Lecture 5

Question 1

What are carbohydrates divided into?

Answer 1

Simple carbs and complex carbs

Question 2

What are simple carbs divided into?

Answer 2

Monosaccharides and disaccharides

Question 3

What are some characteristics of monosaccharides?

Answer 3

• most common is glucose
• naturally occurring
• cannot be hydrolyzed into a smaller unit
• considered a reducing sugar when the anomeric carbon is free

Question 4

What are some characteristics of disaccharides?

Answer 4

• most common is sucrose
• two monosaccharides joined by an acetyl bond (glycosidic bond), formed between two hydroxyl groups, a glycosidic bond can also be alpha or beta
• configuration of the Oh group on the anomeric carbon determines whether the disaccharide is alpha or beta

Question 5

What are complex carbs divided into?

Answer 5

Oligosaccharides and polysaccharides

Question 6

What is a characteristic of oligosaccharides?

Answer 6

short chain monosaccharides

Question 7

What are some characteristics of polysaccharides?

Answer 7

• long-chain monosaccharides
• homo and heteropolysaccharides
• starch (amylose and amylopectin) is rich in plants
• glycogen (animal)
• cellulose (plant)

Question 8

What are monosaccharides divided into?

Answer 8

Triose
Pentose
Hexose

Question 9

What are some characteristics of triose?

Answer 9

• metabolite of glucose
• 3 carbon monosaccharides
• not dietary

Question 10

What are some characteristics of pentose?

Answer 10

• components of dna and rna
• 5 carbon monosaccharides

Question 11

What are some characteristics of hexose?

Answer 11

• nutritionally the most important
• 6 carbon monosaccharides

Question 12

What is stereoisomerism?

Answer 12

When two molecules have the same molecular formula and sequence but differ in 3D space due to chiral carbon atoms (L and D isoforms)

Question 13

What are the two different types of stereoisomers?

Answer 13

Enantiomers (mirror image)
Diastereomers (not a mirror)

Question 14

What is an aldose?

Answer 14

a monosaccharide with a carbon backbone with a carbonyl group on the endmost carbon

Question 15

Where does counting for naming monosaccharides begin for aldose?

Answer 15

counting begins at the anomeric carbon for aldose

Question 16

How do we determine a D vs an L stereoisomer?

Answer 16

Determined by the OH group on the highest chiral carbon
OH on the right = D
OH on the left = L

Question 17

What is a chiral carbon?

Answer 17

A carbon that is bound to four other atoms

Question 18

How to determine the number of stereoisomers for a molecule?

Answer 18

2n (where n = # of chiral carbons)

Question 19

Why are D-monosaccharides important?

Answer 19

Nutritionally important because digestive enzymes are stereospecific for D sugars

Question 20

What is a hemiacetal?

Answer 20

made from an aldose

Question 21

What is a hemiketal?

Answer 21

made from a ketose

Question 22

What are the rules for whats up and down in the haworth model?

Answer 22

1. non-acetyl/non-ketal CH2OH always points up
2. hydroxyl (-OH) groups
   if its right in the fischer, its below in the haworth
   if its left in the fischer, its above in the haworth
3. hemiacetal (alpha or beta)
   alpha has the -OH group pointing down
   beta has the -OH group pointing up

Question 23

LAB vs RBA?

Answer 23

LeftAboveBeta
RightBelowAlpha

Question 24

What is an aldose?

Answer 24

H-C=O

Question 25

What is a ketose?

Answer 25

R-C-R " O

Question 26

What are polysaccharides divided into?

Answer 26

Homopolysaccharides - more abundant in food Heterpolysaccharides

Question 27

What is the advantage of branching in polysaccharides?

Answer 27

allows structure to be compact, elasticity, and energy, more ends to cleave more glucose

Question 28

What are the branching characteristics of amylose, amylopectin and glycogen

Answer 28

Amylose - no branching Amylopectin - alpha 1-6 and alpha 1-4 bonds cause branching Glycogen - lots of branching

Question 29

What is dietary fibre?

Answer 29

- non-digestible complex CHO - structural part of plants - divided into insoluble and soluble fibres

Question 30

What are three insoluble fibres?

Answer 30

cellulose lignin hemicellulose

Question 31

What are three soluble fibres

Answer 31

pectins gums mucilages

Question 32

What are some solubility characteristics of insoluble vs soluble fibre?

Answer 32

Insoluble: - remains intact through intestinal tract (doesn't dissolve in water) - reduces transit time - increases fecal bulk (more bowel movement) Soluble: - forms gel (does dissolve in water) - delays gastric emptying, increases transit time - slows down the rate of nutrient absorption and goes slower through the intestine

Question 33

Why can't digest dietary fibre?

Answer 33

we lack enzymes needed to break down dietary fibre (beta bonds can't be broken by us)

Question 34

What are some characteristics of cellulose?

Answer 34

- both a dietary fibre (naturally occurring in a food) and functional fibre (naturally occurring fibre that is added to a food that normally doesn't have any cellulose) - homopolysaccharide of beta 1-4 glucose units in a linear chain - poorly fermented by human gut bacteria (because humans generally lack cellulose fermenting microbes in their gut microbiome (methanogens)) - rich in brain, legumes, nuts, peas, root vegetables and seeds

Question 35

What are some characteristics of hemicellulose?

