Module 2: Nucleic Acids Flashcards
Describe the structure of a nucleotide
Nucleotides are the monomers of nucleic acids.
Three parts:
Phosphate sugar
Pentose sugar (Deoxyribose in DNA, Ribose in RNA)
Nitrogenous base (ATGCU)
Nucleotides are joined by covalent bonds in a condensation reactions.
The 5 nitrogenous base pairs:
Purines = Adenine & Guanine
Pyrimidines = Thymine, Uracil, Cytosine
In complementary base pairing a purine and pyrimidine will pair together.
Describe the structure and formation of a nucleic acid
Nucleic acids are the polymers of nucleotides. DNA or RNA.
2 nucleotides are joined together with a covalent bond between the phosphate group of 1 and the pentose sugar of the other in a condensation reaction.
The backbone of a nucleic acid is a sugar‐phosphate backbone.
The same pentose sugar is always found in 1 nucleic acid:
- In ribonucleic acids (RNA) this is ribose
- In deoxyribonucleic acids (DNA) it is deoxyribose
What are the similarities and differences between DNA and RNA structure?
Similarities:
Differences:
Explain how complementary base pairs work
Adenine (Purine) always pairs with Thymine (Pyramidine).
Guanine (Purine) always pairs with Cytosine (Pyramidine).
They pair like this because of their structure (shape
[purine/pyramidine] and where they can form H bonds)
2 hydrogen bonds hold adenine and thymine together
3 hydrogen bonds hold guanine and cytosine together
This means that the sugar phosphate backbones are
always the same distance apart.
Outline the steps in DNA replication
- Double helix untwisted.
- DNA unzipped when helicase enzymes break the H bonds between base pairs.
- Both strands act as a template for free DNA nucleotides to align and synthesis and new strand (in the 5’ to 3’ direction) an complementary base pair [C‐G and A‐T].
- Hydrogen bonds between the bases reform.
- DNA polymerase joins the sugar‐phosphate backbones together on the new strands with covalent bonds.
The molecules twist back into a double helix.
There are now 2 identical DNA molecules.
Why id DNA replication known as semi-conservative replication?
This is because 2 identical DNA molecules are made, each with 1 strand from the original molecule (the conserved strand) which acted as a template strand and 1 new strand.
Why id DNA replication known as semi-conservative replication?
This is because 2 identical DNA molecules are made, each with 1 strand from the original molecule (the conserved strand) which acted as a template strand and 1 new strand.
Meselsohn and Stahl worked out that DNA replication was semi conservative.
Outline the role of RNA in the cells of living organisms
In transcription of protein synthesis RNA nucleotides align against the DNA template strand and complementary base pair (A‐U and G‐C). The enzyme RNA polymerase catalyses the formation of temporary hydrogen. The nucleotides are joined together to make a strand of mRNA (it is a copy of the DNA coding strand).
In translation the mRNA is taken to the ribosome (made up of rRNA and proteins). tRNA carries amino acids to the ribosomes to be joined into polypeptide chains.
Define the role of a gene?
A gene codes for a specific protein.
3 Nitrogenous bases = 1 amino acid
Different versions of the same gene = alleles
Transcription and translation
The cell requires a particular protein.
The gene coding for the protein is exposed by splitting the hydrogen bonds holding the double helix together in that region.
Free RNA molecules bind to their complementary exposed bases.
The sugar-phosphate backbone seals to form an mRNA strand – this is the copy of DNA for the particular protein that is needed.
The mRNA strand peels away from the DNA and leaves the nucleus via a nuclear pore.
The mRNA attaches to a ribosome.
The tRNA molecules have an anticodon (three bases) which attach to the mRNA. The tRNA also has a specific amino acid group at the opposite end of the molecule to the anticodon.
The amino acids are close enough together for a peptide bond to form between them, thus forming a protein with a specific primary structure.
