biological molecules Flashcards

Question

what is the structure of glucose

Answer 1

glucose is a hexose (6 - carbon) sugar formula (C6H12O6) atoms of carbon, hydrogen and oxygen can be arranged in many different ways e.g.glucose has two isomers alpha glucose and beta glucose

Answer 2

reduction is a chemical reaction involving the gain of electrons or hydrogen. A reducing sugar is therefore a sugar that can donate electrons to another chemical (it can reduce other chemicals). We can use this quality to identify if sugars are reducing using Benedict's reagent

Answer 3

monosaccharides and disaccharides (e.g. maltose) | are reducing sugars

Answer 4

we use the Benedict's test

Answer 5

Benedict's reagent

Answer 6

Benedict's reagent is an alkaline solution of copper (II) sulfate. When a reducing sugar is heated with Benedict's reagent it forms an insoluble red percipitate of copper (I) oxide

Answer 7

Add 2cm3 of food sample to be tested to a test tube. If the sample is not already in liquid form, grind it up in water Add an equal volume of Benedict's reagent to the test tube Heat the mixture in a gently boiling tube for five minutes and wait for colour change

Answer 8

blue (none) green (very low) yellow (low) orange (medium) red (high)

Answer 9

-glucose joined to glucose forms maltose glucose joined to fructose forms sucrose glucose joined to galactose forms lactose

Answer 10

when a monosaccharide join, a molecule of water is removed and the reaction is therefore called a condensation The bond formed is called a glycocidic bond

Answer 11

when water is added to a disaccharide it breaks down (under suitable conditions) releasing the consituent monosaccharides. This is called hydrolysis (addition of water that causes breakdown)

