CH 10.5: M Phase- Chromosome Segregation & the Division of Cytoplasmic Contents Flashcards
What are the 5 stages of Mitosis?
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
When do we know when Prophase has begun?
-When the individual condensed chromosomes are visible under a microscope
What process continues through Prophase?
-The condensation process
What happens during Prophase?
- The mitotic apparatus forms
- The assembly of Spindles & Centrioles (animals)
- The breakdown of the Nuclear Envelope
What happens to the Microtubule structure in the cell that is disassembled in the G2 phase?
-It is replaced by the Spindle apparatus
What is the Spindle Apparatus?
-It carries out the separation of chromosomes during cell division
What is the Spindle Apparatus made of?
-It is made of Microtubules AKA spindle fibers
Where is the Spindle Apparatus assembled?
-It is assembled during prophase at the equator of the dividing cell
What happens to the 2 centriole pairs in Animal Cells during Prophase?
- They begin to move apart pretty early on
- They form an axis of microtubules (spindle fibers) between them
What happens when the Centrioles in Animal Cells reach their opposite ends of the cell?
-By the time they reach their position, they have established a bridge of microtubules= Spindle Apparatus
What occurs in Plant Cells during Prophase?
-A bridge of microtubules also form between the opposite poles of the cells BUT PLANTS DON’T HAVE CENTRIOLES
What is Aster?
- It is present in Animal Cell mitosis ONLY
- It is a branching group of microtubules that extend from the centrioles towards the plasma membrane
What is the purpose of the Aster?
-Bracing the centrioles against the membrane & stiffens the point of microtubular attachment during the retraction of the spindle
What happens to the Nuclear Envelope during the formation of the Spindle Apparatus in Prophase?
-It breaks down & the ER reabsorbs its components
What are the Microtubules like during the break down of the Nuclear Envelope in Prophase?
-Their spindle fibers extend completely across the cell= from one pole to another
What does the orientation of the Microtubule Spindle Fibers determine during Prophase?
-It determines the plane where the cell will divide= through the center of the cell at right angles to the spindle apparatus
What happens during Prometaphase?
- Condensed chromosomes attach to spindle via their kinetochores
- Microtubule attachment
- Movement of chromosomes to the center of the cell
When does the transition from Prophase to Prometaphase occur?
-It occurs after the nuclear envelope breaks down
How many Kinetochores does each Chromosome have?
-They have 2= each one attached to the centromere region of each sister chromatid
What happens to the Microtubules in Prometaphase?
- A 2nd group of them grow from poles of cells towards the centromere
- They are then captured by the kinetochores that are on the sister chromatids=being connected to opposite poles of the spindle
Why is it important that the Microtubules are attached to the sister chromatids on opposite poles during Prometaphase?
- So that they can split apart
- And so that a daughter cell won’t be missing that chromosome
What are the 2 basic mechs that can be used to move Chromosomes to the equator of the cell during Prometaphase?
- Assembly & disassembly of microtubules provide the force
- Motor proteins located at kinetochore & poles of the cell pull on microtubules to provide force
How can Isolated Chromosomes be pulled during Prometaphase?
-Via microtubule disassembly
What type of protein is involved in the force during the movement of microtubules in Prometaphase?
-Kinetochore proteins
What slows down Chromosomal separation at Anaphase?
-The inhibition of motor protein Dynein
What occurs in Metaphase?
-Chromosomes aligning in the center of the cell
What is the Metaphase Plate?
-It is an indication of the future axis of cell division that is perpendicular to the spindle that passes through the circle of chromosomes along the inner circumference of the cell
How do the Chromosomes line up in the Metaphase Plate?
-They are positioned by the microtubules attached to the kinetochores of their centromeres
What role does Metaphase play?
-A transitional phase/ CHECK POINT where all preparations are checked before the action continues
What occurs in Anaphase?
-The chromatids separate
Which phase is the shortest in Mitosis?
-Anaphase
How does Anaphase begin?
-It begins when the Cohesin proteins at the centromere (the one that holds the sister chromatids) are removed
What is the key event in Anaphase?
-The simultaneous removal of the Cohesin proteins from all chromosomes
What happens after the Cohesin proteins are removed from the sister chromatids in Anaphase?
-They are quickly pulled toward the poles of where their kinetochores are attached
What are the 2 movements that take place at the same time & what are they driven by in Anaphase?
- Anaphase A
- Anaphase B
- They are both driven by Microtubules
What happens during Anaphase A?
-The kinetochores are pulled toward the poles as the microtubules that connect them to the poles shorten
How do the Microtubules that connect the Kinetochores to the poles shorten in Anaphase A?
-Tubulin subunits are removed from the kinetochore end of microtubules= chromatid-bearing microtubules are being disassembled= chromatids are being pulled closer to poles
What happens during Anaphase B?
- The poles move apart as the microtubular spindle fibers physically anchored to opposite poles slide past eachother= away from the center of the cell
- Chromosomes also move
- Membrane elongates
When is Anaphase completed?
-When there are SEPARATED sister chromatids & there’s an accurate split of the replicated genome between the two
What occurs during Telophase?
- The nucleus reforms
- AKA spindle breaks down into tubulin monomers that is used to construct cytoskeletons of daughter cells
- Nuclear Envelope forms over each set of sister chromatids= Chromosomes since they aren’t attached at centromere anymore
- Chromosomes start to uncoil into its more extended form
How can Telophase be viewed as?
-The reversal process of Prophase= bringing cell back into the state of Interphase
When is Mitosis complete?
-At the end of Telophase
What is Cytokinesis?
-The division of the cytoplasm of a cell after its nuclear division (mitosis)
How is Cytokinesis achieved in Animal Cells?
-By a constricting belt of actin filaments=forming Cleavage Furrow
How is Cytokinesis achieved in Plant Cells?
- Via creating a Cell Plate= expanding membrane partition that grows until reaches the interior surface of the plasma membrane & fuses w/ it= divides cell into 2
- Cellulose is then used to create 2 new cell walls
What happens to the space between the daughter cells in the Cytokinesis of Plant Cells?
-They become impregnated w/ pectins= Middle Lamena
What are the Mitotic Spindles made of?
-The protein microtubule
What happens to the Spindles that are attached to the chromosomes?
-They shorten as they pull the chromosomes to their designated poles
What happens to the spindles that are unattached to the chromosomes?
-They elongate= stretches the cell
