Molecular Biology Chapter 9
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Questions and Answers

What is one of the practical applications of DNA analysis mentioned?

  • Language translation
  • Climate change research
  • Genealogy tracing (correct)
  • Astrology predictions

Who were the key scientists credited with determining the structure of DNA?

  • Charles Darwin and Alfred Wallace
  • Francis Crick and James Watson (correct)
  • Linus Pauling and Carl Woese
  • Gregory Mendel and Barbara McClintock

In what year was the structure of DNA discovered?

  • 1960
  • 1953 (correct)
  • 1945
  • 1971

What could be analyzed to determine a predisposition to diseases?

<p>DNA (C)</p> Signup and view all the answers

The technology of molecular genetics has impacted our understanding of what aspect of biology?

<p>The history and relationships between living organisms (C)</p> Signup and view all the answers

Which entities typically contain unique DNA sequences?

<p>Human beings and dolphins (B)</p> Signup and view all the answers

What role does DNA play in the context of inheritance?

<p>It is the genetic material passed from parent to offspring. (D)</p> Signup and view all the answers

Which type of organisms was mentioned as having their entire genome sequenced?

<p>Over a thousand species (D)</p> Signup and view all the answers

What distinguishes ribose in RNA from deoxyribose in DNA?

<p>Ribose has a hydroxyl group at the 2' carbon. (A)</p> Signup and view all the answers

Which nitrogenous base is found in RNA but not in DNA?

<p>Uracil (C)</p> Signup and view all the answers

What type of RNA is primarily involved in the synthesis of proteins from DNA?

<p>Messenger RNA (mRNA) (B)</p> Signup and view all the answers

How is the DNA in prokaryotic cells typically organized?

<p>In a single, circular chromosome found in the nucleoid. (B)</p> Signup and view all the answers

What is the role of supercoiling in prokaryotic DNA?

<p>It helps organize DNA to fit within the cellular structure. (D)</p> Signup and view all the answers

What is the main difference between the chromosomes of eukaryotes and prokaryotes?

<p>Eukaryotic chromosomes are located in a well-defined nucleus. (B)</p> Signup and view all the answers

Which of the following statements about the genome size of Escherichia coli is correct?

<p>It extends about 1.6 mm when stretched out. (C)</p> Signup and view all the answers

What packaging strategy do eukaryotes use for their linear DNA molecules?

<p>They create histone-protein complexes. (D)</p> Signup and view all the answers

What is the significance of adenine pairing with thymine and cytosine pairing with guanine in DNA?

<p>It ensures that the two DNA strands are complementary to each other. (D)</p> Signup and view all the answers

During DNA replication, what are the new strands formed complementary to?

<p>The parental strands. (B)</p> Signup and view all the answers

What is the term used to describe the process where each new DNA double strand consists of one parental strand and one new daughter strand?

<p>Semiconservative replication (C)</p> Signup and view all the answers

What role do histones play in eukaryotic DNA replication?

<p>They bind to DNA to form nucleosomes, making DNA accessible for replication. (B)</p> Signup and view all the answers

What happens during the initiation phase of DNA replication?

<p>The DNA is made accessible for proteins and enzymes required for replication. (B)</p> Signup and view all the answers

How do replication forks form during DNA replication?

<p>As helicase unwinds and opens the DNA helix. (A)</p> Signup and view all the answers

What is the function of helicase in the DNA replication process?

<p>To unwind and open up the DNA helix. (D)</p> Signup and view all the answers

Which stage of DNA replication involves the actual synthesis of new DNA strands?

<p>Elongation (B)</p> Signup and view all the answers

What function does DNA polymerase serve during DNA replication?

<p>It adds DNA nucleotides to the 3' end of the template. (D)</p> Signup and view all the answers

What characterizes the leading strand during DNA replication?

<p>It is synthesized continuously toward the replication fork. (A)</p> Signup and view all the answers

What role do Okazaki fragments play in DNA replication?

<p>They allow the lagging strand to be synthesized in short segments. (A)</p> Signup and view all the answers

Which statement about RNA primers in DNA replication is true?

<p>They provide a starting point for DNA synthesis. (B)</p> Signup and view all the answers

What happens to the RNA primers after DNA synthesis?

<p>They are replaced with DNA nucleotides. (B)</p> Signup and view all the answers

What is the primary function of DNA ligase in DNA replication?

<p>To seal the gaps between Okazaki fragments. (A)</p> Signup and view all the answers

At which point does the DNA unwinding process take place in replication?

<p>Before the addition of primers. (A)</p> Signup and view all the answers

Which of the following best describes the synthesis direction of DNA strands?

<p>Both strands are synthesized in a 5' to 3' direction. (C)</p> Signup and view all the answers

What structure is formed when DNA wraps around histone proteins?

