senescence

Question 1

what is senescence?

Answer 1

it is that mitotically competent cells cant replicate indefinitely and they have a finite replicative lifespan, in normal cells the replicative capacity decreases with each cell division

Question 2

what are telomeres?

Answer 2

they are the end of linear chromosomes

Question 3

what is the normal function of telomeres?

Answer 3

they allow the chromosome to be replicated properly during cell division and prevent chromosomes from fusing and being damaged (loss of genetic info)

Question 4

when is senescence induced?

Answer 4

when all telomeric DNA is lost, as with every cell division a nucleotide of telomeric DNA is lost

Question 5

what does aging lead to?

Answer 5

it leads to a decline of the biological functions and the ability to adapt to metabolic stress of cells, tissues and organs

Question 6

what do stem cells do?

Answer 6

they are found in the body and help to combat the effects of aging, they provide new cells for the body as it grows, and replace specialised cells that are damaged or lost

Question 7

what are the two types of stem cells?

and what are the differences between them?

Answer 7

• embryonic stem cells- can differentiate into any type of cell
• adult stem cells- can differentiate into certian cell lineages

Question 8

whats the difference between stem cells and ordinary cells?

Answer 8

• stem cells can divide and make exact copies of them selves self-renewal
• stemcells can differentiate into progenitor cells that differentiate into specialised cells
• everytime a stem cell divides, it makes a copy of itself and one progenitor cells
• stem cells can keep divinding indefinetly but only divide when a new supply of cells is needed

Question 9

what is aging with reference to stem cells?

Answer 9

aging is the inability of various types of stem cells to continue to replenish the tissue with functional differentiated cells capable of maintaining that tissues original function

Question 10

when is telomerase expressed?

Answer 10

• its active in germ cells and early embryonic cells
• not active in most somatic cells (humans)
• active in 80-90% of all cancers

Question 11

what does adrenaline do?

Answer 11

• it mediated the “fight or flight” response
• it activates PKA in skeletal muscle which leads to the breakdown of muscle glycogen to glucose-6-phosphate which is used to supply the muscles with ATP
• this effect of PKA is via the phosphorylation of key enzymes involved in glycogen breakdown and synthesis

Question 12

hormone signaling in multicellular organisms

Answer 12

• hormones are chemicals released from a cell into the bloodstream that evokes a response in many different cells
• as they are released into the bloodstream, they have access to all the cells in the body
• cells that respond to hormones do so because they have specific receptors that recognise that hormone
• hormones are able to coordinate cellular activities

Question 13

how does the reversal of the cellular response to adrenaline work?

Answer 13

• as the levels of signalling molecule (ligand) fall, the no. of active receptors also does
• the α subunit hydrolyses its GTP to GDP and reassociates with β/γ to form inactive G-protein
• levels of cAMP fall as adenylyl cyclase isnt being activated and phosphodiesterase converts cAMP to AMP
• reduced levels of cAMP lead to an inhabition of PKA
• protein phosphatases remove phosphate groups from proteins, reversing the effects of PKA