DNA Composition and Structure Flashcards
DNA structure
What does DNA consist of what does this form?
What is a molecule of DNA made up of?
DNA consists of two molecules (polynucleotide stands) that form a double helix structure
A molecule of DNA is made up of millions of tiny subunits called nucleotides.
What does each nucleotide consist of?
Each nucleotide consists of:
- Phosphate group
- Pentose sugar
- Nitrogenous base
(Diagram of a nucleotide on OneNote)
What forms the backbone of the DNA molecules and what forms the rungs?
The phosphate and sugar form the backbone of the DNA molecule
(sugar - phosphate backbone)
The bases form the rungs
What are the four types of nitrogenous bases in DNA?
Adenosine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Each base will only bond with one other specific base.
Which bases pair?
Adenine and Thymine
Cytosine and Guanine
This is complementary base pairing
(so %A = %T and %G = %C)
Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.
(Diagram on OneNote)
(Diagram to show this on OneNote)
How are the 2 DNA strands held together?
The strands are held together by complementary base - pairing.
The bases are joined by hydrogen bonds.
How many Hydrogen bonds are Adenosine and Thymine held together by?
How many Hydrogen bonds are Guanine and Cytosine held together by?
Adenosine and Thymine are held together by 2 hydrogen bonds
Guanine and Cytosine are held together by 3 hydrogen bonds
What does Chargaff’s Rule tell us?
% of Guanine and Cytosine are equal
% of Adenine and Thymine are equal
So Purines = pyrimidines
Which bases are Purines and which are Pyrimidines?
Purines = Adenine and Guanine (Large bases/ double rings)
Pyrimidines= Cytosine and Thymine (smaller bases/ single ring)
Remembering the Base Pairings
Mnemonic Device
AT the Grand Canyon
A to T
G to C
What is a codon?
What does each codon code for?
Codon is a sequence of 3 bases.
Each codon codes for a specific amino acid
What is a gene?
What does each unique gene contain?
A gene is a section of DNA that codes for a protein.
Each unique gene has a unique sequence of bases.