Food Chemistry+ proteins/enzymes 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
energy content units
kJ/g kJ/mol or kJ/g (100g)
features of simple calorimetry
-measures change in temp of water in calorimeter pot and is used to determine energy of food being combusted
-major limitation is that heat is lost to the environment
where does the reaction take place in a bomb calorimeter
a sealed ‘bomb’ vessel
where does the reaction take place in solution calorimeters
in a solution
features of bomb calorimeter
-measures heat of combustion of GASEOUS products
-occurs in reaction chamber that withstands high pressure and temp whilst maintaining volume
-chamber is wired to a electrical circuit to ignite (start combustion)
-reaction chamber surround by a vessel of water so heat energy transferred can be measured
-insulation around reaction vessel ensures even distribution of heat in water
-kj/g
features of solution calorimeter
-can occur in a polystyrene cup (constant pressure)
-insulated container holds a known volume of water in which a reaction in solution occurs
-increase or decrease in temperature of surrounding water determines if the reaction is endothermic or exothermic
limitations of solution calorimeter
-polystyrene cup absorbs some energy and hence the delta T value is slightly lower than real value
-solution calorimeters can not measure energy content of food as they can’t be combusted in aqueous state
what do bomb calorimeters measure
heat content of fuels and food
what do solution calorimeters measure
heat of solution, neutralisation
what type of reactions occur in the two different calorimeters
only EXOTHERMIC in bomb whereas there are exo and endothermic reactions in solution calorimeters
define calorimetry
method by which chemists measure the heat released or absorbed by a chemical reaction, such as combustion
Random errors with calorimeters
-not all food substance was combusted/ incomplete combustion –> lower energy content
-the temperature recorded was incorrect (delta T changes) –> increase or decrease in energy content depending on change
REPEAT TO COUNTER THESE RANDOM ERRORS
Systematic errors arising with calorimeters
-poorly insulated calorimeter
-incorrect calibration –> low CF means low energy content and vice versa
-incorrect calibration measurements eg voltage, time, amperes
Elements in carbohydrates
CHO
carbohydrate general formula
Cx(H2O)y
what type of reaction are carbohydrate monomers joined by
condensation (polymerisation)
what bond forms when carbohydrate monomer join
glycosidic bond /ether link
what groups do carbohydrate monomers join by
adjacent OH groups
general formula for disaccharides
C12H22O11
general characteristics of monosaccharides
sweet, crystalline and water soluble
what unique bond does glucose contain
-Fischer rep.
aldehyde
what unique bond does fructose contain
ketone
endothermic reaction involving glucose
carbon dioxide + water –> glucose + oxygen
exothermic reaction involving glucose
glucose + oxygen –> carbon dioxide + water
structural difference between glucose and galactose
The OH group and H varies of the 4th carbon in the ring
maltose made of
glucose and glucose
sucrose made of
glucose and fructose
lactose made of
glucose and galactose
How many water molecules are released in a condensation reaction
n-1
where n is the number of monomers
Starch is made of
amylose and amylopectin
(ALPHA GLUCOSE)
Glycogen is made of
alpha glucose
Cellulose is made of
beta glucose
what is starch function
energy storage component of plants
Describe the structure of amylopectin
-occasional crosslinks between glucose molecules (glycosidic link forms between C1 and C4 and also C1 and C6)
-chained molecules means less effective packing and lower attraction between OH groups
-Weaker H bonds
Describe structure of amylose
-linear molecule that packs tightly
-more attraction between OH groups
-stronger H bonds between glucose molecules
Overall glycogen structure
Highly branched
Overall structure of cellulose
large, tightly packed consistent linear structure
What is aspartame made of
aspartic acid, phenylalanine, methanol
what functional groups are in aspartame
carboxyl, amine, amide, ester and phenyl
How can aspartame be beneficial
-aspartame is approx. 180x sweeter than any common sugar
-far less artificial sweetener can be used to ‘sweeten’ foods which means overall energy decreases (b/c similar energy content) aids diets that need to be low in energy/ low calories
what does amylase break down
salivary amylase breaks down starch in body to maltose (disaccharide)
how’s maltose broken down
maltase breaks down maltose in small intestine
what happens to excess glucose that isn’t utilised after hydrolysis
undergoes condensation reaction to form glycogen
what happens to excess glucose that isn’t utilised after hydrolysis
undergoes condensation reaction to form glycogen (stored in liver and muscle cells)
Why is cellulose indigestible
