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PROTEINS

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Functions of globular proteins Receptor ... structure * FIGURE 3-21 The four ... sequence is coded for by DNA and is unique for each kind of ... – PowerPoint PPT presentation

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Title: PROTEINS


1
PROTEINS
2
Proteins
  • Proteins do the nitty-gritty jobs of every living
    cell.
  • Proteins are made of long strings of individual
    building blocks known as amino acids.

3
Amino acids contain an amino group, a carboxyl
group, a carbon and a unique R group
4
3.2.2
  • Identify amino acids ... from diagrams showing
    their structure.

5
Polar R groups make the amino acid hydrophilic
Non-polar R groups make the amino acid hydrophobic
6
Ionic R groups make the amino acid hydrophilic
7
7.5.3
  • Explain the significance of polar and non-polar
    amino acids.

8
There are 20 commonly occurring amino acids that
are found in proteins
  • leucine - leu - L
  • lysine - lys - K
  • methionine - met - M
  • phenylalanine - phe - F
  • proline - pro - P
  • serine - ser - S
  • threonine - thr - T
  • tryptophan - trp - W
  • tyrosine - tyr - Y
  • valine - val - V
  • alanine - ala - A
  • arginine - arg - R
  • asparagine - asn - N
  • aspartic acid - asp - D
  • cysteine - cys - C
  • glutamine - gln - Q
  • glutamic acid - glu - E
  • glycine - gly - G
  • histidine - his - H
  • isoleucine - ile - I

Essential Amino Acids are those that must be
ingested in the diet (our body cant make them)
9
Peptide Bonds join amino acids Its a
condensation reaction (meaning that H20 is
released when the bond is formed). Two amino
acids form a DI-PEPTIDE POLYPEPTIDES are
formed from more than two amino acids bonded
together
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11
  • 3.2.5 Outline the role of condensation and
    hydrolysis in the relationships between amino
    acids and polypeptides.
  • 7.4.5 Draw and label a diagram showing the
    structure of a peptide bond between two amino
    acids.

12
Proteins have four levels of organization
13
Primary structure is the amino acid sequence
14
The amino acid sequence is coded for by DNA and
is unique for each kind of protein
15
The amino acid sequence determines how the
polypeptide will fold into its 3D shape
16
Even a slight change in the amino acid sequence
can cause the protein to malfunction
  • For example,
  • mis-formed hemoglobin causes sickle cell disease

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Proteins have four levels of organization
19
Secondary structure results from hydrogen bonding
between the oxygen of one amino acid and the
hydrogen of another
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The alpha helix is a coiled secondary structure
due to a hydrogen bond every fourth amino acid
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The beta pleated sheet is formed by hydrogen
bonds between parallel parts of the protein
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A single polypeptide may have portions with both
types of secondary structure
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Proteins have four levels of organization
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Tertiary structure depends on the interactions
among the R group side chains
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Types of interactions
  • Hydrophobic interactions amino acids with
    nonpolar side chains cluster in the core of the
    protein, out of contact with water

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Types of interactions
  • Hydrogen bonds between polar side chains

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Types of interactions
  • Ionic bonds between positively and negatively
    charged side chains

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Types of interactions
  • Disulfide bridge (strong covalent bonds) between
    sulfur atoms in the amino acid cysteine

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Proteins have four levels of organization
42
Quaternary structure results from interactions
among separate polypeptide chains.
43
  • For example, hemoglobin is composed of
  • 4 polypeptide chains

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Proteins have four levels of organization
46
The folding of proteins is aided by other
proteins, called chaperones
  • Act as temporary braces as proteins fold into
    their final conformation
  • Research into chaperones is a area of
    research in biology

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7.5.1
  • Explain the four levels of protein structure,
    indicating the significance of each level.

49
Denaturation results in disruption of the
secondary, tertiary, or quaternary structure of
the protein
50
Denaturation may be due to changes in pH,
temperature or various chemicals

51
Protein function is lost during denaturation,
which is often irreversible
52
3.6.4
  • Define denaturation.

53
Folded proteins are placed into two general
categories
54
Fibrous proteins have polypeptide chains
organized in long fibers or sheets
  • Water insoluble
  • Very tough physically, may be stretchy

55
Functions of fibrous proteins
  • Structural proteins function in support
  • Insects and spiders use silk fibers to make
    cocoons and webs
  • Collagen and elastin are used in animal tendons
    and ligaments
  • Keratin is the protein in hairs, horns and
    feathers

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Functions of fibrous proteins
  • Contractile proteins function in movement
  • Actin and myosin contract to create the cleavage
    furrow and to move muscles
  • Contractile proteins move cilia and flagella

59
Globular proteins have their chains folded into
compact, rounded shapes
  • Easily water soluble

60
Functions of globular proteins
  • Storage proteins function in the storage of amino
    acids
  • Ovalbumin is the protein in egg whites
  • Casein is the protein in milk, source of amino
    acids for baby mammals

61

62
Functions of globular proteins
  • Transport proteins function in the movement of
    other substances
  • Hemoglobin, the iron containing protein in blood,
    transport oxygen from lungs to other parts of the
    body (C3032H4816O872N780S9Fe4)
  • Membrane transport proteins such as channels for
    potassium and water

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Functions of globular proteins
  • Hormone proteins function as cellular messenger
    molecules that help maintain homeostasis
  • Insulin sends message allow sugar into cells
    (when blood glucose levels are high, cells will
    transport glucose into the cells for use or
    storage)
  • Glucagon sends message we need more sugar in
    the blood (when blood glucose is too low, cells
    will release glucose)

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Functions of globular proteins
  • Receptor proteins allow cells to respond to
    chemical stimuli
  • Growth factor receptors initiate the signal
    transduction pathway when a growth hormone
    attaches

67
Functions of globular proteins
  • Cholesterol receptors on the cell membrane allow
    LDL to be endocytosed into the cell

68
Functions of globular proteins
  • Protective proteins function as protection
    against disease
  • Antibodies combat bacteria and viruses

69
Functions of globular proteins
  • Enzymes speed up chemical reactions
  • Amylase and other digestive enzymes hydrolyze
    polymers in food
  • Catalase converts hydrogen peroxide H2O2 into
    water and oxygen gas during cellular respiration

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  • 7.5.2
  • Outline the difference between fibrous and
    globular proteins, with reference to two examples
    of each protein type.
  • 7.5.4
  • State four functions of proteins, giving a named
    example of each.
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