The principal cells reabsorb sodium and water from the lumen and secrete potassium ions into the lumen

TLS Online TPP Program

#Id: 3503

#Unit 2. Cellular Organization

Single-base substitutions at the junctions between introns and exons causes an exon to be left out of the product or an intron to be included, or make splicing occur at a different site.

TLS Online TPP Program

#Id: 3504

#Unit 2. Cellular Organization

In multicellular eukaryotes most genes are interrupted, and the introns are usually much longer than exons, so genes are considerably larger than their coding regions.

TLS Online TPP Program

#Id: 3505

#Unit 2. Cellular Organization

Parity rules by Erwin Chargaff

Rule of complementarity (First parity rule)

Rule of Equal amount applies more closely to introns than to exons (Second parity rule)

Cluster rule – Purines in nontemplate strand applies more closely to Exons (Third parity rule)

GC Rule- GC content tends to be greater in exons than in introns (Fourth parity rule

TLS Online TPP Program

#Id: 3506

#Unit 2. Cellular Organization

Potential for secondary (hairpin) structure is found to be greater in introns than exons

TLS Online TPP Program

#Id: 3507

#Unit 2. Cellular Organization

Introns have negative Fold Potential i.e. potential to form stem loop

TLS Online TPP Program

#Id: 3508

#Unit 2. Cellular Organization

Genes that share a common ancestry have similar organizations with conservation of the positions of the introns.