The proteins
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Transcript of The proteins
Biochemistry for nurses: Unit 1
THE PROTEINS
Biochemistry for nurses: Unit 3
DEFINITION OF THE PROTEIN
• The proteins are the more complex molecules in the living cells.
• A human body has around 100.000 differents types of proteins.
• A protein is a biological macromolecule composed by one or several peptides.
• A peptide is a polymer (= chain) of amino acids (AA) linked between them by a
peptide bond.
•Protein = AA > 100; Peptide = 10 ≤ AA ≤ 100; Oligopeptide = AA ≤ 10 (including
Tripeptide (AA = 3); Dipeptide (AA = 2))
Biochemistry for nurses: Unit 3
The amino acid
The amino acid is the basic unity of the protein.
The amino acid is composed by
a carbone (C) on which is linked:
• An amino group (NH2)
• An acid group (COOH)
• A variable chemical group (R)
• A hydrogen (H)
Biochemistry for nurses: Unit 3
20 standard amino acids
Biochemistry for nurses: Unit 3
20 standard amino acids
Biochemistry for nurses: Unit 3
20 standard amino acids
Biochemistry for nurses: Unit 3
Amino acids abbrevation table
Biochemistry for nurses: Unit 3
The peptide bond
• The amino acid (AA) molecules are linked each other one by peptide bonds.
• A peptide bond is a covalent bond between the carboxylic group (CO) of one
amino acid and the amino group (NH2) of another amino acid molecule.
• The formation of a peptide bond releases a water molecule (H2O) = reaction
of condensation.
• The assembly of several AA molecules gives a peptide (AA ≤ 20)
• The assembly of several peptides gives a protein (AA ≥ 20)
Biochemistry for nurses: Unit 3
The peptide bond
Biochemistry for nurses: Unit 3
Protein synthesis (= Transcription + Translation)
• The protein synthesis has 2 steps: the transcription of the DNA into a mRNA,
and the translation of the mRNA into a protein.
•The proteins are assembled from amino acids according the informations
provided by the RNA messenger.
Biochemistry for nurses: Unit 3
• The translation is the application of the genetic informations provided by the mRNA.
The amino acids are free inside the cytoplasm before to be assembled to form the
proteins during the translation step.
•Translation = Ribosome + amino acids + tRNA + mRNA
Biochemistry for nurses: Unit 3
Essential and non-essential amino acids
• An essential amino acid is an indispensable amino acid that cannot be synthesized
by the human body: THEY ARE PROVIDED BY THE NUTRIENTS (FOODS)
• A conditionally non-essential amino acid is an amino acid which becomes
essential in some cases (premature baby).
• A non-essential amino acid can be synthesized by the human body.
Biochemistry for nurses: Unit 3
The primary structure:
• The primary structure
corresponds to the amino
acids sequence according
the mRNA gene.
• We see the primary
structure only during a
short time, i.e, during the
elongation process of the
protein synthesis.
THE PROTEIN STRUCTURE
Biochemistry for nurses: Unit 3
The secondary structure:
• The variable chemical groups (R) of the AA have differents properties:
Hydrophobic, hydrophilic, charges (+) or (-) , -SH groups…
Intramolecular chemical
interactions: Hydrogen
bonds, Disulfide bridges,
Ionic bonds, hydrophobic
and hydrophilic
interactions…
Alpha-helice and
Beta-sheet structures
Biochemistry for nurses: Unit 3
Biochemistry for nurses: Unit 3
The tertiary structure:
• The tertiary structure is the final form of the protein.
• The function of the protein is strongly related to its final
form (structure).
• The final structure can be destroyed in case of a heating
process or extrem pH = Denaturation process
Biological function is lost!
Biochemistry for nurses: Unit 3
The quaternary structure:
• In case of proteins composed by
tertiary assembled subunits
(Hemoglobin, Immunoglobin…)
Biochemistry for nurses: Unit 3
According their compositions:
1. Holoprotein = Protein composed only by amino acids.
2. Conjugated protein = protein composed by amino acids and by
something else (carbohydrates: Glycoprotein, lipids: lipoprotein).
Protein classification
According
their
functions:
Biochemistry for nurses: Unit 3
What is an enzyme?
• Enzymes are proteins
produced in living cells.
• Enzyme are biological
catalysts = They speed up the
rate of chemical reactions.
Biochemistry for nurses: Unit 3
What is an enzyme?
• Enzyme are specific to a particular substrate (Key-Lock:
sucrose-sucrase, maltose-maltase,…).
Biochemistry for nurses: Unit 2
The cytoskeleton
The cytoskeleton is a dynamic
protein structure: It is a
skeleton and a musculature in
same time for the cells. The
cytoskeleton has the function to
maintain the shape of the cell,
to create a cell movement. It is
involved in the cell division.
Biochemistry for nurses: Unit 3
Clinical correlation
Biochemistry for nurses: Unit 3
• The Alzheimer’s disease is a chronic
neurodegenerative disease = a progessive
destruction of the brain neurones over time
until death.
• Most often begins in people over 65 years.
• It was first described in 1906 by the german
psychiatrist and pathologist Alois Alzheimer.
• The cause is almost unknown: The most
probable hypothesis is a genetic anomaly.
• No treatments stop or reverse its
progression.
• No medications or supplements decrease
the risk factor.
ALZHEIMER’S DISEASE
(AD)
Biochemistry for nurses: Unit 3
AD is caused by 2 types of protein accumulation,
Intra and extracellular, which cause plaques and tangles in the Brain.
Disintegration of the microtubules
accumulation
= Tangles of Tau porteins
Destroying the structure of the
cell’s cytoskeleton = Death of the cell
Intracellular: Anomaly of TAU proteins
Biochemistry for nurses: Unit 3
Accumulation
Senile plaques
Destruction of the
surrounding neurones
Extracellular: Anomaly of Amyloid proteins
Biochemistry for nurses: Unit 3
The Alzheimer’s disease slowly invades the different areas of the brain
and gets worse over time. The disease causes progressively visibles
symptoms according the affected brain areas.