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A-Level Biology > 1B | More Biological Molecules > Flashcards

1B | More Biological Molecules Flashcards

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1
Q

Outline the function of DNA.

A

DNA is used to store genetic information - that’s all the instructions an organism needs to grow and develop from a fertilized egg to a fully grown adult.

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2
Q

Give one function of RNA.

A

One of the RNA’s main functions is to transfer genetic information from the DNA to the ribosomes, wherein polypeptides are made.

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3
Q

Find A,B and C:

https://media.discordapp.net/attachments/352951793187029005/812073655928225842/unknown.png

What is this molecule called?

A 
A = Phosphate group
B = Pentose sugar
C = Nitrogenous base

Nucleotide

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4
Q

What are the monomers of DNA and RNA?

A

Nucleotide

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5
Q

What is the sugar in DNA called?

A

Deoxyribose

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6
Q

What is the sugar in RNA called?

A

Ribose

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7
Q

List the four bases of DNA.

A

Guanine
Cytosine
Thymine
Adenine

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8
Q

List the four bases in RNA.

A

Guanine
Cytosine
Uracil
Adenine

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9
Q

What is a sugar-phosphate backbone?

A

The sugar-phosphate backbone is a chain of phosphates connected to nucleotides’ pentose sugars.

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10
Q

In what reaction do nucleotides join together?

A

Condensation reaction

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11
Q

Name B to G:

https://media.discordapp.net/attachments/440608931182673931/812106149150326794/unknown.png

Name this structure.

A 
B = Phosphodiester bond
C = Phosphodiester bond
D = Base
E = Base
F = Phosphate Group
G = Pentose Sugar

Sugar-phosphate backbone

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12
Q

What is a phosphodiester bond?

A

A phosphodiester bond is a bond between two sugar groups and a phosphate group.

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13
Q

How many polynucleotide chains are there in DNA?

A

Two

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14
Q

How many hydrogen bonds are formed between Cytosine and Guanine?

A

Three

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15
Q

How many hydrogen bonds are formed between Adenine and Thymine?

A

Two

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16
Q

Adenine is complementary to…

A

Thymine

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17
Q

Guanine is complementary to…

A

Cytosine

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18
Q

In a DNA molecule, 20% of the bases are Adenine.

Calculate the percentage of bases which are Thymine.
Calculate the percentage of bases which are Guanine.

A

Thymine = 20%
This is because it is complementary to Adenine, so it must be a equal percentage.

G and C are the same and must be the same amount as the 2 remaining between the remaining 60%.
60 / 2 = 30

Guanine = 30%

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19
Q

Pick the right word:

In a DNA molecule, the polynucleotide strands are (parallel/antiparallel)

A

Antiparallel

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20
Q

How many polynucleotide chains are made of RNA?

A

One

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21
Q

DNA replication is described as semi-conservative.

What does semi-conservative mean in this context?

A

Semi-conservative replication refers to the fact that half of the new strands in each new DNA molecule are from the original DNA molecule.

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22
Q

Describe the process of semi-conservative DNA replication.

A

Firstly, DNA helicase, an enzyme, will enter the double stranded molecule of DNA.

DNA helicase separates the two strands in DNA by breaking the hydrogen bonds between the complementary bases.

This makes the helix begin to unwind in order to form two single strands.

Each original single strand acts as a template for a new strand, and so as DNA Helicase goes down the molecule, free-floating bases in the cytoplasm become attracted to the newly exposed bases on the single strands.

Two DNA polymerases, which are both enzymes, start to go down the single strands of exposed DNA and begin to join the complementary, attracted bases to each other by condensation reactions.

This creates two new strands of DNA, each combined with one template strand.

As a result of this, each new DNA molecule has a strand from the original DNA and one new strand.

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23
Q

In a DNA molecule, one polynucleotide strand has a 5’ end at the top and a 3’ end at the bottom.

For the second polynucleotide chain, where would the 5’ and 3’ ends be located?

A

5’ would be at the bottom
3’ would be at the top

This is due to the fact that polynucleotide chains in DNA are antiparallel.

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24
Q

Two DNA polymerases work on different polynucleotide chains.

DNA polymerase moves from the 3’ end to the 5’ end.
Polynucleotide chain 1 in the DNA has a 3’ end at the top.

