A1.2- Nucleic Acids

DNA (Deoxyribonucleic Acid)

The molecule that provides the long-term stored genetic information for all organisms on earth.

RNA (Ribonucleic Acid)

Molecule responsible for translating genetic information from DNA into proteins.

4 nitrogenous bases +5th in RNA

Adenine, Thymine, Guanine and Cytosine + Uracil (RNA)

Genes

The sequences of nitrogenous bases that code for certain traits.

Structure of a nucleotide

• 1 phosphate group

• 1 5-carbon monosaccharide (pentose sugar)

• 1 nitrogenous base (thymine, adenine, cytosine, guanine or uracil)

All bonded together covalently

Sugar - Phosphate backbone

Pentose sugar of one nucleotide covalently bonded to the phosphate group of another nucleotide.

Difference between DNA and RNA nucleotides

RNA contains a ribose sugar, and DNA contains a deoxyribose sugar. RNA has a (-OH) group at the 2nd carbon atom, whereas DNA has only (-H)

RNA structure

Single chain of nucleotides

DNA structure

2 chains of DNA arranged antiparallel to one another, creating a double helix shape.

Bond between two nucleotides of opposite strands in DNA

Hydrogen Bonds

Complimentary Base Pairs

• Adenine + Thymine (or Uracil)

• Guanine + Cytosine

Differences between DNA and RNA

• DNA is double stranded, RNA is single stranded

• DNA has deoxyribose sugars, RNA has ribose sugars

• DNA - Thymine, RNA- Uracil

• DNA- Double helix, RNA- Variety of shapes depending on type

• DNA- Permanent genetic code, RNA- non permanent genetic code EXCEPT for viruses

Messenger RNA (mRNA)

Genes that exit the nucleus of a cell and transfer genetic information in order to create proteins.

Transfer RNA (tRNA)

When a protein is synthesised, tRNA transfers the correct amino acid into the chain to create the protein.

Adenosine Triphosphate (ATP)

Single-nucleotide nucleic acid used in cells as a type of chemical energy.

Why is complimentary base pairing important?

It is important for DNA replication- when the DNA is split into two, for two identical copies of DNA to be made, the bases have to be complimentary to one another.

Triplet Codon

Sequence of 3 nucleotides that contain genetic information. There are 64 possible combinations of nucleotides.

What do the 3’ and 5’ ends in DNA refer to

The 3rd and 5th carbon atoms in the deoxyribose sugars

Purines

Nucleotides with double ring structure - Adenine and Guanine

Pyrimidines

Nucleotides with single ring structure- Cytosine and Thymine (Uracil)

Structure of a Nucleosome

Strand of DNA wrapped around 8 histone proteins, with an additional histone holding it in place. Linker DNA attaches one nucleosome to another. Many nucleosomes then coil around other proteins and arrange themselves into chromosomes.

What did the Hershey-Chase Experiment address?

To determine whether the genetic material of living organisms were amino acids or nucleic acids.

Explain the Hershey - Chase Experiment

1. A bacteriophage and bacteria E. Coli was used, as well as radioisotopes.

2. The researchers grew bacteriophages in two different cultures with radioisotopes, phosphorus 32 and sulfur 35. Sulfur is not present in DNA and therefore only detectable in the protein shell.

3. The two types of bacteriophage were then allowed to infect the e.coli bacteria.

The E.coli infected with phosphorus was radioactive, which indicated the presence of phosphorus within the cell- DNA.

The E.coli infected with Sulfur had no radioactivity.

This led them to conclude that DNA and not amino acids were the genetic material.