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A Level Biology > Nucleic Acids > Flashcards

Nucleic Acids Flashcards

1
Q

What does DNA and RNA do in all living cells?

A

DNA holds genetic information
RNA transfers genetic information from DNA to the ribosomes

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2
Q

What is the polymer of a nucleotide?

A

Polynucleotide

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3
Q

What is the monomer of a polynucleotide?

A

Nucleotide

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4
Q

Draw the Nucleotide in DNA

A
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4
Q

Draw the Nucleotide in RNA

A
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5
Q

What do DNA nucleotides consist of?

A

-deoxyribose sugar
-a phosphate group
-a nitrogenous base (Adenine, Cytosine, Guanine or Thymine)

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6
Q

What do RNA nucleotides consist of?

A

-ribose sugar
-a phosphate group
-a nitrogenous base (Adenine, Cytosine, Gusnine or Uracil)

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7
Q

How are polynucleotides formed?

A

the removal of water between two nucleotide monomers to form a phosphodiester bond

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8
Q

How are sugar phosphate backbones formed?

A

-polynucleotides are formed when many nucleotides link to form a long chain
-a phosphodiester bond between the phosphate group of one nucleotide to the 3rd carbon of the deoxyribose/ribose sugar in the next nucleotide
-forms a very strong and stable sugar phosphate backbone

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9
Q

What are the two groups of organic nitrogenous bases?

A

pyrimidine (single ring) and purine (double ring)

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10
Q

Which bases are pyrimidine?

A

-thymine
-cytosine
-uracil (ONLY IN RNA)

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11
Q

Which bases are purines?

A

-adenine
-guanine

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12
Q

What structure does DNA have and what does it consist of in terms of Watson and Crick’s DNA model?

A

-double helix structure
-consists of 2 polynucleotide chains held together by many weak H bonds between specific complimentary base pairs

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13
Q

How many hydrogen bonds form between the bases?

A

-two hydrogen bonds between Adenine and Thymine
-three hydrogen bonds between Cytosine and Guanine

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13
Q

What is the sequence of bases along a nucleotide chain?

A

it is variable

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14
Q

If you are given the % of 1 base how can you work out the rest of the bases?

A

If Adenine =30% Thymine is also 30% because they are complimentary
Take the total of these away from 100=40%
40/2=20%
Cytosine and Guanine =20% each

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15
Q

What is the function of DNA?

A

it codes for the sequence of amino acids (3 bases=triplet=1 amino acid)
long strands of DNA code for the primary structure of polynucleotide chains and proteins

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16
Q

How many bases make up 1 amino acid?

A

3 bases- a triplet

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17
Q

What is mRNA and what does it do?

A

it is a relatively short polynucleotide chain
it is normally a single stranded helix
-used to transfer genetic information from DNA to ribosomes

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18
Q

How are nucleotide strands arranged in a DNA molcecule?

A

-adenine pairs with thymine and cystosine with guanine
-the 2 strands run in opposite directions
-antiparallel
-(if the arrow points down, the arrow bit/bottom is the 3 prime end 3’ and the plain bit/the top is the 5 prime)

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19
Q

Why is the 5’ end and the 3’ end of a molecule labelled?

A

indicated which carbon is involved in the phosphodiester bond

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20
Q

How does the structure of DNA allow it to carry out its function?

A

-long molecule SO stores lots of information
-helical/coiled SO compact
-many weak H bonds SO DNA is a stable structure
-complimentary base pairs (A-T and C-G) ALLOWS accurate replication
-double stranded SO replication can occur semi conservatively because each strand can act as a template

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21
Q

Which two enzymes are involved in semi conservative replication?

A

DNA Polymerase + DNA Helicase

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22
Q

What is the role of DNA Polymerase in semi conservative replication?

A

-catalyses the condensation reaction between DNA nucleotides to form the sugar phosphate backbone of the new strand

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23
Q

What is the role of DNA Helicase in semi conservative replication?

A

-breaks the hydrogen bonds between complimentary base pairs so each strand can act as a template
(unzips helix)

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24
Q

How does semi conservative replication occur?

A
  1. the enzyme DNA Helicase moves along the DNA molecule unwinding the DNA and breaking Hydrogen bonds between base pairs
  2. the 2 strands seperate
  3. Each strand acts as a template
  4. New DNA nucleotides are attracted to exposed complimentary bases on template strands by base pairing
  5. The enzyme DNA Polymerase joins adjacent nucleotides together through a condensation reaction, forming phosphodiester bonds between new nucleotides in a 5’ to 3’ direction
  6. semi conservative replication ensures that each new DNA molecule contains an original and a new strand
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25
Q

How does DNA polymerase catalyse a condensation reaction?

