DNA/RNA

DNA is a nucleic acid which is made up of smaller repeating units called nucleotides

Nucleotides are made up of 3 parts:

1. Phosphate2. Sugar3. Nitrogen Base

In DNA, the sugar is deoxyribose.

But in RNA, the sugar is ribose

This is why DNA is called deoxyribonucleic acid and RNA is just ribonucleic acid.

Sugar and Phosphate remain unchanged from nucleotide to nucleotide and serve as the support and scaffolding for the DNA structureThis is why we call

the sides of the DNA the sugar-phosphate backbone due to its rigidity and constancy

Now, what does change are the nitrogen bases

There are 4 nitrogen bases but each one is different from the other. However, some patterns and similarities exist amongst some of them.

There are 4 nitrogen bases but each one is different from the other. However, some patterns and similarities exist amongst some of them.

2 Rings 1 Ring

Purines Pyrimidines

1011001010001011010101101011101100010111001

DDDDDDDDDDDDDDDDDDDDDDDDDDDD

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DNA is a code…

It is the variation in the order and which bases are used that causes differences in DNA and ultimately who WE are.

DNA vs. RNA

DNA RNA

How many strands?

What sugar? What bases?

DNA vs. RNA

DNA RNA

How many strands? 2 1

What sugar? Deoxyribose Ribose

What bases? A, T, C, G A, U, C, G

-Bases pair up by forming hydrogen bonds

-The two strands in DNA are called complementary because they are opposite or matching due to their bases pairing up.

DNA Replication

Replication is…

Write down words that come to mind when you think of replication

Replication is making a complete and identical copy

In which stage of the cell cycle does DNA replication occur?

Which specific phase of that stage?

Replication is making a complete and identical copy

In which stage of the cell cycle does DNA replication occur? Interphase

Which specific phase of that stage?S Phase

The DNA code is in the middle of the helix, so how does it get copied if it’s obscured by the side chains and twist of the helix shape?

???

It must become unwound!

DNA Replication occurs in 3 main steps:

1. The DNA is unwound separating the two strands and exposing the bases

2. New strands of DNA are assembled using the original strands as templates.

3. The replicated DNA is proofread and the mistakes are edited.

The point on DNA where the double helix structure unwinds and separates into two separate strands is called the replication fork.

2

13

1. Helicase will “unzip” or unwind the double helix by weakening H-bonds creating a replication fork where the two chains separate

DNA is replicated in the direction of replication.The 2 strands that are unwound from the DNA double helix are called the leading strand and the lagging strand.

The leading strand is the one that is replicated in the direction of replication

The lagging strand is the one that is replicated in the opposite direction of replication (towards the replication fork)

2. DNA polymerase assembles new DNA using each original strand as a template• Short fragments of DNA called

Okazaki fragments are added near the replication fork

• Then gaps are filled in by DNA polymerase

• Bases are added following the base pairing rules (A-T, C-G)

End ProductIn the end, we end up with 4 identical strands: 2 original parent strands from the DNA that was replicated and 2 copies of those original strands.

Because each new copy of DNA has 1 original strand and 1 new replicated strand, we call this process of replication semiconservative