Answer 12

``` some disaccharides (e.g. sucrose) are known as non - reducing sugars This is because they do not change the colour of Benedict's reagent when heated with it ```

Answer 13

To test for non reducing sugars we must hydrolyse it into its monosaccharides components by hydrolysis If the sample is not in liquid form it must be ground up in water first method: Add 2cm3 of the food sample being tested to 2cm3 of Benedict's reagent in a test tube and filter place test tube in a gently boiling water bath for 5 mins. If the Benedict's regent does not change colour (solution remains blue) , then a reducing sugar is not present Add another 2cm3 of the food sample to 2cm3 of hydrochloric acid in a test tube and place the test tube in a gently boiling water bath for 5 mins. The dilute hydrochloric acid will hydrolyse any disaccharide present into its consituent monosaccharide Slowly add sodium hydrogencarbonate solution to the test tube in order to neutralise the hydrochloric acid. Test with pH paper to check that the solution is alkaline Re- test the solution by heating with 2cm3 of Benedict's reagent in a gently boiling water bath for 5 mins if non- reducing sugar was present in the original sample the reagent should turn orange - brown. This is due to the reducing sugars that were produced from the hydrolysis of the non - reducing sugar

Answer 14

polysaccharides are polymers formed by combining together many monosaccharide molecules

Answer 15

very large molecules they are insoluble molecules. This feature makes them suitable for storage

Answer 16

they are broken down into disaccharides/monosaccharides

Answer 17

starch cellulose glycogen

Answer 18

starch is a polysaccharide that is found in many parts of plants in the form of small grains especially large amount occur in seed and storage organs (potato tubers)

Answer 19

starch is formed by joining 200 and 100000 together alpha glucose molecules by glycosidic bonds in a series of condensation reaction

Answer 20

starch is easily detected by its ability to change colour of the iodine in potassium iodide solution from yellow to blue black method Place 2cm3 of the sample being tested into a test tube (or add two drops of the sample into a depression on a spotting tile) add two drops of iodine solution and shake or stir the presence of starch is indicated by a blue black coloration

Answer 21

the various different ways they combine with the smaller molecules to form them

Answer 22

it forms an important component of food and is the major energy source in most diets

Answer 23

made up of chains of alpha glucose the chains may be branched or unbranded unbranded chains are wound into a tight coils that makes the molecules compact The OH groups are pointing inwards and these form hydrogen bonds that hold the helix in place

Answer 24

insoluble therefore water is not drawn into the cells by osmosis large and insoluble does not diffuse out of the cells compact a lot of it can be stored into a small space when hydrolysed it forms alpha glucose which is both easily transported and readily used in respiration branched form has many ends, each of which can be acted on by enzymes simultaneously meaning that glucose are released very rapidly (for respiration)

Answer 25

starch is never found in animal cells so it is found in plant cells

Answer 26

glycogen is found in animal and bacteria cells but never plant cells

Answer 27

the structure of glycogen is similar to starch but has many shorter chains and is highly branched

Answer 28

major carbohydrate storage of animals the mass of carbohydrates is relatively small because fat is the main storage in animals

Answer 29

in animals it is stored as small granules mainly in the muscles and liver

Answer 30

similar to starch except it is more highly branched than starch. Therefore it has more ends that can be acted on simultaneously by enzymes. This means more rapidly hydrolysed to form glucose monomers which are used in respiration. This is important to animals which have a higher metabolic rate and therefore respiratory rate than plants because they are more active

Answer 31

cellulose is made from beta glucose. This produces a fundamental difference in the structure and function of the polysaccharide e.g. rather than forming a coiled chain like starch, cellulose has straight, unbranded chains

Answer 32

has straight unbranded chains. These run parallel to one another, allowing hydrogen bonds to form cross linkages between adjacent chains the OH group occur on both sides of the molecule so it can form hydrogen bonds with other chains on both sides

Answer 33

while each individual hydrogen bond adds very little to the strength of the molecule, the sheer overall number of them makes considerable contribution to strengthening cellulose This contributes to strengthening cellulose

Answer 34

cellulose molecules group together to form microfibrils which in turn are arranged in parallel groups called fibres cellulose is a major component of plant cell walls and provides rigidity to the plant cell. The cellulose cell wall also prevents the cell from bursting as water enters by osmosis

Answer 35

it does this by exerting an inward pressure that stops any further influx of water. As a result, living plant cells are turgid and push against one another, making woody parts of the plant semi rigid This is especially important in maintaining stems and leaves in a turgid state so that they can provide the maximum surface area for photosynthesis

Answer 36

chains run parallel with each other and are crossed linked by hydrogen bonds which add collective strength these molecules are grouped to form fibres all of which adds more strength

