Give the difference between heterochromatin and euchromatin
Heterochromatin tightly wound DNA, Euchromatin is loosely wound
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Why is transcription not possible when DNA is tightly wound?
RNA polymerase can't access the genes
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Why does DNA coil around histones
DNA is negatively charged and histones are positively charged
12 of 30
Explain the roles of acetyl and methyl groups in histones modification
Acetyl reduce positive charge on histones so DNA coils less tightly, Methyl makes histones more hydrophobic so bind more tightly
13 of 30
What is an operon
Group of genes that are controlled by the same regulatory mechanism and are expressed at the same time
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Name the 3 genes in the Lac operon
LacZ LacY Lac
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Name the regulatory gene involved and its function
LacI - codes for a repressor protein (prevents transcription of LacZ,LacY,LacA)
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What happens when the repressor protein binds to the operator
Prevents RNA polymerase binding to the DNA - no transcription
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What effect does lactose have on the repressor protein
Lactose binds to repressor protein and denatures it
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How can an mRNA sequence be changed
Addition, deletion, subsitution - (form different proteins)
19 of 30
Name 3 ways of regulating protein synthesis
1. Degradation of mRNA (longer stay in cytoplasm = more protein synthesis) 2. Inhibitory protein binds to mRNA (prevents protein synthesis) 3. Activation of initiation factors (aid binding of mRNA to ribosomes)
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What are protein kinases
Enzymes that catalyse the addition of phosphate groups to proteins
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Name 4 ways a protein can be modified after synthesis
1. Adding non-protein group 2. Modify amino acids & form bonds (disulphides) 3. Folding or shortening of protein 4. Modification by cAMP
22 of 30
Define morphogenesis
Regulation of the pattern of anatomical development
23 of 30
Why are drosophila flies used for investigations
Small, easy to keep, short life cycle
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What is a homeobox
Regulatory gene - Section of DNA 180 base pairs long coding for 60 amino acids
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What does the homeodomain do
Binds to DNA and switches other genes on or off
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What is a somite
Segments in the embryo which are directed by hox genes to form body structures
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