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Biology Paper 1 A Level AQA > 3.1- Biological Molecules > Flashcards

3.1- Biological Molecules Flashcards

1
Q

What are biomolecules?

A

Groups of chemicals that are found in living organisms.

4 main types- carbohydrates, lipids, proteins, nucleic acids.

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2
Q

What are monomers? +3 examples

A

Small subunits that can be linked together to form long chains called polymers.

monosaccharides, amino acids, nucleotides

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3
Q

What are polymers? +3 examples

A

Molecules made from a large number of monomers joined together in a chain through process of polymerisation.

starch, DNA, protein

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4
Q

What is a condensation reaction?

A

Joining 2 molecules together with the formation of a chemical bond- involves the elimination (release) of a water molecule. (Giving out of water.)

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5
Q

What is a hydrolysis reaction?

A

A reaction that breaks a chemical bond between 2 molecules- involves the use of water molecule. (Taking in of water.)

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6
Q

What is a solvent?

A

A liquid that has dissolved a substance.

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7
Q

What is a solute?

A

The substance that has dissolved.

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8
Q

What is a solution?

A

Solvent+ Solute

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9
Q

What are carbohydrates?

A

Carbon molecules combined with water: made of C, H, O.

They are the sugars (saccharides.)

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10
Q

What are monosaccharides? +3 examples

A

The simplest carbohydrates, the monomers from which larger carbohydrates form.

Eg- glucose, galactose, fructose.

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11
Q

What does a condensation reaction between 2 monosaccharides form?

A

A glycosidic bond.

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12
Q

How is water formed in condensation reactions?

A

Water is formed through the grouping of a hydroxyl (-OH) from one monomer and a hydrogen (H) from another monomer.

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13
Q

Information about the monosaccharide glucose.

A

6 carbon sugar (hexose), atoms can be arranged in diff ways to produce 2 isomers- a-glucose and B-glucose.

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14
Q

Draw the structure of alpha and beta-glucose.

A

Alpha glucose has right OH group on bottom and H on top, Beta glucose has right OH group on top and H on bottom.

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15
Q

Why can the human body only use alpha-glucose?

A

Many chemical reactions in our bodies are controlled by enzymes.

Only 1 isomer of a given chemical fits the specific active site of the enzyme needed for it to react.

The reactions involving glucose are catalysed by an enzyme that only fits a-glucose in its active site.

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16
Q

What does the condensation of 2 monosaccharides create? +3 examples.

A

A disaccharide.

Eg- sucrose, maltose, lactose.

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17
Q

Word equation for sucrose?
+ what is it hydrolysed by?

A

a glucose + B fructose—-> sucrose + water

hydrolysed by sucrase

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18
Q

Word equation for lactose?
+ what is it hydrolysed by?

A

a glucose +B galactose—-> lactose + water

hydrolysed by lactase

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19
Q

Word equation for maltose?
+ what is it hydrolysed by?

A

a glucose + a glucose—-> maltose + water

hydrolysed by maltase

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20
Q

What are polysaccharides? + 3 examples.

A

Polymers formed by the condensation of many glucose units.

Eg- starch + glycogen (alpha glucose), cellulose (beta glucose.)

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21
Q

What is the test for reducing sugars?

A

Heat the liquid sample with Benedict’s reagent for 5 minutes.

A positive result would turn from blue—> red.

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22
Q

Why does a reducing sugar turn Benedict’s red?

A

It reduces copper (II) sulfate in Benedict’s to form insoluble red precipitate copper (I) oxide.

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23
Q

What is the test for non-reducing sugars?

A

1) The sugars need to be hydrolysed (broken down) into monosaccharides by using dilute HCl in boiling water for 5 mins.
2) Neutralise the acid using sodium hydrogencarbonate as Benedict’s does not work in acidic conditions.
3) Test using Benedict’s reagent as usual- heat and if the colour changes to red then non-reducing sugars are present.

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24
Q

What is the test for starch?

A

Add a few drops of iodine solution to the sample at room temperature.

A positive result would be indicated by a colour change from yellow to blue/black (BRUISE colour.)

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25
Q

What is starch?

A

Polymer of alpha glucose

A large complex polysaccharide found in plants with main role of energy/glucose storage. Insoluble- doesn’t affect osmosis/ water potential in cells.

Quickly hydrolysed- to a-glucose used in respiration.

