Mastering Biology Gene Expression

Operon vocabulary

Can you match terms related to operons to their definitions?

Drag the terms on the left to the appropriate blanks on the right to complete the sentences.

1. A(n) operonis a stretch of DNA consisting of an operator, a promoter, and genes for a related set of proteins, usually making up an entire metabolic pathway. 2. Thegenes of an operonis/are arranged sequentially after the promoter. 3. A(n) promoter is a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place. 4. A(n) regulatory genecodes for a protein, such as a repressor, that controls the transcription of another gene or group of genes. 5. Regulatory proteins bind to the operatorto control expression of the operon. 6. A(n) repressoris a protein that inhibits gene transcription. In prokaryotes, this protein binds to the DNA in or near the promoter. 7. A(n) inducer is a specific small molecule that binds to a bacterial regulatory protein and changes its shape so that it cannot bind to an operator, thus switching an operon on.

Regulation of model operons

The trp and lac operons are regulated in various ways.
How do bacteria regulate transcription of these operons?

operon is not transcribed lac operon: lactose absent trp operon: tryptophan present operon is transcribed, but not sped up through positive control lac operon: lactose present, glucose present trp operon: tryptophan absent operon is transcribed quickly through positive control lac operon: lactose present, glucose absent

Regulation of a hypothetical operon

Drag the labels onto the diagram to identify the small molecules and the states of the regulatory proteins. Not all labels will be used.

For positive control, (a) will be the inactive activator, (b) will be cAMP, and (c) will be the active activator. In other words, the process won’t proceed unless the activator has a molecule bound to it. And the specific molecule necessary, in this case, will be cyclic AMP. For negative control, (d) will be the active repressor that is MISSING a molecule, (e) will be athelose, and (f) will be the inactive repressor which HAS a molecule attached to it. In other words, this process will be repressed unless a specific molecule attaches to the active repressor to allow the process to start. The specific molecule necessary, in this case, will be athelose. Once it binds to the repressor, the repressor will detach and become inactivated, allowing the process to start.

Which statements about the modification of chromatin structure in eukaryotes are true?

Acetylation of histone tails is a reversible process. DNA is not transcribed when chromatin is packaged tightly in a condensed form. Some forms of chromatin modification can be passed on to future generations of cells. Methylation of histone tails in chromatin can promote condensation of the chromatin. Acetylation of histone tails in chromatin allows access to DNA for transcription.

Which statements about the regulation of transcription initiation in these genes are true?

The fantasin gene will be transcribed at a high level when activators specific for control elements A, B, and C are present in the cell. Both the fantasin gene and the imaginin gene will be transcribed at high levels when activators specific for control elements A, B, C, D, and E are present in the cell. Control elements C, D, and E are distal control elements for the imaginin gene.

Which of the following choices represent mRNA molecules that could be produced from the primary RNA transcript by alternative RNA splicing? (In each choice, the yellow part on the left represents the 5′ cap, and the yellow part on the right represents the poly-A tail.)
Select all that apply.

all completely green sequence