The Cell Cycle Flashcards
Cell Proliferation In Prokaryotes
prokaryotes make a copy of their genome and the copy splits into two daughter cells
Binary Fission
- initiated when DNA of the bacterial chromosome is attached by proteins to the inside of plasma membrane
- as chromosome continues to replicate, the cell begins to elongate and the newly synthesized DNA is anchored to the plasma membrane
- cell continues to elongate until 2 DNA attachment sites are at opposite ends of elongated cell
- when DNA replication is complete the cell begins to constrict along midpoint of the cell
- synthesis of a new cell membrane and cell wall which will completely divide the two daughter cells
Eukaryotic Cell Cycle
allows for a unicellular fertilized egg to develop into a complex organism
Interphase
cell makes preparations for cell division which include the replication of DNA and an overall increase in size
S phase
replication of DNA
-new molecule is associated with histones that allow for tight compaction
G1 and G2 phase
prepare the cell for DNA synthesis and mitosis
G0 phase
cells that are not actively dividing pause here, some cells never leave this phase
Prophase
- centrosomes begin to radiate long microtubules forming a mitotic spindle
- centrosomes will become positioned at opposite poles of the cell
- spindle will become crucial for separating the chromosomes into 2 daughter cells
ProMetaphase
- nuclear envelope breaks down
- microtubules are able to attach to kinetochores
- kinetochores pull the chromosomes to the poles of the cell
- other polar microtubules help push poles away
Metaphase
- alignment of chromosomes at the centre of the cell in a region called metaphase plate
- kinetochore microtubules are attached to kinetochores of each sister chromatid
Anaphase
- kinetochore tubules begin to shorten and sister chromatids separate into individual chromosomes that are pulled towards spindle poles
- polar microtubules push against each other and help elongate the cell
- at the end the 2 cells will have equivalent and complete set of chromosomes
Telophase
2 new daughter nuclei form in the cell
- nuclear envelope reforms around the chromosomes at the opposite poles of the dividing cell
- chromosomes de condense and microtubules are broken down
- division of one nucleus into two
- mitosis has to be followed by the division of a cell into 2 individual cells
Cytokinesis
separation of two cells
Cytokinesis in Animal Cells
- formation of a contractile ring made up of motor proteins that contract bundles of actin fibres along the midline of the cell
- formation of a defined cleavage furrow that separates the cell into two separate daughter cells
Cytokinesis in Plant Cells
- lay down a newly developed cell wall along a cell plate region in the middle
- cytokinesis is then complete when the forming cell wall fuses with the original cell wall
Mitosis Promoting Factor
allows for the transition from G2 to M phase and consists of cyclin proteins and cyclin dependent kinase
Kinases
-enzymes that activate/inactivate other proteins by phosphorylating key amino acids on the target proteins
Three Cyclin CDK complexes involved in regulation
- G1 cyclin-CDK complex is needed to transition from the G1 to S phase and helps prepare cell for replication
- S-cyclin-CDK complex helps to initiate DNA synthesis
- M-Cyclin-CDK complex initiates mitosis
Checkpoints in the Cell Cycle
- serve as a form of cellular surveillance and are able to block cyclin-CDK activity if needed
- can pause cell division or can repair damage
Three Major Checkpoints
- DNA damage checkpoint at the end of G1 - only undamaged DNA will be able to enter S-phase
- DNA replication checkpoint at end of G2-only when all DNA is replicated it will enter mitosis
- Spindle assembly checkpoint before anaphase- only complete mitosis if all chromosomes are attached to a microtubule from the mitotic spindle
Hunt
- added radioactive labelled amino acids to sea urchin eggs
- took samples of rapidly dividing embryo every ten minutes and used gel electrophoresis to visualize change in levels
- found that protein bands became darker as cell division progressed
- found one protein oscillated between increasing and decreasing called cyclin
