AS Booklet 2- Biological Molecules 2 Flashcards
What is a protein?
A protein contains the elements carbon, hydrogen, oxygen and nitrogen and occasionally sulphur formed from monomers (amino acids).
Proteins can contain one or more polypeptide chains.
What is an amino acid?
An amino acid is a monomer/sub-unit used to make polypeptides such as proteins.
They all contain an amine group (NH2) and carboxylic acid group (COOH) but their R group is different.
What is the generalised structure of an amino acid?
R
|
H2N—C—COOH
|
HHow many common amino acids are there?
20 different, commonly occurring amino acids.
How do you hydrolyse a protein?
- Heat with an acid (e.g. dilute HCl)
* With the specific enzyme (a protease) at its optimum pH and temperature.
What are the four structures of proteins?
• Primary Structure:
The sequence of amino acids.
• Secondary Structure:
Alpha double helix or beta-pleated sheets.
• Tertiary Structure:
Folding and coiling of secondary structure. Disulphide bridges, ionic bonds and H bonds allow this to happen.
• Quaternary Structure:
More than one polypeptide chain and sometimes an inorganic/synthetic group (e.g. haemoglobin have a haem group, 2 beta-pleated sheets and 2 alpha double helices).
What is a globular protein?
A protein that is soluble and has highly folded and coiled polypeptide chain(s) with a complex tertiary structure.
Enzymes and antibodies are two examples of globular proteins.
How can a protein be denatured?
Hydrogen and ionic bonds are broken down by something, such as:
• Temperature above optimum.
• Extreme pH changes.
• Heavy metals
Disulphide bridges are not broken at the temperatures which break H and ionic bonds.
Why is it bad for a protein to become denatured?
Because proteins have specific tertiary structures that are suited to their function, and if this tertiary structure changes it can cause the protein to become useless.
For example, when enzymes become denatured, the active site changes shape due to some bonds in the tertiary structure breaking, meaning it cannot catalyse the reactions it is meant to.
What is the Biuret test for proteins?
- Add Biuret agent.
- Purple indicates protein is present.
- If solution remains blue, no protein is present.
What is an enzyme?
What are the functions of an enzyme?
An enzyme is a protein and biological catalyst.
Regulates biological processes in living organisms.
Why and how do enzymes lower activation energy?
How is it beneficial?
Lowering the activation energy means rate of reaction is increased because less energy is required for molecules to react when there is a successful collision.
The energy is lowered due to the enzymes holding the reactants in a way that makes the reaction more likely to happen.
What is meant by enzyme specificity?
Enzymes are specific to substrates of complementary shape(or other things) due to the tertiary structure being folded and coiled in a certain way to create a specific active site.
For example, amylase act on a single substrate whereas lipases are specific to chemical bonds.
What are the two models of enzyme-substrate complexes?
Lock and Key model:
• Complementary substrate enters active site to creat enzyme-substrate complex.
• Enzyme-product complex as reaction has been catalysed.
• Products leave active site.
Induced Fit model:
• Complementary substrate enters active site.
• This induces the active site to change shape slightly and mould itself around the substrate (forming e-s complex).
• Reaction is catalysed forming an e-p complex.
• Products leave active site.
What factors affect the rate of enzyme-catalysed reactions?
- Substrate concentration
- Enzyme concentration
- Temperature
- pH
- Inhibitors
How does substrate concentration affect enzyme-catalysed reactions?
An increase in substrate concentration increases rate of reaction (ROR) until constant maximum rate reached (Vmax).
- ROR increases as collisions between substrate and enzyme molecules are more likely.
- ROR levels out as all enzyme active sites are taken up (saturation and Vmax).
- ROR is now limited by concentration of enzymes.
- Only was to increase ROR is to add more enzyme.
How does enzyme concentration affect enzyme-catalysed reactions?
- When concentration of substrate is in excess, an increase in enzyme concentration increases ROR.
- More enzyme molecules = more available active sites.
- Increases number of successful collisions between active sites and substrates, forming e-s complexes.
- Directly proportional and line on graph continues at a constant rate (diagonal).
How does temperature affect enzyme-catalysed reactions?
- An increase of temperature up to the optimum gives the molecules of both enzymes and substrates more KE and therefore there are more successful collisions forming e-s complexes.
- Increases ROR.
- Optimum temperature
- Past optimum temperature, enzymes denature because their ionic and H bonds in their tertiary structure get broken, meaning active site shape changes and e-s complexes can no longer be formed (as substrate cannot bind to active site).
How does pH affect enzyme-catalysed reactions?
Most enzymes have narrow pH range in which they can function.
• Change in pH alters ionic charges on acidic and basic groups.
• H and ionic bonds are broken, tertiary structure changes, active site change so substrate can’t bind and e-s complexes can’t be formed.
What are the two types of enzyme inhibitors and how do they affect enzyme-catalysed reactions?
Competitive and non-competitive inhibitors.
Competitive inhibitors compete for the active site as they are complementary in structure to the enzyme and similar in structure to the substrate. This lowers the ROR and it takes longer to reach Vmax.
Non-competitive inhibitors bind elsewhere on the enzyme, not at the active site. This changes the tertiary structure of the enzyme meaning the active site changes and the substrate cannot bind to form e-s complexes. ROR is lowered more than with competitive inhibitors and does not reach Vmax.
What are independent, dependent and controlled variables?
What is a control?
Give an example of each from one experiment.
The independent variable is the variable being changed.
The dependent variable is the variable being tested/measured.
Controlled variables are other factors that must remain constant to ensure a fair test.
Any change to the independent variable directly effects the dependent variable.
A control is separate experiment used for comparing the effects of the independent variable on the dependent. The control does not receive treatment/change.
What are the two named nucleic acids?
How do they differ from one another?
DNA and RNA.
Deoxyribose nucleic acid and ribose nucleic acid.
Their structure is different. Both have pentose sugars but DNA has Deoxyribose and RNA has Ribose.
DNA has C, T, A and G but RNA has C, U, A and G.
DNA has a phosphate group.
What is the structure of DNA?
DNA is a polymer made of polynucleotides.
One polynucleotide is made up of 4 nucleotides.
One nucleotide is made up of a phosphate group, a deoxyribose sugar and a nitrogenous base.
The nucleotides of each strand are joined by phosphodiester bonds, formed in condensation reactions.
The sugar and phosphate form the sugar-phosphate backbone.
The organic nitrogenous based face inwards and are joined to the complementary base on the other strand by weak H bonds (complementary base pairings: A and T, C and G).
How is the structure of DNA adapted to its function?
The sugar phosphate backbone gives strength to the alpha double helix, which protects the genetic code (sequence of bases, which codes for proteins).
Each strand of alpha double helix serves as a template for replication and makes the molecule more stable.
The coiling of DNA means compact shape so more information can be stored in smaller spaces. Large molecule = lots of info.
Complementary base-pairing allows info to be replicated accurately.
Weak H bonds give stability and ease for unzipping during replication.
