Cell Membranes
Phosopholipid Membranes
Tutorial page describing the construction and properties of Biological Membranes.
Biological Membranes
Biological membranes are dynamic structures composed of a diverse set of phospholipid molecules and proteins. In the case of eukaryotic organisms, they also contain the steroid cholesterol. This animation demonstratess some of the key properties of the membranes.
Phase Transition
This tutorial explains how phospholipids bilayers undergo to a cooperative phase transition or melting that is similar to protein denaturation.
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Transport
Signal Transdaction
This animation illustrates how binding of a ligand to its receptor ultimately leads to the production of high levels of cAMP, an important second messenger in the signal transduction pathway. This process is mediated by a protein called G-Protein.
Serine Protease
The tutorial shows the chemical mechanism of serine proteases, enzymes that in the family differ only in their substrate specificity.The Trypsin for example is an extracellular protease that hydrolyzes peptide bonds during digestion in the small intestine.
Uniport - Glucose Transport
The tutorial shows how the glucose transporter molecule is structured with a spiral channel that allows the glucose molecules to passively navigate the channel and move through the membrane.
Symport - Lactose Permease Transporter
The Escherichia coli lactose permease is an example of secondary active transport (Campbell, p. 210). This enzyme is similar in structure to others in the major facilitator superfamily (MFS) of transporters. More than 1000 examples of MFS transporters have been identified in the genomes of bacteria, plants, and animals.
Antiport - ADP/ATP Exchange
This tutorial explains ADP/ATP exchange, a form of Antiport transport, a mechanism where two different molecules facilitate each others pass through the membrane in opposite directions.
ATP Synthesis
This tutorial explains the synthesizing of ATP from a proton gradient across the inner mitochondrial membrane. This gradient was established by the pumping of protons across the membrane during the transport of electrons from NADH and FADH2 to oxygen.
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Endocytosis
Endocytosis/Receptor Mediated Endocytosis
Many macromolecules are taken into the cell by a process described as endocytosis. The macromolecules do not pass through the membrane directly to the cytoplasm but instead are taken up by the cell, processed by cell and then delivered to the cytoplasm. For many of the endocytic processes, the uptake of the molecule is very specific and is controlled by recognition of the molecule by a specific receptor on the surface of the cell. This process is called Receptor Mediated Endocytosis.
Macropinocytosis
This tutorial describes how macromolecules are processed by cell and then delivered to the cytoplasm. For many of the endocytic processes, the uptake of the molecule is very specific and is controlled by recognition of the molecule by a specific receptor on the surface of the cell. This process is called also Receptor Mediated Endocytosis.
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DNA/RNA
DNA Replication
The enzymatic and structural features of DNA replication in all organisms are very similar. These animations illustrate the processes involved in the replication of the Eschericia coli chromosome. The names of the DNA sites, enzymes, and other protein factors differ in viruses and in eukaryotic organisms, however, the basic features have been highly conserved in evolution. In E. coli, DNA replication begins at a single site on the chromosome called "OriC".
DNA Transcription
This tutorial shows the steps involved in transcribing DNA into mRNA. Transcription is illustrated using the E. coli lactose operon (lac) where transcription is regulated negatively by the lac repressor and positively by CAP-cAMP complex.
RNA Translation - Protein Synthesis
The biosynthesis of proteins involves translation of the information contained in the mRNA into a polypeptide sequence. Each triplet of bases in the mRNA encodes one amino acid. The translation is accomplished by the ribosome with the use of specialized RNA molecules called transfer RNA, or tRNA. The tRNA molecules bind to the mRNA and deliver the correct amino acid to the growing polypeptide chain.
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