DNA Structure & Replication

These flashcards cover essential concepts and details about DNA structure and replication.

What are the basic components of a DNA nucleotide?

Deoxyribose sugar, phosphate group, and nitrogenous base.

What are the purines found in DNA?

Adenine (A) and Guanine (G).

What are the pyrimidines found in DNA?

Cytosine (C) and Thymine (T).

What type of bond links deoxyribose and phosphate molecules in DNA?

Covalent bonds.

How are the two strands of DNA oriented in relation to each other?

The strands run antiparallel to one another.

What is the significance of the 5' and 3' ends of a DNA strand?

5' end has a phosphate group attached to the fifth carbon of the deoxyribose sugar; 3' end has a hydroxyl group attached to the third carbon.

How can the structure of DNA be described visually?

As a twisted ladder, where the sides are deoxyribose and phosphate and the rungs are nitrogenous base pairs.

During which phase of the cell cycle does DNA replication occur?

S phase of Interphase.

What is the main role of helicase in DNA replication?

To unwind parental DNA at origins of replication.

What do binding proteins do during DNA replication?

Stabilize separated strands and prevent reformation.

What is the process of DNA replication described as?

Semiconservative.

What does semiconservative DNA replication mean?

Each new daughter molecule contains one old strand and one newly synthesized strand.

What enzyme builds a short RNA primer on the DNA template?

Primase.

What direction does DNA polymerase synthesize new DNA strands?

5' to 3' direction.

What are Okazaki fragments?

Short, discontinuous pieces of DNA synthesized on the lagging strand.

What happens to the RNA primer after DNA synthesis?

It is replaced with DNA.

What is the function of ligase in DNA replication?

To seal the sugar-phosphate backbone of Okazaki fragments.

What occurs in the leading strand during DNA replication?

Synthesis proceeds continuously.

How is the lagging strand synthesized during DNA replication?

In short, discontinuous pieces called Okazaki fragments.

What happens at the replication forks during DNA replication?

Helicase unwinds the DNA, creating a bubble for replication.

What type of bonds are formed between complementary nitrogen base pairs?

Hydrogen bonds.

What are the basic steps of DNA replication?

Unwinding by helicase, primer synthesis by primase, nucleotide addition by DNA polymerase, and sealing by ligase.

What is the diameter of the DNA double helix?

2 nm.

What is the diameter of a nucleosome?

10 nm.

What forms a nucleosome?

DNA wrapped around proteins called histones.

What structure compacts DNA within the nucleus?

Nucleosomes form a 30-nm fiber and loops to compact DNA.

What does the antiparallel structure of DNA allow?

It allows complementary base pairing and proper replication.

What is the role of hydrogen bonds in the DNA structure?

They link the base pairs together.

What is a replication bubble?

A region where DNA is being replicated, formed by unwinding of the double helix.

How is the leading strand synthesized compared to the lagging strand?

The leading strand is synthesized continuously, while the lagging strand is synthesized in fragments.

What must each Okazaki fragment have to initiate synthesis?

Its own RNA primer.

What is the result of the DNA replication process?

Two DNA molecules, each with one old and one new strand.

What is one characteristic feature of DNA replication?

It relies on specific base pairing.

What describes the relationship between the old and new strands after replication?

Each daughter DNA molecule contains one old (template) strand and one new strand.

What does complementary base pairing in DNA entail?

A pairs with T and G pairs with C.

What is the appearance of the DNA double helix?

It resembles a twisted ladder.

What stabilizes the single stranded DNA during replication?

Binding proteins.

How many origins of replication are typically involved in DNA replication?

Multiple origins of replication.

Why is it critical for DNA replication to occur quickly?

To ensure rapid cell division and function.

What enzyme proofreads the newly synthesized DNA strands?

DNA polymerase.

What happens to the Okazaki fragments after they are synthesized?

They are linked together by DNA ligase.

In what way do the nucleosomes contribute to DNA compaction?

They help package DNA into a compact structure for fitting inside the nucleus.

What must happen to the RNA primer after DNA synthesis?

It must be replaced by DNA.

What directional challenge does the lagging strand face during replication?

It must be synthesized in short segments due to its antiparallel orientation.

Why do DNA strands need to run antiparallel?

To maintain proper base pairing and replication processes.

What is another name for the DNA synthesis process on the leading strand?

Continuous synthesis.

What component of the DNA molecule indicates the potential for directionality?

The 5' and 3' ends.

What visual analogy is used to describe the structure of DNA?

A twisted ladder.

How is the DNA of eukaryotes organized?

DNA is wrapped around histones, forming nucleosomes.

What characteristic do all the strands of DNA have?

They consist of alternating sugar and phosphate groups.

How does the cell ensure that DNA replication is accurate?

Through proofreading by DNA polymerase and the specificity of base pairing.

What happens to the DNA strands during the unwinding phase?

They separate and expose the bases for replication.

What role does the 3' hydroxyl end play in DNA synthesis?

It is the end where new nucleotides are added.

What facilitates the initial stages of DNA synthesis?

The action of helicase, primase, and DNA polymerases.

What characteristic defines histones in relation to DNA?

They are proteins that help package and organize DNA.

What does DNA replication depend upon?

Specific base pairing with each parental strand serving as a template.

What is a common misconception about the direction of DNA synthesis?

That it can occur in both directions; it can only occur in the 5' to 3' direction.

How would you illustrate the concept of antiparallel DNA strands?

They run in opposite directions, with one strand oriented 5' to 3' and the other 3' to 5'.

Which strands of DNA are synthesized continuously?

The leading strands.

In DNA, what is the consequence of improper base pairing?

It can lead to mutations and inaccuracies in the genetic information.

What is the size comparison between a chromatid and a nucleosome?

A chromatid is 700 nm in diameter, while a nucleosome is 10 nm.

What defines the 'leading' and 'lagging' strands during replication?

Leading is synthesized continuously; lagging is synthesized in fragments.

What major role does the enzyme ligase play during DNA replication?

It joins Okazaki fragments to create a continuous strand.

What structural role do hydrogen bonds play in the double helix of DNA?

They hold the two strands of DNA together at the nitrogen base pairs.

How does DNA polymerase ensure the accuracy of DNA replication?

By proofreading each nucleotide added to the growing strand.

Why does DNA coil into a compact structure in eukaryotic cells?

To fit within the nucleus and allow for efficient organization.

What is the visual metaphor often used to describe the DNA's structure?

A twisted ladder with rungs formed by base pairs.

What do you call the specific locations where DNA replication begins?

Origins of replication.