Chapter 8

Question 1

What is RISC?

Answer 1

RNA-induced silencing control

Multiprotein complex, which incorporates one strand of a single-stranded RNA (ssRNA) fragment, such as miRNA, siRNA.

The single strand acts as a template for RISC to recognize complementary mRNA transcript. Once found, Argonaute in RISC activates and cleaves the mRNA.

This process is called RNA interference (RNAi) and it is found in many eukaryotes; it is a key process in gene silencing and defense against viral infections.

Involved in post-transcriptional control

Question 2

What is the spliceosome?

Answer 2

A spliceosome is a large and complex molecular machine found in the cell nucleus of eukaryotic cells.

The spliceosome removes introns from a transcribed pre-mRNA, a type of primary transcript.

Involved in post-transcriptional control

Question 3

What is a dicer

Answer 3

Dicer cleaves dsRNA into short double-stranded RNA and pre-miRNA into microRNA

Dicer facilitates the activation of RISC, which is essential for RNA interference.

Involved in post-transcriptional control

Question 4

What is a mediater?

Answer 4

Multiprotein complex that functions as a transcriptional coactivator in all eukaryotes.

Question 5

What is miRNA and how does it regulate gene expression?

Answer 5

MicroRNA

Can form RISC to recognize target RNA based on base pairing

Binds to complementary sequences of mRNAs and silencing the mRNA by cleaving into two pieces or destabilization through shortening of its poly(A) tail.

Question 6

What is siRNA and how does it regulate gene expression?

Answer 6

Small interfering RNA

Double stranded RNA molecules
Can form RISC to recognize target RNA based on base pairing

Interferes with expression of specific genes with complementary sequences by degrading mRNA after transcription, preventing translation

Question 7

What is a coactivator?

Answer 7

A coactivator is a type of transcriptional coregulator that binds to an activator (TF) to increase the rate of transcription of a gene or set of genes.

Question 8

What is RNAi?

Answer 8

RNA interference is a biological process in which RNA molecules inhibit gene expression or translation, by neutralizing targeted mRNA molecules.

Question 9

What is RITS?

Answer 9

RNA-induced transcriptional silencing complex

Triggered by short RNA molecules like siRNA, which functions as guide RNA recognizing complemenrary transcripts to help position the RITS complex near chromatin

When included in RITS, siRNA directs heterochromain formation.

Recruits writer proteins, which modify histone tails with a repressive chromatin mark

Question 10

What is a genetic screen?

Answer 10

A search through a large collection of mutants for a mutant with a particular phenotype.

Question 11

What is polymophism?

Answer 11

One of a number of common sequence variants that coexist in the population

Question 12

What is an allele?

Answer 12

One of a set of alternative forms of a gene

Question 13

What is a phenotype?

Answer 13

The observable character of a cell or an organism

Question 14

What is Epistasis analysis?

Answer 14

Comparing the phenotypes of different combinations of mutations to determine the order in which the genes act

Question 15

What is a haplotype?

Answer 15

Ancestral chromosome segment that has been inherited with little genetic rearrangement across generations

Question 16

What is a transgenic organism?

Answer 16

Animal or plant that has been permanently engineered by gene deletion, gene insertion, or gene replacement

Question 17

What is a genotype?

Answer 17

The genetic constitution of an individual cell or organism

Question 18

What defines a gain-of-function mutation?

Answer 18

A gain-of-function mutation increases the activity of the protein product or gives it novel activity.

The change in activity following a gain-of-function mutation happens even when the normal version of the protein is present therefore such mutations are often dominant.

Question 19

What defines a loss-of-function mutation?

Answer 19

Mutation that causes a gene product having less or no function

Question 20

What defines a dominant-negative mutation?

Answer 20

A dominant-negative mutation gives rise to a protein product which interferes with the function of the normal protein and therefore gives rise to a loss-of-function phenotype despite the presence of a normal version of the protein.

Question 21

What are single-nucleotide polymorphisms (SNPs)?

Answer 21

SNPs are single nucleotide differences between individuals.

Question 22

What is genome-wide associated study (GWAS)?

Answer 22

Genome-wide association study (GWAS) link SNPs (that represent haplotypes) with a specific trait, for example a disease and determine the probability of having a certain trait or developing a disease for carriers of different SNP variants.

Question 23

What is Cre-lox recombination?

Answer 23

Used to carry out deletions, insertions, translocations and inversion at specific sites in the DNA

Allows the DNA modification to be targeted to a specific cell type or trigger by a specific external stimulus.

Question 24

Define knockout of a gene

Answer 24

An existing gene is inactivated, “knocked out”, by replacing it or disrupting it with an artificial piece of DNA

Question 25

Define knock-down of a gene

Answer 25

RNA interference (RNAi) is silencing of genes with mRNA degradation.

siRNA are introduced into the cytoplasm.

Question 26

What are deletions?

Answer 26

Part of a chromosome or a sequences of DNA is lost during DNA replication

Question 27

What are insertions?

Answer 27

Addition of one or more nucleotides into a DNA sequence

Question 28

What are chromosomal translocation?

Answer 28

Chromosomal segment is moved from one location to another, either within the same chromosome or to another chromosome

Question 29

What are inversions?

Answer 29

Chromosome arrangement where a chromosome is reversed end to end, inverted.

Question 30

How does Cre-lox recombiantion work?

Answer 30

An enzyme, Cre recombinase, recombines a pair of short target sequences called “lox sequences”.

Cre recombinase catalyses a site specific recombination event between two loxP recognition sites.

What happens depends on the position ond directions of the loxP sites

Insertion - turn toward each other

Deletion - Turned same direction

Translocation - Same direction of different strands.

Question 31

What is Holliday Junctions?

Answer 31

Cross-shaped structures that forms during genetic recombination, when two double-stranded DNA become seperated into four strands in order to exchange information

Question 32

What is recombination?

Answer 32

Two molecules of DNA exchange pieces of their genetic material with each other

Pieces of DNA are broken and recombinated to produce new combination of alleles.

Causes offspring with traits that can differ from those found in the parents.

Question 33

What is alternative splicing?

Answer 33

Process during gene expression that results in a single gene coding for multiple proteins.

Exons may be included or excluded from the final mRNA

Question 34

Describe PCR

Answer 34

Polymerase Chain Reaction

Laboratory technique to amplify a single copy or copies of a segment of DNA

PCR uses a DNA polymerase from a thermophilic bacterium

Most of the resulting pool of dsDNA molecules will have DNA from primers at the 5’ ends

Question 35

What does it take to drive the expression of a gene?

Answer 35

Physical contact between a regulatory region and a gene is sufficient to drive the expression - but only if the regulatory gene is active