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A Level Biology > Topic 1 > Flashcards

Topic 1 Flashcards

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1
Q

What is the extent of the variety of life, both past and present?

A

The variety of life, both past and present, is extensive, but the biochemical basis of life is similar for all living things.

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2
Q

What are monomers?

A

Monomers are the smaller units from which larger molecules are made.

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3
Q

What are polymers?

A

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

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4
Q

Give examples of monomers.

A

Examples of monomers include monosaccharides, amino acids, and nucleotides.

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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, such as glucose, galactose, and fructose.

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8
Q

Which common monosaccharides are there?

A

Glucose, galactose, and fructose.

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9
Q

how is a glycosidic bond formed between two monosaccharides

A

condensation reaction removing a molecule of water

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10
Q

How is maltose formed?

A

Maltose is a disaccharide formed by the condensation of two glucose molecules.

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11
Q

How is sucrose formed?

A

Sucrose is a disaccharide formed by the condensation of a glucose molecule and a fructose molecul

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12
Q

How is lactose formed?

A

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

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13
Q

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

A

The two isomers of glucose are α-glucose and β-glucose.

alpha glucose has a hydroxyl group below and beta glucose has a hydroxyl group above

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14
Q

How are polysaccharides formed?

A

Polysaccharides are formed by the condensation of many glucose units.

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15
Q

Which polysaccharides are formed by the condensation of α-glucose?

A

Glycogen and starch.

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16
Q

Which polysaccharide is formed by the condensation of β-glucose?

A

Cellulose.

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17
Q

Describe the basic structure and function of glycogen.

A

Polysaccharide of a-glucose;
OR
polymer of a-glucose;

(Joined by) glycosidic bonds
OR
Branched structure;

Hydrolysed (to glucose);
Glucose used in respiration;

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18
Q

describe the basic structure and function of starch.

A

Starch is a mixture of amylose (unbranched)

and amylopectin (branched) used by plants to store glucose for energy.

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19
Q

Describe the basic structure and function of cellulose.

A

Cellulose is a linear polysaccharide that provides structural support in plant cell walls due to its high tensile strength.

Straight chains of cellulose interact with each other with hydrogen bonds.

This forms structures known as microfibrils.

These microfibrils provide strength to the cellulose
structure..

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20
Q

test for reducing sugars

A
  1. Heat with Benedict’s reagent (1);
  2. colour change from blue to brick-red (1)
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21
Q

test for non-reducing sugars

A
  1. Heat with Benedict’s reagent and no colour change (1);
  2. boil with acid (HCl) and then neutralise with (NaHCO3) (1);
  3. re- heat with Benedict’s reagent and colour change from blue to brick-red (1)
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22
Q

test for starch

A

add iodine

should turn blue-black

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23
Q

What are the two main groups of lipids?

A

Triglycerides and phospholipids.

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24
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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25
Q

What type of reaction forms an ester bond between glycerol and a fatty acid?

A

A condensation reaction.

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26
Q

What is the structural difference between saturated and unsaturated fatty acids?

A

saturated fatty acids have no double bonds between carbon atoms,

while unsaturated fatty acids have one or more double bonds.

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27
Q

How do phospholipids differ from triglycerides in their structure?

A

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

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28
Q

What are the implications of the structural differences between triglycerides and phospholipids?

A

TRIGLYCERIDES are good for energy storage because of there long hydrocarbon tails which contain lots of chemical energy.

They are also insouble so they dont affect water potential

PHOSPHOLIPIDS make up the bilayer of the cell membranes

their heads are hydrophilic and their tails are hydrophobic so they form a double layer with their heads facing out towards the water on either side.

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29
Q

What is the emulsion test for lipids?

A

The emulsion test involves mixing a sample with ethanol, then adding water. If lipids are present, a milky emulsion will form.

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30
Q

What is the significance of the R-group in fatty acids?

A

The R-group determines whether a fatty acid is saturated or unsaturated, which affects the physical properties of the lipid, such as melting point and fluidity.

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31
Q

What are the primary functions of triglycerides in the body?

A

Triglycerides serve as a major form of energy storage and provide insulation and protection for organs.

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32
Q

What role do phospholipids play in cells?

