BIO 150 CHAPTER 12 [THE CELL CYCLE]

CANCER AND THE CELL CYCLE

a disease of uncontrolled cell division

cells start dividing when they shouldnt

in a multi cellular organism there has to be a controlled rate of cell division

BACTERIAL CELL DIVISION

dna is will replicate

binary fission is the process to building new cells

EUKARYOTIC CHROMOSOMES

every species has a different number of chromosomes

humans have 46 chromosomes in 23 nearly identical pairs

additional or less chromosomes is fatal

CHROMOSOMES

composed of CHROMATIN- complex of DNA and protein

DNA of a single chromosome is one long continuous double stranded fiber

typical human chromosome 140 million nucleotides long

in the nondividng nucleus

HETEROCHROMATIN - not expressed

EUCHROMATIN - expressed

STRUCTURE

NUCLEOSOME

complex of DNA and 8 HISTONE proteins

nucleosomes wrapped into higher order coils

during mitosis, chromatin coils arranged around scaffold of protein to achieve maximum compaction

Karyotype

array of chromosomes from an individual organism

humans are DIPLOID(2n)

2 complete sets of chromosomes

46 total chromosomes

Haploid(sex cells)- 1 set of chromosomes - 23 in humans

Pairs of chromosomes are - HOMOLOGOUS

each one is a homologue

REPLICATION

Prior to replication, each chromosome composed of a single DNA molecule

After replication, each chromosome composed of 2 identical DNA molecukes

Visible as 2 strands held togheter as chromsome becomes more condensed

• One chromosome composed 2 sister chromatins

Need to know what Centromere is.

Eukaryotic Cell Cycle

interphase( G1 - Gap phase 1, S - Synthesis, G2 - Gap phase 2, Mitosis,

1. G1 (gap phase 1) - primary growth phase, longest phase

2. S (synthesis) - replication of DNA

3. G2 (gap phase 2) - organelles replicate, microtubules organize)

4. M (mitosis) - subdivided into multiple phases

5. C (cytokinesis) - separation of 2 new cells

Know the phases by pictures for lab and lecture exam

Interphase (G2)

Prophase

Prometaphase

Metaphase

Alignment of chromosomes along metaphase plate

• Not an actual structure

• Future axis of cell division

Anaphase

Telophase

Cytokinesis

• cleavage of the cell into equal halves

• animal cells - construction of actin filaments produces a cleavage furrow

• plant cells - cell plate forms between the nuclei

Control of the Cell Cycle

Current view integrates 2 concepts

1. Cell cycle has two irreversible points

   • replication of genetic material

   • separation of the sister chromatids

2. Cell cycle can be pu for accuracy and can be halted if there are errors

   • Allows cell to respond to interna and external signals

Checkpoints

1. G1/S checkoint

   • Cell “decides” to divide

   • Primary point for external signal influence

2. G2/M checkpoint

   • cell makes a commitment to mitosis

   • assesses success of DNA replication

3. Late metaphase (spindle) checkpoint

   • cell ensures that all chromosomes are attached to the spindle

Cyclin-dependent kinases (Cdks

• enzymes that phosphorylate proteins

• primary mechanism of cell cycle control

• Cdks partner with different cyclins at different pointts in the cell cycle

• Activity of Cdk is also controlled by the pattern of phosphorylation

• - Phosphorylation at one site (red) inactivates Cdk

• - Phosphorylation at another site (green) activates Cdk

Cancer

unrestrained, uncontrolled growth of cells

failure of cell cycle control

two kinds of gene can disturb the cell cycle when they are mutated

1. Tumor-supressor genes (break pedal)

2. Proto-onco genes (gas pedal)

Tumor-suppressor genes

p53 plays a key role in G, checkpoint

p53 protein monitors integrity of DNA

• If DNA damaged, cell division halted and repair enzymes stimulated

• If DNA damaged is irreparable, p53 directs cell to kill itself

Prevent the development of cells containing mutations

p53 is absent or damaged in many cancerous cells

Both copies of a tumor-suppressor gene must lose function for the cancerous phenotype to develop

First tumor-suppressor identified was the