A

-DNA Polymerase has a specific shape active site, only complimentary to the 5’ end of the incoming free DNA nucleotide and the 3’ end of the developing strand
-this catalyses a condensation reaction forming phosphodiester bonds between the last DNA nucleotide in the developing strand (3’) and new incoming DNA nucleotide (5’)

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26
Q

Describe the Messelson & Stahl DNA replication experiment

A

-used a heavy and a light isotope of nitrogen
-first has 2 N15
-then has 2 lots of N15 and 2 lots of N14 (first generation)
-split again to get 2 lots of n15 and 6 lots of N14 (second gen)
-split again to get 14 lots of N14 and 2 lots of N15 (3rd gen)

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27
Q

Messelson & Stahl

A

revise in booklet

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28
Q

What does an ATP molecule consist of?

A
  • a ribose sugar
    -3 phosphate groups
    -an adenine base
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29
Q

How is ATP formed?

A

-adenine diphosphate+ inorganic phosphate (phosphorylation)
-requires energy to add a phosphate group to ADP to form ATP creating a high energy bond
-involves a condensation reaction and the enzyme ATP synthase

30
Q

What are the uses of ATP?

A

-used as energy source in cells to carry out essential life processes (active transport, muscle contraction, protein synthesis)
-Phosphorylation (lowers activation energy making substrates more reactive by altering tertiary structures)

31
Q

Why is ATP useful?

A

-releases small amounts of energy
-instant energy source
-phosphorylates other compounds making them more reactive
-can be rapidly resynthesised
-does not leave cells but is soluble

32
Q

How can ATP return back to ADP and Pi?

A

-hydrolysed
-bond between the second and third phosphate breaks releasing small managebale amounts of usable energy
-ATP breaks down to ADP and Pi in a hydrolysis reaction (requires a water molecule and ATP Hydrolase)
-Pi can be used to phosphorylate other compounds and make them more reactive

33
Q

Where is ATP produced?

A

IN respiration and photosynthesis (NOT FOR THEM)

34
Q

Draw an ATP molecule

A
35
Q

Give 2 ways in which ATP is a suitable energy source for cells to use (2)

A

-releases small amounts of energy
-releases energy instantaneously
-phosphorylates other compounds making them more reactive
-can be rapidly resynthesised
-does not leave cells

36
Q

Give 2 ways in which the hydrolysis of ATP is used in cells (2)

A

-phosphorylates other compounds making them more reactive
-provides energy for active transport/muscle contraction

37
Q

Describe how ATP is resynthesised in cells (2)

A

-ADP + Pi
-by ATP Synthase
-In respiration

38
Q

Contrast the structures of ATP and a nucleotide found in DNA (2)

A

-ATP has ribose and DNA nucleotides have deoxyribose
-ATP has 3 phosphate groups and DNA nucleotides have 1
-in ATP the base is always adenine but in DNA nucleotides bases change/vary

39
Q

What are the important properties of water?

A

-is an important solvent in which metabolic reactions occur
-is a metabolite in many metabolic reactions, including condensation & hydrolysis reactions
-has a relatively high SHC which buffers changes in temp
-large latent heat of vaporisation=cooling effect
-strong cohesion between water molecules which supports columns of water

40
Q

What type of molecule is water?

A

dipole/polar
-has 2 slight charges

41
Q

In water, are electrons equally shared?

A

no, there is a slight negative charge on oxygen atoms

42
Q

How does water act as a solvent?

A

-polar molecules dissolve in water
-more molecules dissolve in water than anything else so it is known as the “universal solvent”
-major component of the cytoplasm as it allows chemicals and enzymes to dissolve

43
Q

more detailed facts about water

A

booklet

44
Q

Give 2 properties of water that are important in biology. Explain the importance of each property you identify (4)

A

-polar molecule- acts as a universal solvent
-a metabolite- in condensation reactions
-high SHC-reduces fluctuations in temperature

45
Q

Suggest why water becomes lighter when it expands (2)

A

-density= mass/volume
-ice has the same mass as water but a greater volume

46
Q

Suggest one biological advantage of this property of water (density) (2)

A

-ice is colder than water
-lighter than water so ice floats on water
-reduces freezing of water below ice

47
Q

Scientists looking for extra-terrestrial life are looking for planets with evidence of free water. Explain why water is considered so important for life to occur (6)

A

-life is thought to have evolved in water
-water provides support for bodies of organisms
-water is a major component in cytoplasm
-water is a universal solvent
-water is a metabolite (in condensation reactions)
-water stabilises external temperatures

48
Q

How does an ion form?

