The Cell Cycle & Mitosis Chapter 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 cytokinesisinto 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.
DNA plus proteins (histones) is called chromatin. • Each chromosome is composed of two chromatids • Sister chromatids are held together at the centromere. • Telomeresprotect 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.
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
5.3 – Regulation of the Cell Cycle • Key Concept: • Cell cycle regulation is necessary for healthy growth.
Internal and external factors regulate cell division. External Factors: come from outside cell Internal Factors: come from inside cell Kinases and cyclins Kinases: enzymes in cells Cyclins: proteins Both help to advance a cell to different parts of the cell cycle May be triggered by external factors • Include physical and chemical signals • Cell to cell contact: when one cell touches another, they stop growing • Growth factors: chemical signals released by cells that tell other cells to grow • Trigger internal factors, which affect the cell cycle
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 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.