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Plant Biotechnology > Secondary Structure of Nucleic Acids > Flashcards

Secondary Structure of Nucleic Acids Flashcards

1
Q

ssDNA folds back on itself to create

A

+ Single-stranded loop

+ Base-paired stem

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2
Q

Hairpin structures

A

+ Loop: size varies

+ Stem: homologous bases paired

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3
Q

Cruciform structures

A

Form if inverted repeats base pair with the complementary sequence on strand

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4
Q

Inverted repeats cause

A

Stem

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5
Q

Base separating inverted repeats cause

A

Loop

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6
Q

T or F: Cruciform DNA probably does not form in vivo.

A

False

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7
Q

Holiday structures

A

+ Junction of 4 loops

+ Permit crossing over during meiosis

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8
Q

Lacks free ends

A

Closed DNA

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9
Q

Circular genomes

A

Closed DNA

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10
Q

Bacteria form nucleoids

A

Closed DNA

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11
Q

Where are circular genomes found?

A

+ Viruses
+ Chloroplast
+ Mitochondria

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12
Q

Twist in DNA duplex along axis in space

A

Supercoiled DNA

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13
Q

DNA placed under tension

A

Supercoiled DNA

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14
Q

Only occurs in closed molecule

A

Supercoiled DNA

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15
Q

Single nick releases tension and supercoiling

A

Supercoiled DNA

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16
Q

1 twist

A

1 superhelical turn

17
Q

No supercoils

A

Relaxed DNA

18
Q

Applies to open or closed DNA

A

Relaxed DNA

19
Q

Twist DNA opposite to the duplex

A

Negative supercoils

20
Q

Relieves torsional stress by unwinding helix

A

Negative supercoils

21
Q

If sufficient stress, strand separation occurs

A

Negative supercoils

22
Q

Twist DNA in same direction as duplex

A

Positive supercoils

23
Q

Winds duplex tighter

A

Positive supercoils

24
Q

Never occurs in vivo

A

Positive supercoils

25
Q

Superhelical density =

A

Number of superhelical turns of helix per 10 bp

26
Q

Linking number =

A

Number of times that the duplex crosses itself (deltaW =deltaT)

27
Q

W =

A

writhe (turning of double helix in space)

28
Q

T =

A

twist (rotation of strands around each other)

29
Q

Writhe is increased

Twist unchanged

A

Negative supercoil

30
Q

Twist decreased

Writhe unchanged

A

Underwound

31
Q

Higher L means

A

Higher negative supercoiling or unwinding

32
Q

Lower L means

A

Lower negative supercoiling or overwinding

33
Q

Toposiomers

A

A topologically distinct isomer

34
Q

Topoisomerases (Topo)

A

+ Change L

+ Break 1 or both strands

35
Q

Helicases

A

+ Separate strands

+ Do not change L

36
Q

DNA gyrase

A

Facilitates supercoiling

Plant Biotechnology (8 decks)

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