Answer 37

lipids are varied group of substances that share certain characteristics

Answer 38

they contain carbon, hydrogen and oxygen they are insoluble They are soluble in organic solvents such as alcohols and acetone Fats are solid at room temp (10-20 C) whereas oils are liquid

Answer 39

the main groups of lipids are triglycerides (fats and oils) and phospholipids

Answer 40

lipids have many roles : IN MEMBRANES SOURCE OF ENERGY WATERPROOFING INSULATION PROTECTION

Answer 41

IN MEMBRANES one role of lipids is in the cell membranes (cell - surface membranes and membranes around organelles). Phospholidpids contribute to the flexibility of membranes and the transfer lipid soluble substance across them

Answer 42

SOURCE OF ENERGY | when oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water

Answer 43

WATERPROOFING lipids are insoluble in water and therefore useful as a waterproofing. Both plants and insects have waxy , cuticles that conserve water, while mammals only produce oily secretion from the sebaceous glands in the skin

Answer 44

fats are slow conductors of heat and when stored beneath the body surface help to retain body heat. They also act as electrical insulators in the myelin sheath around the nerve cells

Answer 45

fat is often stored around delicate organs, such as the kidney

Answer 46

triglycerides are a type of lipids three (tri) fatty acids combined with glycerol (glyceride)

Answer 47

in triglycerides, each fatty acids forms an ester bond with glycerol in condensation reaction. Three water molecules are produced. The fatty acids may not all be identical (hydrolysis of this lipid produces glycerol and three fatty acids)

Answer 48

as the glycerol molecule in all triglycerides are the same, the difference in the properties of different fats and oils come form variations in the fatty acids

Answer 49

over 70 different fatty acids | all have a carboxyl (-COOH-) group with a hydrocarbon chain attached to it

Answer 50

If the hydrogen chain has no carbon- carbon bonds, the fatty acids is then described as saturated (all the carbon atoms are linked to the maximum possible number of hydrogen atoms) a single double bond is mono- unsaturated more than one double is present, it is polyunsaturated

Answer 51

triglycerides have a high ratio of energy storing carbon - hydrogen bonds to carbon atoms therefore they are an excellent source of energy low mass to energy ratio, making them good storage molecules . This is especially beneficial to animals as it reduces the mass they have to carry as they move around large, non polar molecules, triglycerides are insoluble on water. This means their storage does not affect osmosis in cells or the water potential of them

Answer 52

phospholipids are similar to triglycerides except that one of the fatty acid molecules is replaced by a phosphate molecule

Answer 53

whereas fatty acid molecules repel water (are hydrophobic) phosphate molecules attract water (are hydrophilic) therefore a phospholipid is made of two parts: 1. a hydrophilic head interacts with water (is attracted to it) but not with fat 2.a hydrophilic tail that orients itself away from water but mixes with fat

Answer 54

we say that the molecule is polar

Answer 55

they position themselves so that the hydrophilic heads are close to the water as possible and the hydrophobic tails are as far from the water as possible

Answer 56

phospholipids are polar molecules . This means that in an aqueous environment, phospholipids molecules form a bilayer within cell surfaced membranes . As a result, a hydrophobic barrier is formed between the inside and outside of a cell the hydrophilic phosphate heads of phospholipid molecules help to hold the surface of cell- surface membrane phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell surface membrane. These glycolipids are important in cell recognition

Answer 57

take a completely dry and grease free test tube take 2cm3 of the sample being tested, add 5cm3 of ethanol 3. shake the test tube thoroughly to dissolve any lipids in the sample 4. Add 5cm3 of water and shake gently 5. a milky - white emulsion indicates the presence of a lipid 6. as a control, repeat the procedures using water instead of the sample; the final solution should remain clear

Answer 58

are large molecules that are made up of chains of polypeptides. Polypeptides basic sub unit are amino acids

Answer 59

amino acids are the basic monomer units which combine to make up a polymer called a polypeptide. Polypeptides can combine to form proteins

Answer 60

about 100 amino acids have been identified, of which 20 occur naturally in proteins - the fact that the same 20 amino acids in all living organisms provides indirect evidence for evolution

Answer 61

all of these groups are attached to a single carbon atom amino group (-NH2) from which the amino part of the name amino acid is derived the carboxyl group (-COOH) an acidic group which gives the amino acid the acid of its name hydrogen atom (-H) R (side) group - a variety of different chemical groups. Each amino acid has a different R group. These 20 naturally occurring amino acids differ only in their R (side) group

Answer 62

the primary structure is the sequence of amino acids found in a polypeptide chain. This process happens through a series of condensation reactions where many amino acid monomers join together to form a polypeptide chain.

Answer 63

this sequence is determined by DNA

Answer 64

as polypeptides have many (usually hundreds) of the 20 naturally occurring amino acids joined in different sequences, it follows that there is an almost limitless number of possible combinations, and therefore types of primary protein structure

