The Cell Cycle & MitosisChapter 5

5.1 – The Cell Cycle• Key Concept:• Cells have distinct phases of growth, reproduction, and normal

functions.

When a living thing grows, what happens to its cells?•Does an animal get larger because

each cell increases in size or because it produces more of them?•What are some things that all cells in

your body must have?

The cell cycle has 4 main stages.• The cell cycle is a regular pattern of growth, DNA replication, and

cell division.

The main stages of the cell cycle are: Gap 1, Synthesis, Gap 2, & Mitosis.

• Gap 1 (G1): cell growth and normal functions, copy organelles (most cells spend most of their time here)• Only proceed to S if the cell has enough nutrition, adequate size,

undamaged DNA

• Synthesis (S): copies DNA

• Gap 2 (G2): additional growth

• Mitosis (M): includes division of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis)• Mitosis occurs only if the cell is large enough and the DNA

undamaged.

Cells divide at different rates.• The rate of cell division varies with the need for that type

of cell.

• Some cells are unlikely to divide• Example: neurons – stay in G0

Cell size is limited.• Cell volume increases faster than surface area.• Cells need to stay small to allow diffusion and osmosis to work

efficiently.

• Surface area must allow for adequate exchange of materials.• Cells that must be large have unique shapes (i.e. neurons)

5.2 – Mitosis & Cytokinesis• Key Concept:• Cells divide during mitosis and cytokinesis into two new daughter cells.

Chromosomes condense at the start of mitosis.• Chromosomes: carry genetic information (DNA) that is passed from

one generation of cells to the next. • DNA wraps around proteins (histones) that condense it.

• Chromatin: DNA plus proteins (histones) is called chromatin.

• Chromatid: Each duplicated chromosome is composed of two chromatids

• Centromere: Sister chromatids are held together at the centromere.

• Telomeres: protect DNA and do not include genes (like the caps on shoelaces)

Mitosis and cytokinesis produce two genetically identical daughter cells.

• Interphase prepares the cell to divide.

• DNA is duplicated.• Includes G1, S, G2

Mitosis divides the cell’s nucleus in four phases - PMAT

• Prophase – first & longest• Chromosomes condense, spindle fibers

form, and the nuclear membrane disappears.

Mitosis divides the cell’s nucleus in four phases.

•Metaphase•Chromosomes line up across the middle of the cell.

Mitosis divides the cell’s nucleus in four phases.

•Anaphase•Sister chromatids are pulled apart to opposite sides of the cell.

Mitosis divides the cell’s nucleus in four phases.

• Telophase• Two nuclei form at opposite ends of the cell,

the nuclear membranes reform, and the chromosomes uncoil back into chromatin

Cytokinesis differs in animal and plant cells.• Cytokinesis is when the cytoplasm

separates

• Animal cells: membrane pinches the two new cells apart

• Plant cells: a cell plate (new cell wall) separates the two new cells

Mitosis in a Plant Cell

http://schoolworkhelper.net/wp-content/uploads/2011/02/onion-mitosis-3-lab.jpg

• http://www.youtube.com/watch?v=VlN7K1-9QB0

• http://www.youtube.com/watch?v=Wy3N5NCZBHQ

5.3 – Regulation of the Cell Cycle

• Key Concept:• Cell cycle regulation is necessary for healthy growth.

Internal and external factors work together to regulate cell division.

External Factors: come from outside cell

• Include physical and chemical signals• Cell to cell contact: when one

cell touches another they stop growing.

• Growth factors: chemical signals released by the cell to tell other cells to grow.

• Trigger internal factors, which affect the cell cycle

Internal Factors: come from inside cell

• Kinases: Enzymes in cells• Cyclins: Proteins in cells• Help to advance a cell to

different parts of the cell cycle• May be triggered by external

factors

What happens when the cell cycle isn’t regulated properly?

Cell division is uncontrolled in cancer.• Cancer cells form disorganized clumps called tumors.• Benign tumors remain clustered and can be removed.• Malignant tumors metastasize, or break away, and can form more

tumors.

Apoptosis is programmed cell death.• Apoptosis is the process of programmed cell death.• Normal feature in healthy organisms• Caused by a cell’s production of self-destructive enzymes• Example of apoptosis in healthy organisms: Occurs during fetal

development(responsible for

separation of fingers and toes)

• Cancer cells do not carry out normal cell functions (this is part of why they’re so bad!)

• Cancer cells come from normal cells with damage to genes involved in cell-cycle regulation.

• Carcinogens are substances known to cause cancer (they damage those genes)• Chemicals, tobacco smoke, X-rays, UV rays, HPV

• Cancer can also be caused by genetics (i.e. BRCA1)• Standard cancer treatments typically kill both cancerous and

normal, healthy cells.

5.4 – Asexual Reproduction• Key Concept:• Many organisms reproduce by cell division.

Binary fission is similar to mitosis.• Asexual reproduction is the creation of

offspring from a single parent – leads to genetically identical offspring.• Binary fission produces two daughter cells

genetically identical to the parent cells.• Binary fission occurs in prokaryotes.

Environment determines which form of reproduction is most advantageous

• Asexual reproduction is an advantage in consistently favorable conditions.

• Sexual reproduction is an advantage in changing conditions.

Some eukaryotes reproduce by mitosis.

• Budding forms a new organism from a small projection growing on the surface of the parent.

• Fragmentation is the splitting of the parent into pieces that each grow into a new organism.

• Vegetative reproduction forms a new plant from the modification of a stem or underground structure on the parent plant.

5.5 – Multicellular Life• Key Concept:• Cells work together to carry out complex functions.

• Multicellular organization allows movement, digestion, internal circulation of nutrients, excretion of waste, and reproduction to be subdivided amongst specialized groups of cells.

Multicellular organisms depend on interactions among different cell types.

• Tissues are groups of cells that perform a similar function.• Organs are groups of tissues that perform a specific

or related function.• Organ systems are groups of organs that carry out

similar functions.

Specialized cells perform specific functions.

• Cells develop into their mature forms through the process of cell differentiation.

• Cells differ because different combinations of genes are expressed.• A cell’s location in an embryo helps determine how it will

differentiate.