Growth 1 - features / problems of growth Flashcards
What is anisotropy?
We do not continue to grow in a sphere forever
- directional growth
What is proportionality?
everything is size matched
What is discontinuous scaling?
- organs are proportionally scaled to the size of the organism
- cells are relatively the same size across different organisms
- cells are the largest thing that do not scale
- grow by having more cells, not making our cells bigger
Name 3 limits to cellular growth
- transport - moving components across the cell becomes trickier
- communication / coordination - time delays communicating within and outwith the cell
- mRNA synthesis - can only transcribe mRNA at a maximum rate if there are two copies in the cell. Might not be able to make proteins fast enough for the whole cell
What are 4 ways you could make a bigger cell?
- vacuoles in plant cells - takes up most of the space in plant cells
- syncytia - large cell with many nuclei
- polytene chromosomes - DNA has replicated so much to make a much larger chromosome - repeated replication with no division
- helper cells
What are syncytial?
large cell with many nuclei
Give an example of syncytia
muscle cells
- my oblasts fuse to make one big cell with many nuclei
viruses
- some add proteins to the membrane of a cell causing it to fuse to other cells
- this large cell with many nuclei is grate for viral replication
Give an example of a helper cell
oocyte and granulosa
granulosa - smaller cells with cytoplasmic bridges to oocyte. Metabolism of oocyte is done by granulosa
When will a cell decide it is ready to divide?
- once it is twice the volume that it started off
How do cyclins control progression of the cell cycle?
by activating cycling dependant kinases (CDKs)
How does the large single celled egg go to multicellular with cells of normal size?
- cells divide without the embryo getting any larger
- this is done until cells reach normal size
Explain the cell cycle in embryos
All cells undergo the cell cycle at the same time
Explain the role of CDKs
- CDK will bind to specific cyclins
- active CDKs activates the transcription of the next cyclin
- production of the next cyclin inactivates the production of the previous cyclin
What is the G2 checkpoint?
DNA damage checkpoint
What is the G1 -> S checkpoint?
blocked unless:
- cells have enough resources
- cells have enough room
- cell has external signals asking it to divide
- there are no signals saying not to divide
