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AS Biology 9700 > Biological Molecules (2) > Flashcards

Biological Molecules (2) Flashcards

1
Q

What is the formula of glucose

A

C6H12O6

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2
Q

Qualitative test meaning

A

A test that indicates whether a substance is absent or not

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3
Q

Quantitative test meaning

A

A test that allows for the concentration of a substance to be determined

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4
Q

How to do the benedicts’ test for reducing sugars

What are the results

A
  1. Add benedict’s reagent to a sample solution in a test tube
  2. Heat the test tube in a water bath or beaker of water that has been brought to a boil for a few minutes

Reducing sugar present - colored precipitate forms as copper (II) sulfate reduced to copper (I) oxide which is insoluble in water
Color change from blue to brick-red.

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5
Q

What are the benedicts’ test

A

Semi-quantitative as degree of color change gives an indication of how much concentration of sugar is present

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6
Q

What is the iodine test for starch

A

To test for the presence of starch in a sample, add a few drops of orange/brown iodine in potassium iodide solution to the sample

The iodine is in potassium iodide solution as iodine is insoluble in water

If starch is present, iodide ions in the solution interact with the center of starch molecules, producing a complex with a distinctive blue-black color

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7
Q

What is the iodine test useful for

A

Showing that starch sample has been digested by enzymes

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8
Q

What is the emulsion test for lipids

A

Lipids are nonpolar molecules that do not dissolve in water but will dissolve in organic solvents such as ethanol

Add ethanol to the sample to be tested, shake to mix and then add the mixture to a test tube of water

If lipids are present, a milky emulsion will form (the solution appears ‘cloudy’); the more lipid present, the more obvious the milky colour of the solution

If no lipid is present, the solution remains clear

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9
Q

What is the biuret test for proteins

A

A liquid solution of a sample is treated with sodium or potassium hydroxide to make the solution alkaline

A few drops of copper (II) sulfate solution (which is blue) is added to the sample

Biuret ‘reagent’ contains an alkali and copper (II) sulfate

If a colour change is observed from blue to lilac/purple, then protein is present.

The colour change can be very subtle, it’s wise to hold the test tubes up against a white tile when making observations)

If no colour change is observed, no protein is present

For this test to work, there must be at least two peptide bonds present in any protein molecules, so if the sample contains amino acids or dipeptides, the result will be negative

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10
Q

How to do a semi-quantitative benedicts test

A

A semi-quantitative test can be carried out by setting up standard solutions with known concentrations of reducing sugar (such as glucose)

These solutions should be set up using a serial dilution of an existing stock solution

Each solution is then treated in the same way:

Add the same volume of Benedict’s solution to each sample

Heat in a water bath that has been boiled (ideally at the same temperature each time) for a set time (5 minutes or so) to allow colour changes to occur

It is important to ensure that an excess of Benedict’s solution is used

Any colour change observed for each solution of a known concentration in that time can be attributed to the concentration of reducing sugar present in that solution

The same procedure is carried out on a sample with an unknown concentration of reducing sugar which is then compared to the stock solution colours to estimate the concentration of reducing sugar present

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11
Q

How can we change the benedict’s test to standardize it

A

It is also possible to standardise this test but instead of waiting a fixed amount of time for a range of colours to be observed, time how long it takes for the first colour change to occur (blue to green)

The higher the concentration of reducing sugar in a sample, the less time it would take for a colour change to be observed

To avoid issues with human interpretation of colour, a colourimeter could be used to measure the absorbance or transmission of light through the sugar solutions of known concentration to establish a range of values that an unknown sample can be compared against a calibration curve

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12
Q

How can we make serial dilutions

A

Serial dilutions are created by taking a series of dilutions of a stock solution. The concentration decreases by the same quantity between each test tube

They can either be ‘doubling dilutions’ (where the concentration is halved between each test tube) or a desired range (e.g. 0, 2, 4, 6, 8, 10 mmol dm-3)

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13
Q

What are serial dilutions for

A

Serial dilutions are completed to create a standard to compare unknown concentrations against

The comparison can be:

Visual

Measured through a calibration/standard curve

Measured using a colourimeter

They can be used when:

Counting bacteria or yeast populations

Determining unknown glucose, starch, protein concentrations

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14
Q

What is a colorimeter

A

A colorimeter is an instrument that beams a specific wavelength (colour) of light through a sample and measures how much of this light is absorbed by the sample

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15
Q

How is a colorimeter used

A

A colorimeter is an instrument that beams a specific wavelength (colour) of light through a sample and measures how much of this light is absorbed by the sample

Colour filters are used to control the light wavelength emitted

The colour used will be in contrast to the colour of the solution, e.g. Benedict’s solution turns orange in the presence of sugar, so the colorimeter will assess the intensity of the orange colour; in order to do this a blue light filter would be used to shine blue light through the sample

Blue light is absorbed by an orange solution as orange light is reflected to give the orange appearance

The extent to which the blue light is absorbed will differ depending on the intensity of the orange colour; a solution that is orange/green will absorb less blue light than a solution that is brick red

The absorbance value therefore provides a quantitative measure of the strength of the orange colour

