Chapter 16: The molecular basis of inheritance

Put it all together! Make a detailed list of the steps that occur in the synthesis of a new strand of DNA.

1. Helicase unwinds the parental double helix. 2. Molecules of single-stranded binding protein stabilize the unwound template strands. 3. The leading strand is synthesized continuously in the 5' to 3' direction by DNA polymerase III after being primed by primase. 4. Primase begins synthesis of the RNA primer for the lagging strand. 5. DNA polymerase III synthesizes discontinuously the lagging strand in the 5' to 3' direction. 6. DNA polymerase I removes all the RNA primer sections and replaces them with DNA nucleotides. 7. The replacement of the primer with DNA leaves the new DNA nucleotides with a free 3' end. DNA ligase joins the free 3' end to its adjacent 5' end, forming a continuous and unbroken strand of DNA on both the leading and lagging strands.

What did Griffith conclude from his experiment with mice?

He concluded from his experiments with Streptococcus Pneumoniae that R cells had acquired from the dead S cells the ability to make the polysaccharide coats so this trait must be inheritable.

Draw and label three components of a molecule.

In notebook. Phospate, pentose sugar, nitrogenous base

Define the origins of replication.

Site where the replication of a dna molecule begins, consisting of a specific sequence of nucleotides.

Explain Telomere erosion and the role of telomerase.

Telomeres provide their protective function by postponing the erosion of genes located near the ends of DNA molecules. Telomeres become shorter during every round of replication. Telomeric DNA tends to be shorter in dividing somatic cells of older individuals and in cultured cells that have divided many times. Importantly, some cell genomes (such as germ cells) must persist virtually unchanged from an organism to its offspring over many generations. In order to accomplish this, an enzyme called telomerase catalyzes the lengthening of telomeres in eukaryotic germ cells, thus restoring their original length and compensating for the shortening that occurs during DNA replication.

Explain how Meselson and Stahl confirmed the semiconservative mechanism of DNA replication.

The first replication in the N medium produced a band of hybrid dna. This result eliminated the conservative model. The second replication produced both light and hybrid DNA, a result that refuted the dispersive model and supported the semiconservative model. They therefore concluded that dna replication is semiconservative.

Distinguish between the leading and the lagging strands during DNA replication.

The leading strand is the new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5' ----3' direction. The lagging strand is a discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5' ---3' direction away from the replication fork.

How did Watson and Crick's model explain the basis for Chargaff's rules?

The model showed that for the DNA double helix structure to work, A must pair with T, and C must pair with G.

Explain what is meant by 5' and 3' ends of the nucleotide and what is meant by the two strands of DNA being antiparallel?

The two free ends of the polymer are distinctly different from each other. One end has a phosphate attached to a 5' carbon, and the other has a hydroxyl group on the 3' carbon. We refer to these as the 5' and the 3' end respectively.

What is a bacteriophage and how does it destroy a bacterial cell?

-A virus that infects and replicates within a bacterium. - The phage attaches to the cell, inserts its DNA, takes over cellular machinery, and goes through lytic cycle to break/destroy the cell.

Describe the structure of DNA relative to each of the following: a. distance across molecule b. Components of the backbone c. components of the "rungs" d. Bond type and number of bonds that holds nucleotides together e. bond type that hold the backbone of the DNA strands together

a. 1nm b. sugar-phosphate c. A T G C d. Phosphodiester bonds e. hydrogen bonds

Which enzyme does each of the following? a. Untwists and separates strands b. holds DNA strands apart c. Synthesizes RNA primer d. adds DNA nucleotides to new strands e. relieves strain caused by unwinding f. joins dna fragments together g. removes rna primer and replaces with dna

a. helicases b. single-strand binding proteins c. primase d. DNA polymerases e. topoisomerase f. topoisomerase g. DNA polymerases

Name the 5 nitrogenous bases, and label each base as a pyrimidines or purines and explain the base pair rules. Indicate if the base is found in DNA, RNA or both.

adenine, thymine, guanine, cytosine, uracil A Both T DNA (T=A) G Both C Both U RNA (U=A)

Given that the DNA of a certain fly species consists of 27.3% adenine and 22.5% guanine, use Chargaff's rules to deduce the percentages of thymine and cytosine.

A=T G=C

How is a bacterial chromosome different than a eukaryotic chromosome?

Bacterial chromosomes are circular, meaning that they start and end at the same point. A eukaryotic chromosome is linear and has 2 "free end." Like a rubberband (bacterial) and a shoelace (eukaryotic).

Explain the roles of each of the following enzymes in DNA proofreading and repair.

DNA polymerase: Fills the gap left after nuclease excises damaged segments of the DNA strand Nuclease: DNA-cutting enzyme Ligase: Joins the sugar-phosphate backbones of all the Okazaki fragments into a continuous DNA strand. Repair Enzymes: Proofread and repair DNA.

Describe the means by which Hershey and Chase established that only the DNA of a phage enters an E. coli cell. What conclusions did these scientists draw based on these observations?

E. coli were infected by the phage, and there was more radioactive phosphorus that entered. They concluded that DNA carried the genetic information to produce DNA and proteins.

What is the direction of synthesis of the new strand?

5'---3' direction

What are Chargaff's rules?

A pairs with T, C pairs with G. He arrived at this when he noticed specific ratios in same species.

What did Avery, McCarty and MacLoed determine to be the transforming factor?

DNA

What are Okazaki fragments? How are they welded together?

Okazaki fragments are short segments of DNA synthesized away from the replication fork on a template strand during DNA replication. Many such segments are joined together by the enzyme DNA ligase to make up the lagging strand of newly synthesized DNA.

Label the figure below. Include 3' and 5' strands, RNA primer, primase, SSBP, topoisomerase, helicase, leading strand, lagging strand, DNA Polymerase, DNA ligase, parental DNA, and new DNA.

On paper.

Distinguish between the structure of pyrimidines and purines.

Pyrimidines have organic ring, purines have 2 organic rings. Pyrimidines-C,T, and U Purines- A,G

Explain the semiconservative model of replication?

Type of DNA replication in which the replicated double helix consists of one old strand, derived from the parental molecule, and one newly made strand.

Who built the first model of DNA and shared the 1962 Nobel Prize for discovery of its structure?

Watson and Crick.

What was the role of Rosalind Franklin in the discovery of the double helix?

X-ray Crystolography