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OCR Biology AS H020 > DNA > Flashcards

Flashcards in DNA Deck (75):
1

What is an individual nucleotide made up of?

A pentode monosaccharide, a phosphate group (PO4 2-) and a nitrogenous base.

2

How are nucleotides linked together?

In condensation reactions forming polynucleotides and phosphodiester binds.

3

Where do phosphodiester bonds formed?

The 5th carbon of the pentose sugar and the OH group of the 3rd carbon of the adjacent pentose sugar.

4

How are phosphodiester bonds broken?

Hydrolysis

5

What is the sugar in DNA?

Deoxyribose

6

Where in the O missing from deoxyribose?

Carbon 2

7

Define pyrimidines...

Smaller bases with single carbon ring structures... T and C

8

What bases are pyrimidines?

Thymine and cytosine.

9

Define purines...

Larger bases which contain double carbon ring structures. A and G.

10

Which bases are purines?

Adenine and guanine.

11

Thymine pairs with...

Adenine

12

How many hydrogen bonds to thymine and adenine form?

2

13

Cytosine pairs with...

Guanine

14

How many hydrogen bonds do cytosine and guanine form?

3

15

What structure does a molecule DNA form?

A double helix.

16

How is it described when the right bases pair together?

Complementary base pairing.

17

How are the two stands in a DNA double helix held together?

Hydrogen bonds.

18

How are bases held together?

Hydrogen bonds

19

What direction do the two stands run?

Antiparallel

20

Why does a purine always bind to a pyrimidine?

To maintain a constant distance between the two polynucleotide chains meaning they are parallel.

21

What is the pentose sugar in RNA?

Ribose

22

In RNA what is thymine replaced with?

Uracil

23

What happens to RNA molecules after protein synthesis?

They are degraded in the cytoplasm.

24

Describe semi conservative replication...

DNA helicase unwinds/unzips and separates the 2 strands of DNA by breaking the hydrogen bonds. During the unzipping process free DNA nucleotides that have been activated pair with their complementary bases forming hydrogen bonds with the template strand. DNA polymerase catalyses the formation of phosphodiester bonds between DNA nucleotides. 2 identical molecules of DNA are formed, each strand has 50% original and 50% new.

25

Describe Okazaki fragments...

DNA polymerase works from 3' to 5' direction. One strand is the leading strand and one strand is the lagging strand that undergoes discontinuous replication.

26

What direction does DNA polymerase work in?

3' to 5'

27

What is a mutation?

Random errors in the base sequence.

28

What is the genetic code?

DNA codes for a sequence of amino acids.

29

What is the triplet code?

A sequence of 3 bases called a codon, codes for 1 amino acid.

30

What is a gene?

A section of DNA with a complete sequence if codons for a protein.

31

Explain the term universal...

All organisms use the same code.

32

Explain the term degenerate...

There are 64 possible codons but only 20 amino acids.

33

Explain the term non-overlapping...

There are start/stop codons so genes are read in sequence.

34

Describe transcription...

DNA helicase unwinds and unzips the section of DNA containing a specific gene beginning at a start codon. Hydrogen bonds are broken. The sense strand runs from 5' to 3' and contains the genetic code hence the antisense strand is used as the template strand. Free RNA nucleotides pairs with complementary bases when the DNA unzips. Uracil binds to adenine stead of thymine. Phosphodiester bonds are formed between RNA nucleotides by RNA polymerase. The mRNA detaches from the DNA and leaves the nucleus through a nuclear pore. The DNA double helix reforms, the mRNA travels to a ribosome in the cytoplasm.

35

In transcription, which enzyme unwinds and unzips a section of DNA?

DNA helicase

36

In transcription, what direction does the sense strand run?

5' to 3'

37

In transcription, which strand is used as the template strand?

The antisense strand

38

In transcription, which enzyme forms phosphodiester bonds between RNA nucleotides?

RNA polymerase

39

In transcription, how does the mRNA leave the nucleus?

Through nuclear pores.

40

In semi conservation replication, what enzyme unwinds/unzips the DNA?

DNA helicase

41

Describe the process of translation...

mRNA binds to the small subunit of the ribosome at the start codon (AUG). A tRNA with the complementary anticodon binds to the mRNA start codon by complementary base pairing attached to the tRNA is the corresponding amino acid. The ribosome moves along the mRNA adding the correct tRNA anticodons and amino acids. Peptide bonds form between amino acids, this reaction is catalysed by peptidyl transferase in the RNA. When the ribosome reaches a stop codon the polypeptide is released.

42

In translation, where does mRNA bind?

The small subunit at the start codon.

43

What is the start codon?

AUG

44

What is attached to tRNA?

Corresponding amino acid

45

What type of bonds form between amino acids in translation?

Peptide bonds

46

Which enzyme catalyses the formation of peptide bonds in translation?

Peptidyl transferase

47

What is the role of mRNA?

Carries the genetic code from DNA in the nucleus to the ribosomes.

48

What is the function of tRNA?

It is an amino acid binding site it has an anticodon which carries an amino acid to a ribosome.

49

What are the 3 main activities that cells require energy for?

Synthesis, transport and movement.

50

What does ATP stand for?

Adenosine triphosphate

51

What is ATP also known as

Universal energy currency

52

What is an ATP molecule composed of?

Ribose (pentose sugar), adenine (nitrogenous base) and 3 phosphate groups.

53

What is the enthalpy change when a liberated phosphate group combines with ADP.

30.6KJmol-1

54

What is added to ATP to form ADP?

Water - hydrolysis

55

What elements do nucleic acids contain?

Carbon, hydrogen, oxygen, nitrogen and phosphorus.

56

Why is the hydrolysis of ATP said to be coupled?

It's reaction does not happen in isolation but in association with other energy requiring reactions.

57

Why is ATP a poor long term energy store?

The phosphate bonds of ATP are instable.

58

The energy from which process is used to create ATP?

Breakdown of fats and carbohydrates - cellular respiration.

59

What is phosphorylation?

The addition of a phosphate group to ADP in a condensation reaction to form ATP.

60

Why is ATP a good intermediate store of energy?

The interconversion of ATP and ADP.

61

State the properties of ATP that means it is suited to its function...

Small - moves easily into and out of cells.
Water soluble - energy requiring processed happen in aq environments.
Phosphate bonds have intermediate energy - large enough for cellular reactions but not too large that energy is wasted.
Easily regenerated.

62

During DNA extraction, why do you grind the sample?

To break down the cell walls.

63

During DNA extraction, why do you use detergent?

To break down the cell membrane.

64

During DNA extraction, why do you use salt?

To break the hydrogen bonds between water and DNA.

65

During DNA extraction, why do you use protease?

To break down the proteins associated with DNA.

66

During DNA extraction, why do you use alcohol?

So DNA precipitates out if the solution.

67

What is the correct order of operations to extract DNA.

Grind, detergent, salt, protease, alcohol.

68

What test is used to indenting proteins?

Biuret test

69

What is the basis of the biuret test?

Peptide bonds form violet coloured complexes with copper ions in alkaline solution.

70

What does biuret reagent consist of?

NaOH and CuSO4

71

Which practical is used to separate amino acids?

Thin layer amino acids

72

Briefly describe thin layer chromatography...

Butan-1-ol, glacial ethanoic acid and water as solvent. Fume cupboard and lid. Leave to dry. Spray paper with ninhydrin solution, they turn purple.

73

How do you calculate an Rf value?

Distance travelled by spot/distance travelled by solvent.

74

What is a mobile phase?

The liquid solvent moving.

75

What is the stationary phase?

The paper or silica gel.