Explain how the presence of double bonds affects membrane integrity at low temperatures.

1. Presence of C=C double bonds in fatty acid phospholipid hydrocarbon tails causes kinks, thus preventing close packing of phospholipids. [1] [what do C=C double bonds do to the structure of the cell membrane?]
2. This lowers the temperature at which the membrane becomes less fluid. [1]
3. Hence, membranes with more double bonds / unsaturated hydrocarbon tails are more fluid / tend to maintain membrane integrity at low temperatures / vice versa. [1]

Describe a non-viral gene delivery system which can be used to deliver the functional [something] allele to stem cells.

1. Liposome-mediated gene transfer
2. Plasmid containing normal functional allele is inserted into the aqueous core of an artificial phospholipid bilayer sphere
3. The liposome fuses with the stem cell's plasma membrane, releasing the plasmid containing the normal allele into the cell's cytoplasm.

How does an enhancer sequence work?

When activators bind to enhancers, spacer DNA bends, allowing the activator to directly interact with RNA polymerase/general transcription factors at the promoter.

Controlling strength of promoter in prokaryotes to regulate transcription

Strength of promoter is determined by how similar the -10 and -35 sequences are to the consensus sequences which are:

-10: 5' - TATAAT - 3'

-35: 5' - TTGACA - 3'

Stronger promoters have higher frequency of transcription.

In what way does the alpha helix (of some protein) and RNA differ?

 Helical structures in RNA is a result of it folding back on itself. The helical structures in the protein is a result of the regular coiling of the alpha helix;

 The helical structures in RNA are due to complementary base pairing between different segments of the same strand. The helical structures in protein are due to presence of hydrogen bonds within a single segment of polypeptide.

 The sections in RNA are made up of a double helix. The sections in protein are made of a single helix.

Why is [disease] suitable for treatment using gene therapy?

1. caused by a single gene
2. caused by recessive allele
3. ease of access to affected area
4. no invasive surgery needed