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AS Level Biology flashcards > Biology Topic 1 > Flashcards

Biology Topic 1 Flashcards

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1
Q

What is a monomer?

A

Smaller units from which larger molecules are made.

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2
Q

What is a polymer?

A

Molecules made from a large number of monomers joined together.

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3
Q

What are some examples of monomers?

A

Monosaccharides such as glucose, amino acids and nucleotides.

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4
Q

What is a condensation reaction?

A

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

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5
Q

What is a hydrolysis reaction?

A

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

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6
Q

How are glucose polysaccharides produced?

A

They are formed by the condensation of many glucose units. The glucose monosaccharides are joined by glycosidic bonds.

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7
Q

Describe the structure of alpha glucose (hydroxyl group).

A

The hydroxyl group is at the bottom in an alpha glucose molecule.

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8
Q

Describe the structure of beta glucose (hydroxyl group).

A

The hydroxyl group is at the top in a beta glucose molecule.

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9
Q

What do two monosaccharides combine to produce?

A

They produce a disaccharide and a water molecule.

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10
Q

What are the names of common polysaccharides? What type of glucose are they made from?

A

Glycogen and starch - formed by the condensation alpha glucose.

Cellulose - formed by the condensation beta glucose.

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11
Q

What is glycogen?

A
  • Glycogen, a polymer of alpha glucose, is the main energy storage in animals.
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12
Q

Why is it beneficial that glycogen has a large number of side branches?

A
  • It has a large number of side branches meaning that energy can be released quickly as enzymes can act simultaneously on these branches.
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13
Q

Why is it beneficial that glycogen is a large but compact molecule?

A

As it is large but compact, the amount of energy that it can store is maximised.

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14
Q

Why is it beneficial that glycogen is insoluble?

A

It will not affect the water potential of cells and cannot diffuse out of cells.

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15
Q

What does starch do? What is it a mixture of?

A

Starch, a polymer of alpha glucose, stores energy in plants. It is a mixture of two polysaccharides: amylose and amylopectin.

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16
Q

What is amylose?

A

It is an unbranched chain of glucose molecules joined by glycosidic bonds.

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17
Q

Due to the 1, 4 glycosidic bonds, what is amylose’s structure like?

A

Amylose is coiled and so a very compact molecule that stores a lot of energy.

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18
Q

What is amylopectin’s structure like?

A

It is branched.
Due to the presence of many side branches, they can be acted on simultaneously by many enzymes and thus broken down to release energy.

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19
Q

What are the key properties of starch?

A

It is insoluble so it won’t affect water potential.

It is branched, making the molecule compact.

Large, so can’t cross the cell membrane.

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20
Q

What is cellulose composed of?

A

It is composed of long, unbranched chains of beta glucose which are joined by glycosidic bonds.

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21
Q

Why is cellulose important?

A

It has long and straight chains that become linked together by many hydrogen bonds to form
fibrils. This provides strength to the cell wall.

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22
Q

Test for a non-reducing sugar

A
  • Add 2cm^3 of food sample to 2cm^3 of Benedict’s reagant.
  • Warm in a water bath for 5 minutes.
  • No colour change = reducing sugar is not present.
  • Add 2cm^3 of food sample in a new test tube and also add -2cm^3 of HCl. Warm in a water bath for 5 minutes.
    -Add some sodium hydrogencarbonate in order to neutralise the test tube .
    -Retest new solution by adding 2cm^3 of Benedict’s solution and heating for 5 minutes.
    -Blue –> brick red.
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23
Q

How are triglycerides formed?

A

Triglycerides are formed by the condensation of one molecule of
glycerol and three molecules of fatty acid. The removal of three molecules of water is also involved.
- Ester bonds are also formed.

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24
Q

What type of bond does the condensation reaction between glycerol and a fatty acid produce?

A

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

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25
Q

Describe the structure of a phospholipid.

A

In phospholipids, one of the fatty acids of a triglyceride is
substituted by a phosphate-containing group.

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26
Q

What makes being large and non-polar an advantage for triglycerides?

A

They are insoluble in water and therefore their storage does not affect the water potential of cells.

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27
Q

Are the fatty acid chains in a phospholipid saturated or unsaturated?

A

One chain is saturated, the other is unsaturated.

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28
Q

The features of phospholipids and how they relate to their structure.

A
  • As they have a hydrophilic head and hydrophobic tail, they can form a bilayer.
  • In an aqueous environment, being polar means a bilayer can be formed.
  • The hydrophilic heads can be used to hold at the surface of the cell-surface membrane.
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29
Q

How do you carry out the emulsion test?

