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IB Biology HL > 7.1 DNA Structure and Replication (HL) > Flashcards

7.1 DNA Structure and Replication (HL) Flashcards

1
Q

Who understood that it was DNA and not protein that is the genetic material of a cell?

A

Alfred Hershey and Martha Chase

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2
Q

How did we understand that DNA is the genetic material of cells?

A

One batch of bacteriophages were grown in a radiolabelled sulphur (present in proteins) medium and another was grown in radioactive phosphorous (present in DNA)
They then infected E. coli and found only the phosphorous was passed on by gene transmission and not the sulphur

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3
Q

How did Rosalind Franklin and Maurice Wilkins investigate the structure of DNA?

A

Using X-ray diffraction

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4
Q

Describe the process of X ray diffraction

A

DNA is purified and the fibres are stretched in a thin glass tube
This is then targeted with an X ray beam which is diffracted when it hits an atom
This creates a scatter pattern

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5
Q

What inferences can be made from DNA scatter patterns?

A

DNA is double stranded
Nitrogenous bases are closely packed together on the inside and phosphates form an outer backbone
The DNA twists at regular intervals to form a double helix

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6
Q

How often does the DNA molecule twist?

A

Every 34 Angstrom

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7
Q

Who proposed the current structure of the DNA model?

A

James Watson and Francis Crick

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8
Q

Which molecules in DNA are purine?

A

Adenine

Guanine

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9
Q

What molecules are pyrimidines?

A

Cytosine

Thymine

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10
Q

How do adenine and thymine bond?

A

2 H bonds

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11
Q

How do guanine and cytosine bond?

A

3 H bonds

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12
Q

What is the function of helicase?

A

Unwinds and separated the double stranded DNA (replication)

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13
Q

How does helicase complete it’s function?

A

Breaking hydrogen bonds between base pairs

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14
Q

What is an origin of replication?

A

A specific region which is replicated

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15
Q

What is a replication fork?

A

The name given to the two strands running in antiparallel direction after being unwound by Helicase

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16
Q

What is the function of DNA Gyrase?

A

Reduces the torsional strain from unwinding (from helicase)

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17
Q

How does DNA Gyrase complete it’s function?

A

Relaxing the supercoils (via negative supercoiling)

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18
Q

What are SSB proteins?

A

Single stranded binding proteins

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19
Q

What is the function of SSB proteins?

A

Prevent re-annealing

Prevent the single stranded DNA from being digested by nucleases

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20
Q

When do SSB proteins dislodge from the DNA?

A

When a complimentary strand is synthesised onto the single strand

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21
Q

What is the function of DNA Primase?

A

Generates a short RNA primer on each template strand

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22
Q

What is needed before any base pairs can be added to a new nucleotide strand?

A

Primers

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23
Q

How long are most RNA primers?

A

(10 to 15 nucleotides)

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24
Q

What is the function of an RNA primer?

A

It is an initiation point for DNA polymerase III

25
Q

What is the function of DNA polymerase III?

A

To synthesise a new complementary strand of DNA onto the original parent strand

26
Q

On what end of the primer does DNA polymerase III attach?

27
Q

In which direction does DNA polymerase synthesise?

28
Q

How does DNA pol III move in two directions art once?

A

On the leading fork DNA pol II moves towards the replication fork
On the lagging strand DNA pol III moves away from the replication fork and synthesises in pieces

29
Q

What is the function of DNA polymerase I?

A

Removing the extra RNA primers that have to be added to create the Okazaki fragments on the lagging strand

30
Q

What is the function of DNA ligase?

A

Joins the Okazaki fragments together to form a continuous strand

31
Q

How are Okazaki fragments joined?

A

Covalently bonded joining the sugar-phosphate backbones together with phosphodiester bonds

32
Q

In replication, which strand is the leading strand?

A

The one where DNA pol moves towards the fork and thus copies continuously

33
Q

In replication, which strand is the lagging strand?

A

DNA pol moves away from the replication fork and copies discontinuously

34
Q

What is a ddNTP?

A

A dideoxynucleotide does not have the 3’ hydroxyl group necessary to form phosphodiester bonds therefore ending replication as they cannot be elongated

35
Q

How can ddNTP and PCR help us in sequencing?

A

PCR can be used to generate all the possible, terminating fragments for a particular base
These can then be ordered by length and thus the base sequences can be determines

36
Q

What is the sanger method?

A

A method for determining the sequencing of DNA

37
Q

What proportion of our DNA is non-coding?

A

More than 98%

38
Q

Give examples of non-coding DNA

A 
Satellite DNA
Telomeres
Introns
Non-coding RNA genes
Gene regulatory sequences
39
Q

What is the function of satellite DNA?

A

Structural component of heterochromatin and centromeres - used in DNA profiling

40
Q

What is the function of telomeres?

A

Regions of repetitive DNA at the end of the chromosome that protect against deterioration during replication

41
Q

What is the function of introns?

A

Non-coding sequences within genes

42
Q

How are introns removed?

A

By splicing before the formation of mRNA

43
Q

What is the function of non-coding RNA genes?

A

Codes for RNA molecules which are not translated into protein

44
Q

Give an example of a non-coding RNA gene

A

The genes for tRNA

45
Q

What is the function of gene regulatory sequences?

A

Sequences that are involved in the process of transcription

46
Q

Give examples of gene regulatory sequences

A

Promoters
Enhancers
Silencers

47
Q

What are STRs?

A

Short tandem repeats (a type of satellite DNA) where a long stretch of DNA is made of repeating elements

48
Q

How can we use STRs in profiling?

A

They can be excised using restriction enzymes and separated with gel electrophoresis
As they are often different lengths they are usually unique

49
Q

What are nucleosomes?

A

A complex with a compacted structure created when DNA is packaged with 8 histone proteins (an octomer)

50
Q

Why does DNA supercoil?

A

To protect DNA from damage

To allow chromosomes to be mobile during mitosis/ meiosis

51
Q

What is a chromatosome?

A

Nucleosomes that are linked together with an extra H1 histone protein to form a string

52
Q

How are less active chromatosomes structured within the DNA?

A

The coil into solenoid structures (~6 chromatosomes per turn)

53
Q

How do long chains of solenoids fold?

A

In a 30nm fibre

54
Q

In what form is the 30nm fibre of DNA during interphase?

55
Q

In what form is the 30nm fibre of DNA during metaphase?

A

Chromosome

56
Q

What is the order (from small to large) of DNA structures?

A 
Naked DNA
Nucleosome
Chromatosomes
Solenoid
30 nm fibre
Chromatin/ chromasomes
57
Q

In which structures are active genes?

A

Nucleosome

Chromatosomes

58
Q

In which structures are inactive genes?

A

Solenoids

30 nm fibre

59
Q

How does DNA form around nucleosomes?

A

Negatively charged DNA associates positively with charged amino acids on the surface of histone proteins

IB Biology HL (35 decks)

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