Exam 3: Chromosome Structure and transposons

Question 1

Why does tight DNA present a problem for cellular function?

Answer 1

Packing renders the DNA inaccessible for reading or copying

Question 2

What is supercoiling?

Answer 2

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

Question 3

How does positive supercoiling compare to negative supercoiling?

Answer 3

Positive occurs when molecules are over-rotated.

Negative occurs when molecules are under-rotated

Question 4

what role do topoisomerases play in supercoiling?

Answer 4

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

-can induce and relieve supercoiling

Question 5

Advantages of negative supercoiled DNA over nonsupercoild DNA.

Answer 5

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

Question 6

Euchromatin

Answer 6

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

-Light band

Question 7

Heterochromatin

Answer 7

remains in a highly condensed state throughout the cell cycle.

Very dark band

Question 8

Nucleosome

Answer 8

core particle of DNA plus 8 histone proteins

Nucleosome plus H1 = 157 bp of DNA

Question 9

histones that form the nucleosome

Answer 9

H2A H2B H3 H4 (2 each)

H1 attaches the DNA to the nucleosome

Question 10

Polytene chromosome

Answer 10

created by repeated rounds of DNA replication with no cell division

Question 11

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

Answer 11

true

Question 12

What are centromeric sequences?

Answer 12

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

Question 13

How are centromeres defines

Answer 13

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

Question 14

What do centromeres signal?

Answer 14

the beginning of anaphase

Question 15

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

Answer 15

telomeres may stabilize ends of chromosomes

Question 16

describe telomeric sequences, how are they oriented

Answer 16

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

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

Question 17

what is the relationship between shelterin and telomeres?

Answer 17

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

Question 18

C value

Answer 18

the amount of DNA per cell in a given organism

Question 19

Unique sequence DNA. Gene Family

Answer 19

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

Question 20

Moderately repetitive DNA

Answer 20

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……..

Question 21

Highly repetitive DNA

Answer 21

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

Question 22

unique sequence DNA

Answer 22

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)

Question 23

How much of the human genomes is repetitive DNA

Answer 23

about half

Question 24

Tandem repeat sequences

Answer 24

arranged in tandem and clustered at particular locations on the chromosomes

Question 25

Interspersed repeat sequences

Answer 25

scattered throughout the genome. Most are transposable elements

Question 26

How much of the human genome is composed of LINEs?

Answer 26

17%

Question 27

Transposable elements

Answer 27

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

Question 28

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

Answer 28

short flanking - do not travel with the transposable element. - regenerated at the point of insertion.

Question 29

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

Answer 29

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

Question 30

What are terminal, inverted repeats?

Answer 30

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.

Question 31

How do transposons cause mutations?

Answer 31

inserting into another gene. | promoting DNA rearrangements.

Question 32

explain copy and paste transposition

Answer 32

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.

Question 33

Transposase

Answer 33

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.

Question 34

Resolvase

Answer 34

encoded either by cellular genes or by transposable element. | responsible for resolution

Question 35

what is cut and paste transposition

Answer 35

transposable element is excised from old site and inserted into a a new site. does not increase the number of copies

Question 36

Retrotransposons

Answer 36

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

Question 37

SINEs

Answer 37

Constitute about 11% of the human genome, Include Alu

Question 38

LINEs

Answer 38

approx 900,000 copies of LINEs in the human genome. Constitute about 21% of the total Human DNA

Question 39

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

Answer 39

TRUE

Question 40

What are genomic parasites?

Answer 40

transposable elements