Chapter 12

What are the chemical components of a DNA nucleotide?

A nitrogenous base, a 5-carbon sugar called deoxyribose, and a phosphate group.

What is DNA?

A nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds. They can be joined in any order.

DNA replication is carried out by a series of _____.

enzymes

The tips of chromosomes are known as the ______

telomeres

In eukaryote, DNA

A; is located in the nucleus

What is the role of DNA polymerase in replication?

It is an enzyme that joins individual nucleotides to produce a new strand of DNA.

Who built a model that explained the structure of DNA?

James Watson and Francis Crick.

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 dozen or hundreds of places.

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

anaphase

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

nucleotide

What are the four kinds of nitrogenous bases in DNA?

Adenine, guanine, cytosine, and thymine,

What is explained by Chargaff's rule?

Adenine=Thymine and Guanine=Cytosine.

In what way is DNA like a book?

B; DNA has stored information that can be copied and passed on

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

B; GATCCA

What binds to the prokaryotic chromosome to start DNA replication?

B; regulatory proteins

Because of base pairing in DNA, the percentage of

B; thymine in DNA is about equal to the percentage of adenine

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

Because each strand can be used to make another strand.

In figure 12-2, what is adding base pairs to the strand?

C; DNA polymerase

What happens when a piece of DNA is missing?

C; genetic information is lost

What could make up one nucleotide found in DNA?

D; deoxyribose+phosphate group+cytosine

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

Exist between nitrogen bases to hold DNA model together.

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

Hydrogen bonds

Where are nitrogenous bases found within a DNA strand?

On the "rung of the ladder".

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.

Explain the difference between a nucleic acid and a nucleotide.

Nucleotides make up nucleic acids.

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

Opposite directions

When does replication occur?

Right before interphase.

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 telomre.

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.

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

The double-helix structure of DNA.

What is DNA polymerase

The principle enzyme involved in DNA replication

What is replication?

The process of copying DNA prior to cell division

What is a telomere?

The repetitive DNA at the end of a eukaryotic chromosome

What does the double-helix model show?

The two strands in the double-helix run in opposite directions, with the nitrogenous base 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. The bonds are easily broken allowing DNA strands to separate. Hydrogen bonds form only between certain base pairs-adenine with thymine, and cytosine with guanine-called base pairing.

What is the first step in eukaryotic DNA replication?

The two strands of the double helix unzip forming replication forks.

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.

Define base pairing

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