LECTURE 15 Flashcards
What do the signals that control cell division for eukaryotes related to?
The function of the entire organism, not the individual cell.
Do eukaryotes of multiple origins and if so, why?
Yes, because their chromosomes are very long
Why is eukaryotes DNA segregation more complicates then prokaryotes
- nuclear envelope
- multiple chromosomes
- each chromosome can be very long
Replicated DNA molecules becomes very ___________ in the __________ before they segregate in eukaryotes
Condensed Nucleus
Chromatin
A complex of DNA and proteins that are the building materials for chromosomes
Sister chromatids
Two copies of replicated DNA that are connected to each other
Centromere
A physical construction of the duplicated chromosome. Sister chromatids attach at this site.
Eukaryotes cytokinesis
- division of cytoplasm
- final stage of cell reproduction
- different in plant and animals cells
Do the number of chrome men’s correlate with the complexity of the organism ?
NO
Each chromosomes form each parent are closely matched in :
- physical appearance
- genetic info content (NOT identical)
All parts of interphase
M = mitotic phase G1 = Gap phase S = DNA synthesis phase G2 = Gap 2 phase
Interphase
- chromosomes present but NOT visible
- metabolic activity and growth occur, control decisions to grow.
G1 phase
Prepares the cell for DNA replication by growing in size.
Start of S phase
DNA replication when the two strands of helix unwind (starting at the origin)
- each serves as a template for synthesis of a new strand
REPLICATION OF DNA
End of S phase
Each chromosome (there are 2) consists of one old strand and one new strand
- chromatids are tight to associated at Centro mere region
G2 phase
cell prepares for chromes segregation and cell division
- centrioles duplicate (new one (daughter centriole, d) grows out of the older centriole (mother centriole, m))
- Nucleolus visible
- chromes duplicated but NOT condensed
When do centriole duplicate
G2
Prophase
The two centrosomes gets in to separate.
- nucleoli disappear
- chromatin fibbers becomes more condensed and visible
- sister chromatids visible
- centrosome visible
Why do the centrosomes separate in prophase
because of microtubule growth and motor proteins pushing against opposite microtubules
Prometaphase
Nuclear envelope begins to breakdown.
- kinetochores grab onto microtubules and holds on the end of microtubules
- microtubules grow and shrink
How does the nuclear envelope breakdown in prometaphase ?
Liam is disassemble, and membrane forms small vesicles that remain around the chromosomes
What does the breakdown fo the nuclear envelope during prometaphase allow?
Allows microtubules to grow into the area and make contact with kinetochores
Kinetochores
Each chromatid has ONE kinetochore; the pair face in the opposites directions. The kinetochores captures microtubules and is required for proper chromosome congregation and separation of sister chromatids.
What are kinetochores made of ?
Larger structure made of many types of proteins.
Where doe kinetchore protujens assemble on ?
They assemble on the centromeric DNA
What holds chromatids together
Cohesins
Cohesins
Special protein complexes that hold chromatids together
Do cohesins remain intact during anaphase?
YES
When all chromosomes are at the met phase splats and properly attached to microtubules, a signal is sent that results in…
A part of cohesins getting destines by protease called separase. This opens the ring, along the sister chromatids to separate.
Before anaphase a protector protein (called _____) prevents the _________ of cohesins
Securin. Destruction
At the start of anaphase, securin gets destroyed by a protein degration machine called the
Anaphase-promoting complex
Or
APC
Loss of securin results in the
Cohesin ring opening up or breaking apart
Anaphase
- shortest stage
- begins when cohesin protests are cleaved
- tensions builds due to kinetochore microtubules pulling equally in opposite directions
- this tensions released and chromatids move rapidly apart, with kinetochore leading away
Mitotic chromatid segregation can occur by two different events:
1) short eating the distance between poles and chromatids (anaphase A)
2) movement of spindle poles (chromosomes) apart (anaphase B)
Cell may use either or both of these methods
Telophase
- Two daughter nuclei form in cell
- nuclear envelope start to reform
- chromosomes start to de-condense
- spindle microtubules depolymerize
- nucleoli reappear
- results in 2 identical daughter cells
Plant mitotic spindles
- sue chromatin (not centrosomes) to uncleared microtubules
- spindle assembles in an “inside-out” fashion
Some animal cells and many female meiotic spindles assemble
Without centrioles
Mitotic spindles in prometaphase
Microtubules start to form around the chromatin as soon as nuclear envelop starts to break down
Mitotic spindles in metaphase
Kinetochore-microtubules form alongside non-kinetochore microtubules (bipolar spindles forms)
Mitotic spindles in anaphase and telophase
Microtubules become cross linked (microtubule motor proteins involved) - this proved stable structure for chromatid segregation
