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AQA A Level Biology > 3.1 Chapter 2- Nucleic Acids, Water and Inorganic Ions > Flashcards

3.1 Chapter 2- Nucleic Acids, Water and Inorganic Ions Flashcards

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1
Q

What do nucleic acids do?

A

Nucleic acids carry the genetic code. for the production of proteins. Information carrying molecules.

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2
Q

Where are nucleic acids found and what is this evidence for?

A

The genetic code is common to viruses and all living organisms, it is found in all living cells, providing indirect evidence for evolution.

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3
Q

What does DNA do?

A

DNA stores genetic information and passes on genetic information as it is hereditary material The variety of sequences of bases in DNA provides genetic diversity.

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4
Q

What does RNA do?

A
  • RNA transfers genetic information from DNA to the ribosomes, and is read to make polypeptides in translation.
  • RNA is combined with proteins to form ribosomes.
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5
Q

What are the similarities between RNA and DNA?

A

Both RNA and DNA are polynucleotides formed in a condensation reaction between a pentose sugar and a phosphate group forming phosphodiester bonds. Both have a sugar phosphate backbone formed by the nucleotide chains.

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6
Q

Describe the structure of RNA.

A
  • Relatively short polynucleotide chain- made of nucleotide monomers
  • Single stranded
  • 3 types
  • Nucleotides contain ribose pentose sugar, a phosphate group and an organic nitrogenous base of either adenine, cytocine, guanine or uracil which replaces thymine.
  • Nucleotides are joined together by phosphodiester bonds between the ribose and the phosphate group forming a sugar- phosphate backbone.
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7
Q

Describe the structure of DNA.

Not enough space on original paper

A
  • Long polynucleotide chain- polymer of nucleotides.
  • Double helix - two strands in a spiral held together by hydrogen bonds. Double helix forms a structural backbone.
  • The strands run antiparallel and in opposite directions.- the phosphate at one end and the pentose sugar at the other end.
  • Each nucleotide contains a deoxyribose pentose sugar, a phosphate group and a nitrogenous organic base of either adenine, thymine, cytocine or guanine.
  • The nucleotides are joined together by phosphodiester bonds between the pentose sugar and the phosphate group formed in a condensation reaction catalysed by DNA polymerase.
  • Bases held together by hydrogen bonds to form the double helix: adenine and thymine have two hydrogen bonds, cytosine and guanine have three hydrogen bonds.
  • The DNA is tightly coiled to store a large amount of genetic information in a small space.
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8
Q

What is deoxyribose made of vs ribose?

A

Deoxyribose- OH and H
Ribose- OH and OH

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9
Q

What are the 3’ and 5’ ends and what does “’” mean?

A

’= prime. 3’- third carbon of pentose sugar unattatched. 5’- phosphate attatched to 5th carbon.

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10
Q

How are phosphodiester bonds formed in DNA?

A
  • Condensation reaction occurs
  • Bonds formed between phosphate and deoxyribose
  • Loss of water
  • catalysed by DNA polymerase.
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11
Q

What type of molecules are DNA and RNA and what are they made of?

A

Polymers of nucleotides- polynucleotides made of nucleotide monomers.

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12
Q

What does DNA stand for?

A

Deoxyribosenuceic acid.

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13
Q

What does RNA stand for?

A

Ribosenucleic acid

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14
Q

What are nucleotides made of?

A
  • A pentose sugar (5 carbons), deoxyribose or ribose.
  • A nitrogenenous organic base (adenine, thymine, cytocine, guanine or uracil)
  • A phosphate group
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15
Q

Draw a nucleotide and label it (including the carbons)

A

Answer on revision card.

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16
Q

Draw DNA.

A

Answer on revision card.

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17
Q

How are nucleotide components joined together?

A

By a condensation reaction

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18
Q

What did two mononucleotides form and how do they form it?

A
  • Form dinucleotides in a condensation reaction
  • Contain phosphodiester bonds between the pentose sugar and the phosphate group.
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19
Q

What happens if mononucleotides keep on joining?

A

A polynucleotide forms.

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20
Q

What was there some doubt about surrounding DNA and RNA and how was this disproved?

A
  • There was doubt about DNA and RNA carrying the genetic code as they are very simple molecules. Some argued that protiens carried the genetic code.
  • Virus and mouse experiments involving bacteria disproved this
  • DNA structure was worked out by Franklin, Crick and Watson.
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21
Q

What are pyrmadines and describe their structure?

A
  • One ringed structure bases
  • Thymine, cytocine and uracil
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22
Q

What are purines and describe their structure.