Describe what direction (Up or down) DNA polymerase will be going in Polynucleotide chain 1 & 2.

A

Since DNA polymerase moves from the 3’ end to the 5’ end, this means that DNA polymerase begins at the top of Polynucleotide chain 1 and goes down.

Polynucleotide chain 1 = down

Polynucleotide chains are antiparallel. This means Polynucleotide chain 2 must have a 5’ end at the top and a 3’ end at the bottom.

This means that DNA polymerase starts from the bottom and goes up.

Polynucleotide chain 2 = up

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25
Q

Describe the experiment carried out by Meselson and Stahl which provided evidence for the Semi-Conservative replication of DNA.

A

Two samples of bacteria were grown, one in a broth containing light nitrogen, and one in a broth with heavy nitrogen.

As the bacteria reproduced, they took nitrogen from the broth to help make nucleotides for the new DNA. So, the nitrogen gradually became part of the bacteria’s DNA.

A sample of DNA was taken from each batch of bacteria, and spun in a centrifuge. The DNA from the heavy nitrogen bacteria settled lower down the centrifuge tube than the DNA from the light nitrogen bacteria because it is heavier.

Then, the bacteria grown in the heavy nitrogen broth were taken out and put in a broth containing only light nitrogen.

The bacteria were then left for one round of DNA replication, and then another DNA sample was taken out and spun in the centrifuge, meaning two DNA samples were taken from the bacteria this time.

If replication was conservative, the original heavy DNA, which would still be together, would settle at the bottom and the new light DNA (formed in conservative replication) would settle at the top.

If replication was semi-conservative, the new bacterial DNA molecules would contain one strand of the old DNA containing heavy nitrogen and one strand of the new DNA containing light nitrogen.

So, the DNA in semi-conservative replication would settle out in the middle of the centrifuge (because light nitrogen settled at top and heavy at bottom, top + bottom = middle)

As it turned out, the DNA settled out in the middle, showing that DNA molecules contained a mixture of heavy and light nitrogen. The bacterial DNA has replicated semi-conservatively in the light nitrogen.

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26
Q

List the three Pyrimidines.

A

Thymine (DNA)
Uracil (RNA)
Cytosine

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27
Q

List the two Purines.

A

Guanine

Adenine

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28
Q

What type of bond joins the nucleotides together at the sugar-phosphate backbone?

A - Glycosidic
B - Ester
C - Peptide
D - Phosphodiester

A

Phosphodiester

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29
Q

What kind of bond forms between the complementary base pairs?

A - Hydrogen
B - Phosphodiester
C - Ionic
D - Disulphide

A

Hydrogen

30
Q

What type of base are Thymine and Cytosine?

A - Purines
B - Pyrimidines
C - Riboses
D - Nucleotides

A

Pyrimidines

31
Q

What base would you find complementary to Cytosine in DNA?

A - Adenine
B - Guanine
C - Thymine

A

Guanine

32
Q

DNA is made up of 2 polynucleotide chains in what type of structure?

A

Double helix structure

33
Q

DNA is made up of 2 polynucleotide chains.

How do they stay together?

A

They are joined together by hydrogen bonding between their bases.

34
Q

What’s the key difference between the conservative and semi-conservative theories of DNA replication?

A

In semi-conservative DNA replication theory, the key feature is that the new DNA molecule has no polynucleotide strand belonging to the original DNA molecule.

In Semi-conservative DNA replication theory, the key difference is that the new DNA molecule has 1 polynucleotide strand belonging to the original DNA molecule, and 1 new polynucleotide strand.

Thus the key difference between them is in the way the new DNA molecule is formed as a product of DNA replication - in Semi conservative, the new DNA molecule has 1 polynucleotide strand from the original DNA, and in conservative, the new DNA molecule has no polynucleotide strand that belonged to the original DNA.

35
Q

Water makes up what % of a cell’s contents?

A

80%

36
Q

Give three features of water that makes it useful in living organisms.

A

Water is a metabolite - it is important in loads of metabolic reactions, including condensation and hydrolysis.

Water is a solvent, meaning some substances dissolve in it. Most metabolic reactions take place in a solution (e.g. in the cytoplasm) so water is pretty essential.

Water helps with temperature control because it has a high latent heat of vaporization and a high specific heat capacity.

Water molecules are very cohesive (they stick together) which helps water transport in plants as well as transport in other organisms.

