Density-dependent factors affect population size in relation to the population’s density.

Density-dependent factors down into two categories. 

Negative density dependence 

Positive density dependence (inverse density dependence

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#Unit 2. Cellular Organization

Cohesins 

The protein ring complexes that establish linkages between sister chromatids

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#Unit 2. Cellular Organization

Cohesins establish linkages between the replicated DNA molecules, which are essential for their accurate segregation later in the cell cycle. This linking mechanism is coupled to DNA replication.

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#Unit 2. Cellular Organization

Cohesins are composed of four subunits: 

Smc1, Smc3, Scc1, and Scc3

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#Unit 2. Cellular Organization

Smc1 and Smc3 are members of the structural

maintenance of chromosomes (SMC) protein family, characterized by globular domains at the N- & C-termini connected by a long α helix, bind and hydrolyze ATP.

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#Unit 2. Cellular Organization

The ATPase domains interact with the proteins

Scc1 and Scc3, which together form a cohesin ring structure which embrace one or both copies of the replicated DNA.

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#Unit 2. Cellular Organization

Cohesin-mediated cohesion between sister chromatids is established by a two-step process:

1.Loading and unloading of cohesins

2. Stabilization of cohesins