Unraveling DNA: Exploring the Antiparallel Structure
Lesson Description
Video Resource
Antiparallel structure of DNA strands | Biology | Khan Academy
Khan Academy
Key Concepts
- DNA's double helix structure
- Antiparallel arrangement of DNA strands (5' to 3' directionality)
- Phosphodiester linkages and the sugar-phosphate backbone
- Complementary base pairing (Adenine-Thymine, Cytosine-Guanine)
- The role of hydrogen bonds in stabilizing the DNA structure
- 5' and 3' carbon numbering on deoxyribose
Learning Objectives
- Students will be able to describe the molecular structure of DNA, including the sugar-phosphate backbone and nitrogenous bases.
- Students will be able to explain the concept of antiparallel structure in DNA and its significance.
- Students will be able to identify and label the 5' and 3' ends of a DNA strand.
- Students will be able to describe how the orientation of the sugars gives rise to the 5' to 3' directionality
- Students will be able to describe the chemical basis for DNA being called an acid.
Educator Instructions
- Introduction (5 mins)
Begin by reviewing the basic structure of DNA (double helix, nucleotides, base pairing) from previous lessons. Ask students why understanding DNA structure is important. - Video Viewing (10 mins)
Play the Khan Academy video 'Antiparallel structure of DNA strands'. Instruct students to take notes on key terms and concepts presented. - Guided Discussion (15 mins)
Facilitate a class discussion using the discussion questions below. Focus on clarifying the concept of antiparallel structure and the numbering of carbons on deoxyribose. - Interactive Modeling Activity (15 mins)
Engage students in the interactive exercises described below. - Assessment (10 mins)
Administer the multiple-choice and fill-in-the-blank quizzes to assess student understanding.
Interactive Exercises
- DNA Strand Modeling
Provide students with pre-cut pieces representing deoxyribose sugars, phosphate groups, and nitrogenous bases (A, T, C, G). Have them construct a short segment of a DNA molecule, paying attention to the antiparallel arrangement and correct base pairing. Use different colors for each of the molecules for better visualization. - 5' and 3' Identification
Provide diagrams of DNA strands and have students label the 5' and 3' ends based on the orientation of the deoxyribose sugar. They should also label each carbon in the deoxyribose and phosphodiester linkages.
Discussion Questions
- What does it mean for DNA strands to be 'antiparallel'?
- Why is it important that the two strands of DNA run in opposite directions?
- How does the numbering of carbons on the deoxyribose sugar relate to the 5' and 3' ends of a DNA strand?
- Why is DNA considered an acid?
- How does the antiparallel structure contribute to DNA's overall stability?
Skills Developed
- Critical thinking
- Scientific reasoning
- Model building
- Data interpretation
- Vocabulary development
Multiple Choice Questions
Question 1:
What does it mean when we say that DNA strands are antiparallel?
Correct Answer: The strands run in opposite directions.
Question 2:
Which carbon atoms of deoxyribose are involved in the phosphodiester linkages that form the DNA backbone?
Correct Answer: 3' and 5'
Question 3:
Which nitrogenous base pairs with adenine (A) in DNA?
Correct Answer: Thymine (T)
Question 4:
What chemical group is responsible for DNA's acidic properties?
Correct Answer: Phosphate group
Question 5:
If one strand of DNA has the sequence 5'-ATGC-3', what is the sequence of the complementary strand?
Correct Answer: 3'-TACG-5'
Question 6:
What type of bond holds the nitrogenous bases together in the center of the DNA double helix?
Correct Answer: Hydrogen bonds
Question 7:
On the deoxyribose sugar, which carbon is directly attached to the nitrogenous base?
Correct Answer: 1' carbon
Question 8:
In a double-stranded DNA molecule, if one strand runs 5' to 3' from left to right, the other strand runs:
Correct Answer: 3' to 5' from left to right
Question 9:
What is the name of the bond between the phosphate group and the sugar molecule in the DNA backbone?
Correct Answer: Phosphodiester linkage
Question 10:
Why is the antiparallel arrangement of DNA strands important for replication?
Correct Answer: All of the above.
Fill in the Blank Questions
Question 1:
The two strands of DNA run in __________ directions, which is why they are called antiparallel.
Correct Answer: opposite
Question 2:
The 5' end of a DNA strand terminates with a __________ group attached to the 5' carbon of deoxyribose.
Correct Answer: phosphate
Question 3:
The 3' end of a DNA strand terminates with a __________ group attached to the 3' carbon of deoxyribose.
Correct Answer: hydroxyl
Question 4:
__________ and guanine are the two purines found in DNA.
Correct Answer: adenine
Question 5:
Cytosine and __________ are the two pyrimidines found in DNA.
Correct Answer: thymine
Question 6:
The bases in DNA are linked by __________ bonds.
Correct Answer: hydrogen
Question 7:
The backbone of a DNA strand is composed of alternating sugar and __________ groups.
Correct Answer: phosphate
Question 8:
The sugar found in DNA is called __________.
Correct Answer: deoxyribose
Question 9:
__________ linkages connect the nucleotides in a DNA strand.
Correct Answer: phosphodiester
Question 10:
The negative charge on DNA comes from the __________ group.
Correct Answer: phosphate
Educational Standards
Teaching Materials
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