Concept 9.2: Mitotic Phase and Interphase

Shortest part of the cell cycle

Mitosis

90% of the cell cycle

Interphase

Parts of interphase

G1, S, G2

What happens in G1 phase

Cell grows by producing proteins and cytoplasmic organelles such as mitochondria and ER

What happens in S phase

Duplication of chromosomes

What happens in G2 phase

Grows even more as it completes preparations for cell division

What happens in mitosis

Cell divides

Most variable phase

G1 is the most variable phase in different types of cells

5 stages of mitosis

Prophase, Prometaphase, Metaphase, Anaphase, Telophase

Cytokinesis

Overlaps with anaphase/telophase. Mother cell splits into 2 daughter cells

Formation of mitotic spindle

Forms during prophase, consists of microtubules and associated proteins. While it assembles, the other microtubules of the cytoskeleton temporarily disassemble to provide material for spindle

Centrosome in mitosis

Mitotic spindle begins forming here, organizes cells microtubules. Joined by pair of centrioles at center of chromosome (not essential for mitosis)

Centrosome movement in mitosis

2 centrosomes start near nucleus and move apart during prophase/prometaphase. By the end of prometaphase, centrosomes are at opposite ends of the cell

Components of mitotic spindle

Centrosomes, aster, and microtubules

What is a kinetochore

Structure made up of proteins, 2 of em assemble on sections of chromosomes at each centromere, facing opposite directions. During prometaphase, some of the spindle microtubules attach to each kinetochore. Microtubules are able to move chromosomes because of their attachment to kinetochores

Metaphase plate

Centromere of duplicated chromosomes are in the middle of the cell, lined up horizontally

Spindle microtubules not attached to kinetochore

Work to elongate the cell by pushing against each other

What is an aster

Radial microtubules at top of cell that come out of centrosome. Kind of look like sun rays

When does anaphase begin

When the cohesins holding together the chromatids are cleaved by enzyme seperase

2 ways that chromosomes are moved when attached to microtubules

Because of motor proteins that help them “walk” and also microtubules reel them in

Prophase important shit

1. Chromatin fibers become tightly coiled, able to see discrete chromosomes

2. Nucleoli disappears

3. Each duplicated chromosome appears as sister chromatids

4. Mitotic spindle begins to form

5. Centrosomes move away from each other

Prometaphase important shit

1. Nuclear envelope fragments

2. Chromosomes are full condensed

3. 2 kinetochores form

4. Some spindles attach to kinetochores, some interact with other spindles on opposite side of cell to lengthen it

Metaphase important shit

1. Centrosomes are at opposite poles

2. Chromosomes are at metaphase plate

Anaphase important shit

1. Shortest stage, only few mins

2. Begins when cohesin proteins are cleaved by seperase

3. Each chromatid becomes an individual chromosome

4. 2 new daughter chromosomes move to opposite sides of cell

5. Cell elongates

6. At the end, both sides of equivalent and complete collections of chromosomes

Cytokinesis important shit

1. Cleavage furrow forms to split cell into 2

2. Daughter cells appear shortly after end of mitosis

What is a cleavage furrow

Groove in cell surface near metaphase plate. On the cytoplasmic side, there is a contractile ring made of actin microfilaments which interact with myosin molecules, causing the ring to contract (like pulling a drawstring)

Cytokinesis in plant cells

No cleaved furrow, cell plate forms instead which fuses with plasma membrane and. 2 daughter cells appear and cell wall arises from contents of cell plate

Binary fission in bacteria

Cell grows to double its size and divides to form 2 new cells (cell division AND cell reproduction)

BF- origin of replication

Specific place where DNA of bacteria begins to replicate, 2 origins are produced which move to opposite sides of cell. The cell pinches off, each getting a complete genome

Evolution of mitosis

Mitosis evolved from simpler prokaryotic mechanisms of cell division/reproduction

1. Some proteins involved in mitosis are also in binary fission

2. Some ancestral mechanisms in certain species have remained unchanged over time