A complete set of notes on the DNA & Meiosis Section of the IEB Matric / Grade 11 Syllabus for Life Sciences [Biology]. These notes helped me to achieve a distinction for my Life Science Prelim.
- 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
- 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
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