chap11 - 11 Regulation of Gene Expression Several...

Info iconThis preview shows pages 1–15. Sign up to view the full content.

View Full Document Right Arrow Icon
Regulation of Gene Expression 11
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Several Strategies Are Used to Regulate Gene Expression Gene expression is tightly regulated . Gene expression may be modified to counteract environmental changes, or gene expression may change to alter function in the cell. Constitutive proteins are actively expressed all the time. Inducible genes are expressed only when their proteins are needed by the cell.
Background image of page 2
Potential Points for the Regulation of Gene Expression
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Genes can be regulated at the level of transcription . Gene expression begins at the promoter where transcription is initiated. In selective gene transcription a “decision” is made about which genes to activate. Two types of regulatory proteins—also called transcription factors —control whether a gene is active.
Background image of page 4
These proteins bind to specific DNA sequences near the promoter: Negative regulation—a repressor protein prevents transcription Positive regulation—an activator protein binds to stimulate transcription
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Positive and Negative Regulation (Part 1)
Background image of page 6
Positive and Negative Regulation (Part 2)
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Acellular viruses use gene regulation to take over host cells. A phage injects a host cell with nucleic acid that takes over synthesis. New viral particles ( virions ) appear rapidly and are soon released from the lysed cell. This lytic cycle is a typical viral reproductive cycle—in a lysogenic phase, the viral genome is incorporated into the host genome and is replicated too.
Background image of page 8
A bacteriophage may contain DNA or RNA and may not have a lysogenic phase. The lytic cycle has two stages: Early stage —promoter in the viral genome binds host RNA polymerase and adjacent viral genes are transcribed Early genes shut down transcription of host genes, and stimulate viral replication and transcription of viral late genes. Host genes are shut down by a posttranscriptional mechanism. Viral nucleases digest the host’s chromosome for synthesis in new viral particles.
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Late stage —viral late genes are transcribed They encode the viral capsid proteins and enzymes to lyse the host cell and release new virions. The whole process from binding and infection to release of new particles takes about 30 minutes.
Background image of page 10
A Gene Regulation Strategy for Viral Reproductio n
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Human immunodeficiency virus ( HIV ) is a retrovirus with single-stranded RNA. HIV is enclosed in a membrane from the previous host cell—it fuses with the new host cell’s membrane. After infection, RNA-directed DNA synthesis is catalyzed by reverse transcriptase . Two strands of DNA are synthesized and reside in the host’s chromosome as a
Background image of page 12
The Reproductive Cycle of HIV
Background image of page 13

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Host cells have systems to repress the invading viral genes. One system uses transcription “terminator”
Background image of page 14
Image of page 15
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/09/2012 for the course BIO 160 taught by Professor Howardhaemmerle during the Winter '12 term at Bellevue College.

Page1 / 67

chap11 - 11 Regulation of Gene Expression Several...

This preview shows document pages 1 - 15. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online