DNA Structure Lesson 3

DNA Structure

By Rahan Rahman

Introduction

Earth is the only known planet to sustain life...

Life refers to the diversity of living things that inhabit the planet.



Biology is the study of living things

Students will be able to visualise the structure of DNA and explain its 3 main components.

Success Criteria

Students will be able to understand that DNA is a double-helix structure made of nucleotides.

Learning Intention

Today we will learn...

Poll

Do you think life exists on other planets?

• Yes

• No

Cell Theory

The Cell Theory states:

•Cells are the structural and functional units of living things

•All living things are made of cells, or the product of cells

•Every cell arises from a pre-existing cell

•Cells contain DNA

​Cell theory in action...

Last Lesson we learnt a bit about DNA

DNA is made up of bases
A = Adenine
T = Thymine
C = Cytosine
G = Guanine

Bases are held together by..

The Sugar-phosphate backbone:
Which consists of:
Sugar (DeoxyRibose)
Phosphate

A sugar, phosphate and base is also called a Nucleotide

The basic structural unit of DNA

Multiple Choice

What is a nucleotide?

• The building block of proteins
• A type of carbohydrate
• A component of cell membranes
• The basic structural unit of DNA

This back bone links toghether to create a ladder.

Complementary Bases

In DNA, the two strands are complementary.

Bases in one strand, pair with the bases in the other.

Adenine (A) always pairs with Thymaine (T)
Cytosine (C) always pairs with Guanine (G)

Multiple Choice

Adenine's complementary base is?

• Thymine
• Uracil
• Guanine
• Cytosine

Multiple Choice

Guanine's complementary base is?

• Cytosine
• Adenine
• Thymine
• Uracil

Multiple Choice

The following DNA sequence has what complementary base pairs? ATCGAG

• ATCGAG

• GAGCTA

• TAGCTC

• AAATTT

DNA is double stranded

Multiple Choice

What is the shape of the DNA molecule?

• Single strand
• Square
• Double helix
• Triangle

Multiple Choice

What type of bond holds the 2 strands of DNA together?

• Hydrogen bonds
• Van der Waals forces
• Covalent bonds
• Ionic bonds

Multiple Choice

The building blocks of DNA are called?

• amino acids
• proteins
• carbohydrates
• nucleotides

Multiple Choice

Which of the following components are found in the backbone of a DNA molecule?

• Deoxyribose sugar and phosphate groups
• Adenine and guanine
• Ribose sugar and nitrogen bases
• Thymine and cytosine

Fun facts about DNA

Length of DNA: If you could unravel all the DNA in a single human cell and stretch it out, it would be about 2 meters (6 feet) long. If you did this with all the DNA in all of your cells, it would stretch from the Earth to the Sun and back about 600 times!

​DNA Similarity:

Humans share about 99.9% of their DNA with every other human. That 0.1% difference is what makes each person unique.

Humans share approximately 98% of their DNA with chimpanzees and about 50% with bananas.

​DNA Replication Speed:

During cell division, DNA replication occurs at an astonishing rate. In human cells, it replicates at a rate of about 50 nucleotides per second. The replication enzyme spins faster than a jet engine!

​Three Billion Letters: The human genome consists of approximately 3 billion base pairs. If you were to type out the entire sequence, typing at a rate of 60 words per minute for 8 hours a day, it would take about 50 years to complete!

​DNA Storage: DNA is incredibly efficient at storing information. Just one gram of DNA can hold up to 215 petabytes (215 million gigabytes) of data.

​DNA Fingerprinting: DNA fingerprinting, a technique used to identify individuals, relies on variations in specific regions of DNA called short tandem repeats (STRs). It’s so accurate that the probability of two people having the same DNA fingerprint is extremely low, except for identical twins.

A Bit of History

In the 1860's, Friedrich Miescher, a Swiss chemist first identified DNA, albeit almost by accident, while studying a type of white blood cell.

Dr Rosalind Franklin then came onto the scene (1950's), using a X Ray Diffraction machine she was able to "photograph" DNA.

The story here gets interesting! James Watson and Francis Crick also scientists at Cambridge (like Rosalin) also saw this picture, thus beginning the hypothesis race! what could this picture mean?

James Watson and Francis Crick were eventually recognised as the scientists who deterimined DNA's double helix structure and won the nobel prize in 1962.

Open Ended

What did you like about the lesson?
What are the 3 main components of DNA?

Lets keep things organised!

Just as DNA has special strategies to stay organised, we must to!

1. Create a notebook or document on your laptop. Call it "Notes on genetics."
2. At the end of the lesson, I will list the key points that you must remember for the test at the end of unit.
3. Record these key points at the end of the lesson, this way you have something to come back to when studying for the test :)

​Key Points

DNA is a double helix structure that is made from a Deoxyribose sugar and phosphate backbone. These hold toghether bases. (A,T,C,G)

A sugar, phosphate and base is also called a Nucleotide. This is the structual unit of DNA.

DNA has complementary bases. Adenine (A) joins with (Thymine (T) and Cytosine (C) joins with Guanine (G).

The DNA strands are held toghether by hydrogren bonds between the bases.

DNA Structure Vocabulary

1. Genetics: The science of how traits are passed from one generation to the next. 

2. DNA: Deoxyribose Nucleic Acid is the genetic code made of bases that is unique to every individual. It is the hereditary material in humans and almost all other organisms

3. Gene: The basic unit of heredity passed from parent to child. These are made up of a sequence of bases.

4. Chromosomes: Is a package of DNA, contained within the nucleus.

5. Bases: Made up of Carbon, Nitrogen, Oxygen and Hydrogen, are the fundamental units within the DNA. There are 4 bases in DNA: Adenine (A), Cytosine (C), Thymine (T) and Guanine (G).

6. Deoxyribose Sugar: Is the sugar molecule located on the backbone of DNA, this molecule holds the DNA base (A,T,C or G)

7. Phosphate group: The phosphate group is also part of the DNA backbone and is used to link the backbone of the DNA molecule together.

8. Nucleotide: Is the structural unit of DNA, It contains a DNA base pair, a deoxyribose sugar and a phosphate group.

9. Hydrogen bond: Is a hydrogen bond between two complementary base pairs.

DNA Extraction practical

​For this practical we will be visualising real DNA by extracting DNA from strawberries.

Method (Steps/Instructions)