Structural carbohydrates

Question 1

What are the main functions of carbohydrates?

Answer 1

• main source of energy
• serve as strucutral components

Question 2

Name 3 monsaccharides?

Answer 2

1. Glucose
2. fructose
3. galactose

Question 3

What are the 2 forms that enantiomers can be? For glucose enantiomers, what form occurs in nature?

Answer 3

D or L.

For glucose enantiomers, only the D enantiomer occurs in nature. L has to be synthesised in a lab

Question 4

When glucose is in cyclic form, what is it called?

Answer 4

Glucosepyranose

Question 5

Whats the position of the OH group in alpha and beta forms?

Answer 5

Alpha: The OH is down position

Beta: the OH is in the up position

Question 6

Draw the most stable chain conformation of beta-D-galactopyranose

Answer 6

Question 7

What are structural carbohydrates?

Answer 7

Polysaccharides (glycans) in which monosaccharide units are joined as in these disaccharides

Question 8

What bond joins monosaccharides together?

Answer 8

glycosidic bonds

Question 9

Name some strucutral carbohydrates in plants? (4 of them)

Answer 9

1. cellulose
2. Hemi-cellulose
3. Pectin
4. Agarose

Question 10

Tell me about cellulose and about it’s linkages?

Answer 10

• most abundant polymer on the planet
• major structural components in plants
• organised into microfibrils
• important biofuel
• Linear polymer of D-glucose connected by beta1–> 4

Question 11

What structural carbohydrate is this?

Answer 11

Question 12

What type of sugar is Hemi-cellulose?

Answer 12

pentose sugar

Question 13

Tell me about the structure of Hemi-cellulose ?

Answer 13

• Beta1–>4 polymer of D-xylopyranose
• sidegroups of various carbohydrates such as xylose, mannose, galactose, rhanmose and arabinose
• 500-3000 sugar units per polymer
• good as cross-linking (branched polymer)

Question 14

Tell me about pectins structure and what its used for?

Answer 14

• family of a mixture of branched polysaccharides rich in alpha1-4
• linked D-galacturonic acid
• gelling agent in jams and marmalades

Question 15

Tell me about the structure of Agarose? and where it can be found?

Answer 15

• D-galactose Beta1-4 with galactose
• ether bridge connecting C3 and C6 (some of these molecules also have a sulphate group)
• complex polysaccharide with lots of substitutions
• carbon 6 has an ether bond between the oxygen and CH2

Some plants such as red algae use agarose in their cell walls

Question 16

What structural carbohydrate is this?

Answer 16

Question 17

Name some structural carbohydrates found in animals?

Answer 17

1. chitin
2. Glycosaminoglycans

Question 18

What is chitin the main component of?

Answer 18

the exoskeleton of nearly a million species of arthropod e.g. insects and crabs

Question 19

What is chitin a polymer of and what bonds/linkages does it contains?

Answer 19

• Polymer of N-acetyl glucosamine (glucose with an acetylated amino group at C2)
• contains Beta 1–>4 linkages arranged in extended fibres in a similar way to cellulose

Question 20

What strucutral carbohydrate is this?

Answer 20

Chitin

Question 21

Why is the carbohydrate Glycosaminoglycans important?

Answer 21

its important as a matrix to hold together protein components of skin and connective tissue

Question 22

What is proteoglycan? what is it made of/ its structure?

Answer 22

• it is a structure in cartilage
• made of protein and sugar units

Explanation of the structure in the image:

• dark blue are core proteins
• proteins stem off of the core proteins and then there are carbohydrate polymers coming off of those proteins on the stems

Question 23

What are bacterial cell walls made of?

Answer 23

polysaccharides

Question 24

What is the name of the polysaccharide-peptide complex that bacterial cells walls are made from?

Answer 24

peptidoglycan

Question 25

What are the two classes that bacteria fall into?

Answer 25

Gram positive and gram negative

Question 26

Tell me the properties of gram +ve bacteria

Answer 26

* cytoplasmic lipid membrane * thick peptidoglycan layer * retains the gram stain of dye-iodine complex which shows a blueish colour (helps to identify if gram +ve or -ve)

Question 27

Tell me the properties of gram negative bacteria?

Answer 27

* cytoplasmic membrane * thin peptidoglycan layer * outer membrane containing lipopolysaccharides * **periplasmic space** between cytoplasmic membrane and outer membrane

Question 28

What is peptidoglycan composed of?

Answer 28

alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) linked tetrapeptides of (L-Ala)-(D-Glu)-(L-Lys)-(D-Ala)

Question 29

Does this show a gram +ve or gram -ve bacteria?

Answer 29

gram +ve

Question 30

Does this show a gram +ve or gram -ve bacteria?

Answer 30

gram -ve

Question 31

What's meant by the word **glycan**?

Answer 31

its another term for a polysaccharide

Question 32

Whats **glycosylation?**

Answer 32

The attachment of oligosacchrides (sugars) to proteins

Question 33

Proteins that are glycosylated mostly pass thorugh where?

Answer 33

the secretory pathway (ER and golgi)

Question 34

Do cytoplasmic proteins tend to be glycosylated?

Answer 34

no

Question 35

Whats are the two types of glycosylation? which one is most common? where does each occur?

Answer 35

**1. N-linked** Occurs in the ER modified in golgi most common type **2. O-linked** occurs in golgi

Question 36

What enzyme in golycosylation attaches the N-linked oligosaccharide in the ER?

Answer 36

**oligosaccharyl transferase**

Question 37

What species lipid helps the precursor oligosaccharide in the ER membrane duirng glycosylation?

Answer 37

dolichol

Question 38

in N-linked oligosaccharides, what is it linked to?

Answer 38

The **-NH2 groups of an asparagine residue**

Question 39

What are the three major types of N-glycans?

Answer 39

1. **High-mannose oligosaccharide** 2. **Hybrid oligosaccharide** 3. **Complex oligosaccharide**

Question 40

What are O-linked oligosaccharides linked to?

Answer 40

either serine, threonine or hydroxyproline

Question 41

what type of protein functions does glycosylation lead to?

Answer 41

* helps proteins fold in the ER * help direct proteins to their final destination * helps proteins function

Question 42

What helps proteins fold in the ER?

Answer 42

* **ER chaperones calnexin and calreticulin** bind to oligosaccharide of partially folded proteins to stop aggragate and reain them in the ER

Question 43

What helps to direct proteins to their final destination?

Answer 43

carbohydrate proteins called **lectins** help guide ER to golgi transport and protein sorting in the trans-golgi network

Question 44

What types of protein functions does glycosylation help with?

Answer 44

* improve stability * inprove solubility * cell signalling