Carbohydrates Flashcards
What is the difference between aldoses and ketoses
An aldose has and aldehyde group on C1 while a ketose has a keto group on C2
What is a sugar with an amino group called?
Amino Sugars
What is starch a polymer of?
Glucose
Define glycogen
a storage polymer of glucose in animals
Where is glycogen mainly stored?
The liver and muscles
What comprises a sugar acid?
Terminal carbon has a carboxylic acid (COO-)
What comprises a sugar alcohol?
The carbonyl group is reduced to an alcohol group (-OH)
What polymer is comprised of amino sugars and uronic acids?
Glucosaminoglycans
Describe the path and significant enzymes involved in carbohydrate digestion before entering metabolism in the liver
-Mouth: digestive amylase
-Small Intestine: pancreatic alpha amylase breaks down polysaccharides to dia- and monosaccharides
-Brush border of small intestine: enzymes hydrolyze diasaccharides to monosaccharides
-Monosaccharides enter enteric circulation
-Released into portal vein
What are the 3 fates of monosaccharides after digestion?
-oxidation into energy
-storage as glycogen
-fatty acid synthesis
What organ is the major regulator of glucose metabolism?
the liver
What cells store glycogen but DOES NOT export glucose?
muscle cells
What two protein hormones regulate blood glucose concentration?
Insulin
Glucagon
Where is insulin released from?
pancreatic beta cells
Where is glucagon released from?
pancreatic alpha cells
What processes does insulin trigger?
-Speeds up entry of glucose into cells
-Fatty acid synthesis
-Glycogen synthesis
-Protein synthesis
What processes does glucagon trigger?
Glycogenolysis
Lipolysis
Gluconeogenesis
Ketogenisis
What transporters allow glucose to enter cells?
GLUTs
SGLTs
Which GLUT transporter do liver cells, small intestinal cells, and renal cells have?
GLUT 2
What GLUT transporter do adipocytes, skeletal, and cardiac muscle cells have?
GLUT 4
What is the difference between GLUT2 and GLUT4 transporteres?
GLUT2s are bidirectional and not insulin dependent
GLUT4s are regulated by insulin
Once in cells how are glucose molecules kept in the cells? what enzymes perform this function?
Phosphorylation
Glucokinase and Hexokinase
What are the 4 characteristics of hexokinase?
-In most mammalian cells
-Low Km (works efficiently at low glucose concentrations)
-Strongly inhibited by G-6-P
-NOT regulated by insulin
What are the characteristics of Glucokinase?
-ONLY in liver and pancreatic beta cells
-Higher Km
-NOT inhibited by G-6-P
How is glucokinase regualted?
Increase of insulin and decrease of glucagon regulate glucokinase transcription
How do you get glucose out of a cell?
dephosphorylate with Glucose - 6- phosphatase
What are the only two organs with Glucose-6-phosphatase?
the liver and kidneys
How is glucose-6-phophatase regulated?
Insulin regulates gene expression
Where does glycogen synthesis primarily occur? what part of the cell?
the cytosol of muscle and liver cells
What is the rate limiting step of glycogen synthesis?
Protein phosphatase 1. This activates glycogen synthase
What is the rate limiting step of glycogenolysis?
Glycogen phosphorylase. Shortens chains from branch, releases G-1-P
Where can you regulate glycogenolysis?
-Activation of glycogen phosphorylase by cAMP second messenger
- Ca2+ messaging, increase in Ca activate phosphorylase kinase, which activates glycogen phosphorylase
Define glycogen storage diseases
Affect enzymes associated with glycogen synthesis or glycogenolysis depending on the type
What is the glycogen storage disease in horses?
Polysaccharide storage myopathy
-Affects glycogen synthase causing too much muscle glycogen
What part of the cell does glycolysis occur?
cytosol
Where does anaerobic glycolysis mainly occur?
-Where quick energy is needed
-Areas w/ limited blood supply
-cells w/out mitochondria
What enzymes are you able to regulate glycolysis with?
-Hexokinase/glucokinase (inhibited by glucagon)
-Phosphofructokinase 1 (inhibited by ATP)
- Pyruvate kinase (inhibited by ATP and glucagon)
What are the 4 different fates of G-6-P?
- glycolysis
2.HMS - Uronic acid pathway
- glycogen
What are the products of HMS? where are they later used?
Ribose-5-phosphate (nucleotide and nucleic acid formation)
NADPH (fatty acid synthesis and steroid biosynthesis)
What are the two phases of HMS?
Oxidative and non oxidative
What two products does the uronic acid pathway yield?
Ascorbic acid (Vit.C) and UDP-Glucuronate
What 6 enzymes are used in glycogen synthesis?
Hexokinase/Glucokinase
Protein phosphatase 1
Glycogen synthase
Phosphoglucomutase
UDP pyrophosphorylase
Branching enzyme
What 4 enzymes are used in glycogenolysis?
Glycogen phosphorylase
Debranching enzyme
Phosphoglucomutase
Glucose 6 phosphatase
What 9 enzymes are used in glycolysis?
Hexokinase/Glucokinase
Phosphohexose isomerase
Phosphofructokinase
Aldose
Phosphotriose isomerase
Phosphoglycerate kinase
Phosphoglycerate mutase
Enolase
Pyruvate transferase
What 4 enzymes are used in the Uronic Acid Pathway?
Phosphoglycomutase
UDP-Glc pyrophosphorylase
NAD dependent UDP-Glc dehydrogenase
L-Gulonolactone oxidase
