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Chromosomes

Chromosomes. http://ed.ted.com/lessons/the-twisting-tale-of-dna-judith-hauck. Chromosome Overview. A chromosome is a coiled molecule of DNA that contains many genes A gene is a segment of DNA that determines an organism’s traits. QUESTION!.

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Chromosomes

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  1. Chromosomes http://ed.ted.com/lessons/the-twisting-tale-of-dna-judith-hauck

  2. Chromosome Overview • A chromosome is a coiled molecule of DNA that contains many genes • A gene is a segment of DNA that determines an organism’s traits.

  3. QUESTION! Since chromosomes contain DNA, where do you think you would find chromosomes inside of the cell?

  4. Chromosome Overview Structure of a Chromosome: • chromatin- thin strands of DNA & protein found in the nucleus • copied before cell division • chromatin is “thin and thread-like” • chromatid- one of 2 exact copies of DNA that make up a chromosome • chromosome- coiled up chromatin • centromere- where the two chromatids attach (it holds them together)

  5. Centromere DNA Chromatin Chromatid Chromosome Chromosome Chromosomal Hierarchy Draw and label in your notes:

  6. Chromosome Overview • chromosomes are found in your somatic cells • somatic cells are “body cells” that make up your liver, heart, skin, hair, etc etc • ALL of your cells EXCEPT for sperm or eggs

  7. Chromosome Overview • humans have 23 pairs of chromosomes in every somatic (body) cell • this is equal to 46 chromosomes total in every somatic cell • you receive one of each pair from your mom and one of each pair from your dad

  8. Chromosomes and Cell Cycle • Cell Division • Cell Cycle • Mitosis • Cytokinesis

  9. Cell Basics • There are trillions of cells in your body. • Cells are microscopic • Cells have DNA inside a structure called the nucleus • The nucleus is “surrounded” by a structure called the nuclear envelope • Cells are filled with a jelly like substance called the cytoplasm

  10. A Cell Nuclear Envelope Nucleus DNA Cytoplasm

  11. Cell Division • Cell division is the splitting of a single cell into two daughter cells that are identical to each other • mitosis – process of nuclear division (dividing the nucleus) • cytokinesis - process of division of the cytoplasm

  12. Cell Division Cells divide because the organism needs to: • Grow- our cells don’t get bigger in size, they get bigger in number • Repair- needed because of worn out or injured cells (your skin cells are replaced every 28 days; your stomach every 7) • Reproduce: • asexual – one parent; offspring identical to parent – mitosis or binary fission • sexual – combination of genetic material from two parents – meiosis (more on this later!)

  13. Asexual • asexual reproduction • binary fission

  14. Asexual • asexual reproduction • mitosis

  15. Why are cells small? Cells are small to allow the surface area to volume ratio to remain high. This allows the cell: • To take in sufficient nutrients and oxygen to maintain life • To remove waste • To move molecules across the cell efficiently When cells in an organism divide, growth and repair result.

  16. High Surface Area to Volume Ratio????? Surface area = 6 x height x width = 6 Volume = l x w x h = 1 Ratio = 6:1 = 6 Surface area = 6 x height x width = 150 Volume = l x w x h = 125 Ratio = 150:125 or 1.2 6 is higher than 1.2!

  17. The Cell Cycle Cell Cycle- • occurs in somatic cells • What are somatic cells? • a set of events that results in two new daughter cells, which then start the process again. • Interphase • G1  S  G2 • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis Growth and Preparation- 90% of the time spent here Mitosis- division of the nucleus Division of the cytoplasm

  18. The Cell Cycle Interphase • 90% of the time, the cell is in this phase • the cell grows • performs operations unique to the type of cell (stomach cells make digestive enzymes, some white blood cells make antibodies, etc) Three stages of interphase: • G1 (growth stage 1) • S (synthesis) • G2 (growth stage 2)

  19. The Cell Cycle • GROWTH 1 STAGE – G1 • decides whether or not the cell will divide • makes its structural proteins and enzymes to perform its functions • a pancreas cell will produce and secrete insulin • salivary gland cells will produce and secrete enzymes in the mouth to aid in digestion

  20. The Cell Cycle S Synthesis (DNAReplication) • each of the chromosomes is copied

  21. The Cell Cycle GROWTH 2 PHASE – G2 • DNA replication is checked by DNA repair enzymes • cell prepares for mitosis • proteins organize themselves to form a series of fibers called the spindle

