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AS-Level Biology > Biological Molecules > Flashcards

Biological Molecules Flashcards

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1
Q

How is starch adapted for its function?

A
  • Main role is energy storage
  • Insoluble -> no water potential so water not drawn into cells
  • Large -> doesn’t diffuse out of cells
  • Compact -> a lot of it can be stored in a small space
  • Forms alpha glucose when hydra loses -> easily transported and readily used for respiration
  • Branched form has many ends -> each can be acted on by enzymes meaning glucose can be released rapidly
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2
Q

How is Glycogen adapted for its function?

A
  • Main role is energy storage
  • Insoluble -> no water potential so doesn’t draw water into the cell
  • Large -> doesn’t diffuse out of cells
  • Compact -> a lot of it can be stored in a small space
  • Forms alpha glucose when hydra loses -> easily transported and readily used for respiration
  • More highly branched form than starch -> so has more ends that can be acted on simultaneously by enzymes which means it is more rapidly broken down. Important as animals have a higher metabolic rate.
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3
Q

How is cellulose adapted for it structure?

A
  • in plant cell walls and provides rigidity to the plant
  • Made up of beta glucose -> forms long straight, unbranched chains which run parallel to other beta glucose chains and are held together by a hydrogen bond between layers. As they are crossed linked and have lots of hydrogen bonds there is a huge amount of collective strength.
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4
Q

What characteristics do lipids share?

A
  • They contain carbon, hydrogen and oxygen
  • The proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates
  • They are insoluble in water
  • They are soluble in organic solvents such as alcohols and acetone
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5
Q

What are the roles of lipids ?

A
  • source of energy
  • waterproofing
  • insulation
  • protection
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6
Q

How are lipids a good source of energy?

A
  • When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water
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7
Q

How are lipids good for waterproofing?

A
  • Lipids are insoluble in water and therefore useful as a waterproofing. Both plants and insects gave waxy, lipid cuticles that conserve water, while mammals produce an oily secretion from the sebaceous glands in the skin.
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8
Q

How are lipids good for insulation?

A
  • 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 nerve cells.
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9
Q

How are lipids used for protection?

A
  • Fat is often stored around delicates organs, such as the kidney that have no ribcage.
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10
Q

What are triglycerides?

A
  • They have three fatty acids .combined with glycerol.
  • Each fatty acid forms an ester bond with glycerol in a condensation reaction
  • Hydrolysis of a triglyceride therefore produces glycerol and three fatty acids.
  • Different properties in lipids come from variation in the fatty acids which all have a carboxyl group with a hydrocarbon chain attached.
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11
Q

What makes a lipid saturated?

A
  • If the chain of fatty acids has no carbon-carbon bonds, the fatty acid is then saturated.
  • If it is a single double bond then it is mono-unsaturated
  • If it is more than one double bond then it is polyunsaturated
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12
Q

Why are polyunsaturated lipids oils instead of fats?

A
  • The double bonds cause the molecule to bend.
  • They cannot therefore pack together so closely making them liquid at room temperature.
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13
Q

What are Phospholipids?

A
  • Similar to lipids except that one of the fatty acids is replaced with a phosphate molecule.
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14
Q

Why are there two different ends in a phospholipid?

A
  • One end is the hydrophilic head which interacts with water but not with fat. This is the end of the phosphate molecule.
  • The other end is the hydrophobic tail which orients itself away from water but mixes readily with fat. This is the end with the fatty acids.
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15
Q

What are the consequences of the phospholipid having two ends?

A
  • Molecules with two end (poles) that behave differently in this way are said to be polar.
  • This means that when these polar phospholipid molecules are placed in water they position themselves so that the hydrophilic heads are as close to the water as possible and the hydrophobic heads are as far away from the water as possible.
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16
Q

How does the structure of the phospholipid relate to its properties?

