U4AOS2: food chemistry Flashcards
aerobic respiration
requires oxygen and is the main source of energy for the human body
anaerobic respiration
does not require oxygen and yields less energy
calorimetry
the experimental methods of measuring the heat energy released or absorbed by a chemical reaction or physical process, such as by combustion of a fuel or a food
q=
mcAT
simple calorimetry
-measures the change in temperature of water in the calorimeter pot and this is used to determine the energy provided by the food being combusted
-limitation: heat loss
bomb calorimetry
-used to measure the heat of combustion of chemical reactions that involve gaseous reactants or products
-occurs in a reaction chamber made to withstand high pressures and high temp, maintaining constant volume
-contents can be electrically ignited to start comb, must have sufficient oxygen
solution calorimetry
-an insulated container holds a known volume of water in which a reaction in solution occurs like the dissolution of a solid
-limitation: cup may absorb some heat from water/cannot measure energy content of food as comb cannot occur in an aq sol
calibration factor
VIt/delta T = E/T
random errors with calorimeters
-poorly insulated calorimeters
-not all of the food/substance was combusted
-the temp recorded when the food was combusted was inaccurate
-impact of errors can be overcome by repeating multiple times
systematic errors
-problematic because will lead to results being consistently inaccurate
-calorimeter was calibrated incorrectly
-measurements used to calibrate the calorimeter were measured incorrectly
biomolecules
molecules present in living organisms including macronutrients such as carbs, proteins and triglycerides - created and synthesised by them
carbohydrates
-composed of carbon, hydrogen and oxygen with general formula Cx(H2O)y
-provide a source of energy, way of storing energy and structural material in plants
general structure of carbs
simplest = monosaccharides
can be joined by condensation polymerisation reaction between OH groups - with ether/glycosidic bond (only in carbs_
photosynthesis
go -> cow
endothermic reaction and absorbs energy
disaccharide formations
glucose + glucose -> maltose + water
glucose + fructose -> sucrose + water
glucose + galactose -> lactose + water
molar mass of carbs
mr (glucose) x how many molecules so 180n
subtract (n-1) water molecules, mr=18
starch - amylose and amylopectin
-made from alpha glucose molecules
-energy storage component of plants
-amylose = unbranched, linear polymer of starch that packs well together bc results in stronger hydrogen bonds and harder to break
-amylopectin = branched and occasional crosslinks, so less effective packing and weaker H bonds
glycogen
-made from alpha glucose molecules
-energy storage structure in humans and animals
-even more highly branched, less linear than amylopectin
-convert glucose into glycogen and store it in liver and muscle cells
cellulose
-made from beta glucose molecules
-structural material found in plants
-forms a tightly packed structure that leads to its strength as a plant fibre
-large, consistent linear structure and each glycosidic bond is inverted
artificial sweeteners
-artificial sweetener are similar sized molecules to many common sugars but are significantly sweeter than sugars
-allows people to require lower energy/calorie diets to obtain same amount of sweetness with much lower energy intake
aspartame
-made from condensation reaction between aspartic acid, phenylalanine, and methanol
-brings more 100-150 times more sweetness than sucrose
why can humans not digest cellulose?
-cellulose considered the dietary fibre as it helps food pass through the body in bulk amounts and reduces likelihood of constipation, cancers
-we lack the necessary enzyme cellulase, so cannot break it down for nutritional value
lactose intolerance
when people lack the sufficient amount of the enzyme lactase to hydrolyse the sugar.