-b/c humans lack the enzyme (cellulase) to break down/hydrolyse/digest cellulose
-then the rate at which its broken down is at too slow of a rate and passes through the body quickly
-therefore humans can’t gain any nutritional value from cellulose
NB-cellulose can still be beneficial, for example adding bulk to faeces decreasing risk of cancers and constipation/ aid digestion(dietary fibre)
Why does lactose intolerance occur
-individuals with lactose intolerance are unable to synthesise a sufficient amount of the enzyme (lactase) that breaks down lactose into glucose and galactose
-> bloating, diarrhoea, cramps
Define GI
glycemic index
a measure of how quickly glucose is released into the bloodstream/hydrolysed after consuming a carbohydrate when compared to 100 grams of pure glucose
name a few low GI foods
lentils, fruit, beans, porridge
name a few high GI foods
lollies, white bread, potatoes
Explain how amylopectin and amylose impact GI of foods
-b/c amylose has a linear structure and is able to pack closer together than amylopectin which has a branched structure, there is a difference in rate of hydrolysis
-then amylose is hydrolysed into glucose at at a slower rate than amylopectin and glucose enters the bloodstream at a slower rate than glucose from amylopectin
Why are low GI foods beneficial for diabetics
release glucose slowly into bloodstream and help reduce the risk of blood sugar levels spiking and rising (decrease stress on beta cells to produce insulin)
list sugars in increasing sweetness order
glucose , sucrose, fructose, aspartame
what class of molecules are triglycerides
esters
how are triglycerides formed
a condensation reaction between three fatty acids and a glycerol molecule
what link forms when a triglyceride forms
ester link between each OH group in the glycerol and COOH group of the fatty acids
how many waters are released when a triglyceride forms
3H2O
Define a saturated fatty acid
a fatty acid with only single bonds present between carbons, for example most animal fats
Are triglycerides polar molecules
no, they are relatively large non polar molecules
Monounsaturated vs polyunsaturated fatty acids
Monounsaturated contains one carbon carbon double bond whereas polyunsaturated contains more than one carbon carbon double bond
general formula of saturated fatty acids
Cn H2n+1 COOH
general formula of monounsaturated fatty acids
Cn H2n-1 COOH
general formula of polyunsaturated fats
Cn H2n-x COOH
where x is 2 times the number of double bonds minus 1
For example lipid w 7 C=C has formula CnH2n-13COOH
is hydrolysis endo/exo thermic
exothermic (breakdown) +catabolic
two ways fatty acids are metabolised
-used to produce energy (respiration)
-adipose storage
What is needed and produced from hydrolysis of triglycerides
-enzyme and 3water needed
-glycerol and 3x fatty acids are produced
Why are enzymes needed for hydrolysis of triglycerides
lowers the Ea to a sufficient/sustainable amount/ensures the rate of reaction is sufficient
What is the difference between essential and non essential fatty acids
essential fatty acids can’t be synthesised by the body whereas fatty acids that the body can synthesis are referred to as non essential.
two categories of fatty acids
omega-3 and omega-6 fatty acids
How are omega-3 and omega-6 fatty acids distinguished
the 3 and 6 refer to the position of the first carbon carbon double bond from the omega end (opposite of the alpha/acid end)
How are trans fats produced
-because trans fats are rarely found in nature
-they can undergo hydrogenation, where the fat becomes partially saturated by adding H across the double bond and most cis bonds that remain unsaturated are converted into trans double bonds
3 ways triglycerides are broken down
oxidative (near double bond)
microbial (e.g interaction with bacteria in gut)
hydrolytic (in body-stomach/small intestine)
define oxidative rancidity
when a triglyceride reacts with oxygen, the carbon carbon double bonds (or bonds near) in unsaturated fatty acids are broken to form single bonds with oxygen, producing highly volatile aldehydes and ketones resulting in unpleasant smells and flavours.
suggest ways to reduce the effect/rate of rancidity
-store food in cool, dark places-fridge
-vacuum packaging food
-use dark containers
-fill containers to lid
Describe how antioxidants work
-antioxidants donate a free electron from their OH group to free radicals this means that the antioxidant is preferentially oxidised, interrupting the propagation of free radicals and delaying/slowing the oxidation of the triglyceride
what class of compound are antioxidants
often vitamins eg E,C
2-amino acid is another name for
alpha amino acid
what reactions do amino acids undergo to form dipeptides
condensation
essential vs non essential amino acids
Essential amino acids can not be synthesised by the body (must be obtained through food) whereas non essential amino acids are produced in the body.
