DNA replication

Each new cell is genetically identical to the parent nucleus Parent cell Chromosomes Have been replicated Daughter Cells Each cell has the same genetic makeup as the parent cell Before the cell can divide, the genetic information (DNA) must be replicated so each daughter cell has the original copy.

Deoxyribonucleic Acid

STUCTURE OF DNA Sugar= Deoxyribose Nitrogen Bases = Adenine Thymine Cytosine Guanine Bonds that occur between the bases hold the DNA together. Each nucleotide has a sugar, phosphate and a nitrogen base.

Guanine always pairs with Cytosine Adenine always pairs with Thymine These are called complementary pairs

When the cell prepares to divide, DNA forms into Chromosomes. RoundRod

Organized into 23 pairs. The 23 rd pair determines sex. XX= female; XY = male

An enzyme breaks apart the nitrogen based complimentary pairs Another enzyme brings in new nitrogen bases to pair with the separated strand. Result = Two New DNA strands DNA Lab activity

Cell Division Once the DNA has been replicated, the cell continues to divide.

The cell simply divides into 2.

Step Three: A cell wall forms near the center and the cell pinches into two= CYTOKINESIS Step Two: The chromosomes separate to opposite ends of the cell= called chromosome segregation Step One: DNA gets copied (2 chromosomes)

Like prokaryotic division there are three steps Interphase: DNA replicates Mitotic phase: Nucleus divides Cytokinesis: Cytoplasm splits and cell divides

1.Rapid Growth and doing the cell’s function Makes proteins needed for DNA replication Copies some organelles Most of the life of the cell is in interphase 2. Synthesis Phase DNA is copied and DNA replicates Two copies called sister chromatids attach at a center pointed called the centromere. 3. Growth Phase 2 The cell gets ready to divide Makes proteins Copies the rest of the organelles

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Cell Cycle The longest phase in the cell cycle is interphase. The 3 stages of interphase are called G 1, S, and G 2.

The nucleus must divide, which includes the separation of the chromosomes. This process is called mitosis and it has 4 phases.

This is the division of the rest of the cell. Cytoplasm divides You get 2 daughter cells

Cell Division All living cells come from other living cells. During mitosis, the nucleus of the cell divides, forming two nuclei with identical genetic information. Can you name the stages? Prophase Cytokinesis Anaphase Metaphase Telophase

Mitosis Mitosis produces two genetically identical cells. Mitosis is referred to in the following stages: prophase, metaphase, anaphase, and telophase.

Prophase In prophase, the cell begins the process of division. The chromosomes condense.

chromatin duplicated chromosome

Prophase Nuclear envelope disappears.

Prophase Aster Sister chromatids Centromere Centriole Spindle fibers Centrioles migrate to opposite poles of the cell. Asters and spindle fibers form.

Metaphase The chromosomes line up at the equator of the cell (metaphase plate), with the centrioles at opposite ends and the spindle fibers attached to the centromeres. Centriole Spindle fibers Metaphase plate

Anaphase In anaphase, the centromeres divide. At this point, each chromosome goes from having 2 sister chromatids to being 2 separate chromosomes

Anaphase The spindle fibers contract and the chromosomes are pulled to opposite poles.

Telophase In telophase the nucleus actually divides. The chromosomes are at the poles of the cell. The nuclear envelope re- forms around the two sets of chromosomes.

Cytokinesis The division of the cytoplasm. In animal cells, a Cleavage Furrow forms and separates Daughter Cells Cleavage furrow in a dividing frog cell.

Cytokinesis In plant cells, a Cell Plate forms and separates Daughter Cells. Cell Plate forming

ANIMAL CELL – Centriole and aster present – Daughter cells separated by cleavage furrow PLANT CELL – No visible centriole or aster – Daughter cells separated by cell plate

Mitosis: Can you name the stages? Prophase Metaphase Anaphase Telophase Cytokinesis _share/vis_sim/chm05_pg71_celldiv/chm05_p g71_celldiv.htmlhttps:// _share/vis_sim/chm05_pg71_celldiv/chm05_p g71_celldiv.html Matching

 Phases of cell cycle- IPMATC Interphase Cytokinesis I mportant P eople M ust A nalyze T asks C orrectly

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Reproduction is how organisms produce offspring. The ability to reproduce is a characteristic of all living things. In some species, all the offspring are genetically identical to the parent. In other species, each offspring is genetically unique. There are two types of reproduction: Sexual & asexual. Look at the kittens in Figure They are brothers and sisters, but they are all different from each other. Why does this happen in some species but not others?

