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AQA AS Biology > biological molecules > Flashcards

biological molecules Flashcards

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1
Q

what is a monomer ?

A

Monomers are the smaller units from which larger molecules (polymers) are made.

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2
Q

what are polymers?

A

Polymers are molecules made from a large number of monomers joined together.

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3
Q

what are 3 examples of monomers?

A

Monosaccharides, amino acids and nucleotides are examples of monomers.

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4
Q

what are some examples of polymers?

A

Starch, cellulose and glycogen are examples of polymers.

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5
Q

what is a condensation reaction?

A

A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water.

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6
Q

what is a hydrolysis reaction?

A

A hydrolysis reaction breaks a chemical bond between two molecules and involves the use of a water molecule.

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7
Q

what are monosaccharides?

A

Monosaccharides are the monomers from which larger carbohydrates are made. They’re simple sugars.

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8
Q

name 3 examples of monosaccharides?

A

Glucose, galactose and fructose are common monosaccharides.

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9
Q

what bond forms between 2 monosaccharides joined by a condensation reaction?

A

A condensation reaction between two monosaccharides forms a glycosidic bond.

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10
Q

what’s a disaccharide?

A

Disaccharides are formed by the condensation of two monosaccharides.

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11
Q

what’s maltose and how’s it formed?

A

maltose is a disaccharide formed by condensation of two alpha glucose molecules

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12
Q

what’s sucrose and how’s it formed?

A

sucrose is a disaccharide formed by condensation of a glucose molecule and a fructose molecule.

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13
Q

what’s lactose and how’s it formed?

A

lactose is a disaccharide formed by condensation of a glucose molecule and a galactose molecule.

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14
Q

what are the 2 isomers of glucose?

A

α-glucose and β-glucose

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15
Q

what’s the general formula of a monosaccharide?

A

(CH2O)n where n = any number from 3-7

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16
Q

how are glycogen and starch formed?

A

Glycogen and starch are formed by the condensation of α-glucose.

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17
Q

how is cellulose formed?

A

Cellulose is formed by the condensation of β-glucose.

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18
Q

structure related to function: glycogen

A

Glycogen is the storage polysaccharide of animals and fungi, it is highly branched and not coiled
-branched chains of alpha glucose, similar to amylopectin but with more side-branches. This gives it a large surface area for enzyme action to release glucose when energy is needed. It is more compact that amylopectin, which means more can be stored in a cell.

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19
Q

structure related to function: starch

A

Starch is the storage polysaccharide of plants.
Starch is constructed from two different polysaccharides:
- Amylose: unbranched spiralling chains of alpha-glucose molecules. Its coiled structure means that it is very compact so lots of amylose can be packed into a cell.

  • Amylopectin: branched chains of alpha-glucose molecules. Its branches increase its surface area which means that enzyme can quickly break it apart when glucose is needed for respiration.
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20
Q

structure related to function: cellulose

A

long unbranched chains of beta-glucose molecules. Multiple chains are linked together by hydrogen bonding to form strong structures called micofibrils. The strong microfibrils in the cell wall help to give plant cells their shape and structural support.

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21
Q

how do you test for reducing sugars?

A

1- Add Benedict’s reagent (which is blue as it contains copper (II) sulfate ions) to a sample solution in a test tube
2- Heat the test tube in a water bath
3- 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
- brick red colour = positive test

(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))

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22
Q

how’s the test for reducing sugars semi-quantitative?

A

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

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23
Q

examples of reducing sugars?

A
  • galactose
  • glucose
  • fructose
  • maltose
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24
Q

test for non reducing sugars?

A

1- Add dilute hydrochloric acid to the sample and heat in a water bath
2- 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)
3- Then carry out the Benedict’s test as normal; add Benedict’s reagent to the sample and heat in a water bath – if a colour change occurs, a non-reducing sugar is present

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25
Q

why is HCl added to carry out the test for non reducing sugars?

A

to hydrolyse any glycosidic bonds present in any carbohydrate molecules

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26
Q

why’s sodium hydrogen carbonate added in a non reducing sugars test?

A

because the conditions need to be slightly alkaline for the Benedict’s test to work.

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27
Q

test for starch?

A

1- add a few drops of potassium iodide solution to the food sample

2- 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

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28
Q

how are triglycerides formed?

A

Triglycerides are formed by the condensation of one molecule of glycerol and three molecules of fatty acid.

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29
Q

what bond is formed by the condensation reaction between glycerol and a fatty acid (RCOOH)?

A

A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond.

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30
Q

The R-group of a fatty acid may be …

A

saturated or unsaturated

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31
Q

what’s meant by “saturated”?

