biology honors final (gene expression portion)
What is the job of a trp operon?
Allows bacteria to stop making certain essential molecules when the molecules are already present in the environment
List four processes happening in the nucleus that affect gene expression
DNA unpacking, transcription, addition of cap & tail, and splicing
Define transcription factors
In the eukaryotic cell, a protein that functions in initiating or regulating transcription. Transcription factors bind to DNA or to other proteins that bind to DNA.
Eukaryotic RNA polymerase needs the assistance of transcription factors. The binding of __________ to enhancers initiates transcription.
activators
An operon does not contain
an inducer
In a prokaryote, a section of DNA responsible for turning on and turning off of specific genes is called
an operon
In prokaryotes, when the inducer enters the cell it activates the gene by
binding with the repressor
repressor
binds to the operon to turn genes off; turns off transcription, protein that functions by binding RNA polymerase to the promoter
regulatory genes
codes for the repressor; expressed continually so the cell always has a small supply of repressor molecules
In ________ mammals, one X chromosome is inactive in each cell.
female
When the repressor binds to the operator, RNA polymerase cannot move from
promoter to the genes
In prokaryotes, the substance that binds to the repressor is the
inducer
Define silencers
A eukaryotic DNA sequence that functions to inhibit the start of gene transcription; may act analogously to an enhancer by binding a repressor
Define enhancers
A eukaryotic DNA sequence that helps stimulate the transcription of a gene at some distance from it. An enhancer functions by means of a transcription factor called an activator, which binds to it and then to the rest of the transcription apparatus.
Define activators
A protein that switches on a gene or group of genes
In eukaryotes what is more important, activators or repressors?
Activator proteins seem to be more important in eukaryotes than repressors. In multicellular eukaryotes, the "default" state for most genes seems to be "off." A typical animal/plant cell needs to turn on (transcribe) only a small percentage of its genes, those required for the cell's specialized structure and function.
What is alternative splicing and why is it important?
Alternative splicing is a type of regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns. It's important because an organism can get more than one type of polypeptide from a single gene.
What happens to the introns after transcription before the RNA leaves the nucleus?
Before the RNA leaves the nucleus, the introns are removed.
List four processes happening in the cytoplasm that affect gene expression
Breakdown of mRNA, translation, cleavage/modification/activation, and breakdown of protein
Describe how proteins are made (transcription and translation)
DNA is a code in your body for your proteins. For this to happen, first the DNA molecule is transcribed into mRNA, which leaves the nucleus into the cytoplasm. Translation begins when an mRNA strand attaches to the ribosome. Then, tRNA molecules, each carrying a specific amino acid, meet the ribosome. The 3 tRNA anticodons need to match with the 3 mRNA codons for the amino acid to be left and attached to the chain of amino acids. This chain forms a protein. The process starts with a start codon (AUG) and ends with a stop codon.
_________ ________ in eukaryotic chromosomes helps regulate gene expression
DNA packing
If a nerve cell and a skin cell in your body have the same genes, how can the cells be so different?
Each cell type must be expressing certain genes that are present in, but not expressed in, the other cell types
What is different about the promoters in bacteria vs. eukaryotes?
Each eukaryote usually has its own promoter and other control sequences
Explain how breakdown of mRNA affects gene expression
Enzymes in the cytoplasm break down mRNA and the timing of it is an important factor regulating the amounts of various proteins that are produced in the cell. Long-lived mRNAs can be translated into many more protein molecules than short-lived ones.
Early understanding of gene control came from studies of the bacterium
Escherichia coli (E.coli)
In multicellular eukaryotes, when do cells become specialized (differentiated)?
From selective gene expression, the turning on and off of genes; as a zygote develops into a mature organism
Explain one biological significance of gene expression
Gene expression prevents the same genes from being copied all the time. The operon turns off specific genes at specific times so we have the correct amount of what we need (ex. 2 arms, 10 fingers). The operon turns the genes on and off so they can be made and stop being made.
Discuss how genes are expressed or regulated in prokaryotes
In prokaryotes, genes are turned off and on using an operon. An operon is a section of DNA that contains a regulator, promoter, operator, and structural genes. To turn the gene off, a repressor attaches to the operator. This doesn't allow the RNA polymerase to go from the promoter to the structural genes. To turn the gene on, the repressor is taken off the gene when the inducer from the environment attaches to the repressor and goes past the operator and transcribes the structural gene into mRNA to build chains of polypeptides. The regulator is a section of DNA that codes for the repressor.
What is the difference between mRNA lifetimes between prokaryotes and eukaryotes?
Prokaryotic mRNAs have very short lifetimes and are degraded by enzymes within a few minutes after their synthesis. In contrast, eukaryotic mRNA can have lifetimes of hours or even weeks.
Explain how protein inactivation affects gene expression
Protein inactivation affects gene expression. Post-translational control mechanisms in eukaryotes often involve the cleavage of a polypeptide to yield a smaller final product that is the active protein, able to carry out a specific function in the organism. Protein inactivation creates an inability for the functions to be carried out.
How does dense packing of DNA in chromosomes prevent gene expression?
RNA polymerase and other proteins required for transcription do not have access to the DNA in tightly packed regions of a chromosome.
What is this cutting and pasting process called?
RNA splicing
_________ inhibit the start of transcription.
Silencers
What is the importance of the cap and tail?
The cap and tail facilitate the export of the mRNA from the nucleus, protect the mRNA from attack by cellular enzymes, and help ribosomes bind to the mRNA.
Explain how the initiation of translation affects gene expression
The process of translating mRNA into polypeptide also offers opportunities for regulation. Among the molecules involved in translation are a lot of proteins that control the start of polypeptide synthesis.
Explain why many eukaryotic genes are longer than the mRNA that leaves the nucleus?
These genes have introns, noncoding sequences of nucleotides that are spliced out of the RNA transcripts.
Explain how protein breakdown affects gene expression
This regulation allows a cell to adjust the kinds and amounts of its proteins in response to changes in its environment. It also enables the cell to maintain its proteins in prime working order.
When does X inactivation happen?
early in embryonic development
Coordinated gene expression in eukaryotes seems to depend on the association of specific ______ with groups of genes.
enhancer
Gene regulation is much more complex in ________ ________ than in __________
eukaryotic organisms; bacteria
Complex assemblies of proteins control ______ ______
eukaryotic transcription
DNA can fit into a chromosome because of dense packing. DNA winds around clusters of _______ proteins, forming a string of bead-like _______ . The beaded fiber coils, supercoils, and further folds into _______ ________.
histones; cluster; metaphase chromosome
The DNA is made of introns and exons. The ______ contain the code for the protein amino acids to be made and the ______ are considered noncoding segments of DNA. Before leaving the nucleus as mRNA, eukaryotic transcripts are modified or processed in several ways.
mRNA; introns
So, in gene expression if a gene is turned on, DNA is transcribed into _________, and that message is translated into a specific ________ _________
mRNA; protein molecule
Cellular differentiation results from selective turning ____ or _____ of genes at multiple control points
on; off
Differentiated cells (cells that have been specialized) express a _____ percentage of their genes and they _____ retain a complete set of genes
small; can
inducer
something that triggers the production of the protein
The control of gene expression makes it possible for cells to produce
specific kinds of proteins when and where they are needed
operator
the location where a repressor attaches to turn off a gene; acts as a switch; determines whether RNA polymerase can attach to the promoter and start transcribing the genes
Gene regulation is
the turning on and off of genes
promoter
usually determines the rate of transcription; site where the transcription enzyme, RNA polymerase, attaches and initiates transcription
