Chapter 7: 7.1 Carbohydrates

Question 1

What are carbohydrates involved in?

Answer 1

• Postranslational modifications
• Cell recognition

Question 2

What are carbohydrates also referred to as?

Answer 2

Sugars

Question 3

Define:

Monosaccharides

Answer 3

The simplest carbohydrate
* Has the formula: (CH2O)n

Question 4

How are carbohydrates named as?

Answer 4

Named based on the number of carbons they have
* E.x. triose, tetrose, pentose, hexose, heptose…

Question 5

What are aldoses? What are ketoses?

Answer 5

1. Aldoses: Carbohydrates have an aldehyde at C1
2. Ketoses: Carbohydrates have a ketone at C2

• E.x. Ketohexose, aldotriose…

Question 6

In Fischer Projections:

What do L and D represent?

Answer 6

L and D are in reference to the different enantiomers of the sugar structure (asymmetry)

Question 7

In Fischer Projections:

What do enantiomers depend on?

Answer 7

Dependent on the chiral carbon furthest from the carbonyl group

Question 8

In Fischer Projections:

What does it mean that enantiomers are optically active?

Answer 8

Rotate polarized light either to:
* The right (+, D)
* The left (-, L)

Question 9

In Fischer Projections:

What determines the possible number of stereoisomers? State the formula

Answer 9

The number of chiral carbons (x)
* Possible number of stereoisomers = 2^x

Question 10

Describe:

Carbohydrate Cyclization

Answer 10

The hydroxyl group nycleophilically attacks the aldehyde or the ketone (very reactive) forming the ring

Question 11

In carbohydrate cyclization:

What types of rings are formed?

Answer 11

1. Furan (5 membered ring)
2. Pryan (6 membered ring)

Question 12

What types of bonds can be formed in carbohydrate cyclization?

Answer 12

1. Hemiacetal (from aldehyde)
2. Hemiketal (from ketone)

Question 13

In carbohydrate cyclization:

It result in — possible ——-

Answer 13

1. Two
2. Anomers

Question 14

What are the two possible anomers resulting from carbohydrate cyclization?

Answer 14

1. α (E.x. α-D-Glucose)
2. β (E.x. β-D-Glucose)

Question 15

In carbohydrate cyclization:

Which anomer is more stable?

Answer 15

β

Question 16

Define:

Isomers

Answer 16

Same formula, different structures

Question 17

What types of stereoisomers are there?

Answer 17

• Enantiomers
• Diastereoisomers

Question 18

Define:

Enantiomers

Answer 18

Mirror images (not superimposable)

Question 19

Define:

Diastereoisomers

Answer 19

Not mirror images (superimposable)

Question 20

Define:

Anomers

Answer 20

Differs at a new asymmetric carbon in the ring conformation

Question 21

True or False:

Anomers are a type of diastereoisomer

Answer 21

True

Question 22

Define:

Reducing Sugars

Answer 22

Sugars able to act as a reducing agent due to a free aldehyde or free ketone group (all monosaccharides)

Question 23

In reducing sugars:

What are aldehydes converted to?

Answer 23

Converted to carboxylic acids

Question 24

In reducing sugars:

What are ketones converted to?

Answer 24

Tautomerized into aldehydes and then reduced to carboxylic acids

Question 25

# True or False: Disaccharides are reducing sugars

Answer 25

Partially true. Disaccharides are reducing sugars as long as one of the units have an open chain with an aldehyde

Question 26

Is maltose a reducing sugar? Is sucrose a reducing sugar?

Answer 26

1. Maltose is reducing 2. Sucrose is not reducing

Question 27

What modifications are made to make complex carbohydrates?