Naturally occurs as amylose and amylopectin.

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26
Q

What is the structure of starch?

A

Alpha glucose molecules can join by condensation reactions to make glycosidic bonds at either 1-4 or 1-6 carbon atoms.

2 types of chains made- branched + unbranched.

Amylose- Unbranched polymer chain of a-glucose joined by 1-4 glycosidic bonds: coil tightly to form helical chains so lots can be stored in small space. As it is unbranched, it will be hydrolysed slowly. Insoluble

Amylopectin- Branched polymer of a-glucose with 1-4 and 1-6 glycosidic bonds:
more ends for rapid breakdown by enzymes simultaneously releases lots of glucose quickly. Insoluble. Not as compact due to branching.

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27
Q

Where is amylose/ amylopectin broken down by amylase?

A

In the mouth- by salivary amylase (pH 6.5-7)

The duodenum in small intestine- by pancreatic amylase (pH is 7-8 due to bile salts)

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28
Q

What is glycogen?

A

Polysaccharide of a-glucose joined by glycosidic bonds formed in condensation reactions.

Storage for animals +bacteria.

In animals= small granules stored in muscles and the liver.

Mass is not high in animals as fat is main energy storage molecule.

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29
Q

What is the structure of glycogen?

A

Highly branched chains with mix of 1-4 and 1-6 glycosidic bonds so there are more ends and enzymes can easily access+ hydrolyse glycosidic bonds to release glucose for respiration. The multiple ends allow simultaneous hydrolysis to occur.

Insoluble in water so will have no osmotic effect on the cell which could cause it to burst.

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30
Q

What is cellulose?

A

Polysaccharide made from 1-4 glycosidic bonds between beta-glucose monomers which forms long, straight, unbranched chains.

Chains held in parallel by many hydrogen bonds to form fibrils.

Found in plant cell walls.

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31
Q

What is the structure of cellulose?

A

It does not need to be broken down after it is made due to its function, so there is no branching.

Many hydrogen bonds provide collective strength for the cell wall.

Insoluble so won’t affect water potential of the cell.

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32
Q

Why is cellulose not broken down by animals?

A

They do not have cellulase

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33
Q

What are lipids? +2 main groups

A

They are biomolecules that are insoluble in water but soluble in organic solvents such as chloroform or acetone.

They are composed of fatty acids and glycerol or other alcohol backbones.

2 main groups- Triglycerides, phospholipids.

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34
Q

What are lipids main roles?

A

1) Flexibility and transfer role in plasma membrane.
2) An energy source
3) Waterproofing- insoluble in water-waxy cuticles of plants+insects.
4) Insulation- slow heat conductors
5) Protection- stored around delicate organs eg kidneys.

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35
Q

What are triglycerides?

A

Fats and oils- fats solid at room temp, oils liquid at room temp.

Called triglycerides: 3 fatty acids joined to 1 glycerol- formed by the condensation of 1 glycerol molecule and 3 fatty acid molecules.

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36
Q

Structure of triglycerides?

A

All have same basic structure- carboxyl group (-COOH) but hydrocarbon tail (R group) varies.

The difference in properties of fats +oils come from variations in the fatty acid/tail.

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37
Q

Why are lipids insoluble in water?

A

The hydrocarbon tails are hydrophobic- they repel water molecules.

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38
Q

How are triglycerides formed?

A

By the condensation of one molecule of glycerol and three molecules of fatty acid.

A condensation reaction between glycerol and each fatty acid chain (RCOOH) forms an ester bond. 3 water molecules are removed.

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39
Q

What are the 2 types of fatty acids R group?

A

Saturated + unsaturated.

Saturated- these do not have any double bonds between their carbon atoms.

Unsaturated- these have at least 1 double bond between their carbon atoms.
The double bond causes the chains to have a kink and the molecules to bend, they cannot pack closely together so they are liquid at RT (oils.)

1 double bond= monounsaturated, more than 1= polyunsaturated.

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40
Q

Compare triglycerides and phospholipids.

A

Both contain a glycerol molecule and fatty acids.

Triglyceride contains 3 fatty acid chains whereas phospholipid only has 2 fatty acid chains as 1 is replaced by a phosphate group

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41
Q

Structure of phospholipids?

A

Made of a glycerol molecule, 2 fatty acid chains and a phosphate group (attached to the glycerol.)