A

Phospholipids are key components of cell membranes,

heads hydrophilic and tails hydrophobic so form a double layer

forming bilayers that separate the cell’s interior from its external environment.

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33
Q

What are the different properties of triglycerides and phospholipids, and how do these relate to their structure

A

Triglycerides are primarily used for energy storage and insulation due to their hydrophobic nature,

making them insoluble in water.

Phospholipids, on the other hand, have both hydrophobic (fatty acid tails) and hydrophilic (phosphate group) regions,

allowing them to form the bilayer structure of cell membranes,

creating a barrier between the cell and its environment and facilitating cell signaling and transport.

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34
Q

What are amino acids and what is their general structure?

A

Amino acids are the monomers from which proteins are made.

The general structure of an amino acid includes an amine group (NH2), a carboxyl group (COOH),

and a side chain (R group) that varies among different amino acids.

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35
Q

How do the twenty common amino acids differ?

A

The twenty amino acids that are common in all organisms differ only in their side chain (R group).

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36
Q

What is formed during a condensation reaction between two amino acids?

A

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

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37
Q

What is a dipeptide?

A

A dipeptide is formed by the condensation of two amino acids.

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38
Q

What is a polypeptide?

A

A polypeptide is formed by the condensation of many amino acids.

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39
Q

What might a functional protein contain?

A

A functional protein may contain one or more polypeptides.

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40
Q

What roles do hydrogen bonds, ionic bonds, and disulfide bridges play in proteins?

A

Hydrdogen bonds are involved in the secondary structure of proteins forming between amino acids

ionic bonds and disulphide bridges are involved in the tertiary structure

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41
Q

What are the four levels of protein structure and their importance?

A

Primary structure: The sequence of amino acids in a polypeptide chain.

Secondary structure: The local folding of the polypeptide chain into alpha-helices and beta-pleated sheets.

Tertiary structure: The overall 3D shape of a polypeptide, stabilized by interactions such as hydrogen bonds, ionic bonds, and disulfide bridges.

Quaternary structure: The structure formed by the assembly of multiple polypeptide chains into a functional protein.

Importance: Each level of structure is crucial for the protein’s function.

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42
Q

What is the Biuret test for proteins?

A

The Biuret test for proteins involves adding Biuret reagent to a solution.

If proteins are present, the solution will change color to purple due to the reaction of copper ions with peptide bonds.

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43
Q

How do enzymes affect the activation energy of reactions?

A

Reduces activation energy;
Accept ‘reduces Ea’.

Due to bending bonds
OR
Without enzyme, very few substrates have sufficient energy for reaction;

Accept ‘Due to stress/pressure/tension on bonds’
OR ‘Due to weakening bonds.

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44
Q

What is the induced-fit model of enzyme action?

A

(before reaction) active site not complementary to/does not fit substrate;

  1. Shape of active site changes as substrate binds/as enzyme-substrate complex forms;.
  2. Stressing/distorting/bending bonds (in substrate leading to reaction);
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45
Q

How does the tertiary structure of an enzyme relate to its function?

A

The tertiary structure of an enzyme determines the shape and properties of its active site,

which is crucial for the enzyme’s ability to bind to specific substrates

and form enzyme-substrate complexes.

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46
Q

Why are enzymes specific to their substrates?

A

Enzymes are specific because their active sites have a unique shape

and chemical environment that only fits and interacts with specific substrate molecules,

ensuring that enzymes catalyze only particular reactions.

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47
Q

How does enzyme concentration affect the rate of enzyme-controlled reactions?

A

Increasing enzyme concentration generally increases the rate of reaction,

as more enzyme molecules are available to catalyze the reaction.

However, this effect plateaus when the substrate concentration becomes the limiting factor.

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48
Q

How does substrate concentration affect the rate of enzyme-controlled reactions?

A

Increasing substrate concentration increases the rate of reaction up to a point,

after which the rate levels off because all the enzyme active sites are occupied (saturation point).

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49
Q

What is the effect of competitive inhibitors on enzyme activity?

A
  1. Inhibitor similar shape to substrate;
    Reject same shape
    Accept ‘complementary to active site’
  2. Fits/binds to active site;
  3. Prevents/reduces enzyme-substrate complex forming;
50
Q

What is the effect of non-competitive inhibitors on enzyme activity?

