DNA

Genetic Material

K-W-L

• List 3 things that you already KNOW about DNA:

• List 3 things that you WANT to know about DNA:

DNA

• DNA is found in the nucleus in each one of your cells.

• Each of you have your own unique DNA.

• The primary function of DNA is to store and transmit genetic information.

DNA Structure

• Watson and Crick• Discovered the

structure of DNA• Found that DNA is

made of two strands in a double helix

• Each strand is made of linked nucleotides

• Discovery was made in 1953

DNA Structure Cont…

• A molecule of DNA is made of 2 phosphate backbones and 4 Nitrogen bases.

• The backbone is formed by a chain of alternating phosphates and sugars. Connected by strong covalent bonds.

• Each sugar provides an attachment site for one of the bases.

Nucleotide

• Nucleotides are the building blocks of DNA. Many nucleotides linked together make a molecule of DNA.

• Nucleotides have three main parts– Phosphate

- Deoxyribose sugar

- Nitrogen containing base pair

Nitrogen Base Pairs

• Nitrogen base may be any one of four kinds:– Adenine (A)– Guanine (G)– Thymine (T)– Cytosine (C)– They make the rungs

of the ladder– Bases connect to each

other through weak hydrogen bonds.

Nitrogen Bases

• Nitrogen bases can be categorized as either pyrimadines or purines. – Purines = adenine and Guanine– Pyrimidines= thymine and cytosine

Base Pairing Rules

BASE PAIR RULES:

A & T Pair

C & G pair

Example: if the sequencing strand is AGTC

The complementary strand would be TCAG

DNA Sequencing

• Practice these sequencing problems:– 1. ATCG– 2. AAGGT– 3. ACTGGAC

DNA Sequencing Answers

– 1. ATCG

TAGC– 2. AAGGT

TTCCA

– 3. ACTGGAC

TGACCTG

Post Questions

1. How is the structure of DNA like a ladder?

2. Why are the 2 strands of the double helix described as “complementary”?

Post Question Answers

1. the rails are the sugar-phosphate backbone, and the rungs are the nitrogen bases.

2. Each strand provides one member of a nitrogen pair.

REPLICATION

PREVIEW QUESTION

• 1. Why would a cell need to duplicate its DNA?

PREVIEW QUESTION

• 1. When would your cells want to make a copy of your DNA?

• Answer: DNA must duplicate itself when a cell divides to make a new cell. This ensures each cell has an exact copy of DNA. This will happen before a cell divides.

Terms To Know

• Replication: The copying of DNA

• Replication fork: Point where two DNA chains separate

• Helicase: Enzyme that unzips DNA

• DNA polymerase: Enzyme that assembles new DNA

• Mutation: A change in the DNA

• Gene: A segment of DNA which codes for a specific protein

Replication

• Replication begins with the breaking of hydrogen bonds separating the nucleotides

• This is done by helicases

Replication Fork

DNA polymerase

• DNA polymerase then binds to each strand and assembles new complementary strands of DNA.

• This can happen at multiple spots on the same DNA strand.

Replication

• Replication concludes with two identical DNA molecules

Error In Replication

• Errors can occur rarely in the replication process.

• This is called a mutation. This could create cancer or genetic variation.

Point Mutation

• Mutations can have a serious effect on the cell.

• Point mutation is a change of a single nitrogen base.

Point Mutation

Mutations

• Mutations can be caused by several factors– Chemicals– Ultraviolet rays from the sun– Error in replication process

Post Questions

• 1. What enzymes are involved in replication and what do they do?

• 2. A change in a single nitrogen base is called a what?

1. What enzymes are involved in 1. What enzymes are involved in replication and what do they do?replication and what do they do?Helicase breaks hydrogen bonds and Helicase breaks hydrogen bonds and unzips the base pairs of the parent unzips the base pairs of the parent strand of DNA. DNA polymerase binds to strand of DNA. DNA polymerase binds to each strand of DNA and assembles the each strand of DNA and assembles the new complementary strand of DNA.new complementary strand of DNA.

2. A change in a single nitrogen base is 2. A change in a single nitrogen base is called a what?called a what?Point mutationPoint mutation