Asexual reproduction is simpler than sexual reproduction. It involves just one parent. The offspring are genetically identical to each other and to the parent. All prokaryotes and some eukaryotes reproduce this way. There are several different methods of asexual reproduction. They include binary fission, fragmentation, and budding.

Binary fission occurs when a parent cell simply splits into two daughter cells. This method was described in our last chapter on ’Cell Division.’ Bacteria reproduce this way.

Fragmentation occurs when a piece breaks off from a parent organism. Then the piece develops into a new organism. Sea stars, like the one in Figure 2.12, can reproduce this way. In fact, a new sea star can form from a single “arm.” Planarian Fragmentation

Q18 Budding occurs when a parent cell forms a bubble-like bud. The bud stays attached to the parent while it grows and develops. It breaks away from the parent only after it is fully formed. Hydra budding Yeast Budding

Review of the 3 forms of asexual reproduction!

Sexual reproduction is more complicated. It involves two parents. Special cells called gametes are produced by the parents. In humans, a gamete produced by a female parent is called an egg, while a gamete produced by a male parent is called a sperm. An offspring forms when two gametes unite. The union of the two gametes is called fertilization.

You can see a human sperm and egg uniting in Figure 2.14.

In species with sexual reproduction, each cell of the body has two copies of each chromosome. For example, human beings have 23 different chromosomes. Each body cell contains two of each chromosome, for a total of 46 chromosomes.

The number of different types of chromosomes is called the haploid number. In humans, the haploid number is 23. The number of chromosomes in normal body cells is called the diploid number. The diploid number is twice the haploid number. In humans, the diploid number is two times 23, or 46.

The two members of a given pair of chromosomes are called homologous chromosomes. We get one of each homologous pair, or 23 chromosomes, from our father. We get the other one of each pair, or 23 chromosomes, from our mother. A gamete must have the haploid number of chromosomes. That way, when two gametes unite, the zygote will have the diploid number. How are haploid cells produced?

The answer is meiosis. Meiosis is a special type of cell division. It produces haploid daughter cells. It occurs when an organism makes gametes.

Cells prepare for meiosis begin by replicating their DNA. Next they go through two divisions, meiosis I and meiosis II. This results in four haploid daughter cells. Meiosis I and meiosis II each have four phases: prophase, metaphase, anaphase, and telophase. The phases of meiosis are similar to mitosis, but there are important differences that allow for the cell to divide evenly with the appropriate DNA content. Following meiosis the four daughter cells continue to develop before they become gametes. – For example, in males, the cells must develop tails, among other changes, in order to become sperm.

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1.What is meiosis? 2.What is diploid? How many chromosomes are in a diploid human cell? 3.What is a zygote? How does the zygote form the organism? 4.What is the result of crossing-over? 5.How many cell divisions occur during meiosis? 6.Why are you genetically distinct? Review 1.Define meiosis. 2.What is the difference between a haploid cell and a diploid cell? 3.Describe the steps of Meiosis I and Meiosis II. 4.Describe crossing-over. When does crossing-over occur? 5.What is the outcome of meiosis? minutes

Advantage of Asexual Reproduction Asexual reproduction can happen very quickly. It doesn’t require two parents to meet and mate. Under ideal conditions, 100 bacteria can divide to produce millions of bacteria in just a few hours! Most bacteria don’t live under ideal conditions. Even so, rapid reproduction may allow asexual organisms to be very successful. They may crowd out other species that reproduce more slowly.

Sexual reproduction results in offspring that are all genetically different. This can be a big plus for a species. The variation may help it adapt to changes in the environment. It happens in three ways: crossing over independent assortment union of gametes occurs randomly.

crossing over Crossing over occurs during prophase of meiosis I. The paired chromosomes exchange bits of DNA. This recombines their genetic material.

Independent assortment Independent assortment occurs during metaphase of meiosis I. Chromosomes line up randomly and which ones end up together at each pole is a matter of chance.

Random union of gametes In sexual reproduction, two gametes unite to produce an offspring. Which two gametes is a matter of chance. The union of gametes occurs randomly. Due to these sources of variation, each human couple has the potential to produce more than 64 trillion unique offspring. No wonder we are all different!

Lesson Review Questions Recall 1. What are three methods of asexual reproduction? For each method, give an example of an organism that can reproduce that way. 2. Briefly describe sexual reproduction. 3. Define haploid and diploid numbers. Which cells are haploid and which are diploid? Apply Concepts 4. If you don’t have an identical twin, how likely is it that a brother or sister would be just like you? Think Critically 5. A single-celled organism belongs to the Eukarya Domain. Apply lesson concepts to describe how the organism divides.” 6. Some organisms can reproduce sexually or asexually. Under what conditions might each type of reproduction be an advantage?