IEB: DNA & Meiosis Notes

DNA: The Code of Life

- Nucleic Acids are found in every cell
- Nucleic acid monomers are nucleotides
• Amino acids are protein monomers

• Cells are organism monomers

• Deoxyribonucleic acid [DNA]
- Found in the nucleus
- Controls the functioning of the cell
- Stores information about the number and order of amino acid that every
protein needs
- Every cell in the body has a copy
• Ribonucleic acid [RNA]
- Synthesis of proteins


Deoxyribonucleic Acid [DNA]
- Found on the chromosomes in the nucleus


Chromosomes
- Found inside the nucleus of every cell
- Contains DNA that helps the nucleus to:
• Nucleus controls activities of the cell

• Contains all the genetic code that stores information to pass onto the next
generation of cells
- This is why DNA is the code of life
- Majority of its life, nucleus does not contain chromosomes
- DNA occurs in thin threads
• Chromatin

, • Each nucleus contains 1 metre of chromatin threads
- In cell division:
• Full set of DNA is passed on to nucleus of each daughter cell

• DNA is organised to move safely without breaking
- Carefully winds up into larger structures [chromosomes]
- DNA is protected and supported by histones [proteins] in a chromosome


Genes
- Gene:
• A small piece of a DNA molecule that carries information on how to make a specific
chemical that are proteins that the body needs
- Hold information about:
1. How to build cells and keep them in a healthy state
- Nucleic Acids store this information
- Chromosomes hold the DNA [nucleic acid]
- Find genes as pieces of DNA molecule on a chromosome or chromatin threads
- Each gene is length of DNA or RNA molecule
- Locus: the specifi c place on a chromosome where a gene lies


Extranuclear DNA
- DNA found outside of the nucleus & inside:
• Mitochondria

• Plastids
- Genes in DNA in mitochondria and chloroplasts important for organelles to work and
cells to stay alive



II. Discovery of the Structure of DNA

- DNA first isolated in 1869
• Swiss physician: Friedrich Miescher

, • Discovered a microscopic substance in pus on discarded surgical bandages

• Called this substance “nuclein” - discovered in nuclei of white blood cells


- 1951 - 1953
• Maurice Wilkins & Rosland Franklin

• Took x-ray photographs that showed patterns on the images used to determine the
position of DNA molecule’s atoms

• Described the molecule as long and thin


- James Watson & Francis Crick examined structure of DNA
• Used x-ray photographs of DNA fibres [Franklin & Wilkins] and discovered its x
shape or characteristic of helix

• 1953: Described the double helix structure of DNA


- Watson, Crick & Wilkins awarded with Nobel Prize in 1962 for Medicine
- Franklin died from cancer before prize awarded


- Discovery perceived as the greatest scientific discovery of 20th century
- Changed sciences of biochemistry and genetics and led to new branch of science,
genetic engineering



III. Structure of DNA

- Three different kinds of chemicals make up DNA


1. Phosphates


- Common chemicals in soil and food we eat
- Has bonds to join it to other parts of the molecule

, 2. Sugars


- Five carbon atoms
- Pentose sugars
- Pentose sugar in DNA is deoxyribose
- Has bonds to join it to other parts of the molecule


3. Nitrogenous bases


- Has special bonds that attract and attach to another nitrogenous base
• Hydrogen bonds
- Four types:
1. Adenine

2. Thymine
Apples on a Tree
3. Cytosine Adenine with Thymine
4. Guanine
- They code for traits
- Longer bases: Purines
1. Adenine

2. Guanine
- Shorter bases: Pyrimidines
1. Thymine

2. Cytosine


- Nucleotide:
• One phosphate, one sugar, one nitrogenous base

• Four different types because there are four different types of nitrogenous bases
- Nucleotides join end to end to make a long strand
• Backbone of alternating phosphate and sugar units