BIOL 1010 Lecture Notes - Cytokinesis, Interphase, Chromatin

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25 Oct 2012
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The Cell Cycle
Lecture 23
Omnis cellula e cellula
- The cell cycle is an ordered set of events culminating in cell growth and division into two
daughter cells
1. The role of cell division- what is a need to divide?
2. The mitotic cell cycle- how to divide?
Chromosome duplication and distribution during mitosis
1. The role of cell division
- In reproduction
o Main difference between living organism and
nonliving matter
- In growth
o For multicellular organism (including cell renewal
and cell repair)
Important definitions
- Cell division is a finely controlled process that
results in the distribution of identical hereditary
material DNA- to two daughter cells
- A dividing cell:
o Precisely replicates its DNA
o Allocates the two copies of DNA to opposite ends of the cell
o Separates into two daughter cell contain identical hereditary information
- The DNA is distributed among 1 to more than 50 ling linear stretches called chromosomes
- The number of chromosomes is a characteristic of eukaryotes
o For example our somatic cells-all cells except reproductive- contain 46
chromosomes (2n). Our gametes- sex cells- have only 23 chromosomes (n)
- The total DNA of the chromosomes of an organism is referred to as its gamete
- Chromosome contains thousands of genes- units of DNA that contains the information to
specify synthesis of single polypeptide chain
- Characteristics of chromosomes:
o They are supercoils of DNA-proteins complex called chromatin. Each chromosomes
consists of:
o They exist in characteristic numbers (somatic 2n, gametes n)
o They exist in different states
Loosely folded during interphase
Highly folded during mitotic phase
o The DNA structure is maintained via association with different protein-formation of
DNA-protein complex- chromatin
o Before the cell can divide all DNA must be copied and then separated into daughter
o After copying- each duplicated chromosome consists of two sister chromatids-
identical copies of chromosomal DNA molecule
2. The mitotic cell cycle
- The cell cycle is composed of interphase (I) and mitotic (M)
- Interphase consists of several sub phases
- Mitotic phase consists of both mitosis and cytokinesis. The
former one is divided to five sub phases with special
characteristic for each one.
Short summary of interphase
- Comprised by three (four) sub phases: G1, (G0), S and G2
- Common feature of all (expect G0) sub phases:
o Growth of the cell by producing proteins and
cytoplasmic organelles
- G1- “first gap”
- S Phase- chromosome duplication
- G2- “second gap”, DNA repair