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DNA Notes

How was the DNA model formed?

• 1) In the 1950’s a biochemist named Erwin Chargaff found that the amount of the nitrogen base adenine (A) in DNA always equaled thymine (T), as is the same for cytosine (C) and guanine (G). Soon after this discovery was known as

• Chargaff’s Rule:

A = T G= C

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• 2) Soon after a young chemist named Rosalind Franklin created images of DNA using a technique known as X-ray diffraction. Franklin used X rays to create images on film and found that the general shape of DNA is a spiral shape

• 3) In 1953 JamesWatson, an American biochemist, and FrancisCrick, an English physicist, worked together in Cambridge, England to develop a model for DNA. Watson and Crick were the first scientist to discover the true shape of DNA.

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• *DNA stands for:

Deoxyribonucleic Acid

Shape of DNA

• DNA has a very distinct shape. It is arranged in a form of a helix. A helix is a shape of a coiled spring. However, a DNA molecule is a double helix.

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What is DNA made of?

• DNA is made up of subunits called nucleotides.

• Each nucleotide is composed of 3 parts:– Deoxyribose (a 5-carbon sugar)

– A phosphate group

– A nitrogen base

There are 4 different types of nitrogen bases

(A)- Adenine T)- Thymine

(G)- Guanine (C)- Cytosine

All living things have the same 4 bases, but the order (arrangement) matters!

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What does the letters in your DNA code for?

• Your DNA sequence is a message for your cells to make specific proteins. It is essentially like a recipe so your cells know what ingredients to put into your proteins. The proteins that are made allow you to express the specific traits that you inherit.

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How do all of our cells have the same

information???

*DNA is copied

before each

Cell division!

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How does DNA make a copy of itself?• One of the unique

characteristics of DNA is that it can copy itself using one of the strands as a template. DNA can replicate and match base pairs to make complementary strands

EX:

• Strand 1: A T C C G T A G C

• Strand 2 ____________________

• Strand 1: T T G A T C T C C

• Strand 2 ____________________

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DNA Replication: a complicated process, but

our cells make it look easy!

Mistakes in DNA Replication• Sometimes mistakes happen when DNA is

copied, similar to how we might make a typo.

• Mutation – change in DNA sequence.

Sometimes they are random, and sometimes

they are caused by external factors called

mutagens.

• Mutagens – cause mutations. Examples

include x-rays, UV light, chemicals in cigarettes

• Types of Gene Mutations:

– Substitution – a base is SWITCHED in the

sequence

– Deletion – a base is REMOVED from the

sequence

– Insertion – a base is ADDED to the

sequence

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Mistakes in DNA Replication• Sometimes mistakes happen when DNA is

copied, similar to how we might make a typo.

• Mutation – change in DNA sequence.

Sometimes they are random, and sometimes

they are caused by external factors called

mutagens.

• Mutagens – cause mutations. Examples

include x-rays, UV light, chemicals in cigarettes

• Types of Gene Mutations:

– Substitution – a base is SWITCHED in the

sequence

– Deletion – a base is REMOVED from the

sequence

– Insertion – a base is ADDED to the

sequence

Gene Mutations