3.2 M Phase

DNA combines with what proteins to form chromatin?

Histone Proteins

At what point in the cell does chromatin condense, and individual chromosomes can be seen with a light microscope?

Before cell division

During interphase, what key points allow for the moving forward of the cell cycle

• Cell size was increased

• DNA was replicated

• the centrosome is duplicated

Centrosome

• The centrosome contains the centrioles and the spindle fibers needed for cell division

• serves as the main microtubule-organizing center (MTOC) of animal cells

• each centrosome contains 2 centrioles

Small, cylindrical structures made of microtubules, arranged perpendicular to each other

Centromeres

• Hold sister chromatids together

• The site where the kinetochore forms

• The enzyme separase splits the centromere by cleaving cohesin proteins that hold the sister chromatids together

Kinetochores

• protein structure that attaches chromosomes to spindle fibers during cell division

Prophase

• the sister chromatids condense and mitotic spindle assembles

Mitotic Spindle

• consists of microtubules

• during mitotic spindle assembly in prophase, the centrosomes move to opposite sides of the cell, identifying the poles in which the chromosomes will move towards

Prometaphase

• The nuclear envelope breaks down, and the chromosomes can attach to spindle microtubules through kinetochores

Metaphase

• At this point, the chromosomes become aligned at the metaphase plate

• the metaphase plate is an imaginary plane in the middle of the cell where the chromosomes line up

Anaphase

• The sister chromatids are pulled apart/separated to form two daughter chromosomes

• Each is pulled toward a spindle pole on opposite sides of the cell

• This segregation is accomplished by the shortening of kinetochore microtubules and the spindle poles growing further apart.

During anaphase, how is separation of sister chromatids controlled?

M phase cyclin-CDK

M phase cyclin-CDK

If proper attachments are formed between the chromatids and the spindle, and they are correctly aligned at the metaphase plate, M phase cyclin-CDK activates APC

APC (Anaphase promoting complex)

• APC activates separase by terminating securin through the attachment of ubiquitin

• Securin normally inhibits separase

• When securin is destroyed, separase is released and becomes active.

• Separase cleaves cohesin, and the centromere is removed

Cohesin

• Cohesin is a protein complex that holds sister chromatids

• In pro-metaphase, most of cohesin is removed, except for some at the centromere

• At the end of metaphase, Separase cleaves the last remaining cohesin, and the daughter chromosomes become separated

What is the consequence of improper spindle attachments?

• Nondisjunction - the failure of genetic information to separate properly during
  cell division, resulting in daughter cells with an abnormal number of chromosomes

• Causes Aneuploidy

Aneuploidy

• the presence of an abnormal number of chromosomes in a cell

Telophase

• The two sets of daughter chromosomes arrive at the poles of the spindle and decondense

• New nuclear envelopes begin to assemble

• Contractile ring begins to contract 

Cytokinesis

• The cytoplasm is divided into two and the contractile ring pinches the cell in two to create two daughter cells

• The contractile ring is composed of actin and myosin

Contractile Ring compoisition

• composed of actin and myosin