Ch. 13 Flashcards
What are glycans?
Synonym for carbohydrate
- Class of molecules with the formula (CH2O)n where n is greater than 2
What is glycobiology?
Study of the biological functions of glycans
What are the 3 major groups of carbohydrates?
- Simple sugars
- Polysaccharides
- Glycoconjugates
What are simple sugars?
Monosaccharides, disaccharides, and oligosaccharides
What do simple sugars often function as?
Metabolic intermediates in energy conversion pathways
What are polysaccharides?
Glucose homopolymers or disaccharide heteropolymers
- 1 of the 2 sugars is a hexosamine
What are glycoconjugates?
Protein or lipid with covalently linked glycans
- Role in cellular communication
What do glycoconjugates have a role in?
Cellular communication
What are glycotransferases?
Enzymes that catalyze the ADDITION of glycan units to proteins and lipids to form glycoconjugates
What are glycosidases?
Enzymes that catalyze that REMOVAL of glycan units from glycoconjugates
What are 4 the glycobiology principles?
Glycan…
1. Biochemistry
2. Biosynthesis
3. Diversity
4. Recognition
What is a glycosidic bond?
Bond that joins a carbohydrate to another molecule
What is an anomeric carbon?
The carbonyl carbon in the acyclic form of a carbohydrate
What are oligosaccharides?
Simple sugars that range from 3 to 20 branched and unbranched sugar residues
What examples of oligosaccharides?
- Lacto-N-tetraose
- Stachyose
- Raffinose
How do we know that related oligosaccharides are derived from the same disaccharide?
Because of the biochemical characterization of oligosaccharides in human breast milk and the raffinose series of plant oligosaccharides
What is the common disaccharide of human breast milk oligosaccharides?
Lactose
What is the common disaccharide of raffinose-related oligosaccharides?
Sucrose
What happens when some people eat foods high in raffinose-type oligosaccharides?
Can lead to GI discomfort because humans don’t have the enzyme (α-galactosidase) that breaks it down
How do polysaccharides differ from each other?
- ID of recurring monosaccharide units
- Length of chain
- Degree of branching
- Type of bonds linking the units
What are homopolysaccharides?
Made of 1 type of monosaccharide
What are heteropolysaccharides?
Made of more than 1 type of monosaccharide
What are the storage forms of glucose?
Starch and glycogen
What does starch contain?
Amylose, amylopectin, and other polysaccharides
What is amylose?
An α(1⟶4) linear form of starch (unbranched)
What is amylopectin?
An α(1⟶6)–branched form of starch
- it also has α(1–>4) linkages in the straight part
Compare and contrast glycogen and amylopectin.
Similar structure but glycogen is more branched
What is glycogen?
Storage polysaccharide in animal cells
Where is glycogen abundant?
In the liver
What are glycoproteins?
Major class of glycoconjugates characterized by glycans covalently linked to protein molecules
What are glycolipids?
Major class of glycoconjugates characterized by glycans covalently linked to lipid molecules
What are proteoglycans?
Type of protein glycoconjugate where most of the macromolecule consists of carbohydrates
TL;DR - More carb than protein
What is peptidoglycan?
Bacterial proteoglycan made of peptide-linked chains of repeating hexosamines; the major component of bacterial cell walls
What are the functions of proteoglycans?
- Protein binding activites
- Regulate signal transduction
- Facilitate cell migration
What are the two classes of proteoglycans?
- Cell surface
- Extracellular matrix
What are N-linked oligosaccharides?
Linkage of short chains of glycans to the amide nitrogen atom in the side chain of asparagine in a glycoprotein
What are O-linked oligosaccharides?
Linkage of short chains of glycans to the oxygen atom in the side chain of serine or threonine in a glycoprotein
What are mucins?
O-linked glycoproteins that are secreted and bound to the cell surface
- Aid in maintenance of mucosal barriers around epithelial cells
What amino acids do carbohydrates link to in glycoproteins?
- Asparagine (N-linked)
- Serine or threonine (O-linked)
Where are oligosaccharides added to proteins in cells?
Added to newly synthesized proteins in the ER and are elaborated in the Golgi complex
Why are oligosaccharides added to proteins in cells?
- Destination labels
- Increase solubility of proteins
- Quality control
- Negative charge cluster protects proteins from proteolytic degradation
List biomedical examples of glycoconjugates.
- Macular corneal dystrophy
- Bacterial cell walls
- Blood groups and glycotransferases
What determines ABO blood types?
Variant glycosyltransferases
What are ABO blood groups?
System for typing blood based on presence of GalNAc and/or galactose bound to O antigen of glycoproteins and glycolipids on surface of RBCs
What is type O blood?
Neither GTA nor GTB enzymes present
What is type A blood?
Only GTA enzyme
What is type B blood?
Only GTB enzyme
What is type AB blood?
Both GTA and GTB enzymes present
What do β-lactam antibiotics target?
Peptidoglycan synthesis
What is Gram-positive bacteria?
Have a thick peptidoglycan layer that retains the Gram stain
What is Gram-negative bacteria?
Have a thin peptidoglycan layer that does not retain the Gram stain
What color are gram-positive vs gram-negative bacteria after staining?
Gram-positive: dark purple
Gram-negative: pink-red
What does the thick layer of peptidoglycan contain?
Lipotechoic acid (negatively charged polymer of ribitol phosphate or glycerol phosphate)
- Structural support
Which type of bacteria has LPS?
Gram-negative (outer membrane)
What is an endotoxin?
LPS in outer membrane of Gram-negative bacteria that becomes toxic to the host after the bacteria have lysed
How does penicillin work?
Blocks bacterial cell wall biosynthesis by inhibiting the enzyme transpeptidase
What makes some bacteria resistant to penicillin?
They produce an enzyme called β-lactamase, which inactivates penicllin by hydrolyzing the β-lactam ring in penicillin
What causes macular corneal dystrophy?
Defect in the enzyme that sulfates keratan
- Cornea become opaque due to decreased sulfation of keratan
What is the role of keratan sulfate?
- Help maintain a hydrated environment
- Functional role in promoting structural organization
What is the structure of glucose?
What is the structure of GlcNac?
