Carbohydrates 2: the return

Question 1

Name the 3 important hexoses

Answer 1

Glucose
Galactose
Fructose

Question 2

Name the 3 important disaccharides

Answer 2

Maltose - Glu&Glu
Sucrose - Glu&Fru
Lactose - Glu&Gal

Question 3

What feature makes some sugars be called ‘reducing sugars’

Answer 3

Anomeric C1 can be oxidised

The anomeric carbon is the only residue that can be oxidised on these sugars

Question 4

Which disaccharides are reducing sugars and which aren’t?

Answer 4

Maltose & Lactose are reducing sugars

Sucrose is not a reducing sugar, as it does not have an anomeric C1 that can be oxidised

Question 5

What is the difference between heteropolysaccharides and homopolysaccharides

Answer 5

Homopolysaccharides have one monomeric species

Heteropolysaccharides have more than one monomeric species

Question 6

What 2 types of glucose polymers make up starch

Answer 6

Amylose

Amylopectin

Question 7

What is the difference between amylose and amylopectin

Answer 7

Amylose is straight chained and has a(1-4) linkages

Amylopectin is more abundant, and is branched.
It has a(1-6) bonds every 24 - 30 residues

Question 8

How is glycogen different from starch?

Answer 8

Glycogen is more extensively branched than starch (amylopectin)

Much higher ‘energy density’ than starch

Glycogen is used in animals, starch is used in plants

Question 9

Why is glycogen (and starch) an effective energy storage molecule?

Answer 9

1) Compact - lots of glucose can be stored in a small volume
2) Branched - many non-reducing ends means it can be degraded/synthesised quickly to release/store energy
3) Insoluble - osmotically inactive so does not interfere with osmotic activity

Question 10

What are glycoproteins?

Answer 10

Class of proteins which have carbohydrate groups attached to the polypeptide chain

Question 11

What effects can adding a carbohydrate to a protein have?

Answer 11

Increase solubility

Influence conformation/shape

Protect it from degradation

Act as communication between cells

Question 12

What are Glycosaminoglycans?

also called mucopolysaccharides

Answer 12

Un-branched polymers

Repeating units of hexuronic acid and an amino-sugar, which alternate through the chains

Question 13

Where are glycosaminoglycans mainly found?

What does this indicate about their properties?

Answer 13

Mucus and in synovial joints

Lubricant properties as chains easily slide over each other

Question 14

What are proteoglycans?

Answer 14

A compound consisting of a protein bonded to mucopolysaccharide groups, present especially in connective tissue

Question 15

What is the difference between glycoproteins and proteoglycans?

Answer 15

Glycoproteins are proteins with carbohydrates attached

Proteoglycans are GAG’s with proteins bonded to them

Question 16

What is the group of genetic disorders associated with glycosaminoglycans?

Answer 16

Mucopolysaccharidoses

Absence/malfunction of enzymes required for the breakdown of glycosaminoglycans/mucopolysaccharides

Question 17

What general health problems are associated with mucopolysaccharidoses

Answer 17

GAG’s build up in connective tissue, blood and other tissues

Can cause:

• dementia
• heart problems
• inflammation to joints
• stunting of bones
• damage to endothelial structures

Question 18

Where is most glycogen stored?

Answer 18

Liver and skeletal muscle

Question 19

What is the difference between how glycogen is broken down in the liver and skeletal muscle?

Answer 19

In liver, glycogen is sequentially broken down into Glucose-6-phosphate, which is then dephosphorylated by G-6-phosphotase before entering the blood

In skeletal muscle, there is no G-6-phosphotase, so after glycogen is broken down to G-6-P, it undergoes glycolysis (substrate level phosphorylation) and forms lactate

Question 20

What disease is characterised by Glucose-6-phosphotase deficiency in the liver, kidney and intestines

This disease shows symptoms such as high liver [glycogen], fasting hypoglycaemia and lacticacidaemia (high blood [lactate])?

Answer 20

Von Gierke’s disease

Question 21

What disease is characterised by Skeletal muscle phosphorylase deficiency

This disease will show symptoms in early adulthood, with high muscle [glycogen], weakness & cramps and no blood [glucose] increase after exercise?

Answer 21

McArdle’s disease

Question 22

What is glycolysis?

Answer 22

Sequential, cellular, anaerobic degradation of glucose, to produce pyruvic/lactic acid, yielding a relatively small amount of ATP

Question 23

What is the net energy product of glycolysis?

Answer 23

2 ATP and 2 NADH per glucose molecule

Question 24

What is redox balance, and why is it necessary in glycolysis?

Answer 24

NAD+ is necessary in glycolysis, but is limited in cells

Glycolysis uses up NAD+

All fates of pyruvate, produced from glycolysis will produce NAD+, thus regenerating it at the same rate that it is used up

Therefore, there is no net change in the amount of NAD+

Question 25

What are the two main fates of pyruvate produced from glycogen?

Answer 25

Aerobic conditions = conversion to Acetyl CoA then entry to Citric acid cycle

Anaerobic conditions = entry to Cori cycle = lactate

Question 26

What process converts Lactate to glucose?

Answer 26

Gluconeogenesis

Question 27

What is the Cori cycle?

Answer 27

Metabolic pathway in which lactate produced by anaerobic glycolysis in the muscles moves to the liver and is converted to glucose, which then returns to the muscles and is metabolised

Question 28

In what conditions would the Cori cycle be relied upon?

Answer 28

Intense exercise such as sprinting

The body can’t supply cells with enough oxygen for oxidative phosphorylation

Question 29

Where does gluconeogenesis take place?

Answer 29

Liver

Question 30

What is gluconeogensis?

Answer 30

Metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids

Question 31

What is the purpose of the ‘side step reactions’ in gluconeogenesis?

Answer 31

Avoids the irreversible reactions that take place in glycolysis

Question 32

What is the basic sequence of molecules in gluconeogenesis

Answer 32

Pyruvate 
Oxaloacetate 
PEP
G-3-P 
(DHAP)
F-1,6-P
G-6-P
Glucose

Question 33

What is the basic sequence of molecule products in glycolysis?

Answer 33

Glucose 
G-6-P
F-1,6-P
(DHAP)
G-3-P
PEP
Pyruvate

Question 34

In gluconeogenesis, where does the first side step reaction, in which Pyruvate is converted to PEP, largely take place?

Answer 34

Mitochondria

In the liver

Question 35

What is the pentose phosphate pathway?

Answer 35

Metabolic pathway which generates NADPH and pentose sugars, precursors for DNA/RNA synthesis from glucose

Question 36

What are the two phases of the pentose phosphate pathway?

Answer 36

Oxidative, irreversible phase: generates NADPH

Non-oxidative, reversible phase: generates precursors for nucleotides

Question 37

The pentose phosphate pathway produces NADPH

What is this used for?

Answer 37

‘Provides energy’ for fatty acid synthesis (anabolism)

Question 38

Describe how being drunk would inhibit gluconeogenesis

Answer 38

When the body breaks down and processes a lot of ethanol, the amount of NAD+ in your body drops

This leaves very little NAD+ available for gluconeogenesis

This means that gluconeogenesis cant take place, which can lead to hypoglycaemia and lacticacidaemia

Question 39

What are the 2 anabolic pathways in this brainscape

Answer 39

Gluconeogenesis

Pentose phosphate pathway - although this has some catabolic stages