Chapter 5
The structure and function of large biological molecules
Macromolecules
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A macromolecule is a very large molecule, built from monomers.
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Four main molecules of life
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Carbohydrates
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Lipids
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Proteins
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Nucleic acids
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Dehydration synthesis
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A process in which polymers are made from monomers by removing water.
Hydrolysis
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A process in which polymers are broken down into monomers by adding water.
How do these actually occur?
1.Carbohydrates
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Definition: Organic compound chiefly consisting of carbon, hydrogen and oxygen in 1:2:1 ratio.
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Formula: CnH2nOn
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Example: sugar, starch, cellulose and gums.
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It is fuel and building material.
monosaccharide -> disaccharide -> polysaccharide
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Monosaccharide: monomers (glucose, fructose, ribose)
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Polysaccharide:
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Storage (starch in plants, glycogen in animals).
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Structure (cellulose in plants, chitin in anthropods).
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Monosaccharide
Linear and ring forms of glucose
Linear and ring forms of glucose
Cellulose vs Starch
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Starch is stored in plants while glycogen is stored in animals.
Cellulose vs Chitin
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Cellulose can be used to create cell wall (màng thành xenlulôzơ).
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Chitin is the main ingredient in the exoskeletons of arthropods and crustaceans (các loài giáp xác).
2.Proteins
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Protein is derived from the Greek word 'proteios', meaning "primary".
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They make up approximately 50% of the dry weight of a cell.
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It contains C,H,O,N,S.
Protein structures
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There are four levels of structures.
- Primary structure: A linear sequence of amino acids which are linked by peptide bonds.
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Secondary structure: The sequence of amino acids are linked by hydrogen bonds which either creates alpha helix or beta pleated sheet.
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Tertiary structure: The way a polypeptide folds and foils to form a complex molecular shape as a result of bonds formed between the R groups.
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Quaternary structure: A protein consists of more than one amino acid chain.
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Overall, the process looks something like this:
Amino acids -> Polypeptides -> Proteins
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Chaperonins belong to a family of proteins called chaperones, and these proteins help maintain protein folding.
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Both physical and chemical factors can effect protein structure and function.
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Changes in temperature
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Higher temperatures reduce the strength of hydrogen bonds which may denature the protein.
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Changes in pH
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Going to change the electrostatic interactions between charged amino acids. Amino acids are polar. A change in pH means a change in the concentration of hydrogen ions (H+). Hydrogen ions are positively charged. This can denature the protein as well.
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Changes in Salt concentration
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Like the previous one. It is going to change the electrostatic interactions as well.
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Presence of reducing agents
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It is going to break the disulfide bonds (S-S).
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-> All of these can unfold or denature the protein.
Change in structure = change in function
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A change in the primary structure from Glutamic to Valine deforms the protein structure. The distortion creates the exposed hydrophobic region. Because hydrophobic region doesn't 'like' water, it starts to connect to other subunit to separate itself from water.
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Protein functions:
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Enzymes (Enzym)
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Antibodies (kháng thể)
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Storage (found in milk protein-bột sữa đạm)
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Transport (hemoglobin)
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Hormones (insulin)
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Receptors
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Movement (motor proteins such as myosin or kinesin)
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Structure (keratin in hair)
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3.Nucleic Acids
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Its major function is to store and transfer genetic information.
DNA vs RNA
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Nucleotides are monomers of DNA/RNA.
Nucleotide = Sugar + Phosphate + Nitrogenous Base
Remember!
Thymine in DNA
Uracil in RNA
The Journey of DNA
DNA -> RNA -> Protein
In a eukaryotic cell, DNA in the nucleus is transcribed into messenger RNA (mRNA), which travels to the cytoplasm and binds to ribosomes. As a ribosome moves along the mRNA from 5'-3', amino acids go through dehydration synthesis, and the polypeptide is created.
4. Lipids
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Fats (triglyceride) are found in your fat cells and used as energy source.
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Fats can be saturated (bão hòa), unsaturated (không bão hòa), and polyunsaturated (không bão hòa đa).
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Saturated vs Unsaturated
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Steroids are hormones and nonpolar.
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For example: cholesterol, progesterone, and testosterone.
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Phospholipids have the same structure as a neutral fat except one bonded fatty acid is replaced by a group that contains phosphate.
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They are used to create lipid bilayer of cell membrane.
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Remember!
Phospholipid molecule has a hydrophilic head and a hydrophobic tail. The hydrophilic head "loves" water, so it contacts with water. The hydrophobic tail "hates" water, so it is on the interior of the membrane. Only nonpolar molecules can pass through the lipid bilayer membrane by simple diffusion.
Sources:
Reece, J. B., L. A. Urry, M. L. Cain, S. A. Waasserman, P. V. Minorsky, and R. B. Jackson. "The Structure and Function of Large Biological Molecules." In Campbell Biology, 115-140. 10th ed. San Francisco, CA: Pearson, 2011.