HC7 - Immortalization

Question 1

serial passaging for

Answer 1

determining the maximum number of divisions in vitro

Question 2

exceeding the number or allowed doublings leads to

Answer 2

cells ceasing to proliferate or enter apoptosis

Question 3

senescence

Answer 3

inability to re-enter the cell-cycle

Question 4

scenescent cells remain

Answer 4

metabolically active

Question 5

appearence senescent cells

Answer 5

fried egg like > large cytoplasm

Question 6

marker senescent cells

Answer 6

beta-galactosidase

Question 7

number of replecative doublings depend on

Answer 7

• species from which the cells are
• tissue of origin
• age of the donor organism

Question 8

embryonic stem cells with proper nutrients are

Answer 8

immortal

Question 9

immortal

Answer 9

unlimited replicative potential

Question 10

immortality is a feature of

Answer 10

the cell lineage, not the individual cell

Question 11

cancer cells resemble

Answer 11

embryonic stem cells (ECS)

Question 12

HeLa cells (1951)

Answer 12

immortal cancer cells from aggresive cervical adenocarcinoma

Question 13

tumor growth is not

Answer 13

exponential > 2000 generations in colon carinomas instead of 40

Question 14

limited division potential can

Answer 14

inhibit tumorigenesis

Question 15

amount of divisions is limited by (2)

Answer 15

• accumulation of physiological stress
• recording number of cell divisions

Question 16

in senescence the expression of the following CDK inhibitors is increased

Answer 16

P16^INK4A, p21^cip1, p53 > often mutated in cancers

Question 17

reduction of culture atmosphere oxygen concentration leads to a

Answer 17

substantial increase in replicative lifespan in vitro

Question 18

hyperoxia leads to

Answer 18

progressive breakdown of mitochondrial function and accumulation of ROS

Question 19

physiological stress for cells in culture

Answer 19

culturing cells on plastic and unsuitable medium

Question 20

senescence of human cells eliminated by

Answer 20

expression of SV40 large T antigen

Question 21

SV40 T large antigen inactivates

Answer 21

pRb and p53 > control cell survival pathway

Question 22

Ki67

Answer 22

proliferation marker

Question 23

triggers for senescence (2)

Answer 23

• hyperoxia
• DNA damage

Question 24

senescent cells release

Answer 24

pro-inflammatory cytokines > can stimulate tumorigenesis

Question 25

proliferation of human cells is limited by

Answer 25

telomere length

Question 26

chromosome

Answer 26

long DNA molecule

Question 27

chromosomes are linear because of

Answer 27

telomeres

Question 28

telomeres

Answer 28

protective shields for chromosomal ends

Question 29

telomeres prevent

Answer 29

end-to-end fusion

Question 30

hexanucleotide sequence

Answer 30

5’-TTAGGG-3’

Question 31

size hexanucliotide sequence

Answer 31

5-10.000 bp > shortens each growth-and-division cycle

Question 32

short telomeres cannot protect ends and leads to

Answer 32

crisis and apoptosis

Question 33

no protection of ends chromosome can lead to

Answer 33

breakage-fusion-bridge cycle

Question 34

G-rich strand telomere has a

Answer 34

3’ overhang of telomeric DNA

Question 35

T-loop

Answer 35

invades double-stranded piece of telomere > 3 stranded DNA = big

Question 36

D-loop

Answer 36

displacement loop > 3 stranded DNA

Question 37

T-loops are bound by

Answer 37

shelterin complex

Question 38

no ends sticking out

Answer 38

protection from degradation

Question 39

shortening of telomeres > end replication problem because of (2)

Answer 39

• the need for a RNA primer on 3’ lagging strand
• under-replication of parental strand because primer cannot sit precisely at the end of template strand

Question 40

exonucleases cause

Answer 40

telomere erosion

Question 41

telomere erosion

Answer 41

50-100 bp lost / division

Question 42

short telomeres enter

Answer 42

BFB cycle

Question 43

protection from BFB cycle for cells is to enter crisis to

Answer 43

prevent transformation

Question 44

cancer cells can escape crisis by

Answer 44

overexpressing telomerase

Question 45

hTERT

Answer 45

catalytic subunit of telomerase in human cells

Question 46

telomerase-independent alternative lengthening of telomeres (ALT)

Answer 46

interchromosomal copying mechanism

Question 47

interchromosomal DNA transfer

Answer 47

uneven crossing over between 2 chromosomes