The 2 fatty acids bond to the glycerol via 2 condensation reactions, resulting in 2 ester bonds.

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42
Q

Properties of phospholipids?

A

Due to the negative charge of phosphate group, the head is hydrophilic- it can attract and interact with water.

The fatty acid chains do not have any charge so they are hydrophobic- they repel water but are able to attract and interact with lipids.

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43
Q

What is the emulsion test for lipids?

A

1) Add ethanol to sample
2) Dissolve sample by shaking vigorously
3) Add water, shake gently
4) Positive result= white/milky EMULSION

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44
Q

What happens when phospholipids are placed in water?

A

They arrange themselves in a 2 layer structure = phospholipid bilayer

This is the structure we see on membranes, cell surface membranes, or membranes on organelles in eukaryotic cells.

They are polar- due to 2 different charged regions: tails move inwards as they are repelled by water and hydrophilic heads move to the outside as they can interact with water.

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45
Q

What are proteins?

A

Polymers (and macromolecules) made of monomers called amino acids.

The sequence, type + number of the amino acids within a protein determines its shape and therefore its function.

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46
Q

What are proteins made of?

A

Large polymer biomolecules made up from amino acids (containing mostly hydrogen, carbon, nitrogen, oxygen) which are joined together by peptide bonds.

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47
Q

What is the test for proteins?

A

Add Biuret to sample.

Positive result = blue—>purple

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48
Q

What is general structure of amino acids?

A

A central carbon atom bonded to:
1) An amine group -NH2/ H2N
2) A carboxylic acid group -COOH
3) A hydrogen atom
4) An R group (how each amino acid differs + why amino acid properties differ e.g. whether they are acidic or basic or whether they are polar or non-polar.)

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49
Q

What is a peptide bond?

A

When a condensation reaction forms a bond between 2 amino acids.

Made by combining C atom of one amino acid and N atom of another atom.

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50
Q

How is water made in peptide bond?

A

Combining the -OH of carboxyl group of 1 amino acid and -H from the other amino acid.

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51
Q

What is a dipeptide?

A

The molecule formed when two amino acids react together in a condensation reaction

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52
Q

What is a polypeptide?

A

A polymer made of many amino acids joined together by peptide bonds.

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53
Q

What are the structural levels of proteins?

A

Primary structure

Secondary structure

Tertiary structure

Quaternary structure

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54
Q

What is the primary structure?

A

The sequence of amino acids bonded by covalent peptide bonds.

DNA of cell determines primary structure of a protein by instructing the cell to add certain amino acids in specific quantities in a certain sequence- affects the shape + function of the protein.

Specific for each protein.

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55
Q

What is the secondary structure?

A

Occurs when the weak negatively charged nitrogen and oxygen atoms interact with the weak positively charged hydrogen atoms to form hydrogen bonds.

2 shapes that can form within proteins due to the hydrogen bonds:

α-helix: polypeptide is wound to form a helix, held by H bonds running parallel with the long helical axis. Very stable+ strong

β-pleated sheet: polypeptide chain zigzags forming a sheet of antiparallel strands.

Secondary structure only relates to hydrogen bonds forming between the amino group and the carboxyl group

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56
Q

What is the tertiary structure?

A

Further folding of the secondary structure giving the protein its complex 3D shape, depends on primary structure for the side chain bonds.

The additional bonds forming between the R groups (side chains)

The additional bonds are:

  • Hydrogen (weak bonds between uncharged R groups)
  • Disulphide (only occurs between cysteine amino acids)
  • Ionic (occurs between charged R groups)
  • Weak hydrophobic interactions (some amino acids may be hydrophobic
    while others are hydrophilic) , in a water based env., a globular protein will orientate itself so that its hydrophobic parts are
    towards its centre + its hydrophilic parts are towards its edges.
57
Q

What are the 2 types of tertiary structure?

A

1) Fibrous proteins- look like rope: long, thin, insoluble. Keratin in hair, collagen in bone. Structural functions.

2) Globular proteins- more spherical in shape: soluble with no regular repeating pattern in primary structure. Enzymes, receptors. Biochemical functions.

58
Q

What are ionic bonds in the tertiary structure?

A

Formed between any carboxyl and amino groups that are not involved in forming peptide bonds.

Weaker than disulphide bridges, easily broken by changes in pH.

59
Q

What is the quaternary structure?

