CELL CYCLE CHAPTER 12

Figure 12.0 Mitosis

Figure 12.1a The functions of cell division: Reproduction

Figure 12.1b The functions of cell division: Growth and development

Figure 12.1c The functions of cell division: Tissue renewal

Figure 12.2 Eukaryotic chomosomes

Vocabulary Chromatin – long, thin fibers of DNA wrapped around proteins Chromosome – one long DNA molecule; condensed and clearly visible during cell division Chromatid – two identical DNA molecules attached by a centromere (sister chromatids)

NEW VOCABULARY Centrosome – microtubule organizing center which includes a pair of centrioles Centrosomes replicate in interphase and move to opposite poles in prophase Centromere – region where 2 chromatids are attached to one another Kinetochore – specialized region of centromere where spindle fibers attach

Figure 12.3 Chromosome duplication and distribution during mitosis

CELL CYCLE Interphase G1 (first gap – cell grows) S (DNA synthesis = chromosomes replicate) G2 (second gap – cell grows) Mitosis Prophase Metaphase Anaphase Telophase Cell Cycle Animation Mitosis Animation

Figure 12.4 The cell cycle

Prophase Chromosomes visible Centrosomes move towards opposite poles and begin making spindle fiber Nuclear membrane, nucleus, and nucleolus disintegrate Spindle fiber form and some attach to the kinetochores of the centromeres

Metaphase Chromosomes line up at the middle of the cell

Figure 12.6 The mitotic spindle at metaphase

Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase; prometaphase

Anaphase Sister chromatids are pulled apart and move toward opposite ends of the cell by the spindle fiber Nonkinetochore spindle help elongate the cell Cell plate begins to form in plant cells (immature cell wall)

Telophase and Cytokinesis Events are opposite those of prophase Nuclear membranes, nuclei, and nucleoli form in each new cell Chromosomes unravel and become chromatin again Spindle fibers disintegrate Cytokinesis occurs – formation of cleavage

Figure 12.5 The stages of mitotic cell division in an animal cell: metaphase; anaphase; telophase and cytokinesis.

Figure 12.5x Mitosis

Figure 12.8 Cytokinesis in animal and plant cells

Figure 12.9 Mitosis in a plant cell

Figure 12-09x Mitosis in an onion root

BINARY FISSION Bacteria only have one chromosome so steps of mitosis are not needed Bacteria replicate via binary fission DNA replicates at a specific point (origin of replication)

Figure 12.10 Bacterial cell division (binary fission) (Layer 3)

Evolution of Mitosis Prokaryotic and eukaryotic cell division share some similar proteins that are involved in cell division Possible intermediates: Current examples in some protists Nuclear envelopes remain intact and replicated chromosomes attach to envelope As nucleus elongates, chromosome separate Spindle forms inside nucleus Prokaryotic proteins also involved in tubulin and actin proteins

REGULATION OF CELL CYCLE Checkpoints – critical points in cell cycle where process can stop or go ahead according to signals Kinases – enzymes that can activate or inactivate something via phosphorylation

Figure 12.13 Mechanical analogy for the cell cycle control system

Restriction point or G1 checkpoint – the most critical of checkpoints During G1, if signaled to proceed then cell usually completes cell cycle and divides If no signal to proceed, cell goes into nondividing state, G0 Most cells are in G0 Go signal means enter S and replicate DNA

Cyclin is a protein that activates kinases that are called cyclin-dependent kinases or Cdks MPF (maturation promoting factor) – combination of Cdks and cyclin

Cyclins accumulate during G2 and associate with Cdk’s to make MPF MPF initiates mitosis at G2 checkpoint by phosphorylating various proteins Nuclear membrane is phosphorylated and this causes it to break down Proteolytic enzymes break down MPF which helps end mitosis

Figure 12.14 Molecular control of the cell cycle at the G2 checkpoint

M Phase Checkpoint M phase (metaphase checkpoint) Kinetochores not attached yet to spindle send delay signals to prevent anaphase from starting too early. Why must the cell wait for all of the chromosomes to line up in the middle of metaphase before proceeding to anaphase?

OTHER SIGNALS A signal that delays anaphase so that right number of chromosomes end up in each new cell Growth factors – external signals that can stimulate cell division

Density-dependent inhibition – cells stop dividing when crowded Anchorage-dependent – most animal cells must be attach to substratum

Figure 12.16 Density-dependent inhibition of cell division

CANCER Cancer – cells that divide excessively and invade other tissues Metastasis – spread of cancer cells Tumor – mass of abnormal cells Benign – cells stay “put”, not cancer Malignant – cells move (metastasis), cancer

Figure 12.17 The growth and metastasis of a malignant breast tumor

Figure 12-17x1 Breast cancer cell

Figure 12-17x2 Mammogram: normal (left) and cancerous (right)

MEIOSIS CHAPTER 13

REPRODUCTION Asexual reproduction – single parent passes on all of its genes to its offspring Sexual reproduction – two parents give rise to offspring that have a combination of genes inherited from two parents

Figure 13.1 The asexual reproduction of a hydra

VOCABULARY Karyotype – picture of an organisms chromosomes Homologous chromosomes – pair of similar chromosomes Haploid – single chromosome set (n=23 for humans) Diploid – two sets of chromosomes (2n=46 for humans) Zygote – fertilized egg

Fertilization or syngamy – fusion of sperm and egg Somatic cell – body cells Gametes – sex cells Sex chromosomes – determine gender Autosomes – all other chromosomes Sister chromatids – copies of same chromosome

HUMAN FEMALE

HUMAN MALE

Figure 13.x1 SEM of sea urchin sperm fertilizing egg

Figure 13.4 The human life cycle

MEIOSIS A process that halves the chromosome number Mitosis vs. Meiosis Genetic recombination

Figure 13.6 Overview of meiosis

Figure 13.7 Meiosis I

Figure 13.7 Meiosis II

Figure 13.8 Mitosis vs. Meiosis

Figure 13.8 Mitosis vs. Meiosis

Figure 13.9 Different possible sex cells (Independent Assortment of Chromosomes)

MORE GENETIC POSSIBILITIES Synapsis – pairing of homologous chromosomes in prophase I Chiasmata or crossing over– when homologous portions of two nonsister chromatids trade place

Figure 13.10 Crossing over during meiosis