A

contains NO double C=C bonds

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32
Q

what’s meant by “unsaturated”?

A

contains double C=C bonds

33
Q

how are phospholipids formed?

A

phospholipids are formed by the condensation of one molecule of glycerol and 2 molecules of fatty acid and 1 phosphate containing group.

34
Q

Triglycerides: Structure & Function

A

Triglycerides are mainly used as energy storage molecules
- This is because the long hydrocarbon tails of the fatty acids in triglycerides contain large amounts of chemical energy, which can be released when the fatty acids are broken down
- Triglycerides are also suitable as energy storage molecules because they are insoluble, meaning that they don’t affect the water potential inside the cell
- Inside cells, triglycerides form insoluble droplets, with the hydrophobic (water-repelling) fatty acids on the inside and the glycerol molecules on the outside

35
Q

phospholipids: structure to function

A
  • phosphate group is hydrophilic (water-loving), whereas the two fatty acids are hydrophobic (like in triglycerides). This makes phospholipids suitable for making up the bilayer of cell membranes, with the fatty acids facing inwards and the phosphate groups facing outwards
  • This is also useful as it means the centre of the phospholipid bilayer is hydrophobic, meaning water-soluble substances cannot easily pass through
  • This allows the cell membrane to act as a barrier, controlling what substances enter and leave the cell
36
Q

how is the emulsion test carried out?

A
  • Add ethanol to the liquid 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 more lipid present, the more obvious the milky colour of the solution
  • If no lipid is present, the solution remains clear
37
Q

what monomers are proteins made from?

A

Amino acids are the monomers from which proteins are made.

38
Q

general structure of an amino acid?

A

R
|
H2N—C—COOH
|
H

NH2 represents an amine group, COOH represents a carboxyl group and R represents a side chain.

39
Q

how many different amino acids are there, and how do they differ?

A

twenty amino acids that differ only in their side group.

40
Q

what bond is formed when a condensation reaction happens between two amino acids?

A

A condensation reaction between two amino acids forms a peptide bond.

41
Q

what are some functions of proteins?

A
  • structure: Forms supporting frameworks inside cells and forms body structures
  • enzymes: Catalyse biological reactions
  • hormones
  • antibodies
42
Q

what’s the primary structure of a protein?

A

The sequence of amino acids bonded by covalent peptide bonds.

43
Q

what’s the primary structure of a protein?

A

The sequence of amino acids bonded by covalent peptide bonds.

44
Q

what’s the secondary structure of a protein?

A

The secondary structure only relates to hydrogen bonds forming between the amino group and the carboxyl group which causes the sequence of amino acids to coil into α-helices or fold into β-pleated sheets

45
Q

what’s the tertiary structure of a protein?

A

Further conformational change of the secondary structure leads to additional bonds forming between the R groups (side chains)
The additional bonds are:
- Hydrogen (these are between R groups)
- Disulphide (only occurs between cysteine amino acids)
- Ionic (occurs between charged R groups)
- Weak hydrophobic interactions (between non-polar R groups)

46
Q

what’s the quaternary structure of a protein?

A

Occurs in proteins that have more than one polypeptide chain working together as a functional macromolecule, for example, haemoglobin

47
Q

how do you test for proteins?

A

Biuret ‘reagent’ contains an alkali and copper (II) sulfate
- add biurets reagent to sample
- 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

48
Q

how is the biuret test qualitative?

A

it does not give a quantitative value as to the amount of protein present in a sample

49
Q

what is an enzyme?

A

a biological catalyst that lowers the activation energy of the reaction it catalyses.
it speeds up a chemical reaction without being used up itself.

50
Q

The induced-fit model of enzyme action

A

as an enzyme and substrate come together, their interaction causes a small shift in the enzyme’s structure (active site) .
The shift means that the enzyme and substrate can bind to form an enzyme-substrate complex and catalyse a reaction.

51
Q

The specificity of enzymes

A
  • Every enzyme has a specific active site that is complementary to the specific substrate.This jigsaw puzzle-like match between an enzyme and its substrates is what makes enzymes highly specific.
52
Q

The effects of enzyme concentration, on the rate of enzyme-controlled reaction

A

Increasing the concentration of enzyme in a solution means there are more enzyme molecules available to catalyse the substrate in a given amount of time, increasing the rate.