A

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

Each polypeptide chain in the quaternary structure is referred to as a subunit of the protein.

60
Q

What is the overall structure of proteins?

A

Amino acids are the monomers from which proteins are made- amino acids are joined together by peptide bonds formed in condensation reactions.

61
Q

What are enzymes?

A

-Globular (spherical) proteins with a tertiary structure.

-They catalyse specific reactions-usually only 1 to increase rate of reactions.

-They bind with the substrate(s) to release product(s)

62
Q

What is the substrate?

A

The molecule on which enzymes act on.

63
Q

How do enzymes work?

A

They lower the activation energy required for the reaction to occur by putting a strain on the bonds involved.

64
Q

What is activation energy?

A

The minimum initial amount of energy needed for a reaction to start.

65
Q

Types of enzymes?

A

Intracellular (within cells)- e.g. respiration enzymes, or extracellular (outside cells)- e.g. digestive enzymes.

66
Q

What is the structure of enzymes?

A

-They have a specific 3D tertiary structure as a result of their primary structure (specific sequence of amino acids)

-The specific area of enzymes that is functional = the active site which is a small depression within the larger enzyme molecule.

-The shape+size of the active site is part of the proteins tertiary structure which is determined by the primary structure.

unique primary structure—> unique tertiary structure—> unique shape of active site—> only catalyses 1 reaction

67
Q

What is the enzyme- substrate complex?

A

The substrates have a specific complementary shape to the active site.

The substrate is temporarily held within the active site by bonds between the amino acids of the active site and chemical groups on the substrate=
ENZYME-SUBSTRATE COMPLEX

In the ESC, the substrate is converted into products which is then free to leave the active site- enzyme can take on another substrate.

68
Q

What happens when an enzyme denatures?

A

The shape of the active site changes so it is no longer complementary to the substrate so fewer/ no enzyme substrate complexes formed.

69
Q

Explain the lock and key enzyme model.

A

One enzyme is specific to one substrate like one key is specific to one lock.

Made the enzyme’s active site to appear rigid and inflexible which it is not so the model has changed.

70
Q

Explain the new induced fit model.

A

Before the reaction, the active site is not complementary to the substrate.

The shape of the active site changes as the substrate binds in the enzyme-substrate complex.

This bends the bonds in the substrate leading to the reaction.

71
Q

What does rate mean?

A

A quantity measured and compared to another quantity measured.

Always expressed per unit of time- eg seconds.

72
Q

What happens in a graph measuring the product formed in an enzyme reaction?

A

Concentration increases, then plateaus.

-Initial ROR is high as lots of substrate is present, there are many empty active sites so high chance of ESC forming.

-All enzyme active sites are filled at any moment (peak ROR/steepest curve)

-As reaction proceeds, substrate is used up and more product made.

-Reaction slows as less substrate available so less successful collisions.

-Graph plateaus= all substrate has been used up!

73
Q

What happens in a graph measuring the substrate used in an enzyme reaction?

A

Concentration decreases, then plateaus.

74
Q

What 5 factors affect the rate of enzyme-controlled reactions?

A

Enzyme concentration, substrate concentration, concentration of competitive and of non-competitive inhibitors, pH and temperature

75
Q

Effect of temperature on rate of enzyme activity?

A

Increasing the temp. increases the kinetic energy: the particles move faster so there are more successful collisions. More substrates hit active site= more ESC’s formed.

After optimum temp., ROR decreases as too much kinetic energy causes the hydrogen bonds to break, the enzyme denatures. The active site loses its shape and it is no longer complementary to the substrate = no more ESC’s formed.

76
Q

Effect of pH on rate of enzyme activity?

A

Increasing pH increases ROR until optimum pH.

Above optimum pH, ionic bonds break causing the enzyme to denature. Active site loses its shape and is no longer complementary to the substrate= no more ESC’s formed.

77
Q

How do you calculate the pH?

A

pH = -log [H⁺]

78
Q

Effect of enzyme concentration on rate of enzyme activity?

A

Increasing enzyme conc. increases ROR as there are more active sites for the substrates to bind to= more ESC’s formed. Enzyme conc.= limiting factor

After certain point, there are more active sites than substrates so there is no further effect on ROR. substrate conc. = limiting factor.

79
Q

Effect of substrate concentration on rate of enzyme activity?

A

Increasing substrate conc. increases ROR as there are more collisions between the enzyme and the substrate= more ESC’s formed. Substrate conc.= limiting factor.

