Figure 5.18d

Hydrogenbond

Disulfidebridge

Polypeptidebackbone

Ionic bond

Hydrophobicinteractions andVan der Waalsinteractions

PROTEIN STRUCTURE DISRUPTED DENATURED PROTEIN

• The sequential events of the cell cycle are directed by a distinct cell cycle control system, which is similar to a clock

• The cell cycle control system is regulated by both internal and external controls

• The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received

Stop and Go Signs: Internal and External Signals at the Checkpoints

• Three important checkpoints are those in G1, G2, and M phases

Figure 12.15G1 checkpoint

G2 checkpointM checkpoint

G1

G2M

SControlsystem

Figure 12.17a

G1 checkpoint

G0

G1

Without go-ahead signal,cell enters G0.

(a) G1 checkpoint

G1

With go-ahead signal,cell continues cell cycle.

Figure 12.17b

G1

M G2

G1

M G2

M checkpoint

Without full chromosomeattachment, stop signal isreceived.

PrometaphaseAnaphase

G2 checkpointMetaphase

With full chromosomeattachment, go-ahead signalis received.

(b) M checkpoint

• It is critical that checkpoint proteins function properly. (they need the correct structure!)

• Broken Stop sign TUMOR• Mutated Stop sign TUMOR• There are DNA REPAIR ENZYMES to fix

mutated genes prevent malformed proteins. (link), (and this time, to music…)

• BRCA1 and BRCA2 = tumor suppressor genes• Code for DNA repair enzymes• They fix mutations prevent the

production of misshaped proteins.

• What happens if BRCA1 or BRCA2 mutated?• Some mutations may go un-repaired.

• Increased RISK of a tumor:

Mutated Stop Sign TUMORMutated Stop Sign, Repaired NO TUMORMutated Stop Sign, REPAIR ENZYME BROKEN TUMOR

LINK TO ANJELINA JOLIE DOUBLE MASTECTOMY, REMOVAL OF OVARIES AND FALLOPIAN TUBES- CNN

Figure 12.20a

Tumor

Glandulartissue

A tumor growsfrom a singlecancer cell.

1 Cancer cells invadeneighboring tissue.

Cancer cells spread through lymph and blood vessels to otherparts of the body.

2 3