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What is the 'lock and key' hypothesis?

A reaction can only be catalysed (sped up) if an enzyme's active site matches the shape of its substrate molecules- the substrate fits into the active site like a key into a lock. This shape is highly specif...
EE
Answered by Emily E. • Biology tutor
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Explain the sliding filament model of skeletal muscle contraction

An action potential on a motor axon reaches the axon terminal, causing acetylcholine to be released. It diffuses across the neuromuscular cleft in synaptic vesicles and binds with acetylcholine receptors on ...
MP
Answered by Maddie P. • Biology tutor
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Describe active transport

Active transport is the movement of a substance against its concentration gradient across a selectively permeable membrane. In order for an organism to carry out active transport energy is required to overco...
AH
Answered by Alexander H. • Biology tutor
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Describe the stages of transcription

Transcription begins with DNA helicase unwinding the DNA into two seperate strands.As the DNA unwinds, RNA nucleotides form hydrogen bonds with their complementary base pairs. Uracil binds to adenine, and gu...
EA
Answered by Edward A. • Biology tutor
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Explain how you would test for the presence of lipids and proteins in an unknown solution. Give details on any observations you would expect to make.

To test for the presence of lipids, you would carry out the emulsion test. To do this, you take the sample and mix it with equal volumes of ethanol and water followed by shaking. A cloudy white emulsion will...
CJ
Answered by Chelsea J. • Biology tutor
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