After certain point, there are not enough enzymes as all the active sites are full. Enzyme conc.= limiting factor.

80
Q

What are enzyme inhibitors? +2 types

A

Substances which interfere with the functioning of the active site of an enzyme therefore reducing activity.

2 types= competitive and non-competitive.

81
Q

Effect of competitive inhibitors on rate of enzyme activity?

A

A competitive inhibitor has a similar shape to the substrate.

The inhibitor can bind to the active site of the enzyme, therefore blocking the ESC from being formed.

82
Q

How can effect of competitive inhibitors be reduced?

A

By increasing the concentration of substrate, the effect of the competitive inhibitor will be reduced as there is more substrate entering the active site. More substrate than inhibitor.

83
Q

Effect of non-competitive inhibitor on rate of enzyme activity?

A

A non competitive inhibitor binds away from the active site, at the allosteric/ binding site.

When the NCI binds to the enzyme, it changes the tertiary structure of the enzyme and the shape of its active site.

This means the substrate molecules are no longer complementary to the active site, so no ESC’s can be formed.

Increasing substrate conc. has no effect on rate of enzyme activity.

84
Q

Difference between reversible and non- reversible inhibition?

A

Some inhibitors bind reversibly on their enzyme, meaning their effects can be reversed.

Reversible inhibitors form weak hydrogen or ionic bonds with their enzymes which can be easily broken.

Irreversible inhibitors typically form strong covalent bonds with their enzymes which cannot be broken.

85
Q

Example of a drug that works as an inhibitor?

A

Penicillin inhibits the enzyme that helps proteins form in bacterial cell walls.

Penicillin- an antibiotic that inhibits the enzyme transpeptidase in a bacteria’s cell walls, which weakens it and causes the bacteria to eventually rupture.

86
Q

What is end-product inhibition?

A

An example of negative feedback- (keeps levels of set molecules within a range, non-competitive inhibition ( as it takes place through the allosteric site of the enzyme.)

Many enzymes partake in a large metabolic pathway, a series of reactions which are all catalysed by enzymes. Eg- the product made by the 1st enzyme is used as a substrate for the 2nd enzyme.

In EPI, the final product in the pathway inhibits an early stage enzyme, reducing the rate of the metabolic pathway.

87
Q

What are the 2 main nucleic acids?

A

DNA and RNA

DNA holds genetic information and RNA transfers genetic information from DNA to the ribosomes, both are polymers of nucleotides.

88
Q

What are the 3 nucleotide components?

A

A pentose sugar (5 C atoms) , a nitrogen-containing organic base and a phosphate group.

89
Q

What are the components of a DNA nucleotide (monomer) ?

A

A pentose sugar (DEOXYRIBOSE), a phosphate group and one of the organic nitrogen-containing bases adenine, cytosine, guanine or THYMINE.

90
Q

How are DNA nucleotides joined together?

A

Condensation reactions between the deoxyribose sugar of one nucleotide and the phosphate group of another nucleotide, forming a phosphodiester bond.

These are strong covalent bonds which help ensure that the genetic code is not broken down.

91
Q

What is the sugar-phosphate backbone?

A

A way to describe the alternating sugar and phosphate groups. This is the backbone that supports the molecule, holding it together.

92
Q

What are the 2 base pairs of DNA?

A

C and G

A and T

93
Q

Structure of a DNA molecule?

A

A double helix with 2 polynucleotide chains which are anti-parallel held together by H-bonds between complementary base pairs:

  • Adenine=Thymine = 2 Hydrogen bonds (always equal amounts of A + T)
  • Cytosine☰Guanine 3 Hydrogen bonds (always equal amounts of C + G)

Sugar-phosphate backbone protects the genetic info.

94
Q

What would the evidence be for an organism containing single-stranded DNA?

A

If the complementary bases are different meaning there is no complementary base pairing.

If the % of A does not equal the % of T
If the % of G does not equal the % of C

95
Q

Where is DNA found?

A

DNA is found in the nucleus of eukaryotes and in the organelles, chloroplasts, and mitochondria. In prokaryotes, the DNA is not enclosed in a membranous envelope.

96
Q

How does the structure of DNA aid its function?

A

The phosphodiester bonds between the deoxyribose sugar and the phosphate groups create the sugar-phosphate backbone, forming a double helix: the stronger covalent bonds are on the outside of the helix and the weaker H bonds are in the middle of the helix ( they are protected).

