Carbohydrates Flashcards
What are carbohydrates
Highly oxidisable
Store potential energy
Major energy source
What are the monosaccharides
Glucose
Galactose
Fructose
What are disaccharides
Formed from monomers
Linked by glycosidic bonds
What are the three important Disaccharides
Maltose
Lactose
Sucrose
What is maltose
Breakdown product of starch
Between maltose, lactose, sucrose, which are reducing sugars
Maltose and lactose
What is the structure of Lactose
Galactose + glucose combined with glycosidic bond
What % of our diet carbs is sucrose
25%
What are polysaccharides
Polymers of medium-high molecular weight
What are the types of polysaccharides
Homopolysaccharides - Single monomer
Heteropolysaccharides - Two or more monomers
What are the two types of starch
Amylose - 20-25%, D-glucose residues
Amylopectin - 75-80%, Glycosidic bonds
What is glycogen and where is it found
Polymer of glucose
90% in:
Liver - replenishes glucose
Skeletal muscle - Produces ATP
What is used to digest carbs in the mouth
Salivary amylase hydrolyses starch
What digests starch in the stomach
No digestion
What digests starch in the duodenum
Pancreatic amylase
What are the final digestions in the Jejunum
Isomaltase - Hydrolyses a1-6 bonds
Glucoamylase- removes glc sequentially
Sucrase -> sucrose
Lactase ->Lactose
How is glucose and galactose absorbed
Na+ pump maintains low Na+ content
Allows glucose to be moved into cells
Works when glucose moves against cg
How is fructose absorbed
Bind to channel protein GLUT5
Moves down its cg
Can Cellulose and Hemicellulose be digested
Nope
What happens after glucose is absorbed
Glc diffuses through intestinal cells->blood->liver
Phosphorylated->G-6-P by hepatocytes
G-6-P can’t diffuse out of cell as GLUT transporters no longer recognise it.
What are the enzymes for glucose
Glucokinase- liver
Hexokinase- skeletal muscle
What is Vmax and Km
High number = efficient enzyme
Low Km = high affinity for substrate
What is the Km andVmax for hexo/glucokinase
When blood glc normal - liver doesnt grab all glc
Blood glc high - Liver grabs Glc
High glckinase Vmax - phosphorylates Glc quickly
Hexokinase low Km - tissues grab Glc at low Glc
Hexokinase low Vmax - tissues easily satisfied
What does hexokinase and glucokinase convert glucose to
Glucose 6 phosphate
Where is glycogen converted
In liver: glycogen->G6P->Glc in blood
In skeletal muscle: Glycogen->G6P->lactate and ATP via glycolysis
What are steps of synthesis of glycogen
Glycogenin binds Glc from UDP-glc to form 8 glc residues
Glycogen synthase extends the chain
Chains then broken by glycogen-branching enzyme
Re-attached via (a1-6) bonds
What are the steps of glycogen degradation?
Glc monomers removed one by one
Glc removed by de-branching enzyme
Transferase activity of de-branching enzyme removes 3 Glc at a time
Attaches them to nearest nonreducing end via (a1→4bond)
Glucosidase removes final Glc by breaking(a1→6) linkage
Leaves unbranched chain
What are the two glycolysis phases
Preparatory phase: 1 Glc passes through
2 molecules of G3P produced
Payoff phase: For each Glc 2ATP used in prep phase
4ATP gained in payoff phase
What are the irreversable steps of glycolysis
Step 1. Phosphorylation of glucose
Glc -> G6P, catalysed by hexokinase
Uses 1ATP
Step 3. Phosphorylation of F6P -> F1,6-bisP catalysed phosphofructokinase-1
1ATP used
Step 10. Transfer of P from PEP to ADP
Catalysed - pyruvate kinase
2ATP produced
What are the three substances pyruvate can be converted to
Lactate
Acteyl COA
Ethanol
What is the Cori cycle
ATP produced via substrate level phosphorylation
Produced lactate
Lactate converted to Glc via gluconeogenesis
What is the function of gluconeogenesis
4 reactions that sidestep the 3 irreversable glycolysis reactions
What are the A and B gluconeogenesis reactions
Pyruvate->Oxaloacetate->malate->Oxaloacetate->PEP
Takes place in mitochondria
What happens in reaction C
Fructose1,6-bisP->F6P
Fructose 1,6 bisphosphatase catalyses this
