2.1.2 biological molecules Flashcards
how are the hydrogen atoms bonded to the oxygen atom
2.1.2(a)
covalently bonded
why is a oxygen atom slightly negative and hydrogen atoms slightly positive
2.1.2(a)
the oxygen atom has more protons in its nucleus so it exerts a stronger attraction for the electrons
this means the oxygen atoms become slightly negative and the hydrogen atoms slightly positive
what is a polar molecule
2.1.2(a)
where one end of the molecule is delta positive and the other is delta negative
what is a hydrogen bond
2.1.2(a)
a hydrogen bond is a weak interaction where the delta positive atom of one molecule forms an electrostatic attraction to the delta negative atom in another molecule
this bond is weaker than an ionic or covalent bond
what are the properties of water
2.1.2(a)
- Water is liquid at room temperature, due to the hydrogen bonding between molecules making it difficult for a molecule to escape and turn into a gas. Because of this:
o it is able to form aquatic habitats
o it can provide an aqueous environment inside cells and tissues for chemical reactions
o it can provide an effective transport medium e.g. blood, water in xylem vessels - Ice is less dense than liquid water because the hydrogen bonds hold it in a crystal lattice structure as it freezes
o ice floats on top of water, insulating aquatic habitats and preventing them from freezing - Water is a good solvent because polar or charged substances are able to dissolve in it
o this allows chemical reactions between solutes to take place
o and also allows transport of charged or polar molecules around organisms - Water shows cohesion where water molecules stick together due to hydrogen bonding
o allows a continuous column of water to be pulled up the xylem
o and insects like pond-skaters can walk on water due to the surface tension (ability of surface of water to resist force applied to it) - Water has a high specific heat capacity, which is the amount of heat energy needed to raise the temperature of 1kg of water by 1oC.
o SHC of water = 4.2 kJ kg-1 oC-1
o This means that water does not change temperature easily
o Provides stable aquatic environments
o Helps organisms maintain stable internal temperatures - Water has a high latent heat of vaporisation, which is the energy absorbed by liquid water before it turns into a gas (evaporates)
o allows animals to pant or sweat to cool down
o the water in the saliva / sweat absorbs heat from their bodies and then evaporates
o this removes the heat from their body (blood)
what is a monomer
2.1.2(b)
small molecule
what is a polymer
2.1.2(b)
many monomers bonded together
what is a condensation reaction
2.1.2(b)
forms a covalent bond between two monomers
h2o is a product
what is hydrolysis
2.1.2(b)
breaks a covalent bond between monomers
h2o is used/reactant
which molecules are organic molecule
2.1.2(c)
all biological molecules EXCEPT water
table?
2.1.2(c)
….
what is a monosaccharide
2.1.2(d)
a single sugar unit
simplest carbohydrate
monomer
what ae monosaccharides an immediate source of
2.1.2(d)
energy inside cells-the most important example of this is glucose
what is the solubility of monosaccharides
2.1.2(d)
monosaccharides are soluble in water
what type of sugar is glucose
2.1.2(d)
hexose sugar
why is glucose needed by all living things
2.1.2(d)
as an immediate source of energy for respiration to produce ATP
what are the polymers of glucose and what are they useful for
2.1.2(d)
starch and glycogen (storage)
cellulose (tensile strenght)
where is the OH group in Beta glucose
2.1.2(d)
above the ring on C1
draw the structure of alpha vs beta glucose
2.1.2(d)
in booklet
what type of sugar is ribose
2.1.2(d)
pentose sugar (5C)
which structure is ribose needed for
2.1.2(d)
it is needed for the structure of RNA
what structure is deoxyribose needed for
2.1.2(d)
DNA molecules
it has a similar structure to ribose
where is deoxyribose missing an oxygen atom
2.1.2(d)
oxygen is missing on the 2cd carbon
draw ribose vs deoxyribose
2.1.2(d)