DNA is double stranded so 1 strand can be used as a template during DNA replication.

The H bonds between the complementary bases are weak so the bonds can easily be broken with a low amount of energy during DNA replication.

Although DNA is large, as it has a double helix it can coil and condense tightly so lots of information can fit in a small space.

Complementary base pairing allows identical copies to be made in DNA replication.

97
Q

What are the components of an RNA nucleotide?

A

A pentose sugar (RIBOSE), a phosphate group and one of the organic nitrogen-containing bases adenine, cytosine, guanine or URACIL.

98
Q

How are RNA nucleotides joined together?

A

Nucleotides join together to form polynucleotide strands.

Condensation reactions between the ribose sugar of one nucleotide and the phosphate group of another nucleotide, forming a phosphodiester bond.

99
Q

Structure of an RNA molecule?

A

1 polynucleotide strand which is shorter than DNA polynucleotides. RNA is single stranded.

100
Q

What are the 2 base pairs of RNA?

A

C and G

A and U

101
Q

Difference in structure between DNA and RNA?

A

RNA has a hydroxyl group on the second carbon of the ribose but there is only a hydrogen on the second carbon of the deoxyribose - so deoxyribose is “missing” an -OH group.

Different base pairing- DNA uses the bases adenine, thymine, cytosine and guanine= pairs A+T, C+G. RNA uses adenine, uracil, cytosine and guanine= pairs A+U, C+G.

DNA polymers are longer than RNA polymers.

DNA is double-stranded, RNA is single-stranded.

DNA is limited to the nucleus, although RNA is made in the nucleus it can travel out of it.

102
Q

Differences between DNA and RNA monomers?

A

DNA contains the base thymine, RNA contains the base uracil.

DNA contains the pentose sugar deoxyribose, RNA contains the pentose sugar ribose.

103
Q

Differences between DNA and RNA polymers?

A

DNA is much larger as it contains all of the genes whereas RNA is shorter as it is only the length of one gene.

DNA is double stranded, RNA is single stranded.

104
Q

What are the 3 types of RNA?

A

rRNA, mRNA, tRNA

105
Q

What is messenger RNA? (mRNA)

A

A copy of 1 gene in the DNA: at the start of protein synthesis in the nucleus the DNA can slightly unravel and a copy of this is made in mRNA

DNA is too big to leave the nucleus to provide the genetic code to make proteins and it could be hydrolysed by enzymes which would destroy the genetic code, so a copy of the gene needed to make the protein is copied into mRNA.

mRNA is much shorter than DNA as it is just a copy of the bases from one gene so it can leave the nucleus.

mRNA is quickly degraded because it is only needed to code for a protein and by the time enzymes would have hydrolysed it, the mRNA would have already carried out its function.

It is single-stranded and 3 bases code for an amino acid. 3 bases are called codons.

106
Q

What is transfer RNA? (tRNA)

A

Only found in the cytoplasm

Single stranded but it folds in on itself to create a ‘clover leaf’ shape which is held in place by hydrogen bonds.

Its function is to transfer one of the 20 amino acids to the ribosome to create the polypeptide chain.

There are 3 exposed bases at the top which is where the amino acids attach: amino acid attachment site.

tRNA can attach and bring a specific amino acid to the mRNA which is attached to the ribosome. There is an anti-codon on tRNA that is complementary to the codon on mRNA.

107
Q

What is ribosomal RNA? (rRNA)

A

rRNA combines with a protein to make a ribosome.

108
Q

Where is RNA found?

A

mRNA- made in the nucleus before leaving the nucleus and entering the cytoplasm, it is destroyed after a few days.

tRNA- free moving around the cytoplasm.

rRNA- part of the ribosomes- made in the nucleus and sent to cytoplasm. Some are bound to the ER, some float freely.

109
Q

How does the extra hydroxyl group help RNA?

A

It is useful when converting the genetic code into mRNA as it makes RNA susceptible to degradation, also decreasing its stability .

110
Q

What type of replication does DNA do?

A

Semi-conservative replication.

111
Q

What is the parental DNA?

A

The name given to the original DNA that is going to be copied.

112
Q

What is the process of semi-conservative replication?

