Cell Division
Ability to grow and self-replicate are the distinctive features of
living things
Aspects of Cell Division
1. Synthesize & divide cell contents 2. Replicate and
precisely partition the genome - all the genetic information
Cell Division in bacteria: Binary Fission
Cytokinesis
Division of the cytoplasm
Actin
Contractile ring of Micro-filaments
Aspects of cytokinesis
Synthesize more of everything in the cytoplasm
No precise distribution of the contents
Each daughter cell gets plenty
chromosomes
Each is a single DNA molecule + many proteins
Daughter cells genomes = ?
Original cell genome
How to divide the nucleus?
Can't physically partition the nucleus like the cytoplasm
Sister chromatids
Replication products of a DNA molecule
Daughter cells
same chromosomes content as starting cell
Replicated chromosome has ?
2 sister chromatids
Metaphase
1. Chromosomes aligh at equator
2. Spindle connects to them to opposite centrosomes
Interphase
1. Chromosomes replicating
2. Start to condense
3. Centrosomes replicate
Prophase
1. Sister Chromatids form
2. Mitotic Spindle (MT's) from centrosome
Prometaphase
1. Envelope breaks down
2. MT's attach to chromosomes at kinetochore
3. Centrosomes move to opposite sides
Anaphase
1. Sister chromatids seperate
2. Pulled by MT's to opposite sides
Telophase
1. Chromosomes decondense
2. Spindle breaks down
3. 2 envelopes form
Purpose of cell division
Reproduce asexually
Increase surface/volume ratio
Build a multicellular body
Respond to environment
Repair/replace tissues
Basics of cell division
1. Check your environment/development status
2. Grow in size
3. Replicate everything - DNA and cell contents
4. Distribute everything and partition the cell
Interphase = ?
G1 + S + G2
G1
Size
Nutrition
Development
S-Phase
DNA synthesis chromosomes duplicate
G2
Prep for division
Replicated chromosomes = 2 identical chromatids
IPPMAT
Interphase
Prophase
Pro Metaphase
Metaphase
Anaphase
Telosphase
Red Queen Hypothesis
Organisms must constantly adapt and evolve to survive against
competing species or one would go extinct
Sexual Reproduction: offspring genome differ from parents
Diploid Cell
2 sets of chromosomes
Called: Homologs or homologous pair
Characteristic chromosome number, n
n = number of unique chromosomes that make up the "chromosome set
Ploidy
number of chromosome sets; 1n, 2n, 3n
What are X thing called
Sister chromatids
Relationship between X and X
Homologous chromosomes
Relationship between X and x
Non-Homologous chromosomes
Meiosis 1: Seperate Homologous Chromosomes
Homologs
Crossing over
Non-sister chromatid exchange
Chiasmata
Homologs are not joined all along length, but are held together at
the cross-over points
Meiosis I What happens to 1 Diploid
1 diploid->2 haploid
homologs go to opposite poles
sister chromatids stay together
Meiosis II what happens to 2 haploid
Meiosis II: 2 haploid-> 4 haploid
sister chromatids to opposite poles