Deserts are not very efficient at converting huge amounts of incident energy from sunlight into plant biomass.  Most ecosystems based on phytoplankton have very low efficiencies, usually less than 0.5%.

Photosynthetic efficiency of an ecosystem as a whole varies between 1% and 2%.

TLS Online TPP Program

#Id: 8622

#Unit 2. Cellular Organization

Cyclins are degraded through the action of two different E3-ligases:

1. SCF (Skp1, Cullin, and F-box proteins) 

2. APC/C or cyclosome

TLS Online TPP Program

#Id: 8623

#Unit 2. Cellular Organization

SCF and APC/C are multisubunit ubiquitin-protein ligases that belong to the RING finger family of ubiquitin-protein ligases.

TLS Online TPP Program

#Id: 8624

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 8625

#Unit 2. Cellular Organization

Human SCF complexes contain: 

Three core components - Cul1 subunit, RBX1, Skp1 

and a substrate-targeting F-box protein

TLS Online TPP Program

#Id: 8626

#Unit 2. Cellular Organization

RBX1 is a RING finger–containing protein that binds the E2 ubiquitin-conjugating enzyme.

TLS Online TPP Program

#Id: 8627

#Unit 2. Cellular Organization

phosphoserine/threonine-binding F-box protein is Skp2, which uses a series of leucine-rich repeats to bind to target proteins only when they are phosphorylated.