Module 7 Molecular Genetics

3.7.2 page 3

Lesson Summary

You will now see how the structure of DNA has lead directly to its ability to be copied and passed on to the new cells during cell division. The double-stranded DNA can unwind and serve as two template strands. New strands of DNA form to compliment these template strands. Two new, identical molecules of DNA result.  Since an original strand of DNA is found in each new DNA molecule, the process is considered semi-conservative.

In this lesson you looked at four important enzymes and how they function in DNA replication. You have learned the difference between the leading and lagging strands, and how elongation differs on each of these strands. Throughout this lesson you were asked to think about where errors could occur, causing mistakes in DNA replication. In Lesson 4, these mistakes will be discussed in more detail. In the next lesson, you will see how the DNA structure codes for, and is used to build proteins that our cells and bodies use in different structures and to fulfill various functions. Do not confuse the process of DNA replication that you have learned about in this lesson with the process of translation to be discussed in Lesson 3.

Glossary

DNA ligase: enzyme that splices together Okazaki fragments during DNA replication of the lagging strand, or sticky ends that have been cut by a restriction endonuclease

DNA polymerase: an enzyme that slips into the space between two strands of DNA during replication to add nucleotides in order to make complementary strands

DNA replication: the process of creating an exact copy of a molecule of DNA

Elongation: the process of joining nucleotides to extend a new strand of DNA; relies on the action of DNA polymerase

Genome: The sum, or all of the DNA carried in an organism’s cells

Lagging Strand: the strand that is replicated in short segments during DNA replication

Leading strand: that strand that is replicated continuously in DNA replication

Okazaki fragments: short nucleotide fragments synthesized during DNA replication of the lagging strand

Primase: enzyme in DNA replication that forms a primer which is used as a starting point for the elongation of nucleotide chains

Replication bubble: oval-shaped, unwound area within a DNA molecule that is being replicated

Replication fork: during DNA replication, Y-shaped points at which the DNA helix is unwound and new strands develop

Replication Origin: specific nucleotide sequence where replication begins

RNA primer: short strand of RNA that is complementary to a DNA template and serves as a starting point for the attachment of new nucleotides

Semi-conservative: term used to describe replication where each new molecule of DNA contains one strand of the original complementary DNA, and one new strand, conserving half of the original molecule

Termination: the completion of the new DNA strands and the dismantling of the replication machine