Protein

Question 1

essential amino acids list

Answer 1

lysine, leucine, isoleucine

Question 2

non essential amino acids list

Answer 2

alanine, aspargine, cysteine

Question 3

formation of a dipeptide bond

Answer 3

a carboxyl group of one amino acid joins with an amino group of the next amino acid. A molecule of water is lost. this is the condensation reaction. a dipeptide bond is formed.

Question 4

hydrolysis

Answer 4

during digestion the reverse of the condensation reaction occurs. peptide bonds are broken by the addition of water, producing single amino acids

Question 5

classification of proteins

Answer 5

simple and conjugated

Question 6

simple proteins animal

Answer 6

fibrous - collagen

globular - albumin

Question 7

simple proteins plant

Answer 7

prolamins - gliadin in wheat

glutelins - glutenin in wheat

Question 8

conjugated proteins

Answer 8

lipoproteins - lecithin

phosphoproteins - casein

Question 9

supplementary role of proteins

Answer 9

protein foods deficient in one or more essential amino acids can make up for the deficiency by being paired with foods rich in that amino acid in the same meal.
eg beans on toast
beans - high in lysine low in methionine
toast - low in lysine high in methionine

Question 10

primary structure

Answer 10

the order or sequence of amino acids in protein chains
can be arranged in many different combinations
eg Insulin, one of the simplest proteins, contains 51 amino acids

Question 11

secondary structure

Answer 11

folding of the primary structure of proteins into definite shapes
either fold on themselves or cross link with another polypeptide chains
this causes them to form a spiral shape
Disulphide links - two sulphur inked together on a chain or across two chains eg two cysteine
Hydrogen bonds- occur in polypeptide chains when one hydrogen links with an oxygen in a nearby chain eg collagen

Question 12

tertiary structure

Answer 12

the pattern of folding into 3D shapes

chains are held in place by cross links to form fibrous (straight or zig zag) or globular (ball shaped) structures

Question 13

High biological value

Answer 13

contains all essential amino acids

mainly from animal sources except soya beans

Question 14

low biological value

Answer 14

lack one or more essential amino acids

mainly from plant sources except gelatine

Question 15

properties of protein

Answer 15

denaturation and coagulation
solubility 
maillard reaction
elasticity 
gel formation

Question 16

denaturation and coagulation

Answer 16

change in the nature of a protein chain
involves the unfolding of a protein chain, resulting in an irreversible change in shape
brought about by physical or chemical means including:
heat, chemicals, mechanical action, enzymes
results in the hardening or setting of protein foods known as coagulation

Question 17

solubility

Answer 17

most are insoluble in water except collagen (hot water) and albumin (cold water)

Question 18

maillard reaction

Answer 18

non enzymic browning of food due to a reaction between certain amino acids and sugars under dry heat
produces an attractive brown colour and a crust with appetising flavour

Question 19

elasticity

Answer 19

gluten is very elastic - allows bread to rise

Question 20

gel formation

Answer 20

a gel is a semi solid viscous solution with a 3D network in which molecules of water can become trapped.
1. gelatine absorbs water and swells to form a gel
2. when heated the gel becomes liquid, a sol
3. on cooling, the sol sets and becomes solid
eg jellies, souffles

Question 21

biological functions of structural proteins

Answer 21

growth and repair
production of cells, muscles and skin 
deficiencies:
stunted growth
delayed healing of wounds

Question 22

biological functions of physiologically active proteins

Answer 22

production of hormones, enzymes, antibodies, blood proteins and nucleoproteins
deficiencies:
illness and infections
malfunction of body systems and organs

Question 23

biological functions of nutrient proteins

Answer 23

provide essential amino acids
excess converted to energy
deficiencies:
lack of energy

Question 24

energy value

Answer 24

1g = 4kcal energy

Question 25

RDI

Answer 25

1g per 1kg of weight

Question 26

deamination of proteins

Answer 26

excess proteins are deaminated by the liver

1. the amino group of the amino acid is converted to ammonia and then urea.
2. urea is excreted from the body in urine
3. the carboxyl group is oxidised (used for heat and energy)
4. excess is stored in the body as glycogen(energy store)

Question 27

stomach digestion

Answer 27

gastric juice-pepsin-protein-peptones

Question 28

pancreas digestion

Answer 28

pancreatic juice- trypsin-peptones-peptides

Question 29

small intestine (duodenum)

Answer 29

intestinal juice- peptidase- peptides- amino acids

Question 30

absorption

Answer 30

amino acids are absorbed by blood vessels in the villi of the small intestine and transported to the liver via the hepatic portal vein

Question 31

utilisation

Answer 31

used in the liver to
repair and maintain liver cells
form new cells, repair damaged tissues
make hormones enzymes and antibodies

excess are deaminated

Question 32

elemental composition of proteins

Answer 32

carbon, hydrogen, oxygen, nitrogen

Question 33

chemical composition of proteins

Answer 33

large molecules composed of amino acids

joined together by peptide links to form long polypeptide chains

Question 34

basic structure of amino acid

Answer 34

amino group (NH2)
carboxyl group (COOH)
central carbon
hydrogen
variable group

Question 35

foam formation

Answer 35

when an egg white is whisked, protein chains unfold and air bubbles form
protein chains entrap air, creating a foam
whisking creates heat which begins to set the egg albumin = temporary foam
will collapse unless heated to coagulate and set as permanent foam
eg meringue