<p>Nucleosome (C)</p> Signup and view all the answers

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

<p>S phase (A)</p> Signup and view all the answers

What is the approximate width of chromosomes at the metaphase stage of mitosis?

<p>700 nm (B)</p> Signup and view all the answers

Which region of the eukaryotic chromosome typically contains inactive genes?

<p>Both A and B (B)</p> Signup and view all the answers

What is linked between nucleosomes in the 'beads on a string' structure?

<p>Short strands of free DNA (B)</p> Signup and view all the answers

What role does telomerase play in DNA replication?

<p>It prevents degradation of chromosomes (A)</p> Signup and view all the answers

In eukaryotic chromosomes during interphase, which type of regions have active genes?

<p>Lightly staining regions (A)</p> Signup and view all the answers

What is the primary purpose of DNA replication in cell division?

<p>To ensure identical DNA in daughter cells (D)</p> Signup and view all the answers

Which enzyme is most likely mutated if the joining of Okazaki fragments is impaired?

<p>Ligase (A)</p> Signup and view all the answers

What is the primary function of telomerase in eukaryotic cells?

<p>To lengthen the telomeres (A)</p> Signup and view all the answers

In which types of cells is telomerase typically active?

<p>Germ cells and adult stem cells (C)</p> Signup and view all the answers

What sequence is repeated in human telomeres?

<p>TTAGGG (C)</p> Signup and view all the answers

What problem arises during DNA replication at the ends of eukaryotic chromosomes?

<p>Shortening of telomeres (D)</p> Signup and view all the answers

What does telomerase attach to during the process of DNA replication?

<p>The end of the chromosome (D)</p> Signup and view all the answers

Which scientist received the Nobel Prize for the discovery related to telomerase?

<p>Elizabeth Blackburn (D)</p> Signup and view all the answers

Which of the following statements about telomeres is false?

<p>Telomeres contain coding sequences. (A)</p> Signup and view all the answers

Flashcards

DNA structure

Double helix; two strands of nucleotides wound around each other.

DNA role in organisms

Carries genetic information, passed from parents to offspring.

Unique DNA

Except for identical twins, each person has unique DNA sequences.

DNA applications

Crime solving, paternity testing, genealogy, disease diagnosis, etc.

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Molecular genetics

Study of DNA's role in heredity and evolution.

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Watson and Crick

Scientists who discovered the structure of DNA.

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Eukaryotic DNA organization

DNA packaged into chromosomes within the cell nucleus.

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Prokaryotic DNA organization

DNA organized in a circular, single chromosome.

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RNA Nucleotides

RNA nucleotides contain adenine, cytosine, guanine, and uracil (instead of thymine).

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Prokaryotic Chromosome

Prokaryotes have a single, circular chromosome located in the cytoplasm's nucleoid region.

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Eukaryotic Chromosome

Eukaryotes have multiple linear chromosomes found inside the nucleus.

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Supercoiling

A way DNA is twisted beyond the double helix to fit into a small space.

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DNA Packaging (Prokaryotes)

Supercoiling is used to fit a large DNA molecule into a small prokaryotic cell.

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DNA Function

DNA provides instructions to build molecules like proteins, doing cell functions.

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DNA Complementarity

The two strands of DNA are complementary, meaning the sequence of bases in one strand determines the sequence of bases in the other. Adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G).

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DNA Replication: Semiconservative

The process of creating two identical DNA molecules from one original molecule. Each new DNA molecule contains one original strand and one newly synthesized strand.

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Replication Fork

The Y-shaped structure formed during DNA replication, where the double helix is unwound and separated.

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Origins of Replication

Specific nucleotide sequences on the DNA molecule where replication begins.

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Helicase Enzyme

An enzyme that unwinds and separates the two strands of DNA during replication.

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Eukaryotic DNA Replication: Initiation

The first stage of DNA replication in eukaryotic cells, where DNA becomes accessible to enzymes by unwinding and separating at specific origins of replication.

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Nucleosomes

Structures formed by DNA wrapping around histone proteins in eukaryotic cells.

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Eukaryotic DNA Replication Stages

DNA replication in eukaryotic cells occurs in three main stages: initiation, elongation, and termination.

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Leading Strand

The new DNA strand synthesized continuously in the 5' to 3' direction, following the movement of the replication fork.

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Lagging Strand

The new DNA strand synthesized discontinuously in short fragments (Okazaki fragments) in the 5' to 3' direction, moving away from the replication fork.

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Okazaki Fragments

Short DNA segments synthesized on the lagging strand during DNA replication. These fragments are later joined together to form a continuous strand.

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DNA Polymerase

The enzyme responsible for adding new nucleotides to the growing DNA strand, using the existing strand as a template.

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RNA Primer

A short sequence of RNA nucleotides that provides a starting point for DNA polymerase to initiate DNA synthesis.

