Unit 8: The Cell Cycle

1. Unit 8: The Cell Cycle

2. Why do Cells Divide? To make copies of cells for growth (you started out as 1 cell, today you have around 10 trillion)

3. Why do cells divide? To make copies of cells for repair (cells wear out and need to be replaced)

4. Why do cells divide? To carry on the species – during ASEXUAL reproduction organisms undergo MITOSIS to make exact copies of themselves to create offspring. During SEXUAL reproduction two gametes (egg and sperm) get together to create offspring. Gametes are made through a process called MEIOSIS.

5. Chromosomes In eukaryotic cells, the genetic information that is passed from one generation of cells to the next is carried by chromosomes. Chromosomes are made up of DNA.

6. Chromosomes Chromosomes are not visible in most cells, except for during cell division. At the beginning of cell division, chromosomes condense and become visible.

7. Chromosomes Before cell division, each chromosome is replicated (remember DNA replication). Because of this each chromosome is made of 2 identical “sister” chromatids.

8. Chromosomes When the cell divides the “sister” chromatids separate from each other. One chromatid goes to each of the two new cells.

9. Chromosomes Each pair of chromatids is attached at an area called the centromere (usually in the middle of the chromatids)

10. Chromosomes Humans have 46 chromosomes. There are 23 pairs. 23 chromosomes come from their father and 23 from their mother. 2 of the chromosomes are sex chromosomes (represented by an X and Y).

11. The Cell Cycle The cell cycle is the series of events that cells go through as they grow and divide. During the cell cycle a cell: grows, prepares for division (copies organelles), and divides to form two new “daughter” cells.

12. 4 Phases of the cell cycle • G1 Phase – cells grow, make proteins and organelles • S Phase – (longest phase) Chromosomes are replicated and new DNA is made. • G2 Phase – (shortest) organelles are duplicated • M Phase – cells undergo mitosis and cytokinesis

13. Interphase - the non-dividing part of the cell cycle, and it consists of G1 phase, S phase, and G2 phase.

14. Cyclins – a group of proteins that regulates when a cell should divide. Cancer cells do not respond to the signals that regulate the growth of cells.

15. Mitosis Mitosis – cell division in eukaryotic cells that creates two identical daughter cells that are diploid (2N). Diploid – the cells have two sets of chromosomes (example: humans have 46 chromosomes, 23 pairs)

16. Mitosis Interphase The cell grows and replicates its DNA, organelles, and centrioles

17. Mitosis Step 1: Prophase The chromatin condenses into chromosomes. The centrioles separate, and a spindle begins to form. The nuclear envelope breaks down.

18. Mitosis Step 2: Metaphase The chromosomes line up across the center of each cell. Each chromosome is connected to a spindle fiber at it’s kinetochore (part of the centromere)

19. Mitosis Step 3: Anaphase The sister chromatids separate into individual chromosomes and are moved apart.

20. Mitosis Step 4: Telophase The chromosomes gather at opposite ends of the cell and lose their shapes. Two new nuclear envelopes will form.

21. Mitosis Cytokinesis In animal cells a cleavage furrow pinches the cytoplasm into 2 new cells. In plants a cell plate forms to divide the cells. 2 identical diploid daughter cells are formed.

22. Mnemonic to remember Mitosis P M A T

23. Mitosis P – Prophase – Prepare M A T

24. Mitosis P M – Metaphase – Meet in middle A T

25. Mitosis P M A – Anaphase – Apart T

26. Mitosis P M A T – Telophase – Two new nuclei

27. Meiosis Differences between Mitosis and Meiosis Mitosis • Occurs in somatic (body) cells • Produces identical daughter cells • Makes 2 diploid (2N) cells • No crossing over • Occurs in germ (sex) cells • Produces gametes (eggs and sperm) • Makes 4 haploid (1N) cells • Crossing over occurs

