L21 - Proteins & enzymes Flashcards

1
Q

What are proteins?

A

Large molecules composed of amino acids

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2
Q

Amino acids

A

Most plant derived products contain some essential amino acids, but usually in low amounts.

20 amino acids → 9 are essential = cannot be produced by
humans

Nitrogen (N) main component

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3
Q

Protein deposition in

plant organs

A

• The seed is the best studied example of protein deposition
and storage
• Amount of protein in seeds: 10 40%
• Storage proteins play a major role in protein deposition

Formed at the ER and transported to
protein storage vacuoles and protein
bodies (PB)

Classified into:
- Vegetative storage proteins (VSPs)
- Seed storage proteins (SSPs) : 
 Source of nutrients during germination
 Protective role in plant
defence
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4
Q

Enzymes. Are all enzymes proteins?

A

All enzymes are proteins, but NOT ALL PROTEINS are enzymes

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5
Q

Enzymatic browning

A
  1. Hydroxylation of
    monophenols to diphenol
  2. Oxidation of diphenols to o quinone
Enzymatic browning
requires exposure to O2 after:
• Bruising,
• Cutting,
• Compression, ...

Wounding allows
chloroplastic PPO enzyme to interact with
vacuolar substrates.

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6
Q

Example

A

o-quinone

• highly unstable yellow
compounds that form complexes
with amino acids or proteins
• polymerization of these intermediates and condensation of o quinones produce melanins (reddish/brown coloured polymers)

Phenylalanine ammonia lyase: 
Key enzyme that catalyses the
first step in the synthesis of a
variety of polyphenyl
compounds
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7
Q

Household trick against enzymatic browning?

A
  • Coating in sugar/syrup: reduce oxygen diffusion
  • Lemon juices: antioxidants + lower pH
  • Heating: inactivating PPO
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8
Q

Cell wall degrading enzymes

A
  • Hemicellulases
  • Pectinases
  • Cellulases
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9
Q

Important enzymes are: PPO, PAL, PG and PME

A
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