Chapter 8: Control of Gene Expression

Question 1

miRNA

Answer 1

• noncoding (does not turn into protein)
• Humans express more than 400 different miRNAs

-these regulate at least one third of all protein coding genes

-they act by base pairing with specific mRNAs and

-regulate stability and translation

Question 2

siRNAs

Answer 2

noncoding (does not turn into protein)

-primitive immune system: stops proliferation of retrotransposons and viral RNA

Question 3

Name the three major post transcriptional controls

Answer 3

• microRNAs direct the destruction of target mRNAs
• small interfering RNAs protect cells from infections
• thousands of long noncoding RNAs may also regulate mammalian gene activity

Question 4

Describe microRNAs destroying target mRNAs

Answer 4

Each precursor miRNA transcript is processed to form a double-stranded intermediate, which is further processed to form a mature, single-stranded miRNA

This miRNA assembles with a set of proteins into a complex called RISC, which then searches for mRNAs that have a nucleotide sequence complementary to its bound miRNA

Depending on how extensive the region of complementarity is, the target mRNA is either rapidly degraded by a nuclease within the RISC or transferred to an area of the cytoplasm where other nucleases destroy it

Question 5

Describe RNAs protecting cells from infections

Answer 5

Double-stranded RNAs from a virus or transposable genetic element are first cleaved by a nuclease called Dicer. The resulting double-stranded fragments (known as siRNAs) are incorporated into RISCs, which discard one strand of the duplex and use the other strand to locate and destroy foreign RNAs that contain a complementary sequence

Question 6

RISC

Answer 6

RNA induced silencing complex

Question 7

RITS

Answer 7

RNA induced transcriptional silencing

Question 8

Transcriptional silencing

Answer 8

a single-stranded siRNA is incorporated into a RITS complex, which uses the single-stranded siRNA to search for complementary RNA sequences as they emerge from a transcribing RNA polymerase.

The binding of the RITS complex attracts proteins that promote the modification of histones and the formation of tightly packed heterochromatin.

This change in chromatin structure, directed by complementary base-pairing, causes transcriptional repression. Such silencing is used in plants, animals, and fungi to hold transposable elements in check

Question 9

Long noncoding RNAs can serve as scaffolds

Answer 9

As described in Chapter 7, RNAs can fold into three-dimensional structures that can be recognized by specific proteins.

By engaging in complementary base-pairing with other RNA molecules, these long noncoding RNAs can, in principle, localize proteins to specific sequences in RNA or DNA molecules

Question 10

Crisper Cas

Answer 10

-cuts out segment of DNA to be replaced
-extremely difficult
- can change hereditary conflicts

weird repeated sequences

Question 11

How did Crisper Cas come to be in bacteria?

Answer 11

• short viral DNA sequence is integreated into CRISPR Locus
• RNA is transcribed from CRISPR locus, processed, and bound to Cas protein
• small crRNA in complex with Cas seeks out and destroys viral sequences