Lecture 7: Cell Cycles Flashcards
How did you get to where you are
1) growth
2) divison
DNA in prokaryotes
- DNA as hereditary information
- Vast majority have singular circular DNA (bacterial chromosome)
the rate at which prokaryotic cells divide
maximum rate where DNA replication occupies most of period between cytoplasmic divisions
when replication is complete
cytoplasm divides
the bacterial cell cycle (3 periods)
1) growth of cells and initiation of DNA replication at origin of replication site (ORI)
2) DNA replication
3) Cell divides by binary fission
What is the origin of replication site
ORI (nucleotide site where replication originally starts)
- in the middle of the cell where enzymes for DNA replication are located
- Ori is at the middle because the enzymes are at the middle
Binary fission
division of cytoplasm to divide cells and chromosomes, where each cell gets 1 chromosome (for prokaryotes)
Step 1 of bacterial replication
INITIATION OF REPLICATION
- replication of bacterial chromosome begins at ORI
Step 2 of bacterial replication
DNA REPLICATION
- once the original duplicates, 2 ori’s will migrate towards the two ends of the cell as the rest of the chromosome is replicated
- active movement distributes two replicated chromosomes to two ends of cell (on opposite ends)
Cell Cycle
a period of growth followed by nuclear division and cytokinesis
- eukaryotes: mitosis and meiosis
Eukaryotic Cell Cycle
- multicellular eukaryotic organisms require strict control of cell division (out of ctrl growth can lead to tumors/cancer)
- ultimately results in a mature body composed of different subpopulations of cells (i.e. WBC, rbc, skin cells that are formed through mitosis are the same genetically but are specialized, so they have different functions)
Step 3 of Bacterial replication
CYTOPLASMIC DIVISION
- inward growth of plasma membrane leads to pinching to eventually produce 2 daughter cells
- new cell wall material assembled
- cut cell into 2 parts (binary fission)
Cell Division
Mitosis: divides replicated DNA equally and precisely
- genetically similar to original cell (CLONE)
Meiosis: daughter cells with 1/2 the number of chromosomes
- genetically different from original cell
Clone
- genetically similar to original cell
essentially produces through mitosis, but the specialization makes the cells different but they are genetic clones
Difference between mitosis and meiosis
1) MITOSIS
- 2 new daughter cells
- clones
2) MEIOSIS
- 4 daughter cells
- 1/2 the number of chromosomes from parents: good because it makes them different genetically allowing for variation
DNA of eukaryotic cells
- divided among individual, linear chromosomes
- located in cell nucleus
what are chromosomes
nuclear units of genetic information that are divided and distributed
what is Ploidy
number of chromosome sets (cell or species)
- diploid (2n)
- haploid (n)
Diploid
humans: in majority of cells we will have 2 sets of chromosomes (46 chromosomes)
Haploid
specific algae, specific protists, prokaryotes will have haploids
Sister chromatids
- Replication of DNA of each individual chromosome forms sister chromatids (2 identical molecules)
- Attached pair of duplicated chromosomes, at this point they’re only considered 1 chromosomes (they’re formed before forming new cells, its just the product of multiplying chromosomes)
Polyploidy
multiple chromosome sets
- triploid and tetraploid are also possible, plant species
Non homologous
Chromosome with different genes
- chromosome 4 and 19 for example are non-homologs
Homologs chromosomes
chromosomes have same genes arranged in same order
Ex. the pair within a set
For ex: We have diploids: such as 2 chromosome 11’s those are homologs, they are the same gene arranged in the same order
sister chromatids are 2 ____ molecules
2 identical molecules
Sister chromatids eventually become
independent daughter cells
Mitotic cell cycle
-2 major phases: interphase (period of growth) and mitosis (period of division)
MITOSIS HAS 5 PHASES
1) prophase
2) prometaphase
3) metaphase
4) anaphase
5) telophase
Chromosome segregation
Separation of sister chromatids and equal distribution to each of 2 cells resulting from cell division
G1
*period of growth before DNA replicates
- majority of growth occurs here
- spend most of their time here: amount of time depends on the
the time spent in G1 depends on
- signals the cell gets
- environment of the cell
- type of cell
G0
- cell cycle arrest
- cell exit cycle:
- no longer participate in cell cycle
what’s an example of a cell that would exit G0
nerve cells
- therefore, its difficult to replace nerve tissue because its hard to replace them since they exit therefore neurodegenerative diseases are hard to treat
Interphase
G1,G2,S (majority of cycle)
G2
- period after DNA replicates
cell prepares for division
SHORT
Mitosis
- cytoplasm divides independent of mitosis beginning but occurs at end of mitosis
where does interphase end
parent cell
Timing for cell cycle
G1: Variable Time
S: 10-12 H
G2: 4-6 H
Mitosis: 1-4 H
Phase 1: Interphase
- G1 PHASE
New cells goes straight here
- Daughter cell from previous
division cycle enters initial period of cytoplasmic growth (building new macromolecules, organelles, etc)
- No DNA replication
GOES TO S commitment
Phase 1: Interphase
- S PHASE
- DNA replication (building new DNA, each chromosome replicates)
- Chromosomes duplicate (stay together at sister chromatids)
Phase 1: Interphase
- G2 PHASE
- synthesize RNA and protein
- NO DNA replication
- Get ready for cell division
building more RNA and DNA to prep for cell