6.10.1 Eukaryotic Gene Control: Transcriptional Controls

Question 1

gene

Answer 1

• a distinct unit of hereditary information composed of a specific nucleotide sequence in DNA

Question 2

note

Answer 2

• All of the cells of an organism contain the same genes, but they don’t necessarily use the same genes. Eukaryotic cells employ a number of control mechanisms to ensure that genes are expressed only when they are needed.
• There are several control points during gene expression. Pretranscriptional controls include DNA methylation and histone acetylation. Transcriptional controls involve transcription factors, which are necessary in order for transcription to occur.
• Pretranscriptional gene control involves the physical availability of genes. Two examples are DNA methylation and histone acetylation.

Question 3

Enhancers

Answer 3

• sequences of DNA that are up to thousands of nucleotides away from the promoter. Transcription factors called activators bind to enhancers and help form the transcription initiation complex.
• are sequences of non-coding DNA that are involved in the control of DNA transcription. Unlike promoters, an enhancer is physically farther away from the gene that it controls and can be either upstream (toward the 5’ end) or downstream (toward the 3’ end) from the gene.

Question 4

DNA methylation:

Answer 4

DNA methylation is the addition of methyl groups (-CH3) to an intact DNA strand, typically to the cytosine bases. DNA methylation results in the inactivation of DNA

Question 5

Histone acetylation:

Answer 5

Histone acetylation is the attachment of acetyl groups (-COCH3) to specific amino acids of histones. Acetylation changes the histone’s conformation, and loosens its grip on DNA. Acetylated DNA is transcribed more readily.

Question 6

transcription factors

Answer 6

• regulate the control of gene expression once a gene is physically available.
• Transcription factors called activators bind to the enhancer. The DNA then folds over and the activators bind to the transcription factors at the promoter, forming the transcription initiation complex. Tran-scription then proceeds.
• Transcription factors have a DNA-binding domain, which is part of its three-dimensional structure and allows it to bind to DNA. The three main types of DNA-binding domains include helix-turn-helix, the zinc finger, and the leucine zipper.
  a) The left side of the illustration shows the helix-turn-helix DNA binding domain. Notice how the two cylindrically shaped portions of a transcription factor, which are alpha helices, wrap around the DNA strand.
  b) The DNA binding domain known as zinc finger consists of repeating units of an alpha helix and beta pleated sheat held together by a zinc atom. These repeating units wrap around the DNA strand.
  c) The leucine zipper consists of two polypeptide chains that consist of many leucines. The chains are coiled around each other, bringing two polypeptides together.

Question 7

review

Answer 7

• A promoter is a sequence of DNA near the gene
  that regulates eukaryotic gene transcription.
  RNA polymerase requires the presence of transcription
  factors in order to bind to the promoter. One transcription factor recognizes the TATA box within the promoter while the other transcription factors recognize proteins (including each other and RNA polymerase). Transcription only proceeds when the transcription initiation complex is formed.

Question 8

Which of the following correctly describes the manner in which histone acetylation affects gene regulation?

Answer 8

• The acetyl group binds to the histone to loosen the bond between DNA and the histone to allow transcription

Question 9

True or false?
Transcription factors called enhancers bind to activators, which are sequences of non-coding DNA that are involved in the control of DNA transcription.

Answer 9

• false

Question 10

Transcription factors are regulatory proteins that work with control elements to affect regulation of gene expression. Control elements

Answer 10

• are non-coding regions of DNA.
• bind transcription factors.
• include enhancers and promoters

Question 11

The TATA box functions as

Answer 11

• a binding site for regulatory proteins on the DNA strand

Question 12

The attachment of −CH3 to DNA bases to effect long-term DNA inactivation is called

Answer 12

• DNA methylation.

Question 13

Gene expression cannot be controlled by

Answer 13

• reverse transcriptase.

Question 14

The functionality of different types of cells depends upon

Answer 14

• the types of genes that are expressed in the cell.