ch10howcellsdivide...• chromosomes move to equator of the cell • all chromosomes are aligned at...

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Bacterial cell

Septum

Bacterial chromosome: Double-stranded DNA

Origin of replication

1 2

3


Chromosome Rosettes of Chromatin Loops Chromatin Loop Solenoid

Nucleosome Histone core

Chromatin loop

Scaffold protein Scaffold protein

DNA

DNA Double Helix (duplex)

4

5


Homologous chromosomes Homologous chromosomes

Sister chromatids Sister chromatids

Centromere

Replication

Kinetochore

Kinetochores

Cohesin proteins Centromere

6


G1

G2

S Interphase

Mitosis M Phase

Cytokinesis

M Phase

G2

S G1

Metaphase

Prophase Anaphase

Telophase Prometaphase

7


Chromatid

Kinetochore

Cohesin proteins

Centromere region of chromosome

Metaphase chromosome

Kinetochore microtubules

8


INTERPHASE G2 Prophase Prometaphase Metaphase Anaphase Telophase

Nucleus Nucleolus

Aster Chromosomes

Polar microtubule

Nucleus reforming

Cleavage furrow

80 µm 80 µm 80 µm

CYTOKINESIS MITOSIS

Centrioles (replicated; animal cells only)

Nuclear membrane

• DN A has been replicated • Centrioles replicate (animal cells) • Cell prepares for division

• Chromosomes condense and become visible • Chromosomes appear as two sister chromatids held together at the centromere • Cytoskeleton is disassembled: spindle begins to form • Golgi and ER are dispersed • Nuclear envelope breaks down

• Chromosomes attach to microtubules at the kinetochores • Each chromosome is oriented such that the kinetochores of sister chromatids are attached to microtubules from opposite poles. • Chromosomes move to equator of the cell

• All chromosomes are aligned at equator of the cell, called the metaphase plate • Chromosomes are attached to opposite poles and are under tension

• Proteins holding centromeres of sister chromatids are degraded, freeing individual chromosomes • Chromosomes are pulled to opposite poles (anaphase A) • Spindle poles move apart (anaphase B)

• Chromosomes are clustered at opposite poles and decondense • Nuclear envelopes re-form around chromosomes • Golgi complex and ER re-form

• In animal cells, cleavage furrow forms to divide the cells • In plant cells, cell plate forms to divide the cells

Polar microtubule

Kinetochore microtubule

Chromatin (replicated)

80 µm 80 µm 80 µm 80 µm

Mitotic spindle beginning to form

Condensed chromosomes

Centromere and kinetochore

Mitotic spindle

Chromosomes aligned on

metaphase plate Kinetochore microtubule

Polar microtubule


© Andrew S. Bajer, University of Oregon

9


Centrioles

Sister chromatids

Aster

57 µm


Metaphase plate

Polar microtubule

© Andrew S. Bajer, University of Oregon

10


Metaphase

Pole Pole

Pole Pole 2 µm

Overlapping microtubules

Late Anaphase

Overlapping microtubules

© Dr. Jeremy Pickett-Heaps 11 12


Cell wall Nucleus

0.7 µm

Vesicles containing membrane components fusing to form cell plate

© B.A. Palevits & E.H. Newcomb/BPS/Tom Stack & Associates

13


Septum

FtsZ protein

Chromosome

Chromosome Microtubule

Nucleus


Centrioles Kinetochore

Polar microtubule

Spindle pole body


Centriole

Prokaryotes Some Protists Other Protists Animals


Polar microtubule

No nucleus, usually have single circular chromosome. After DNA is replicated, it is partitioned in the cell. After cell elongation, FtsZ protein assembles into a ring and facilitates septation and cell division.

Nucleus present and nuclear envelope remains intact during cell division. Chromosomes line up. Microtubule fibers pass through tunnels in the nuclear membrane and set up an axis for separation of replicated chromosomes, and cell division.

A spindle of microtubules forms between two pairs of centrioles at opposite ends of the cell. The spindle passes through one tunnel in the intact nuclear envelope. Kinetochore microtubules form between kinetochores on the chromosomes and the spindle poles and pull the chromosomes to each pole.

Nuclear envelope remains intact; spindle microtubules form inside the nucleus between spindle pole bodies. A single kinetochore microtubule attaches to each chromosome and pulls each to a pole.

Spindle microtubules begin to form between centrioles outside of nucleus. Centrioles move to the poles and the nuclear envelope breaks down. Kinetochore microtubules attach kinetochores of chromosomes to spindle poles. Polar microtubules extend toward the center of the cell and overlap.

Yeasts

Central spindle of microtubules

Fragments of nuclear envelope

14


G1 S G2 M G2 M G1 S G2 M

Co

nce

ntr

atio

n

Low

High MPF activity Cyclin

15


G2

M

S G1

Spindle checkpoint G2/M checkpoint

G1/S checkpoint (Start or restriction point)

16


Cyclin

P

Cyclin-dependent kinase (Cdk)

P

17


• Growth factors

• Size of cell

G2

M

S G1

Spindle Checkpoint APC Cdc2/Mitotic Cyclin

• Chromosomes attached at metaphase plate

• Replication completed • DNA integrity

G2/M Checkpoint

G1/S Checkpoint

Cdk1/Cyclin B

• Nutritional state of cell

18


• Growth factors

• Size of cell

G2

M

S G1

Spindle Checkpoint APC Cdk1/Cyclin B

• Chromosomes attached at metaphase plate

• Replication completed • DNA integrity

G2/M Checkpoint

G1/S Checkpoint

Cdc2/G1Cyclin

• Nutritional state of cell

19


1. DNA damage is caused by heat, radiation, or chemicals.

2. Cell division stops, and p53 triggers enzymes to repair damaged region.

3. p53 triggers the destruction of cells damaged beyond repair.

p53 allows cells with repaired DNA to divide.

1. DNA damage is caused by heat, radiation, or chemicals.

2. The p53 protein fails to stop cell division and repair DNA. Cell divides without repair to damaged DNA.

3. Damaged cells continue to divide. If other damage accumulates, the cell can turn cancerous.

DNA repair enzyme

Cancer cell

p53 protein

No

rmal

p53

A

bn

orm

al p

53 Abnormal

p53 protein

20

ch10howcellsdivide...• chromosomes move to equator of the cell • all chromosomes are aligned at...

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