when is a disaccharide formed
2.1.2(e)
when two monosaccharides are joined together by a condensation reaction forming a glyosidic bond
like monosaccharides what are disaccharides
2.1.2(e)
sweet and soluble
which sugars are reducing
2.1.2(e)
maltose and lactose
which sugars are non-reducing
2.1.2(e)
sucrose
what is maltose made from
2.1.2(e)
alpha glucose + alpha glucose
what is sucrose made from
2.1.2(e)
alpha glucose + fructose
what is lactose made from
2.1.2(e)
beta glucose + galactose
how does a condensation reaction take place
2.1.2(e)
in booklet
what are polysaccharides
2.1.2(e)
polymers of monosaccharides
what is starch a mixture of
2.1.2(f)
polymers of alpha glucose found in plants
what is the function of starch
2.1.2(f)
to provide a store of alpha glucose
how are alpha glucose monomers released
2.1.2(f)
by hydrolysis reactions at the end of polymer chains
what is the name of the two polymers that make up starch
2.1.2(f)
amylose and amylopectin
what is amylose a long chain of
2.1.2(f)
alpha glucose molecules
how is amylose joined together
2.1.2(f)
by alpha 1,4 glyosidic bond
what is the structure of amylose
2.1.2(f)
it has a compact spiral shape held together by hydrogen bonds between the OH groups
what does amylopectin consist of
2.1.2(f)
long chains of alpha glucose molecules
what is amylopectin joined together by
2.1.2(f)
alpha 1,4 glyosidic bonds
it also has alpha 1,6 glyosidic bonds that allow branches off of the main chain
where is the alpha glucose molecule in glycogen found
2.1.2(f)
in animals
what does glycogen consist of
2.1.2(f)
very many chains of alpha glucose monomers
how is glycogen held together
2.1.2(f)
by alpha 1,4 glyosidic bonds
it also has alpha 1,6 glyosidic bonds which give them a branched structure (it has more 1,6 bonds than amylopectin)
what is the cell wall polysaccharide in plants
2.1.2(f)
cellulose
what are the long chains in cellulose made from
2.1.2(f)
it is made of long chains of beta glucose, joined by condensation reactions forming beta 1,4 glyosidic bonds
what is the structure of cellulose
2.1.2(f)
-not branched
-parallel side by side cellulose chains are held together by hydrogen bonds
what is the orientation of beta glucose molecules in plants
2.1.2(f)
180 degrees
what helps keep the chains straight
2.1.2(f)
flipping of beta molecule 180 degrees
intramolecular (within an individual cellulose chain) hydrogen bonds
how are microfibrils and macrofibrils formed
2.1.2(f)
cellulose chains lie side by side and bundle together through intermolecular hydrogen bonds
what is the main function of glucose
2.1.2(g)
to provide an immediate source of energy to be released at ATP in respiration
what type of sugar is glucose
2.1.2(g)
reducing sugar
since glucose is a reducing sugar what properties does this give it
2.1.2(g)
its very reactive so easily enters metabolic reactions
since glucose is a polar what properties does this give it
2.1.2(g)
glucose is polar due to exposed OH groups meaning it is soluble in water
since glucose is soluble what properties does this give it
2.1.2(g)
o So it dissolves in the cytoplasm and can therefore take part in metabolic reactions in the cytoplasm
o And it can be transported easily e.g. by dissolving into the blood plasma
what are amylose and amylopectin storage molecules for
2.1.2(g)
alpha glucose molecules
since amylose and amylopectin have a coiled structure what properties does this give them
2.1.2(g)
- The coiled structure is compact, so large amounts of glucose can be stored in relatively small volumes in the cell
what can happen to the ends of the chain in amylose and amylopectin
2.1.2(g)
- The ends of the chains can be hydrolysed to release alpha-glucose
since amylopectin is branched what properties does this give it
2.1.2(g)
o Amylopectin is branched due to alpha-1,6-glycosidic bonds, which means there are more exposed chain ends, increasing the surface area available for hydrolytic enzymes to act on
are polysaccharides soluble
2.1.2(g)
no
since polysaccharides aren’t soluble what don’t they effect
