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Unit 5
Gene Expression and Control
Structure of RNA- Ribonucleic acid:
Made up of ribose nucleotides instead of deoxyribose like in DNA
Uracil replaces Thymine
RNA is single stranded
RNA is shorter than DNA

3 types of RNA:
mRNA- Made up of thousands of mononucleotides- It is a long stand…

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Cytosine or Thymine pyrimidine base Cytosine or Uracil pyrimidine base Cytosine or Uracil pyrimidine base
Found mostly in nucleus Manufactured in the nucleus but Manufactured in the nucleus but
found throughout the cell found throughout the cell
Hydrogen bonding between strands No hydrogen bonding Present in some parts of the…

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The non-coding, non-functional, sequences within genes are introns and the coding
sequences are exons. The introns need to be removed before the mRNA can be translated
into protein. This removal is called post-transcriptional modification/splicing.
The Pre-mRNA is an exact copy of the gene on the DNA, so it contains exons…

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Mutations
Any change to one or more nucleotide bases or arrangement of bases in DNA during DNA
replication is a mutation. There are three types of mutations- Substitution, deletion and
addition. Only deletion and addition case a frame shift- mutation to occur.
Substitution mutations only affect one amino acid- little…

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anti-oncogenes. For a cancer to occur, one or more tumour suppressor genes must also be
mutated, so their control is removed and cells divide out of control. So a cancer is usually the
result of several different mutations building up.:






Homeostasis
Principles
Homeostasis- The maintenance of a constant internal environment.…

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the amount of area on the body exposed to the sun, conduct the heat to the ground, convect
it to the surroundings or radiate it. Ectotherms use less energy than endotherms so they can
survive for weeks without eating. However, when it is really cold for example, they have to…

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Control of blood glucose concentration
The main source of blood glucose is the digestion and absorption of carbohydrate, mostly
starch. Blood from the intestine goes directly to the liver in the hepatic portal vein before
being carried to the rest of the body.
If the concentration of glucose becomes too…

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Animals don't normally synthesise glucose, but when dietary glucose is scarce proteins and
nucleic acids can be used to synthesise glucose (gluconeogenesis).




The Pancreas
The pancreas is a large pale-coloured gland which is situated in the upper abdomen behind
the stomach.
It produces protease, amylase and lipase which are used…

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This results in a lower blood glucose concentration because the rate of absorption of glucose
in the cells, especially muscle cells, increases. The rate of respiration also increases so more
glucose is used up decreasing the amount in blood. The conversion of glucose to glycogen in
the liver and muscles…

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Secondly, IRS actives the enzyme glycogen synthase, which synthesises glycogen from
cytoplasmic glucose. Here: IRS activates one enzyme, which activates another, which
activates another, which activates glycogen synthase. This cascade amplifies the effect, so
each molecule of insulin can activate thousands of molecules of glycogen synthase. If present
in the…

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