1) Amylopectin and glycogen are both branched polysaccharides. Let us say that a

Question

1) Amylopectin and glycogen are both branched polysaccharides. Let us say that a large sample of each polymer was available and each sample was made up of an identical number of glucose monomers. These samples were then each exposed to identical amounts of phosphorylase for a fixed time period. This time was too short for either polysaccharide to be completely degraded, but did allow for glucose monomers to be cleaved from each sample. In a qualitative sense, how do you anticipate that the number of glucose monomers generated from each sample would vary?

More glucose would be released from amylopectin

More glucose would be released from glycogen

Equal amounts of glucose would be released from each sample

Neither sample would allow glucose monomers to be released

2) The enzyme Phosphokinase C (PKC) is activated via a signaling cascade that begins with the action of the enzyme Phospholipase C in a cell membrane. The following chemical entities are involved in this cascade:

i) Ca2+

ii) IP3

iii) Diacylglycerol

Which of these is/are directly involved in binding to PKC?

i)

ii)

iii)

i) and iii)

ii) and iii)

More glucose would be released from amylopectin

More glucose would be released from glycogen

Equal amounts of glucose would be released from each sample

Neither sample would allow glucose monomers to be released

Explanation / Answer

1 (B) More glucose would be released from glycogen

Glycogen is very similar to amylopectin except that it (glycogen) is highly and more frequently branched than amylopectin. Thus, more will be the branches, more will be the glucose units produced. The phosphorylase (glycogen phosphorylase) can only act in straight chains of glucose (glycogenolysis). It needs two more enzymes, the debranching enzyme and alphe-(1,6)-glucosidase, to overcome a branch. As the reaction only involves the phosphorylase enzyme, the glucose units will produced only from the outer branches.

2. (iii)

Hhosphatidyl inositol bisphosphate (PIP2), in the plasma membrane is hydrolysed by phospholipase-C which produces diacylglycerol (DAG) and inositoll,4,5-trisphosphate (IP3). DAG stimulates PKC and IP3 stimulates and Ca2+ release from endoplasmic reticulum. PKC plays important roles in cell growth and differentiation.

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