Answer 27

* Phosphorylation * Methylation * Addition of N-containing groups * Hydroxyl groups removed

Question 28

# Describe: Naming of sugar complexes:

Answer 28

* Monosaccharide = 1 * Disaccharide = 2 * Oligosaccharide = 3-20 * Polysaccharides = 1000s

Question 29

# Describe: Disaccharide formation

Answer 29

Condensation reaction forming a glycosidic bond

Question 30

# In disaccharide formation: What type of glycosidic bonds are there?

Answer 30

1. O-glycosidic bond 2. N-glycosidic bond

Question 31

# In disaccharide formation: List the linkage to proteins

Answer 31

1. O-linkages (to Ser/Thr) 2. N-linkages (to Asn)

Question 32

# Define: Glycosyltransferase

Answer 32

The enzyme responsible for linking sugars via O-glycosidic bonds

Question 33

How does glycosyltransferase work?

Answer 33

Uses UPD-glucose to attach sugars onto other sugars or proteins

Question 34

# Define: UPD glucose

Answer 34

A high energy sugar nucleotide used by glycosyltransferase

Question 35

------ are cleaved into --------------- via -------

Answer 35

1. Sugars 2. Monosaccharides 3. Enzymes

Question 36

# True or False: Monosaccharides are a source of fuel

Answer 36

True

Question 37

What enzymes are used to cleave sugars into monosaccharides?

Answer 37

Lactase, maltase, sucrase

Question 38

# Explain: Naming Disaccharides

Answer 38

1. Identify N or O linkage 2. Configuration of the first sugar plus the name ending in -yl 3. The number identifiers of the carbons linked together 4. Configuration of the second sugar plus the name ending in -ose

Question 39

What are polysaccharides also referred to as?

Answer 39

Glycans

Question 40

# Describe: Polysaccharides

Answer 40

Consist of 1000s of monosaccharides (linked either linearly or branched)

Question 41

Polysaccharides play roles in...

Answer 41

* Energy storage * Cell structure * Cell recognition

Question 42

# Define: Homopolymers

Answer 42

Polysaccharides made up of the same repeating monosaccharide

Question 43

# Define: Heteropolymers

Answer 43

Polysaccharides made up of different monosaccharide repeats

Question 44

# Define: Glycogen

Answer 44

A energy storage homopolymer with a multibranched structure

Question 45

What is the repeating monosaccharide in glycogen?

Answer 45

Glucose

Question 46

# Describe structure of: Glycogen

Answer 46

Consists of branched glucose units surrounding a glycogenin protein at its core * Chain lengths of 8-12 of linearly linked glucose molecules (α(1-4) glycosidic bonds) with branches forming α(1-6) glycosidic bonds

Question 47

What is starch comprised of?

Answer 47

1. Amylose 2. Amylopectin

Question 48

# Describe structure of: Amylose

Answer 48

Linear linkages of glucose (α(1-4) glycosidic bonds)

Question 49

# Describe structure of: Amylopectin

Answer 49

Linear linkages of glucose (α(1-4) glycosidic bonds) with α(1-6) glycosidic linkages occuring every 30 glucose units

Question 50

# Explain the function of: α-amylase

Answer 50

Cleaves glycogen and starch at random locations yielding maltose and maltotriose

Question 51

What secretes α-amylase?

Answer 51

Pancreas

Question 52

# Explain the function of: β-amylase

Answer 52

Hydrolyzes glucose units in glycogen and starch systematically at non-reducing ends, producing maltose

Question 53

# True or False: β-amylase is produced in the pancreas

Answer 53

False, β-amylase is not produced by mammals

Question 54

# Define: Cellulose

Answer 54

Structural components in plants

Question 55

# Describe the structure of: Cellulose

Answer 55

* Formed by β(1-4) glycosidic linkages * Linear chains * Formula: (C6H10O5)n * More crystalline than starch

Question 56

# True or False: Cellulose is digestible by humans

Answer 56

False, cellulose is not digestible by humans

Question 57

# List: Common monosaccharides to know

Answer 57

1. **Glucose** (Glucopyranose) 2. **Fructose** (Fructofuranose) 3. **Galactose** (Galactopyranose) 4. **Mannose** (Mannopyranose) 5. **Ribose** (Ribofuranose) 6. **Deoxyribose** (Deoxyribofuranose)