2. Introduction to DNA Flashcards
How is DNA packaged?
DNA (double helix) wraps around histone proteins, to form nucleosomes. This is the “beads on a string” structure which euchromatin is in.
The nucleosomes fold together to form a 30nm Solenoid fibre. This is heterochromatin, and is not expressed.
The solenoid fibre coils further to form the chromatids that make up chromosomes.
What is the genome?
The entire DNA sequence. Human genome is 24 chromosomes (22 autosomal plus 2 sex chromosomes, X and Y)
What is the difference in structure between a nucleoside and a nucleotide?
Base + Sugar = nucleoside
Base + sugar + phosphate = nucleotide
How do the structures of ribose and 2-deoxyribose differ?
They are both pentose sugars.
Deoxyribose does not have an OH group on it’s 2’ carbon, it simply has a H. Only OH on 3’ carbon.
Ribose has a H group at 2’ carbon as well as an OH on it’s 3’ carbon.
Ribose is the pentose sugar present in RNA.
2-Deoxyribose is the pentose sugar present in DNA.
What types of nitrogenous bases exist in DNA and RNA?
2 Types: Purines and pyramidines
Purines: Adenine and Guanine
Pyramidine: Cytosine and Thymine, uracil (replaces T in RNA)
What bond links nucleotides together to form a DNA/RNA polymer?
Phosphodiester bonds between sugars.
5’-3’ polarity of chain.
What type of bond forms between base pairs?
Hydrogen bonds.
G-C: 3 hydrogen bonds
A-T / A-U : 2 hydrogen bonds
How would you describe the secondary structure of DNA?
Anti-parallel
Right-handed double helix
Major and minor grooves
At which stage in the cell cycle does DNA replication take place?
S phase
Which bases contain 2 rings?
Purines contain 2
How many chromosomes are there after DNA replication?
Still the same number (46 - 23 pairs) but each now consists of 2 sister chromatids joined by a centromere, thus containing 2 DNA molecules