A
  • Two ringed structure bases
  • Guanine and Adenine
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23
Q

How are two polynuclear strands joined together?

A

Two polynucleotide strands are joined by hydrogen bonds between specific complementary bases.

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24
Q

Describe the different bond structures between bases.

A

Guanine and Cytocine- 3 hydrogen bonds- more stable
Adenine and Thymine- 2 hydrogen bonds
There are always equal amounbts of adenine and thymine, and guanine and cytocine.

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25
Q

What is hugely important about nitrogenous bases?

A

Their sequence- determines the genetic code.

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26
Q

Describe how DNA suits its purpose.

A
  • Sugar phosphate backbone- protects the bases as well as the helix structure
  • Hydrogen bonds keep the molecule upright, stable and together. Easily broken which allows the strand to separate for protein synthesis and DNA replication by enzymes.
  • Stability- passes from one cell to another without change, mutations rare and often repaired
  • Large molecule- stores lots of genetic information
  • Double helix wrapped around histones- keeps the structure compact to store large amounts of genetic information in a small space
  • Complementary base pairing- accurateand easy DNA replication.
  • Two strands- both can act as templates for DNA replication
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27
Q

When and why does DNA replicate and how does it replicate to ensure this

A
  • Copies itself before cell division
  • Ensures each cell has a full set of DNA, and is genetically identical to the parent cell.
  • Replicated semi-conservatively to ensure genetic continuity.
28
Q

What is required to drive DNA replication?

A

A source of chemical energy.

29
Q

Describe DNA replication.

A
  1. DNA helicase breaks the hydrogen bonds between complementary bases. The helix unwinds and forms two single separate strands which become template strands that determine the order of nucleotides/ bases.
  2. The original strand acts as a template strand that free floating DNA nucleotides are attracted to by complementary base pairing rule. The nucleotides are attracted to their complementary exposed base (Guanine to Cytocine, Adenine to Thymine) and form complementary base pairs and therefore strands.
  3. Adjacent DNA nucleotides are joined together in condensation reactions between the sugar and the phosphate catalysed by the enzyme** DNA polymerase** forming phosphodiester bonds. Hydrogen bonds form between the original and the new strand.
  4. Each molecule contains one original strand and one new strand- semi-conservative replication.
30
Q

What is polymerase complementary to and how does this affect DNA replication?

A
  • DNA polymerase has an active site that has a specific shape that is only complementary to the 3’ end and only binds to this end of the new DNA molecule as the shape of each end of the nucleotide is different.
  • The new strand is therefore made in a 5’ to 3’ direction.
  • DNA Polymerase moves down the template strand in a 3’ to 5’ direction.
  • Because DNA is antiparallel the DNA polymerase working on the old template strand moves in opposite directions to the DNA polymerase working on the new strand. This creates fragments on one side- okasaki fragments- that have to be sealed.
31
Q

What were the evidence for DNA as hereditary material?

A
  • Test with non-harmful and harmful bacteria injected into mice
  • Test using radioactively labelled viruses to infect bacteria
  • Discovery of the structure of DNA by Franklin, Crick and Watson
32
Q

Describe the test for DNA as hereditary material involving mice.

Hint: 5 steps

A
  • Inject seperate mice firstly with non-harmful living bacteria, then dead harmful bacteria, then with both dead harmful bacteria and live non-harmful bacteria.
  • The mice injected with both the dead harmful and the live non-harmful bacteria become ill.
  • This suggests there was a transforming principle passed between the bacteria
  • The transforming principle can be found by removing different molecules within the bacteria.
  • Only when DNA is destroyed using DNAase does the bacteria become non-harmful and the mouse become not ill, suggesting DNA was the genetic material passed between bacteria to make the bacteria harmful.
33
Q

Describe the test for DNA as hereditary material involving viruses.

Hint: 5 steps

A
  • A virus is taken and some viruses have their proteins coat labelled radioactively and some have their DNA labelled radioactively.
  • One bacteria sample was infected by viruses with radioactive protien and another bacteria sample was infected by viruses with radioactive DNA.
  • Only the viruses with the DNA labelled caused the bacteria to become radioactive and produce more radioactive viruses.
  • The radioactive protien coats remained outside of the bacteria and the viruses produced by these bacteria were not radioactive.
  • This evidenced that DNA had provided the genetic information used to make viruses as only the DNA was passed between viruses- DNA heriditary material
34
Q

What theory did Crick and Watson suggest, and who was this verified by?

A
  • Suggested semi-conservative replication theory over the previous theory of conservative replication.
  • Meselson and Stahl proved this
35
Q

Describe the experiment for testing semi-conservative DNA replication.

