Carbohydrates

Question 1

What kind of bond forms between monosaccharides to form disaccharides/polysaccharides?

Answer 1

Glycosidic bond

Question 2

What differs between aldoses and ketoses?

Answer 2

Aldoses have an aldehyde (CHO) group, ketoses have a ketone (C=O) group.

Question 3

Define enantiomer.

Answer 3

Enantiomer = stereoisomers that are mirror images of each other.

Question 4

Are monosaccharides reducing or oxidising agents? Give an example of a test for the presence of these.

Answer 4

Monosaccharides are reducing agents and can be oxidised by relatively mild oxidising agents. Fehling’s reaction = semi-quantitative test for reducing sugars.

Question 5

Describe the process of gluconeogenesis.

Answer 5

Pyruvate / lactate -> oxaloacetate in the citric acid cycle

-> Phosphoenolpyruvate -> Glucose 6-phosphate

Question 6

Describe the process of glycolysis.

Answer 6

Glucose + 2ATP -> Fructose 1,6-bisphosphate

-> Glyceraldehyde 3-phosphate + 2 phosphate -> 1,3-bisphosphoglycerate

+ NAD+ + 2ADP -> 2 pyruvate (forming 2 ATP molecules)

Question 7

How is Acetyl Co-A produced from pyruvate?

Answer 7

Pyruvate + CoA + NAD+ acetyl CoA + NADH + H+ + CO2

Question 8

How is glycolysis allowed to continue under anaerobic conditions?

Answer 8

Lactate dehydrogenase catalyses formation of lactate from pyruvate, forming NAD+

Question 9

How many molecules of ATP does complete oxidation of glucose produce?

Answer 9

32 molecules of ATP

Question 10

What is the structure and function of starch?

Answer 10

Storage polysaccharide in plant cells - unbranched amylose and branched amylopectin chains.

Question 11

What is the structure and function of glycogen?

Answer 11

Storage in animals (liver and muscle cells) - linear chain of alpha 1,4 and 1,6 linkages.

Question 12

What are the adaptations of glycogen?

Answer 12

Extensively branched = broken down quickly.

More compact than starch.

Question 13

What is the structure and function of cellulose?

Answer 13

Structural in plant cell walls - linear unbranched beta glucose chains.

Question 14

List three functions of information-carrying poly/oligosaccharides.

Answer 14

1. Provide communication between cells and their extracellular surroundings.
2. Label proteins for transport to specific organelles or for destruction.
3. Recognition sites for extracellular signalling molecules (e.g. growth factors/bacteria).

Question 15

What are the functions of the glycocalyx?

Answer 15

Cell-cell recognition and adhesion, blood clotting, immune response, wound healing.

Question 16

Describe proteoglycans.

Answer 16

Found on cell surface or in ECM.

Contain glycosaminoglycan chains attached to Ser residues.

Question 17

Describe glycoproteins.

Answer 17

Found on cell surface or in ECM.

Contain oligosaccharides covalently-linked to Ser, Thr, or Asn residues.

Question 18

Describe glycolipids.

Answer 18

Found on extracellular surface.

Plasma membrane lipids covalently linked to oligosaccharides.

Question 19

Define lectin and state the role of these.

Answer 19

Lectins = proteins that bind carbohydrates.

Cell-cell recognition, signalling and adhesion.

Found on extracellular surface.

Question 20

What are the actions of selectins?

Answer 20

Selectins = family of plasma membrane lectins.

Mediate cell-cell recognition and adhesion in processes, e.g. movement of leukocytes at sites of infection/inflammation.