Protein Flashcards
essential amino acids list
lysine, leucine, isoleucine
non essential amino acids list
alanine, aspargine, cysteine
formation of a dipeptide bond
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.
hydrolysis
during digestion the reverse of the condensation reaction occurs. peptide bonds are broken by the addition of water, producing single amino acids
classification of proteins
simple and conjugated
simple proteins animal
fibrous - collagen
globular - albumin
simple proteins plant
prolamins - gliadin in wheat
glutelins - glutenin in wheat
conjugated proteins
lipoproteins - lecithin
phosphoproteins - casein
supplementary role of proteins
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
primary structure
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
secondary structure
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
tertiary structure
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
High biological value
contains all essential amino acids
mainly from animal sources except soya beans
low biological value
lack one or more essential amino acids
mainly from plant sources except gelatine
properties of protein
denaturation and coagulation solubility maillard reaction elasticity gel formation
denaturation and coagulation
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
solubility
most are insoluble in water except collagen (hot water) and albumin (cold water)
maillard reaction
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
elasticity
gluten is very elastic - allows bread to rise
gel formation
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
biological functions of structural proteins
growth and repair production of cells, muscles and skin deficiencies: stunted growth delayed healing of wounds
biological functions of physiologically active proteins
production of hormones, enzymes, antibodies, blood proteins and nucleoproteins
deficiencies:
illness and infections
malfunction of body systems and organs
biological functions of nutrient proteins
provide essential amino acids
excess converted to energy
deficiencies:
lack of energy
energy value
1g = 4kcal energy
RDI
1g per 1kg of weight
deamination of proteins
excess proteins are deaminated by the liver
- the amino group of the amino acid is converted to ammonia and then urea.
- urea is excreted from the body in urine
- the carboxyl group is oxidised (used for heat and energy)
- excess is stored in the body as glycogen(energy store)
stomach digestion
gastric juice-pepsin-protein-peptones
pancreas digestion
pancreatic juice- trypsin-peptones-peptides
small intestine (duodenum)
intestinal juice- peptidase- peptides- amino acids
absorption
amino acids are absorbed by blood vessels in the villi of the small intestine and transported to the liver via the hepatic portal vein
utilisation
used in the liver to
repair and maintain liver cells
form new cells, repair damaged tissues
make hormones enzymes and antibodies
excess are deaminated
elemental composition of proteins
carbon, hydrogen, oxygen, nitrogen
chemical composition of proteins
large molecules composed of amino acids
joined together by peptide links to form long polypeptide chains
basic structure of amino acid
amino group (NH2) carboxyl group (COOH) central carbon hydrogen variable group
foam formation
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
