Cytoplasmic Division Mechanisms Cytoplasmic division is not a part of mitosis Differs in plant and animal cells

How Do Animal Cells Divide? Cytoplasmic division in animals: ____________ Cytokinesis occurs by means of a ____________ ____________, a thin indentation in the plasma membrane halfway between the poles at the equator The flexible plasma membrane of animal cells can be squeezed in the middle to separate the two daughter cells

How Do Animal Cells Divide? Parallel arrays of microfilaments slide past one another at the cleavage furrow This ring of actin microfilaments is called the ____________ _________ This pulls the plasma membrane inward, until the cytoplasm is partitioned Each daughter cell ends up with:

_____________: Animal Cells Figure 8.8, pg 132

Figure 8.8a, pg 132

Each daughter cell ends up with: a nucleus cytoplasm (with organelles) a plasma membrane

How Do Plant Cells Divide? The cytoplasm of plant cells cannot just be pinched in two because of the rigid cell wall A band of microtubules and microfilaments forms around the nucleus before mitosis starts and marks where the cell plate will form Vesicles containing remnants of the microtubular spindle form a disk-like structure called a ______ __________between the two new cells The cell plate becomes a cross-wall that partitions the cytoplasm

How Do Plant Cells Divide? Figure 8.8b, pg 132

Results of Cell Division: a Human Embryo

Precise mechanisms assure that cells will be produced in the right numbers at the right times and places Failure to do this can result in genetic disorders and cancer

The Cell Cycle The cell cycle has built-in checkpoints where proteins can advance, delay, or block forward progress of the cycle The proteins are the products of checkpoint genes For example: ______________ regulates ph0sphorylation; can signal the end of DNA replication ________ __________ activate genes that simulate cells to grow and divide; signal the start of mitosis

When Control is Lost When checkpoint mechanisms fail, a cell loses control over its replication cycle In some cases, mitosis repeats over and over In others, the cells do not die as they are supposed to Other times, damaged DNA is replicated

When Control is Lost Mutant checkpoint genes can cause _________ by disrupting normal controls as the protein cannot function properly A tumor is an abnormal mass formed by continually dividing descendents of the cell containing the mutation Figure 8.11, pg 134

Checkpoint Failure and Tumors Proto-oncogenes code for proteins that stimulate mitosis Tumor suppressors inhibit mitosis _________________ are abnormal masses of cells that have lost control over their growth and cell divisions ___________ ___________ pose no threat to the body

_____________ All cancers are abnormally growing and dividing cells of a ___________ neoplasm They physically and metabolically disrupt the surrounding tissues All cancer cells display three characteristics

Characteristics of Cancer 1. They grow and divide abnormally Lack the controls that keep cells from getting overcrowded; cell populations reach extremely high densities 2. Both the cytoskeleton and the plasma membrane of cancer cells become altered Membrane is leaky and can be missing proteins Cytoskeleton shrinks and/or becomes disorganized 3. Cells have a weakened capacity for adhesion They can break away to move to other sites in the body

Characteristics of Cancer Cancerous cells that break off a tumor can move to other parts of the body and establish a growing colony Metastasis: the process of abnormal cell migration and tissue invasion Allows cancer to spread through the body

Neoplasms: Benign and Malignant Figure 8.12, pg 135

Benign TumorMalignant Tumor Figure 8.12, pg 135

3 Cancer cells creep or tumble along inside blood vessels, then leave the bloodstream the same way they got in. They start new tumors in new tissues. 1 Cancer cells break away from their home tissue. 2 The metastasizing cells become attached to the wall of a blood vessel or lymph vessel. They release digestive enzymes onto it. Then they cross the wall at the breach. Figure 8.12, pg 135

Chapter 8 Homework Self Quiz 1-10 Explain numbers 1 and 9 Critical Thinking #1 and #3