A

Attaches to the enzyme at a site other than the active site;
Accept ‘attaches to allosteric/inhibitor site’

Changes (shape of) the active site
OR
Changes tertiary structure (of enzyme);

(So active site and substrate) no longer complementary so less/no substrate can fit/bind;

Accept ‘no longer complementary so less/no enzyme-substrate complexes form’

Accept abbreviations of enzyme-substrate complex.

51
Q

How does pH affect enzyme activity?

A

Enzymes have an optimal pH at which they function most efficiently.

Deviations from this optimal pH can lead to changes in the enzyme’s structure by breaking the bonds and a decrease in activity.

Extreme pH levels can denature the enzyme.

52
Q

How does temperature affect enzyme activity?

A

Temperature increases enzyme activity up to an optimal point by increasing molecular movement and collision rates.

Beyond this optimal temperature, enzyme activity declines as the enzyme denatures and loses its functional shape.

53
Q

How have models of enzyme action changed over time?

A

Early models, like the lock-and-key model, proposed that enzymes and substrates fit together perfectly.

This evolved into the induced-fit model,

which suggests enzymes are flexible and adapt their shape to better fit the substrate upon binding,

enhancing the catalytic process.

54
Q

What types of reactions do enzymes catalyze?

A

Enzymes catalyze a wide range of reactions,

including both intracellular reactions (within cells) such as DNA replication and cellular respiration, and extracellular reactions (outside cells)

such as digestion in the gastrointestinal tract.

55
Q

How do intracellular enzyme reactions contribute to cellular function?

A

Intracellular enzyme reactions regulate metabolic pathways,

control energy production,

and facilitate the synthesis and breakdown of molecules necessary for cell maintenance, growth, and division.

56
Q

How do extracellular enzyme reactions contribute to whole-organism functions?

A

Extracellular enzyme reactions, such as those involved in digestion,

break down complex molecules into simpler ones that can be absorbed and utilized by the body,

supporting overall nutrition, growth, and health.

57
Q

Why is enzyme specificity important for cellular and whole-organism function?

A

Enzyme specificity ensures that metabolic reactions occur in a controlled and efficient manner,

preventing unwanted side reactions and allowing precise regulation of biological pathways critical for health and development.

58
Q

What are the main functions of DNA and RNA in living cells?

A

DNA holds genetic information, and RNA transfers genetic information from DNA to the ribosomes.

59
Q

What are ribosomes made of?

A

Ribosomes are formed from RNA and proteins.

60
Q

What are DNA and RNA made of?

A

Both DNA and RNA are polymers of nucleotides.

61
Q

What are the components of a nucleotide?

A

A pentose sugar, a nitrogen-containing organic base, and a phosphate group.

62
Q

What components make up a DNA nucleotide?

A

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

63
Q

What components make up an RNA nucleotide?

A

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

64
Q

what is the bond between nucleotides called

A

a phosphodiester bond

65
Q

Describe the structure of a DNA molecule.

A

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

66
Q

Describe the structure of an RNA molecule.

A

An RNA molecule is a relatively short polynucleotide chain.

67
Q

Which bases pair together in DNA?

A

Adenine pairs with thymine, and cytosine pairs with guanine.

68
Q

Which bases pair together in RNA?

A

Adenine pairs with uracil, and cytosine pairs with guanine.

69
Q

What is the difference between the sugars in DNA and RNA nucleotides?

A

DNA contains deoxyribose, whereas RNA contains ribose.

70
Q

Why did many scientists initially doubt that DNA carried the genetic code?

A

The relative simplicity of DNA, with its seemingly repetitive structure and limited variety of components, led many scientists to doubt that it could carry the complex genetic code.

71
Q

What is the significance of semi-conservative replication of DNA?

A

It ensures genetic continuity between generations of cells.

72
Q

What happens to the DNA double helix during semi-conservative replication?

A

unwinding of the double helix

breakage of hydrogen bonds between complementary bases
in the polynucleotide strands

DNA helicase unwinds DNA breaking its hydrogen bonds

attraction of new DNA nucleotides to exposed bases on
template strands and base pairing

DNA polymerase joins adjacent nucleotides.

