DNA Structure Flashcards
What are the 3 components of nucleic acids?
- Base Pair
- Phosphodiester/Phosphate Group
- (Deoxy)ribose/sugar
What is DNA?
DNA is a polymer composed of two polynucleotide chains that coil around each other
What are the two forms of nucelobases?
- Pyrimidine
- Purine
What are the 5 base pairs?
- Cytosine
- Thymine
- Uracil
- Adenine
- Guanine
What are the base pairs that are based from pyrimidine?
- Cytosine
- Thymine
- Uracil
What are the base pairs that are based from purine?
- Adenine
- Guanine
How many hydrogen bonds are between adenine and thymine?
2 - DA/AD
How many hydrogen bonds are between guanine and cytosine?
3 - ADD/DAA
How is deoxyribose produced?
It is generated from ribose 5-phosphate by enzymes called ribonucleotide reductases which catalyse the deoxygenation process
What is the main link between two nucleotides?
Phosphodiester link 5’ to 3’
What are the base pairs called?
Nucleobases
What is a base and a sugar called?
Nucleoside
What is a base, sugar and phosphate called?
Nucleotide
What are the 5 nucleosides called?
- Adenosine
- Cytidine
- Guanosine
- Thymidine
- Uridine
What are teh 5 nucleotides called?
- Adenosine 5’-phosphate
- Cytidine 5’-phosphate
- Guanosine 5’-phosphate
- Thymidine 5’-phosphate
- Uridine 5’-phosphate
What is the anti-parallel duplex?
One side of the DNA strand going from 5’-3’ down and the other side 5’-3’ up
What is the primary structure of DNA?
The sequence of nucleotides
How is the duplex formed?
Strand of complementary sequence (complementary bases in opposite order)
How do you find the complementary sequence?
- Split the strand into three-base units for clarity
- Write down the complementary bases
- Reverse order to give strand in 5’ to 3’ format
What are the main features of a DNA strand?
Lengths/heights and grooves
- 1 turn = 33 Å
- Width = 20 Å
- 10.5 nucleotides per turn
- Major groove and minor groove
- 3.3 Å base stacking distance
- Right handed
Why is DNA in a double helix?
- Negatively charged phosphates repel each other - when they are separated there is a reduced electrostatic repulsion
- Stacking of nucleobases through hydrophobic / Van der Waals interactions compacts duplex vertically - removal of water (water would disrupt the hydrogen bonding), hydrophobic collapse, pi-stacking
What are the alternate forms of the double helix?
- B-DNA: right handed
- A-DNA: right handed
- Z-DNA: left handed
What is the main form of the double helix?
B-DNA
Where are B-DNA ususally found?
Found in cells under physiological conditions
Where does A-DNA usually occur?
Under dehydrated conditions or in a hybrid DNA-RNA
How is Z-DNA formed?
After DNA has undergone methylation - common in some diseases (Alzheimers)
What is triplex DNA?
3 strand binded together with the 3rd strand binded in the major groove
What is quadruplex DNA?
- 4 strands of DNA around a metal ion
- Found in telomeres (end of chromosomes)
- Protects DNA ends and stop DNA repair systems from treating them as damaged
- Allows coping of ends which wouldn’t be possible with 3’ end
What are some examples of tertiary structures of DNA?
- Hairpin (small loop)
- Stem-loop (large loop)
- Holliday junction
What are the differences between DNA and RNA structures?
DNA:
* 2-Deoxyribose
* Thymine
* Usually double stranded
* Stores genetic information
* Located in the nucleus
RNA
* Ribose
* Uracil
* Usually single stranded
* Protein synethesis and gene regulation
* Located in the cytoplasm
Why is ribose more easily hydrolysed than 2-deoxyribose?
Further possible H-bonding patterns from an extra OH, phosphodiester more easily hydrolysed
What is a nucelosome?
- DNA colled around proteins
How are chromosomes produced?
DNA is coiled around proteins called histones to produce nucleosomes, whihc are futher packed to produce chromosome
How is nanotechnology used with DNA?
Predictable sequence-specific hybridisation can be used to create 3D nanostructures for a wide variety of nanotechnological applications
What are the functions of DNA?
- DNA directs the machinery of a cell to make specific proteins
- Stores the hereditary information of an indivdual
- Has the ability to mutate - allows for new characteristics (evolution)