Hint: 7 steps. Not enough paper on original.

A
  1. Put bacteria in heavy nitrogen and the bacteria absorb the nitrogen and use it to make their DNA.
  2. Transfer the bacteria into light nitrogen and let it replicate for one generation.
  3. The DNA in the baceria was centrifuged to seperate it and show its density. The lighter the DNA the more it would float to the top of the tube.
  4. The mass of new bacteria shows which model occured.
  5. The bacteria grown in heavy nitrogens DNA sunk to the bottom whereas the bacteria grown for one generation in the light nitrogen’s DNA floated to the middle suggesting semi conservative replication as half the DNA had one strand of new light nitrogen and half the DNA had one strand of old heavy nitrogen.
  6. This opposed conservative replication as the DNA would split into two seperations with being one heavy old DNA molecules sinking to the bottom and one being light new DNA molecules floating to the top.
  7. Further proved by allowing the bacteria to replicate for a second time. This time the bacterias DNA did split as due to semi conservative DNA replication half of the DNA was made of purely new light nitrogen strands and half the DNA was made of a mixture of light and heavy strands. This proved that the model wasn’t dispersive (random mix of old and new) as more than two seperations would occur in generation two.
36
Q

What does ATP stand for?

A

Adenosine Triphosphate

37
Q

What is the role of ATP?

A

Carries energy around the cell to where it’s needed.

38
Q

Describe ATP’s structure .

A
  • A nucleotide.
  • Ribose (pentose sugar)
  • Adenine (an organic nitrogenous base)
  • 3 phosphate groups
39
Q

Draw ATPs structure and label it.

A

Answer on revision card.

40
Q

Describe how ATP is formed.

A
  • ATP is formed in a condensation reaction between ADP (Adenosine Diphosphate) and inorganic phosphate (Pi).
  • Requires energy from an energy releasing reaction (e.g. respiration or photosynthesis)
  • Catalysed by ATP synthase.
  • This process is known as phosphorylation as a phosphate molecule is added to the ADP.
41
Q

When is ATP synthesised?

A
  • During photosynthesis- photophosphorylation
  • During respiration- oxidative phosphorylation
  • When phosphate groups are transferred from donor molecules to ADP- substrate-level phosphorylation
42
Q

How does ATP store energy and what are the features of this store?

A
  • Stores energy made in respiration in the chemical store of the phosphate bonds (bonds between phosphate groups).
  • ATP diffuses ot parts of the cell that need energy.
  • Unstable and low activation energy, easily breakable.
43
Q

How is energy released from ATP?

A
  • ATP hydrolase (ATPase) breaks the phosphate bonds in a hydrolysis reaction (requiring water).
  • Hydrolysing bonds- releases energy, splits the ATP into a ADP (Adenosine Diphosphate) and inorganic phosphate (Pi).
  • The chemical energy released can then be used by the cell.
44
Q

What type of reaction is the hydrolysis of ATP and give details of this.

A
  • A reversible reaction.
  • ADP and Pi are recycled to form ATP again.
45
Q

What is the formula of ATP reactions?

A

ATP + H2O ⇌ ADP + Pi

46
Q

What are the benefits of using ATP as an energy source?

A
  • Energy released in smaller, more manageable amounts, as it stores less energy, meaning little energy lost as heat.
  • Small, soluable molecule- easily transported around the cell.
  • ATP can be rapidly reformed once used up.
  • Can’t leave cells so cells always have an immediate supply of energy.
  • Immediate energy release- easily broken down by single reaction hydrolysis vs glucose/ other stores release- long process, several steps.
  • Can make other molecules more reactive by transferring one of it’s phosphate groups (phosphorylation).
47
Q

What are the problems of using ATP as an energy source?

A
  • Not a long term energy source- can’t be stored as immediate energy source due to unstable phosphate bonds, whereas carbohydrates and fats can be used as storage.
  • Stores less energy than glucose/ other stores.
48
Q

Why does ATP have to be constantly remade and what does this require?

A
  • Immediate energy release due to unstable bonds and single reaction hydrolysis.
  • Requires ATP to be constantly remade in the mitochondria.
  • Explains the large number of mitochondria.
49
Q

What are the uses of ATP?

A
  • Metabolic processes- provides energy for making macromolecules e.g. starch, DNA.
  • Muscle contraction- used for movement- more ATP hydrolysis means more muscle contraction.
  • Active transport- changes the shape of carrier proteins.
  • Secretion- needed to form lysosomes.
  • Phosphorylation- activation of molecules- inorganic phosphate (Pi) can be added to other compounds to make them more reactive- lowers the activation energy especially in enzyme catalysed reactions.
50
Q

Describe ATP coupling.

