Lecture 5 - Carbohydrates Flashcards
What is the most common monosaccharide
glucose
What is the most common disaccharide
sucrose
How are polysaccharides stored in animals vs plants
animals = glycogen
plants = cellulose & starch
What carbon count monosaccharides are the most important for nutrition
hexoses
What are enantiomers
mirror images
What are diastereoisomers
not a mirror image
What is a chiral carbon
carbon surrounded by 4 molecules
What determines D vs L configuration
determined by the -OH group on the highest chiral carbon (furthest from carbon 1)
- if -OH is on left, its L, if -OH is on right, its D
What is the equation for the # of stereoisomers
2^n where n is the number of chiral carbons
What is Fischer projection
the linear configuration of a sugar
What is a Haworth model
the ring configuration of a sugar
What is the different between a hemiacetal and a hemiketal
hemiacetal = made from aldose
hemiketal = made from ketose
How to determine whether a sugar is alpha or beta
in Fischer, if the -OH is on the left, it will point up in Haworth, if the -OH is on the right, it will point down in Haworth
- up = beta, down = alpha
What type of bond connects monosaccharides to make a disaccharide
a glycosidic bond between 2 OH groups
What is sucrose
found in sugar cane and fruits
glucose + fructose
non-reducing - both anomeric carbons are occupied
What is lactose
found in milk
galactose + glucose
reducing
What is maltose
found in beer and liquor
glucose + glucose
reducing
What is the benefit of insoluble fibre
increases intestinal movement (remains intact and reduces transit time)
What is the benefit of soluble fibres
gives good health benefits by increasing transit time and slowing down the rate of nutrient absorption
What is the make up of cellulose
homopolysaccharide of B-1,4 glucose units
Why can’t humans digest cellulose
lack the cellulose-fermenting microbes in their gut microbiome
Want is the make up of hemicellulose
a mixture of alpha and beta glycosidic linkages
can contain both pentoses and hexoses
What is pectin and where is it found
backbone of unbranched a-1,4-linked-D galacturonic acid
- part of cell wall in plants
What is resistant starch and where is it found
found in plant cell walls
resistant to amylase activity
What fibre is good for decreasing constipation
insoluble
What fibre is good for increasing satiety
soluble fibre
Why do insoluble fibres decrease constipation
because they don’t dissolve, so they stimulate muscle movement, decreasing constipation
How can soluble fibre increase health and decrease disease risk
decrease cardiovascular disease risk by lowering blood cholesterol
What is the function of a-amylase in the mouth
breaks down a-1,4 glycosidic bonds
What sugars are resistant to a-amylase
cellulose and lactose
What inactivates a-amylase digestion
in the stomach, pH drops and a-amylase is inactivated
How does a-amylase continue digestion in the small intestine
secreted from the pancreas and activated again in small intestine due to neutral pH
What is the other name for isomaltase and what is its function
alpha-dextrinase
- breaks a-1,6 linkages
What is the other name for invertase and what is its function
sucrase
- breaks sucrose down
What is maltase and what is its function
enzyme - breaks down maltose
What is lactase and what is its function
enzyme - breaks down lactose
What causes lactose intolerance
under normal circumstances lactase breaks down lactose into galactose and glucose
under the circumstance where lactase is not present, lactose is broken down by gut bacteria which causes build up of gases and irritation, leading to the side effects of lactose intolerance
What takes up monosaccharides in the body for absorption
enterocytes
What happens to glucose
small amounts leak back out into lumen from the enterocyte
small amounts diffuse into blood through basolateral membrane
most is transported to blood by GLUT-2
Transport of glucose and galactose from lumen to blood is dependant on…
Na-K ATPase activity
Transport of fructose is facilitated by…
facilitated transport (GLUT 5)
glucose, galactose, and fructose are all sent to bloodstream via…
GLUT 2
What are the main functions of carbs in the body
glucose is the main energy source
carbs spare protein (prevent the breakdown of protein for energy)
carbs prevent ketosis (breakdown of fats for energy)
