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Proteins

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2.4 U1 Amino acids are linked together by condensation to form polypeptides. Amino acids are the sub units of proteins and they bond together to form polypeptides. – PowerPoint PPT presentation

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Title: Proteins


1
Proteins
  • Topic 2.4
  • IBHL Biology

2
Introduction
  • Proteins are a very important biological
    molecules that are involved in almost every
    activity that organisms do.
  • They comprise more than 50 of the dry mass in
    most cells.
  • They are involved in chemical reactions,
    structures, transport, cell to cell
    communication, movement, and immunity.
  • They are also the structural component of
    enzymes.
  • Proteins are constructed from polymers of amino
    acids and are referred to as polypeptides. They
    are held together by peptide bonds.

3
2.4 U1 Amino acids are linked together by
condensation to form polypeptides.
  • Amino acids are the sub units of proteins and
    they bond together to form polypeptides.
  • There are 20 different amino acids and they are
    distinguished by their R-group but they all have
    the same generalized structure.

4
Condensation of Amino Acids
  • Condensation reactions can join two amino acids
    together to form dipeptides or many amino acids
    together to form large chains called polypeptides
    (proteins).
  • As each bond (peptide bond) is formed a molecule
    of water is produced.
  • This process is performed by ribosomes in a
    process known as translation.

5
2.4 S1 Drawing molecular diagrams to show the
formation of a peptide bond
  • Draw the formation of a peptide bond in your
    sketch book.

6
2.4 A2 There are 20 different amino acids in
polypeptides synthesized on ribosomes
  • There are 20 different amino acids used to build
    thousands of different proteins. The amino acids
    are distinguished from one another by their R
    group also known as a side chain.
  • The amino acids can be grouped according to the
    properties of their side chains. There are polar
    amino acids, non-polar amino acids and
    electrically charged amino acids.

7
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8
20 Different Amino Acids
  • You do not need to know the names of the 20
    different amino acids however you should know
    that organisms can arrange them in polypeptides
    to produce thousands of different proteins.
  • Also, some amino acids can have variations in
    their structure which changes their
    characteristics.
  • For example, a modified version of the amino acid
    proline known as hydroxyproline is found in the
    protein collage. It gives collagen, a structural
    protein found in ligaments, tendons, skin and
    blood vessels, more stability.

9
2.4 U3 Amino acids can be linked together in
any sequence giving a huge range of possible
polypeptides.
  • The possibilities of amino acid sequences are
    huge.
  • Polypeptides contain amino acid numbers ranging
    from 20 to tens of thousands.
  • This table identifies the infinite possibilities
    for polypeptide sequences.

of amino acids Number of possible amino acid sequences Number of possible amino acid sequences
1 201 20
2 202 400
3 203 8 000
4 204 160 000
5 205 3 200 000
6 206 64 000 000
10
2.4 U4 The amino acid sequence is coded for by
genes
  • The information needed to produce proteins is
    stored in DNA. It is coded for by genes that
    contain three base pairs per amino acid. The
    sequence of base pairs controls the building of
    polypeptides during translation. We will cover
    this in detail in unit 5.

11
2.4 U5 - A protein may consist of a single
polypeptide or more than one polypeptide linked
together
  • Some polypeptides are two or more strands linked
    together. Integrin is an example of a protein
    that has two separate polypeptides that work
    together to make connections between structures
    that are inside
    and outside
    of cells.
  • Some polypeptides are a single polypeptide such
    as lysozyme.
  • It is an enzymes secreted in nasal mucus and
    tears that kills bacteria by digesting their cell
    walls.

12
2.4 U5 - A protein may consist of a single
polypeptide or more than one polypeptide linked
together
  • Hemoglobin is composed of 4 polypeptides along
    with a non-polypeptide group known as a heme
    group.
  • This protein transports
    o oxygen in the blood.
  • Collagen is composed of three polypeptides. It
    is a structural protein.

13
2.4 U6 The amino acid sequence determines the
three dimensional conformation of a protein
  • The conformation of a protein refers to its three
    dimensional shape. There are 4 levels of protein
    structure and the level it conforms to is
    dependent on its amino acid structure. (see
    handout)
  • Proteins are often described as being globular or
    fibrous. The sequence of amino acids determines
    the shape of the protein.
  • Fibrous proteins have a structural role and
    globular proteins have functional roles in a
    cells metabolism.

http//www.youtube.com/watch?vyZ2aY5lxEGE
14
Fibrous Proteins
  • Fibrous proteins have a long and narrow shape and
    are mostly insoluble in water.
  • They are composed of many polypeptide chains
    organized into a long, narrow shape.
  • Some examples are collagen, a protein that plays
    a structural role in human connective tissues and
    actin, a protein found in muscle which plays a
    role in muscular contractions.

15
Globular Proteins
  • Globular proteins have a rounded shape (three
    dimensional) and they are mostly soluble in
    water.
  • Hemoglobin is an example of a globular protein
    and it is involved in delivering oxygen to body
    tissues.
  • Insulin is another example of a globular protein
    and it plays a role in regulating blood glucose
    levels in humans.

16
2.4 U7 Living organisms synthesize many
different proteins with a wide range of functions.
  • Organisms synthesize thousands of different
    proteins in their cells and each protein is
    different. They have different sequences of
    amino acids and as mentioned earlier, that
    sequence determines the shape of the protein and
    the shape determines the function.
  • Refer to the handout mentioned earlier for a
    summary of the functions and variety of proteins.

17
Use the following terms to complete the chart on
your handout
  • Muscle contraction
  • Membrane transport
  • Hormones
  • Cytoskeletons
  • Tensile strengthening
  • Cell adhesion
  • Immunity
  • Blood clotting
  • Receptors
  • Catalysis
  • Packing of DNA
  • Transport of nutrients gases

18
2.4 A1 Rubisco, insulin, immunoglobulins,
rhodopsin, collagen and spider silk as examples
of the range of protein functions.
  • Refer to handout and chart completed in class.

19
2.4 U8 Every individual has a unique proteome.
  • A proteome is defined as all the proteins
    produced by a cell, a tissue or an organism.
  • We can use a process known as gel electrophoresis
    to extract proteins from samples and determine
    how they are being produced. Antibodies with
    fluorescent markers are used to identify the
    proteins.
  • Proteomes are variable from cell to cell due to
    the fact that cells differ in their functions and
    activities.
  • While there are many similarities within species,
    individuals still have many variations within
    their proteomes which can be due to small
    differences in the amino acid sequences of
    proteins.

20
2.4 A2 Denaturation of proteins with a wide
range of functions.
  • The three dimensional structure of proteins is
    maintained or stabilized by bonds or interactions
    between the R-groups of amino acids. These
    bonds or interactions are weak and can be broken
    or disrupted fairly easily.
  • When this occurs it cause a change in the
    conformation of the protein and this is known as
    denaturation.
  • When a protein is denatured it changes shape and
    these changes can be temporary or permanent. Two
    factors than can denature proteins are heat and
    pH.

21
2.4 A2 Denaturation of proteins with a wide
range of functions.
  • Extreme changes in pH can cause proteins to
    denature. It causes changes in the charges on R
    groups which breaks the bonds or causes new bonds
    to form. This will alter the structure of the
    protein. Some proteins are exceptions such as the
    stomach enzyme pepsin (pH 1.5)
  • Heat can denature proteins because it causes
    vibrations in the molecule that breaks bonds.
  • Proteins vary in their tolerance of heat and can
    cause temporary or permanent changes.
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