In eukaryotes, heritable information is passed to the next generation via processes that - PowerPoint Presentation

Slide1

In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization

Cell Cycle and Mitosis 8.1 to 8.11Slide2

Genetic information is stored and transmitted through DNA

All the DNA in a cell constitutes the cell’s

genome

A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells)

DNA molecules in a cell are packaged into

chromosomesSlide3

Fig. 12-3

20 µmSlide4

Genetic Information is stored and transmitted through DNA

Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus

Somatic cells

(

nonreproductive

cells) have two sets of

chromosomes - DIPLOIDGametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells - HAPLOIDEukaryotic chromosomes consist of

chromatin, a complex of DNA and protein that condenses during cell divisionSlide5

Fig. 12-4

0.5 µm

Chromosomes

Chromosome

duplication

(including DNA

synthesis)

Chromo-

some arm

Centromere

Sister

chromatids

DNA molecules

Separation of

sister chromatids

Centromere

Sister chromatidsSlide6

The cell cycle is a complex set of stages that is highly regulated with checkpoints, which determine the ultimate fate of the cellSlide7

Interphase

Majority of the cell cycle

Time when a cell’s metabolic activity is very high and the cell performs various functions

3 stages

G1 – cell growth

S – DNA replication (Synthesis of DNA)

G2 – prepare for mitosisSlide8

M Phase (mitotic phase)About 10% of the cell cycle

2 stages

Mitosis – nuclear division

Cytokinesis – cytoplasm division

Results in two genetically identical cellsSlide9

The cell cycle is directed by internal controls or checkpoints.Slide10

Cell Cycle Checkpoints

For many cells, the G

1

checkpoint seems to be the most important one

If

a cell receives a go-ahead signal at the G

1 checkpoint, it will usually complete the S, G2, and M phases and divide

If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G

0 phaseSlide11

Cell Cycle Checkpoints

Two types of regulatory proteins are involved in cell cycle control:

cyclins

and

cyclin-dependent

kinases (Cdks)The activity of cyclins and Cdks

fluctuates during the cell cycleMPF (maturation-promoting factor) is a cyclin-Cdk

complex that triggers a cell’s passage past the G2 checkpoint into the M phaseSlide12

Fig. 12-17

M

G

1

S

G

2

M

G

1

S

G

2

M

G

1

MPF activity

Cyclin

concentration

Time

(a) Fluctuation of MPF activity and cyclin concentration during

the cell cycle

Degraded

cyclin

Cdk

G

1

S

G

2

M

Cdk

G

2

checkpoint

Cyclin is

degraded

Cyclin

MPF

(b) Molecular mechanisms that help regulate the cell cycle

Cyclin accumulationSlide13

Internal and External signals provide stop-and-go signs at the checkpoints

An example of an internal signal is that

kinetochores

not attached to spindle microtubules send a molecular signal that delays

anaphase

Some external signals are

growth factors, proteins released by certain cells that stimulate other cells to divideFor example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in cultureSlide14

Fig. 12-18

Petri

plate

Scalpels

Cultured fibroblasts

Without PDGF

cells fail to divide

With PDGF

cells prolifer-

ate

10 µmSlide15

Fig. 12-19

Anchorage dependence

Density-dependent inhibition

Density-dependent inhibition

(a)

Normal mammalian cells

(b)

Cancer cells

25 µm

25 µmSlide16

Mitosis passes a complete genome from the parent cell to the daughter cell

Mitosis is conventionally divided into five phases:

Prophase

Prometaphase

Metaphase

Anaphase

TelophaseCytokinesis is well underway by late telophaseSlide17

Fig. 12-6b

Prometaphase

Prophase

G

2

of Interphase

Nonkinetochore

microtubules

Fragments

of nuclear

envelope

Aster

Centromere

Early mitotic

spindle

Chromatin

(duplicated)

Centrosomes

(with centriole

pairs)

Nucleolus

Nuclear

envelope

Plasma

membrane

Chromosome, consisting

of two sister chromatids

Kinetochore

Kinetochore

microtubuleSlide18

Fig. 12-7

Microtubules

Chromosomes

Sister

chromatids

Aster

Metaphase

plate

Centrosome

Kineto-

chores

Kinetochore

microtubules

Overlapping

nonkinetochore

microtubules

Centrosome

1 µm

0.5 µmSlide19

Fig. 12-6d

Metaphase

Anaphase

Telophase and Cytokinesis

Cleavage

furrow

Nucleolus

forming

Metaphase

plate

Centrosome at

one spindle pole

Spindle

Daughter

chromosomes

Nuclear

envelope

formingSlide20

Fig. 12-8b

Kinetochore

Microtubule

Tubulin

Subunits

Chromosome

Chromosome

movement

Motor

proteinSlide21

Fig. 12-9

Cleavage furrow

100 µm

Contractile ring of

microfilaments

Daughter cells

(a) Cleavage of an animal cell (SEM)

(b) Cell plate formation in a plant cell (TEM)

Vesicles

forming

cell plate

Wall of

parent cell

Cell plate

Daughter cells

New cell wall

1 µmSlide22

Summary of Mitosis

What must occur before mitosis?

DNA replication

Pass G2 checkpoint

What is “checked” at the ‘M’ checkpoint?

Chromosome attachment to microtubule

What follows mitosis?Cytokinesis What are the products of the mitosis?2 genetically identical cellsWhy do we need mitosis?Growth, repair, asexual reproduction