A
  • Add 2cm^3 of your food sample to 5cm^3 of ethanol. Shake the test tube to dissolve the lipid in the solution.
  • Add 5cm^3 of distilled water and shake gently.
  • Cloudy white colour = presence of a lipid.
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30
Q

How are dipeptides formed?

A

Dipeptides are formed by the condensation reaction of two amino acids.

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31
Q

How are polypeptides formed?

A

Polypeptides are formed by the condensation of many amino acids.

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32
Q

How many polypeptides might a functional protein contain?

A

A functional protein may contain one or more polypeptides

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33
Q

Describe the primary structure of a protein.

A
  • It is the order and number of amino acids in a sequence.
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34
Q

What sequence does the primary structure of a protein contain? Why is this beneficial?

A

It contains the initial sequence of amino acids. This will determine the proteins function in the end.

35
Q

What does the secondary structure of a protein determine?

A
  • It is the shape that the chain of amino acids make: either alpha helix or beta-pleated sheet.
36
Q

What do the charges on -NH and -C=O cause?

A

Hydrogen in -NH has a slight positive charge. O in -C=O has a slight negative charge. As a result, weak hydrogen bonds can form, leading to alpha helixes or beta-pleated sheets.

37
Q

What does the tertiary structure of a protein relate to?

A
  • The 3D shape of the protein that is formed by twisting and folding.
38
Q

How is a disulfide bridge formed? What are its properties?

A

Disulfide bridges: interactions between the sulfur in the R group of the amino acid cysteine. These are strong and not easily broken.

39
Q

How is an ionic bond formed? What are its properties?

A
  • Form between carboxyl and amino groups that are not involved in the peptide bond. These are easily broken by pH and are weaker than disulfide bridges.
40
Q

What are properties of hydrogen bonds?

A

There are numerous of them and they are easily broken.

41
Q

What are globular and fibrous proteins?

A

Globular proteins are compact, e.g. enzymes.

Fibrous proteins are long and thus can be used to form fibres, e.g. keratin.

42
Q

Describe the biuret test for proteins.

A

Make the solution alkaline (add a few drops of sodium hydroxide to your solution).
- Add a few drops of copper sulfate solution and mix gently.
- A purple colour indicates the presence of a protein. Negative result = remains blue.

43
Q

What are enzymes (in terms of protein structure)?

A

They are 3D tertiary structured globular proteins whose shape is determined by the primary sequence of amino acids.

44
Q

What is the induced fit model?

A

When the enzyme and substrate bind they form an E-S complex, and the structure of the enzyme is altered so that the active site of the enzyme fits around the substrate.

45
Q

What factors affect the rate of an enzyme-controlled reaction?

A

Temperature, pH, enzyme concentration, substrate concentration, concentration of competitive inhibitors and concentration of non-competitive inhibitors.

46
Q

How does temperature impact the rate of an enzyme-controlled reaction?

A
  • Rate increases up to the optimum temperature due to an increase in KE.
  • Beyond this temperature, rate decreases as the enzyme becomes denatured.
47
Q

How does the PH impact the rate of an enzyme-controlled reaction?

A
  • pH affects the enzyme’s shape by disrupting the bonds in the tertiary structure.
  • All enzyme’s work at different optimum PH’s.
48
Q

How does enzyme concentration impact the rate of an enzyme-controlled reaction?

A
  • Rate increases as enzyme concentration increases. This is because there are more active sites for substrates to bind to.
  • After a certain point, there is no effect on rate as there are more active sites than substrates. This means that substrate concentration is the limiting factor.
49
Q

How does substrate concentration impact the rate of an enzyme-controlled reaction?

A
  • Rate increases as substrate concentration increases. This is because more E-S complexes are formed. Beyond a certain point, rate no longer increases as enzyme concentration becomes the limiting factor.
50
Q

How does concentration of competitive inhibitors impact the rate of an enzyme-controlled reaction?

A

As the concentration of competitive inhibitors increases, rate of reaction decreases. This is because active sites are temporarily blocked, so substrates cannot bind to them.

51
Q

How does concentration of non-competitive inhibitors impact the rate of an enzyme-controlled reaction?

A

As concentration of non-competitive inhibitors increases, rate of reaction decreases as the shape of the enzyme is altered by the inhibitors.

52
Q

What are the functions of DNA and RNA?

A

DNA holds genetic information, whereas RNA transfers this genetic information from DNA to ribosomes for protein synthesis.

53
Q

What are ribosomes made up of?

