9/18/2013 6:40:00 PM
Lecture 7: Inheritance of Sameness
Independent Study Outcomes
The overall Outcome for this material is for you to identify the various
mechanisms by with cells ensure the "inheritance of sameness". That is,
how do cells ensure that their genomes are inherited intact and unchanged
by their daughter cells. Make a list of all the factors that help cells pass on
More specifically, in multiple choice format, identify the . . .
1. stages and main characteristics of the stages of mitosis.
2. stage of cell division, given a micrograph of a dividing cell.
3. role and mechanism of the mitotic spindle.
4. role of cell cycle check points.
5. changes in amount of DNA throughout the cell cycle.
In multiple choice questions, identify the
mechanisms that ensure "inheritance of sameness" (how cells ensure
that daughter cells get same genome with limited amount of errors)
- Complementary base pairing
-cell cycle checkpoints
location of actively cycling cells in multi-cellular animals/plants
-Skin, gametes (seasonal) in gonads, any cell that can regenerate
themselves i.e. stem cells, inside gut lining, hematopoeitic sys. (replenishing
blood supply), WOUND REPAIR
-feathers/hair/nails not really b/c made of cells- they are products of cells Tree: Tips of roots, epidermis, meristem (not stem cells, but mitotically
active tissue in plants), shoot/root tips, around bark, anything that’s
growing, wound repair
function of rapid cycling cells at various stages of the life cycle
- protection, wound repair, get energy/nutrients/water (in plants’
examples of situations in which cells would be programmed to die by
Maybe they’re just old, so they should die before they turn into a tumour
cell, as part of a developmental program, some cells in immune system so
you won’t get a surplus, skin cells die also b/c of developmental program,
cell walls i.e. xylem b/c functions as skeleton in plants
main features of each stage of mitosis with respect to cytoskeleton
G1 of interphase: Chromosomes are unreplicated and extend throughout the
G2 of interphase: After replication during the S phase of interphase, each
chromosome is double at all points of two sister chromatids. The centrioles
within the centrosome have also doubled into pairs.
Prophase: During prophase, the greatly extended chromosomes that were
replicated during interphase begin to CONDENSE into compact, rod-like
structures. Each diploid human cell contains 2n of DNA distributed among 23
pairs of chromosomes. Condensation during prophase packs these long DNA
molecules into units small enough to be divided successfully during mitosis.
As they condense, the chromosomes appear as thin threads under the light
microscope. While condensation is in progress, the nucleolus becomes
smaller and eventually disappears in most species. The disappearance
reflects a SHUTDOWN of all types of RNA synthesis, including the
ribosomal RNA made in the nucleolus. In the cytoplasm, mitotic spindle
begins to form between the two centrosomes as they start migrating toward the opposite ends of the cell to form the spindle poles. The spindle develops
as bundles of microtubules that radiate from the spindle poles.
Prometaphase: Bundles of microtubues grow from centrosomes at the
opposing spindle poles toward the centre of the cell. Some of the developing
spindle enters the former nuclear area and attaches the chromosomes.
Metaphase: Spindle reaches its final form and the spindle microtubules move
the chromosomes into alignment at the spindle midpoint (aka metaphase
plate). The chromosomes complete their condensation in this stage and
assume their characteristics shape as determined by the location of the
centromere and the length and thickness of the chromatid arms.
Anaphase: Sister chromatids separate and move to opposite spindle poles.
The first signs of chromosome movement can be seen at the centromeres as
the kinetochores are the first sections to move toward opposite poles. The
movement continues until the separated c