A

1) The enzyme DNA helicase breaks the hydrogen bonds between complementary bases on opposite strands of the DNA molecule, causing the double helix to unwind and the 2 strands to separate.

2) Each separated parental DNA strands acts as a template so the free floating nucleotides within the nucleus are attracted to their complementary base pairs (A+T, C+G) on the template strands. Nucleotides are not joined yet.

3) Once the nucleotides are bound, the enzyme DNA polymerase joins adjacent DNA nucleotides together by condensation reactions, forming phosphodiester bonds. Creates a DNA polymer.

4) 2 sets of daughter DNA contain 1 strand of parental DNA and 1 newly synthesised DNA strand.

113
Q

Why was the type of DNA replication discovered?

A

Watson and Crick discovered the structure of DNA in 1953 with the help of Rosalind Franklin’s research on x-ray diffraction.

They decided that DNA must replicate semi-conservatively or conservatively.

114
Q

Difference between semi-conservative and conservative DNA replication?

A

Semi-conservative is when each replicated DNA molecule contains one original (parental) DNA strand and one newly synthesised DNA strand.

Conservative replication is when the original DNA remains intact after replication and the 2 newly synthesised strands of DNA would combine together.

115
Q

What is the background behind the Meselson and Stahl experiment?

A

DNA bases contain nitrogen.

Nitrogen exists as 2 isotopes- 14N which is lighter and 15N which is heavier.

When bacteria grow, they can take in the nitrogen isotopes to make new DNA nucleotides.

Bacteria grown in a medium containing 14N will have DNA that only contains this isotope and will be lighter, bacteria grown in a medium containing 15N will have DNA that only contains that isotope and will be heavier.

DNA samples can be spun in a centrifuge and the DNA from the 15N would settle at the bottom as it is more dense but the DNA from the 14N would settle much higher up the test tube as it is less dense.

116
Q

What does the experiment mean by generation?

A

How many rounds of division have been allowed to occur.

Eg- generation 1 is 1 round of division.

117
Q

Outline the Meselson and Stahl experiment

A

1) They grew E Coli in a growth medium containing only 15N, all of DNA was made of 2 15N strands. After centrifugation, all of the DNA settled at the bottom.

2) Removed all E Coli from this medium and placed in growth medium containing only 14N, allowing it to divide once. Double helix split into 2 and the new DNA will form from the 14N isotope, all DNA contains 1 strand 15N and 1 strand 14N. After centrifugation, the DNA settled higher up the test tube.

3) Bacteria stays in 14N growth medium and replicates for the 2nd time. The 2 double helices split so there are 2 14N strands and 2 15N strands acting as a template. All new strands are made using 14N isotope so now there are 2 double helices with 1 strand 15N, 1 strand 14N and 2 double helices with 2 strands of 14N. After centrifugation, the middle band is 1 strand 15N, 1 strand 14N and the 2nd higher band is only made of 2 strands 14N.

4) 3rd round of division, bacteria grows in 14N medium. Now have 8 double helices, 1/4 have 1 strand 14N and 1 strand 15N and 3/4 have 2 strands 14N (THICKER LINE IN TEST TUBE).

118
Q

What does ATP stand for?

A

Adenosine Triphosphate

119
Q

Why are the phosphate groups inorganic?

A

They do not contain any carbon atoms, could be shown as P or Pi in a word equation.

120
Q

What is ATP + its structure?

A

The energy carrying molecule within living cells, it is an immediate energy source but cannot be stored so it is continuously reformed.

1 molecule of ATP contains a molecule of ribose ( a pentose sugar), a molecule of adenine ( a nitrogenous base) and 3 inorganic phosphate groups.

121
Q

Where does ATP production stop?

A

On the membranes of cells.

122
Q

How does ATP store energy?

A

In the bonds between its phosphate groups, when the pyrophosphate bond between the 2nd and 3rd phosphate group is broken, energy is released and can be used by the cells.

123
Q

What is the reversible reaction for the synthesis and hydrolysis of ATP?

A

ATP + water <——-> ADP + Pi (energy)

124
Q

How is ATP hydrolysed?

A

The bonds between the phosphate groups in ATP are unstable and easily broken, they have a low activation energy that needs to be overcome for hydrolysis to occur.

The enzyme ATP hydrolase catalyses the hydrolysis of ATP to Adenosine Diphosphate (ADP) and the inorganic phosphate group Pi.

125
Q

How does ATP transfer energy to different compounds?