various effects/symptoms = cramping/discomfort/bloating/diarrhoea
GI
-glycaemic index
-measure of how quickly glucose is released into the bloodstream after consuming food
-it is a comparison of how quickly glucose from carbs is released, compared to pure glucose via hydrolysis
low gi foods
-beans, fruits, lentils, milk, porridge
-slow hydrolysis, prolonged digestion
-slow rise in blood sugar
high gi foods
-potatoes, white bread, lollies
-fast hydrolysis, rapid digestion
-rapid rise in blood sugar
amylose vs amylopectin
linear vs branched
tight vs loose packing
low GI vs high GI
triglycerides
-they are esters
-contain CHO
-formed from a condensation reaction btw glycerol and three fatty acids
how to break up triglycerides
-reaction can be reversed by hydrolysis
-requires 3x water molecules and a catalystof lipase
general formulas for fatty acids
saturated: CnH2n+1COOH
monounsaturated: CnH2n-1COOH
diunsaturated: CnH2n-3COOH
define essential biomolecules
ones that cannot be synthesised by the human body, and must be consumed in diet
define non essential
molecules that can be synthesised by the human body, so don’t have to be consumed
omega-3 vs omega-6
the number after omega depends on the position of the first carbon-carbon double bond from the methyl end of the fatty acid (non carboxylic acid)
define rancidity
a notable deterioration/breakdown of fats and oils, resulting in deteriorated smell or taste
define oxidative rancidity
-the higher the degree of unsaturation of a triglyceride, the more susceptible it is to oxidation
-refers to fats and oils breaking down in presence of oxygen
-leads to formation of unpleasant smelling and potentially harmful short-chain aldehydes and ketones
auto oxidation
-formation of free radicals
-the fatty acid radical reacts with oxygen, forming another radical which also reacts with another fatty acid
-the reaction ends when two radicals combine
vitamins
are substances that are essential to our diet but in lower proportions - they are diverse molecules that are necessary to prevent various diseases like scurvy and rickets
water-soluble vitamins
water-soluble vitamins: contain higher proportion of hydroxyl groups, stored in aqueous environment of blood and not retained.
diet needs to regularly include intake of water soluble vitamins
fat-soluble vitamins
have long hydrocarbon chains but are low on hydroxyl groups, so cannot dissolve in water.
so, stored in fats (adipose cells) as fats contain many dispersion forces
how to prevent/slow rancidity
-vacuum packaging or using nitrogen
-filling containers up to the lid
-storing food in the dark and cold
-restricting access to copper, iron and nickel
-using dark containers or opaque containers for photooxidation
antioxidants
-can be natural or synthetic
-help slow down oxidation and prevent food from spoiling
-they are reducing agents, so preferentially oxidised
2-amino acid
an amino acid whose carboxyl and amino group is are bonded to the same central carbon atom
primary structure
sequence of amino acids joined together.
held by peptide bonds = strong covalent.
formed from condensation reaction, requires high heat or enzymes
secondary structure
composed of the primary structure folded into alpha helices or beta pleated sheets.
contains hydrogen bonds, formed between the H from CONH link, and the =O in another non-adjacent amide link
what are the 9 essential amino acids
isoleucine
leucine
lysine
methionine
phenylalanine
threonine
tryptophan
valine
histidine
zwitterion
contains a positive and negative polar region
no overall net charge
when amino acids are placed in acidic solution…
acts as a base
when amino acids are placed in a basic solution…
acts as an acid
amino acids within the protein are referred to as…
residues
tertiary structures
3D structure composed of folded secondary structure -forms a more complex shape
-bonds: covalent, disulphide bridges, hydrogen bonds, dipole interactions, ionic interaction and dispersion forces
quaternary structure
2 or more polypeptide chains joined together
held by similar bonds as tertiary structure
stages of digestion and reagents
proteins break down into smaller peptides in stomach via enzymes eg. pepsin.
then to amino acids in small intestine through hydrolysis via enzymes eg. trypsin.
also need water for hydrolysis.
explain how the body uses the a.as formed after hydrolysis
-some are absorbed into the bloodstream and used to synthesis more proteins in various parts of the body.
