Carbs and Posttranslational Modifications Flashcards
What is a glycosidic linkage?
Formations of bond between anomeric carbon of one monosaccharide and hydroxyl of another
What monosaccharides form lactose? Is it a reducing sugar?
Galactose linked by beta(1,4) linkage to glucose
Reducing sugar
What monosaccharides make up maltose? Is it a reducing sugar?
2 glucose linked by alpha(1,4) linkage.
Reducing sugar
What monosaccharides make up sucrose? Is it a reducing sugar?
Glucose connected to fructose by alpha,beta(1,2) linkage.
Non reducing
What are homoglycans? Name 4 examples
Polyners of one type of sugar/modified sugar
Chitin, starch, glycogen, cellulose
What sugar makes up chitin?
Beta(1,4) linked N-acetyl-beta-D-glucosamine
What is the structure of starch
Consists of amylose and amylopectin
Amylose - alpha 1,4 links; linear polymer with left hand helix
Amylopectin - alpha 1,4 and 1,6 links resulting in branching
What is the structure of glycogen?
Similar to amylopectin, but more branching
What is the structure of cellulose
beta 1,4 glycosidic bonds
intermolecular H bonds between chains of cellulose
What are heteroglycans?
High MW polymers with multiple types of sugars
What are N linked oligosaccharides?
Linked via beta glycosidic bond between N-acetyl glucosamine anomeric carbon and side chain amide nitrogen of asparagine
What are O linked oligosaccharides?
Similar linkage to N linked, but to OH of Ser/Thr
Which has more carbohydrates– N/O glycans or proteoglycans? Which has more protein?
N/O glycans - more protein
Proteo - more carb
What is the glycocalyx?
Carbohydrate groups attached to the glycoprotein, proteoglycan, and glycolipid components of cell surface
What are lectins?
Carb binding proteins that translate the “sugar code”/glycocalyx
NOT antibodies
Which type of protein modification has highest coding capacity?
Glycosylation
When does posttranslational modification occur?
After polypeptide formation
What posttranslational modifications occur in prokaryotes?
Proteolytic processing- removal of formylmethionine and signal peptide sequence
Methylation, phosphorylation, lipidation
e.g methylation affects histidine kinase
What posttranslational modifications occur in eukaryotes?
Proteolytic cleavage- removal of N terminal methionine and signal peptides, activates proteins
Glycosylation, lipidation, phosphorylation, methylation, hydroxylation, carboxylation
What is glycosylation?
Attach oligosaccharidr to asparagine (N) or serine/threonine
Usually in ER
What happens to proteins in the ER?
They are checked for misfolding and proper sugar labeling.
Chaperones try to fix misfolding–if this does not work, proteins are degraded.
What is lipidation? How does it occur?
Lipophilic modification (lipidation) of proteins, including acylation and prenylation, occurs via covalent attachment of fatty acids.
Examples: farnesyl, geranylgeranyl, myristoyl, palmitoyl attachment
What is phosphorylation? What purpose does it serve?
Adding phosphates to Serine, Tyrosine, Threonines. Aka, to large polar AAs.
Plays roles in metabolic regulation and signal transduction.
What is methylation? What purpose does it serve?
Methylation occurs at aspartate, lysine, histidine and arginine and it may regulate the protein turnover or cellular function
Methylation of lysine/arginine in histones is central to epigenetic gene expression
What is hydroxylation?
Addition of OH groups to proline and lysine–part of collagen structural integrity
What is carboxylation necessary for?
Carboxylation of glutamate side chain is necessary for blood clotting.