Answer 65

the primary structure of the amino acid determines the proteins ultimate shape and therefore its function

Answer 66

a change in just a single amino acid in the primary sequence can lead to a change in the shape of the protein and may stop it carrying out its function less well, or differently

Answer 67

the secondary structure of a protein is the shape which the polypeptide chain forms as a result of hydrogen bonding. This shape is a spiral known as a helix (alpha helix)

Answer 68

The linked amino acids that make up a polypeptide possess both -NH and -C=O groups on either side of every peptide bond. The hydrogen of the -NH group has an overall positive charge while the O of the -C=O group has an overall negative charge. These two groups therefore readily form weak bonds called hydrogen bonds. This causes the long polypeptide chain to be twisted into a 3-D shape - alpha helix.

Answer 69

the tertiary structure of a protein is the bending and twisting of the polypeptide helix into a compact structure The alpha-helices of the secondary protein structure can be twisted and folded even more to give the complex and often specific 3-D structure of each protein. This structure is maintained by a number of different bonds. Where these bonds occur depends on the primary structure of the protein

Answer 70

disulfide bridges - fairly strong and are not easily broken ionic bonds - normally forms between the carboxyl groups and amino groups that are not involved in forming peptide bonds. Are weaker than disulfide bridges and are easily broken by changing the pH hydrogen bonds - numerous but easily broken

Answer 71

It is the 3D shape of a protein that is important when it comes to how it functions. It makes each protein distinctive and allows it to recognise and be recognised by other molecules. It can then interact with these molecules in a very specific way

Answer 72

the quaternary structure is the combination of a number of different polypeptide chains and associated non - protein (prosthetic) groups into a large, complex protein e.g. haemoglobin large proteins often form complex molecules containing a number of individual polypeptide chains that are linked in various ways. It may also contain prosthetic groups associated with the molecules e.g. iron-containing haem group in haemoglobin

Answer 73

it is the sequence of the amino acids in the primary structure that determines the 3D shape in the first place

Answer 74

through a series of condensation reactions which is essentially the removal of water. The water is made by combining an -OH from the carboxyl group of one amino acid with an -H from the amino group of another amino acid. The two amino acids then become linked by a new peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other

Answer 75

the peptide group can be broken by the addition of water (hydrolysis). The dipeptide would be broken into its two constituent amino acids

Answer 76

the most reliable test for proteins is the Biuret test. The biuret test detects peptide bonds METHOD: 1. place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature 2. add a few drops of very dilute (0.05%) copper (II) sulfate solution and mix gently 3. a purple colouration indicates the presence of peptide bonds and hence a protein. If no protein is present, the solution remains blue

Answer 77

enzymes are globular proteins that act as catalyst They alter the rate of a chemical reaction without undergoing permanent changes themselves. They can be reused repeatedly and are therefore effective in small amounts

Answer 78

enzymes lower the activation energy of an reaction . Therefore enzymes allow the reaction to take place at a lower temperature than normal This enables some metabolic processes to occur rapidly at the human temperature 37C which is relatively low in terms of chemical reactions

Answer 79

for reactions to happen naturally a number of conditions must be satisfied: 1. molecules must collide with sufficient energy to alter the arrangement of their atoms 2. free energy of the products must be less than that of the substrates (exothermic reaction) 3. many reactions require an initial amount of energy to start. This energy is the minimum amount of energy required to start the reaction (activation energy)

Answer 80

the activation energy is like an energy barrier, which must initially be overcome before the reaction can proceed

Answer 81

without enzymes, reactions happening in our body would proceed too slowly to sustain life as we know it

Answer 82

enzymes being globular proteins, have a specific 3D shape that is the result of amino acids enzymes also have a specific region known as the active site

Answer 83

the active site is made up of a relatively small number of amino acids The active site forms a small depression within the much larger enzyme molecule

Answer 84

the substrate molecule neatly fits into this depression (active site) and forms an enzyme- substrate molecule ( E-S complex) The substrate is held within the active site by the bonds temporarily formed between amino acids of the active site and groups on the substrate molecule

Answer 85

induced fit model of enzyme action proposes that the active site forms as the enzyme and substrate interact ( a change in the environment of the enzyme) In other words, the enzyme is flexible and can mould itself around the substrate in the way that a glove mould itself to the shape of the hand e.g. enzymes has general shape, like a glove, but alters in presence of the substrate

Answer 86