-some are reassembled into new proteins, others converted to glucose and energy
define denaturation
-change in the structure or function of a large molecule
-in reference to proteins, describes the loss of structure or function of a protein at extreme temperature or pH
-particularly impacts tertiary structure + R groups, whilst primary structure is unchanged
what are coenzymes
-often derived from vitamins
-bind to the active site of an enzyme during catalysis, changing the surface shape and binding properties of the active site to enable function as intermediate carriers of electrons or groups of atoms
how does an enzyme function
-protein biological catalysts that catalyse chemical reactions that would otherwise be too slow to support human life
-provide an alternate reaction pathway that requires a lower activation energy
lock and key model
-substrate fits perfectly into the active site of the enzyme, so it is perfectly complementary and specific
-forms an enzyme substrate complex
induced fit model
-proposes that the shape of the substate is not perfectly complementary to the shape of the active site, so it adjusts slightly
define enzyme activity
the rate of conversion of a substrate into a product by an enzyme is measured by a quantity called enzyme activity = the amount of substrate converted to product per unit time
can be monitored by looking at change in conc
what impacts enzyme activity
pH
temperature
heavy metals
change in ion concentrations
how do extreme pH levels impact enzymes
altering pH levels means that charges of amino acids are changed, depending on acidic or alkaline side chains. this impacts the ionic interactions, resulting in breakdown of bonds in tertiary structures
how does high temperature impact enzymes
increases kinetic energy
molecules vibrate so rapidly that bonds and interactions between secondary/tertiary/quaternary structures are disrupted
enzymes and enantiomers
active site is specific and complementary to only one enantiomer, so does not bind to all optical isomers of compounds
give functions of proteins in humans
-production of enzymes
-muscle development
-tissue repair and maintenance
give functions of fats in humans
-vitamin storage
-fatty acid production
-insulation
-organ protection
what features must be present for an emulsifying agent?
-polar regions on the molecule to help promote solubility in water component
-non polar regions to form attractions via dispersion forces to fat component
define metabolic reactions
chemical reactions occurring in the body
what is a glycaemic indiex?
the measure of the rate/how quickly 100g of carbs release glucose to be absorbed into the bloodstream
why is aspartame good for low GI diets?
aspartame does not hydrolyse into glucose, but into phenylalaline, aspartic acid and methanol.
does not contribute to any glucose being absorbed into the bloodstream, so no change in GI
explain the differences between GI of amylose and amylopectin
-amylopectin is branched structure, so more hydroxyl groups are occupied with cross links, and also are exposed and able to form H bonds with water. more water soluble enzymes can gain access to hydrolyse molecules more rapidly, so higher GI
-amylose is a linear structure, so less exposed OH groups and less soluble, so less quickly hydrolysed by enzymes
calorimetry calibration order
- place food
- add water
- ignite
NEED TO ADD WATER BEFORE IGNITION
is a compound has 70% carbon and 0% nitrogen and 11% oxygen, what is it likely to be?
-not a carbohydrate bc oxygen and carbon are usually similar in content
-not a protein bc does not contain nitrogen
-likely to be a fat
state symbol of maltose
solid
state symbol of fatty acids and fuels
NOT AQ
liquid
impact of not insulating calorimeter on calibration factor
-leads to a lower temperature change bc some heat energy is lost to surrounding
-hence higher calibration
a vitamin is defined as a compound that…
is essential for growth and nutrition and protection against diseases, but is not generally synthesised in the body
in determining the optimum temp of an enzyme, what may be a limitation in a conclusion made?
-not enough temperatures to conclude what the close, accurate optimum is
-test was only carried out once
how does a coenzyme function
a coenzyme is specific and complementary to the enzyme’s active site. it binds to the active site. the substrate then binds to the coenzyme
what key structural feature distinguishes glycine from other a-amino acids
it has no chiral carbon
what functional groups are present in a disaccharide?
hydroxyl and glycosidic/ether
explain why it is possible to form amylose and amylopectin from the same monomer
the two structures are possible bc the hydroxyl group on C6 that is part of CH2OH can undergo condensation reactions with the hydroxyl group present on another carbon
what bonds may form between an amino acid and enzyme?
