First people to suspect that DNA is a helix

A helix is the shape of a twisted strand of a DNA molecule

They made models with scraps of metal held together by by binds of wire to depict this

Picture of the helix model proposed by Watson and Crick

In 1950, Edwin Chargaff made two important discoveries about DNA and made two rules

Chargaff's First Rule: the amounts of thymine and adenine are identical as well as the amount of cytosine and guanine (A=T and G=C)

Chargaff's Second Rule: The DNA of different species have different amounts of adenine and guanine

Picture of Edwin Chargoff
How Base Pairs Bind

Hydrgen bonds between the internal bases bind the strands together.

There are two kinds of base pairings that form: A to T and G to C and are the same in all molecules of DNA.

The strands are complementary, meaning the base on each nucleotide on one strand pairs with its suitable partner.

What Are Chromosomes?

A chromosome is a structure that consists of DNA and the associated proteins

A chromosome carries some or all of a cell's genetic information

Each chromosome consists of one DNA molecule

What is a Karyotype?

The cells of the human body have 23 sets of chromosomes- two of each type

Having two sets of chromosomes means that the cells are diploid

A Karyotype is an image of a persons diploid set of chromosomes

How does DNA replicate?

In preparation for cell division, a cell copies its chromosomes so that it has two sets on a process called DNA replication

In order to begin DNA replication, enzymes break the hydrogen bonds that hold the double helix together and the two strands unwind and separate

After this another enzyme co structure primers, or short single strands of nucleotides that serve as attachments for polymerase

The primer base pairs with a complementary strand of DNA

This establishment of base pairing between two strands of DNA is called nucleic acid hybridization

The DNA polymerases attach to the hybridized primers and begin DNA synthesis

Each nucleotide provides energy for its own attachment to the end of a growing strand of DNAh

The enzyme DNA Logan's seals any gaps so the new DNA strands are continuous

Than both of the two strands of the parent molecule are copied at the same time

As each new DNA strands become longer it winds up with its template strand into a double helix.

What Causes Damage to DNA?

Ionizing radiation from x-rays, most UV light, and gamma rays may cause DNA damage by:

Breaking down DNA

Causeing covalent bonds to form between bases on opposite strands

Fatally altering nucleotide bases

Causing adjacent nucleotide diners to form

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