Reproduction of cellular explanation with images and words

Explains cellular reproduction

1. Cellular Reproduction Biol 160 Chapter 6

2. Cell division Even large multicellular organisms start as a single fertilized egg or zygote Every other cell in the organism is a result of cellular division

3. Genome All of the DNA in a cell is referred to as a genome Prokaryotic genomes consist of a single circular double-stranded DNA molecule Eukaryotic organisms Linear DNA molecules that are combined with proteins and called chromosomes Humans chromosomes come in matching pairs for most cells Somatic cells or body cells have 46 chromosomes or 23 pairs Diploid = matching pairs of Homologous chromosomes Same genes in same location on each homologous chromosome Sex cells or gametes are haploid and only have 1 of each chromosome 23 total Chromosomal DNA in a human somatic cell

4. The Cell Cycle Ordered series of events involving cell growth and division that produces two daughter cells Two major phases: Interphase: when cell grows and DNA is replicated Mitotic phase: When the replicated DNA and cytoplasm separated and cell divides Cell Cycle Diagram

5. Interphase G 1 Phase: (1 st gap phase) little visible change but cell is quite biochemically active Getting building blocks of chromosomal DNA and accumulating energy for replication

6. Interphase S Phase: (synthesis phase) Cell creates identical copies of each chromosome, forming sister chromatids Centrosome is duplicated Each centrosome consists of a pair of centrioles These give rise to the mitotic spindle that moves chromosomes in mitosis and help organize cell division

7. Interphase G 2 Phase: (2 nd gap phase) Cell replenishes energy and makes proteins necessary for chromosome manipulation Some organelles are duplicated Cytoskeleton is dismantled Additional cell growth

8. Mitotic Phase First step of mitotic phase is Mitosis Composed of 5 different stages that perform nuclear division Prophase, Prometaphase, Metaphase, Anaphase, Telophase Second stage is Cytokinesis When the cytoplasmic components are physically divided into two daughter cells

9. 1 st phase of Mitosis: Prophase Several steps occur to provide access to the chromosomes Sister chromatids begin to coil more tightly Study tip: You should know the steps of mitosis and what occurs at each step of mitosis

10. 2 nd phase of Mitosis: Prometaphase Mitotic spindle microtubules attach to the sister chromatids at the kinetochore or protein complex that forms at the centromere Centromere: name for region on chromosomes where microtubules attach and kinetochore forms

11. 3 rd phase of Mitosis: Metaphase Chromosomes align at the metaphase plate midway between the poles of the cell Chromosomes are maximally condensed

12. 4 th phase of Mitosis: Anaphase Sister chromatids are split apart at the centromere Cell becomes physically elongated

13. 5 th phase of Mitosis: Telophase All of the events that occurred in the first three phases of mitosis are reversed

14. Cytokinesis Physical separation of cellular components into two daughter cells Slightly different for animals and plants

15. Alteration to classic cell cycle: G phase Sometimes, cells don’t just jump back into interphase after the mitotic phase G phase is when cells are not actively preparing to divide and appear inactive Can be temporary until an external signal triggers G 1 to start Other cells remain in G permanently (e.g. nerve cells and mature muscle cells)

16. Regulation at Internal Checkpoints Cell Cycle Checkpoints : points at which the cell cycle can be stopped to prevent abnormal cell formations Occur at three points in the cell cycle G1 checkpoint: restriction point where cell irreversibly commits to the cell-division process Checks for adequate energy, cell size and DNA damage G2 checkpoint: ensures all chromosomes were replicated and no DNA was damaged Prevents entry into Mitotic phase if issues found M checkpoint: makes sure spindle microtubules are correctly attached to sister chromatids Separation of sister chromatids is irreversible

17. Cancer and the cell cycle Cancer is a general term for many diseases that are caused by uncontrolled cell division Can occur from small, uncorrected errors, that occur to DNA and are passes on to daughter cells and accumulate over time Even when all cell cycle controls are functioning there are still a small number of errors or “mutations” to genes that occur Most mutations don’t impact the cell, but some cause mutated proteins that can cause cancer

18. Proto-oncogenes Proto-oncogenes are normal genes that, when mutated, form oncogenes or genes that cause a cell to be cancerous Example: mutation to Cdk gene Cdk is a protein that is involved with cell cycle regulation A mutation can activate this protein before it should Pushes cell cycle past a checkpoint before it’s ready Once a proto-oncogene is altered in a way that increases the rate of the cell cycle it becomes an oncogene

19. Tumor Suppressor genes Some genes, when activated, prevent a cell from undergoing uncontrolled cell division (e.g. p53) Damage to these genes can cause cancer

20. Prokaryotes divide by binary fission

21. Mitosis and binary fission result in identical daughter cells How come we don’t look exactly like our parents? Meiosis! Sex cells (gametes) are haploid 1 chromosome instead of pairs These single chromosomes combine during fertilization to create a diploid zygote

22. Meiosis is how haploid cells are formed Similar to mitosis, but does have distinct differences ONLY OCCURS IN SEX CELLS or GAMETES Occurs after interphase similar to mitosis DNA duplicated into sister chromatids There are two rounds of Meiosis Meiosis I: consists of prophase I, prometaphase I, and so on Meiosis II: consists of prophase II, prometaphase II, and so on

23. Meiosis I: Prophase 1 First step in Meiosis Nuclear envelop broken down and homologous pairs brought really close together Crossing over occurs This is when chromosome segments from non-sister chromatids are exchanged resulting in chromatids that are a mix of maternal and paternal chromosomes

24. Crossing over during Prophase 1

25. The next steps in Meiosis I The rest of the steps in Meiosis I occur in a similar way as mitosis Still have sister chromatids in each daughter cell after Meiosis I Two copies of each chromosome in both cells but now are genetically distinct

26. Meiosis II DNA is not duplicated between Meiosis I and Meiosis II At the end of Meiosis II you have four cells with 1 chromosome copy in each cell

27. During Fertilization the Haploid cells combine into one zygote and an animal is formed from this one cell using mitosis

28. Crossing over during Prophase 1

29. Karyotype Contains number and appearance of chromosomes including length, banding patterns, and centromere position Karyogram : visualization of all of an organisms chromosomes in a chart Karyogram of female human immune cell during mitosis. X-inactivation of one X chromosome in females occurs after a female embryo is just a few thousand cells - Tightly condense one X chromosome -How females compensate for the “double genetic dose of X” Random whether it’s the maternal or paternal X chromosome in each cell

30. Females have two X chromosomes for chromosome 23 Males have an X and a Y chromosome for chromosome 23 Can you see the difference? Looking at a karyogram is a way to identify genetic abnormalities

31. Nondisjunction Improper separation of chromosomes during meiosis Can occur in Miosis 1 or 2

32. Diseases from Nondisjunction Down Syndrome 3 copies of chromosome 21 Turner syndrome Only 1 X chromosome in Females

33. Genetic mutations occur constantly over an individual’s lifetime and the older you are, the more likely one will occur in an important gene region. Figure 7.9: the incidence of having a fetus with trisomy 21 increases dramatically with maternal age Affects 1 out of every 700 babies in USA (CDC)

34. Translocation A piece of one chromosome breaks off and attaches to another chromosome or a different part of the same chromosome Found to cause certain cancers, including chromic myelogenous leukemia