Warm-UpOctober 6, 2014

• What do you already know about DNA? Be specific.

Objective

• SWBAT describe the structure of DNA.

Agenda

1. Forensic Files2. Crime 3603. Structure of DNA4. DNA Paper Model5. OJ Simpson Documentary6. Exit Slip

Forensic Files

T. Trimpe 2008 http://sciencespot.net/

Crime 360DNA Extraction

1. True or False?When testing for DNA, investigators must use all of the sample to make sure they get an accurate test.

2. Where do we find DNA in a cell?A. Cell membrane B. Vacuole C. Nucleus

3. How long does the sample sit in the heat block?A. 1 hour B. 2 hours C. 3 hours

4. What instrument is used to spin the sample?A. Centrifuge B. Extraction Tube C. Washing machine

5. In which layer would we find DNA? A. Top layer B. Middle layer C. Bottom layer

Watch the video and then answer the questions.Video Link: http://www.aetv.com/crime-360/video/dna-testing

1. True or False?When testing for DNA, investigators must use all of the sample to make sure they get an accurate test.

2. Where do we find DNA in a cell?A. Cell membrane B. Vacuole C. Nucleus

3. How long does the sample sit in the heat block?A. 1 hour B. 2 hours C. 3 hours

4. What instrument is used to spin the sample?A. Centrifuge B. Extraction Tube C. Washing machine

5. In which layer would we find DNA? A. Top layer B. Middle layer C. Bottom layer

The answers are …

What is DNA?DNA stands for deoxyribonucleic acid and contains genetic information. It is found on chromosomes located in the nucleus of our cells.

DNA Image: http://science.howstuffworks.com/genetic-science/dna-evidence.htm

What makes up DNA?• The sides or backbone of the DNA molecule are made up of sugar (deoxyribose) and phosphate molecules.

• The rungs that form the middle of the molecule are made up of pairs of nucleotides or nitrogen bases. Adenine (A) pairs with thymine (T), while guanine (G) always pairs with cytosine (C).

• The order of the bases determines the genetic code.

Double Helix

Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved.www.CrosscuttingConcepts.com

Introduction – The ABC’s of DNADNA (deoxyribonucleic acid) is a negatively-charged double-

stranded chain of nucleotides.

• Purine Bases• Adenine (A)• Guanine (G)

• Pyrimidine Bases• Thymine (T)• Cytosine (C)

Introduction – The ABC’s of DNA

This chain also includes a ‘backbone’ made from molecules of sugar (deoxyribose) and phosphate.

In 1950, biochemist Erwin Chargaff discovered that the number of Adenine and Thymine were equal and that

the same was true for Guanine and Cytosine.

What conclusions can you draw from Chargaff’s discovery?

Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved.www.CrosscuttingConcepts.com

DNA Double Helix DNA has directionality – each chain has a ‘top’ and a ‘bottom’ end.

– ‘Top’ end is called Five Prime (5’)– ‘Bottom’ end is called Three Prime (3’)

Two nucleotide chains together wind into a double helix.

Hydrogen bonds between paired bases hold the two DNA strands together..

DNA strands are antiparallel and complementary to each other.

Copyright © 2013 Crosscutting Concepts, LLC. All Rights Reserved.www.CrosscuttingConcepts.com

Label the DNA molecule shown below.

BACKBONE

ADENINE

THYMINE

H BONDS

CYTOSINE

GUANINE

Word List: Cytosine Adenine Thymine Guanine Backbone

Nitrogen (H) Bonds

How is DNA used as evidence?• Each person’s DNA is different from other people (except identical twins).

• DNA collected from a crime scene can either link a suspect to the evidence or eliminate a suspect, similar to the use of fingerprints.

• DNA can identify a victim through DNA from relatives, even when no body can be found.

• DNA can link crime scenes together by linking the same perpetrator to different scenes locally, statewide, and across the nation.

• DNA can place an individual at a crime scene, in a home, or in a room where the suspect claimed not to have been.

• DNA can refute a claim of self-defense and put a weapon in the suspect's hand.

• It can change a story from an alibi to one of consent.

DNA Strand Image & information : http://www.dna.gov/audiences/investigators/know/

What factors affect DNA evidence?Several factors can affect the DNA left at a crime scene, such as environmental factors (e.g., heat, sunlight, moisture, bacteria, and mold). Therefore, not all DNA evidence will result in a usable DNA profile. Further, DNA testing cannot identify when the suspect was at the crime scene or for how long.  

DNA information : http://www.dna.gov/audiences/investigators/know/

CODIS stands for COmbined DNA Index System, which is an electronic database of DNA profiles that can identify suspects. DNA profiles from individuals convicted of certain crimes, such as rape, murder, and child abuse, are entered into CODIS and help officers identify possible suspects when no prior suspect existed.

What is CODIS?

Did you know?Each human cell contains three billion DNA base pairs. Our unique DNA amounts to 0.1% or 3 million base pairs.

DNA Paper Model

Homework

• Read Chapter 9, pages 316-323

Exit SlipOctober 6, 2014

1. Get out a mobile device or use one of the computers and go to m.socrative.com. You can also use one of the iPads that has the Socrative app. 2. When prompted, enter 417101 for the room number.QUESTION: Describe the structure of DNA.