Upload
colten-cleeton
View
234
Download
0
Tags:
Embed Size (px)
Citation preview
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 8.11
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 chromosomes
Fig. 12-3
20 µm
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 - DIPLOID
Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells - HAPLOID
Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division
Fig. 12-40.5 µm Chromosomes
Chromosomeduplication(including DNAsynthesis)
Chromo-some arm
Centromere
Sisterchromatids
DNA molecules
Separation ofsister chromatids
Centromere
Sister chromatids
The cell cycle is a complex set of stages that is highly regulated with checkpoints, which determine the ultimate fate of the cell
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 mitosis
M Phase (mitotic phase)
About 10% of the cell cycle
2 stages◦Mitosis – nuclear division◦Cytokinesis – cytoplasm division
Results in two genetically identical cells
The cell cycle is directed by internal controls or checkpoints.
Cell Cycle Checkpoints
• For many cells, the G1 checkpoint seems to be the most important one
• If a cell receives a go-ahead signal at the G1 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 G0 phase
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 cycle
MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase
Fig. 12-17
M G1S G2
M G1S G2
M G1
MPF activity
Cyclinconcentration
Time(a) Fluctuation of MPF activity and cyclin concentration during the cell cycle
Degradedcyclin
Cdk
G 1S
G 2
M
CdkG2
checkpointCyclin isdegraded
CyclinMPF
(b) Molecular mechanisms that help regulate the cell cycle
Cyclin
accu
mula
tion
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 divide
For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture
Fig. 12-18
Petriplate
Scalpels
Cultured fibroblasts
Without PDGFcells fail to divide
With PDGFcells prolifer-ate
10 µm
Fig. 12-19
Anchorage dependence
Density-dependent inhibition
Density-dependent inhibition
(a) Normal mammalian cells (b) Cancer cells25 µm25 µm
Mitosis passes a complete genome from the parent cell to the daughter cell
Mitosis is conventionally divided into five phases:◦Prophase◦Prometaphase◦Metaphase◦Anaphase◦Telophase
Cytokinesis is well underway by late telophase
Fig. 12-6b
PrometaphaseProphaseG2 of Interphase
Nonkinetochoremicrotubules
Fragmentsof nuclearenvelope
Aster CentromereEarly mitoticspindle
Chromatin(duplicated)
Centrosomes(with centriolepairs)
Nucleolus Nuclearenvelope
Plasmamembrane
Chromosome, consistingof two sister chromatids
Kinetochore Kinetochoremicrotubule
Fig. 12-7
Microtubules Chromosomes
Sisterchromatids
Aster
Metaphaseplate
Centrosome
Kineto-chores
Kinetochoremicrotubules
Overlappingnonkinetochoremicrotubules
Centrosome 1 µm
0.5 µm
Fig. 12-6d
Metaphase Anaphase Telophase and Cytokinesis
Cleavagefurrow
Nucleolusforming
Metaphaseplate
Centrosome atone spindle pole
SpindleDaughterchromosomes
Nuclearenvelopeforming
Fig. 12-8b
Kinetochore
MicrotubuleTubulinSubunits
Chromosome
Chromosomemovement
Motorprotein
Fig. 12-9
Cleavage furrow100 µm
Contractile ring ofmicrofilaments
Daughter cells
(a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM)
Vesiclesformingcell plate
Wall ofparent cell
Cell plate
Daughter cells
New cell wall
1 µm
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 cells
Why do we need mitosis?◦Growth, repair, asexual reproduction