MCAT Content / Control Of Gene Expression In Eukaryotes / Dna Binding Proteins Transcription Factors

DNA binding proteins, transcription factors

Topic: Control Of Gene Expression In Eukaryotes

DNA binding proteins help to regulate protein production, cell growth and division, and storing DNA inside the nucleus. Histones, repressors and activators are examples of proteins that bind to DNA.

Eukaryotes require several other proteins, called transcription factors, to first bind to the promoter region and then help recruit the appropriate polymerase. The completed assembly of transcription factors and RNA polymerase bind to the promoter, forming a transcription pre-initiation complex.

Transcriptional repressors bind to promoter or enhancer regions and block transcription whereas the transcriptional activators promote transcription.

Enhancer regions are binding sequences, or sites, for transcription factors. They can be located upstream of a gene, within the coding region of the gene, downstream of a gene, or maybe thousands of nucleotides away. When a DNA-bending protein binds to an enhancer, the shape of the DNA changes. This shape change allows the interaction between the activators bound to the enhancers and the transcription factors bound to the promoter region and the RNA polymerase to occur. Whereas DNA is generally depicted as a straight line in two dimensions, it is actually a three-dimensional object. Therefore, a nucleotide sequence of thousands of nucleotides away can fold over and interact with a specific promoter.

 

Practice Questions

 

Khan Academy

Cell membranes and trafficking disorders

 

MCAT Official Prep (AAMC)

Official Guide B/B Section Passage 2 Question 5

Section Bank B/B Section Passage 8 Question 57

Sample Test B/B Section Question 57

Practice Exam 1 B/B Section Passage 4 Question 20

Practice Exam 1 B/B Section Passage 4 Question 23

Practice Exam 4 B/B Section Passage 1 Question 4


Key Points

• Transcription factors bind to the promoter region and then help recruit the appropriate polymerase to begin transcription.

• Enhancers can be located upstream of a gene, within the coding region of the gene, downstream of a gene, or thousands of nucleotides away.

• When a DNA-bending protein binds to the enhancer, the shape of the DNA changes, which allows interactions between the activators and transcription factors to occur.

• Repressors respond to external stimuli to prevent the binding of activating transcription factors.


Key Terms

Enhancer: a short region of DNA that can increase transcription of genes

Repressor: any protein that binds to DNA and thus regulates the expression of genes by decreasing the rate of transcription

Activator: any chemical or agent which regulates one or more genes by increasing the rate of transcription

Transcription factor: a protein that controls the rate of transcription of genetic information from DNA

Promoter: a region of DNA where transcription of a gene is initiated

RNA polymerase: an enzyme that turns DNA into RNA



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