Hello!

Chapter 16 sec 1 & 2 RQ1. What is a virus that infects

bacteria called? 2. Who actually took the X-ray

diffraction photo of DNA’s structure?

3. What are the bonds between nitrogenous bases?

4. What does the “semiconservative model” describe?

5. What does “topoisomerase” do?

bacteriophage

Rosalind Franklin

Hydrogen bonds

DNA replication

Relieves the strain of replicating DNA molecules; breaks, swivels, and rejoins DNA strands

Why researchers originally thought protein was the genetic material.

• Proteins are macromolecules with great heterogeneity and functional specificity

• Little was known about nucleic acids• The physical and chemical properties of

DNA seemed too uniform to account for the multitude of inherited traits

The experiment that led to the discovery that DNA was the genetic material in

cells.

• Frederick Griffith in 1928• Trying to find a vaccine to fight pneumonia• Experimented with the two strains of

pneumococcus; smooth & rough• Smooth caused the disease, rough did not• When dead S strain was mixed with live R,

the mice DID die, indicating an acquired ability

Transformation and viruses and their effects on bacteria.

• Change in phenotype due to the assimilation of external genetic material by a cell

• Viruses can inject their information into cells and cause drastic changes in behavior

Hershey & Chase experiment

The three components of a nucleotide.

1. Pentose (5-C sugar)

2. Phosphate3. Nitrogenous

base

The nitrogenous bases found in DNA; pyrimidines and purines.

Pyrimidines• 6 membered ring

of carbon and nitrogen

• C – cytosine• T – thymine (DNA)• U – uracil (RNA)

Purines• 5 membered ring

with 6 membered ring

• A – adenine• G – guanine

How Watson and Crick deduced the structure of DNA and what evidence they

used.

• Built models to conform to x-ray data- sugar phosphate backbone- nitrogenous base interior

The “base-pairing rule” and it’s significance.

• A – T : 2 hydrogen bonds

• G – C : 3 hydrogen bonds

• Suggests the mechanisms for DNA replication

• Dictates combination of complementary pairs

The structure of DNA and the kind of chemical bond that holds the two strands together.

• Hydrogen bonds hold the nitrogen bases together

• Van der Waals forces help keep helix spiral shape

• Covalent bonds link the sugar-phosphate backbone

Semiconservative replication and the Meselson-Stahl experiment.

Chapter 6 Sections 2 & 3 RQ

1. What does primase synthesize?2. Okazaki fragments make up which

replicating strand?3. _____ are special nucleotide sequences

found at the ends of eukaryotic chromosomal DNA molecules.

4. Which proteins make up almost half of chromatin?

5. The less compacted, more dispersed, “true chromatin” is called _______.

A primer

lagging

Telomeres

histones

euchromatin

The process of DNA replication and the role of helicase, single strand binding protein, DNA polymerase, ligase,

and primase. 1. The helical molecule untwists while it copies its 2

antiparallel strands simultaneously2. Very rapid – 50 nucleotides are copied per second3. Very accurate – one in ten billion nucleotides are

incorrect Helicase catalyzes the unwinding of the parental

double helix to expose the template Single strand binding protein keeps the

separated strands apart and stabilizes the unwound DNA

Topoisomerase – relieves twisting strain Polymerase and ligase catalyze the filling-in

process Primase the enzymes that polymerize the short

segments of RNA (primers) to get the DNA replication started

The energy source that drives the endergonic synthesis of DNA.

• It is the hydrolysis of nucleoside triphosphates, which are nucleotides with a triphosphate covalently linked to the 5’ carbon of the pentose

• Exergonic hydrolysis of this phosphate bond drives the endergonic synthesis of DNA it provides the required energy to form the new covalent linkages between nucleotides

Antiparallel DNA strands and why continuous synthesis of both is not

possible.

• Antiparallel the sugar-phosphate backbones of the 2 complementary DNA strands run in opposite directions

• DNA can only elongate in the 5’ to 3’ direction due to polarity issues- 3’ end has a hydroxyl group- 5’ end has a phosphate

The leading strand and the lagging strand.

• Leading continuous DNA synthesis, it is synthesized as a single polymer in the 5’ to 3’ direction towards the replication fork

• Lagging the DNA strand that is discontinuously synthesized against the overall direction of replication

The lagging strand is synthesized when DNA polymerase can add nucleotides only to the 3’

end.

• The lagging strand is produced as a series of Okazaki fragments in the 5’ 3’ direction

• Fragments are ligated by DNA ligase which catalyzes the formation of a covalent bond between the 3’ end of each fragment to the 5’ end of the chain

The role of DNA polymerase, ligase, and repair enzymes in DNA proofreading and repair.

• DNA polymerases and ligase catalyze the filling-in process of the new DNA strands

• Repair enzymes excise ( remove) the damaged segments and the gap is filled in by the correct nucleotides

Pictures

the role of telomeres in solving the end-replication problem with the lagging DNA

strand.

• Telomere series of short tandem repeats at the ends of eukaryotic chromosomes; prevents chromosomes from shortening with each replication cycle

• Telomerase enzyme that periodically restores this repetitive sequence to the ends of DNA molecules

prokaryotic and eukaryotic genomes.

Prokaryotic• Usually circular• Smaller• Found in the

nucleoid region• Less elaborately

structured and folded

Eukaryotic• Complexed with a

large amount of protein to form chromatin

• Highly extended and tangled during interphase

• Found in the nucleus

the current model for progressive levels of DNA packing.

• Nucleosome basic unit of DNA packing [formed from DNA wound around a protein core that consists of 2 copies each of the 4 types of histone (H2A, H2B, H3, H4)]

• A 5th histone (H1) attaches near the bead when the chromatin undergoes the next level of packing

• 30 nm chromatin fiber next level of packing; coil with 6 nucleosomes per turn

• the 30 nm chromatin forms looped domains, which are attached to a nonhistone protein scaffold (contains 20,000 – 100,000 base pairs)

• Looped domains attach to the inside of the nuclear envelope

how histones influence folding in eukaryotic DNA.

• Histones small proteins rich in basic amino acids that bind to DNA, forming chromatin

• Contain a high proportion of positively charged amino acids which bind tightly to the negatively charged DNA

heterochromatin and euchromatin.

Heterochromatin• Chromatin that

remains highly condensed during interphase and is NOT actively transcribed

Euchromatin• Chromatin that is

less condensed during interphase and IS actively transcribed

• Becomes highly condensed during mitosis