73
Q

Who are the key scientists credited with proposing the double helix model of DNA?

A

James Watson and Francis Crick.

74
Q

What was the significance of the Meselson-Stahl experiment in validating the Watson-Crick model of DNA replication?

A

It provided experimental evidence for the semi-conservative mechanism of DNA replication.

75
Q

How did the Meselson-Stahl experiment demonstrate semi-conservative replication?

A

By using nitrogen isotopes to label DNA and showing that after replication,

each DNA molecule consisted of one old and one new strand.

76
Q

What is the structure of a single molecule of adenosine triphosphate (ATP)?

A

A single molecule of ATP is a nucleotide derivative formed from a molecule of ribose,

a molecule of adenine, and three phosphate groups.

77
Q

Which enzyme catalyzes the hydrolysis of ATP to ADP and Pi?

A

The enzyme ATP hydrolase catalyzes the hydrolysis of ATP to adenosine diphosphate (ADP) and an inorganic phosphate group (Pi).

78
Q

How can the hydrolysis of ATP be utilized within cells?

A

The hydrolysis of ATP can be coupled to energy-requiring reactions within cells,

providing the necessary energy for these processes.

79
Q

How is ATP resynthesized in the cell?

A

ATP is resynthesized by the condensation of ADP and Pi,

a reaction catalyzed by the enzyme ATP synthase during photosynthesis or respiration.

80
Q

What can the inorganic phosphate (Pi) released during ATP hydrolysis be used for?

A

The inorganic phosphate (Pi) released during ATP hydrolysis can be used to phosphorylate other compounds, often making them more reactive.

81
Q

What role does ATP synthase play in the resynthesis of ATP?

A

ATP synthase catalyzes the condensation of ADP and Pi to resynthesize ATP during photosynthesis or respiration.

82
Q

During which cellular processes is ATP synthesized by ATP synthase?

A

ATP is synthesized by ATP synthase during photosynthesis and respiration.

83
Q

important properties of water that are important in biology

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.

84
Q

What role does water play in metabolic reactions?

A

Water acts as a metabolite in many metabolic reactions,

including condensation and hydrolysis reactions.

85
Q

How does water function as a solvent in biological systems?

A

Water is an important solvent in which metabolic reactions occur.

‘It dissolves a variety of substances, facilitating chemical reactions within cells.

86
Q

Why is water’s high heat capacity important in biological contexts?

A

Water’s relatively high heat capacity helps buffer changes in temperature,

providing a stable environment for biochemical reactions and living organisms.

87
Q

What is the significance of water’s large latent heat of vaporisation?

A

Water’s large latent heat of vaporisation provides a cooling effect with minimal water loss through evaporation.

This is crucial for temperature regulation in organisms, especially through sweating and transpiration.

88
Q

How does the cohesion between water molecules benefit plants?

A

The strong cohesion between water molecules supports columns of water in the tube-like transport cells of plants (such as xylem).

This cohesion also produces surface tension where water meets air,

which helps insects to walk on water and plants to transport nutrients and water efficiently.

89
Q

What role do hydrogen ions (H⁺) play in biological systems?

A

Hydrogen ions (H⁺) determine the pH of a solution, which affects enzyme activity and metabolic processes.

90
Q

What is the role of iron ions (Fe²⁺) in haemoglobin?

A

Iron ions (Fe²⁺) are a key component of haemoglobin, allowing it to bind and transport oxygen in the blood.

91
Q

Role of sodium ions

A

Sodium ions (Na⁺) facilitate the co-transport of glucose and amino acids across cell membranes via symporters, utilizing the sodium gradient.

92
Q

Why are phosphate ions (PO₄³⁻) important in DNA?

A

Phosphate ions (PO₄³⁻) form part of the backbone of DNA, linking together the deoxyribose sugars to create the structural framework.

93
Q

amylopectin and amylose

A

AMYLOSE
long and unbranched,

coiled structure so compact

so good for storage

AMYLOPECTIN
branched

so enzymes can break it down easily

94
Q

Which elements do all carbohydrates contain?

