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DNA basic structure

Content objective:

What are we learning and why are we learning this? Content, procedures, or skills.

Vocabulary objective

Tier II: High frequency words used across content areas. Key to understanding directions & relationships, and for making inferences.

Tier III: Low frequency, domain specific terms.

Building on what we already know

Make connections to prior knowledge. This is where we build from.


Here we go! The amazing cell and DNA size and scale app! website.

What is DNA? How is it related to heredity?

DNA, or deoxyribonucleic acid, is a very long chemical that stores information on how to build cells, and all the instructions necessary to build an entire living organism.

Let’s start building DNA, from the ground up. DNA starts with small pieces (bases), then builds into larger pieces (nucleotides), then much longer pieces (genes) and finally into huge assemblies called chromosomes.

Here are the four bases of DNA

{ http://faculty.ccbcmd.edu/~gkaiser/biotutorials/dna/fg4.html }


When in a gene, these always pair up with their compliment:

A with T,  and G with C

We call them complimentary pairs

{ http://weloveteaching.com/0bio105/lectures/organics/nucleotides.html }


Here we see a cytosine and a guanine coming together. The dotted lines show hydrogen bonds.

Then we see an adenine and a thymine coming together, similarly.

AT GC base pairing

As we look along a stretch of DNA we see the base-pairing pattern like this.

DNA Helix base pairing

These bases are held together with a sugar-phosphate backbone:

The base connects with a sugar, and a phosphate to make a nucleotide.


Here we see an Adenine base bond together with a deoxyribose (sugar,) and then a phosphate group bonds to the sugar.

base nucleoside nucleotide


What is a helix?

Let’s examine this shape.

{ http://solidwize.com/fun-with-sketched-bends/}


Here is a spiral staircase, in the Old State House, Boston, Massachusetts

{ http://www.joeyblsphotography.com/slideshow/historic-old-state-house-antique-spiral-staircase-in-boston/ }

The Spiral Staircase in the Old State House in Boston

{ http://www.britannica.com/EBchecked/media/95480/Old-State-House-Boston }

What is a double helix?

It is the shape made when you take a ladder, and twist it like this:

{ http://lanbob.com/lanbob/H-Biology/H-Biology-001.htm }


Let’s take nucleotides and assemble them into a double-helix, like this:

{ http://www.slideshare.net/coachpointer/dna-notes-7177774 }


There are other chemicals that have to do with genetics: Not just DNA, but also RNA.

We’ll get into RNA later.

Note that while DNA usually has a double helix shape,
RNA usually has a single helix shape, like this:

{ http://mappingignorance.org/2013/04/30/life-and-deeds-of-rna-i-william-wallace-and-the-fate-of-the-cell/ }


To think about:

* Describe DNA’s function in genetic inheritance.

* What is the purpose of doubling up (complimentary) the base pairs?

Learning Expectations

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

8.MS-PS1-1. Develop a model to describe that (a) atoms combine in a multitude of ways to produce pure substances which make up all of the living and nonliving things that we encounter.

HS-LS1-1. Construct a model of transcription and translation to explain the roles of DNA and RNA that code for proteins that regulate and carry out essential functions of life.

HS-LS1-6. Construct an explanation based on evidence that organic molecules are primarily composed of six elements, where carbon, hydrogen, and oxygen atoms may combine with nitrogen, sulfur, and phosphorus to form monomers that can further combine to form large carbon-based macromolecules.

College Board Standards for College Success: Science

LSM-PE.5.2.2 Construct a representation of DNA replication, showing how the helical DNA molecule unzips and how nucleotide bases pair with the DNA template to form a duplicate of the DNA molecule.

Benchmarks for Science Literacy, AAAS

The information passed from parents to offspring is coded in DNA molecules, long chains linking just four kinds of smaller molecules, whose precise sequence encodes genetic information. 5B/H3*

Genes are segments of DNA molecules. Inserting, deleting, or substituting segments of DNA molecules can alter genes. An altered gene may be passed on to every cell that develops from it. The resulting features may help, harm, or have little or no effect on the offspring’s success in its environment. 5B/H4*

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