Module 04 - Introduction to Carbohydrates and Carbohydrate Digestion (Section 01)

Question 1

What are the 5 main cellular functions of Carbohydrates?

Answer 1

1. Provide energy in the diet
2. Provide a storage form of energy (glycogen, starch)
3. Form of componenets of mammalian cell membranes
4. Comprise the cell wall in plants and bacteria
5. Form components of insect chitin exoskeleton

Question 2

Monosaccharides: 3 Carbon generic name & example?

Answer 2

triose, glyceraldehyde

Question 3

Monosaccharides: 4 Carbon generic name & example?

Answer 3

tetrose, erythrose

Question 4

Monosaccharides: 5 Carbon generic name & example?

Answer 4

pentose, ribose

Question 5

Monosaccharides: 6 Carbon generic name & example?

Answer 5

hexose, glucose

Question 6

Monosaccharides: 7 Carbon generic name & example?

Answer 6

heptose, sedoheptulose

Question 7

Monosaccharides: 9 Carbon generic name & example?

Answer 7

nonose, neuraminic acid

Question 8

What are Aldoses?

Answer 8

contain an aldehyde which has a hydrogen , R group, and =O attached to the carbon

Question 9

What are Ketoses?

Answer 9

contain a keto group, which has 2 other carbons attached to the C and =O

Question 10

How do monosaccharides form their ring?

Answer 10

the aldehyde or keto group react with an alcohol on the same molecule, closing the molecule into a ring

Question 11

What happens to the carbonyl carbon (C1) when a monosaccharide forms its ring structure? What does the position of
the hydroxyl determine?

Answer 11

it becomes the anomeric carbon, which is a stereocentre; the position of the hydroxyl on the anomeric carbon determines whether the molecule is in the alpha (down) or beta (up) conformation

Question 12

What is a Stereocentre? (aka chiral centre)

Answer 12

an atom with three or more different attachments where interchanging of two of these attachments leads to another stereoisomer

Question 13

How many monosaccharides does a Disaccharide have? What are some examples of Disaccharides?

Answer 13

• two
• lactose, sucrose, maltose

Question 14

How many monosaccharides does a Oligosaccharide have?

Answer 14

3-10

Question 15

How many monosaccharides does a Polysaccharide have?

Answer 15

10+
- can be 100s sugars long

Question 16

How many types of sugar does a Homopolysaccharide have? What is an example of a Homopolysaccharide?

Answer 16

• one
• glycogen

Question 17

How many types of monosaccharides does a Heteropolysaccharide have?

Answer 17

• more than one

Question 18

What is a Complex Carbohydrate?

Answer 18

sugars that are attached to non-carbohydrate stuctures by glycosidic bonds

Question 19

What is a Glycosyl Residue?

Answer 19

• the sugar that participates in the complex carbohydrate glycosidic bond

Question 20

What are sugars found to bind to? (4)

Answer 20

1. purine/pyrimidine bases in nucleotides
2. aromatic rings in steroids and bilirubin
3. proteins to form glycoproteins
4. lipids to form glycolipids

Question 21

What is the bond called when it binds to and NH2 group? What amino acid is used for this bond?

Answer 21

• N-glycoside
• asparagine

Question 22

What is the bond called when it binds to and OH group? What two amino acids are used for this bond?

Answer 22

• O-glycoside
• serine or threonine

Question 23

What is an Isomer? Give examples

Answer 23

• compounds that have the same chemical formula but different structures
• glucose, mannose, galactose, fructose (C6H12O6)

Question 24

What is an Epimer? Give examples

Answer 24

• compounds that differ in configuration at one specific carbon atom
• type of isomer
• e.g. glucose and mannose (C-2)

Question 25

What is an Enantiomer?

Answer 25

- structures that are mirror images of each other (D- or L- conformations) - type of isomer

Question 26

What is a Hydrolysis Reaction?

Answer 26

a reaction where a molecule of water is added or consumed

Question 27

What is Carbohydrate Digestion? Where does it occur?

Answer 27

- the process by which the body breaks down food into usable subunits - the mouth and small intestine

Question 28

What is released during chewing at the beginning of carbohydrate digestion? What does this do?

Answer 28

- alpha-amylase is released by the salivary glands - begins to break apart the polysaccharide starch by cleaving alpha (1-->4) bonds

Question 29

Why can humans not digest cellulose?

Answer 29

we lack enzymes that can cleave beta-(1-->4) bonds between glucose molecules in the polysaccharide

Question 30

Where does digestion of carbohydrates stop? Why?

Answer 30

- in the stomach - acidic environment of the stomach causes amylase to denature

Question 31

What happens in the intestines during carbohydrate digestion?

Answer 31

- pancreatic alpha-amylase continues digestion

Question 32

How is final carbohydrate digestion completed?

Answer 32

- by enzymes made by the intestinal mucosal cells lining the jejunum - these enzymes are specific to a particular disaccharide, referred to as brush border enzymes

Question 33

Where does intestinal absorption occur?

Answer 33

in the duodeum and upper jejunum, where the monosaccharides are passed into the circulatory system to be used by the body

Question 34

What is Lactose Intolerance cause by?

Answer 34

a loss of lactase activity, either through lactase deficiency or through age-dependent loss of lactase activity