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DNA Ligase

The enzyme that seals the gaps between Okazaki fragments on the lagging strand, creating one continuous DNA strand.

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Okazaki fragment joining

The process of linking short DNA fragments (Okazaki fragments) together during lagging strand replication.

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Telomere

The protective cap on the end of a chromosome, made of repetitive DNA sequences, preventing degradation and loss of genetic information.

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Telomerase

An enzyme that adds repetitive DNA sequences to the ends of chromosomes, maintaining telomere length and preventing degradation.

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Why are telomeres important?

Telomeres protect vital genetic information at the ends of chromosomes, ensuring that DNA replication does not lead to a gradual loss of genes.

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Telomere shortening

Each round of DNA replication leads to a shortening of telomeres, as the lagging strand cannot be completely copied.

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Germ cells and telomerase

Germ cells (sperm and egg) have active telomerase, ensuring that the offspring inherit complete chromosomes with intact telomeres.

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Somatic cells and telomerase

Somatic cells (body cells) have inactive telomerase, leading to gradual telomere shortening and ultimately cell senescence.

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Telomerase and cancer

Cancer cells often have reactivated telomerase, allowing them to divide indefinitely and avoid cell senescence.

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Chromatin Fiber

A complex of DNA and proteins that forms the structure of chromosomes in eukaryotic cells, composed of tightly packed nucleosomes.

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How are chromosomes compacted?

DNA is first wrapped around histone proteins to form nucleosomes. These nucleosomes then stack onto each other to create a 30-nm fiber, which is further coiled and compacted into a thicker structure.

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Chromosome State in Mitosis

Chromosomes are at their most compacted during the metaphase stage of mitosis when they are lined up at the cell's center, forming visible structures.

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Chromosome State in Interphase

During the interphase stage of the cell cycle, chromosomes are more relaxed and decondensed compared to their state in mitosis.

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Euchromatin

Less condensed regions of a chromosome that are generally active during gene expression. They often contain genes that are being transcribed.

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Heterochromatin

Densely packed regions of a chromosome, usually inactive in genes, with DNA tightly wound around histones.

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DNA Replication Purpose

DNA replication ensures that each daughter cell receives an identical copy of the parent cell's DNA during division, maintaining genetic information.

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Study Notes

Chapter 9: Molecular Biology

  • DNA is now associated with various applications like crime solving, paternity testing, and genetic testing.
  • DNA's unique sequence allows identification of individuals (except identical twins).
  • DNA analysis is used in diagnostics, vaccine development, and cancer therapy, also for tracing genealogy and identifying pathogens.
  • DNA is the genetic material passed to offspring in all life forms on Earth.
  • Molecular genetics helps understand evolutionary relationships and life history.
  • Thousands of species and human genomes have been sequenced, providing insights into human disease and evolutionary relationships with other life forms.

9.1 The Structure of DNA

  • DNA structure was determined by Watson and Crick in collaboration with other scientists in the 1950s.
  • X-ray crystallography was used to study molecular structures, helping understand DNA's structure.
  • Rosalind Franklin’s data was crucial in determining the structure.
  • DNA is a double helix, with two strands twisted around each other.
  • Purines (adenine and guanine) pair with pyrimidines (cytosine and thymine).
  • Base pairing is complementary (adenine with thymine, and guanine with cytosine).
  • The strands run antiparallel.
  • DNA is composed of nucleotides, each containing a sugar, phosphate, and a nitrogenous base.
  • Two strands are held together by hydrogen bonds between nitrogenous bases.
  • Specific nucleotide sequences are called origins of replication.

9.2 DNA Replication

  • DNA replication is crucial for cell division
  • It occurs during the S phase of the cell cycle.
  • Both parental strands serve as templates.
  • The process is semi-conservative, meaning each new DNA molecule has one original and one new strand.
  • Enzymes like helicase and DNA polymerase are involved in unwinding and building new strands.
  • Okazaki fragments form the lagging strand by replication.
  • DNA polymerase adds nucleotides to the 3' end of the template.
  • Origins of replication are necessary for the process to begin and can be multiple in eukaryotes.
  • Telomeres are repetitive DNA sequences at the ends of chromosomes
  • Telomeres aid in the replication of chromosome ends, preventing loss during replication.

9.5 How Genes Are Regulated

  • DNA's regulation affects processes like crime-solving, paternity testing, and disease predisposition.
  • Analyzing genes reveals predispositions to diseases.

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Chapter 9 Molecular Biology PDF

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Explore the fascinating world of molecular biology in Chapter 9, where we delve into the structure and applications of DNA. Learn how DNA sequencing plays a crucial role in various fields such as medicine, forensics, and genealogy. Discover the groundbreaking contributions of scientists like Watson, Crick, and Franklin to our understanding of genetic material.

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