2.1.2(g)
- Polysaccharides are not very soluble, so they do not affect the water potential of the cell cytoplasm, and so will not cause water to enter by osmosis
what is glycogen the storage molecule for
2.1.2(g)
alpha-glucose in animals
why do animals have a higher metabolic rate than plants
2.1.2(g)
as animals are able to move around
what does the structure of glycogen make it good for
2.1.2(g)
storage
rapid release of alpha-glucose
what structure does glycogen have
2.1.2(g)
- Compact coiled and branched structure, so large amounts of glucose can be stored in small volumes in the cell
since glycogen is highly branched what does this give it
2.1.2(g)
Glycogen is highly branched, giving it a very high surface area with very many exposed alpha-glucose molecules at the ends of the branches
since glycogen has very many exposed alpha-glucose molecules at the ends of the branches
2.1.2(g)
o Hydrolytic enzymes can therefore release alpha-glucose from glycogen very quickly
o This provides alpha-glucose rapidly to meet the demands of animals’ high metabolic rate and rate of respiration
is glycogen soluble
2.1.2(g)
- Glycogen is not very soluble so doesn’t affect the water potential of cell cytoplasm, and so will not cause water to enter by osmosis
what properties do cellulose microfibrils and macrofibrils have
2.1.2(g)
very high tensile strength due to the hydrogen bonding between adjacent chains
ms
-inert
-insoluble
what does the high tensile strength of the cell wall prevent
2.1.2(g)
- High tensile strength of the cell wall prevents plant cells from bursting when they take in water by osmosis, becoming turgid instead
what do lipids contain large amounts of and what do they contain smaller amounts of
2.1.2(h)
they contain large amounts of carbon and hydrogen
and smaller amounts of oxygen
why are lipids insoluble in water
2.1.2(h)
because they are not polar and so do not attract water molecules
what do lipids dissolve in
2.1.2(h)
they do dissolves in alcohols eg-ethanol
why are alcohols such as ethanol known as non-polar solvents
2.1.2(h)
alcohols,such as ethanol are known as non-polar solvents due to their ability to dissolve non-polar molecules
what are triglycerides, phospholipids and steroids
2.1.2(h)
the three most important lipids in living things
they are examples of macromolecules
why are triglycerides, phospholipids and steroids not polymers
2.1.2(h)
because they are not made up of repeating units
what are triglycerides made from
2.1.2(h)
1 glycerol and 3 fatty acids
what are triglycerides joined by and when are they formed
2.1.2(h)
chemically joined by ester bonds formed duing a condensation reaction
what are some properties of a triglyceride
2.1.2(h)
-large
-non-polar
-hydrophobic-insoluble in water
draw the structure of a triglyceride
2.1.2(h)
in booklet
what is glycerol and what is it an example of
2.1.2(h)
glycerol is a three carbon molecule with three OH groups
it is an example of an alcohol
-
draw the structure of glycerol
2.1.2(h)
in booklet
structure of fatty acids
2.1.2(h)
Fatty acids have a carboxyl group -COOH at one end, attached to a hydrocarbon tail, made of only C and H atoms
how long is the hydrocarbon tail
2.1.2(h)
This could be short or up to >22 carbons in length
why is a fatty acid an acid
2.1.2(h)
A fatty acid is therefore an acid because it can produce free H+ ions.
what is the difference between saturated and unsaturated fatty acids
2.1.2(h)
if its saturated it contains no c=c so fully saturated with hydrogens
in unsaturated fatty acids there is atleast one c=c not fully saturated with hydrogens
how does having more more than one c=c change the shape of the hydrocarbon
2.1.2(h)
Having one of more C=C bonds changes the shape of the hydrocarbon chain, giving it a kink where the double bond is. Because these kinks push the fatty acid molecules apart slightly, fewer intermolecular forces are able to form between the fatty acids, and the fatty acids do not pack closely together. As a result, the melting point of the fatty acids is lowered.
