The Cell CycleChapter 12

Mitosis

Cell division Produce 2 daughter cells Same genetic information

Mitosis

Asexual reproduction Growth Repair

Genome

Genetic information Prokayotes Nucleoid Circular DNA No nucleus

Genome

Eukaryotes Chromosomes: DNA Associated proteins Chromatin: Complex of DNA & proteins Makes up chromosomes Humans 46 chromosomes Dogs 78 chromosomes

Eukaryotes

Somatic cells: Body cells 46 chromosomes Gametes: Sex cells Sperm & eggs 23 chromosomes

Eukaryotes

Chromatid: Duplicated chromosome Centromere: Attachment to another chromatid Prior to cell division chromosomes

replicates

                      

                               

Fig. 12-4 0.5 µm Chromosomes

Chromosomeduplication(including DNAsynthesis)

Chromo-some arm

Centromere

Sisterchromatids

DNA molecules

Separation ofsister chromatids

Centromere

Sister chromatids

Fig. 12-5

S(DNA synthesis)

MITOTIC(M) PHASE

Mito

sis

Cytokinesis

G1

G2

Cell cycle

Cell cycle: Events that occur to produce two

cells 1. Interphase (G1, S, G2) 2. Mitosis 3. Cytokinesis

Interphase

Growth phase of the cell G1, S, G2

Interphase

Where most of cycle is spent Rate of division depends on job of cell. Liver cells may divide rapidly Mature muscle cells do not divide at all Few cells will be in mitosis at a time Most are in interphase

Interphase

G1 or Gap 1 phase Cell is doing its job Preparing for the S phase. Chromosomes are single Can last weeks to years or happen

very quickly

Interphase

S phase DNA replication happens 2 sister chromatids G2 or Gap 2 phase cell prepares for

division Mitochondria & other organelles replicate Microtubules begin to form Chromosomes condense

Interphase

Mitosis

Nucleus & its contents divide Distributed equally Forming two daughter cells Prophase, metaphase, anaphase

and telophase

Prophase

Beginning of mitosis Chromosomes continues to

condense Mitotic spindle forms Begins to move chromosomes to

center Nuclear membrane disintegrates Nucleolus disappears

Prophase

Metaphase

Chromosomes line up in center of cell

Centromeres become aligned along the cells center

Metaphase

Anaphase

Microtubules shorten Separates the sister chromatids Chromosomes move towards the

poles

Anaphase

Telophase

Chromosomes are at the poles Nuclear envelope reforms Nucleolus reappears Chromosomes uncoil or de-

condense

Telophase

Cytokinesis

Cytoplasm separates Animal cells: cleavage furrow pinches the cells

in two Plant cells: cell plate is formed between the

cells Grows until a new cell wall is formed

Cytokinesis

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

Binary fission

Prokaryotes produce 2 daughter cells by binary fission

Binary fission

1. Replication of the DNA Origin of replication: Specific location on the DNA 2. Two DNA molecules move to the

ends of the cell 3. Septation Formation of a new cell membrane

& a septum.

Binary fission

4. Septum begins to grow inward 5. Cell pinches into two cells.

Cell cycle control system

Check points Control point with stop & go signals G1, G2 and M phases

Fig. 12-14

SG1

M checkpoint

G2M

Controlsystem

G1 checkpoint

G2 checkpoint

Cell cycle control system

Special proteins Protein kinases & cyclins Cdks – cycle dependent kinases MPF-cyclin-Cdk complex “M-phase promoting factor” Regulate if cell stops or proceeds in

the cycle

Fig. 12-17b

Cyclin isdegraded

Cdk

MPF

Cdk

MS

G 1G2

checkpoint

Degradedcyclin

Cyclin

(b) Molecular mechanisms that help regulate the cell cycle

G2

Cyclin

accum

ulatio

n

Figure 12.16a

M M M G1G2G2G1 G1S S

MPF activity

(a) Fluctuation of MPF activity and cyclinconcentration during the cell cycle

Time

Cyclinconcentration

Cell cycle control system

Go-ahead signal at G1 Divides No signal G0 phase Does not divide

Figure 12.17G1 checkpoint

G0

G1

Without go-ahead signal,cell enters G0.

(a) G1 checkpoint

G1

G1

G2

S

M

M checkpoint

(b) M checkpoint

Without full chromosomeattachment, stop signal isreceived.

PrometaphaseAnaphase

M G2

G1

M G2

G1

With go-ahead signal,cell continues cell cycle.

G2 checkpoint

Metaphase

With full chromosomeattachment, go-ahead signalis received.

Cell cycle control system

Receives signals The environment Other cells Growth factors Density-dependent inhibition Anchorage dependence

Tumor

Abnormal growth of cells Malfunction in control system Abnormal cells grow uncontrollably Benign: Non-cancerous growth

Tumor

Malignant: Cancerous growth Metastasis: Spread of cancer to distant

locations

p53

Protein Works at a checkpoint at G1 p53 determines if DNA is damaged If so stimulates enzymes to fix it Cell division continues Unable to repair damage Cell suicide occurs

p53

Helps keep damaged cells from dividing Cancer cells p53 is absent or damaged p53 protein is found on the p53 gene Considered a tumor-suppressor gene Cigarette smoking causes mutations in

this gene

Henrietta Lacks

1951 developed cervical cancer Before cancer treatment Cells were removed First cells to grow in vitro Outside of the body Cell line is now known as HeLa cell

line Helped in biomedical research