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30 Cards in this Set
- Front
- Back
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Why is control of gene expression more complex in eukaryotes than prokaryotes? |
-Bigger genomes -Eukaryotic DNA packaged into chromatin -Needs to respond to more signals -Some have differentiated cells with different functions |
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How are genes regulated pre transcription? |
Gene copy number Gene re-arrangements Modulating access of genes to transcription |
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What is acetylation? |
Addition of acetyl groups to the N terminal of histones, decreasing strength of binding to DNA |
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What is methylation? |
Methylation occurs on cytosine bases to make 5-methylcytosine. Done to specific bases with DNA methyltransferase enzymes. |
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What are CpG islands? |
Regions of the genome with a high CG content, surrounded by unmethylated regions. Methylation of these regions indicates whether nearby genes are expressed. |
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How are methylation patterns inherited? |
Inherited when the strand replicates due to action of methyltransferase Dnmt1. |
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What is meant by the term 'epigenetics' |
Information that is additional to gene sequence |
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How do transcription factors help regulate gene expression? |
Different transcription factor binding sites are present on the Eukaryotic genome |
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What is an enhancer binding site? |
A site that binds transcription factors - effects are normally indirect i.e. changing chromatin structure |
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What are the two main domains of transcription factors? |
Activation domain (for polymerase II) DNA binding domain |
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Where do alpha helices bind on the DNA molecule? |
Major groove where the specific DNA sequence is |
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Describe the helix-turn motif |
Two alpha helices joined by a flexible turn |
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What is a homeodomain? |
A special class of helix-turn motifs that bind DNA as dimers. Only found in eukaryotes. |
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What is a leucine zipper? |
Two monomers form a coiled coil Two helices coil round each other Interactions between leucines between chains Interacts with major groove |
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What is a zinc finger? |
Alpha helix and two segment antiparallel beta sheets Four cysteins (or two cys and two his) interact with a zinc atom |
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What is an activation domain? |
Protein that recruits transcription factors and other proteins to stimulate transcription from a nearby promoter |
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What is the mediator complex? |
Bridge between transcription factor and RNA polymerase II |
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How do steroid hormones reach the nucleus? |
-Pass through plasma membrane -Bind to intracellular receptor which dimerises -Activated receptor-steroid complex enters nucleus -Binds to regulatory sites on DNA -Gene expression changed |
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Describe the MAP kinase pathway |
-Signal molecule causes receptor dimerization -Chain of phosphorylation events -Signalling cascade -Phosphorylated transcription factor binds to regulatory sites on DNA -Large effect on many genes |
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What is NFkB? |
Rapid acting primary transcription factor complex - regulates genes to do with the innate immune system |
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Describe how a microarray is produced |
-mRNA isolated from two different cell types -Reverse transcriptase used to produce cDNA -Combine cDNA and hybridise to produce a microarray |
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What is alternative splicing? |
Splicing different introns of mRNA to make different products |
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Name three proteins associated with iron metabolism |
-Transferrin - transport protein which carries iron in septum -Transferrin receptor - Binds iron loaded transferrin -Ferretin - storage protein found in liver and kidneys |
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How is ferritin expression controlled? |
Ferritin has a loop region in mRNA called iron-response element. It binds to Iron-binding protein at low iron concentration, stopping translation. Iron binds to iron-binding protein, changing its conformation so it cannot bind to ferratin mRNA. |
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How is transferrin receptor expression controlled? |
Transferrin receptor mRNA also has iron response elements. Binds to IRP at low iron concentration, helping prevent IRP degradation of mRNA. Iron binds to IRP, preventing IRP binding to mRNA and promoting degradation of mRNA. |
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What is miRNA? |
micro RNA - binds to mRNA with complementary sequence and guides Argenaut complex to cleave mRNA. |
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How are proteins degraded? |
Ubiquitin molecules mark protein for destruction Degraded via the proteosome |
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How does phosphorylation control expression? |
Can activate or inactivate proteins |
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What is glycosylation? |
Attachment of carbohydrates to form glycoproteins - occurs in ER. Promotes correct folding and can increase resistance to degradation by proteosome. |
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How are GTPases activated or inactivated? |
Active form bound to GTP Inactive form bound to GDP |