A

ATP hydrolysis can be coupled to energy requiring reactions in the cell. The energy released is used directly to make reactions happen rather than being lost as heat.

51
Q

What is water made of?

A

Two hydrogen atoms convalently bonded to one oxygen atom

52
Q

Why does the search for life involve the search for water?

A

Water is the most common component of life.

53
Q

How is water polar?

A
  • Water is dipolar (a polar molecule) but has no overall charge
  • The hydrogen atom has a slightly positive charge (δ+) as its electrons are pulled towards the oxygen and the oxygen has a slightly negative charge (δ-) as it doesn’t share its electrons but gains electrons from the hydrogen.
54
Q

Describe the bonding of water.

A
  • Forms hydrogen bonds
  • The positive poles are attracted to the negative poles and form weak hydrogen bonds that cause the water to stick together.
55
Q

Name and describe the properties of water.

Hint: 9 points

A
  • Transparent- photosynthesis underwater and sight.
  • Reactive- important metabolite used in photosynthesis, hydrolysis and condensation reactions as well as other reactions. e.g. formation of ATP and polymers.
  • Solvent- ions get surrounded by water molecules and dissolve, due to the polarity of water attracting it to the charges. Lots of metabolic reactions use dissolved ionic substances as metabolites in chemical reactions. Dissolving allows substances to be transported around the body, e.g. gases, wastes, ATP, amino acids, monosaccharides, enzymes.
  • Not easily compressed- enables support. e.g. turgid plant cells, skeleton of animals e.g. jelly fish.
  • High specific heat capacity- due to hydrogen bonds the water can gain and lose energy without a temperature change and a large amount of energy is needed to change the temperature because more heat energy is needed to break the hydrogen bonds and less energy is available to raise the temperature. No rapid temperature changes occur. Buffers the temperature change, keeps habitat and an internal body temperature stable and constant.
  • High latent heat of vaporisation- hydrogen bonding hard to break- lots of energy required. Water carries away large amount of heat energy, which creates a cooling effect through evaporation. Organisms can cool down through sweat without using much water.
  • Cohesion- molecules stick together due to hydrogen bonds and polar attraction, making water flow and travel up tubes, e.g. xylem, columns of water.
  • High surface tension- when reaches air, supports a small organisms e.g. pondskaters and forms droplets.
  • Solid form of ice- lower density than water- floats above water forming two habitats so that organisms living underneath the water don’t die and organisms can also live above the water.
56
Q

What are ions?

A
  • Charged particles.
  • Positive ions are cations
  • Negative ions are anions.
57
Q

What are inorganic ions?

A

Ions that don’t contain carbon.

58
Q

Where do inorganic ions occur and how do they vary?

A
  • Ions occur in solution (e.g. the cytoplasm, body fluids) and as part of larger molecules.
  • Ions can vary in concentration from very high to very low depending on their role.
59
Q

Name the main inorganic ions.

A
  • Hydrogen ions
  • Iron ions
  • Sodium ions
  • Phosphate ions
60
Q

What are functions of ions related to?

A

Their properties.

61
Q

What is the role of hydrogen ions?

A
  • Concentration determines the pH.
  • High concentration equals a lower pH- inverselly proportional
  • Affects of the function of enzymes.
62
Q

Describe the function of iron ions.

A
  • Found in haemoglobin in red blood cells- binds to oxygen and transports it around the body.
  • Haemoglobin is made of 4 polypeptide chains with Fe2+ in the centre of each haemoglobin molecule.
  • Fe2+ binds to the oxygen and becomes Fe3+ until release.
63
Q

What is the function of sodium ions?

A
  • Sodium ions are used in the co-transport of glucose and amino acids.
  • Move by active transport, create a diffusion gradient which affects the water potential/ concentration gradient.
64
Q

What is the function of phosphate ions?

A
  • PO43-
  • Once attatched to another molecule, becomes a phosphate group
  • Used in DNA and RNA in phosphodiester bonds and the sugar phosphate backbone
  • Used in ATP to store energy
  • Affect the water potential
  • Phosphorylates compounds making them more reactive
  • Forms the hydrophillic part of the phospholipid bilayer
65
Q

What do all ions do to the water potential?

A
  • Lower the water potential of the area
  • Water moves in the area by osmosis.
66
Q

How are ions transported?

A
  • By active transport/ co-transport with carrier protiens
  • By channel proteins in facilitated diffusion.

AQA A Level Biology (12 decks)

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