Colorimeters must be calibrated before taking measurements

This is completed by placing a blank into the colorimeter and taking a reference; it should read 0 (that is, no light is being absorbed)

This step should be repeated periodically whilst taking measurements to ensure that the absorbance is still 0

The results can then be used to plot a calibration or standard curve

Absorbance against the known concentrations can be used

Unknown concentrations can then be determined from this graph

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16
Q

What is the difference between reducing and non-reducing sugar

A

Sugars can be classified as reducing or non-reducing; this classification is dependent on their ability to donate electrons (a reducing sugar that is able to donate electrons is itself oxidised)

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17
Q

How to test for nonreducing sugars

A

Add dilute hydrochloric acid to the sample and heat in a water bath that has been brought to the boil

Neutralise the solution with sodium hydrogencarbonate

Use a suitable indicator (such as red litmus paper) to identify when the solution has been neutralised, and then add a little more sodium hydrogencarbonate as the conditions need to be slightly alkaline for the Benedict’s test to work

Then carry out Benedict’s test as normal; add Benedict’s reagent to the sample and heat in a water bath that has been boiled – if a colour change occurs (orange-red precipitate), a non-reducing sugar is present

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18
Q

What is the explanation behind test for nonreducing sugars

A

The addition of acid will hydrolyse any glycosidic bonds present in any carbohydrate molecules

The resulting monosaccharides left will have an aldehyde or ketone functional group that can donate electrons to copper (II) sulfate (reducing the copper), allowing a precipitate to form

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19
Q

What are the reducing and nonreducing sugard

A

Reducing
1. Galactose
2. Glucose
3. Fructose
4. Maltose

Nonreducing
1. Sucrose

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20
Q

What forms does glucose have

A

Glucose exists in two structurally different forms – alpha (α) glucose and beta (β) glucose and is therefore known as an isomer

This structural variety results in different functions between carbohydrates

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21
Q

What are polysaccharides

A

Made of many sugar units from condensation reactions where they are joined by a glycosidic bond

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22
Q

What are monomers

A

One of the many small molecules that combine to form a polymer

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23
Q

What is a monosaccharide

A

A single sugar monomer, all of which are reducing sugars

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24
Q

What is a disaccharide

A

A sugar formed from two monosaccharides joined by a glycosidic bond in a condensation reaction