what state are unsaturated fatty acids ART
2.1.2(h)
liquids
what are phospholipids made from
2.1.2(h)
2 fatty acids, 1 glycerol and 1 phosphate group (charged)
what does a triglyceride consist of
2.1.2(i)
one glycerol molecule bonded to three fatty acids
how does a condensation reaction occur in a triglyceride
2.1.2(i)
A condensation reaction happens between the -COOH group of the fatty acid and the -OH of the glycerol
what else is produced when making a triglyceride
2.1.2(i)
a water molecule
a covalent bond known as an ester bomd
how can ester bonds be broken
2.1.2(i)
The ester bonds can also be broken by adding water in a hydrolysis reaction, forming a di- or monoglyceride
how are phospholipids formed
2.1.2(i)
Phospholipids are formed in exactly the same way as triglycerides – condensation reactions forming ester bonds between a glycerol molecule, one phosphate group, and two fatty acids
what are the functions of triglycerides
2.1.2(j)
-energy source
-insulation
-buoyancy
-protection
what are the two ways triglycerides can be used as an energy source
2.1.2(j)
triglycerides are first hydrolysed to form fatty acids and glycerol. These can then enter the respiration reactions to produce ATP
triglycerides are insoluble so can be stored inside cells. In mammals, triglycerides are stored inside adipose cells
how can triglycerides be used as insulation
2.1.2(j)
adipose tissue is a thermal insulator. Lipids are also found surrounding neurons, where they act as electrical insulators
how do triglycerides show buoyancy
2.1.2(j)
lipids are less dense than water, and so can be used by aquatic animals to help them stay afloat
how do triglycerides provide protection
2.1.2(j)
visceral fat surrounds organs and acts as a shock absorber
what do phospholipids form
2.1.2(j)
Phospholipids form the phospholipid bilayer
hydrophilic head orientate out an form hydrogen bonds to water
hydrophobic tails point inwards and can form hydrogen bonds to water
draw a diagram of a phospholipid
2.1.2(j)
in booklet
are the fatty acid tails polar or non-polar
2.1.2(j)
The two fatty acid tails are non-polar and so are hydrophobic and tend to orientate away from water
what group of lipids is cholesterol a part of
2.1.2(j)
Cholesterol is part of a group of lipids called steroid
what structure are steroids based on
2.1.2(j)
Steroids are based on a ring structure
how many carbon-based rings does cholesterol have and what properties does it have
2.1.2(j)
Cholesterol has four carbon-based rings. It is small and hydrophobic
what cells are cholesterol found is
2.1.2(j)
Cholesterol is only found in animal cells, never in plant cells
what can cholesterol be converted into
2.1.2(j)
Cholesterol can be converted into steroid hormones including testosterone and oestrogen, amongst others. These hormones are able to cross the cell surface membrane
what does cholesterol do when external temperature decreases
2.1.2(j)
When the external temperature decreases, cholesterol increases the fluidity of the cell surface membrane by preventing fatty acid tails from packing too closely together
what does cholesterol do when external temperature increases
2.1.2(j)
When the external temperature increases, cholesterol decreases the fluidity of the cell surface membrane by helping the phospholipids to pack more closely together
what are amino acids the monomer of
2.1.2(k)
Amino acids are the monomers that make up polypeptides and therefore protein
draw the structure of an amino acid
2.1.2(k)
in booklet
draw the structure of an amino acid
2.1.2(k)
in booklet
which part of an amino acid can differ between different amino acids
2.1.2(k)
The R group is the part that can differ between different amino acids
different R groups will have different BLANK properties
and name examples
2.1.2(k)
Different R groups have different chemical properties.
charged
polar
hydrophilic
non-polar
hydrophobic
what will the chemical properties of the R group have an impact on
2.1.2(k)
The chemical properties of the R groups of the amino acids making up a polypeptide will have a large impact on the structure and function of the final protein.
what are amino acids joined together by
2.1.2(l)
Amino acids are joined together by covalent bonds called peptide bond
what does making and breaking a peptide bond involve
2.1.2(l)
Making this bond involves a condensation reaction, and breaking it involves a hydrolysis reaction
what are 2 amino acids joined together known as
2.1.2(l)
Two amino acids joined together are known as a dipeptide
what does joining a longer chain of amino acids form
2.1.2(l)
Joining a longer chain of amino acids together by peptide bonds forms a polypeptide.
Glycine’s R group is H. Draw two glycine molecules. Circle the parts of the molecules that will take part in the condensation reaction.
2.1.2(l)
in booklet
Draw the dipeptide that would be formed & include the other product. Label the bond between the two amino acids
2.1.2(l)
in booklet
what is a protein
2.1.2(m)
A protein is a long chain of amino acids joined by peptide bonds (a polypeptide), usually folded into a specific three-dimensional shape
how are proteins diverse in structure and function
2.1.2(m)
Because there are 20 different amino acids, and a polypeptide can be up to around 30,000 amino acids long, proteins are extraordinarily diverse in structure and function
what is the primary structure
2.1.2(m)
sequence of amino acids bonded by peptide bonds
what is the secondary structure
2.1.2(m)
folding of the polypeptide chain held in place by hydrogen bonds-alpha helix or beta pleated sheet
what is the secondary structure held together by
2.1.2(m)
The secondary structure is held together by hydrogen bonds between the -NH group of one amino acid, and the -CO group of another
why are the secondary structure motifs not unique to any one protein
2.1.2(m)
These groups are found in every amino acid -NH and -CO
what are the two secondary structure motifs called
2.1.2(m)
The two secondary structure motifs are alpha-helices and beta-pleated sheets.