-hydrogen bonds
-ionic interactions
-dispersion forces
as a result, the existing bonds within the substrate are weakened and an alternative reaction pathway, with lower Ea, is providedg
why is the high pressure of oxygen needed in a bomb calorimeter?
supply of excess oxygen at a high pressure helps to ensure that the reaction goes to completion and complete combustion occurs
where is glycogen stored
liver and skeletal muscle cells
breakdown of carbohydrates
-Mechanical breakdown and chemical digestion begins in the mouth - salivary amylase is the enzyme that catalyses the hydrolysis of starch to produce disaccharides
-Disaccharides are hydrolysed in the small intestine to produce monosaccharides (glucose) via amylase and maltase (produced in the pancreas)
-Glucose may subsequently undergo cellular respiration to produce ATP
breakdown of proteins
-Polypeptides are broken into dipeptides and tripeptides in the stomach via the enzyme pepsin
-Proteases in the intestine are then used to break down these shorter chains (by hydrolysing peptide bonds) into amino acids
-Amino acids are absorbed by epithelial cells lining the intestine
-Generally, these amino acids will be used in the creation of proteins for growth but in times of starvation may be deaminated (amino group removed) and oxidised to produce ATP
breakdown of triglycerides
-mechanical digestion in mouth
-bile (produced in the liver and stored in the gall bladder) is released into the small intestine, functions to emulsify fats – breaks them down into smaller droplets to increase s.a for lipase
-lipase (produced in the pancreas and released into the small intestine) catalyses the hydrolysis of the ester bonds found in triglycerides – producing 1 glycerol and 3 fatty acids from each molecule
-fatty acids may be oxidised to release ATP
are animal or plant based fats unsaturated?
plant based
define a vitamin
a substance that is essential to the human body to function properly but is needed in much smaller quantities than the three major food groups
what might preservatives that have OH grps vc C=O groups show?
the preservative with the OH group may be in higher quantity
this is bc it can act as an antioxidant and be oxidised from the hydroxyl group to a carbonyl group
what does a disulfide link look like
-S-S- not use dotted lines bc it is a convalent bond
explain why two possible dipeptides could be formed from reaction between lysine and cysteine
the structure of the dipeptide formed depends upon the location the condensation reaction occurs between the C-terminal and N-terminal of the amino acids involved. not enough to talk about order of dipeptide
glycaemic load equation
GL = (GI x amount of carbohydrate) / 100
why does an insulated calorimeter overcome the lack of insulation compared to a bad setup?
-minimises heat loss through proper insulation eg. lid, vessel, sealed
-BE SPECIFIC: this means there is greater energy transfer from combustion into the water, so more accurate rise in temp recorded and increase Hc
why do other optical isomers not attach to enzyme?
The ability of the coenzyme to attach to the enzyme (active site) depends on the coenzyme
having a (complementary) shape that allows it to bind to the original shape of the active site.
The enzyme has a specific shape (spatial geometry) that only matches up with L-ascorbic
acid.
Different optical isomers have different spatial arrangement of the atoms and so do not match
up with the enzyme.
The arrangement of atoms that allows for effective binding to the surface of the enzymes in the
body is not present in the other optical isomers (mirror images) of ascorbic acid.
what are the bonds in the primary structure?
COVALENT peptide bonds
how can vitamin C be used as coenzyme in collagen synthesis?
-changes shape of active site
-but, also oxidised during oxidation, so acts as a reductant by donating electrons to the enzyme substrate complex to facilitate the reaction
fatty acids are…
oxidised to release energy
how many times sweeter is aspartame than sucrose?
180 times
bonds in structure of proteins
primary = covalent peptide
secondary = hydrogen only
tertiary = multiple
quat = multiple but not covalent