A
  • Phospholipid molecules form a bilayer within cell-membranes. As a result, a hydrophobic barrier is formed between the inside and outside of the cell.
  • The hydrophilic phosphate heads of phospholipid molecules help to hold at the surface o f the cell-surface membrane.
  • The phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane. These glycolipids are important in cell recognition.
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17
Q

What is the test for lipids?

A
  1. Take completely dry and grease-free test tube.
  2. To 2cm of the sample being tested, add 5 cm of ethanol.
  3. Shake the tube to dissolve any lipid in the sample.
  4. Add 5cm 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.

The cloudy colour is due to any lipid in the sample being finely dispersed in the water to form an emulsion. Light passing through this emulsion is refracted as it passes from oil droplets to water droplets, making it appear cloudy.

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18
Q

What are proteins made of?

A
  • Proteins are made up of carbon, oxygen, hydrogen, nitrogen and sometimes Sulphur, Phosphorus and other elements.
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19
Q

What kinds of proteins are there?

A
  • Enzymes catalyse reactions.
  • Channel proteins transport molecules across membranes
  • Antibodies defend against disease
  • Structural proteins support cells and tissues
  • Hormones transmit information
  • Transport proteins such as haemoglobin carry oxygen.
  • Contractile proteins enable muscles to contract
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20
Q

How do proteins they work ?

proteins

A
  • Proteins can carry out all these different functions because each different protein has a specific molecular shape which enables the protein to do its job.
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21
Q

What are proteins made up of?

A
  • Proteins are polymers molecules
  • The monomers molecules making up proteins are called amino acids.
  • There are 20 different naturally occurring amino acids. There are over 100,000 combinations of amino acids forming known proteins.
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22
Q

Describe the general structure of amino acids

A
  • Amino acid units come together to form a peptide.
  • Every amino acid has a central carbon atom to which four different chemical groups are attached to :
  • amino group (-NH2) a basic group from which the amino part of the name amino acid is derived.
    carboxyl group (-COOH) an acidic group which give the amino acid the acid part of its name
  • hydrogen atom
  • R ( side) group - a variety of different chemical groups. Each amino acid has a different R group. The 20 naturally occurring amino acids differ only in their R ( side) group
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23
Q

How does a peptide bond form?

A
  • amino acids undergo a condensation reaction
  • The water is made from combining the -OH from the carboxyl group of one amino acid with an -H from the amino group of another amino acid.
    The two amino acids are now linked by a new peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other.
  • The peptide bond can be broken by hydrolysis
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24
Q

What is the primary structure of proteins?

A
  • Many amino acids are joined together in the process of polymerisation.
  • The resulting chain of many hundreds of amino acids is called a polypeptide.
  • The primary structure is the sequence of amino acid.
  • The primary structure determines its shape and function
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25
Q

What is the secondary structure of a protein?

A
  • 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 weak intermolecular bonds are called hydrogen bonds.
  • This causes the long polypeptide chain to be twisted into a 3D shape such as a coil known as an alpha helix.
26
Q

What is the tertiary structure of proteins?

A
  • 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.
  • This structure is maintained by a number of different bonds:
    disulfide bridges - which are fairly strong and therefore are not easily broken
    ionic bonds - which are formed between carboxyl and amino groups that are not involved in the peptide bonds. They are weaker than disulfide bonds and are easily broken by a change in PH
    hydrogen bonds which are numerous but easily broken
27
Q

Why is the structure of a protein so important?

A
  • 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 them in a very specific way.
28
Q

What is the quaternary structure?

A
  • Large proteins often form complex molecules containing a number of individual polypeptide chains that are linked in various ways.
  • There are also non-protein (prosthetic) groups associated with the molecules, such as the iron containing haem group in haemoglobin.
29
Q

What is the test for proteins?

A
  • Biuret test detects peptide bonds
  • Place a sample of solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temperature.
  • Add a few drops of very dilute (0.05%) copper (II) sulphate solution and mix gently.
  • A purple colour indicates the presence of peptide bonds and hence a protein. If no protein is present the solution will stay blue.
30
Q

What are the two types of molecular shapes?