53
Q

The effects of temperature , on the rate of enzyme-controlled reaction

A
  • Increasing the temperature will increase the kinetic energy of the molecules.
  • This increases the chance of a collision between the enzyme and substrate and so more collisions are likely in a set period of time. In other words, the rate of reaction is faster.
54
Q

The effects of pH , on the rate of enzyme-controlled reaction

A
  • Changing the pH changes the number of hydroxide ions and hydrogen ions (OH− and H+) surrounding the enzyme.
  • These interact with the charges on the enzyme’s amino acids, affecting hydrogen bonding and ionic bonding, so resulting in changes to the tertiary structure.
  • At extreme pH values, the enzyme’s structure may be changed. This is called a denatured enzyme.
55
Q

The effects of substrate concentration, on the rate of enzyme-controlled reaction

A
  • Increasing the concentration of the substrate increases the numbers of substrate molecules that can form enzyme-substrate (ES) complexes at any one time.
  • This increases the initial rate of reaction but when all the enzyme molecules are engaged in ES complexes the rate cannot increase any further.
  • The rate will then plateau because the enzyme is said to be saturated.
56
Q

The effects of competitive inhibitors , on the rate of enzyme-controlled reaction

A

decreases rate as Competitive inhibitors are similar in shape to the usual substrate and affect the active site directly, blocking access for the formation of ES complexes.

57
Q

The effects of non - competitive inhibitors , on the rate of enzyme-controlled reaction

A

decreases rate as Non-competitive inhibitors affect another part of the enzyme molecule causing a change to the shape of the active site.
The active site is no longer complementary to the substrate molecules.

58
Q

DNA holds…

A

genetic information

59
Q

RNA transfers…

A

genetic information from DNA to the ribosomes.

60
Q

ribosomes are formed from…

A

Ribosomes are formed from RNA and proteins.

61
Q

what monomers make up DNA and RNA?

A

Both DNA and RNA are polymers of nucleotides.

62
Q

nucleotide structure

A

Each nucleotide is formed from a pentose, a nitrogen-containing organic base and a phosphate group

63
Q

components of a DNA nucleotide?

A

deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine.

64
Q

components of an RNA nucleotide?

A

ribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or uracil.

65
Q

what bond is formed when a condensation reaction between two nucleotides occurs?

A

A condensation reaction between two nucleotides forms a phosphodiester bond.

66
Q

dna molecule structure?

A
  • double helix
  • two long polynucleotide chains (5’ end and 3’ end)
    held together by hydrogen bonds between specific complementary base pairs.
    (A-T, C-G)
  • The polynucleotide chains are coiled anti-parallel. This means that in DNA double helix, the two polynucleotide chains are arranged opposite to each other
  • the amount of Adenine in DNA is equal to the amount of Thymine, and the amount of Guanine is equal to that of Cytosine
67
Q

rna molecule structure?

A

An RNA molecule is a relatively short polynucleotide chain.

68
Q

The process of semi-conservative replication of DNA…

A

1- DNA helicase breaks hydrogen bonds between complementary bases, causing the double helix to unwind. These og strands act as templates for new strands of dna
2- DNA polymerase catalyses the condensation reaction when free nucleotides join to the exposed bases of the template.
3- new H bonds form between complementary bases and phosphodiester bonds form between nucleotides.
4- new strands of DNA are made

69
Q

structure of ATP?

A

a molecule of ribose, a molecule of adenine and three phosphate groups

70
Q

hydrolysis of ATP…

A

forms adenosine diphosphate (ADP) and an inorganic phosphate group (Pi)

71
Q

what enzyme catalyses the hydrolysis of ATP?

A

ATP hydrolase

72
Q

how is ATP resynthesised ?

A

by the condensation of ADP and Pi

73
Q

what enzyme catalyses the resynthesis of ATP?

A

ATP synthase during photosynthesis, or during respiration.

74
Q

5 key 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 a 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.
75
Q

where do inorganic ions occur?

A

Inorganic ions occur in solution in the cytoplasm and body fluids of organisms, some in high concentrations and others in very low concentrations.

76
Q

role of hydrogen ions? (H+)

A

Hydrogen ions are protons.
- pH values represent the concentration of H+ in a solution.
- more H+ = more acidic

77
Q

role of iron ions? (Fe2+)

A

Iron ions are the central part of the haem group in haemoglobin, allowing red blood cells to transport O2 and CO2.

78
Q

role of sodium ions? (Na+)

A

Transport of sodium ions across the cell membrane of cells in the intestine allows the co-transport of glucose and amino acids.

79
Q

role of phosphate ions? (PO4 3-)

A
  • Phosphate ions are an essential part of the sugar-phosphate backbone of DNA molecules.
  • Adenosine triphosphate (ATP) can form ADP and release a phosphate ion along with energy.
  • ADP can also store energy by gaining a phosphate ion and taking in energy.
  • ATP is the universal energy currency of living organisms.

AQA AS Biology (6 decks)

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