Answer 35

- heteropolysaccharide that varies between plants - a mixture of alpha and beta glycosidic linkages (partly broken down) - can contain both pentoses and hexoses (xylose is the most common monosaccharide in hemicellulose) - exists as both branched and linear structures - the solubility and fermentability of hemicellulose depends on the sugar composition - found in bran, whole grains, nuts and some vegetables/fruits

Question 36

What are some characteristics of pectin?

Answer 36

- both a dietary and functional fibre - heterogeneous polysaccharide - part of the primary cell wall of plants - backbone of unbranched alpha 1-4 linked-D galacturonic acid (able to be broken down) - stable of low pH - highly fermented by gut bacteria (considered to be a good bulking agent in animal feeds) - rich in fruits, such as apples, oranges, lemons and grapefruit

Question 37

What are some characteristics of resistant starch?

Answer 37

- four main types, termed RS1 - 4 (found in different foods) - typically found in plant cell walls - resistant to amylase activity - conveys some advantages of both soluble and insoluble fibres (green banana has resistant starch)

Question 38

What are the health benefits of fibre?

Answer 38

- maintains function and health of the gut - lower constipation (insoluble fibre) - stimulates muscle contraction to break down (push fecal contest through GIT) - decreases risk of bacterial infections - higher satiety (soluble fibre) - delays gastric emptying - slows down nutrient uptake

Question 39

How can soluble fibre decrease cardiovascular disease risk?

Answer 39

- by lowering blood cholesterol removes cholesterol from stomach and into intestine (absorbs it), only about 10% of cholesterol, mostly reduces LDL cholesterol

Question 40

Where are the three places that carbohydrate digestion takes place in the body?

Answer 40

Mouth Stomach Small Intestine

Question 41

What occurs in the mouth for carbohydrate digestion?

Answer 41

- alpha amylase (salivary) breaks down an alpha 1,4-glycosidic bonds - very specific - produces only a few monosaccharides - cellulose and lactose are resistant, as are alpha 1,6 bonds

Question 42

What occurs in the stomach for carbohydrate digestion?

Answer 42

- alpha amylase digestion continues until pH drops, then enzyme is inactivated by HCl stomach acid - at this point, the pool of dietary CHO consists if small polysaccharides and maltose

Question 43

What occurs in the small intestine for carbohydrate digestion?

Answer 43

- alpha amylase (secreted from the pancreas) - active at a neutral pH - alpha 1,6 bonds are resistant and eventually produce isomaltose

Question 44

What are the four enzymes that function at the brush border?

Answer 44

Maltase - breaks maltose into two glucose Alpha dextrinase (breaks down alpha 1,6 glycosidic bonds) - (also known as isomaltase) breaks isomaltose into two glucose Invertase (also known as sucrase) - breaks sucrose into glucose and fructose Lactase - breaks lactose into glucose and galactose

Question 45

What is the function of the enzymes at the brush border?

Answer 45

enzymes break disaccharides at brush border to be absorbed by epithelial cells

Question 46

What happens to the lactose in the large intestine when a person is lactose intolerant?

Answer 46

Normal - lactose is broken down into glucose and galactose by lactase Intolerance - Lacks lactase, therefore lactose is not broken down and becomes bacteria which is fermented, this causes gases and irritation

Question 47

What is the process of monosaccharides absorption in the intestine?

Answer 47

Glucose and Na+, Cl- and H2O can enter the blood from the intestinal lumen in multiple ways. Firstly, they can be transported through enterocytes (intestinal cells) through SGLT1 (sodium glucose transport 1), which will pass them down to glucose shuttle or NaK atpase shuttle, this process doesn't require ATP. Secondly some molecules can go through the sides of the epithelial cells. This process works on a concentration gradient, meaning it doesn't require ATP

Question 48

What are some characteristics of monosaccharide absorption through the intestine into the blood?

Answer 48

- very efficient - nearly all monosaccharides are taken up by enterocytes - what happens to the glucose them: small amounts leak back into the intestinal lumen, small amount diffuse into blood through the basolateral membrane, majority is transported into blood through GLUT2 - transport of glucose and galactose from lumen into blood is dependent on basolateral Na-K ATPase activity - in contrast, fructose taken up by facilitated transport

Question 49

How do glucose, galactose and fructose enter the blood?

Answer 49

basolateral GLUT2

Question 50

What are the three factors of a nutrient that determine the transport mechanism that is used?

Answer 50

1. solubility 2. concentration gradient 3. molecular size

Question 51

What are the three functions of carbohydrates in the body?

Answer 51

- glucose is the primary source of energy for cells (essential for proper functioning of cells in the CNS and RBC) - carbohydrates spare protein - prevents breakdown of protein for energy - allows protein to concentrate on building, repairing and maintaining body tissue - carbohydrates prevent ketosis - when carbs are limited, fats are broken down for energy, this leads to ketone body prod., causing high acidity