjected to dry or moist heat

Example: egg proteins solidify upon cooking (boiling, frying)

38
Q

Effects of dry and moist heat on protein
Colour change

A

Dry and moist heat make proteins change colour

Example: myoglobin (red) in meat turns brown (haematin)

39
Q

Effects of dry and moist heat on protein
Maillard reaction (dry heat)

A

Dry heat causes browning of food when amino acids and carbohydrates react together

Example: roast potatoes

40
Q

Effects of dry and moist heat on protein
Tenderising (moist)

A

Collagen in meat changes to gelatine, causing the fibres to fall apart and the meat to become more digestible

Example: lamb casserole

41
Q

Effects of dry and moist heat on protein
Overcooking - indigestible

A

Prolonged cooking causes proteins to become indigestible

Example: overcooking meat will make it tough and difficult to digest

42
Q

Supplementary/complementary value of promete in

A

Eating two low biologung value protein foods together can ensure that all 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 is low in lysine but high in methionine

43
Q

Stomach

A

Secretion: gastric juice
Enzyme: rennin, pepsin
Substrate: caseinogen proteins
Product: casein peptones

44
Q

Pancreas

A

Secretion: pancreatic juice
Enzyme: trypsin
Substrate: peptones
Product: peptides

45
Q

Ileum

A

Secretion: intestinal juice
Enzyme: peptidase
Substrate: peptides
Product: amino acids

46
Q

Amino acids in the liver

A

They are used to maintain and repair liver cells
They are sent into the bloodstream to form new cells, repair damaged cells and manufacture hormones, enzymes, antibodies, blood proteins, nucleoproteins
The excess is deaminated to produce heat and energy

Home Economics (12 decks)

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