37
Q

Water is cohesive.

Describe why this is important for the function of some living organisms.

A

Water molecules being cohesive means they stick together, thus this helps water transport through the xylem and phloem and as well as transport in other organisms.

38
Q

Water is a metabolite for which reactions?

Describe why metabolites are important for the function of some living organisms.

A

Being a metabolite for many important reactions, such as condensation and hydrolysis means that many essential reactions require the use of water molecules, which are needed by organisms to survive.

You can see this in the energy release of ATP where a hydrolysis reaction is necessary, as well as the joining of amino acid monomers which are condensation reactions to manufacture proteins such as enzymes to function in the body.

39
Q

Water is a solvent.

Describe why this is important for the function of some living organisms.

A

Water is a solvent, meaning some substances dissolve in it.

Most metabolic reactions take place in a solution (e.g. in the cytoplasm) so water is pretty essential.

40
Q

Describe the structure of a water molecule.

A

A molecule of water is one atom of oxygen joined to two atoms of hydrogen by shared electrons.

The way the electrons of hydrogen are joined to the Oxygen makes water a polar molecule - it has a partial negative charge on on side and a partial positive charge on the other.

41
Q

Water has a high latent heat of vaporization.

Describe what this is and why it is important in organisms.

A

Latent heat of vaporization refers to the amount of energy required to break the hydrogen bonds between water molecules, meaning that it’d start turning into a gas.

Water has a high latent heat of vaporization, meaning that a lot of energy is required and used up for water to evaporate.

This is useful for living organisms because it means they can use water loss through evaporation to cool down without losing too much water.
This also means, that in hot weather, living organisms will not lose too much water from evaporation due to it’s high latent heat of vaporization.

42
Q

Water can buffer (resist) changes in temperature.

Describe why this is possible and why it is important in organisms.

A

The hydrogen bonds between water molecules absorb a lot of energy.

So, water has a high specific heat capacity - it takes a lot of energy to heat up.

This is useful for living organisms because it means that water doesn’t experience rapid temperature changes.

This makes water a good habitat because the temperature under water is likely to be more stable than on land.
The water inside organisms also remains at a fairly stable temperature, meaning they can maintain a constant internal body temperature.

43
Q

What is cohesion?

A

Cohesion is the attraction between molecules of the same type.

44
Q

There is strong cohesion between water molecules.

Describe why this is useful for living organisms.

A

Strong cohesion helps water to flow, making it great for transporting substances. For example, it’s how water travels in columns up the xylem in plants.

Strong cohesion means that water also has a high surface tension when it comes into contact with air. This is the reason why sweat forms droplets, which evaporate from the skin to cool organisms down.

45
Q

Why is water cohesive?

A

Water is cohesive, meaning that the attraction between water molecules are often strong.

This is due to the fact that they are polar.

46
Q

Briefly describe the structure of a water molecule.

A

Water molecules contain one atom of oxygen and two atoms of hydrogen joined together by shared electrons.

One end of the water molecule has a partial positive charge, while the other end has a partial negative charge.

47
Q

In hot temperatures, elephants commonly spray themselves with water.

With reference to the structure and properties of water, explain why this behavior acts as a cooling mechanism for the elephant.

A

As the water evaporates from the surface of the elephant’s body, some of the elephant’s heat energy is used to break the hydrogen bonds which old the water molecules together.

This cools the surface of the elephant’s body.

48
Q

In hot temperatures, elephants commonly spray themselves with water.

With reference to the structure and properties of water, explain why water forms droplets when the elephant sprays it from it’s trunk.

A

Water is highly cohesive, meaning that the attraction between other water molecules are strong. This means that they are likely to join together.

As well as this, water has a high surface tension when it comes into contact with air, and as a result, it forms droplets when it comes in contact with the air.

49
Q

What does ATP stand for?

A

Adenosine Triphosphate

50
Q

Describe the structure of ATP.

A

ATP is consists of a nucleotide base, which is Adenine, with a hexose sugar known as Ribose which is joined to three phosphate groups.

51
Q

What is ATP’s function?

A

ATP’s function is to supply energy to the parts of the cell that need it.

52
Q

Where is the energy in ATP stored?

A

It is stored in high energy bonds between the phosphate groups. It’s released via hydrolysis reactions.

53
Q

When energy is needed by a cell, what happens?

