Gene Expression Review

Operon

Cluster of genes controlled by the same promoter site

Operator

A sequence of nucleotides near the start of an operon where an active repressor can attatch

Repressor

Protein that can turn off the operon

Negative Gene Control

Operons are switched off by the active form of the repressor

Positive Gene Control

An activator can increase the rate of transcription

Activator

Protein that binds to DNA and stimulates transcription

Differential Gene Expression

The expression of different genes by cells with the same genome

Histone Acetylation

Acetyl groups are attached to lysines in the histone tails

Histone Methylation

Addition of methyl groups to histones, can promote condensation of the chromatin

DNA Methylation

Certain bases in the DNA can be methylated (usually cytosine)

Genomic Imprinting

Expression of an allele in offspring depends on whether the allele is inherited from the male or female parent, due to methylation 

Epigenetic Inheritance

Inheritance traits transmitted by things not directly involved with the nucleotide sequence

Control Elements

Segments of noncoding DNA that help regulation transcription by binding to certain proteins

Transcription Factors

Increase the level of transcription

Enhancers

Distol control element

Mediator Protein

Interact with proteins at the promoter

Silencing 

Repressors recruit proteins that deaceylate the histones and reduce transcription

Alternative RNA Splicing

Different RNAs are made from the same transcript, depending on which introns are cut out

Inducible Operon

Typically inactive but can be turned on (induced) by a specific molecule

Repressible Operon

Typically active but can be turned off by the presence of a corepressor

mRNA Degeneration

How long is the “lifespan” of an MRNA molecule in the cytoplasm?

MicroRNA (miRNA)

Small, single stranded RNA made from a hairpin structure, can degrade or prevent translation of an mRNA

RNA Interference

A technique used to silence the expression of selected genes, uses RNA molecules that match the sequence of a gene to start the breakdown of mRNA genes

What is an operon?

A cluster of genes controlled by the same promoter site

List and explain the functions of the parts of an operon

1. Promoter- the DNA sequence where RNA polymerase binds to start transcription

2. Operator- a sequence of nucleotides near the start of an operon where an active repressor can attach 

3. Regulator Gene- codes for the repressor protein that controls the operon

4. Structural Genes- the genes that code for proteins/enzymes needed for a specific function

Explain how a repressible operon works

It is usually turned on but can be turned off when a corepressor is present, it helps the repressor protein attach to the operator, RNA polymerase is then blocked so transcription stops

Explain how an inducible operon works

It is usually turned off but can be turned on when an inducer molecule is present, it binds to the repressor protein and makes it active. This allows RNA polymerase to continue transcribing genes 

In what ways can metabolic pathways be controlled?

Gene Regulation, Feedback Inhibition, and Activators/Repressors

How are proteins broken down in cells?

Small molecules of ubiquitin are attached to mark the protein for destruction, proteasomes destroy them

Explain positive control of operons

Uses an activator protein to help RNA polymerase bind to the promoter and start transcription

Explain multiple mutations

When more than 1 change occurs in DNA, usually leading to cancer overtime

3 categories of genetic changes that could cause a proto-oncogene to become an oncogene

Movement of DNA, Amplification, and Point Mutation