Chapter 12: The Cell Cycle Tomorrow Pre-lab – Mitosis only (NOT meiosis – Lab 3) Mitosis lab (Make-up is Thursday 7:30 AM)b turn in notebooks at end (Have respiration lab finished!!)

1.When is cell division important? -Reproduction – unicellular organisms – binary fission in bacteria -Growth & development from fertilized egg -Repair (& replacement) of damaged cells Chapter 12: The Cell Cycle 20 µm 100 µm 200 µm (a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM). (b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM). (c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM).

1.When is cell division important? 2.What is an organism’s genome? -Total hereditary endowment in the cell of a species -Nuclear & extra-nuclear (mito & chloro) 3.How many chromosomes do we have? -46 – somatic cell (cells of the body) -2n -diploid -23 – gamete (sex cells – sperm & egg) -n-n -haploid 4.What are chromosomes made of? -Chromatin -DNA & proteins Chapter 12: The Cell Cycle

0.5 µm Chromosome duplication (including DNA synthesis) Centromere Separation of sister chromatids Sister chromatids Centrometers Sister chromatids A eukaryotic cell has multiple chromosomes, one of which is represented here. Before duplication, each chromosome has a single DNA molecule. Once duplicated, a chromosome consists of two sister chromatids connected at the centromere. Each chromatid contains a copy of the DNA molecule. Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells. Fig 12.4 Chromosome duplication & distribution during cell division

INTERPHASE G1G1 S (DNA synthesis) G2G2 Cytokinesis Mitosis MITOTIC (M) PHASE 1.When is cell division important? 2.What is an organism’s genome? 3.How many chromosomes do we have? 4.What are chromosomes made of? 5.What are the 2 major phases of the cell cycle? -Interphase – 90% -Mitotic phase – 10% Chapter 12: The Cell Cycle

1.When is cell division important? 2.What is an organism’s genome? 3.How many chromosomes do we have? 4.What are chromosomes made of? 5.What are the 2 major phases of the cell cycle? -Interphase -Mitotic phase 6.What are the steps of the cell cycle? -IPMAT -Interphase -Prophase -Metaphase -Anaphase -Telophase Chapter 12: The Cell Cycle

G 2 OF INTERPHASEPROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule Nonkinetochore microtubules Combine pro- & prometaphase Chromosomes appear as Pairs

METAPHASEANAPHASETELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming Centrosome at one spindle pole Daughter chromosomes MiddleApartTwo

1.When is cell division important? 2.What is an organism’s genome? 3.How many chromosomes do we have? 4.What are chromosomes made of? 5.What are the 2 major phases of the cell cycle? 6.What are the steps of the cell cycle? 7.What is the difference between animal and plant cytokinesis? -Animal – cleavage furrow – cell forms from outside in -Plants – cell plate – cell forms from inside out Chapter 12: The Cell Cycle

Cleavage furrow Contractile ring of microfilaments Daughter cells 100 µm 1 µm Vesicles forming cell plate Wall of patent cell Cell plate New cell wall (a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (SEM) Figure 12.9 Cytokinesis in animal and plant cells

1.When is cell division important? 2.What is an organism’s genome? 3.How many chromosomes do we have? 4.What are chromosomes made of? 5.What are the 2 major phases of the cell cycle? 6.What are the steps of the cell cycle? 7.What is the difference between animal and plant cytokinesis? 8.How is the cell cycle regulated? -Checkpoints -Make sure cell has enough “ingredients” to move to next stage Chapter 12: The Cell Cycle

Control system G 2 checkpoint M checkpoint G 1 checkpoint G1G1 S G2G2 M Figure Mechanical analogy for the cell cycle control system

Figure The G 1 checkpoint G 1 checkpoint G1G1 G1G1 G0G0 (a) If a cell receives a go-ahead signal at the G 1 checkpoint, the cell continues on in the cell cycle. (b) If a cell does not receive a go-ahead signal at the G 1 checkpoint, the cell exits the cell cycle and goes into G 0, a nondividing state. Most functioning cells are in G 0

1.When is cell division important? 2.What is an organism’s genome? 3.How many chromosomes do we have? 4.What are chromosomes made of? 5.What are the 2 major phases of the cell cycle? 6.What are the steps of the cell cycle? 7.What is the difference between animal and plant cytokinesis? 8.How is the cell cycle regulated? -Checkpoints -Make sure cell has enough “ingredients” to move to next stage -Cyclins -Cyclin-dependent kinase (CDK) -MPF -maturation promoting factor -Cyclin + CDK = MPF Chapter 12: The Cell Cycle

Accumulated cyclin molecules combine with recycled Cdk mol- ecules, producing enough molecules of MPF to pass the G 2 checkpoint and initiate the events of mitosis. MPF promotes mitosis by phosphorylating various proteins. MPF‘s activity peaks during metaphase. 3 During G 1, conditions in the cell favor degradation of cyclin, and the Cdk component of MPF is recycled. 5 During anaphase, the cyclin component of MPF is degraded, terminating the M phase. The cell enters the G 1 phase. 4 2 Synthesis of cyclin begins in late S phase and continues through G 2. Because cyclin is protected from degradation during this stage, it accumulates. 1 Cdk G 2 checkpoint Cyclin MPF Cyclin is degraded Degraded Cyclin G1G1 G2G2 S M G1G1 G1G1 S G2G2 G2G2 S M M MPF activity Cyclin Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle (b) Molecular mechanisms that help regulate the cell cycle Relative Concentration Fig Molecular control of the cell cycle at the G2 checkpoint