what does the tertiary structure give an individual protein
2.1.2(m)
gives an individual protein its unique three-dimensional shape
what is the tertiary structure held in place by
2.1.2(m)
Tertiary structure is held together by several different types of bond, between the R groups of amino acids in the primary structure
what may the bonds be between the R groups of the amino acid
2.1.2(m)
Hydrogen bonds between polar R groups
· Ionic bonds between positively and negatively charged R groups
· Disulphide bridges – very strong covalent bonds between S atoms on the R groups of cysteine amino acids
· Hydrophobic and hydrophilic interactions – hydrophobic R groups tend to associate together, pointing towards the inside of the polypeptide. Hydrophilic R groups tend to fold towards the outside, to form hydrogen bonds with water
what is the quaternary structure
2.1.2(m)
more than one polypeptide chain
what is the bonding in the quaternary structure
2.1.2(m)
Usually the quaternary structure is held together by hydrogen bonding between the different polypeptides
what shape and structure does a globular protein have
2.1.2(n)
spherical structure
tertiary structure
what is a globular proteins solubility
2.1.2(n)
soluble in water
what roles do globular proteins carry out
2.1.2(n)
They often have metabolic roles within an organism and a specific tertiary structure that allows them to carry out this role
what are some examples of globular proteins
2.1.2(n)
enzymes, eg-pepsin
hormones eg-insulin
transport proteins eg- haemoglobin
what does pepsin do
2.1.2(n)
Pepsin is an enzyme that catalyses hydrolysis of proteins into amino acids during digestion
what is the solubility of pepsin
2.1.2(n)
It is soluble in water so that it is able to catalyse reactions in an aqueous environment
as hydrophillic R groups point out
what is the tertiary structure in pepsin held together by
2.1.2(n)
The tertiary structure is held together by hydrogen bonds and disulphide bridges
what do disulphide bridges do
2.1.2(n)
Disulphide bridges help to stabilise the tertiary structure.
since pepsin has lots of amino acids with acidic R groups what does this help stabilize
2.1.2(n)
Pepsin has very many amino acids with acidic R groups, which also helps to stabilise the enzyme at the very low pHs in the stomach
since pepsin has a highly specific are called the active site what does this mean
2.1.2(n)
The highly specific area called the active site. The specificity of this area means that pepsin is able to bind to its complementary substrate.
what are hormones
2.1.2(n)
Hormones are chemicals that travel in the blood and bind to cell surface receptors on target cells, which then carry out a response
what type of hormone is insulin
2.1.2(n)
Insulin is a peptide hormone, meaning that it is made of polypeptides.
how many polypeptide chains is insulin made from
2.1.2(n)
Insulin is made of two polypeptide chains, which are each folded into a tertiary structure, and then bonded to each other by disulphide bridges
why is insulin soluble in the blood plasma
2.1.2(n)
Insulin is soluble in the blood plasma because the amino acids with hydrophilic R groups are folded to the outside of the polypeptides, so that they can hydrogen bond to water
where are hydrophobic R groups folded
2.1.2(n)
Hydrophobic R groups are folded into the middle of the polypeptides so that they don’t interact with water.
why does insulin need a highly specific tertiary structure
2.1.2(n)
. This is needed because it has to bind to its complementary cell surface receptor on target cells. Insulin binds to glycoprotein receptors on the cell surface receptors on fat and muscle cells to increase their uptake of glucose from the blood.
what type of protein is hemoglobin
2.1.2(n)
Haemoglobin is a transport protein found in red blood cell
what does hemoglobin bind to here
2.1.2(n)
It binds to oxygen in the lungs and then releases oxygen in order to transport it around the body
what is hemoglobin made up of
2.1.2(n)
It is made of 4 polypeptide chains , two α and two β, which are held together by ionic bonding, hydrogen bonds and hydrophobic interaction
with 4 haem groups
what type of structure does hemoglobin have
2.1.2(n)
Because it’s made of more than 1 polypeptide chain, hemoglobin has a quaternary structure
why is it important for hemoglobin to be soluble in water
2.1.2(n)
Because haemoglobin is found in red blood cell cytoplasm it is important for it to be soluble in water. The hydrophilic R groups in the polypeptide chains are folded to the outside of the molecule so that they can form hydrogen bonds with water
what type of component does hemoglobin have in each polypeptide chain
2.1.2(n)
Haemoglobin also has a non-protein component in each polypeptide chain
why is haemaglobin a conjugated protein
2.1.2(n)
so haemoglobin is a conjugated protein because it has a non-protein prosthetic group
what is the name of the prosthetic group in haemaglobin
2.1.2(n)
The name of the prosthetic group in haemoglobin is a haem group
what is there in the centre of the haem group
2.1.2(n)
In the centre of the haem group there is an iron ion, which is the part that can bind to oxygen
unlike globular proteins what do fibrous proteins have
2.1.2(o)
fibrous proteins have regular, repetitive structures insoluble in water-form connective tissues
strong-high tensile strength
what do these features enable them to do
2.1.2(o)
These features enable them to form fibres, which tend to have a structural function
what aren’t fibrous proteins
2.1.2(o)
metabolically active
what type of proteins is collagen
2.1.2(o)
Collagen is a major structural protein, making up about ¼ of all the protein in your body.