A

Carbon, Hydrogen and Oxygen

95
Q

Compare and contrast the structure and properties of triglycerides and phospholipids. [5 marks]

A
  1. Both contain ester bonds (between glycerol and fatty acid);
  2. Both contain glycerol;
  3. Fatty acids on both may be saturated or unsaturated;
  4. Both are insoluble in water;
  5. Both contain C, H and O but phospholipids also contain P;
  6. Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group;
  7. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region;
  8. Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don’t;
96
Q

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.

[4 marks]

A
  1. Glucose and galactose;
  2. Joined by condensation (reaction);
  3. Joined by glycosidic bond;
  4. Added to polypeptide in Golgi (apparatus);
97
Q

Describe the role of two named enzymes in the process of semi-conservative
replication of DNA.
[3 marks]

A
  1. (DNA) helicase causes breaking of hydrogen/H bonds (between DNA strands);
  2. DNA polymerase joins the (DNA) nucleotides;
  3. Forming phosphodiester bonds;
98
Q

Formation of an enzyme-substrate complex increases the rate of reaction. Explain how.
[2 marks]

A
  1. Reduces activation energy;
  2. Due to bending bonds
    OR
    Without enzyme, very few substrates have sufficient energy for reaction;
99
Q

Give two named examples of polymers and their associated monomers to illustrate
your answer.
[5 marks]

A
  1. A condensation reaction joins monomers together and forms a (chemical) bond and releases water;
  2. A hydrolysis reaction breaks a (chemical) bond between monomers and uses water;
  3. A suitable example of polymers and the monomers from which they are made;
  4. A second suitable example of polymers and the monomers from which they are made;
  5. Reference to a correct bond within a named polymer;
100
Q

Describe the biochemical tests you would use to confirm the presence of lipid in a sample (2)

A
  1. Add ethanol/alcohol then add water and shake/mix
    OR
    Add ethanol/alcohol and shake/mix then pour into/add water;
  2. White/milky emulsion
    OR
    emulsion test turns white/milky;
101
Q

Explain five properties that make water important for organisms.
[5 marks]

A
  1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
  2. A solvent so (metabolic) reactions can occur OR
    A solvent so allowing transport of substances;
  3. High heat capacity so buffers changes in
    temperature;
  4. Large latent heat of vaporisation so provides a cooling effect (through evaporation);
  5. Cohesion (between water molecules) so supports columns of water (in plants);
  6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;
102
Q

Describe the biochemical tests you would use to confirm the presence of non-reducing sugar (3)

A
  1. Do Benedict’s test and stays blue/negative;
  2. Boil with acid then neutralise with alkali;
  3. Heat with Benedict’s and becomes red/orange (precipitate);
103
Q

Describe the biochemical tests you would use to confirm the presence of amylase in a sample.
[2 marks]

A
  1. Add biuret (reagent) and becomes purple/violet/mauve/lilac;
  2. Add starch, (leave for a time), test for reducing sugar/absence of starch;
104
Q

Describe how a non-competitive inhibitor can reduce the rate of an enzyme-controlled reaction. (3)

A
  1. Attaches to the enzyme at a site other than the active site;
  2. Changes (shape of) the active site
    OR
    Changes tertiary structure (of enzyme);
  3. (So active site and substrate) no longer complementary so less/no substrate can fit/bind;
105
Q

Describe how an enzyme can be phosphorylated. (2)

A
  1. Attachment/association of (inorganic) phosphate (to the enzyme);
  2. (Released from) hydrolysis of ATP OR
    (Released from) ATP to ADP + Pi;
106
Q

Describe the role of DNA polymerase in the semi-conservative replication of DNA.
[2 marks]

A
  1. Joins (adjacent DNA) nucleotides;
  2. (Catalyses) condensation (reactions);
  3. (Catalyses formation of) phosphodiester bonds (between adjacent nucleotides);
107
Q

Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other end. (2)

A
  1. One amine/NH2 group joins to a carboxyl/COOH group to form a peptide bond;
  2. (So in chain) there is a free amine/NH2 group at one end and a free carboxyl/COOH group at the other
    OR
    Each amino acid is orientated in the same direction in the chain;
108
Q

