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A Level Biology: Nucleic acids > 2.1 - structure of RNA and DNA > Flashcards

2.1 - structure of RNA and DNA Flashcards

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1
Q

what 3 components are individual nucleotides made out of

A
  • a pentose sugar
  • a phosphate group
  • a nitrogen containing organic base. (these are: cytosine (C), thymine (T), uracil (U), adenine (A) and guanine (G)
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2
Q

how are the pentose sugar, phosphate group, and organic bases joined in a nucleotide structure

A
  • condensation reactions to form a single nucleotide (mononucleotide)
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3
Q

how many mononucleotides are joined as a result of a condensation reaction between between the deoxyribose sugar of one nucleotide and the phosphate group of another

A

2

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4
Q

what is the bond between between nucleotides called

A

phosphodiester bond

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5
Q

what do you call 2 mononuleotides joined together

A

dinucleotide
–> more than 2 is called a polynucleotide

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6
Q

what is Ribonucleic acid

A

polymer - made up of nucleotides

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7
Q

describe the structure of Ribonucleic acid

A
  • single, relatively short polynucleotide chain in which:
    1. pentose sugar = ribose
    2. the organic bases = A,G,C,U
  • 1 type of RNA: transfers genetic info from DNA –> ribosomes
  • The ribosomes themselves: made out of proteins and another type of RNA
  • 3rd type of RNA: involved in protein synthesis
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8
Q

who worked out the structure of DNA

A
  • 1953: James Watson and Francis Crick
  • following previous pioneering work on the X-ray diffraction patterns of DNA
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9
Q

describe the structure of DNA

A
  1. the pentose sugar = deoxyribose
  2. the organic bases =A,T,G,C
    - made of 2 strands of polynucleotides
    - each strand = long + joined together by hydrogen bonds between certain bases
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10
Q

describe what is meant when we say that DNA can be thought as a ladder

A
  • a ladder, where the phosphate and deoxyribose molecules alternate to form the uprights
  • and the organic base pair together to form the rungs
  • the 2 strands are twisted around, so that the uprights of Phosphate and deoxyribose wind around each other, forming a double helix
  • this forms the structural backbone of the DNA molecule
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11
Q

how do the bases on the two strands of DNA attach together?

A

hydrogen bonds, its these bonds that hold the 2 strands together

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12
Q

is base pairing specific

A
  • yes
  • adenine ALWAYS PAIRS WITH thymine
  • Guanine ALWAYS PAIRS WITH cytosine
  • therefore they’re complementary to each other
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13
Q

describe the quantities of A,T,G,C in DNA

A
  • A same quantity as T
  • G same quantity as C
  • However ratio of A and T, to G and C = varies from species to species
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14
Q

why is DNA a stable molecule

A
  • The phosphodiester backbone protects the more chemically reactive organic base inside the double helix
  • Hydrogen bonds link the organic base pairs forming bridges (rings) between the phosphodiester uprights. Because there’s 3 hydrogen bonds between C and G, the higher the proportion of C–G pairings, the more stable the DNA molecule
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15
Q

what is the function of DNA

A
  • DNA is the hereditary material responsible for passing genetic information from cell to cell and generation to generation
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16
Q

what are some the ways that DNA molecules are adapted to carry out their function

A
  • very stable structure which normally passes from generation to generation without change. Only rarely does it mutate
  • 2 separate strands are joined only with hydrogen bonds = allows them to separate during DNA replication and protein synthesis
  • It is an extremely large molecule = carries an immense amount of genetic information
  • by having the base pairs within the helical cylinder of the deoxyribose-phosphate backbone = genetic info is protected from being corrupt by outside chemical/physical forces
  • base pairing = DNA being able to replicate and to transfer info as mRNA
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17
Q

what does the function of DNA rely on

A

the sequence of base pairs that it possesses

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18
Q

Asses the advantages of scientists questioning the validity of a current theory rather than automatically accepting it

