Chapter 8: Carbohydrates Flashcards
The most abundant biomolecule?
Carbs
Play a role in metabolism as an energy source and as a structural molecule
Carbs
Glycoconjugates
Covalently linked oligosaccharides to proteins or lipids
Oligosaccharides
2-10 units of monosaccharides
Sugar derivatives that are L isomers
glycoconjugates
Hemiacetal is formed by _____
Aldehyde + alcohol in 1:1 ratio via nucleophilic attack
*creates a new chiral center
How is glucose cyclized?
The OH group of carbon 5 attacks the aldehyde on carbon 1 VIA hemiacetal linkage
*creates racemic mixture of alpha and beta anomers
Mutarotation
interconversion of alpha and beta anomers
How is fructose cyclized?
The OH of carbon 5 attacks ketone of carbon 2 (carbon 1 is the carbon from ketone)
What are pyranoses and furanoses?
Cyclic forms of 5 carbon and 1 oxygen atom sugar
Cyclical forms of glucose and fructose, respectively
a-D-glucopyranose and a-D-fructofuranose
How is maltose formed?
OH of one glucose molecule condenses with intramolecular hemiacetal of another glucose molecule to form glycosidic bond
*hemiacetal on the right molecule is the reducing end
Maltose contains:
Glucose + Glucose
*used in brewing
Lactose contains:
Glucose + Galactose
*transport sugar in milk
Sucrose contains:
Glucose + Fructose
*transport sugar in plants
Glycosidic bonds look like:
Most common linkage is alpha - 1 - 4
(gives sugar a helical structure and used for energy storage mainly)
In starch, what happens to the non-reducing end?
It will get enzymatically cleaved to release glucose monomeric units
What sugars is starch composed of?
Amylose (straight chain) and Amylopectin (branched chain)
(both polysaccharides)
What is the structure of starch?
1.) Amylose and amylopectin form a double-helical structure
2.) When energy needs to be used, glucose residues from nonreducing end is enzymatically cleaved for utilization
Chitin
A polysaccharide that makes up exoskeleton, homopolymer of N-acetyl-D-glucosamine in Beta-1-4 linkage
(ex. beetle shell)
yotube
Proteoglycans
macromolecules of cell surface or extracellular matrix in which one or more sulfated glycosaminoglycan chains are joined covalently to a membrane protein.
Glycoprotein
proteins covalently linked to one or more oligosaccharides of varying complexity
Glycolipids
membrane lipids where hydrophilic head group is an oligosaccharides
Two families of proteoglycans?
Syndecan and Glypican
Sydnecan
Proteoglycan with single transmembrane domain and extracellular domain (held together by hydrophobic interactions)
Glypican
Proteoglycan attached covalently to the membrane by a lipid anchor
A heparin sulfate chain contains:
NA and NS domains, regions rich in sulfated sugars.
NS domains bind specifically to extracellular proteins/signaling molecules
What are the four types of protein interactions with NS domains of heparin sulfate?
a.) conformational activation
b.) enhanced protein-protein interaction
c.) coreceptor for extracellular ligands
d.) cell surface localization/concentration
Aggrecan molecule diagram:
Hyaluronan is the core/backbone of proteoglycan aggregates
The association between cells and the proteoglycan of the extracellular matrix is mediated by?
A membrane protein (integrin) and an extracellular protein (fibronectin) with binding site for both integrin and proteoglycan
O-linked glycosydic bond diagram:
N-linked glycosydic bond diagram:
O linked oligosaccharides structure:
glycosidic bond to the hydroxyl group of Ser or Thr residues
*Mucins are secreted or membrane glycoproteins that contain large numbers of O-linked oligosaccharide chains
N linked oligosaccharides structure:
N-glycosyl bond to amide nitrogen of Asn residue
Serve as cell-to-cell recognition, signaling, and adhesion processes. Also in intracellular targeting of newly synthesized proteins.
Lectins
Where are lectins found?
All organisms, are proteins that bind carbs with high specificity and moderate to high affinity.
The Role of lectin-ligand interactions in lymphocyte movement:
At the site of inflammation, there will be stronger interactions between integrin in the capillary surface and its ligand in the neutrophil surface which leads to tight adhesion. Signals will start extravasation and escape through the capillary wall toward the site of inflammation.
How are ulcers made?
Helicobacter pylori bacteria causes ulcers by interaction between a bacterial surface lectin and Leb oligosaccharide (a blood group antigen) of the gastric epithelium.
Roles and steps of oligosaccharides in recognition and adhesion at the cell surface:
a.) Oligosaccharides are in glycoproteins/glycolipids on the outer surface of plasma membranes, and they interact with high specificity and affinity with lectins in the extracellular milieu
b.) Viruses that infect animal cells, such as the influenza virus, bind to cell surface glycoproteins as the first step in infection
c.) Bacterial toxins, such as the cholera, bind to a surface glycolipid before entering a cell
d.) Some bacteria, such as H. pylori, adhere to and then colonize or infect animal cells
e.) Selectins (lectins) in the plasma membrane of certain cells mediate cell-cell interactions, such as those of neutrophils with the endothelial cells of the capillary wall at an infection site
Oligosaccharides are in glycoproteins/glycolipids on the outer surface of plasma membranes, and they interact with high specificity and affinity with lectins in the extracellular milieu
Viruses that infect animal cells, such as the influenza virus, bind to cell surface glycoproteins as the first step in infection
Bacterial toxins, such as the cholera, bind to a surface glycolipid before entering a cell
Some bacteria, such as H. pylori, adhere to and then colonize or infect animal cells
Selectins (lectins) in the plasma membrane of certain cells mediate cell-cell interactions, such as those of neutrophils with the endothelial cells of the capillary wall at an infection site
The mannose 6-phosphate receptor/lectin of the trans Golgi complex binds to the oligosaccharide of lysosomal enzymes, targeting them for transfer into the lysosome.