A

when atom loses or gains an electron

49
Q

Where are inorganic ions found?

A

in solutions in the cytoplasm and the bodily fluids of organism, some in very high concentrations and some in very low concentrations

50
Q

What is the function of a hydrogen/ acid ion?

A

-effects the acidity of solutions (PH)
-H+ is used in respiration to provide energy to make ATP

51
Q

What is the function of a hydroxide/OH-/ alkali ion?

A

-H+ used in photosynthesis to provide energy to make ATP

52
Q

What is the function of an iron ion?

A

-structural component of haemoglobin (binds O2) to allow the transport of oxygen to respiring tissues

53
Q

What is the function of a sodium ion?

A

-used in the co transport of glucose and amino acids
-used in nervous conduction

54
Q

What is the function of a phosphate ion?

A

components of phospholipids- DNA, RNA and ATP

55
Q

What is the function of nitrate ions?

A

-taken up from the soil by plant roots
-used in making amino acids

56
Q

what is the function of chloride ions?

A

-used in regulating the water potential of the small intestine

57
Q

What are the inorganic ions?

A

-hydrogen
-hydroxide
-iron
-sodium
-phosphate
-nitrate
-chloride

58
Q

Why might the gene for a polypeptide contain more than the number of bases? (1)

A

-there are 2 DNA strands

59
Q

What is the name of the bond between nucleotides?

A

phosphodiester

60
Q

The enzymes DNA Helicase and DNA polymerase are involved in DNA replication. Describe the function of each of these enzymes (2)

A

DNA Helicase- unzips complimentary base pairs so strands can seperate and act as templates
DNA Polymerase- Joins adjacent nucleotides

61
Q

Explain why the arrows in DNA strand production point in opposite directions (3)

A

-DNA has antiparallel strands
-enzymes have active sites with a specific shape
-only substrates with complimentary shapes can bind to the active site

62
Q

Explain why new nucleotides can only be added in a 5’ to 3’ direction after strands seperate to act as templates (4)

A

-DNA Polymerase
-is specific
-only complimentary to the 5’ end
-shape of the 5’ end and 3’ end are different

63
Q

Describe the role of DNA polymerase in DNA replication (1)

A

-joins adjacent nucleotides to catalyse a condensation reaction

64
Q

Other than being smaller, give 2 ways in which prokaryotic DNA is different to eukaryotic DNA (2)

A

-prokaryotic is circular
-prokaryotic does not associate with proteins/ histones

65
Q

Use your knowledge of DNA structure and function to explain how humans and grasshoppers have a similar percentage of each base in their DNA but are very different organisms (2)

A

-have different genes
-as triplets are in a different sequence

66
Q

Give two features of DNA and explain how each one is important for semi conservative replication of DNA (2)

A

-2 strands so each acts as a template
-weak H bonds between complimentary base pairs so it can unzip easily

67
Q

Explain why DNA helicase is important in DNA replication (2)

A

-breaks the hydrogen bonds between complimentary base pairs
-so each strand can act as a template

68
Q

Name the 2 scientists who proposed models of the chemical structure of DNA and of DNA replication (1)

A

Watson and Crick

69
Q

Describe how a phosphodiester bond is formed between 2 nucleotides within a DNA molecule (2)

A

-formed by a condensation reaction
-between the phosphate group of one nucleotide -to the third carbon of the deoxyribose sugar in the next nucleotide

70
Q

Describe how the separation of strands occurs in semi conservative replication (2)

A

-DNA Helicase
-unwinds the DNA and breaks hydrogen bonds between complimentary base pairs

71
Q

Describe the biochemical test to show that a solution contains a non reducing sugar (3)

A

-add benedict’s and it should give a negative result (stay blue)
-boil it with an acid then neutralise with an alkali
-if NRS is present it should form a red/orange precipitate

72
Q

State and explain the property of water that can help to buffer changes in temperature (2)

A

High SHC can buffer changes in temperature (keep the same temp) as it takes more energy to heat water than air

73
Q

Name 2 products of ATP hydrolysis

A

-ADP
-Pi
(adenosine diphosphate and inorganic phosphate)

74
Q

Why is ATP useful in so many biological processes (4)

A

-releases energy in small manageable amounts
-instant energy source
-phosphorylates other compounds to lower activation energy
-easily reformed

75
Q

Describe the chemical reactions involved in the conversion of monomers to polymers and polymers to monomers with named examples (5)

A

-condensation reaction/ loss of water joins monomers together and releases water and forms a bond
-a hydrolysis reaction breaks a chemical bond between monomers using water
-polymers must contain many monomers
-beta glucose &cellulose
-amino acids &polpeptides

A Level Biology (7 decks)

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