Biology Chapter 12 Flashcards

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Questions and Answers

Define base pairing.

the principle that bonds in DNA can form only between adenine and thymine and between guanine and cytosine

What is replication?

The process of copying DNA prior to cell division

What is DNA polymerase?

The principal enzyme involved in DNA replication

What is a telomere?

The repetitive DNA at the end of a eukaryotic chromosome Signup and view all the answers

What are the chemical components of a DNA nucleotide?

A nitrogenous base, a 5-carbon sugar called deoxyribose, and a phosphate group. Signup and view all the answers

What is DNA?

A nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds. Signup and view all the answers

What are the four kinds of nitrogenous bases in DNA?

Adenine, guanine, cytosine, and thymine. Signup and view all the answers

Explain the difference between a nucleic acid and a nucleotide.

Nucleotides make up nucleic acids. Signup and view all the answers

What role do hydrogen bonds play in the structure of DNA?

They exist between nitrogen bases to hold the DNA model together. Signup and view all the answers

What is explained by Chargaff's rule?

Adenine = Thymine and Guanine = Cytosine. Signup and view all the answers

Where are nitrogenous bases found within a DNA strand?

On the 'rung of the ladder'. Signup and view all the answers

What happens when a piece of DNA is missing?

Genetic information is lost. Signup and view all the answers

In what way is DNA like a book?

DNA has stored information that can be copied and passed on. Signup and view all the answers

What could make up one nucleotide found in DNA?

Deoxyribose + phosphate group + cytosine. Signup and view all the answers

Because of base pairing in DNA, the percentage of thymine in DNA is about equal to the percentage of adenine.

True Signup and view all the answers

During DNA replication, a DNA strand that has the bases CTAGGT produces a strand with the bases.

GATCCA. Signup and view all the answers

In eukaryotes, DNA is located in the nucleus.

True Signup and view all the answers

What is adding base pairs to the strand during DNA replication?

DNA polymerase. Signup and view all the answers

What binds to the prokaryotic chromosome to start DNA replication?

Regulatory proteins. Signup and view all the answers

In eukaryotes, DNA replication proceeds in ________ along the DNA molecule.

opposite directions Signup and view all the answers

The structure labeled X in figure 12-3 is a ______.

nucleotide Signup and view all the answers

__________ are weak bonds that hold the two strands of DNA together, but also allow the DNA to separate and replicate.

Hydrogen bonds Signup and view all the answers

DNA replication is carried out by a series of _____ .

enzymes. Signup and view all the answers

The tips of chromosomes are known as the ______.

telomeres. Signup and view all the answers

What is the role of DNA polymerase in replication?

It is an enzyme that joins individual nucleotides to produce a new strand of DNA. Signup and view all the answers

How does replication in eukaryotes differ from replication in prokaryotes?

Prokaryotes: DNA is in cytoplasm, one circular DNA molecule, and starts at a single point and splits into two directions. Eukaryotes: DNA is in nucleus, 1000 times more DNA, and occurs in a dozen or hundreds of places. Signup and view all the answers

What did Erwin Chargaff show?

That the percentages of adenine and thymine are almost always equal in DNA. The percentages of guanine and cytosine are also almost equal. Signup and view all the answers

What did Rosalind Franklin's X-ray diffraction studies reveal?

The double-helix structure of DNA. Signup and view all the answers

Who built a model that explained the structure of DNA?

James Watson and Francis Crick. Signup and view all the answers

What does the double-helix model show?

The two strands in the double-helix run in opposite directions, with the nitrogenous bases in the center. Each strand carries a sequence of nucleotides, arranged almost like the letters in a four-letter alphabet for recording genetic information. Hydrogen bonds hold the strands together. Signup and view all the answers

What is the first step in eukaryotic DNA replication?

The two strands of the double helix unzip forming replication forks. Signup and view all the answers

Why are strands of a DNA molecule said to be complementary?

Because each strand can be used to make another strand. Signup and view all the answers

Explain the processes of replication.

The two strands of the double helix unzip, forming replication forks. New bases are added, following the rules of base pairing. Each new DNA molecule has one original strand and one new strand. DNA polymerase is an enzyme that joins individual nucleotides to produce a new strand of DNA. During replication, DNA may be lost from the tips of chromosomes, which are called telomeres. Signup and view all the answers

What enzyme makes it less likely that DNA will be lost from telomeres during replication? How does it work?

Telomerase. Works by adding a short repeated DNA sequence to the telomere. Signup and view all the answers

Is DNA replication always a foolproof process?

No. Damaged regions of DNA are sometimes replicated resulting in changes to DNA base sequences that may alter two genes. Signup and view all the answers

When does replication occur?

Right before interphase. Signup and view all the answers

Two copies of the DNA are closely attached until the cell enters _____ of mitosis.

anaphase. Signup and view all the answers

Study Notes

DNA Structure and Function

Base pairing occurs between adenine and thymine, and guanine and cytosine, ensuring DNA stability.
DNA is a nucleic acid composed of nucleotides that form long strands through covalent bonds.
Nucleotides consist of a nitrogenous base, deoxyribose sugar, and a phosphate group, serving as the basic units of DNA.
The four nitrogenous bases in DNA are adenine, guanine, cytosine, and thymine.
The "rungs of the ladder" in a DNA structure are formed by nitrogenous bases which are connected by hydrogen bonds.

DNA Replication Process

Replication is the process of duplicating DNA before cell division, essential for genetic continuity.
DNA polymerase is the primary enzyme responsible for adding nucleotides during DNA replication.
Replication initiates at regulatory proteins binding to the prokaryotic chromosome, while eukaryotic DNA replication progresses in multiple locations.
Following the rules of base pairing, a DNA strand with bases CTAGGT produces a complementary strand of GATCCA.

Role of Enzymes and Cellular Components

A series of enzymes, including DNA polymerase, conduct DNA replication, ensuring accurate nucleotide pairing and strand formation.
Telomerase helps prevent loss of genetic information from telomeres, the repetitive DNA sequences at chromosome ends.

Chargaff's Rule and DNA Stability

Chargaff's rule states that the amount of adenine equals thymine, and guanine equals cytosine, highlighting base pairing specificity.
Hydrogen bonds, although weak, provide stability to the DNA double helix and allow separation during replication.

DNA Discovery and Model

Erwin Chargaff demonstrated the base pairing principles, confirming equal percentages of specific nitrogenous bases in DNA.
Rosalind Franklin's X-ray diffraction studies revealed the double-helix structure of DNA, which was further explained by the model built by James Watson and Francis Crick.

Characteristics of Eukaryotic vs. Prokaryotic DNA

Prokaryotic DNA is located in the cytoplasm, typically circular, and starts replication at a single origin, while eukaryotic DNA is linear, found in the nucleus, and exhibits more complexity.
Eukaryotic DNA replication can involve numerous starting points, splitting in opposite directions along the molecule.

Implications of DNA Replication

Replication is not always error-free; damaged DNA regions may replicate incorrectly, causing changes in genetic material.
The DNA double helix consists of two antiparallel strands, each carrying a sequence of nucleotides essential for genetic coding.
Replication occurs before interphase, with two newly formed DNA copies remaining attached until anaphase of mitosis.

Overall Mechanisms

Strands in a DNA molecule are complementary, allowing each strand to serve as a template for the formation of a new strand through replication.
The first step of eukaryotic DNA replication involves the unwinding of the double helix, forming replication forks to facilitate new strand synthesis.

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Test your knowledge with these flashcards from Biology Chapter 12. They cover essential concepts such as base pairing, DNA replication, and the role of DNA polymerase. Perfect for reinforcing your understanding of DNA structure and function.