28. Amniocentesis • Having abnormalities in chromosomes can be devastating so… • _________________OR amniotic fluid test Amniocentesis • Medical procedure used in ________ diagnosis of ________ abnormalities and fetal infections • - A small amount of ________ fluid, (which contains fetal tissues) is extracted from the amniotic sac surrounding a developing fetus • - The _____ _____is examined for genetic abnormalities (using a karyotype) prenatal genetic amniotic fetal DNA

29. Human Chromosomes 46chromosomes 23 pairs • Humans have ___ ______________… _______ • 2 are called sex chromosomes… X and Y • __________ Karyotype • Karyotype is a test to identify and evaluate the size, shape, and number of _________________ in a sample of body cells • _______, missing, or ___________ positions of chromosome pieces can cause problems with a person's growth, development, and body functions. chromosomes Extra abnormal

30. ________ Cell = Body cell Somatic ex: hair, blood, skin diploid 46 chromosomes = ____ = _______ 2N

31. ________ = Sex cell Gamete ex: sperm (males), eggs (females) haploid 1N 23 chromosomes = __ = _______

32. The Cell Cycle is the series of events that cells go through as they _________ and __________. grow divide • During the cell cycle the cell: • prepares for division (copies_____________) • _________to form two daughter cells grows organelles divides There are 4 phases: • 1. ___ phase – cells grows, • makes proteins and • organelles • 2. __ phase – (longest) • synthesize DNA, replicate • chromosomes • ___ phase – (shortest) organelles duplicated • 4. ___ phase – Mitosis and Cytokinesis G1 S Interphase G2 M

33. Meiosis Meiosis – cell division that creates 4 different daughter cells that are gametes (sex cells).

34. Meiosis Each gamete created is haploid (1N), it only contains one set of chromosomes. In humans, the gametes (sperm and egg) each contain 23 chromosomes. When fertilization occurs, then the resulting cell has 46 chromosomes (23 from the sperm and 23 from the egg).

35. Meiosis 1 Prophase 1 Each chromosome pairs with its matching homologous chromosome to form a tetrad. Crossing over occurs between the chromatids.

36. Meiosis 1 Metaphase 1 The homologous chromosomes line up in the middle. Spindle fibers attach to each of the homologous chromosomes.

37. Meiosis 1 Anaphase 1 The spindle fibers pull the homologous chromosomes towards the opposite ends of the cell.

38. Meiosis 1 Telophase 1 and Cytokinesis Nuclear membranes form. The cell separates into two new cells.

39. Meiosis 2 Prophase 2 The chromosomes condense and become visible. NO crossing over occurs.

40. Meiosis 2 Metaphase 2 The chromosomes line up in the middle.

41. Meiosis 2 Anaphase 2 The sister chromatids separate and move to opposite ends of the cell.

42. Meiosis 2 Telophase 2 and Cytokinesis Meiosis 2 results in four daughter cells that are haploid (1N)

43. Definitions Tetrad – four sister chromatids (2 homologous chromosomes) that match up with each other during prophase 1.

44. Definitions Crossing over – When homologous chromosomes switch part of their chromatids. Results in genetic variation.

45. Homologous chromosomes: chromosomes with the same genes as each other, in the same sequence, but do not necessarily have the same allele of those genes.

46. Homologous chromosomes pair up with one another, forming a tetrad (4 chromatids) during prophase I.

47. Crossing Over • A process occurring during meiosis wherein two homologous chromosomes pair up and exchange segments of their genetic material.

48. This occurs at the stage when chromatids of homologous chromosomes pair up during synapsis, forming a tetrad. The chromatids form X-like structures (chiasma or chiasmata). They break into segments, which are then exchanged with one another.

49. Crossing over is important because it results in new combinations of genes that are different from either parent, contributing to genetic diversity (why you look different than your parents & siblings)

50. NON-DISJUNCTION • When the chromosomes do not separate properly during meiosis (either in in anaphase I or in anaphase II). • This leads to the production of gametes that have the wrong number of chromosomes.