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Josh, Genetics > Exam 3: Chromosome Structure and transposons > Flashcards

Exam 3: Chromosome Structure and transposons Flashcards

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1
Q

Why does tight DNA present a problem for cellular function?

A

Packing renders the DNA inaccessible for reading or copying

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2
Q

What is supercoiling?

A

the over-winding or under-winding of DNA, causing it to twist on itself

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3
Q

How does positive supercoiling compare to negative supercoiling?

A

Positive occurs when molecules are over-rotated.

Negative occurs when molecules are under-rotated

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4
Q

what role do topoisomerases play in supercoiling?

A

enzymes that add or remove rotations from DNA
-temp breaks nucleotide strands, rotates ends, and rejoins broken ends.

-can induce and relieve supercoiling

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5
Q

Advantages of negative supercoiled DNA over nonsupercoild DNA.

A

Most DNA is negatively supercoilied. N.B.

Advantages of neg supercoiling
-Makes separation of the two strands easier during replication and transcription.

-Allows DNA to be packed into smaller space compared to relaxed DNA

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6
Q

Euchromatin

A

undergoes the normal process of condensation and decondensation in the cell.

-Light band

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7
Q

Heterochromatin

A

remains in a highly condensed state throughout the cell cycle.

Very dark band

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8
Q

Nucleosome

A

core particle of DNA plus 8 histone proteins

Nucleosome plus H1 = 157 bp of DNA

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9
Q

histones that form the nucleosome

A

H2A H2B H3 H4 (2 each)

H1 attaches the DNA to the nucleosome

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10
Q

Polytene chromosome

A

created by repeated rounds of DNA replication with no cell division

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11
Q

T/F epigenetic changes cause inherited phenotypic change without affecting the DNA sequence

A

true

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12
Q

What are centromeric sequences?

A

the binding sites for the kinetochore, where spindle fibers attach.

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13
Q

How are centromeres defines

A

mostly heterochromatic and defined by epigenetic (nonsequence) changes rather than DNA sequences

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14
Q

What do centromeres signal?

A

the beginning of anaphase

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15
Q

what function is suggest by the fact that chromosomes that have telomeres are not degraded?

A

telomeres may stabilize ends of chromosomes

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16
Q

describe telomeric sequences, how are they oriented

A

repeated sequence of A or T nucleotides followed by several G.

-String of G and C sequence is always oriented away from the centromere.

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17
Q

what is the relationship between shelterin and telomeres?

A

protects ends of mammalian chromosomes from being repaired as double-strand breaks

18
Q

C value

A

the amount of DNA per cell in a given organism

19
Q

Unique sequence DNA. Gene Family

A

similar but not identical copies of unique DNA sequences that arose through duplication of an existing gene.

20
Q

Moderately repetitive DNA

A

150~300 bp long and thousands to 100s of thousands ot repeated units.

-Tandem repeat sequences
-interspersed repeat sequences:
SINEs:short interspersed elem.
LINEs: long inter……..

21
Q

Highly repetitive DNA

A

less than 10 bp long and repeated 100s of thousand to millions of times
-microsatellite DNA

22
Q

unique sequence DNA

A

DNA sequences that are pesent one or only a few times in the genome.

genes present in a single copy represent 25% 50 50% of protein-encoding genes in most multicellular organisms.

may have genes that are similar but not identica (gene family)

23
Q

How much of the human genomes is repetitive DNA

A

about half

24
Q

Tandem repeat sequences

A

arranged in tandem and clustered at particular locations on the chromosomes

25
Q

Interspersed repeat sequences

A

scattered throughout the genome.

Most are transposable elements

26
Q

How much of the human genome is composed of LINEs?

A

17%

27
Q

Transposable elements

A

are mobile DNA sequences found in the genomes of all organisms.

  • make up 45% of Human DNA
  • insert in many different locations
  • often cause mutations
28
Q

______ ______ repeats from 3 to 12 bp long are present on both sides of the transposable elements

A

short flanking

  • do not travel with the transposable element.
  • regenerated at the point of insertion.
29
Q

Replication of single-stranded DNA creates the flanking direct repeats on both sides of the transposon. What can this tell us

A

where the transposon is located since they are the same on each side.

30
Q

What are terminal, inverted repeats?

A

9 to 10bps. Found at ends of many transposable elements.

-sequences are inverted and complementary on same strand.

Recognized by enzymes that catalyze transposition.

required for transposition to take place.

31
Q

How do transposons cause mutations?

A

inserting into another gene.

promoting DNA rearrangements.

32
Q

explain copy and paste transposition

A

new copy of the transposable element is introduced at new site while the old copy remains at original site.

result: increased number of copies of Transposable element.

33
Q

Transposase

A

may be encoded for by cellular gene or often by Transposable element

-makes single-strand breaks at each end of the transposable element and on either side of the target sequence where insertion occurs.

34
Q

Resolvase

A

encoded either by cellular genes or by transposable element.

responsible for resolution

35
Q

what is cut and paste transposition

A

transposable element is excised from old site and inserted into a a new site.

does not increase the number of copies

36
Q

Retrotransposons

A

elements that transpose through an RNA intermediate (instead of DNA).

RNA is transcribed from a DNA transposable element.

RNA is copied back to another DNA site using reverse transcriptase.

only use replicative transposition

more common that DNA transposons in eukaryotes

37
Q

SINEs

A

Constitute about 11% of the human genome, Include Alu

38
Q

LINEs

A

approx 900,000 copies of LINEs in the human genome.

Constitute about 21% of the total Human DNA

39
Q

T/F one of every mutations that cause significant disease results from the transposition of a SINE or LINE?

A

TRUE

40
Q

What are genomic parasites?

A

transposable elements

Josh, Genetics (5 decks)

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