Carbohydrates Flashcards
Definition of carbohydrate
A biomolecule consisting of carbon, hydrogen and oxygen
What is the formula for carbohydrates?
CnH2nOn or Cn(H2O)n where n varies for each carbohydrate
When are aldoses and ketoses formed as carbohydrates?
When n=3
Examples of aldoses and ketoses
Aldoses: glyceraldehyde
Ketoses: dihydroxyacetone
What is the structure of aldoses?
Carbon double bond with oxygen and single bond with hydrogen
What is the structure of ketoses?
Carbon double bond with oxygen
Why are aldehydes (aldoses) called reducing sugars?
Because they are more reactive than ketone (ketoses) due to the hydrogen
What are enantiomers?
A pair of stereoisomers affected by mirror imaging
D-form vs L-form mirror imaging
D-form: OH group on right of carbon
L-form: OH group on left of carbon
What does D-glucose form when it reacts with itself?
A circular structure (α-D-glucose)
What happens when n=5?
The alpha switches to beta and H and OH swap over
Condensation reaction
When 2 monosaccharides form a disaccharide with the release of a water molecule
Name 3 disaccharides
Maltose, lactose and sucrose
Name 2 oligosaccharides
Maltodextrins and inulin
What are the 2 subgroups of polysaccharides?
Starch and non-starch polysaccharides
Examples of starch polysaccharides
Amylose and amylopectin
Examples of non-starch polysaccharides
Glycogen, cellulose and pectin
What are the wheat properties that are good for bread?
- Easy to mill
- Strong flour (high gluten)
- > 13% protein
- Hard endosperm
- High water absorption
- <16% moisture content
- 98% sample purity
How is a high protein content achieved?
Nitrogen support through fertiliser and water
Why does protein content drop?
When the drying temperature is too high
How can alpha amylase content be reduced in wheat?
Prioritising wheat harvest to prevent sprouting
How can ergot (highly toxic) be avoided in rye?
Correct combine harvester settings
What are some of the properties required for barley in distillation?
- 100% germinated
- <1.6% nitrogen
- 2.2-2.8mm grain size
- Uniform grains
- 14.5% moisture content
How can barley be improved?
- Soil should be drained properly
- Soil should not be drought prone
- Early sowing date
- On time harvest
- Nitrogen nutrition should be adequate and on time
How do monosaccharides enter the body?
Absorbed by the gut and transferred to the liver through epithelial cells via the portal vein
Why is glucose needed?
Brain and nervous system and red blood cells
How does glucose become energy?
Glycolysis, citric acid cycle and oxidative phosphorylation
How much glucose is used as ATP?
40% and the rest is used as heat
What are the average levels of blood glucose levels?
- Never below 5mM
- Rises to 7-8mM after food
What is glycogen?
A store of glucose chains synthesized in the liver
What is glycogenesis?
The synthesis of glucose into glycogen and is dependent on insulin
What is glycogenolysis?
Glycogen degraded into glucose catalysed by enzyme phosphorylase
What is gluconeogenesis?
Synthesis of glucose from non-carbohydrates (amino acids, glycerol, lactate)
Insulin
Promotes use of glucose to reduce blood sugar
Glucagon
Completes glycogenesis and gluconeogenesis to increase blood sugar
What are the 2 sub-groups for oligosaccharides?
Glycaemic and non-glycaemic glucans
Glycaemic vs Non-glycaemic glucans
Glycaemic- Digested and absorbed in small intestine
Non-glycaemic- Can’t be broken down and absorbed in large intestine
What is alpha-amylase?
Enzyme in saliva which breaks down amylose and amylopectin
What is the lumen?
An area in the small intestine which hydrolyses starch into maltose and dextrin
How are starchy polysaccharides digested in the small intestine?
Enzymes on enterocytes in villi break down to monosaccharides which can be absorbed into small intestine
How are non-starchy polysaccharides absorbed in the large intestine?
Fermentation by sugars
What are the membranes on the enterocytes?
Apical and basolateral membranes
How does the apical membrane transport monosaccharides?
Sodium-glucose transport protein (SGLT1)
Fructose transport protein (GLUT5)
How does the basolateral membrane transport monosaccharides?
GLUT2 protein
