Ch 16 Flashcards by tiegan radke

Hereditary material of the cell

Chromosomes carry hereditary material and consist of DNA and protein.

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Antiparallel

The two sugar-phosphate backbones of the helix are antiparallel, meaning they run in opposite directions (One is 5’ to 3’ and the other is 3’ to 5’).

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Structural Differences between Purines and Pyrimidines?

Which bases are Purines vs Pyrimidines?

Purines have a double-ring structure, and pyrimidines have a single-ring structure. Purines are adenine and guanine, while pyrimidines are thymine and cytosine.

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Regularity in base ratio

In every species studied, the number of adenine (A) bases equals the number of thymine (T) bases, and the number of guanine (G) bases equals the number of cytosine (C) bases.

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Explain the experiments of Hershey and Chase

Experiment 1: Testing Proteins - Sulfur in Viral Protein coats radiolabeled, bacteria infected, no radioactivity enters cells.
Conclusion: Proteins are not genetic material.
Experiment 2: Testing DNA - Phosphorous in Viral DNA radiolabeled, bacteria infected, radioactivity enters cells.
Conclusion: DNA is the genetic material.

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Erwin Chargaff’s scientific contribution

1) DNA composition is species-specific
2) The amounts and ratios of bases vary from one species to another.

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Reasons researchers thought protein was the genetic material

Proteins have functional specificity, little was known about DNA, and properties of DNA seemed too uniform to account for the multitude of inherited traits.

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Method used by Chargaff to study DNA

Chargaff collected DNA samples from several organisms and used paper chromatography to separate the nitrogenous bases.

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Hershey and Chase’s discovery in 1952

Hershey and Chase discovered that DNA is the genetic material of a T2 bacteriophage (virus) in 1952.

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Watson and Crick’s discovery

Watson and Crick discovered the double helix by building models to conform to X-ray data.

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Each nucleotide is made up of 3 basic parts; what are they?

5-carbon sugar: deoxyribose
Nitrogenous base: A, G, C, or T
Phosphate group (PO₄⁻)

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Why must a purine pair with a pyrimidine?

A purine base on one strand pairs with a pyrimidine base on the other strand to maintain consistent width.

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What determines which purine will pair with the specific pyrimidine?
And which bases pair together?

The structure of a base dictates which pairs of bases can form hydrogen bonds:
A pairs with T; C pairs with G.

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tetranucleotide hypothesis

DNA structure hypothesis from 1897-1947; Scientists thought DNA molecules were composed of four nucleotides repeating in the same order down the polymer

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Role of Rosalind Franklin

Watson saw an X-ray photo of DNA produced by Rosalind Franklin that helped them figure out the structure of DNA.

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DNA is made up of monomers called

Nucleotides

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Can enzymes make repairs to existing DNA?

Yes, Enzymes other than DNA Polymerase III can fix DNA damage in existing DNA.

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What must be added to the template strand in order for DNA polymerase 3 to attach a daughter nucleotide?

Primers are necessary for the addition of new nucleotides in DNA strand formation; they provide the initial 3’ end for DNA poly 3 to build off of.

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Energy for DNA synthesis

Nucleoside triphosphate loses 2 phosphates during the creation of a phosphodiester bond, providing energy for DNA synthesis. DNA Polymerase 3 will use the energy to form the phosphodiester bond.

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Form in which nucleotides arrive

nucleoside triphosphate.

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_____ primer is necessary for replication of the leading strand, versus ______ primers are necessary to replicate the lagging strand.

One; many

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What happens when helicases bind at the origins of replication?

DNA double helix opens at the origin, creating a replication bubble. Replication forks spread in both directions from the central initiation site.

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Continuous synthesis of one daughter strand is known as the _______; this strand is being replicated ______ the replication fork.

leading strand; towards

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Simple description of DNA replication.

DNA replication involves the separation of the parental DNA strands and the synthesis of new complementary strands. During DNA replication, new bases are added to the old strands to form new DNA molecules.

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Role of DNA polymerase III

DNA polymerase III links the nucleotides to the growing strand by creating phosphodiester bonds between the incoming nucleotide and the one before it.

Role of DNA Ligase in DNA replication.

Creates the last phosphodiester bond.

New nucleotides are only added to the ____ end of the growing strand

Watson and Crick's proposal on DNA replication (4 things)

1) The 2 DNA strands separate. 2) Each strand is a template for assembling a complementary strand. 3) Nucleotides line up singly along the template strand (A-T, G-C). 4) Enzymes link the nucleotides together at their sugar-phosphate groups.

When in the cell cycle does DNA replication happen? Be specific.

DNA replication during the S phase of Interphase.

