Control of Gene Expression

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What are 'housekeeping' genes?
Genes that code for enzymes as they are constantly required for things like respiration etc
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What are tissue-specific genes?
They are genes that code for protein based hormones that are only required by certain cells (eg for growth and repair)
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Why is it helpful that genes can be regulated and turned on and off etc?
It helps save vital resources from being wasted
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What are the 4 ways genes are regulated?
Transcriptional, post-transcriptional, translational and post-translational
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Transcriptional gene control
Genes can be turned on and off
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Post-transcriptional gene control
mRNA can be modified regulating translation and the types of proteins that are produced
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Translational gene control
Translation of the gene can be stopped or started
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Post-translational gene control
Proteins produce can be modified after synthesis which can change their functions
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What is chromatin?
DNA wrapped tightly around proteins called histones (this is because DNA is slightly neg and histones are slightly pos)
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What is heterochromatin?
Tightly wound DNA around the histones causing DNA to be visible during cell division
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What is euchromatin?
Loosely wound DNA around the histones, present during interphase
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What happens when DNA is tightly wound?
Transcription can not occur because RNA polymerase can not access the genes, where as it is possible with euchromatin
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What stages are heterochromatin and euchromatin found in meiosis and why?
HC is found during cell division so protein synthesis cant occur and euchromatin is found in interphase when protein synthesis is needed
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How is heterochromatin formed?
Acetyl groups and phosphate groups are added to the histones as they reduces the positive charge making them more negative, making the DNA wind tighter
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How is euchromatin formed?
Methyl groups are added to the histones increasing the positive charge and making the less negative so the DNA winds more loosely
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What is epigenetics?
The name given to the type of gene control when forming heterochromatin or euchromatin
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What is an operon?
A group of genes under the same regulatory mechanism and are expressed at the same time
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Why do we have operons?
They are an efficient way of saving resources
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What is the prefered respiratory substrate in bacteria and what is used when there is a short supply of it?
Glucose and it uses lactose when glucose is in short supply, however this requires different enzymes
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What is the Lac Operon?
A group of 3 genes (LacZ, LacY and LacA) involved in the metabolism of lactose
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What do LacA LacY and LacZ code for and how are they transcribed?
They all are structural genes that code for enzymes needed to metabolise lactose and they are transcribed onto a single molecule of mRNA
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What is LacI and where is it located?
A regulatory gene that codes for a repressor protein and is located near to the Lac operon
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What is the Lac repressor protein?
It is a protein that prevents transcription of the structural genes in the absence of lactose
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Where is the repressor protein bound to?
The operator of the operon which is close to the structural genes
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How does the repressor protein work and what is this process called?
It prevents the RNA polymerase from binding to the genes, this is called down regulation
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What is the promoter?
The section of DNA which is the binding site for DNA polymerase
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What happens at the Lac operon when lactose is present?
The lactose binds to the repressor protein causing it to change shape and so it can no longer bind to the operator, then RNA polymerase is able to transcribe the three structural genes
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What is the role of Cyclic AMP?
To bind to the cAMP receptor protein and up-regulate the rate of transcription
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What is pre-mRNA and what needs to happen to it in order for it to bind to a ribosome
It is the product of transcription and needs to be modified before it is able to be translated (bind to ribosome and synthesised)
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How is pre-mRNA modified?
A cap (modified nucleotide) is added at the 5' end and a tail (long chain of adenine nucleotides) is added to the 3' end to stabilise mRNA and prevent decay. It is cut at introns and exons join.
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What is the difference between an intron and an extron?
They are both sections of DNA, however an intron does not code for anything where as an exon is coding DNA
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What is RNA editing and why is it used?
It is where deliberate substitution, deletion and insertion can occuring the nucleotide sequence resulting in the synthesising of different proteins that may be needed instead
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Name 3 mechanisms used to regulate the process of protein synthesis
Degradation of mRNA, binding of inhibitory proteins and activation of initiation factors
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Degradation of mRNA
Making the mRNA more resistant so it will last longer in the cytoplasm, resulting in a greater quantity of protein synthesised
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Binding of inhibitory proteins
Prevents mRNA from binding to the ribosome and therefore preventing the synthesis of proteins
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Activation of initiation factors
They aid the binding of mRNA to the ribosome
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What are protein kinases?
Enzymes that catalyse the adding of phosphate groups to proteins (so that it changed the tertiary structure thus changing the function of a protein
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What does post translational control involve?
Addition of non-protein groups, modifying amino acids and formation of disulphide bridges, folding or shortening of proteins and modification by cAMP
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Other cards in this set

Card 2

Front

What are tissue-specific genes?

Back

They are genes that code for protein based hormones that are only required by certain cells (eg for growth and repair)

Card 3

Front

Why is it helpful that genes can be regulated and turned on and off etc?

Back

Preview of the front of card 3

Card 4

Front

What are the 4 ways genes are regulated?

Back

Preview of the front of card 4

Card 5

Front

Transcriptional gene control

Back

Preview of the front of card 5
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oliverreddy

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great help

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