Download Smooth vs wrinkled peas

Smooth vs wrinkled peas
R – Round
r – wrinkled
During Seed development
R_
x
rr
Enzyme converts
Sugar to starch.
Defective enzyme
inefficient conversion
of sugar to starch.
No sugar so no excess H2O
taken up as seed develops.
Sugar accumulates,
Water taken up as seed
develops.
When seed dries out, smooth.
When seed dries out,
wrinkled.
Starch is made up of amylopectin and amylose.
Starch is how plants store glucose, (we store it as glycogen).
Both are polymers of glucose.
Amylopectin:
- Insoluble in water.
- Highly branched, 2000 to 200,000 glucose units.
- Glucose units linked in linear way with branching every 24-30 glucose
units.
Amylose:
- Insoluble in water.
- Helix structure, 300 to 3000 glucose units.
- Hard to digest but takes up less space so preferred.
- Iodine molecules fit inside helical structure and bind, causing it to
absorb certain wavelengths of light to show as a blue-black color.
Starch doesn't absorb water osmotically as much as sugar does.
The real difference is the concentration of osmotically active
particles.
The difference between the peas is in a gene for an enzyme that
polymerizes monosaccharides into polysaccharides. In the smooth
peas, the enzyme is expressed normally, and the enzyme makes the
sugar into starch at a rapid rate. As a result, most of the sugar in the
pea is converted into starch early on. This results in large starch
granules. That means that there are fewer osmotically active
particles, and the seed (the pea) absorbs less water osmotically from
the parent plant while it is developing in the pod. Having absorbed less
water in development, the seed has less to lose when dried and its
seed coat is smooth in the dried state because less volume is lost.
In the wrinkled pea, there is a recessive mutation in the same gene
where the enzyme that polymerizes sugar into starch is defective. As
a result, there is an accumulation of sugar in the seed (therefore
smaller starch granules), and more water is accumulated osmotically
by the sugar. The seed, while in the pod, absorbs more water and
swells to a greater size. When dried, there is more water volume to
be lost. The seed coat, having been stretched to a greater size
initially, falls into wrinkles when the seed dries.