A

The inorganic phosphate released during the hydrolysis of ATP can be bonded onto different compounds to make them more reactive. This is called phosphorylation- happens to glucose at the start of respiration to make it more reactive.

126
Q

How is ATP resynthesised?

A

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

127
Q

Difference between ATP and ADP?

A

ADP is similar to ATP as it is also composed of adenine and ribose sugar but it only has 2 phosphate groups, not 3.

ADP is the lower-energy molecule of the 2 because of the absence of the high energy pyrophosphate bond which is only present between the last 2 phosphate molecules.

128
Q

Give 2 ways in which ATP hydrolysis is used in cells.

A

For active transport- it provides energy for the carrier proteins to change shape.

To add phosphate to other compounds to make them more reactive.

129
Q

Why is ATP a better energy source than glucose?

A

1) ATP releases energy in small, manageable amounts so no energy is wasted= Cells do not overheat from wasted heat energy whereas the breakdown of glucose releases large amounts of energy which could result in wasted energy.

2) ATP and glucose are both small and soluble molecules= ATP can move around cytoplasm easily to provide energy for chemical reactions within the cell.

3) Only 1 bond is broken/ hydrolysed to release energy from ATP so the energy release is immediate whereas glucose would need several bonds to break to release its energy.

4) ATP can transfer energy to another molecule by transferring one of its phosphate groups through phosphorylation, glucose cannot do this.

5) ATP cannot pass out of a cell, it cannot diffuse through the cell surface membrane so every cell has a supply of ATP or ADP and Pi, glucose can move out of the cell.

130
Q

Why is water a polar molecule?

A

The oxygen atom has a slight negative charge and the hydrogen atoms have slight positive charges, so water has both negative and positive poles making it polar.

131
Q

Explain the 5 important properties of water.

A

It is a metabolite in many metabolic reactions, it is given out in condensation reactions and taken in in hydrolysis reactions.

is an important solvent in which metabolic reactions occur as it readily dissolves substances such as hydrogen as it is a polar molecule, supporting small organisms.

It has a high specific heat capacity so it can buffer changes in temperature: due to the H bonds so it can gain/lose a lot of heat energy without changing temp.

It has a relatively large latent heat of vaporisation, so it can provide a cooling effect with little loss of water through evaporation.

Has strong cohesion between water molecules; this supports columns of water in the plants and produces surface tension where water meets air- supporting small organisms.

132
Q

What are inorganic ions?

A

They occur in solution in the cytoplasm and bodily fluids of organisms, either in high or low concentrations. They do not contain carbon.

Each ion has a specific role.

133
Q

How does the body regulate ion levels?

A

Through the kidneys.

The process involves, filtration, reabsorption, secretion and hormonal control allowing the body to maintain its internal balance so all cells function properly.

134
Q

What are the 4 main inorganic ions in the body?

A

Iron, phosphate, hydrogen and sodium.

135
Q

Role of iron in the body?

A

Iron irons are key for oxygen transport in haemoglobin- which is mainly found in red blood cells.

Fe 2+ ions bind to the oxygen atoms, so iron is crucial for the survival of most organisms.

136
Q

Role of hydrogen?

A

Hydrogen irons are crucial in regulating the pH- the greater the concentration of hydrogen ions, the lower the pH. The lower the concentration of H+ ions, the higher the pH.

H+ ions help maintain the low pH of gastric juices within the stomach. Pepsin needs acidic conditions to work well, low pH also helps to sterilise food and kill bacteria.

H+ ions are also important in ATP synthesis in the mitochondria during respiration- there is a low concentration of H+ ions in the matrix and a high concentration in the membrane= a proton gradient which is used to generate energy/

137
Q

Role of sodium?

A

Helps molecules across the cell membrane enter a cell through co-transport.

Eg- glucose being absorbed in the samell intestine.

138
Q

Role of phosphate?

A

Phosphate ions are found attached to many biological molecules as phosphate groups- found in DNA, RNA and ATP.

ATP- energy is stored in phosphoanhydride bonds, energy released when the bonds break.

During respiration, chemical energy stored in food is converted to ATP to store it in a readily available form.

Phosphate groups can be added to molecules to make them more reactive through phosphorylation.

Phosphates found in phospholipids forming the phospholipid bilayer- used in cell membrane.

Biology Paper 1 A Level AQA (4 decks)

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