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DNA Structure . Essential Standard 3.1.1 - Explain the double-stranded, complementary nature of DNA as related to its function in the cell. . What is DNA?. DNA stands for D eoxyribo n ucleic A cid. DNA is a nucleic acid. Where is DNA located?.

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DNA Structure

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DNA Structure

Essential Standard

3.1.1 - Explain the double-stranded, complementary nature of DNA as related to its function in the cell.

What is DNA?

DNA stands for Deoxyribonucleic Acid.

DNA is a nucleic acid.

Where is DNA located?

DNA is located in the nucleus of eukaryotic cells and in the nucleoid region of a prokaryotic cell.

DNA and the Eukaryotic Cell

DNA can not leave the nucleus!!!

Can you determine why?

It is too big!!!

DNA’s Jobs!!!

Holds our genetic information.

Has the instructions for making proteins.

DNA Structure

DNA’s Structure

DNA’s structure is described as a double helix.

It shaped like a ladder that is twisted.

Who determined this structure?

James Watson and Francis Crick are given credit for determining the structure of DNA.

Structure determination continued..

Rosalind Franklin also did a lot of background work that Watson and Crick used to help determine the structure.

DNA Structure

DNA is a nucleic acid. Nucleic acids are polymers.

Nucleic acids are made of monomers called nucleotides.

Nucleotides are made of a sugar, phosphate and a base.

The Specifics for DNA

  • Deoxyribose is the sugar found in DNA.

  • There are four different nitrogenous bases found in DNA. They are:

    • Adenine

    • Thymine

    • Guanine

    • Cytosine

DNA’s Bases

  • There are two classes of nitrogenous bases:

    • Purines

    • Pyrimidines

  • Purines have two rings.

    • Adenine and Guanine are purines

  • Pyrimidines have one ring.

    • Cytosine and Thymine are pyrimidines.

DNA’s Bases

How the “pieces” are arranged…

The sugar and phosphate groups alternate on the outside of the strands.

The bases are bonded to the sugar.

The bases are located on the inside of the double helix.

The bases are held together by weak hydrogen bonds.

DNA Structure

DNA Base Pairings

  • Watson and Crick determined that a purine bonds with a pyrimidine.

  • The bonding pairs are:

    • Adenine and Thymine

    • Cytosine and Guanine

  • The bases are held together with hydrogen bonds.

    • A and T are held together by two hydrogen bonds.

    • G and C are held together by three hydrogen bonds.

DNA Strands

The strands of DNA are said to be anti-parallel.








DNA Replication

What is DNA replication?

DNA replication is when DNA makes an exact copy of itself.

Why does DNA replication occur?

Cells need two complete sets of DNA to

give to each of the daughter cells that

result when cells divide.

When does DNA replication occur?

DNA replication occurs during the S phase

of interphase

So…. How does DNA replication occur?

  • The DNA molecule untwists and splits.

    • An enzyme called helicase breaks the

      hydrogen bonds between the base pairs.

      This causes the strands to split.

And then……

2. The building phase begins.

  • New nucleotides move in and match

    with their appropriate bases.

And then…..

  • DNA polymerase forms the hydrogen

    bonds between the base pairs.

    • Two complete molecules now exist.

What else can you tell me?

  • The mode of DNA replication is

    known as semi-conservative.

    • Each new DNA molecule contains one

      strand from the parental DNA and one new strand.

A visual….

DNA Replication Animation

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