A
  • Fibrous proteins, such as collagen, have a structural functions.
  • Globular proteins, such as enzymes and haemoglobin , carry out metabolic functions.
31
Q

Describe the structure of fibrous proteins?

A
  • Form long chains that run parallel to one another.
  • These chains are linked by by cross-bridges and so form very stable molecules.
  • One example is collagen.
32
Q

Describe the structure of collagen

A
  • The primary structure is unbranched polypeptide chain
  • In the secondary structure the polypeptide chain is very tightly wound
  • Lots of the amino acid, glycine helps close packing.
  • In the tertiary structure the chain is twisted into the second helix
  • Its quaternary structure is made up of three such polypeptide chains wund together in the same way as individual fibres are wound together in a rope.
  • Collagen is found in tendons. Tendons join muscles to bones. When a muscle contracts the bone is pulled in the direction of the contraction.
33
Q

What are monomers?

A

Smaller units from which larger molecules are made

34
Q

What are polymers?

A

Are molecules made from a repeating units of monomers joined together

35
Q

What is a condensation reaction?

A

It is a reaction that joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water

36
Q

What is hydrolysis?

A

Hydrolysis reaction breaks a chemical bond between two molecules and involves the use of a water molecule

37
Q

What are monosaccharides?

A
  • The are monomers which larger carbohydrates are made
  • Glucose, galactose and fructose are common monosaccharides.
38
Q

How are two monosaccharides joined together?

A

A condensation reaction between two monosaccharides forms a glycosidic bond to form a disaccharide

39
Q

What is maltose formed from?

A

Maltose is a disaccharide formed from two glucose molecules by a condensation reaction

40
Q

What is sucrose formed from?

A

Disaccharide formed from a glucose and a fructose molecule by a condensation reaction

41
Q

What is lactose formed from?

A

Disaccharide formed from a glucose molecule and a galactose molecule by a condensation reaction

42
Q

What are the isomers of glucose and how do they differ?

A
  • There is alpha glucose and beta glucose
  • The difference between them is the position of the hydroxyl group on the first carbon atom. In alpha glucose it is positioned below the plane of a sugar molecule
43
Q

How is glycogen produced?

A

Glycogen and starch are formed from the condensation reaction of alpha glucose

44
Q

How is cellulose formed?

A

Cellulose if formed by the condensation of beta glucose

45
Q

What is the test for reducing sugars?

A
  • Benedict’s reagent is a blue solution that contains copper (II) sulfate ions (CuSO4 ); in the presence of a reducing sugar copper (I) oxide forms
  • Copper (I) oxide is not soluble in water, so it forms a brick red precipitate
46
Q

How to carry out the Benedict’s test?

A
  • Add Benedict’s reagent (which is blue as it contains copper (II) sulfate ions) to a sample solution in a test tube
  • Heat the test tube in a water bath or beaker of water that has been brought to a boil for a few minutes
  • If a reducing sugar is present, a coloured precipitate will form as copper (II) sulfate is reduced to copper (I) oxide which is insoluble in water
  • It is important that an excess of Benedict’s solution is used so that there is more than enough copper (II) sulfate present to react with any sugar present
  • A positive test result is a colour change somewhere along a colour scale from blue (no reducing sugar), through green, yellow and orange (low to medium concentration of reducing sugar) to brown/brick-red (a high concentration of reducing sugar)
  • This test is semi-quantitative as the degree of the colour change can give an indication of how much (the concentration of) reducing sugar present
  • To produce a quantitative test someone could filter out and weigh the precipitate
47
Q

What is the 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 centre of starch molecules, producing a complex with a distinctive blue-black colour
48
Q

What are enzymes and what do they do?

A
  • Enzymes are biological enzymes made of proteins which lowers the activation energy of the reaction it catalyses.
  • It does this by using the induced- fit model of enzyme action
49
Q

What is an induced-fit model?

