Chapter 4, Section 3 CELL DIVISION

The Cell Cycle The regular sequence of growth and division that cells undergo. A new cell grows, prepares for division, and divides into two “daughter cells” Each daughter begins the cell cycle again

STAGE 1: INTERPHASE During this phase, the cell grows, makes a copy of its DNA, and prepares to divide into two cells The cell makes an exact copy of the DNA in its nucleus; this is called replication REMEMBER: DNA holds all the information that a cell needs to carry out its function The cell produces structures that it will use to divide into two new cells (centrioles)

Table Talk: In your own words, summarize what happens during interphase

STAGE 2: MITOSIS During this stage, the copy of the DNA is distributed to each of the daughter cells There are 4 phases to mitosis: Prophase Metaphase Anaphase Telophase Prophase first stage of mitosis the nuclear membrane disappears the nucleoli disappear a pair of centrioles moves to form each pole the replicated DNA begins to condense into chromosomes

Table Talk: In your own words, summarize what happens during prophase

STAGE 2: MITOSIS (continued) Metaphase the second stage of mitosis alignment of the chromosomes along the middle of the cell. Anaphase third stage of mitosis separation of the chromosomes movement of the replicated chromosomes toward opposite poles.

Table Talk: In your own words, summarize what happens during metaphase and anaphase

STAGE 2: MITOSIS (continued) Telophase the fourth (last) stage of mitosis the chromosomes stop their movement at the poles the nuclear membrane reforms Mitosis is complete with the formation of two nuclei, each with the same number and types of chromosomes

Table Talk: In your own words, summarize what happens during telophase

STAGE 3: CYTOKINESIS Cytokinesis and Daughter Cells division of the cytoplasm formation of the cleavage furrow the cell splits into two cells

STAGE 3: CYTOKINESIS In animal cells: the cell membrane squeezes together around the middle of the cell and pinches off two cells In plant cells: the cell wall is too rigid to pinch off two cells, so a cell plate forms across the middle of the cell Webcode cep-3023 For animation of cell division

Table Talk: In your own words, summarize what happens during cytokinesis

Structure of DNA A chromosome consists of DNA strands (deoxyribose nucleic acid) wound tightly around proteins The two sides of the “ladder” are made up of molecules of sugar, called deoxyribose, alternating with molecules called phosphates Each rung of the ladder is made up of a pair of nitrogen bases. The 4 nitrogen bases are: – Adenine (A) – Thymine (T) --- A & T only pair together – Guanine (G) – Cytosine (C) --- C & G only pair together

Replication of DNA Replication begins when the two side of the DNA molecule unwinds and separates Remember: This is during the Interphase Stage Next, nitrogen bases in the nucleus pair up with the bases on each half of the DNA molecule Because of the way the nitrogen bases pair up, the order of the DNA bases in the new molecule exactly matches that of the old: – Adenine pairs with thymine – Guanine pairs with cytosine – Click on this link for DNA fun facts! 2.discoveryeducation.com//downloaddirector/downloadFil e.aspx?thefile=v2.1\HeadRush%5FNitro\HeadRush_Nitro_ U_256k.wmv&realname=DNA_Length END See BrainPop “Mitosis” hn3sA0ip0http:// hn3sA0ip0 mitosis video