A
  • Ribosomal RNA and proteins.
54
Q

What are the components of a DNA nucleotide?

A
  • Deoxyribose sugar, a phosphate group and one nitrogen-containing base (A, C, G, T).
55
Q

What are the components of an RNA nucleotide?

A
  • Ribose sugar, a phosphate group and one nitrogen-containing base (A, C, G, U).
56
Q

What are nucleotides joined together by?

A
  • Nucleotides are joined together by phosphodiester bonds formed in condensation reactions.
57
Q

What is a DNA molcule?

A

A DNA molecule is a double helix with two polynucleotide chains
held together by hydrogen bonds between specific complementary
base pairs

58
Q

What is an RNA molecule?

A

An RNA molecule is a relatively short polynucleotide chain.

59
Q

What bases usually pair with one another?

A

Adenine always pairs with Thymine.
Guanine always pairs with cytosine.

60
Q

What are the steps of semi-conservative DNA replication?

A

1) DNA helicase causes the 2 DNA strands to separate by breaking the H-bonds between complementary bases.
2) One of the strands is used as a template and complementary base pairing occurs between the template strand and free nucleotides.
3) Once activated nucleotides are bound, DNA polymerase joins them together by forming phosphodiester bonds. Two identical DNA strands are formed.

61
Q

Students should be able to evaluate the work of scientists in
validating the Watson–Crick model of DNA replication.

A

Come back to this later @(mendel and stahls research)
Centrifuging etc.

62
Q

What does a molecule of ATP consist of?

A

ATP is a nucleotide
derivative and is formed from a molecule of ribose, a molecule of adenine and three phosphate groups.

63
Q

Where does the energy in ATP come from?

A

The energy comes from the bonds between the phosphate molecules. The bonds are unstable and have a low activation energy, so they can be broken quickly to release a lot of energy.

64
Q

What can ATP be used to do to other compounds?

A

ATP can be used to phosphorylate other compounds, often
making them more reactive.

65
Q

How is ATP resynthesised?

A

ATP is resynthesised by the condensation of ADP and Pi
This is catalysed by the enzyme ATP synthase during
photosynthesis, or during respiration.

66
Q

What does water act as in metabolic reactions?

A

It is a metabolite in many metabolic reactions, including
condensation and hydrolysis reactions

67
Q

What kind of solvent is water?

A

It is an important and ‘good solvent’ in which metabolic reactions occur.

68
Q

What is the benefit of water having a relatively high heat capacity?

A

Changes in temperature are buffered.

69
Q

What is the benefit of water having a relatively large latent heat of vaporisation?

A

A cooling effect is provided. with little loss of water through evaporation.

70
Q

What is the benefit of water molecules having strong cohesion between one another?

A

This supports
columns of water in the tube-like transport cells of plants and
produces surface tension where water meets air.

71
Q

Where do inorganic ions occur? In what concentrations?

A

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

72
Q

How are hydrogen ions essential in relation to pH?

A

They determine the pH of substances such as blood. (More H+ ions = lower concentration).

73
Q

How are iron ions important?

A

They are a component of haemoglobin: an oxygen carrying molecule in red blood cells.

74
Q

How are sodium ions important?

A

Sodium ions are involved in co-transport of glucose and amino acids.

75
Q

How are phosphate ions important?

A

They are a component of DNA and ATP.

76
Q

Suggest a method, other than
using a colorimeter, that someone could use to measure the quantity of
reducing sugar in a solution.

A

Filter and dry the precipitate.
Find the mass/weight.

77
Q

Why does the use of a colorimeter improve the repeatability of an individual’s results (when completing food tests)?

A

It makes the results quantitative.

78
Q

How do you calculate percentage uncertainty?

A

The uncertainty / volume measured.

79
Q

What kind of glycosidic bonds does glycogen have?

A

1,4- and 1,6- glycosidic bonds.

80
Q

What kind of glycosidic bonds does cellulose have?

A

Only 1,4- glycosidic bonds.

81
Q

How can glycogen act as a source of energy?

A

It can be hydrolysed to glucose. This glucose can then be used in respiration.

82
Q

What is the difference between alpha and beta glucose?

A

The position of hydrogen and hydroxyl groups on carbon atom 1 are inverted.

83
Q

Describe the test for lipids.

A

Dissolve in ethanol then add water and shake. White emulsion = positive result.

84
Q

Suggest and explain a procedure that a scientist could use to stop
a reaction.

A

Add a strong acid. This results in the enzyme being denatured.

AS Level Biology flashcards (5 decks)

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