3. About 2 trillion cells are produced By an adult human body everyday! This is about 2 million new cells Every second!!

4. These new cells are produced When other cells divide. Cell division is also called Cell reproduction. Gametes are an organism’s Reproductive cells.

5. Remember that all of the cells Information is stored in the DNA. So if/when a cell divides, the DNA must also divide and move Into the newly created cell.

6. Bacteria reproduce by a type of Cell division called binary fission. Binary fission is a form of asexual Reproduction that produces Identical offspring. In asexual reproduction, a single Parent passes exact copies Of its DNA to its offspring.

7. Binary fission occurs in 2 stages… 1 st the DNA is copied And 2 nd the cell divides. The bacterium divides by adding A new cell membrane to a point On the membrane between the Two DNA copies.

8. A new cell wall forms around The new membrane. Eventually the dividing bacterium is Pinched into 2 independent cells. Each cell contains one of the circles Of DNA and is a complete Functioning bacterium.

10. Eukaryotic cells form chromosomes Before cell division. A vast amount of information encoded In DNA is organized into units Called genes. A gene is a segment of DNA that Codes for a protein or RNA molecule.

11. A single molecule of DNA has Thousands of genes lined up Like train cars. Genes play an important role in Determining how a person’s Body develops and functions.

12. As a eukaryotic cell prepares to Divide, the DNA and the proteins Associated with the DNA coil into A structure called a chromosome. Before the DNA coils up, the DNA Is copied. The two exact copies of DNA that Make up each chromosome Are called chromatids.

13. The two chromatids of a chromosome Are attached at a point called A centromere.

14. Each human cell normally has 2 Copies of 23 different chromosomes, For a total of 46 chromosomes. The 23 chromosomes differ in size, Shape, and set of genes. Each of the 23 pairs of chromosomes Consists of 2 homologous chromosomes, Also called homologues.

15. Homologous chromosomes are Chromosomes that are similar in Size, shape, and genetic content. Each homologue in a pair of Homologous chromosomes comes From one of the 2 parents.

17. When a cell contains 2 sets of Chromosomes, it is said to be Diploid. Gametes contain only 1 set of Chromosomes. When a cell contains 1 set of Chromosomes, it is said to be Haploid.

18. The haploid number in a human Gamete can be written as n = 23 The diploid number in a cell can be Written as 2n = 46

19. The fusion of 2 haploid gametes, A process called fertilization, A diploid zygote is formed. A zygote is a fertilized egg cell, The 1 st cell of a new individual.

21. Of the 23 pairs of chromosomes in Human somatic cells, 22 pairs Are called autosomes. Autosomes are chromosomes that are Not directly involved in determining The sex of an individual. The sex chromosomes, one of the 23 pairs of chromosomes in humans, Contain genes that will determine The sex of the individual.

22. In humans, and other organisms, The 2 sex chromosomes are Referred to as the X and Y Chromosomes. The genes that create a male are Located on the Y chromosome and The genes that create a female Are located on the X chromosome.

24. Cell division in eukaryotic cells is More complex than bacteria cells. This is because it involves dividing Both the cytoplasm and the Chromosomes.

25. The life of a eukaryotic cell is Usually shown as a cycle. The cell cycle is a repeating sequence Of cellular growth and division.

26. A cell spends 90% of its time in the First 3 phases-these are collectively Called interphase. A cell will enter the last 2 phases Only if it is about to divide.

27. The 5 phases of the cell cycle… 1) First growth phase (G1) During G1 a cell grows rapidly And carries out its routine functions. Cells that are not dividing remain In this phase. Some cells never divide (muscle & nerve) And thus stay in this phase forever.

28. 2) Synthesis (S) phase. A cell’s DNA is copied during this Phase. At the end of this phase, Each chromosome consists of 2 Chromatids attached at the Centromere.

29. 3) Second Growth phase (G2) In G2, preparations are made for the Nucleus to divide. Hollow protein Fibers called microtubules are Assembled. The microtubules Are used to move the chromosomes During mitosis.

30. 4) Mitosis The process during the cell division In which the nucleus of the cell is Divided into 2 nuclei is called Mitosis. Each nucleus ends up with the same Number and kinds of chromosomes As the original cell.

31. 5) Cytokinesis The process during cell division in Which the cytoplasm Divides is called cytokinesis. Mitosis and cytokinesis produce New cells that are identical to The original cells and allow Organisms to grow.

32. If a cell spends 90% of its time in Interphase, how do cells know When to divide? The cell has checkpoints at which Feedback signals from the cell Trigger the next phase of the cycle.

33. The cell cycle in eukaryotes is Controlled by many proteins, control Occurs at 3 principle checkpoints… They are at the end of G1, G2, And at Mitosis. When cells lose their control over When to divide, cancer forms.

35. During mitosis the nucleus divides To form 2 nuclei. Also, the chromatids on each Chromosome are physically moved To opposite sides of the dividing cell.

36. Spindles are cell structures made up Of both centrioles and individual Microtubule fibers that are Involved in moving the chromosomes To opposite sides of the cell.

37. Mitosis has 4 phases… Step 1 -> Prophase Chromosomes coil up and become Visible during prophase. The nuclear Envelope dissolves and a spindle forms.

38. Step 2 -> Metaphase During metaphase the chromosomes Move to the center of the cell and line Up along the equator. Spindle fibers Link the chromatids of each Chromosome to opposite poles.

39. Step 3 -> Anaphase Centromeres divide during anaphase. The 2 chromatids move toward Opposite poles as the spindle Fibers begin to shorten.

40. Step 4 -> Telophase A nuclear envelope forms around the Chromosomes at each pole. Chromosomes, now at opposite poles, Uncoil and the spindle dissolves. Mitosis is complete!

41. As mitosis ends, cytokinesis begins. During cytokinesis, the cytoplasm Of the cell is divided in half, and The cell membrane grows to enclose Each cell, forming 2 daughter cells.