53 WJEC Biology AS Level - Study And Revision Guide - Neil Roberts (1.5 Nucleic Acids And Their Functions) Flashcards
Draw a diagram showing the structure of a double-stranded DNA molecule
How do you extract DNA?
- Grind up a sample of cells in a solution of ice cold salt and washing up liquid.
- The detergent dissolves the lipids in the phospholipid membranes, allowing DNA to be released
- The cold temperature protects the DNA from cellular DNAases.
- Addition of protease will digest any remaining cellular enzymes and the histones that the DNA is wound around.
- Finally, adding ethanol to the salt already present, will cause the DNA to precipitate out from the solution.
How is RNA different from DNA?
- It is usually a shorter, single-stranded molecule.
- Nucleotides also differ in that the sugar is ribose.
- One of the bases thymine is replaced with uracil.
What are the different types of RNA?
Three different types of RNA are involved in protein synthesis:
- mRNA
- rRNA
- tRNA
Describe mRNA.
Messenger RNA is a single-stranded molecule typically 300-2000 nucleotides long.
It is produced in the nucleus using one of the DNA strands as a template during transcription.
Describe rRNA
Ribosomal RNA forms ribosomes with the addition of protein.
Describe tRNA
Transfer RNA is a small molecule that winds itself into a cloverleaf shape.
It has an anticodon at one end, and an amino acid at the other.
As the name suggests, it ‘transfers’ the correct amino acid to the growing polypeptide during translation.
How many hydrogen bonds are there between the bases in DNA?
There are two hydrogen bonds between A and T (remember A Tea for two!),
There are three hydrogen bonds between G and C.
How does the double stranded DNA form a double helix?
The double stranded DNA molecule twists to form a double helix.
What should you remember when comparing DNA and mRNA?
When comparing DNA and mRNA remember that DNA is a double helix and mRNA is a single strand.
