Carbohydrates Flashcards
Bonds in disaccharides (and polysaccharides)
Monomers linked by glycosidic bonds
Maltose (glucose + glucose)
Sucrose (glucose + fructose)
Lactose (glucose + galactose)
What is an (alpha1->4) link?
Glycosidic bond within subunits in chains
What is an (alpha1->6) link?
Glycosidic bond of branches onto chain
What are carbohydrates with carbohydrate attached and what is the benefit?
Glycoproteins
- Increase protein solubility
- Protect from degradation
- Communication between cells
What is mucopolysaccharidoses?
Defective enzyme this should break down gylcosaminogylcans (GAGs) causing it to build up in tissues, blood and damaging structure and function
- Hurler syndorme
Outline digestion
- Chewing and salivary enzymes (lipase, amylase)
- Travel to stomach and HCl breaks it down further
- Bile and pancreatic enzymes released to duodenum
- Large particles –> glucose/fructose/galactose in jejunum
- Absorbed to microvilli by Na/Glu symporter
How is fructose absorbed to microvilli?
Channel protein GLUT 5 into cells then diffuse into blood
Outline absorption of cellulose and hemicellulose
Not digested by gut, like oligosaccharides - polymers broken down by gut bacteria (form CH4 and H2 gas)
Describe lactose intolerance
No lactase enzyme = lactose broken down by gut bacteria so gas build up and irritant acid damaging cell well and draws water from gut to lumen causing diarrhoea
Why is glucose phosphorylated to G-6-P in the liver?
As G-6-P is not able to diffuse out of cells by GLUT transporters, trapping it in cell
Difference between hexokinase and glucokinase
Glucokinase in liver as has high Vmax so phosphorylates Glu rapidly so most Glu->G-6-P trapped in liver
Hexokinase: low Km = HIGH affinity so at low [Glu] it can be converted to G-6-P in tissues and low Vmax means tissues are easily satisfied
Outline synthesis of glycogen (glycogenesis)
- Glucose from UDP-Glucose to form an 8 Glc chain ((alpha1–>4) links)
- Glycogen synthase extends Glc chain
- Glycogen-branching enzyme break Glc chain and re-attach by (alpha1-6) links as a branch
Outline degradation of glycogen
- Glc removed one at a time from non-reducing end by GLYCOGEN PHOSPHATASE - and they’re then called G-1-P
- Debranching enzymes transfers 3 GLC near branch to non-reducing end with (alpha1->4) links
- GLUCOSIDASE removes final Glc on branch breaking (alpha1->6) link
Glucose 6-phosphatase deficiency
- High [liver glycogen]
- Low [blood Glc] - glycogen can’t be used as energy source
- High [blood lactate] in skeletal muscle
What reaction does lactate dehydrogenase catalyse?
Pyruvate –> lactate (produces NAD+)
