DNA Structure Flashcards
What are the four bases found in DNA?
Adenine, Thymine, Cytosine and Guanine
Which two bases are the purines?
Adenine and Guanine are the larger purines
Which bases are the pyrimidines?
Cytosine and Thymine are the smaller pyrimidines (also Uracil in RNA)
How many rings do purines have?
Two
How many rings do pyrimidines have?
One
How many hydrogen bonds are formed between Cytosine and Guanine?
Three
How many hydrogen bonds are formed between Adenine and Thymine?
Two
Which form of chromatin stains lightly?
Euchromatin
Which form of chromatin stains dark?
Heterochromatin
What is a nucleosome?
A nucleosome consists of a length of DNA wrapped around a histone core
What is the ‘beads on a string’ structure?
This is where DNA is wrapped around 8 histones twice to form nucleosomes (euchromatin)
What is the solenoid stucture?
This is where the DNA is packaged as a 30nm fibre of chromatin as a result of the helical winding of nucleosomes (heterochromatin)
In which form of chromatin are genes expressed?
Euchromatin (beads on a string)
In which form of chromatin are genes not expressed?
Heterochromatin (solenoid)
How many chromosomes are in a human diploid cell?
46 chromosomes (23 pairs)
How many chromosomes are in a human haploid cell (gamete)?
23 chromosomes
What is a gene?
A gene is a sequence of nucleotides that carries the code for proteins. They have a specific chromosomal location.
What is the human genome?
The entire DNA sequence of a human
How many chromosomes in the human genome?
24 (22 autosomes plus X and Y)
What is a nucleotide?
Base + Sugar + Phosphate
What is a nucleoside?
Base + Sugar (no phosphate)
What are the two types of pentose sugars?
Ribose (in RNA) and Deoxyribose (in DNA)
For example, what is the nucleoside and nucleotide associated with Adenine in RNA and DNA?
Nucleoside in RNA = Adenosine
Nucleotide in RNA = Adenosine monophosphate (AMP)
Nucleoside in DNA = Deoxyadenosine
Nucleotide in DNA = Deoxyadenosine monophosphate (dAMP)
By what bonds are adjacent nucleotides joined?
Phosphodiester bonds
The DNA chain has polarity. What are the two ends called?
It goes from 5’ to 3’. 5’ is the phosphate end and 3’ is the end with the OH
Name two features of the two strands of DNA
Complementary and anti-parallel
How long is DNA vs what is the size of a cell nucleus?
2 metres of DNA into a 6 micrometre cell nucleus
What is the width of DNA?
2 nanometres
What is the total length of DNA per cell?
2 metres
What is on the 5’ end?
Phosphate
What is on the 3’ end?
OH
What is the difference between the major and minor groove?
The major groove occurs where the backbones are far apart, the minor groove occurs where they are close together.
Which groove of the DNA is easier for proteins to bind to?
Major groove because the backbones are not in the way.
How many base pairs in one complete turn?
10
What is the space between the base pairs?
0.34nm
In which groove are bases exposed?
Major
