DNA Replication Overview and Steps

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Questions and Answers

Match the following scientists with their primary discoveries related to DNA.

Griffith = Demonstrated that genetic material could be transferred between bacteria through transformation. Avery, McCarty, and MacLeod = Identified DNA as the transforming principle, disproving the protein hypothesis. Hershey and Chase = Confirmed DNA as the genetic material using bacteriophages and radioactive labeling. Wilkins and Franklin = Used X-ray diffraction to deduce DNA's helical structure. Watson and Crick = Proposed the double helix model of DNA, incorporating Chargaff's rules and base pairing.

Which of the following describes the process by which DNA replicates?

Conservative replication: The original DNA molecule remains intact, and a completely new copy is created.

Dispersive replication: The original DNA molecule is broken into fragments, and each fragment is replicated, resulting in a mixture of old and new DNA in the daughter molecules.

Semiconservative replication: Each daughter DNA molecule contains one original strand and one newly synthesized strand. (correct)

What are the four nitrogenous bases found in DNA?

Adenine, guanine, cytosine, and thymine.

Which of these is NOT a component of a nucleotide?

Amino acid Signup and view all the answers

DNA polymerase can synthesize a new DNA strand in both the 5' to 3' and the 3' to 5' directions.

False Signup and view all the answers

What is the main function of DNA polymerase III in DNA replication?

Adding nucleotides to the new DNA strand Signup and view all the answers

Which enzyme is responsible for creating RNA primers during DNA replication?

Primase Signup and view all the answers

What are the short, newly synthesized DNA fragments on the lagging strand called?

Okazaki fragments Signup and view all the answers

The enzyme ______ removes torsional strain that builds up ahead of the replication fork during DNA unwinding.

topoisomerase Signup and view all the answers

What is the purpose of telomeres?

They protect the ends of chromosomes from degradation and prevent the loss of genetic information during DNA replication. Signup and view all the answers

Which of the following is TRUE regarding Hayflick's Limit?

It refers to the maximum number of times a normal human cell can divide before senescence. Signup and view all the answers

Which of the following enzymes is NOT directly involved in DNA replication?

RNA polymerase Signup and view all the answers

Which of these is a key characteristic of DNA replication?

It is bidirectional, proceeding in both directions from the origin of replication. Signup and view all the answers

The lagging strand is synthesized continuously in the 5′ to 3′ direction.

False Signup and view all the answers

What is the function of DNA ligase in DNA replication?

DNA ligase seals the gaps between the newly synthesized Okazaki fragments on the lagging strand, creating a continuous DNA molecule. Signup and view all the answers

Study Notes

DNA Replication - Overview

DNA replication is the process of creating two identical DNA molecules from one original DNA molecule.
This process crucial for cell division and heredity.

DNA Replication - Steps

DNA replication begins at specific sites called origins of replication.
The double helix unwinds and unzips.
Each strand serves as a template for a new strand.
Nucleotides are added according to complementary base pairing (A with T, and G with C).
DNA polymerase adds nucleotides to the 3' end of the new strand, always in the 5' to 3' direction.
The leading strand is synthesized continuously in the 5' to 3' direction.
The lagging strand is synthesized discontinuously in short fragments (Okazaki fragments) in the 5' to 3' direction.
Okazaki fragments are joined together by DNA ligase.

Replication Components/Enzymes

Helicase: unwinds the DNA double helix
Topoisomerase (gyrase): relieves strain in the DNA molecule ahead of the replication fork.
Single-stranded binding proteins (SSBs): stabilize the single-stranded DNA during replication.
Primase: synthesizes RNA primers.
DNA polymerase III: adds nucleotides to the 3' end of the growing DNA strand.
DNA polymerase I: removes RNA primers and replaces them with DNA.
DNA ligase: joins Okazaki fragments.

DNA Replication Errors

Errors during DNA replication can occur, but are typically corrected by mechanisms such as proofreading.
Proofreading: DNA Polymerase III can identify and correct errors to ensure accurate DNA replication (errors ~1 in 1,000,000).
DNA repair mechanisms: specialized proteins that scan the newly synthesized DNA and repair any missed errors by DNA Polymerase III.

Telomeres

Telomeres are repetitive sequences of DNA located at the ends of linear chromosomes.
Telomeres protect the chromosomes from degradation and fusion.
Telomeres shorten during each round of replication, leading to cellular senescence.
Telomerase is an enzyme that can extend telomeres, preventing their shortening. This is present in germ cells, stem cells but not most somatic cells which undergo mitosis without telomerase.

DNA Packaging

DNA is packaged into chromosomes as chromatin.
Nucleosomes form by wrapping DNA around histone proteins.

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Description

This quiz covers the essential processes and steps involved in DNA replication. Understand the roles of key enzymes and the mechanisms behind strand synthesis, including leading and lagging strands. Test your knowledge on this fundamental biological process crucial for cell division and heredity.