Upload
dena
View
45
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Macromolecules 3: Proteins. Additional Resources (1). The Tree of Life , proteins and DNA module. Additional Resources (2). Protein structure and conformation links Molecular Workbench DNA and protein module Summary of protein confirmation Protein movie. - PowerPoint PPT Presentation
Citation preview
Macromolecules 3: Proteins
Additional Resources (1)
• The Tree of Life, proteins and DNA module
Additional Resources (2)Protein structure and conformation
links• Molecular Workbench DNA and
protein module• Summary of protein confirmation• Protein movie
7.5.4: State 4 functions of proteins, giving a named example of each
1. Structural support (Fibrous proteins)
Silk: cocoons and webs Keratin: hair, horns, skin, nails, wool, beaksCollagen: tendons and ligamentsPDB 101
2.Enzyme Function (Globular soluble)Amylase CatalasePepsinTrypsinDNA helicaseDNA synthaseEtc etc etc…
3. Protein hormonesGlobular soluble• Insulin• ACTH• Vasopressin• Somatostatin• Prolactin• Growth hormone
4. Transport proteins (Globular, soluble)
Haemoglobin, myoglobin: transport of essential substances (oxygen, carbon dioxide)Myoglobin was the first protein to be thoroughly described
5. Energy storage: solubleOvalbumin, Casein (milk protein), storage proteins in plant seeds
6. Movement proteinsActin and myosin form muscle fibresAnimation of actin/myosin
7. Receptor proteins (also pumps, channel proteins)
• Adrenergic receptors
• G-protein receptors• Cannabinoid
receptors• Opioid receptors• Aquaporin
channels• Na/potassium
pump proteins
8. Immune function:Antibodies (Immunoglobulins)
Globular soluble proteins: IgG, gA, IgM,
Proteins• > 50% of the dry mass of a cell is
proteinProteins are used for:• Structural support• Energy storage• Transport of other substances• Signalling from one part of the
organism to another• Movement• Defence against foreign substance• Enzymes• Humans have tens of thousands of
different proteins• Most structurally sophisticated
molecule, due to unique 3D shape or conformation
Protein Functions
Amino Acid (Monomers)Amino acid structure:
NH2 - C - COOH
Amino acids differ due to the R (functional) group
The structure of the R-group determines the chemical properties of the amino acid
Amino Acids link together to form polypeptides
• 2 Amino Acids form a covalent bond, called a PEPTIDE BOND, through a condensation reaction to form a dipeptide
• Multiple amino acids can bond to each other one at a time, forming a long chain called a POLYPEPTIDE
Peptide Bonds – link amino acids
20 Amino Acids are used in cells
7.5.3: Explain the significance of polar and non-
polar amino acids
Hydrophilic Amino Acids Polar (but uncharged) amino acids are
hydrophilic & can form H-bonds• Serine• Threonine• Glutamine• Asparagine• Tyrosine• Cysteine
Hydrophobic Amino Acids • Glycine• Alanine• Valine• Leucine• Isoleucine• Methionine• Phenylalanine• Tryptophan• Proline)
Nonpolar amino acids are hydrophobic and are usually found in the centre of the protein.
They also found in proteins which are associated with cell membranes.
Electrically charged Amino Acids
The electrically charged amino acids have electrical properties that can change depending on the pH.
Aspartic AcidGlutamic AcidLysineArginineHistidine
Special Amino AcidsCysteine can form covalent disulfide bonds
Proline has a unique structure and causes kinks in the protein chain
‘Essential’ Amino AcidsIn humans, not all
amino acids can be manufactured by the body; 10 (8 in adults)
must be taken in through our diet.
These are the ‘essential’ amino
acids
7.5.1: Explain the four levels of protein structure, indicating the significance of
each level
Four Levels of Protein Structure/ Conformation
1. Primary - unique linear sequence in which amino acids are joined, can have dire circumstances if changed (insulin)
2. Secondary - refers to three dimensional shapes that are the result of H bonding at regular intervals, due to interactions between the amino acid backbones• alpha helix is a coiled
shape• beta pleated sheet is
an accordion shape
3. Tertiary Complex 3-D globular
shape due to interactions between R groups of amino acids in it• Globular proteins such
as enzymes are held in position by these interactions
4. Quaternary Consist of more than one
polypeptide chain subunits, associated with interactions between these chains 2719
Protein Shape Determines Function• Proteins with only primary and secondary structures are
called fibrous proteins (claws, beaks, keratin, wool, collagen, ligaments, reptile scales)
• Proteins with only 1,2,3 shapes are called globular proteins
• If a protein is incorrectly folded, it can’t function correctly
• Not understood how proteins fold themselves, seem to have molecules called chaperone proteins or chaperonins that assist others
• A protein is denatured when it loses its shape and therefore its ability to function correctly
2820
Primary Structure• A unique sequence of
amino acids in a long polypeptide chain
• Involves peptide bonds between the carboxyl and amine groups
• Any changes in primary structure will affect a protein’s conformation and its ability to function• Example: Sickle cell anemia
LYS VAL PHE GLY ARG CYS
Sickle cell anaemiaSickling occurs due to a mutation of the Hb gene, associated with replacement of glutamic acid by valine
Secondary StructureMade by hydrogen bonds between the backbone of the amino acids (amino
group and carboxyl groups)
• α-helices: area with a helical or spiral shape. Held together by H bonds between every 4th amino acid
• β-pleated sheets: area where 2 or more regions of the polypeptide chain lie in parallel
αhelix a β-pleated sheet
• The bonds involved are hydrogen bonds• Large proteins will have regions containing both
structures
Tertiary Structure: FOLDINGThe protein folds up since various
regions on the secondary structure are attracted to each other:
1. Disulfide Bridges: strong covalent bonds between cysteine’s sulfhydryl (-SH) groups
2. Ionic Bonds: between positively and negatively charged side chains
3. Hydrogen Bonds: between polar side groups
4. Hydrophobic Interactions: non-polar side chains end up on the inside of a protein, away from water
Quaternary StructureComplex proteins exist as
aggregations of 2 or more polypeptide subunits
QUATERNARY STRUCTUREE.g. immunoglobulins
• The bonds involved are the same as those for tertiary structure
Chain 1
Chain 3 Chain 2
Protein denaturationProtein denaturation refers to loss of 3 – dimensional structure (and usually also biological function) of a protein – die to changing of the bonds that maintain secondary and 3rd degree structure, even though the amino acid sequence remains unaltered
Denaturation can be caused by:• Strong acids and
alkalis – profound pH change
• Heavy metals – may disrupt ionic bonds
• Heat, radiation, UV radiation
• Detergents and solvents
7.5.2: Outline the difference between fibrous and globular proteins, referring to 2 examples of each
• A review from Cornell University
Fibrous proteinsOnly have primary and secondary structures
• Water insoluble• VERY tough, may also be
supple or stretchy• Parallel polypeptide chains
in long sheets or fibres• STRUCTURAL proteins –
collagen, cartilage, tendons, blood vessel walls
• CONTRACTILE proteins – actin and myosin
Globular proteinsHave all four levels of
protein structure• Water soluble• Tertiary structure critical
to function• CATALYTIC (enzymes)• REGULATORY –
hormones (insulin)• TRANSPORT
(haemoglobin)• PROTECTIVE
(immunoglobulins)