Lecture Two: DNA Function & DNA Replication

What aspect of DNA structure allows it to
carry the coded (genetic) information?

The sequence of nucleotide bases along the DNA strand encodes genetic information, with combinations of adenine, thymine, cytosine, and guanine forming the genetic code.

Who is Rosalind Franklin?

A pioneering scientist known for her work on X-ray diffraction images of DNA, which were crucial in understanding its double helix structure.

-identified sugar-phosphate backbone

-nitrogenous bases on the inside

-DNA is a consistent diameter of 2nm

Who is Erwin Chargaff?

A biochemist who discovered the base pairing rules of DNA, stating that the amount of adenine equals thymine, and the amount of cytosine equals guanine.

Who are James Watson & Francis Crick?

They are the scientists who proposed the double helix model of DNA structure, based on Rosalind Franklin's X-ray diffraction images and Chargaff's base pairing rules.

-A binds with T and C binds with G (complementary base pairing)

How do cells make copies of their DNA in order to
pass it from parent to offspring?

Cells replicate their DNA through a process called DNA replication, which involves unwinding the double helix and using each strand as a template to synthesize new complementary strands.

How is DNA replicated in a cell?

Through a process where the double helix unwinds, and each original strand serves as a template for the synthesis of new complementary strands by DNA polymerase.

What is the main purpose of DNA replication?

To ensure that each new cell receives an exact copy of the DNA during cell division, allowing genetic information to be passed on from parent to offspring.

What are 2 reasons why DNA would replicate?

To prepare for cell division( carry genetic info), and to repair damaged DNA (wounds)

What enzymes are involved in the DNA Replication

DNA polymerase, helicase, and ligase are involved.

DNA Replication is also known as what?

A semi-conservative model

What is the role of Topoisomerase for DNA Replication?

Unwinds the DNA from that double helix into a straight, antiparallel pattern

What is the role of DNA Polymerase for DNA Replication

Synthesizes a new DNA strand by moving along original DNA strand and placing the complementary base-pairings of each nucleotide. Also forms the covalent bonds between them.

What is the role of the Helicase for DNA Replication?

To separate/open the DNA strands and to break apart the weak hydrogen bonds so the DNA Polymerase can have access to the nucleotides to synthesize new DNA strands.

What is the role of Ligase for DNA Replication?

Joins Okazaki fragments on the lagging strand, sealing the gaps between nucleotides to create a continuous DNA strand.

What is the proofreading in the context of DNA Replication?

The process by which DNA Polymerase checks and corrects errors during DNA synthesis, ensuring that the new DNA strand has the correct sequence and minimizing mutations.

Why is DNA Replication said to be semi-conservative?

Each new DNA molecule consists of one original strand and one newly synthesized strand, preserving half of the original DNA molecule.

What is the role of complementary base pairing for DNA Replication?

Ensures that the correct nucleotides are added during DNA synthesis, allowing the new strand to be an accurate copy of the original template strand.

Describe the importance of hydrogen bonds in DNA Replication?

Crucial in DNA replication as they stabilize the double helix structure and facilitate the specific pairing of complementary nucleotides, allowing for accurate copying of genetic information.

Step One of DNA Replication

Topoisomerase unwinds the DNA, making it accessible to other molecules

Step Two of DNA Replication

DNA Helicase unzips the weak hydrogen bonds to open up the DNA at the ORI; exposing the nucleotides on each strand

Step Three of DNA Replication

DNA Polymerase attaches to the exposed nucleotides and places the first 2 complementary base pairing nucleotides to form new DNA strands on each strand. Also then forms the covalent bonds between them as the DNA Helicase is breaking the hydrogen bonds.

Step Four of DNA Replication

DNA Polymerase moves along the DNA strands in 5’-3’ direction adding new nucleotides to make a new complementary DNA strand in 5’-3’ direction. DNA Polymerase also proofreading the newly synthesized strand to ensure accuracy in base pairing.

Step Five of DNA Replication

DNA Polymerase follows the DNA Helicase as it breaks weak hydrogen bonds; making it the leading strand. The other strand however; the DNA Polymerase has to wait until DNA Helicase opens up more nucleotides; so that strand becomes the lagging strand until it is completed in fragments known as Okazaki fragments.

What’s the difference between leading strand and lagging strand in DNA Replication?

The leading strand is synthesized continuously in the direction of the replication fork, while the lagging strand is synthesized discontinuously in short fragments called Okazaki fragments, away from the replication fork.

Step Six of DNA Replication

DNA Ligase joins Okazaki fragments on the lagging strand, sealing gaps between them and finalizing the continuous DNA strand.

Step Seven of DNA Replication

Once all of the DNA has been replicated, TWO IDENTICAL DNA MOLECULES are produced