where is collagen found
2.1.2(o)
It is found in tendons, skin, internal organs, bones and teeth.
what s collagen composed of
2.1.2(o)
Collagen is composed of three polypeptide chains, twisted together in a tight triple helix
what are the properties of collagen?
2.1.2(o)
strong, flexible and insoluble
how many amino acids does each chain have
2.1.(o)
Each chain is over 1400 amino acids long
what form the entire structure of each polypeptide chain in collagen
2.1.2(o)
A repeated sequence of three amino acids forms the entire structure of each polypeptide chain.
what is keratin made of and what is it rich in?
2.1.2(o)
Keratin is made of long polypeptide strands, rich in cysteine
since keratin is rich is cysteine what does this mean
2.1.2(o)
so that neighbouring strands can be held together by disulphide bridges. This makes keratin fibres extremely strong
what is the secondary structure of an individual keratin polypeptide similar to
2.1.2(o)
The secondary structure of an individual keratin polypeptide is similar to an α helix
where is keratin found
2.1.2(o)
Keratin is found in body parts that need to be hard and strong, for example fingernails, claws, hooves, horns, scales, fur and feathers
what does keratin provide
2.1.2(o)
provides mechanical protection, but also an impermeable barrier to infection because it is waterproof
what is elastin made up of
2.1.2(o)
Elastin is made of many coiled and cross-linked polypeptides that make its structure strong and stretchy
once elastin is stretched what does this mean
2.1.2(o)
Once stretched, it can recoil back to its original shape
what tissues is elastin found in
2.1.2(o)
Elastin is found in many tissues, for example skin, lung tissue, the bladder, and blood vessels.
what does the presence of elastin mean
2.1.2(o)
The presence of elastin means that these tissues can stretch and recoil.
eg- lung tissue stretches as the alveoli fill with air.
what key biological processes are inorganic molecules used for
2.1.2(p)
· are essential components of bones and shells
· are involved in the maintenance of correct concentrations of body fluids
· are important for transmission of action potentials and muscle contraction
· maintain the pH balance of the body
· activate enzymes
· are used to synthesise vitamins and hormone
name all the ions
2.1.2(p)
in booklet
how to carry out the biuret test
2.1.2(q)
- the solution needs to be alkaline so add a few drops of NaOH
2.then add some copper(11) sulphate
3.protein=purple
no protein=blue
what is the biuret solution a mixture of
2.1.2(Q)
sodium hydroxide and copper sulphate
how does the lilac colour form in the biuret test
2.1.2(q)
The lilac colour is a complex between the nitrogen atoms in a peptide chain and Cu2+ ions – this test is actually detecting the presence of peptide bonds.
what do reducing sugars include
2.1.2(q)
Reducing sugars include all monosaccharides, and some disaccharides. They are called reducing sugars because they are able to reduce, or give electrons to, other molecules
how do you carry out a test for reducing sugars
2.1.(q)
- Add Benedict’s reagent to a food sample.
