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Enzymes: 12. Enzymes using small molecules to synthesise  bigger molecules e.g. proteins, lipids-fats & complex carbohydrates like glycogen

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Sub-index of biology notes on enzymes and digestion


12. More examples of enzyme controlled reactions

Enzymes and the synthesis of carbohydrates, proteins and lipids

Three examples of 'small' molecules to 'big' molecules!

The previous section on digestion was all about enzymes breaking large molecules down to small molecules to aid digestion and absorption of nutrients.

Here we consider the opposite biochemistry - building up essential large molecules from small substrate molecules.

The molecules so formed are examples of naturally occurring polymers.

Some examples of 'big molecule' synthesis reactions - ALL catalysed by specific enzymes

(Most are the opposite of the digestive chemistry described above)

1. Protein synthesis

Several enzyme catalysts join amino acids together to form proteins - its a complicated process!

Proteins are an example of a natural polymer.

Enzyme reaction word equation: proteins == enzymes ==> protein

synthesis of proteins from amino amino acids

The synthesis of proteins from amino acids in the ribosomes.

For more details see DNA structure and Protein Synthesis  (gcse biology revision notes)

 

2. Lipid synthesis

Again, it takes multiple enzymes to synthesise lipid fats from glycerol and long chain fatty acids.

Enzyme reaction word equation: glycerol + 3 fatty acids === enzymes ===> lipid oil or fat

The synthesis of lipids from fatty acids and glycerol

The synthesis of lipids from fatty acids and glycerol.

The molecular details of lipid oils and fats are not required for GCSE biology, but you should recognise aspects of their structure from your GCSE chemistry course on the equation diagrams below.

e.g. the functional groups: carboxylic acid -COOH, unsaturated' alkene group >C=C< and alcohol C-OH.

 Lipids are NOT polymers

 

3. Complex carbohydrate synthesis

Complex carbohydrates are synthesised by combing together lots of small sugar molecules such as glucose into long polymer molecules such as glycogen (in animals) and starch and cellulose in plants.

The enzyme glycogen synthase (the name says it all), can join lots of simple glucose molecules into long chain glycogen molecules - a natural polymer.

Enzyme reaction word equation: glucose == glycogen synthase ==> glycogen

The synthesis of complex carbohydrates like glycogen from smaller sugar molecules.

The synthesis of complex carbohydrates like glycogen from smaller sugar molecules.

Glycogen is used by animals, like ourselves, as a chemical energy store.

Other enzymes can rapidly convert glycogen back to glucose to fuel respiration - to provide energy for cells to perform all their functions.


Summary of learning objectives and key words or phrases

Be able to describe how enzymes use small molecules to synthesise big molecules e.g. protein synthesis from amino acids, lipid synthesis from fatty acids, carbohydrate synthesis to make starch (plants) or glycogen (animals) from small sugar molecules like glucose.


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INDEX of biology notes on enzymes

(Enzymes are also dealt with in my GCSE chemistry notes chemistry - biotechnology)

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INDEX of biology notes on enzymes and digestion

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