as it changes shape, the enzyme puts a strain on the substrate molecule. the strain distorts a particular bond or bonds in the substrate and consequently lowers the activation energy needed to break the bond

Answer 87

any change in the enzyme's environment will result to change in its shape. The very act of colliding with its substrate is a change in its environment so its shape changes - induced fit

Answer 88

the enzyme, like a lock, is considered to be rigid structure. This is not the case as an enzyme shape can be altered. In other words, its structure was not rigid but flexible. Scientists therefore modified the lock and key model to the induced fit model

Answer 89

for enzymes to work it must: - come into physical contact with its substrate - have an active site which fits the substrate almost all factors that influence the rate at which enzyme works do so affecting on or both of the above

Answer 90

to measure the progress of an enzyme - catalysed reaction we usually measure its time - course that is how long it takes for a particular event to run its course The changes most frequently measured are: -formation of the products of the reaction -disappearance of the substrate

Answer 91

at first there is a lot of substrate but no product it is very easy for substrates to come into contact with empty active sites on the enzyme molecules all enzyme active sites are filled at any given moment and the substrate is rapidly broken down into its products. The amount of substrate decreases as it is broken down, resulting in an increase in the amount of product as the reaction proceeds, there is less and less substrate and more product It becomes more difficult for the substrate to come into contact with the enzyme molecules because there are fewer substrate molecules and also the product molecules may " get in the way" of substrate molecules and prevent them reaching and active site Therefore it takes longer for the substrate molecule to be broken down by the enzyme and so it's rate of disappearance slows down and consequently the rate of the formation of products slows down also slows rate of reaction continues to slow until there is so little substrate that any further decrease in its concentration cannot be measured the graph flattens out because the substrate has been used up and so little substrate that any further decrease in its concentration cannot be measured OR the graph flattens out because all the substrate has been used up and so no product can product can be produced

Answer 92

the rise in temp increases kinetic energy of molecules As a result of, the molecules move around more rapidly and collide with each other more often In enzyme catalysed reactions, this means that the enzyme and substrate molecules come together more often in a given time

Answer 93

on a graph, the effect of temperature gives a rising curve

Answer 94

on rising temperature also begins to cause the hydrogen and other binds in the enzyme molecule to break down This results in the enzyme, including its active site changing shape For many humans this begin to happen at temperatures around 45C

Answer 95

at first, the substrate fits less easily into this changed active site, slowing the rate of the reaction.

Answer 96

at some point, usually around 60C, the enzyme is so disrupted that it stops working altogether. The enzyme is said to have denatured which is a permanent change and once occurred, the enzyme does not function

Answer 97

their will be a falling curve on the graph

Answer 98

the optimum temperature differs from enzyme to enzyme. Our body temperature has evolved to 37C this may be related to the following: - although higher body temperatures would increase the metabolic rate slightly, the advantages are offset by the additional energy (found) that would be needed to maintain the higher temperature - other proteins, apart from enzymes, may denature at higher temps - at higher temps, any further rise in the temp e.g. during illness, might denature the enzymes

Answer 99

different animals have different body temps, e.g. 40C for birds because they have a high metabolic rate for the higher energy requirement of flight

Answer 100

the pH of a solution is a measure of its hydrogen ion

Answer 101

it affects the rate of enzyme action An increase or decrease in pH reduces the rate of enzyme action If the pH is more extreme, then beyond a certain pH,, the enzyme becomes denatured

Answer 102

a change in pH alters the charges on the amino acids that make up the active site of an enzyme. This causes the substrate to no longer become attached to the active site and the enzyme - substrate complex cannot be formed - depending on how significant the change in pH is, it may cause the bonds maintaining the enzymes tertiary structure to break causing the active site to change shape

Answer 103

the arrangement of the active site is partly determined by the hydrogen and ionic bonds between -NH2 and COOH groups of the polypeptide that make up the enzyme The H+ ions ( from the changing of the pH) affects this bonding, causing the active site to change shape

Answer 104

there are too few enzyme molecules to allow substrate molecules to find an empty active site. The rate of the reaction is therefore only half the maximum possible for the number of substrate molecules available

Answer 105

with twice as many enzyme molecules available, all the substrate molecules can occupy an active site at the same time . The rate of reaction has doubles to it's maximum because all active sites are filled

Answer 106

the addition of further enzyme molecules has no effect as there are already enough active sites to accommodate all the available substrate molecules There is no increase in the rate of reaction