DNA replication begins at special sites called origins of replication.

These are specific sequences where the replication process starts.

Prokaryotes have ________ origin of replication.

ONE Unlike eukaryotes, prokaryotic DNA replication starts from a single origin.

Role of helicases in DNA replication.

Catalyze unwinding and unzipping of parental DNA double helix to expose template (break hydrogen bonds).

Describe the role of 6 proteins used in replication and the order in which they are used.

1) Helicase binds at origin; unwinds and unzips DNA 2) SSB proteins stabilized the bubble open 3) Primase polymerizes a primer 4) DNA Polymerase 3 catalyzes the daughter strands off the primer in the 5' to 3' direction 5) DNA Polymerase 1 removes RNA primers and replaces them with DNA nucleotides

What is a primer? What enzyme puts in the primer?

A primer is a short RNA segment that is complementary to a DNA segment. Primase lays down the primer.

Discontinuous synthesis of one daughter strand is known as the _______; this strand is being replicated ______ the replication fork.

lagging strand; away from

Function of single-strand binding proteins (SSB).

Keep separated strands apart and stabilize unwound DNA until new strands can be made.

What two proteins are involved in opening up the parent strands for replication?

Helicases and single-strand binding proteins (SSB).

Function of DNA polymerase I.

Removes the RNA primer and replaces it with DNA nucleotides.

Eukaryotic chromosomes have _______ origins of replication.

MULTIPLE Hundreds to thousands of replication origins form, eventually fusing to create two continuous DNA molecules.

Describe how DNA Polymerase III checks/proofreads nucleotides as they are being added.

DNA Poly III can remove mismatched base from 3’ end of previous nucleotide and then replace it; it can fix mistakes during DNA replication.

Explain what is happening when nucl

incoming nucleoside triphosphate will be added to the growing daughter strand at its 3' end, DNA poly 3 will form the linkage

Describe the Lagging strand production

The lagging strand is produced as a series of short fragments called Okazaki fragments, synthesized in the 5’ to 3’ direction, away from the replication fork, and linked by DNA ligase.

New daughter strands elongate in the ________ direction

5’ to 3’

Why are RNA primers needed to initiate DNA synthesis?

DNA Polymerase III requires an existing 3’ end to add new DNA nucleotides.

Name of Watson and Crick's proposed model for replication of DNA

semiconservative model

Semiconservative model explanation

Each of the two daughter molecules will have one old or conserved strand from the parent molecule and one newly created strand.

What types of cells would be expected to have little to no active telomerase enzyme?

Most normal body (somatic) cells

Function of telomeres

The purpose of telomeres is to prevent chromosomes from losing important base pair sequences at their ends and to prevent chromosomes from fusing to each other.

What two areas of research are the telomeres currently being studied for?

Aging and cancer

Telomeres are controlled by two mechanisms.

1. Erosion (occurs each time a cell divides) 2. Addition (determined by activity of telomerase)

Why does the lagging strand specifically get shorter with each round of replication?

DNA Polymerase I removes the final RNA primers on the end but cannot replace them with DNA since there will not be a 3' end to link to.

What is the name of the enzyme that adds a telomere?

Telomerase

Describe the Effect of telomerase on telomeres during cell division.

Without telomerase, telomeres shorten each time a cell divides, leading to cell death and possibly aging. With telomerase, the enzyme maintains telomeres by adding extra DNA, preventing shortening.

What types of cells would be expected to have increased telomerase enzyme?

Stem cells and germline cells (the cells that will make sperm and egg)

What happens to a cell when it becomes “old” and has shortened telomeres?

Cells with critically short telomeres undergo apoptosis (programmed cell death)..

Where specifically are the chromosomes located?

On the 3' ends of the parent strands, since this side will results in the lagging daughter strands. Telomerase enzyme can only add the telomere to a 3' end.

What happens to the length of the telomere with successive rounds of cell division?

Telomeres shorten with each cell division, losing 25-200 base pairs.

What are telomeres?

Telomeres are protective caps at the ends of chromosomes; repeats the same non-coding sequence of DNA many times.

DNA replication is fast in eukaryotic cells. Why?

Replication occurs at several positions along the DNA molecule

Which molecule is the complete instruction manual found in every cell in your body?

DNA

Which bases are purines?

Adenine and Guanine.

Which sugar is contained in DNA

Deoxyribose

Primer is made of...

RNA nucleotides

The enzyme responsible for creating telomeres added to the ends of DNA is...

Telomerase

Why can DNA Polymerase III can only add on to the 3’ end of the elongating strand

This is due to the enzyme's requirement for a free 3'-OH group, which is essential for forming the covalent bonds that connect nucleotides.