essential idea proteins have a very wide range of functions in living organisms
TRANSCRIPT
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Essential Idea
• Proteins have a very wide range of functions in living organisms.
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Understandings
• Amino acids are linked together by condensation to form polypeptides.
• There are 20 different amino acids in polypeptides synthesized on ribosomes.
• Amino acids can be linked together in any sequence giving a huge range of possible polypeptides.
• The amino acid sequence of polypeptides is coded for by genes.
• A protein may consist of a single polypeptide or more than one polypeptide linked together.
• The amino acid sequence determines the three-dimensional conformation of a protein.
• Living organisms synthesize many different proteins with a wide range of functions.
• Every individual has a unique proteome.
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Proteins have many structures, resulting in a wide range of functions
• Proteins account for more than 50% of the dry mass of most cells
• Protein functions include structural support, storage, transport, cellular communications, movement, and defense against foreign substances
[Animations are listed on slides that follow the figure]
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Enzymes a type of protein
• Enzymes are a type of protein that acts as a catalyst, speeding up chemical reactions
• Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life
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Enzymes
Substrate(sucrose)
Enzyme(sucrose)
Fructose
Glucose
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Polypeptides --linear chain of Amino Acids
• Polypeptides are polymers of amino acids
• A protein consists of one or more polypeptides
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Amino Acid Monomers
• Amino acids are organic molecules with carboxyl (--COOH) and amino groups (--NH2)
• Amino acids differ in their properties due to differing side chains, called R groups
• Cells use 20 amino acids to make thousands of proteins
Amino group Carboxyl group
carbon
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Aminogroup
Carboxylgroup
carbon
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All living organisms using the same 20 Amino Acids.
Below are 9 nonpolar/ hydrophobic amino acids
Isoleucine (Ile)
Methionine (Met) Phenylalanine (Phe) Tryptophan (Trp) Proline (Pro)
Leucine (Leu)Valine (Val)Alanine (Ala)
Nonpolar
Glycine (Gly)
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Asparagine (Asn) Glutamine (Gln)Threonine (Thr)
Polar
Serine (Ser) Cysteine (Cys) Tyrosine (Tyr)
All living organisms using the same 20 Amino Acids.
Below are 6 polar/ hydrophilic amino acids
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LE 5-17c
Electricallycharged
Aspartic acid (Asp)
Acidic Basic
Glutamic acid (Glu) Lysine (Lys) Arginine (Arg) Histidine (His)
All living organisms using the same 20 Amino Acids.
Below are 5 VERY polar/ hydrophilic amino acids
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Ribsomes in the cytoplasm and on the E.R. make proteins
• There are two types of ribosomes:
– Free Ribosomes (located in the cytoplasm)
– Bound Ribosomes (located on the Endoplasmic reticulum)
Both ribosomes make proteins/ polypeptides by stringing amino acids together.
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Amino Acid Polymers
• Amino acids are linked by peptide bonds
• A polypeptide is a polymer of amino acids
• Polypeptides range in length from a few monomers to more than a thousand
• Each polypeptide has a unique linear sequence of amino acids
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Protein Tutorial Below:
Click below for the protein tutorials
•http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP13304
•http://publications.nigms.nih.gov/structlife/chapter1.html#a1
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Condensation reaction of amino acids to form polypeptide bonds and thus proteins
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Hydrolysis vs. Condensation
Hydrolysis
• Adds water
• Breaks down polymers into monomers
• Example: Breaks down starch into glucose
Condensation
• Removes water
• Forms new bonds between monomers forming polymers
• Example: glucose and fructose are bonded together to form sucrose
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IB Assessment Statment
• 7.5.1 Explain the four levels of protein structure, indicating the significance of each.
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PRIMARY STRUCTURE
The sequence of amino acids
© Anne-Marie Ternes
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PRIMARY STRUCTURE
• The numbers of amino acids vary (e.g. insulin 51, lysozyme 129, haemoglobin 574, gamma globulin 1250)
• The primary structure determines the folding of the polypeptide to give a functional protein
• Polar amino acids (acidic, basic and neutral) are hydrophilic and tend to be placed on the outside of the protein.