A
  • When the active site of an enzyme comes into contact with the substrate, the enzyme will attempt to mould itself around the substrate to form an enzyme-substrate complex so that the active sites shape is complimentary to the substrate.
50
Q

What controls the properties of enzymes?

A
  • The tertiary structure of its active site and its ability to combine with complementary substrates to form an enzyme-substrate complex
51
Q

Equation to find PH

A
  • -log [ H+]
52
Q

What is the effect of enzyme concentration on the rate of enzyme controlled reactions?

A
  • An increase in the concentration of enzymes will lead to a proportional increase in the rate of reaction initially
  • This is because excess substrate is now being acted on by the enzymes.
  • If the substrate is limiting, then the increase of enzyme concentration will have no effect because the available substrate is already being used as rapidly as it can be by the existing enzyme molecules.
53
Q

What is the effect of substrate concentration on the rate of substrate controlled reactions?

A
  • Initially the rate of reaction will increase proportionally to the increase in the substrate concentration if the concentration of enzyme is fixed
  • This is because with a low substrate concentration, the enzyme molecules gave only a limited number of substrate molecules to collide with and therefore the active sites are not working at full capacity
  • As more substrate is added, the active sites gradually become filled, until the point where all of them are working as fast as they can.
  • Here the rate of reaction is at its maximum and the addition of substrate will have no effect.
54
Q

What is the effect of temperature on the rate of substrate controlled reactions before its optimum?

A
  • A rise in temperature increases the kinetic energy in molecules.
  • Molecules move around more rapidly and collide with each other more often
  • There are more successful collisions per second so more enzyme substrate complexes being formed per second and so a faster rate of reaction.
55
Q

What is the effect of temperature on the rate of substrate controlled reactions after its optimum?

A
  • The temperature rise will eventually cause hydrogen bonds and other bonds to break.
  • This results in the active site along with the rest of the enzyme changing shape.
  • At first the substrate will fit less easily into this changed active site, slowing the rate of reaction.
  • Eventually the enzyme’s shape is so disrupted that it will stop working completely and enzymes are said to be denatured.
56
Q

What is denaturation ?

A
  • It is the permanent change and once it has occurred the enzyme does not function again.
57
Q

What is the effect of PH on the rate of substrate controlled reactions before its optimum?

A
  • A change of PH away from the optimum reduces the rate of enzyme action.
  • If the change of PH is extreme then proteins can be denatured.
  • The change in PH alters the charges on amino acids so that the substrate can no longer become attached to the active site and a enzyme-substrate complex cannot be formed.
  • A change in PH can also cause ionic and hydrogen bonds to break.
58
Q

What are competitive inhibitors?

A

Competitive inhibitors have a molecular shape which is similar to that of the substrate.
This allows them to occupy the active site of an enzyme.
They therefore compete with the substrate for the available active sites.

59
Q

How do competitive inhibitors have an effect on the rate of reaction?

A
  • It is the difference between the concentration of the inhibitor and the concentration of the substrate that determines the effect that this has on enzyme activity.
  • The higher the concentration of inhibitor to the concentration of substrate, the slower the rate of reaction because the enzyme’s active site is more likely to be taken up by an inhibitor
60
Q

What is a non-competitive inhibitor?

A
  • Attach themselves to the enzyme at a binding site which is not the active site.
  • Upon attaching, it alters the shape of the enzyme and thus its active site in such a wat that substrate molecule can no longer occupy it, and so enzymes cannot function.
  • As they are not competing for the same active site an increase in the substrate concentration does not decrease the effect of the inhibitor.
61
Q

Describe the properties of water?

A
  • is a metabolite in many metabolic reactions, including condensation and hydrolysis reactions.
  • is an important solvent in which metabolic reactions occur
  • has a relatively high heat capacity, buffering changes in temperature
  • has relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation.
  • has strong cohesion between water molecules; this supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air

AS-Level Biology (11 decks)

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