Small RNA's in the Regulation of Biological Processes

Question 1

What is the C-value?

Answer 1

Genome size

Question 2

What is heterochromatin?

Answer 2

Transcriptionally inactive chromatin

Question 3

Which type of RNA is important in X chromosome inactivation?

Answer 3

Long ncRNA

Question 4

Which is better at silencing genes, single stranded RNA or dsRNA?

Answer 4

dsRNA

Question 5

Explain the biochemistry of RNAi, including DICER, AGO and RISC.

Answer 5

dsRNA is derived from viruses to produce siRNA which inhibits the RNA that the dsRNA is derived from. DICER breaks up the dsRNA into 21-25bp fragments. The passenger strand is then removed using Argonaute-PIWI proteins. Multiprotein RISC complexes are formed which cleave mRNA molecules that are complimentary to the siRNA,

Question 6

Therapeutical use of siRNA? Why does it not trigger cytokines?

Answer 6

DNA fragments 25bp or less will not trigger cytokine reactions. siRNA is small enough to get into cells without invoking a cytokine response, therefore can be used to switch off genes we don’t want expressed.

Question 7

What form is siRNA especially useful in?

Answer 7

shRNA

Question 8

Describe how miRNA is formed?

Answer 8

Initially made as pri-miRNA which is processed by RNAse III endonuclease Drosha and is then transported into the cytoplasm as pre-miRNA by exporting in the nuclear membrane. Processing then allows the pre-miRNA to become single stranded and is then passed on to the RISC complex and become miRNA’s.

Question 9

What is gene knockdown?

Answer 9

Decreasing the amount of protein you get from a gene.

Question 10

How much affinity do miRNA sequences have? What regions and names?

Answer 10

Seed region where there is perfect complementarity. Bulge where there’s a bulge and no bonds. Then a region of less stringent complementarity