A
  • alternative theories can be explored and investigated
  • therefore: new facts may emerge and so a new theory is put forward or the existing one is modified
  • In this way, scientific progress can be made
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19
Q

how do scientists use observations, hypothesis’, predictions and investigations

A
  • Scientists work by using observations and current knowledge to form a hypothesis
  • from this, they make predictions about the investigation
  • by doing the investigation a number of times = collect evidence = accept or reject hypothesis
20
Q

explain what is meant by the term ‘hypothesis’ in the scientific sense

A

A suggested explanation of something based on some logical scientific reasoning or idea

21
Q

how are carbon atoms in the pentose molecule numbered

A
  • 3’ (3-prime) and 5’ (5-prime)
  • the 5’ carbon has an attached phosphate group
  • the 3’ carbon has a hydroxyl group
22
Q

how are nucleic acids synthesised and why

A
  • only synthesised ‘in vivo’ in the 5’-to-3’ direction
  • because: the enzyme DNA polymerase that assembles nucleotides into a DNA molecule can only attach to the hydroxyl (OH) group on the 3’ carbon molecule
23
Q

Suggest what the term ‘in vivo’ means in the context of synthesising DNA

A
  • It means ‘in life’
  • in other words the synthesis of DNA by a living organism rather than in a lab
24
Q

From your knowledge of the way enzymes work, explain why DNA polymerase can only attach nucleotides to the hydroxyl (OH) group on the 3’ carbon molecule

A
  • enzymes = specific
  • their active site = specific shape that fits their substrate
  • shape of the 3’ end of the molecule with its hydroxyl group fits the active site of DNA polymerase
  • whereas the shape of the 5’ does not
25
Q

Show all the symbols used to show the various molecules in a nucleotide

A
26
Q

Show the structure of a simple nucleotide like

A
27
Q

Show the structure of a section of an RNA molecule

A
28
Q

Show the structure of a phosphodiester bond between a guanine nucleotide and a cytosine nucleotide

A
29
Q

Show the basic structure of DNA

A
30
Q

Show the structure of a nucleotide, showing the positions of the 3-prime and 5-prime carbon atoms on a Pentose sugar

A
31
Q

Show a DNA molecule, showing the 3-prime and 5-prime carbon atoms. Making sure to explain how the strands run, parallel or antiparallel?

A
32
Q

what is the function of DNA

A
  • sequence of bases in DNA codes for a sequence of amino acids in proteins
33
Q

is DNA a large molecule or a small molecule

A

large

34
Q

what are AT

A

purines

35
Q

what are CGU

A

pyrimidines

36
Q

what features allows you to tell the difference between pyrimidines and purines

A
  • Pyrimidines = 1 ring
  • purines = 2 rings
  • pyrimidines = 3 hydrogen bonds
  • purines = 2 hydrogen bonds
    —-> ‘AT two, CG three’
37
Q

what is the shape of a molecule of DNA

A

double helix

38
Q

how are the 2 strands held together

A

(weak) hydrogen bonds between complementary base pairs

39
Q

how can we work out the number of each type of base in an organism

A
  • if there is 2% adenine = 2% Thymine = because they’re always bonded together
  • therefore there’s 94% of C and G
  • to work our C and G individually, divide 94% by 2
40
Q

what’s the exception to the rule for finding out the number of each type of base in an organism

A

ssDNA

41
Q

why’s ssDNA an exception to the rule for finding out the number of each type of base in an organism

A
  • ssDNA stands for = single strand DNA
  • because it has only 1 strand = there is no complementary pairing
  • therefore we can’t know exact numbers
    –> ssDNA is found in some viral DNA/RNA and some bacteria
42
Q

describe the various types of RNA

A
  • rRNA
  • mRNA
    -tRNA
43
Q

describe the properties of mRNA

A
  • contains uracil instead of thymine
  • short (has a copy of 1 gene)
  • linear molecule with an alpha helix shape
  • small molecule – hence can leave the nucleus
  • carries the code for protein synthesis from the DNA to the ribosomes
44
Q

describe the properties of tRNA

A

shape = clover leaf
- 3 bases exposed at the bottom (called anticodon) –> attaches to the codon on the RNA
- shorter than DNA
- carries 1 amino acid, specific to the 3 bases that make up the anticodon
- binds to the large subunit of a ribosome

45
Q

is All RNA shorter than DNA

A

yes

A Level Biology: Nucleic acids (5 decks)

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