Lecture 21 - DNA I Flashcards
What is the central dogma ? (Definition)
States how genetic information is stored, replicated and read
What is the central dogma ? (Example form)
DNA makes RNA makes protein
What is the definition of a gene ?
Unit of inheritance
What is the lecturers definition of a gene ?
Life forms reproduce themselves and use energy
What is the lecturers definition of a gene ?
Life forms reproduce themselves and use energy
What are genes made of ?
DNA
What did Avery, McCarty and MacLeod discover ?
That genes are made of DNA not protein
What are the four things that DNA must do ?
- Replicate faithfully
- Have the coding capacity to generate the proteins required for cellular functions
- Be transmitted from parent cell to daughter cell
- Orchestrate many functions in organisms
How much DNA does a diploid human cell contain ?
More than 2 meters
Where are genes located in Eukaryotic cells ?
In chromosomes, in the nucleus
Why was there a race to understand the structure of DNA ?
It would go a long way toward understanding the diversity and evolution of life forms
What is the atomic composition of DNA ?
- Carbon
- Hydrogen
- Oxygen
- Phosphorus
- Nitrogen
What are the components of a nucleotide ?
- Phosphate
- Sugar - deoxyribose
- Nitrogenous base
What is the subunits of DNA ?
Nucleotides
How many nitrogenous bases are there ?
4
What are the four nitrogenous bases ?
- Adenine
- Guanine
- Cytosine
- Thymine
Which nitrogenous bases are purines ?
- Adenine
2. Guanine
What nitrogenous bases are pyrimidines ?
- Cytosine
2. Thymine
How would you explain what type of structure is DNA ?
A polymer
How would you explain what type of structure is a nucleotide ?
A monomer
What are the four types of nucleotide ?
- dAMP
- dGMP
- dCMP
- dTMP
What is the 5’ end of a DNA strand ?
Phosphate end
What is the 3’ end of of a DNA strand ?
Hydroxy end
Does the DNA strand have polarity ?
Yes
What is the DNA’s strand directionality/polarity based on ?
The different end groups of the terminal nucleotides
How is the sugar-phosphate backbone formed ?
Monomers linking together
What is a rule concerning the monomer link to form the sugar-phosphate backbone ?
The link can only be made between the 5’ phosphate of one nucleotide and the 3’ hydroxyl of another
How was the 3D structure of DNA determined ?
X-ray crystallography and model building
What provides the fibres for X-ray crystallography ?
Addition of a solution of ethanol
What seen on Rosalind Franklin’s B51 X-ray image of DNA ?
A helical repeat unit of 10 stacked base pairs
What four things did X-ray analysis and model building reveal about the DNA structure ?
- DNA is a 2-stranded helical structure with the sugar-phosphate backbones on the outside
- The bases are stacked on the inside, perpendicular to the helix axis
- Helical repeat unit = 34A (10bp per helix turn)
- DNA double helix is about 20A wide
How many strands does DNA have ?
2
Where are the sugar-phosphate backbones found ?
On the outside of the DNA helical structures
Where are the nitrogenous bases found on the DNA strands ?
On the inside of the strands, perpendicular to the helix axis
What is the helical repeat unit ?
34A (10 base pairs per helix turn)
How wide is the DNA double helix ?
20A
How are the four types of bases arranged within the DNA double helix ?
Base composition and base ratio
What form do the bases exist in ?
Normally keto not enol form
What are tautomers ?
Structural isomers that differ from one another based on the position of protons and double bonds
What is Chargaff’s rule of base composition ratio’s ?
Any species of any organism should have a 1:1 stoichiometric ratio of purine and pyrimidine bases, more specifically, that the amount of guanine should be equal to cytosine and the amount of adenine should be equal to thymine
What are the key proposals of Watson and Crick ?
- The only base pairs permitted are adenine paired with thymine and guanine paired with cytosine
- Implications of base pairing for DNA replication
- The DNA strands are in anti-parallel orientation
How does replication occur ?
Via templating
Why is the replication process called templating ?
A parent strand acts as a template on which the daughter strand is synthesised
What does the sequence of bases on one strand determine ?
The sequence of bases on the other strand
