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How are proteins categorized according to shape?
As fibrous or globular.
What are fibrous proteins? Give examples.
- Usually insoluble in water and are formed from long parallel polypeptide chains. (ppts do NOT fold upon themselves)
- Have many structural functions.
- Collagen- strengthens bones, ligaments, and tendons
- Elastin- provides stretch in skin, blood vessels, and lung tissue
- Keratin- forms structure of hair and nails, and waterproofs the skin
- Dystrophin- reinforces parts of muscle cells
- Fibrin- forms blood clots
- Actin and myosin- involved in contraction of muscle cells, division in all cells, and transport of substances within cells
What are globular proteins? Give examples.
- More or less soluble in water
- Polypeptide chains are spherical in shape (globular)
- Have metabolic functions
- Enzymes- function as catalysts
- Antibodies and complement proteins- help protect against disease
- Hemoglobin- transports oxygen
- Lipoproteins- transport lipids and cholesterol
- Albumins- regulate blood pH
- Membrane proteins- transport substances in and out of cells
- Some hormones such as insulin- helps regulate blood sugar level
What allows proteins to keep their 3 dimensional shapes?
Temperature and chemical composition of body fluids.
What is denaturation?
- When a protein unravels and looses its characteristic shape DUE TO AN ALTERED ENVIRONMENT.
- Denatured proteins are no longer functional and most of the time cannot be reversed.
- EX: fried egg- In a raw egg the soluble egg white protein (albumin) is a clear, viscous fluid. When heat is applied to the egg, the protein denatures, becomes insoluble, and turns white.
What is an enzyme? How are they named?
- A protein molecule that is a catalyst.Catalyze SPECIFIC reactions and reactants.
- Names of enzymes usually end in -ASE.
- Some made of two parts: a protein called an apoenzyme, and an inorganic molecule called a cofactor.
What is an apoenzyme?
A inactive enzyme that a cofactor attaches to which forms an active enzyme.
What is a cofactor?
- An inorganic compound that attaches to an apoenzyme to form an active enzyme. (used to activate enzymes)
- Can be a metal ion such as iron, magnesium, zinc, or calcium.
- OR a nonprotein organic molecule called a COENZYME (often derived from vitamins).
How are enzymes grouped? Examples?
- By the types of chemical reactions they catalyze.
- Oxidases- add oxygen
- Kinases- add phosphate
- Dehydrogenases- remove hydrogen
- ATPases- split ATP
- Anhydrases- remove water
- Proteases- break down proteins
- Lipases- break down triglycerides
What is a substrate?
The reactant molecules that an enzyme acts upon.
What is an active site?
- The part of an enzyme that catalyzes a reaction (where the substrates bind to).
- Fits the substrate like a key in a lock, or the active site can change its shape to fit a substrate that enters it, which is called an induced fit.
- Forms an enzyme-substrate complex when substrates make contact.
What is an enzyme-substrate complex?
A temporary intermediate compound formed from substrates making contact with the active sites of enzymes.
What are the three important properties of enzymes?
- 1.Enzymes are highly specific.
- Each particular enzyme attaches only to specific substrates due to specific 3-D shape. Each enzyme also catalyzes a specific reaction.
- 2.Enzymes are very efficient.
- In optimal conditions can catalyze at rates 100 million to 10 billion times faster then naturally occurring reactions. Between 1-10000 products can be formed a second by a SINGLE enzyme.
- 3.Enzymes are subject to a variety of cellular controls.
- Many enzymes have active and inactive forms in cells which are determined by intracellular environment changes. Their rate of synthesis and concentration are under the control of the cells genes.
What is inhibition in enzymes?
- How they are inactivated.
- Can be competitive inhibition (inhibitor blocks the active site) or allosteric inhibition (change shape of active site)
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