Lecture 17

• The Cell Cycle, Programmed Cell Death and Cell Division

The phases of cell cycle

S phase: DNA duplicationM phase: DNA segregation

Metaphase, anaphase

Gap phases

Interphase: G1, S and G2

23:1

G0

The cell cycles of fission and budding yeasts

The morphology of buddingyeast cells arrested by a cdcmutation

Analysis of DNA content with a flow cytometer

Two key components ofthe cell cycle control system

The core of the cell-cyclecontrol system

Evidence from cell-fusionexperiments for a replicationblock

How DNA damage arrests the cell cycle in G1

An overview of the cell-cycle control system

Apoptosis in development

Cell death

The caspase cascade

Induction of apoptosis by either extracellular or intracellular stimuli

A model of how mitogensstimulate cell division

The function of cell death in matching the number of developingnerve cells to the number of target cells they contact

The effects of a myostatin mutation on muscle size

The M-phase of the cell cycle

Microtubule motors Actin-based motors

Two cytoskeletal machines that operate at M phase

M phase= prophase, prometaphase, metaphase, anaphase, telophase+ cytokinesis

metaphase

The three classes of microtubules ofthe fully formed mitotic spindle

Motor proteinsoperate at ornear the ends

orienting

shape

The major forces that separate daughter chromosomes at anaphasein mammalian cells

Shortening mainly attheir attachment, and, toa lesser extent at the two spindle poles

Motor proteinsat the kinetochore

Motorsat the poles

actin

myosin II

The contractile ring

The cleavage furrowHigh dynamicactin filaments

Microtubules stabilize the ring

The midbody: tether between the two daughter cellsand contains the remains of the central spindle--two setsof antiparallel overlap microtubules tightly packet together

Interesting behavior of mother centrioles in some cells

Some of the components of theresidual midbody oftenremain on the inside of the plasma membrane of each cell-marker on the cortex to orientthe spindle in the subsequentcell division

The special features of cytokinesis in a higher plant cell

Preprophase banddecides division planeand forms before M phase

A new cell wall (cell plate) is builtwith vesicles filled withcell-wall materialplasma membrane and the membrane surrounding the new cell wall fuse

Phragmoplast: remaining overlap MT

Summary

1. Cell cycle, core cell-cycle control system;2. Programmed cell death, caspases;3. Cell cycle and cell death are regulated;4. Cell division, mitosis, cytokinesis5. Mitotic spindle, contractile ring