Chapter 10: Photosynthesis & siRNA

Question 1

Autotrophs

Answer 1

“Self-feeders”- produces of the biosphere

Sustain themselves by producing their organic molecules from CO₂ and other inorganic raw materials obtained from the environment

Photoautotrophs- organisms that use light as a source of energy to synthesize organic substances

Question 2

Heterotrophs

Answer 2

“Other-feeders”- consumers of the biosphere

Sustain themselves by consuming plants or other organisms

Decomposers- consume the remains of other organisms or organic litter such as feces and fallen leaves

Question 3

siRNA structure

Answer 3

Double-stranded, non-coding RNA molecule

Usually between 20 and 24 base pairs

Structure has hydroxylated 3’ and phosphorylated 5’ ends

Question 4

siRNA complementary enzyme

Answer 4

Dicer enzyme

Question 5

siRNA mechanism of action

Answer 5

1. Double-stranded RNA is cleaved by the Dicer enzyme; forms ds siRNA
2. ds siRNA enters the cell and forms the RNA-induced silencing complex (RISC) with other proteins
3. This is unwound which forms the ss siRNA
4. Strand of RNA with the 5’ end base pairing, miR guide strand, that is thermodynamically less stable remains part of the RISC complex
5. Can now scan for complementary mRNA
6. Once this anti-sense strand binds to the target mRNA cleavage is induced
7. Foreign mRNA is recognized by the host cell as abnormal and is degraded, no translation is possible and therefore the gene is silenced