- Heat to 95oC
- Brick-red precipitate will form
when is a orange red precipitate formed
2.1.2(q)
The orange-red precipitate is formed when the reducing sugars donate electrons to Cu2+ ions, reducing them to Cu+ ions. Cu+ forms orange-red copper (I) oxide (Cu2O), which is a solid, so it comes out of solution.
what does it mean if there is a higher concentration of reducing sugars
2.1.2(q)
The higher the concentration of reducing sugars, the more copper (I) oxide will be formed, and so the greater the extent of the colour change
how is the benedict’s test semi-quantitative
2.1.2(q)
The colours of different samples can be compared to each other, giving “semi-quantitative” data e.g. you could conclude which of the samples had the highest concentration of reducing sugars. However, you would not be able to tell exactly what that concentration was
how can you use a reagent test strip to test for reducing sugars
2.1.2(q)
These are dipped into the test solution and compared with a provided colour chart. This can give an estimate of the concentration of reducing sugars in the sample. These are often used to test for glucose in the urine of diabetic people
what are many non-reducing sugars
2.1.2(q)
disaccharides
since non-reducing sugars aren’t vey reactive what does this mean
2.1.2(q)
They are not very reactive and so they are not able to donate an electron to reduce the Cu2+ ions in Benedict’s solution. Therefore they will produce a negative test result (solution remains blue).
to test for non-reducing sugars what do you have to do first
2.1.2(q)
we first have to hydrolyse the glycosidic bond between the monosaccharides. This will free up the reducing groups on each monosaccharide, and therefore a positive result with Benedict’s solution will be obtained
what are the steps to test for a non -reducing sugar
2..2(q)
- Boil the sample with hydrochloric acid to hydrolyse the disaccharide into monosaccharides.
- Cool the solution
- Neutralise the solution using plenty of sodium hydrogencarbonate solution
- Test for reducing sugars following the Benedict’s protocol
how do you test for starch
2.1.2(q)
add iodine
if starch is present the mixture will go from orange to blue/black
how do you test for lipids
2.1.2(q)
- take a food sample mix it with ethanol then filter
2.takw the ethanol/food solution and pour it into water - if a milky emulsion is seen lipids are present
what is a biosensor
2.1.2(r)
A biosensor is a piece of digital equipment that converts a biological or chemical variable into an electrical signal
how does a biosensor work
2.1.2(r)
the transducer can detect the number of binding events in 1 second, and convert this into an electronic signal. The signal conditioner can convert this information into a concentration value, and output this onto a screen
what do cu2+ ions reduce to in benedict’s quantitative test
2.1.2(r)
The reducing sugars reduce Cu2+ to Cu+.
in Benedict’s quantitative solution, the Cu+ ions form white copper (I) thiocyanate. Like copper (I) oxide, this is a solid. Therefore the colour change is from blue to white.
how is the white precipitate separated
2.1.2(r)
The white precipitate is then separated from the liquid using a centrifuge. A centrifuge spins mixtures causing them to separate by density. The solid precipitate will settle at the bottom of the centrifuge tube, allowing the remaining liquid to be analysed
testing for reducing sugars using quantitative test
2.1.2(r)
in booklet
what does a higher concentration of reducing sugars mean
2.1.2(r)
more white precipitate
solutions will be colourless after centrifuge
what does a lower concentration of reducing sugars mean
2.1.2(r)
less white precipitate will form
solution wil be more blue after centrifuge
what happens once the liquid is collected into a cuvette
2.1.2(r)
Once the liquid has been collected into a cuvette, it can be analysed using a colourimeter.
how does a colourimeter work
2.1.2(r)
colourimeter works by shining light through a sample and detecting how much of that light was absorbed or transmitted by the sample. This gives a quantitative value
how are colourimeters zeroed
2.1.2(r)
Colourimeters have to be zeroed between each reading using distilled water, to re-set the value for 100% transmission / 0% absorbance.
why are colour filters used
2.1.2(r)
An appropriate colour filter can optionally be used. This helps to avoid some of the light being reflected (neither transmitted nor absorbed) which would affect the accuracy of the reading. A red filter can be used when measuring blue solutions because a blue solution should not reflect any red light.
what is the aim of chromatography
2.1.2(s)
the aim of chromatography is to separate mixtures into its components
what is the stationary phase
2.1.2(s)
silica gel
what is the mobile phase
2.1.2(s)
a solvent
-if the molecules are non-polar a non-polar solvent would be selected
what is the RF value
2.1.2(s)
distance travelled by spot/solvent front
if the components are colourless what are the two solutions
2.1.2(s)
UV light-TLC plates glow under UV light the spots would appear as dark blobs against the glowing background
ninhydrin-stain that binds to amino acids making the spot of amino acids visible
what 2 properties determine how molecules separate in chromatography
2.1.2 (s)
more soluble in the solvent=travels further
less polar=less adsorption to the stationary phase=travels further