  22. DNA correctly replicated? All proteins built for cell division?

  23. INTERPHASE IN AN ANIMAL CELL INTERPHASE IN A PLANT CELL Note that the DNA is in the form of chromatin – loose and in long strands. The nucleolus is usually visible during interphase, but not during mitosis

  24. Mitosis • Follows interphase when the cell is ready to divide • 4 main parts • prophase, metaphase, anaphase, telophase • P-MAT

  25. PROPHASE ANAPHASE METAPHASE TELOPHASE

  26. MITOSIS • PROPHASE • condensing of 2 sister chromatids • chromatin coils up • chromosomes become visible • centrioles replicate and begin to move to opposite sides of the cell • nuclear envelope (the outside of the nucleus) disappears

  27. Notice that the chromatin begins to coil up and you see “space” in the nucleus between what will soon be evident as separate chromosomes

  28. MITOSIS • METAPHASE • spindle fibers move the chromosomes to the middle • this organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome

  29. Chromosomes in metaphase have their centromeres lined up in the middle and their long arms are trailing from each side. Some students think it looks like Chinese characters, others have compared it to stitches on a zombie mouth.

  30. MITOSIS • ANAPHASE • each chromosome is attached to a spindle which moves it toward one pole • chromatids move apart from one another • results in equal separation and distribution of chromosomes

  31. In anaphase the centromeres are in rows at each end of the cell and the arms of the chromosomes are trailing away toward the middle of the cell Some students think this looks like a scary zombie mouth opening

  32. MITOSIS • TELOPHASE • newly separated chromatids arrive at opposite ends of cell • nuclear envelope reappears around the daughter nuclei • the chromosomes uncoil and are no longer visible • cytokinesis may also begin during this stage • this phase is opposite of prophase in the events that happen • end with two new nuclei (one for each new cell)

  33. In telophase the 2 new cells are preparing to enter interphase The chromosomes uncoil In this picture you can see the cell wall forming between the two “wads” of chromatin This is called a cell plate until it reaches both sides of the old cell and divides it into 2 new cells

  34. Tissue sample showing cells in multiple phases of mitosis

  35. CYTOKINESIS • Process in which the cytoplasm divides and two separate cells (daughter cells) form • In animals, it begins with the formation of a cleavage furrow • In plants, a cell plate forms, then a new cell wall forms

  36. Plant cell plate Animal cell cleavage

  37. Challenge! • What differences do you see between animal cell division and plant cell division? (Hint: does one type of cell have something the other doesn’t?) 1. 2. 3.

  38. Challenge! • Shape • animal cells are round • plant cells are square • Structures • animal cells have structures called centrioles • plant cells do not • Telophase • a cleavage furrow divides animal cells • a cell plate divides plant cells

  39. Can you identify the phase each cell is in?

  40. MITOSIS—Summary PROPHASE- chromosomes visible (P for Phat), nuclear membrane disappearing chromosomes condense/fatten and becomevisible) METAPHASE- sister chromatids lined up in the middle/equator (M for middle, chromosomes lined up in the middle of cell)

  41. ANAPHASE- sister chromatids pulled apart (A for Apart or Away because the chromatids pull apart and move away from center) TELOPHASE- chromosomes are at ends of cell, cells prepare to separate (T for Two new nuclear envelopes are forming) Cleavage furrow Cell plate

  42. Not all cells reproduce… • some leave the cell cycle here and do not undergo cell division • red blood cells – which “kick out” their nucleus to make room for the hemoglobin and therefore can’t divide • brain and spinal cord cells – rarely if ever divide; called G0 (pronounced G naught)

  43. A note about the “not” • G0 • pronounced G “not” • there are some cells, like nerves cells, that do not divide • those cells stay in the G0 phase • for example, nerve cells typically do not undergo mitosis meaning your body cannot make more nerve cells • this is why if nerve damage is usually permanent

  44. Other cells can’t stop reproducing!

  45. Abnormal Cell Cycle: Cancer What causes cancer? • Cancer is caused by mutations (changes) in the DNA, including the genes that regulate the cell cycle • Basically: • uncontrolled cell growth • cancer cells grow and divide as long as they receive nutrients • cancer cells crowd normal cells causing tissues and organs to stop working

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