Amino acids, proteins and DNA Flashcards
Why are amino acids amphoteric?
They contain a basic amino group and an acidic carboxylic group
What other property do amino acids have?
They are chiral molecules and so a solution of a single amino acid enantiomer will rotate plane polarised light.
An exception is glycine as the side chain is a hydrogen
What is a zwitterion?
It is a dipolar ion
Where do zwitterions exist in amino acids?
They only exist near an amino acid’s isoelectric point. This is the pH where the average overall charge on the amino acid is zero.
What technique can be used to identify unknown amino acids?
Thin-layer chromatography
Why is thin layer chromatography used to identify amino acids?
Different amino acids have different R groups and therefore have different solubilities in the same solvent.
What are proteins?
They are condensation polymers of amino acids joined together by peptide links.
Describe the primary structure of proteins
it is a sequence of amino acids in the long chain that makes up the protein
Describe the secondary structure of proteins
The peptide links can form hydrogen bonds with each other meaning the chain is not a straight line. The most common secondary structures are an alpha helix and a B-pleated sheet.
Describe the tertiary structure of proteins
The chain of amino acids is itself often coiled and folded in a characteristic way that identifies the protein. Extra bonds can form between different parts of the polypeptide chain which gives the protein a kind of three-dimensional shape.
How are the secondary and tertiary structures of protein formed?
They are formed by intermolecular forces causing the amino acid chains to fold or twist.
What are the two main types of bonds that hold proteins in shape?
Hydrogen bonding
Disulfide bonds
Which factors affect hydrogen bonding and the formation of disulfide bonds?
Temperature
pH
What are enzymes?
They are proteins that act as biological catalysts
How do enzymes work?
They only work with specific substrates because the substrate has to fit into the active site. ‘Lock and key’ model
What makes the active sites stereospecific?
Enzymes are made up of amino acids and therefore contain chiral centres. This means that only one of the enantiomers of a substrate will properly fit into the active site.
What are inhibitors?
They are molecules that have a similar shape to the substrate
What factors affect the amount of inhibition that occurs?
relative concentrations of inhibitor and substrate
how strongly the inhibitor bonds to the active site
How do some drugs work?
They work as inhibitors by blocking the active site of an enzyme and stops it from working.
How are scientists using technology to develop new drugs?
Computers are used to model the shape of an enzyme’s active site and predict how well potential drug molecules will interact with it. They can quickly examine hundreds of molecules looking for ones with the right shape before they start synthesising and testing things in the lab.
What is DNA?
It is a polymer of nucleotides which contains all the genetic information of an organism
What is nucleotide?
It is made up from a phosphate ion bonded to 2-deoxyribose which is in turn bonded to one of the 4 bases.
How is the sugar-phosphate backbone made?
Nucleotides join together to form a polynucleotide chain. covalent bonds form between the phosphate group of one nucleotide and the sugar of another.
What is the structure of DNA?
DNA is made up of two polynucleotide strands that spiral together to form a double helix structure which is held together by hydrogen bonds between the bases.
Explain how hydrogen bonding between base pairs leads to the two complementary strands of DNA
Adenine always pairs with thymine and guanine always pairs with cytosine.
This leads to the complementary strands because whenever there is an adenine base on one strand, there will be thymine on the other and whenever there is a guanine base on one strand, there will be a cytosine base on the other, and vice versa.
Cisplatin is used as an anticancer drug. How does cisplatin prevent DNA replication in cancer cells?
Cisplatin prevents DNA replication in cancer cells by a ligand replacement reaction with DNA in which a bond is formed between platinum and a nitrogen atom on guanine.
What problems can be caused by cisplatin?
It can bind to DNA in normal cells. This can be a problem for healthy cells that replicate frequently such as hair cells and blood cells. This can cause hair loss and suppress the immune system and also cause kidney damage.
How can the problems caused by cisplatin be reduced?
- giving patients very low doses of cisplatin
- target the humor
Why is cisplatin still used as a chemotherapy drug?
The balance of the long-term positive effects outweigh the negative short-term effects.
