unit 2 cc7

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Questions and Answers

What are the three main types of DNA polymerases?

DNA polymerase I, DNA polymerase II, and DNA polymerase III.

What is the main function of DNA polymerase I?

DNA repair and replication in prokaryotes.

In which process is DNA polymerase II involved?

DNA repair in eukaryotes.

Which enzyme is responsible for DNA replication in both prokaryotes and eukaryotes?

DNA polymerase III. Signup and view all the answers

What is the function of DNA ligase?

Sealing the nicks in the sugar-phosphate backbone of DNA. Signup and view all the answers

What is the role of primase in DNA replication?

Synthesizing short RNA primers that provide a 3' hydroxyl group to which DNA polymerase can add nucleotides. Signup and view all the answers

What is the function of telomerase?

Maintaining the ends of chromosomes (telomeres) and essential for the long-term survival of cells. Signup and view all the answers

Name three models of DNA replication mentioned in the text.

Rolling circle replication, D-loop (mitochondrial) replication, and O(theta) mode of replication. Signup and view all the answers

Describe rolling circle replication.

Type of replication used by some viruses where a single strand of DNA is circularized and replicated continuously. Signup and view all the answers

Explain D-loop (mitochondrial) replication.

Type of replication used by mitochondria where a strand of mitochondrial DNA invades a strand of circular DNA and displaces it, serving as a template for the synthesis of a new DNA strand. Signup and view all the answers

What is O(theta) mode of replication?

Type of replication used by some bacteria, where two replication forks converge at a specific site on the chromosome, resulting in a structure resembling the Greek letter theta (Θ). Signup and view all the answers

Name two accessory proteins involved in DNA replication and their functions.

Helicases: unwind the double helix of DNA. Single-strand binding proteins (SSBs): bind to single-stranded DNA and prevent it from renaturing. Signup and view all the answers

Explain the process of DNA replication.

DNA replication is the process of copying the DNA molecule to produce two identical daughter molecules. It is a bidirectional process where replication forks move in opposite directions from a replication origin, and it is semi-conservative, meaning each daughter molecule contains one strand of the original DNA molecule and one newly synthesized strand. The leading strand is synthesized continuously, while the lagging strand is synthesized in short fragments called Okazaki fragments. Signup and view all the answers

What is the difference between bidirectional and unidirectional DNA replication?

Bidirectional DNA replication involves replication forks moving in opposite directions from a replication origin, while unidirectional replication only involves replication in one direction. Signup and view all the answers

What is semi-conservative replication?

Semi-conservative replication is a process in which each daughter molecule of DNA contains one strand of the original DNA molecule and one newly synthesized strand. Signup and view all the answers

Describe semi-discontinuous replication.

Semi-discontinuous replication involves the leading strand being synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized in short fragments called Okazaki fragments in the 3' to 5' direction. Signup and view all the answers

What are replication forks?

Replication forks are Y-shaped structures that form during DNA replication and move in opposite directions from a replication origin. Signup and view all the answers

What is the leading strand in DNA replication?

The leading strand is the strand that is synthesized continuously in the 5' to 3' direction during DNA replication. Signup and view all the answers

What are Okazaki fragments?

Okazaki fragments are short fragments of DNA synthesized on the lagging strand during DNA replication. Signup and view all the answers

What is the role of a replication origin in DNA replication?

A replication origin is a specific sequence of DNA that marks the start of DNA replication and serves as the site where replication forks begin to form. Signup and view all the answers

Explain the term 'replication origin' in the context of DNA replication.

A replication origin is a specific sequence of DNA that marks the start of DNA replication, where replication forks begin to form and move in opposite directions. Signup and view all the answers

How does DNA replication differ in prokaryotes and eukaryotes?

While the basic process of DNA replication is similar in prokaryotes and eukaryotes, there are differences in the organization of the DNA and the presence of certain proteins and enzymes involved in the process. Signup and view all the answers

What is the significance of DNA replication being a bidirectional process?

The bidirectional nature of DNA replication allows for the efficient and timely synthesis of the entire DNA molecule, as replication can proceed in two directions simultaneously. Signup and view all the answers

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Study Notes

DNA Replication

There are three main types of DNA polymerases: DNA polymerase I, DNA polymerase II, and DNA polymerase III.

DNA Polymerase Functions

DNA polymerase I is responsible for repairing DNA.
DNA polymerase II is involved in leading strand synthesis during DNA replication.
DNA polymerase III is responsible for DNA replication in both prokaryotes and eukaryotes.

Enzymes in DNA Replication

DNA ligase seals Okazaki fragments together in lagging strand synthesis.
Primase synthesizes RNA primers for DNA replication.
Telomerase adds telomeres to the ends of chromosomes.

Models of DNA Replication

Three models of DNA replication are:
- Theta replication
- Rolling circle replication
- D-loop (mitochondrial) replication

DNA Replication Process

Leading strand synthesis is continuous in the 5' to 3' direction.
Lagging strand synthesis is discontinuous in short Okazaki fragments.
Replication forks are the Y-shaped structures formed during DNA replication.
The replication origin is the region where DNA replication initiates.

Accessory Proteins

Helicase unwinds DNA double helix.
Topoisomerase relieves DNA supercoiling during replication.

DNA Replication Characteristics

Semi-conservative replication means each new DNA molecule contains one old strand and one new strand.
Semi-discontinuous replication refers to the combination of continuous leading strand synthesis and discontinuous lagging strand synthesis.
Bidirectional DNA replication occurs in both directions from the origin of replication.
Unidirectional DNA replication occurs in one direction from the origin of replication.

Prokaryotic vs. Eukaryotic DNA Replication

DNA replication differs in prokaryotes and eukaryotes in terms of speed, complexity, and initiation mechanisms.
Bidirectional DNA replication is significant because it allows for faster replication and increased genome stability.

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