Structure and Function of Carbs (biochem)rename
evan406's version from 2016-04-20 19:10
|alpha and beta anomers||alpha anomer: OH pointing down on C1|
beta anomer: OH pointing up on C1
|D vs L configuration||D-configuration has CH2OH pointing up in cyclic form and down in L form|
|Glycogen||glucose units linked by (α1→4) glycosidic bonds. |
linkages cause bends in the chain making helical structures
cannot form long fibers, is highly branched and, very water-soluble.
storage fuel in animals.
abundance of free, nonreducing ends, can be hydrolyzed to release glucose 1-phosphate, available for oxidation and energy production.
|cellulose||glucose units linked by (β1→4) glycosidic bonds. |
β linkages force polymer chain into an extended conformation.
Parallel series of extended chains aggregate into long, tough, insoluble fibers.
Cellulose serves as a structural material in plants
|Glycosaminoglycans||long unbranched polysaccharides consisting of a repeating disaccharide unit. |
repeating unit consists of a hexose or a hexuronic acid, linked to a hexosamine.
chains may be covalently linked to a protein to form proteoglycans.
chains are sulfonated and highly charged.
|Where does the sugar code play essential roles?||1. General regulation/signaling|
2. Blood groups
3. Cell-cell interaction: Inflammation
4. Protein sorting in ER and Golgi complex
5. Protein folding
6. Removal of blood protein and breakdown
|Cell-cell interaction: Inflammation||Leukocytes roll along the vascular wall. This rolling movement is mediated by reversible adhesive interactions via selectins (glycoproteins) and selectin receptors (lectins). |
L-selectins are present on the leukocyte and are important for the rolling. P-selectins are present on the endothelial cell.
P-selectins are transported to the cell membrane after exposure to inflammatory signal molecules. P-selectins bind stronger to the leukocyte, causing the leukocyte to slow down and to enter the wall.
Inflamed tissues have increased amounts of sialylated and fucosylated epitopes on the cell surface, often in sulphated form. L-selectins present on the white blood cells bind to these sugar units.
|Protein sorting in ER and Golgi complex||Cells use specific oligosaccharides to encode important information. Lectins play an important role by recognizing and binding to the different oligosaccharides.|
The sugar code plays an important role in the targeting of for example hydrolase:
- The hydrolase protein contains a signal sequence that is recognized by the SRP particle and as a result the enzyme is guided into the ER during synthesis
- In the ER the lysozyme is glycosylated
- Lysosomal enzymes contain a signal patch that is recognized by an enzyme that phophorylates a mannose residue at the terminus of an oligosaccharide chain
- This residue is recognized by a special receptor (or lectin)
- When a section of the Golgi complex containing this receptor buds off to form a transport vesicle, proteins containing mannose phosphate residues are dragged into the forming bud by interaction of their mannose phosphates with the receptor; the vesicle then moves to and fuses with a lysosome, depositing its cargo therein.
|Removal of blood protein and breakdown|