Explain the function of this ATP hydrolase. (2)

A
  1. (ATP to ADP + Pi ) Releases energy;
  2. (energy) allows ions to be moved against a concentration gradient
    OR
    (energy) allows active transport of ions;
109
Q

Describe the structure of DNA. (5)

A
  1. Polymer of nucleotides;
  2. Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
  3. Phosphodiester bonds (between nucleotides);
  4. Double helix/2 strands held by hydrogen bonds;
  5. (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;
110
Q

Describe how a triglyceride molecule is formed. (3)

A
  1. One glycerol and three fatty acids;
  2. Condensation (reactions) and removal of
    three molecules of water;
  3. Ester bond(s) (formed);
111
Q

Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. (3)

A
  1. Substrate binds to the active site/enzyme
    OR
    Enzyme-substrate complex forms;
  2. Active site changes shape (slightly) so it is complementary to substrate
    OR
    Active site changes shape (slightly) so distorting/breaking/forming bonds in the substrate;
  3. Reduces activation energy;
112
Q

Compare and contrast the structure of starch and the structure of cellulose. [6 marks]

A
  1. Both polysaccharides
    OR
    Both are glucose polymers
    OR
    Both are made of glucose monomers;
  2. Both contain glycosidic bonds (between monomers);
  3. Both contain carbon, hydrogen and oxygen/C, H and O;
  4. Starch has α-glucose and cellulose has β- glucose;
  5. Starch (molecule) is helical/coiled and cellulose (molecule) is straight;
  6. Starch (molecule) is branched and cellulose is not/unbranched;

7.Cellulose has (micro/macro) fibrils and starch does not;

113
Q

Explain how two enzymes with different amino acid sequences can catalyse the same reaction.
[2 marks]

A
  1. (Both) active sites have similar/identical tertiary structures
    OR
    (Both) active sites have identical amino acid sequences;
  2. (So) form enzyme-substrate complexes (with the same substrate);
114
Q

Define the quaternary structure of a protein. (1)

A

More than 1 polypeptide

115
Q

Name the main polymer that forms the following cell walls.
Plant cell wall
Fungal cell wall

A

Cellulose (plants) and Chitin (fungi);

116
Q

Describe how a quaternary protein is formed from its monomers. Do not include the process of translation in your answer.
[5 marks]

A
  1. Amino acids joined by peptide bond(s);
  2. (By) condensation reaction(s);
  3. Secondary structure is formed by hydrogen bonding;
  4. Tertiary structure formed by interactions (between R groups);
  5. Quaternary structure contains >1 polypeptide
    OR
    Quaternary structure formed by interactions/bonds between polypeptides;
117
Q

Two proteins have the same number and type of amino acids but different tertiary structures.
Explain why.
[2 marks]

A
  1. Different sequence of amino acids
    OR
    Different primary structure;
  2. Forms ionic / hydrogen / disulfide bonds in different places;
118
Q

The secondary structure of a polypeptide is produced by bonds between amino acids.
Describe how.
[2 marks]

A
  1. Hydrogen bonds;
  2. Between NH (group of one amino acid) and C=O (group);
    OR
    Forming β pleated sheets / α helix;
119
Q

Describe how a peptide bond is formed between two amino acids to form a dipeptide. [2 marks]

A
  1. Condensation (reaction) / loss of water;
  2. Between amine / NH2 and carboxyl / COOH;
120
Q
A

Iron ions

  1. Haemoglobin binds/associates with oxygen
    OR
    Haemoglobin transports/loads oxygen;

Sodium ions

  1. Co-transport of glucose/amino acids (into cells);
  2. (Because) sodium moved out by active transport/Na – K pump;
  3. Creates a sodium concentration/diffusion gradient;
  4. Affects osmosis/water potential;
    Phosphate ions
  5. Affects osmosis/water potential;
  6. Joins nucleotides/in
    phosphodiester bond/in backbone
    of DNA/RNA/in nucleotides;
  7. Used in/to produce ATP;
  8. Phosphorylates other compounds
    (usually) making them more
    reactive;
  9. Hydrophilic/water soluble part of
    phospholipid bilayer/membrane;
121
Q
A

A Level Biology (10 decks)

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