PROTEINS
Characteristics of Proteins

Contain carbon, hydrogen, oxygen, nitrogen,
and sulfur

Account for more than 50% of dry weight in
most cells

Instrumental in everything the organism does

Basic building block is the amino acid

Vary extensively in structure, each type of
protein has a unique 3-D shape/
Proteins (Polypeptides)
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Amino acids are the monomers, or building
blocks of proteins
 20 different kinds of Amino Acids used to
make proteins
 Amino acids are linked together by
Condensation reactions to form peptide
bonds.
 Proteins are also called polypeptides

Formation of a Dipeptide
Condensation
Amino Acid + Amino Acid --> Dipeptide
Amino Acid + Dipeptide --> Tripeptide
A.A. + A.A. + …..+ Tripeptide --> Polypeptide
Amino Acid
• Amine group acts like a base, tends to be positive.
• Carboxyl group acts like an acid, tends to be negative.
• “R” group is variable, from 1 atom to 20.
• Two amino acids join together to form a dipeptide.
• Adjacent carboxyl and amino groups bond together.
Amino Acids
• 20 different Amino Acids
• 3 different types (according to ‘R’ chain)
– Nonpolar
– Polar
– Electrically Charged (acidic & basic)
• Do not need to know 20 amino acids, but
must recognize polar, nonpolar, and charged
Nonpolar Amino Acids
• Non-polar R side chains
• Hydrophobic
• Found in regions of proteins lined to the
hydrophobic area of cell membrane
• Essential in determining specificity of enzymes
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Nonpolar Amino Acids
Polar Amino Acids
• Polar R side chains
• Hydrophilic properties
• Found in regions of proteins exposed to water
(exterior of cell membrane)
• Create hydrophilic channels through which
polar substances can move
• Essential in determining specificity of enzymes
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Polar Amino Acids
Charged Amino Acids
• Acidic
– R side chains are
negatively charged
– Carboxyl group is
dissociated in cellular pH
levels
• Basic
– R side chains are
positively charged
– Amine groups are
positively charged at
cellular pH levels
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Charged Amino Acids
2 minute convo

How will the different types of amino
acids determine the structure of protein
molecules?
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Proteins (Polypeptides)
Four levels of protein structure:
A. Primary Structure
B. Secondary Structure
C. Tertiary Structure
D. Quaternary Structure
Structure of proteins is closely tied
with its function.
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Primary Structure
Amino acids bonded together by
peptide bonds (straight chains)
unique to each protein
Amino Acids (aa)
aa1
aa2
aa3
aa4
aa5
aa6
Peptide Bonds
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Primary Structure
• Unique sequence of amino acids
• Precise primary structure is determined by inherited genetic
information (DNA)
• Amino Acid sequence at primary structure determines the
next three levels of structure and thus, the 3-D shape of a
protein
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Secondary Structure
• 3-dimensional folding arrangement of a
primary structure into coils and pleats held
together by hydrogen bonds. Does not involve
the use of R-chains
• Two examples:
Alpha Helix
Beta Pleated Sheet
Hydrogen Bonds
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Secondary Structure
• Created by the formation of hydrogen bonds
between the amino and carboxyl groups of
amino acids.
• Contributes to overall structure of protein.
• Two examples:
Alpha Helix
Beta Pleated Sheet
Hydrogen Bonds
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Tertiary Structure
• Secondary structures bent and folded into a
more complex 3-D arrangement of linked
polypeptides.
• Involves interaction of side chains (R groups)
and amino acid backbone.
• Bonds: H-bonds, ionic, disulfide bridges (S-S)
• Call a “subunit”.
Alpha Helix
Beta Pleated Sheet
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• 3-D structure
gives proteins
their functional
properties, such
as active sites on
enzymes.
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Quaternary Structure
• Composed of 2 or more “subunits”
• Overall protein structure results from combination of
subunits
• Form in Aqueous environments
• Example: enzymes (hemoglobin)
• https://www.youtube.com/watch?v=qBRFIMcxZNM
subunits
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2 minute convo
• Discuss how the different levels of protein
structure depend on each other
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Types of Proteins
Globular
Fibrous
Protein Type
• Globular
– 3-D in shape
– Mostly Soluble
– Mostly Functional Proteins
• Hemoglobin (transport)
• Insulin (regulate blood
sugar)
• Amylase (digests starch)
• Fibrous
– Polypeptide chains in long
narrow shape
– Mostly insoluble
– Structural of Functional
Proteins
• Collagen (connective tissue)
• Keratin (hair, nails)
• Actin (muscle contraction
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2 minute convo

What are 2 types of proteins and
examples of each.
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• The specific function of a protein is a property
that arises from the architecture of the
molecule.
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Proteins (Polypeptides)
• Functions of proteins vary extensively because of
the number of amino acids (100s-1000s) and the
range of possible amino acids (20) in each spot
• Six functions of proteins:
1. Storage:
albumin (protein)/Ferritin (Iron)
2. Transport: hemoglobin
3. Regulatory: hormones (insulin)
4. Movement: muscles (actin/myosin)
5. Structural: membranes, hair, nails (keratin)
6. Enzymes: cellular reactions (Amylase)
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Protein Functions
• Storage – Ferritin stores iron in a protein
capsule
• Transport – Hemoglobin contains iron that
transports oxygen throughout the body
• Regulatory – Insulin is secreted by pancreas
and regulates blood glucose levels
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Protein Functions
• Movement – Actin & Myosin cause muscle
contractions and movement
• Enzymatic – Amylase is a digestive enzyme
that breaks down starch
• Structural – Spider silk in webs and Collagen
is in connective tissues in animals
• Immunoglobulins – Antibodies fight bacteria
and viruses
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2 minute convo
• What are 6 different functions of proteins and
examples of each?
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BILL
• 18. List four functions of proteins, giving an
example of each. (Total 4 marks)
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BILL Markscheme
•
Name of function and named protein must both be correct for the mark.
storage – zeatin (in corn seeds) / casein (in milk);
transport – hemoglobin / lipoproteins (in blood);
hormones – insulin / growth hormone / TSH / FSH / LH;
receptors – hormone receptor / neurotransmitter receptor /
receptor in chemoreceptor cell;
movement – actin / myosin;
defence – antibodies / immunoglobin;
enzymes – catalase / RuBP carboxylase;
structure – collagen / keratin / tubulin / fibroin;
electron carriers – cytochromes;
pigments – opsin
active transport – sodium pumps / calcium pumps;
facilitated diffusion – sodium channels / aquaporins;
Mark first four functions only. Allow other named examples.
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