The Cell Cycle Biology

Standards you are responsible for mastering. SB1a: Explain the role of cell organelles for both prokaryotic and eukaryotic cells, including the cell membrane, in maintaining homeostasis and cell reproduction. SB2b: Explain the role of DNA in storing and transmitting cellular information.

The next two slides aren’t for the notes…just pay attention. A Question for you… Cells need to be small. That’s a fact. But, WHY do they need to be small? Why is it better to have many small cells than just a couple of big cells?

Ok, good. So, how do organisms get more cells and prevent cells from getting too large?? Cell Division.

Two main reasons why cells divide: 1.) To prevent DNA overload  if the cell grows too big, there will be an information crisis. 2.) Bigger is not better if the cell grows too large, it would take too long for nutrients and wastes to travel through the cell.

Cell Division A.) the cell divides forming 2 daughter cells before growing too big. B.) solves the problems of: 1.) Information crisis 2.) Increasing size

Cell Division A.) Chromosomes: 1.) pass on genetic information 2.) made of DNA and proteins 3.) every organism has a specific number of chromosomes. (Humans = 46) 4.) are only visible during cell division 5.) are replicated BEFORE cell division a.) chromatids  2 identical “sister” parts of a duplicated chromosome. 1.) are attached at the centromere

Chromosome

Chromosome

The Cell Cycle 1.) The cell cycle is a series of events that the cell goes through as it grows and divides. 2.) During the cell cycle, the cell grows, prepares for division, and divides to form two daughter cells.

The 2 phases of the cell cycle A.) Interphase B.) Cell Division  Mitosis & cytokinesis

Interphase - NOT A PART OF MITOSIS; NOT CELL DIVISION! 1.) contains the G-1, S, and G-2 phases. 2.) G-1 phase  the cells grow in size and make new molecules and organelles. 3.) S phase  chromosomes are replicated 4.) G-2 phase  shortest phase, molecules & organelles needed for cell division are made.

Cell Cycle

Interphase

Interphase

Mitosis 1.) part of the cell cycle when the chromosomes separate from each other and the cell splits in half. 2.) This is how somatic cells reproduce. Somatic cells are normal body cells (i.e., not sperm and egg) 3.) Mitosis has 4 phases: Prophase - Nucleus breaks down, chromosomes become thick (visible) and pair up. Metaphase - Chromosomes line up in the middle of the cell Anaphase - Chromosomes move to the opposite ends of the cell Telophase - Chromosomes unwind (become invisible) and nucleus reforms.

Prophase – more info… 1.) The chromatin condenses to form chromosomes (DNA is visible) 2.) Centrioles separate and the spindle fiber forms. A.) spindle fiber  helps to separate the chromosomes. 3.) The nuclear envelope breaks down

Prophase

Prophase

Prophase

Prophase – Draw This in the Box…

Metaphase …more info 1.) Chromosomes line up at the equator of the cell. 2.) Each chromosome is connected to a spindle fiber at its centromere.

Metaphase

Metaphase

Metaphase

Metaphase – Draw this in the box

Anaphase …more info 1.) The sister chromatids separate into individual chromosomes and are moved to the opposite ends of the cell.

Anaphase

Anaphase

Anaphase

Anaphase – Draw this in the box…

Telophase…more info 1.) Chromosomes gather at opposite ends of the cell. 2.) chromosomes lose their shape 3.) Two new nuclear envelopes form.

Telophase

Telophase

Telophase

Telophase – Draw this in the box…

Cytokinesis - Starts during Telophase 1.) Cytoplasm divides separating the two identical nuclei. 2.) in animals  the cell membrane is pulled inward until the cytoplasm is pinched into 2 almost equal parts. 3.) in plants  a cell plate forms half way between the two new nuclei.

Animal Cell Cytokinesis Cleavage furrow Contractile ring of microfilaments Daughter cells 100 µm (a) Cleavage of an animal cell (SEM) Figure 12.9 A

Plant cell cytokinesis Daughter cells 1 µm Vesicles forming cell plate Wall of patent cell Cell plate New cell wall (b) Cell plate formation in a plant cell (SEM) Figure 12.9 B

End result of Mitosis 2 genetically identical daughter cells.

Review Questions

Review 1 During which part of interphase is the DNA copied? A.) G1 B.) S C.) G2 D.) Mitosis

Review 2 Which stage in a cell’s life cycle is the longest? A.) mitosis B.) metaphase C.) interphase D.) cytokinesis

3 Which of the following is the correct name of DNA when it is uncoiled (not in a chromosome form)? A.) Chromatid B.) Chromatin C.) Chromosome D.) Spindle Fiber

4 If a cell has 32 chromosomes in G1 of interphase, how many chromosomes will each daughter cell have after mitosis & cytokinesis? A.) 16 B.) 32 C.) 64 D.) 128

5 During which stage of mitosis do the chromosomes line up at the equator of the cell? A.) prophase B.) metaphase C.) anaphase D.) telophase

6 Each side of a copied chromosome is called: A.) a chromosome B.) a sister chromatid C.) chromatin D.) centromere

7 The part of a copied chromosome where the two sides are linked together is called the: A.) centriole B.) centromere C.) chromatid D.) spindle fiber

8 During which stage of mitosis do the sister chromatids separate? A.) prophase B.) metaphase C.) anaphase D.) telophase

9 Division of the nucleus is called: A.) interphase B.) cell cycle C.) mitosis D.) cytokinesis

10 Division of the cytoplasm is called: A.) interphase B.) cell cycle C.) mitosis D.) cytokinesis

11 What organelle has the job of pulling on the spindle fibers to separate the chromatids? A.) DNA B.) ribosome C.) centromere D.) centriole