ch8 lesson 3 - more on cell division

cleavage furrow vs cell plate

animal cells:

• cleavage furrow - contracting ring of microfilaments, made up of actin/myosin

• separates sister cells into daughter cells

• occurs during cytokinesis

plant cells:

• cell plate - vesicle deliver cell wall component to the middle of the dividing cell (cellulose)

THREE factors that dividing cells must follow (ADG) all dogs good

physical Anchorage Dependence:

• cells must be attached to a surface for cell division to occur

• prevents cells from growing in the wrong places

• suspension cell culture - liquid, cells are floating around

• adherent cell culture - solid, cells can attach

• absence of density, detects surfaces that initiates “go”

physical Density-Dependent Inhibition:

• cells must stop dividing when crowded by other cells

• prevents cells from dividing more than they should

• detects other cells “stop signal”

chemical Growth Factors:

• cells must only divide when they receive chemical signal that tells them conditions are right to enter the cell cycle

• like domino effect, proteins pass on this signal

• “go” = move forward in cell cycle

cell cycle control system

• cell cycle control system - group of proteins in the cell

  • controls when each step of cell cycle starts and ensure order is correct

  • cell is NOT guaranteed to continue just because it enters cell cycle

• regulated by cell cycle checkpoints

  • mediated by proteins

  • determine if cell has met external and internal requirements

G1 checkpoint

• mainly receives messages about external environmental conditions

1) growth factors must be present

2) cells must be attached to surface

3) cells NOT touching other cells

4) nutrients available

G2 checkpoint

• mainly receives messages about internal environmental conditions

1) DNA must be fully replicated

2) DNA must be undamaged

3) cell must be large enough

M checkpoint

• messages about internal conditions relating to the mitotic spindle

1) mitotic spindle fully assembled

2) chromosomes fully attached to spindle fibers

3) chromosomes lined up on metaphase plate

cancer cells

• do NOT follow control systems in cells

• anchorage & density independent - form clump of overlapping cells

• divide without growth factors

• often form tumors

tumors

benign tumor -

• overgrowth of cells

• follows some rules

• non-invasive - stays in one place, doesn’t dig deep in tissue

• non-metastatic - doesn’t spread to other tissues

malignant tumor -

• aka cancer

• invades surrounding tissues

• can spread to other parts of the body

  • METASTASIS: part of the tumor breaks off and sends signals that dilate blood vessels → cancer cells can enter blood stream & lymph