Carbohydrates

Question 1

What are carbohydrates

Answer 1

Highly oxidisable
Store potential energy
Major energy source

Question 2

What are the monosaccharides

Answer 2

Glucose
Galactose
Fructose

Question 3

What are disaccharides

Answer 3

Formed from monomers
Linked by glycosidic bonds

Question 4

What are the three important Disaccharides

Answer 4

Maltose
Lactose
Sucrose

Question 5

What is maltose

Answer 5

Breakdown product of starch

Question 6

Between maltose, lactose, sucrose, which are reducing sugars

Answer 6

Maltose and lactose

Question 7

What is the structure of Lactose

Answer 7

Galactose + glucose combined with glycosidic bond

Question 8

What % of our diet carbs is sucrose

Answer 8

25%

Question 9

What are polysaccharides

Answer 9

Polymers of medium-high molecular weight

Question 10

What are the types of polysaccharides

Answer 10

Homopolysaccharides - Single monomer
Heteropolysaccharides - Two or more monomers

Question 11

What are the two types of starch

Answer 11

Amylose - 20-25%, D-glucose residues
Amylopectin - 75-80%, Glycosidic bonds

Question 12

What is glycogen and where is it found

Answer 12

Polymer of glucose
90% in:
Liver - replenishes glucose
Skeletal muscle - Produces ATP

Question 13

What is used to digest carbs in the mouth

Answer 13

Salivary amylase hydrolyses starch

Question 14

What digests starch in the stomach

Answer 14

No digestion

Question 15

What digests starch in the duodenum

Answer 15

Pancreatic amylase

Question 16

What are the final digestions in the Jejunum

Answer 16

Isomaltase - Hydrolyses a1-6 bonds
Glucoamylase- removes glc sequentially
Sucrase -> sucrose
Lactase ->Lactose

Question 17

How is glucose and galactose absorbed

Answer 17

Na+ pump maintains low Na+ content
Allows glucose to be moved into cells
Works when glucose moves against cg

Question 18

How is fructose absorbed

Answer 18

Bind to channel protein GLUT5
Moves down its cg

Question 19

Can Cellulose and Hemicellulose be digested

Answer 19

Nope

Question 20

What happens after glucose is absorbed

Answer 20

Glc diffuses through intestinal cells->blood->liver
Phosphorylated->G-6-P by hepatocytes
G-6-P can’t diffuse out of cell as GLUT transporters no longer recognise it.

Question 21

What are the enzymes for glucose

Answer 21

Glucokinase- liver
Hexokinase- skeletal muscle

Question 22

What is Vmax and Km

Answer 22

High number = efficient enzyme
Low Km = high affinity for substrate

Question 23

What is the Km andVmax for hexo/glucokinase

Answer 23

When blood glc normal - liver doesnt grab all glc
Blood glc high - Liver grabs Glc
High glckinase Vmax - phosphorylates Glc quickly
Hexokinase low Km - tissues grab Glc at low Glc
Hexokinase low Vmax - tissues easily satisfied

Question 24

What does hexokinase and glucokinase convert glucose to

Answer 24

Glucose 6 phosphate

Question 25

Where is glycogen converted

Answer 25

In liver: glycogen->G6P->Glc in blood In skeletal muscle: Glycogen->G6P->lactate and ATP via glycolysis

Question 26

What are steps of synthesis of glycogen

Answer 26

Glycogenin binds Glc from UDP-glc to form 8 glc residues Glycogen synthase extends the chain Chains then broken by glycogen-branching enzyme Re-attached via (a1-6) bonds

Question 27

What are the steps of glycogen degradation?

Answer 27

Glc monomers removed one by one Glc removed by de-branching enzyme Transferase activity of de-branching enzyme removes 3 Glc at a time Attaches them to nearest nonreducing end via (a1→4bond) Glucosidase removes final Glc by breaking(a1→6) linkage Leaves unbranched chain

Question 28

What are the two glycolysis phases

Answer 28

Preparatory phase: 1 Glc passes through 2 molecules of G3P produced Payoff phase: For each Glc 2ATP used in prep phase 4ATP gained in payoff phase

Question 29

What are the irreversable steps of glycolysis

Answer 29

Step 1. Phosphorylation of glucose Glc -> G6P, catalysed by hexokinase Uses 1ATP Step 3. Phosphorylation of F6P -> F1,6-bisP catalysed phosphofructokinase-1 1ATP used Step 10. Transfer of P from PEP to ADP Catalysed - pyruvate kinase 2ATP produced

Question 30

What are the three substances pyruvate can be converted to

Answer 30

Lactate Acteyl COA Ethanol

Question 31

What is the Cori cycle

Answer 31

ATP produced via substrate level phosphorylation Produced lactate Lactate converted to Glc via gluconeogenesis

Question 32

What is the function of gluconeogenesis

Answer 32

4 reactions that sidestep the 3 irreversable glycolysis reactions

Question 33

What are the A and B gluconeogenesis reactions

Answer 33

Pyruvate->Oxaloacetate->malate->Oxaloacetate->PEP Takes place in mitochondria

Question 34

What happens in reaction C

Answer 34

Fructose1,6-bisP->F6P Fructose 1,6 bisphosphatase catalyses this