T4M1- The cell cycle Flashcards
What type of material is distributed among daughter cells
Genetically identical
Define binary fission
A form of asexual reproduction
Where does binary fission occur?
Prokaryotes
What happens as the chromosome replicates during binary fission?
Cells elongate and new DNA is anchored to plasma membrane
When do cells stop elongating during binary fission?
Until two DNA attachment sites are at opposite ends of elongated cells
How do you know when replication is complete in binary fission?
Bacterium is double its size
Where does the cell constrict when replication is complete?
Along the midpoint of the cell
What is synthesised during binary fission?
Synthesis of cell membrane and cell wall
What happens during cell division?
Unicellular fertilized egg becomes multicellular complex organism
What are two functions of cell division?
Repair and renewal
Can adult stem cells give rise to all cell types?
No- can only replace non reproducing specialised cells
What are quiescent cells
Non dividing satellite stem cells
What can happen to quiescent cells in muscle cells
Become activated and divide to enable muscle regeneration
What does the activation of muscle stem cells lead to?
Proliferation, differentiation and fusion of muscle precurser cells
What are muscle precursor cells called?
Myoblasts
What do myoblasts form and what are they?
Myofibers- mature muscle cells
List some differences between eukaryotic and prokaryotic reproduction?
- eukaryotes larger
- eukaryotic DNA packed into nucleus
- eukaryotes organized into linear chromosomes
- eukaryotes require more regulated control
What two main phases does mitosis contain?
Interphase and M phase
What does interphase consist of?
S phase, two gap growth phases G1 and G2
What does the M phase consist of?
Mitosis and cytokinesis
What is the purpose of interphase?
Preparation for cell division
What occurs during the s phase?
- replication of DNA in the nucleus
- increase in cell size
What does G1 phase prepare for? When does it occur?
DNA synthesis
Before S phase
What does G2 phase prepare for? When does it occur?
Mitosis- after S phase
When do cells pause?
In G0 phase- between M and S phase
How long do cells pause for?
Can be days or years
What type of cells enter G0 phase?
Eye lens, muscle cells, nerve cells
What do quiescent cells do upon injury?
Activated from dormant phase and re-enter cell cycle
Who discovered the 5 phases of mitosis and how?
Walther Flemming in 1882 by staining salamander embryos to analyze chromosomes of dividing cells
What must happen to chromosomes prior to mitosis
Duplication and condensing
In what form are chromosomes during interphase
long and thin chromatin fibres
What happens to sister chromatids as the M phase progresses?
Sister chromatids of each duplicated chromosome separate and move to 2 new cells
What marks the beginning of M phase?
End of interphase G2 phase
Can chromosomes be identified during interphase?
No
What happens to duplicated chromosomes as the cell transitions from G2 to M phase?
Condense and become visible
First stage of mitosis?
Prophase
How do chromosomes appear in prophase?
Identical sister chromatids joined at centromeres
What do centromeres do in prophase?
Radiate long microtubules forming mitotic spindles
What follows prophase in mitosis?
Prometaphase
What is the defining feature of prometaphase?
Fragmentation of nuclear envelope
What happens to microtubules as a result of nuclear envelope fragmentation? and where?
Microtubules attach to kinetochores in prometaphase
Define kinetochore
Specialised protein structure that associate with each one of sister chromatids on each side of centromere
Why do microtubules attach to kinetochore regions?
Essential to pull chromosomes to pole of cell
What comes after prometaphase in mitosis?
Metaphase
What marks metaphase?
Alignment of chromosomes down the centre of the cell
- metaphase plate
What facilitates the metaphase plate?
kinetochore microtubules attached to centromere
What follows metaphase?
Anaphase
What occurs during anaphase?
Kinetochore microtubules shorten
- sister chromatids separate into individual chromosomes pulled into opposite spindle poles of cell
What elongates cell in anaphase?
Polar microtubules pull against each other
What marks the end of anaphase?
Both ends of cell will have complete set of chromosomes
What comes after anaphase?
Telophase
What marks telophase?
Two new daughter nuclei forming
What happens to nuclear envelope during telophase?
reforms around chromosome at opposite poles of dividing cells
what happens to chromosomes and microtubules in telophase
decondense and spindle microtubules depolymerise (break down)
How does cytokinesis occur in animals?
Begin with formation of contractile ring made of motor proteins with bundles of actin fibres
what forms to separate daughter cells during cytokinesis
cleavage furrow
what do plants form during cytokinesis
lie down new cell wall along cell plate- dividing middle of cell
when is cytokinesis completed in plant cell?
when cell wall fuses with existing wall
What was thought to allow the transition of G2 to M phase in 1970s?
Mitosis promoting factor
What did Tim Hunt do in the 1980’s?
Measured protein level changes in urchin embryos
What did Tim Hunt add to the urchin eggs
Methionine and thought they would be incorporated into new proteins in embryos
How did Tim Hunt measure samples of protein
Used gel electrophoresis every 10 mins to visualise changes in protein
What happened to the protein in Tim Hunt’s experiment
Became darker
What happened to one specific protein and its intensity in Hunt’s experiment?
The cyclin protein band oscillated in intensity
- suspected had something to do with cell cycle progression
What does the mitosis promoting factor consist of
Cyclin protein and cyclin dependent kinase (CDK)
Define the role of kinases
Phosphorylate key amino acid
what is the activity of kinase dependent on?
Being attached to cyclin
What does cyclin-CDK complex do
trigger changes by phosphorylation of target proteins
What does the G1/S cyclin CDK complex do?
Needed for transition from G1 to S phase and prepares for DNA replication
What does S cyclin CDK complex do?
Initiate DNA synthesis
What does M cyclin CDK do?
Prepare cell for mitosis
What is sthe purpose of checkpoints?
- serve as cellular surveillance
- block cyclin CDK if anything goes wrong
- can pause cell division until next step
- allow cells to be repaired
What does G1 phase check for?
DNA damage checkpoint
What does G2 pase check for?
DNA replication checkpoint
What is the M checkpoint?
Spindle assembly checkpoint at the end of anaphase
what happens when damage occurs in a cell?
kinase phosphorylates P53
- used turn on genes that inhibit cell cycle
- tumor cell that suppresses growth
What does p53 produce
CDK inhibitor protein which pauses cell cycle in G1 phase
What can regulatory proteins monitor as early as prometaphase
The degree to which sister chromatids are attached to spindle microtubules at the kinetochore regions
What happens if there are unattached kinetochore regions
Create wait signal which leads to recruitment of spindle assembly protein
How is the recruitment of spindle assembly protein detected
Lack of tension in centromere area
what enzyme breaks sister chromatids
separase
what is the function of kinetochore microtubules
assist with movement of chromosomes
what is the function of nonkinetochore microtubules
forms cage like network which facilitates the activities of cell cycle
- assists in elongating the entire cell during anaphase
what happens to the binding proteins between the sister chromatids during anaphase
break down
describe disjunctional segregation
centromeres of sister chromatids disjoin and segregate
when do chromatids become chromosomes
anaphase
