ch 13

What is transformation?

a process in which one strain of bacteria is changed by
a gene or genes from another strain of bacteria

Who discovered the chemical nature of the gene?

Griffith

Describe the backstory of Griffith’s experiments

The disease-causing bacteria (S strain) had smooth colonies whereas the harmless bacteria (R strain) produced colonies with rough edges.

When Griffith injected mice with S, the mice developed pneumonia and died. For R, the mice stayed healthy.

Describe Griffith’s 2nd experiment

heated the S, then injected that into mice who survived, the cause of pneumonia was not a toxin from these disease-causing bacteria. Then he mixed the heat-killed bacteria with live, harmless bacteria from the R strain and injected the mixture into laboratory mice, who died. The lungs of these mice were filled with the disease-causing bacteria. **Something had transformed the R strain into an S strain.**

What did we get from Griffith’s experiments?

This process is transformation because one type of bacteria had been changed permanently into another.

Oswald Avery’s experiments

Mixed enzymes that destroyed molecules, including the nucleic acid RNA. Transformation still occurred. But he destroyed DNA, and transformation didn’t occur, therefore **DNA was the transforming factor**

Bacteriophage

Bacteria eater / virus that infects bacteria

Hershey and Chase experiments

Grew viruses with phosphorus and sulfur, tested for radioactivity, all the radioactivity in the bacteria was from phosphorus P-32 the marker found in DNA. **The genetic material of the bacteriophage was DNA, not protein.**

What are nucleic acids and where are they identified

long, slightly acidic molecules originally identified in
cell nuclei.

Nucleic acids linked together make…

nucleotides

The 4 nucleotides that make DNA are..

Adenine, guanine, thymine, cytosine

Nucleotides are made up of 3 things…

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

Nucleotides in a DNA strand are joined by

covalent bonds formed between their sugar and phosphate groups.

Chargaffs rules

A=T C=G

Rosalind Franklin discovered what

X-ray diffraction showed an X-shaped pattern showing that the strands in DNA are twisted around each other like the coils of a spring (helix). It suggested that there are two strands in the structure.

Watson and Crick discovered what

hydrogen bonds could form between
certain nitrogenous bases, providing
just enough force to hold the two DNA
strands together.

Are hydrogen bonds weak or strong

Weak, they allow the two strands of the helix to separate

Why is helix separation important?

The ability of the two strands to separate is CRITICAL to DNA’s functions.

Complementary pairings

each strand can be used to make the other

What is DNA polymerase

an enzyme that joins nucleotides to produce a new strand of DNA + proofreads” each new strand to ensure that each molecule is a perfect copy of the original.

Replication process:

1. the DNA molecule separates into two strands. The two strands of the double helix “unzip” by breaking the hydrogen bonds

2. bases are added following the rules of base pairing (A=T and C=G). Each strand of the double helix serves as a template for the new strand.

3. The result of replication is two DNA molecules IDENTICAL to each other and to the original molecule. (These strands are complementary!)

The role of enzymes

Carry out DNA replication,

What is an example of an enzyme and what does it do

DNA helicase is an enzyme that “unzips” a molecule of DNA by breaking the hydrogen bonds between base pairs, results in an unwinding the two strands of DNA

The role of telomeres

Tips of chromosomes that protect the ends of
the chromosome from deterioration.

Telomerase

Enzyme that builds and maintains telomeres + prevents shortening lessens that important gene sequences will be lost during replication.

How does DNA replication differ in prokaryotic cells and eukaryotic cells?

Most prokaryotic cells starts from a **single** point and proceeds in two directions until the single circular chromosome is copied.

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In eukaryotic cells, it begins at **many** places on the DNA molecule, proceeding in both directions until each chromosome is completely copied. (has up to 100x more DNA)

How does DNA get damaged?

their nitrogenous base absorbs UV light because of it’s chemical structure

what does a double helix do

two strands are twisted into one and in the middle the nucleotides are paired, it proves chargaffs rule of pairing

double helix models are anti parallel, what does that mean

they run in opposite directions (one goes down one goes up) This allows the bases to meet in the middle and carry the nucleotide

 what is a okazaki fragment

Short sequences of DNA nucleotides which are synthesized discontinuously

What’s a leading and a lagging strain?

Leading: one of the two parent DNA strands; replicated in the 3’ to 5’ direction
Lagging: the other parent DNA strand; replicated in short section