• Non-polar (hydrophobic) amino acids tend to be placed on the inside of the protein
© 2007 Paul Billiet ODWS
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Infinite variety
• The number of possible sequences is infinite
• An average protein has 300 amino acids,
• At each position there could be one of 20 different amino acids = 10390 possible combinations
• Most are uselessNatural selection picks out the best
© 2007 Paul Billiet ODWS
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SECONDARY STRUCTURE
The folding of the N-C-C backbone of the polypeptide chain using weak hydrogen bonds
© Science Student
© Text 2007 Paul Billiet ODWS
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SECONDARY STRUCTURE
• This produces the alpha helix and beta pleating
• The length of the helix or pleat is determined by certain amino acids that will not participate in these structures (e.g. proline)
© Dr Gary Kaiser © Text2007 Paul Billiet ODWS
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TERTIARY STRUCTURE
The folding of the polypeptide into domains whose chemical properties are determined by the amino acids in the chain
MIL1 protein
© Anne-Marie Ternes © 2007 Paul Billiet ODWS
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TERTIARY STRUCTURE
• This folding is sometimes held together by strong covalent bonds (e.g. cysteine-cysteine disulphide bridge)
• Bending of the chain takes place at certain amino acids (e.g. proline)
• Hydrophobic amino acids tend to arrange themselves inside the molecule
• Hydrophilic amino acids arrange themselves on the outside
© 2007 Paul Billiet ODWS
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Disulfide bonds of tertiary structures of proteins
• Covalent bonds can form between two adjacent cysteine amino acids.
• The bond is covalent.
• The covalent bond stabilises the tertiary shape of a protein.
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© Max Planck Institute for Molecular GeneticsChain B of Protein Kinase C
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QUATERNARY STRUCTURE
Some proteins are made of several polypeptide subunits (e.g. haemoglobin has four)
Protein Kinase C
© Max Planck Institute for Molecular Genetics
© Text 2007 Paul Billiet ODWS
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QUATERNARY STRUCTURE
• These subunits fit together to form the functional protein
• Therefore, the sequence of the amino acids in the primary structure will influence the protein's structure at two, three or more levels
© 2007 Paul Billiet ODWS
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Result
Protein structure depends upon the amino acid sequence
This, in turn, depends upon the sequence of bases in the gene
© 2007 Paul Billiet ODWS
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QUATERNARY STRUCTURE
• In some cases proteins consist of nonpoly-peptide (non-protein) chain called a prosthetic group
• Example: haemoglobin is linked to a heme group (iron contain molecule)
• Proteins with a prosthetic group are called conjugated proteins.
© 2007 Paul Billiet ODWS
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PROTEIN FUNCTIONS
• Protein structure determines protein function
• Denaturation or inhibition which may change protein structure will change its function
• Coenzymes and cofactors in general may enhance the protein's structure
© 2007 Paul Billiet ODWS
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IB Assessment Statement
• 7.5.2 Outline the difference between fibrous and globular proteins with references to two examples of each protein type
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Fibrous proteins
• Involved in structure: tendons ligaments blood clots(e.g. collagen and keratin)
• Contractile proteins in movement: muscle, microtubules (cytoskelton, mitotic spindle, cilia, flagella)
© 2007 Paul Billiet ODWS
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Globular proteins
• most proteins which move around (e.g. albumen, casein in milk)
• Proteins with binding sites: enzymes, haemoglobin, immunoglobulins, membrane receptor sites
© 2007 Paul Billiet ODWS
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Examples to know
1. Rubisco
2. Insulin
3. Immunoglobulin
4. Rhodopsin
5. Collagen
6. Spider silk
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Proteomes• The total of all the proteins produced by a cell, a tissue or an
organism.
Gel electrophoresis is used to identify the proteins in a sample – florescent markers are attached to antibodies for specific proteins.
Proteomes vary, because different cells produce different proteins. The proteome for each individual is unique.
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Application:
• Denaturation of proteins by heat or by deviation of pH from the optimum.