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25
What are macromolecules
A giant molecule
26
What is a polymer
A giant molecule made from many small repeating subunits joined in a chain
27
What structure does glucose have
When in an aqueous solution, it forms a ring structure
28
Where are the hydroxyl groups in Alpha and Beta glucose
Alpha - Below the ring Beta - Above the ring
29
What is a monomer
A simple molecule that is used as a basic building block for the synthesis of a polymer, many monomers are joined together to make the polymer, usually by condensation reactions
30
What is a polymer
A giant molecule made from repeating subunits of monomers
31
Are lipids polymers
No
32
What are macromolecules
These are large and complex molecules that are formed due to the polymerization of smaller monomers
33
What is a monosaccharide
A molecule consists of a single sugar unit, the simplest form of a carbohydrate and cannot be hydrolyzed further. General formula of (CH20)n
34
What is a disaccharide
A sugar molecule consisting of 2 monosaccharides joined together by a glycosidic bond
35
What is a polysaccharide
A polymer whose subunits are monosaccharides joined together by glycosidic bonds
36
What are glycosidic bonds
Covalent bonds that occur between constituent monomers and are formed due to a condensation reaction involving removing a water molecule to form polysaccharides and disaccharides such as sucrose
37
How are glycosidic bonds broken
Hydrolysis (addition of water) can also separate these constituent molecules, which breaks the glycosidic bond between monomers Reverse of condensation This is the reaction that occurs to break non-reducing sugars into reducing sugars when hydrochloric acid is added before benedicts test
38
What is starch
A macromolecule that is found in plant cells Polymer made up of Alpha glucose monomer subunits Contains 1,4 Glycosidic bonds Highly compact and stores energy Made of 2 components - Amylose and Amylopectin
39
What is amylose
Structure - Alpha 1,4 Glycosidic bonds Shape - Helical and more compact Iodine test - Positive
40
What is amylopectin
Structure - Alpha 1,4 and 1,6 glycosidic bonds giving its branched structure Shape - Branched Iodine test - Negative
41
What is glycogen
A macromolecule that is used for the storge of energy in animal cells Polymer made from Alpha glucose subunits The structure of glycogen is similar to that of amylopectin, however it contains more Alpha 1,6 glycosidic bonds and is hence more branched
42
What is cellulose
Found in the cell wall of plant cells Polymer made from Beta glucose units Beta 1,4 glycosidic bonds Alternate Beta glucose molecules are rotated 180 degrees to form these bonds. Hydrogen bonds are also formed between parallel cellulose molecules 60 and 70 cellulose molecules become tightly cross linked to form bundles called microfibrils (10nm) Microfibrils are in turn held together in bundles called fibers (50nm) by hydrogen bonding Fibers increase tensile strength to withstand osmotic pressure, making the plant rigid and determining cell shape Freely permeable
43
What are triglycerides
Formed by condensing 3 fatty acid chains and a glycerol molecule Joined by an ester bond Fatty acid chains are long hydrocarbon chains with a carboxylic head, glycerol is an alcohol containing 3 OH groups Non-polar molecules
44
What are unsaturated fatty acids
Contain C=C bonds that are easier to break and melt easier
45
What are saturated fatty acids
Contain C-C bonds that are solids at room temp
46
What is the role of a triglyceride
Better energy reserves than carbohydrates as more CH bonds Acts as an insulator and provides buoyancy A metabolic source of water gives CO2 and H20 to oxidation in respiration
47
What is a phospholipid
The hydrophilic head contains a phosphate group and glycerol while the hydrophobic tail contains 2 fatty acid chains The partial negative charge on the phosphate group gets attracted to the partial positive charge on the hydrogen atom of the water molecule and thus faces the aqueous environment Not an energy storage but component of cell membrane
48
What is a protein
Made of amino acids which only differ in the R groups/variable side chains and will always contain an amine group, a carboxyl group (acidic) and a hydrogen atom attached to the central carbon atom
49
How do 2 proteins join
A peptide bond is formed by condensation between 2 amino acids forming a dipeptide Many amino acids that join together by peptide bonds form a polypeptide
50
How are peptide bonds broken
When hydrolyzed into amino acids in small intestine and stomach
51
What is the primary structure
The sequence of amino acids in a polypeptide protein A slight change in the sequence can affect the protein's structure and function It has an unique sequence for each protein
52
What is the secondary structure
The structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids 1. Alpha helix - the polypeptide chains twists into a regular spiral and is maintained by hydrogen bonds between the -NH group of one amino acids and the CO- group of another amino acid 4 spaces later in the polypeptide chain 2. Beta pleated sheet - the chain is not tightly coiled and lies in a looser, straighter shape
53
What is the tertiary structure
The compact structure of a protein molecule results form the 3D coiling of the already-folded chain of amino acids Hydrogen bonds between wide varieties of R groups - can be broken by pH and temp changes Disulphide bridges between cysteine molecules - can be broken by reducing agents. Covalent bonds Ionic bonds between R groups containing amine and carboxyl groups - Can be broken by pH changes Hydrophobic interactions between non-polar R groups
54
What is the order of strength of tertiary structure
1. Disulphide 2. Ionic 3. Hydrogen 4. Hydrophobic
55
What is the quaternary structure
The 3D arrangement of two or more polypeptides or a polypeptide and a non-protein component such as haem in a protein molecule The polypeptide chains are held together by bonds in the tertiary structure
56
What are globular proteins
Curl up into a spherical shape with their hydrophobic regions pointing into the center of the molecule and hydrophilic regions pointing outwards Soluble in water
57
What are fibrous proteins
Form long strands are insoluble in water and have structural roles
58
What is hemoglobin
A globular protein that has a quaternary structure with a polypeptide chains , 2 alpha globin and 2 beta globin chains Each chain has a prosthetic haem group containing an iron atom that reversibly binds to an oxygen molecule Oxyhemoglobin is bright red when the haem group is combined with oxygen otherwise its purple
59
What is collagen
A fibrous protein that is present in the skin, bones, teeth, cartilage and walls of blood vessels It is an important structural protein A collagen molecule ha 3 polypeptide chains that are coiled in the shape of a stretched out helix Compact structure and almost every 3rd amino acid is glycine, the smallest amino acid which can form Hydrogen bonds 3 polypeptide strands are held together by hydrogen and covalent bonds Many of these collagen molecules lie side by side linked to each other by covalent cross links between the side chains of amino acids forming fibrils and many fibrils make up a fibre
60
What is water
A water molecule contains 2 hydrogen atoms and one oxygen atom held together by hydrogen bond
61
What is waters role
Water is an effective solvent because of its polarity so that it can form electrostatic interactions with other polar molecules and ions Its a transport medium and reagent for metabolic and other reactions in cells of plants and animals
62
What are properties of water
1. High surface tension and cohesion - Cohesion refers to the attraction of one water molecule to the other - Water molecules have strong, cohesive forces due to hydrogen bonds, thus having high surface tension
63
What is waters density and freezing properties
Ice is less dense than water and floats on it, insulating water and preventing it from freezing, preserving aquatic life underneath it Changes in the density of water with temperature cause currents, which help to maintain the circulation of nutrients in oceans
64
What is waters specific heat capacity
2. High specific heat capacity - The amount of heat energy required to raise the temp of 1kg of water by 1 degree - Water has high SPC due to its hydrogen bonds - Temperature within organisms remains constant compared to external temperature and water bodies also have a slow change in temperature, providing stable aquatic habitats
65
What is waters high latent heat of vaporization
3. High latent heat of vaporization - A measure of the heat energy needed to vaporize a liquid - Water has high LHV due to its high SPC, as H bonds need to be broken before water can be vaporized, cooling the surrounding environment - Sweating is a good cooling mechanism. A large amount of energy is lost for a small amount of water to be vaporized so dehydration is prevented

AS Biology 9700 (4 decks)

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