Biological molecules Flashcards
name the 3 molecules and what chemical elements they contain
carbohydrate - carbon, hydrogen and oxygen
protein - always carbon, hydrogen, nitrogen and
oxygen and in some sulfur
lipids - carbon, hydrogen and oxygen
what is the structure of carbihydrates?
- contain carbon, Hydrogen and Oxygen
- can be made of small and simple sugars of more complex larger molecules
what is the structure of lipids?
- most lipids in the body are made of triglycerides
- their basic unit is one glycerol molecule chemically bonded to three fatty acid chains that vary in size and structure
- divided into fats and oil
what is the structure of proteins?
- formed from long chains of amino acids this forms a protein
- amino acids can be joined in any order resulting in hundreds of thousands of different proteins - different shapes determines the functions
- e.g enzymes or hemoglobin
test for glucose
- add benedict solution to sample solution
- heat in a boiling water bath for 5 mins
- positive test shows blue - orange/brick red
test for starch
- add drops of iodine solution to food sample
- positive test - orange/brown to blue black
test for protein
- add a few drops of biuret solution to food sample
- positive test - blue to violet/purple
test for lipids
- mix food sample with 4cm3 of ethanol and shake
- wait for sample to dissolve
- strain ethanol solution into another test tube
- add ethanol solution to an equal volume of cold distilled water 4cm3
positive test - cloudy emulsion
important hazards
- biuret solution contains copper sulfate which is dangerous if it gets in the eyes - wear goggles
ethanol is highly flammable - keep away from bunsen burner
iodine is irritant to the eyes
Enzymes
proteins that act as biological catalysts to speed up the rate of a chemical reaction without being changed or used up in the reaction
They are biological because they are made in living cells
Enzymes are necessary to all living organisms as they maintain reaction speeds of all metabolic reactions at a rate that can sustain life
For example, if we did not produce digestive enzymes, it would take around 2 - 3 weeks to digest one meal; with enzymes, it takes around 4 hours
Often the products of one reaction are the reactants for another (and so on)
The mechanism of enzyme action
- Enzymes are specific to one particular substrate(s) as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate
- When the substrate moves into the enzyme’s active site they become known as the enzyme-substrate complex
- After the reaction has occurred, the products leave the enzyme’s active site as they no longer fit it and it is free to take up another substrate
Step One: Enzymes and substrates randomly move about in solution
Step Two: When an enzyme and its complementary substrate randomly collide an enzyme-substrate complex forms, and the reaction occurs
Step Three: A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions
Factors Affecting Enzyme Action: Temperature
- Enzymes are proteins and have a specific shape, determined by the amino acids that make the enzyme and held in place by bonds
- This is extremely important around the active site as the specific shape is what ensures the substrate will fit into the active site and enable the reaction to proceed
- Enzymes work fastest at their ‘optimum temperature’
- In the human body, the optimum temperature is 37⁰C
- Heating to high temperatures (beyond the optimum) will break the bonds that hold the enzyme together and it will lose its shape
- This is known as denaturation
- Substrates cannot fit into denatured enzymes as the shape of their active site has been lost
- Denaturation is irreversible - once enzymes are denatured they cannot regain their proper shape and activity will stop
Increasing the temperature towards the optimum increases the activity of enzymes as the more kinetic energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction
This means that low temperatures do not denature enzymes, they just make them work more slowly due to a lack of kinetic energy
Factors Affecting Enzyme Action: pH
The optimum pH for most enzymes is 7
Some enzymes that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2)
Some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9)
If the pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be disrupted/destroyed
This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity
Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop
