5.2 DNA Replication Part 3

Question 1

What is a major difference between bacterial and eukaryotic DNA due to circular versus linear?

Answer 1

eukaryotic has telomeres

Question 2

What does the termini of the eukaryotic chromosomes resemble and why is that a problem?

Answer 2

resembles double stranded breaks and cellular repair machinery cannot distinguish between breaks and telomeres

Question 3

How are double stranded breaks normally repaired and why would this be a problem if it occured at linear chromosomal ends?

Answer 3

normally repaired by joining loose ends together; would be a problem because it would fuse chromosomes together and they would translocate improperly

Question 4

Why can replication not occur properly at the ends of linear chromosomes?

Answer 4

DNA polymerase can only synthesize at the single stranded 5’ end

Question 5

What are telomeres?

Answer 5

short DNA sequence of 5’-TTAGGG-3’ that is repeated thousands of times

Question 6

What is located at the very end of the telomeres?

Answer 6

long chain of GGG

Question 7

What are t-loops in regards to telomeres?

Answer 7

a knot at the end of chromosomes where the long strands can bend back on themselves and form complexes with upstream sequences of the tail

Question 8

What is the shelterin complex?

Answer 8

when a complex of six proteins combines with the t-loops

Question 9

What is the possible function of the shelterin complex?

Answer 9

close off ends of chromosomes and protext then from nuclease digestion and chromosomal fusions

Question 10

What fills in the gap that is left behind once the primer is removed?

Answer 10

DNA Polymerase

Question 11

What is the function of ligase?

Answer 11

seals the DNA together when DNA polymerase fills in the gap that is left by the primer being removed

Question 12

What is the function of telomerase?

Answer 12

binds to the 3’ G rich tail of single stranded DNA and extends the telomere

Question 13

What is the purpose of the RNA component of the telomerase?

Answer 13

serves as a guide to attach the enzyme to the DNA and allows the process of reverse transcription to occur

Question 14

What occurs when telomerase dissociates from the new DNA strand?

Answer 14

DNA primase binds the 5’ end of the new DNA
DNA polymerase fills in the new hap
new DNA is joined to original DNA by ligase

Question 15

Do prokaryotes contain telomerase?

Answer 15

no

Question 16

Which cells express telomerase?

Answer 16

stem cells
cells that need to divide very quickly such as epitherlial, mucosal, and immune cells

Question 17

What occurs to cells once the telomere has been eroded?

Answer 17

cells die due to chromosomal damage or they stop dividing

Question 18

What is senescence?

Answer 18

when cells stop dividing

Question 19

Which cells contain telomerase which allows them to maintain an immortal status?

Answer 19

cancer cells

Question 20

For cancer cells that do not contain telomerase, how can they continue extending the telomere?

Answer 20

alternative lengthening of telomeres (ALT)