A

ATP is broken into ADP and Pi (Adenosine Diphosphate and Inorganic Phosphate).

This is a hydrolysis reaction - a phosphate bond, a bond that contains a lot of energy, is broken and energy is released. This reaction is catalyzed by ATP Hydrolase.

54
Q

What is ATP broken into?

A

ADP and Pi.

55
Q

What does ‘Pi’ stand for?

A

Inorganic Phosphate

56
Q

What does ADP stand for?

A

Adenosine Diphosphate

57
Q

The released inorganic phosphate caused by a hydrolysis of ATP can be ‘put to use’.

How?

A

It can be added to another compound (this is known as phosphorylation), which often makes the compound more reactive.

58
Q

ADP + Pi can be re-synthesized.

What enzyme catalyzes this?

A

ATP Synthase

59
Q

ADP + Pi can be re-synthesized.

What processes cause this to happen?

A

Photosynthesis and Respiration

60
Q

Describe how ADP+Pi is re-synthesized.

A

ADP is adenosine diphosphate - it has 2 phosphates.

The inorganic phosphate, however, shown by the +Pi, should be near it and a condensation reaction to join the inorganic phosphate back to the ATP will occur, catalyzed by ATP Synthase. Energy is used up.

This creates ATP.

61
Q

Describe how ATP is hydrolyzed.

A

ATP is Adenosine triphosphate - it has 3 phosphate.

On the last bond seen between two phosphates, ATP Hydrolase breaks the bond by a hydrolysis reaction, releasing energy. This forms ADP+Pi.

62
Q

What is the base in ATP called?

A

Adenine

63
Q

The sugar in ATP is called what?

A

Ribose

64
Q

What is an ion?

A

An ion is an atom (or group of atoms) that have an electric charge.

65
Q

What is an inorganic ion?

A

An inorganic ion is an atom (or group of atoms) that have an electric charge - it does not contain Carbon.

66
Q

Inorganic ions are extremely important in living organisms.

List 2 inorganic ions.

A

Iron Ions
hydrogen Ions
Sodium Ions
Phosphate Ions

67
Q

Why are iron ions important in some living organisms?

A

Iron ions are an important part of Hemoglobin.

Hemoglobin is a large protein that carries oxygen around the body, in the red blood cells.

It is made up of four polypeptide chains, each with an iron ion in the center.

It’s the iron ion that actually binds the oxygen to the hemoglobin - so it’s a pretty key component. This means that oxygen can be transported through the body, thus giving hemoglobin it’s function.

Without an iron ion, oxygen could not bind to hemoglobin, meaning that the function of hemoglobin becomes removed and it is no longer able to supply oxygen to cells. This is fatal for some living organisms, including humans.

68
Q

Why are hydrogen ions important in some living organisms?

A

Hydrogen ions determine pH.

pH is calculated based on the concentration of Hydrogen ions in the environment.
The more hydrogen present, the lower the pH (more acidic), and vice versa.

Enzyme-controlled reactions are all affected by pH, and they are essential for many reactions as they are biological catalysts.

Therefore, if the Enzyme is not in it’s optimal pH, it can potentially stop working. As a result of this, Hydrogen is often extremely important to create the conditions required for certain proteins to function.

69
Q

Why are sodium ions important in some living organisms?

A

Sodium ions help transport glucose and amino acids across membranes.

A molecule of glucose or an amino acid can be transported into a cell across the cell surface membrane alongside sodium ions. This is known as co-transport.

As a result of this, sodium ions are necessary for the transport of glucose and amino acid molecules which may be necessary for the function of a cell. If sodium ions are not available, cells may not function which will affect the organism.

70
Q

Why are phosphate ions important in some living organisms?

A

Phosphate ions are essential components of ATP and DNA.

When a phosphate ion is attached to another molecule, it is known as a phosphate group.

DNA, RNA and ATP all contain phosphate groups.
It’s the bonds between phosphate groups that store energy in ATP which is then required to be released to give energy to cells.

The phosphate groups in DNA and RNA allow nucleotides to form up to form phosphodiester bonds.

As a result of this, the existence of no phosphate ion in any of these molecules render them useless, as DNA and RNA will not be able to form into strands and ATP will not be able to release energy to cells. This will have an affect on the organism as it will also not be able to function.

A-Level Biology (20 decks)

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