Question

3) Antibodies can be membrane-bound or secreted, depending on whether a stretch of additional amino acids are present or not. What process do you think determines if these amino acids are present?

		postranslational covalent attachment of a membrane spanning domain to the antibody
		alternative RNA splicing
		phosphorylation
		polyadenylation
		ubiquitin addition

10)

How does the Cas9 system target where it produces a double-strand break in the DNA?

		The Cas9 protein binds to a recombinase, allowing it to disable the gene of interest.
		The Cas9 protein contains amino acids that can interact with specific sequences in the DNA, targeting Cas9 to those specific sites.
		A guide RNA molecule is associated with Cas9 and will direct Cas9 to bind at sequences complementary to the guide RNA.
		A guide RNA molecule associated with Cas9 provides the catalytic activity to cleave the DNA where Cas9 binds.

11)

1. snRNAs

   		are removed by the spliceosome during RNA splicing.
   		are translated into snRNPs.
   		are important for producing mature mRNA transcripts.
   		can bind to specific sequences at intron–exon boundaries through complementary base-pairing.

12)

Gene expression differs among mature cell types within an organism. This means that

		different mRNAs and proteins are produced in different cell types.
		different genes are found in the DNA of different cells in the organism.
		DNA sequences are modified in different cell types.
		alternative DNA splicing has occurred.
		the cells had to be infected by a virus.

Answer 1

You have asked multiple questions. As per Chegg Q&A Guidelines, I am answering only the first question.

Antibodies are immunoglobin molecules produced by B-cells. These are formed by VDJ recombination and thus each B-cell produces a unique antibody in multiple copies. Initially the B-cells are inactive and a hydrophobic peptide chain is attached to the antibody which keeps it anchored to the membrane. The B-cells are released into the blood/lymph stream where they might encounter an appropriate antigen. When the membrane-bound antibody does recognize an antigen, the B-cell undergoes maturation and differentiation to form clones of itself. A certain group of these clones still express the antibody in the membrane and form memory cells. Remaining clones which are the majority of the clones undergo a splicing variation that fails to add the hydrophobic tag to the antibody. As a result, the antibody is no longer attached to the membrane but rather is secreted into the extracellular space where it can mount an immune response against the invading antigen.