Thom4/5-Gluconeogenesis, glycoproteins Flashcards
How is fructose metabolized?
- By phosphorylation at the one-position (with fructokinase)
- Then, conversion to intermediates of the glycolytic pathway (with aldolase)
- To F-6-P if [fructose] is very high
- Metabolized primarily in liver, but also in the small intestine and kidneys
What is Essential Fructosuria? :)
- It is a deficiency in fructokinase
- Benign; causes excessive fructose in the urine
What is Hereditary Fructose Intolerance?
- It is a deficiency in Fructose-1-P aldolase activity in aldolase B
- Severe hypoglycemia, liver & kidney damage
- Accumulation of F-1-P & Pi inadequate recycling cause a decrease in ATP & therefore an increase of glycolysis
- No gluconeogenesis because of low ATP
- Treated by limiting sweets
What happens if there is an excessive consumption of fructose?
–> There is sequestering of inorganic phosphate, & so there is inadequate regeneration of ATP
What is the significance of sorbitol in diabetes?
- Fructose can be synthesized from sorbitol (the sugar alcohol of glucose) in the seminal vesicle
- In the lens of the eye, elevated sorbitol levels in diabetes mellitus and galactitol (sugar alcohol of galactose) in galactosemia contribute to cataracts formation
What is classical galactosemia?
- Deficiency of galactose-1-P-uridylyltransferase (GALT)
- Accumulation of galactose-1-P in tissues
- Inhibition of glycogen metabolism and pathways that require UDP sugars
- Galactose in the blood and urine
What is non-classical galactosemia?
- Deficiency of galactokinase results in accumulation of galactose
- Galactose in diet comes from lactose
What are the symptoms in a baby with classical galactosemia?
–> Vomit, weigth loss, jaundice, liver enlargement, and cataracts
–> due to a deficiency of Galactose-1-P uridyltransferase
What are proteoglycans?
- A core protein covalently attached to many long, linear chains of glycosaminoglycans, which contain repeating disaccharide units
- Repeating disaccharides contain hexosamine and a uronic acid
How are proteoglycans synthesized?
1) Attachment of a sugar to a serine or threonine residue of core protein
2) Additional sugar add to non-reducing end (w/ UDP-sugars serving as precursor)
3) excreted from the cells & form EC matrix
What are the properties of glycosaminoglycans/Mucopolysaccharides/Proteoglycans?
–> Protein core with proteoglycan monomers are attached to hyaluronic acid backbone with a link protein
–> Important for normal joints: lubricates joints and surfaces that move along each other, such as cartilage
–>Examples: keratan and dermatan sulfate in cornea, heparin -an anticoagulant, chondroitin sulfate in bone and cartilage, heparan sulfate in skin fibroblasts & aortic wall, hylauronic acid in cell migration
What are some mucopolysaccharides diseases (lysosomal storage diseases)?
- Hurler’s syndrome & Scheie’s: degradation of dermatan & heparan sulfate bc of a-L-Iduronidase deficiency -> mental retardation, corneal clouding, dwarfing
- Sanfilippo’s syndrome: impaired removal of glucosamine residues -> severe nervous system disorders, mental retardation
- Hunter’s syndrome: Iduronate sulfate deficiency -> X-linked -> physical deformity & mental retardation*
- Sly’s syndrome: B-glucuronidase deficiency -> hepatosplenomegaly, physical deformity*
What are glycoproteins?
- Proteins with short chains of carbohydrates, usually branched (composed of glucose, galactose, & their amino derivatives)
- Mannose, L-fucose, & NANA frequently present
- Branched chains may be attached to the amide N of asparagine in the protein OR the O of serine side chain
What are some functions of glycoproteins?
1- Cell surface recognition
2- Cell surface antigenicity
3- Extracellular matrix
4- Mucins
What are the functions of glycolysis other than ATP production?
- > Provides carbon for FA synthesis in the liver
- > Production of glycerol-3-P, (combines with FAs to form triacylglycerols to be secreted in VLDL)
