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Most important macromolecule in the body… Proteins Rule Everything! Functions? Structural parts nails, hair, cell membrane, and cartilage Pigments skin, eyes, and chlorophyll Hormones and receptors Muscle contractions Immunity-Antibodies Enzymes Cytoskeleton Blood clotting Transport of nutrients/gases Cell adhesion Cell membrane transport Packing of DNA
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Molecular Biology
2.4 Proteins
Made of C, H, O and N Proteins are large molecules constructed of
many amino acids Most abundant organic compound found in living
cells
Most important macromolecule in the body… Proteins Rule Everything!
Functions? Structural parts
nails, hair, cell membrane, and cartilage
Pigments skin, eyes, and chlorophyll
Hormones and receptors Muscle contractions Immunity-Antibodies Enzymes
Cytoskeleton Blood clotting Transport of nutrients/gases Cell adhesion Cell membrane transport Packing of DNA
Total energy gain is 4 Calories/gram. (however, energy gain is not their main function).
Amino acids are linked together by condensation reactions to form polypeptides.
The building blocks of proteins are amino acids.
Amino Acids
Centre carbon atomBonded to: Hydrogen (H) Amine group (-NH2) Carboxyl group (-COOH) R- group (different in each amino acid)
Amino acids are linked together by condensation reactions to form polypeptides.
The amino acids are bonded together by peptide bonds to form proteins.
The bond that is formed from the acid group (COOH) and the amino group (NH2)
Water is eliminated = condensation reaction Proteins are frequently called polypeptides
(many peptide bonds).
The smallest polypeptide consists of 20 amino acids (less than that called an “oligopeptide) Insulin contains 2 polypeptides: 21 amino acids
and 30 amino acids Human titin has 34 350 amino acids
There are 20 different amino acids used by ribosomes to make polypeptides
Draw molecular diagrams to show the formation of a peptide bond:
Locate the Amine, Carboxyl, and R-groups Show the formation of a peptide bond between 2 amino acid Try to draw an oligopeptide with all 4
Serine Glutamic acid
Alanine
Glycine
Did you notice? The amine and carboxyl are used in the peptide bonds Chain of atoms linked with single bonds form backbone H attached to N by single bond O attached to C by double bond The R-groups remain
Serine Glutamic acid
Alanine
Glycine
The amine and carboxyl group are used in the condensation reaction
The R-groups give the polypeptide its character
The R-groups provide an amazing range of proteins
Some proteins contain amino acids not contained in the list of 20.
This is due to modification after a polypeptide has been made. Example: hydroxyproline in collagen
Patterns, trends, discrepancies: most but not all organisms assemble polypeptides from the same amino acids.
We can exclude the possibility that this trend is due to chance…
What reasons would account for almost all organisms using the same 20 amino acids?These were the ones produced before lifeThese are the idealAll life evolved from a single ancestral species
Amino acids can be linked together in any sequence giving a huge range of possible polypeptides
Calculate the possibilitiesNumber of Amino Acids in the Chain
Number of possible sequences
1 201
2 202 400
3 8000
4
64 000 000
Shapes – primary (linear) secondary (β-pleated sheets and α-helix) tertiary (bent-coiled) quaternary (compact with a specific structure).
You can unfold a protein (de-nature) by exposing the protein to heat, radiation or a change in pH. (i.e. frying an egg, baking a cake, UV exposure, x-rays).
Questions
1. What 2 functional groups do all amino acids have in common?
2. Draw a generic formation of a peptide bond. Identify the amino terminus, carboxyl terminus, and peptide bond.
3. Define primary structure.4. Name the 2 types of secondary structure.
What type of bond stabilizes this structure?5. Distinguish between polypeptide and protein.6. Why do proteins have more diverse functional
roles than carbohydrates?