identify 4 protein functions
enzymes, proteins, antibodies, skin/cartilage/muscles
what determines the function of the protein
the R group
what’s the backbone for an amino acid
NH2-CH(R)-COOH
what is a zwitterion
they exist in neutral pH and contain an equal number of positive and negative regions so that they have no net charge
other name for zwitterion
dipolar ion
What does a zwitterion do in alkaline conditions
Because the anion is more abundant then it donates a proton from the COOH and hence forms a COO- region
DEPROTONATES
what does a zwitterion do in acidic conditions
-Because the cation is more abundant then it accepts a proton (acts as a base), the NH2 group forms +NH3
PROTONATES
what bond forms between amino acids joined
peptide bond forms between H from (NH2) and O from (C=OO) of different amino acids
what are amino acid residues
amino acids that are present within the protein
what does the dipeptide bond look like
C=O N-H (amide)
what’s the N and C terminal
amino acid commencing at NH2 end is N-terminal and the amino acid that finishes at COOH end is the C-terminal
Identify protein structures
primary, secondary, tertiary and quaternary
Define primary structure
the sequence of amino acids in the polypeptide chain with strong covalent (peptide) bonds linking each amino acid at the amide link
Describe bonds in primary structure
strong covalent bonds between C and N in the peptide links between amino acids
Define secondary structure
primary structure that is folded into alpha helix, beta pleated sheets and random folding
Whats alpha helix
H bonds that occur between non adjacent N-H groups and -C=O groups at different points along the chain
types of secondary structure
alpha helix, beta pleated sheets, random folding
Describe bonds in Secondary structure
H bonds form between the O from C=O and H on N-H of different/adjacent peptide chains (in the backbone) in alpha helix or beta pleated sheets
Define tertiary structure
the overall 3-d shape that allows the protein to carry out its specific and complementary function which is driven by the R group
Identify bonds in tertiary structure
H bonds , dispersion forces, ion dipole interaction, ionic interactions, disulphide bridges, dipole dipole bonds
Define quaternary structure
arrangement of multiple (two or more) folded protein subunits
What happens to proteins in body
-absorbed into bloodstream and transported to cells of body to make new protein
-left over amino acids are broken down in liver (deamination) where NH2 becomes ammonia.
-rest of protein is stored as a secondary energy source
briefly describe how proteins are digested
-proteins broken down into polypeptides in stomach by proteases eg trypsin
-polypeptides broken down into dipeptides in pancreas
-dipeptides broken down into amino acids in the small intestine
Whats needed for hydrolysis of proteins
water and enzymes
what protein level is changed in hydrolysis
primary
Describe the role of an enzyme
The enzyme and substrate are specific and complementary (fit together perfectly)
The enzyme and substrate form a bond, the active site of the enzyme weakens the bonds of the substrate, lowering Ea and providing an alternative reaction pathway. (enzyme unchanged)
Difference between lock and key vs induced fit model
in the lock and key model the substrate and enzyme fit together perfectly whereas in the induced fit model the enzymes active site changes to accomodate and fit the substrate
define enzyme activity
the amount of substrate converted to product per unit time
define coenzyme
organic molecule that attaches to the active site of an enzyme and changes the surface shape (active site) to allow substrate to bind (functions as intermediate carriers of electrons and/or groups of atoms.)
what protein structures are impacted by denaturation
2,3,4
Why isn’t the primary structure impacted by denaturation
bonds that hold primary structure together (covalent bonds/peptide bonds) require too much heat energy to disrupt
How does temperature denaturation affect enzymes
Increase temperature
Increases average kinetic energy
Molecules vibrate so rapidly that H bonds of the secondary structure, forces in tertiary structure and quaternary structure is disrupted
Active site has changed 3d shape and is no longer specific and complementary to substrate
How does pH denaturation affect enzymes
Changes to the pH solution can change the charge of the basic or acidic components of the R/side groups on the amino acids of the proteins
This causes a change to the tertiary structure of the protein and the active site has changed/been disrupted and is no longer specific and complimentary, reducing enzyme activity
do enzymes catalyse enantiomers
only one of them (the one that is s+c to)
Do coenzymes stay the same structure after reacting
no
How are vitamins classified
fat soluble vs water soluble
What is the difference between fat and water soluble vitamins
Water soluble vitamins contain a higher proportion of OH groups and need to be regularly consumed (because they pass through blood) whereas fat soluble vitamins have long hydrocarbon chains and hence are stores in fats (don’t need to be regularly consumed-can be toxic)
what is aspartame made of
methanol
phenylalanine and aspartic acid
what are free radicals
atoms/group of atoms with an unpaired electron in its outer shell
Features of emulsifying agents
-Polar regions to increase solubility for water component
-Non polar regions to attract fatty components
how does increase solubility improve drugs effectiveness.
can travel in the bloodstream and bind at a better rate hence inhibiting the ___
balanced equation for fermentation of glucose
1glucose –> 2ethanol + 2Carbon dioxide
why is glycine a unique a- amino acid
-no chiral carbon centre
-not a optical isomer
-super imposable
-no R group
Why is aspartame good for low GI
-does not hydrolyse into glucose
-does not impact BGL
why pump oxygen into bomb calimoreter at a high pressure
excess oxygen ensures sufficient oxygen for complete combustion
high pressure=high ror
all = ENSURES REACTION GOES TO COMPLETION
how does an amino acid change in low ph
low ph= acidic so amino acid functions as a base and protonates so the amino group gains a proton(H+) to form NH3 +
how does amino acid change in high ph
high ph=alkaline so amino acid function as acid and deprotonates so the carboxyl group loses a proton(H+) to form COO-
