Nucleic Acids

DNA Structure

1. Double helix, 2 strands

2. 2 polynucleotide chains, formed by condensation reactions. Forming phosphodiester bonds

3. Hydrogen bonding between specific complimentary base pairs

Components of DNA

1. Deoxyribose sugar

2. Phosphate group

3. Organic bases: A&T, C&G

RNA Structure

1. Shorter than DNA

2. Single stranded

3. Single polynucleotide chain

Components of RNA

1. Ribose sugar

2. Phosphate group

3. Organic bases: A&U, C&G

Ribosome Components

1. Made up of RNA (ribosomal rRNA) and proteins

Nucleotides Joining Together Reaction

1. It’s a condensation reaction

2. Forms a phosphodiester bond

Why did scientists doubt that DNA carried genetic code

1. DNA is a simple molecule, compared to more complex proteins

Double stranded DNA contained 22% Adenine, what are percentages of other 3 bases.

1. Thymine = 22%, because there is an equal amount of both thymine and adenine

2. Cytosine = 100-44 =56% 56 divide by 2 = 28%

3. Guanine = 28%, equal amount of both guanine and cytosine

   
   

Importance of semi-conservative replication

1. It’s important for cells, because it ensures genetic continuity between generations of cells

2. Meaning daughter cells inherit identical copy of DNA

DNA Helicase

1. Is a enzyme

2. Breaks hydrogen bonds, that links complimentary base pairs

3. To unzip and unwind the the double helix into 2 separate strands

DNA Polymerase

1. Is an enzyme

2. Has active site complimentary to 3’ carbon end with OH group

3. It joins nucleotides adjacent to eachother by condensation reaction

4. Forming phosphodiester bonds.

Anti-parallel Strands

1. The 2 DNA strands run in opposite directions (5’ to 3’, 3’ to 5’)

2. DNA polymerase has active site and tertiary structure that’s only comlentary to 3’ carbon end with OH group

3. And it starts with 3’ of original template DNA, and moves up

4. So DNA polymerase can synthesise a new strand from 5’ to 3’ from the free nucleotides

DNA Replication

1. DNA helicase binds to DNA, unwinds (unzips) the double helix and breaks hydrogen bonds between complimentary base pairs

2. This separates 2 strands. And both original strands act as a template

3. Free activated DNA nucleotides bind to complimentary base pairs

4. Hydrogen bonds reform between the complimentary base pairs

5. DNA polymerase joins adjacent nucleotides together, in a condensation reaction forming phosphodiester bonds

6. (DNA polymerase active site is only complimentary to 3’ end with OH group so it moves up from 3’ to 5’ direction)

7. This forms the new sugar phosphate backbone, resulting in 2 identical DNA molecules (one orignal strand, 1 newly synthesised strand, semi-conservative replication)

8. (The newly synthesised strand runs anti-parellel to original, so its synthesised in the 5’ to 3’ direction)