carbohydrates

Question 1

What are the 3 important monosaccharides?

Answer 1

Glucose
galactose
fructose

Question 2

what are the 3 important disaccharides?

Answer 2

maltose
lactose
sucrose

Question 3

why is maltose known as a reducing sugar?

Answer 3

because the anomeric C1 can be oxidised.

Question 4

sucrose is a reducing sugar; true or false?

Answer 4

False

Question 5

what is the difference between a homopolysaccharide and a heteropolysaccaride?

Answer 5

homopolysaccharide - one monomeric species

heteropolysaccharide - two or more monomer species

Question 6

what two polymers make up starch?

Answer 6

amylose and amylopectin.

Question 7

what is the main difference between amylose and amylopectin?

Answer 7

amylopectin has alpha 1>6 bonds which cause it to be branched.

Question 8

what is the purpose of glycogen?

Answer 8

storage carbohydrate (used to store glucose)

Question 9

why is it beneficial to store glucose in a polymeric form?

Answer 9

compactness - saves space
easy for the polymers to be synthesised or degraded to monomers
polymers are osmotically inactive (as opposed to glucose) - saves energy..

Question 10

what is a glycoprotein?

Answer 10

protein with a carbohydrate covalently attached

Question 11

What are glycosaminoglycans formed from?

Answer 11

Repeating units of hexuronic acid and an amino sugar (unbranched)

Question 12

how are proteoglycans formed?

Answer 12

from Glycosaminoglycans covalently attaching to proteins

Question 13

what are mucopolysaccharidoses?

Answer 13

group of genetic disorders caused by the absence or malfunction of enzymes that are required for the breakdown of glycosaminoglycans. e.g hurler syndrome.

Question 14

what facilitates diffusion of glucose into the epithelial cells of the intestine?

Answer 14

Na+-glucose symporter, which is driven by high extracellular Na+

Question 15

what are disaccharide deficiencies characterised by?

Answer 15

abdominal distension and cramps

Question 16

what is the most common disaccharide deficiency?

Answer 16

lactose intolerance

Question 17

why does lactase deficiency cause disaccharide deficiency symptoms?

Answer 17

undigested lactose is broken down by gut bacteria which causes gas build up and irritant acids
lactose is osmotically active, so it draws water from the gut into the lumen, which causes diahorrea

Question 18

how is glucose “trapped” in the cell?

Answer 18

it is phosphorylated to glucose-6-phosphate.

Question 19

what catalyses conversion of glucose to glucose-6-phosphate?

Answer 19

hexokinase and glucokinase

Question 20

when would glucokinase and hexokinase be used?

Answer 20

glucokinase - when there is a high concentration of glucose

hexokinase - when there is a low concentration of glucose

Question 21

what are 3 fates of G-6-P?

Answer 21

glycolysis
conversion to glycogen for storage
pentose phosphate pathway

Question 22

where is the majority of glycogen in the body stored?

Answer 22

the liver and skeletal muscle.

Question 23

why is G-6-P converted to lactate in skeletal muscle but not in the liver?

Answer 23

skeletal muscle does not have glucose-6-P phosphatase enzyme.

Question 24

how is glycogen synthesised?

Answer 24

glycogenin covalently binds Glc from UDP, forming chains of approx. 8 Glc residues
then glycogen synthase takes over and extends the Glc chains
chains formed by glycogen synthase are then broken by glycogen branching enzyme and are re-attached (alpha 1,6,) bonds to give branching points.

Question 25

how is glycogen degraded (mobilised)?

Answer 25

glucose monomers are removed one at a time from the non reducing ends as glucose-1-phosphate Glc near the branch is removed in a 2-step process by a de-branching enzyme transferase activity of de-branching enzyme removes a set of 3 Glc residues from the branch and attaches them to the nearest non-reducing end via an (alpha 1,4,) bond glucosidase removes. final branched glucose by breaking (alpha 1,6) linkage.

Question 26

How many new molecules of ATP are formed during glycolysis per mol of glucose?

Answer 26

2 ( 4 overall but 2 are used to start the process of glycolysis)

Question 27

what catalyses the conversion of glucose to G-6-P and is this reaction reversible or irreversible?

Answer 27

hexokinase/glucokinase | irreversible

Question 28

what catalyses conversion of G-6-P to F-6-P and is this reaction reversible or irreversible?

Answer 28

Phosphohexose isomerase | reversible

Question 29

what catalyses phosphorylation of F-6-P to F-1,6-bisP and is this reaction reversible or irreversible?

Answer 29

``` PFK-1 (this reaction uses 1 ATP) essentially irreversible (this reaction is the first committed step of glycolysis) ```

Question 30

what catalyses cleavage of F-1,6-bisP and is this reaction reversible or irreversible?

Answer 30

aldolase | readily reversible

Question 31

what catalyses interconversion of triose sugars and is this reaction reversible or irreversible?

Answer 31

triose phosphate isomerase | readily reversible

Question 32

what triose sugar can participate in glycolysis?

Answer 32

glyceraldehyde-3-phosphate (other triose sugar is converted to G-3-P)

Question 33

what catalyses phosphate transfer from 1,3-bisPG to ADP and is this reaction reversible or irreversible?

Answer 33

phosphoglycerate kinase | reversible (due to being coupled to step 6, the oxidation of G-3-P)

Question 34

what catalyses phosphate transfer from PEP to ADP and is this reaction reversible or irreversible?

Answer 34

``` pyruvate kinase essentially irreversible (this reaction also produces pyruvate) ```

Question 35

what steps in glycolysis are irreversible?

Answer 35

1,3,10

Question 36

Why does NAD need to be regenerated?

Answer 36

NAD is required for the reduction of various intermediate metabolites.

Question 37

what are the 3 fates of pyruvate?

Answer 37

conversion to either lactate, acetyl coA or ethanol

Question 38

what is the interaction between breakdown of glucose in skeletal muscle and formation of glucose in the liver?

Answer 38

Cori cycle

Question 39

what catalyses conversion of pyruvate to lactate?

Answer 39

lactate dehydrogenase

Question 40

what catalyses conversion of pyruvate to acetyl coA?

Answer 40

pyruvate dehydrogenase

Question 41

how many "bypass reactions" are there in gluconeogenesis?

Answer 41

4

Question 42

what are the steps for direct conversion of pyruvate to oxaloacetate?

Answer 42

pyruvate>oxaloacetate (within mitochondrion)>malate>oxaloacetate (outside mitochondrion)

Question 43

what enzyme catalyses conversion of pyruvate to oxaloacetate?

Answer 43

pyruvate carboxylase

Question 44

what enzyme catalyses conversion of oxaloacetate to PEP?

Answer 44

PEP carboxykinase