Chapter 30- Amino acids, proteins and DNA Flashcards
What is an amino acid?
An organic compound containing both a carboxylic acid group -COOH and amine group -NH2
How are amino acids named?
All have amine group on C atom number 2, as C in acid group is number 1, so named 2- amino… oic acid
Why can amino acids show optical isomerism?
Carbon atom 2 is often bonded to four different groups making it a chiral centre, however in nature most exist only as one enantiomer so they ‘fit’ into correct cells
What is a zwitterion?
A molecule with separate positively and negatively charged groups
How do amino acids react?
As they have both -COOH and -NH2 groups they can react as both acids and bases, undergo reactions of carboxylic acids and amines
How do amino acids behave in acidic conditions (low pH)?
Lone pair on N accepts H+ ion, producing positive acidic -NH3 + end
How do amino acids behave in alkaline conditions (high pH)?
H+ ion in -COOH group is lost, producing negative basic -COO - end
How are zwitterions formed?
Zwitterions formed when overall pH of molecule is zero -COOH group donate H+ ion to -NH2 group, producing both -NH3 + and -COO - ends
What are the properties of zwitterions?
Contain both + and - end but overall neutral
Ionic bonding between molecules therefore high melting point so solid at room temp.
Soluble in water due to charges
What is a protein?
A molecule made up of amino acids joined by amide/ peptide links
How can proteins be broken down into their constituent amino acids?
Hydrolysis
What happens in acid hydrolysis of proteins?
Protein boiled in 6M HCl (aq) for 24 hours, producing amino acids with -NH3 + end due to acidic conditions, and -OH comes from aqueous conditions. Amide links are broken
What happens in alkaline hydrolysis of proteins?
Protein reacts with conc. NaOH (aq), producing the sodium salt of the amino acids with -COONa end, amide links are broken
How can hydrolysis happen in nature?
Process carried out by enzymes so doesn’t require harsh conditions
What is the primary structure of a protein?
The sequencing of a chain of amino acids that make up a protein, containing amide/ peptide links
What is the secondary structure of a protein?
The structure of a protein when hydrogen bonds form
between the amino acid chains. 2 types of secondary protein structure: α-helix and β-pleated sheet
What is the tertiary structure of a protein?
The three dimensional structure of a protein. This contains ionic bonds, disulfide bridges, hydrogen bonding and induced dipole-dipole interactions
How does disulfide bonding/ sulfur- sulfur bonding bridges form in proteins?
Disulfide bridges are formed between sulfur atoms in amino acid R groups. Both lose a hydrogen atom and covalently bond to each other, holding tertiary structures together and keeping the protein stable.
How do hydrogen bonds form in proteins?
Hydrogen bonds form between lone pairs on O in C=O and H in N-H both in peptide links, also between R groups with H bonded to N, O, F atoms
How do ionic bonds form in proteins?
If -COOH group and -NH2 group from two R groups are adjacent, H is donated from acid to amine group, producing -COO - and -NH3 + group and an ionic bond forms between them
What are enzymes?
A biological catalyst made of proteins. They are proteins with a tertiary structure and have stereospecific active sites that bind to a certain substrate molecule
What is a substrate?
A molecule that binds to the active site of an enzyme during a reaction
What is an active site?
The region of an enzyme where the substrate binds during a reaction
What is an enzyme inhibitor?
A substance that reduces the activity of an enzyme. This might be a drug which blocks the active site, preventing a substrate molecule binding, which can be designed by computers
What is DNA (deoxyribonucleic acid)?
A condensation polymer formed from a sugar, phosphate and a base, which make up nucleotides
What is a nucleotide?
A molecule made from a phosphate ion bonded to 2-deoxyribose which is bonded to one of the 4 bases of DNA (adenine, cytosine, guanine and thymine)
What is the structure of DNA?
Bonds between sugar and phosphate join nucleotides together forming polynucleotide strand which forms the sugar-phosphate backbone
Bases in one strand pair up with bases from another strand so two strands bond via hydrogen bonds to form the double helix structure of DNA
How do bases in DNA pair up?
Bases pair up in specific complementary pairs:
Guanine and cytosine bond with 3 hydrogen bonds
Thymine and adenine bond with 2 hydrogen bonds
What is cisplatin?
A square planar complex of platinum II used as an anticancer drug. It is the cis isomer of Pt II with two Cl and two NH3 ligands
How does cisplatin actually work?
Cisplatin bonds to two adjacent guanine bases, preventing mutated DNA from replicating. Ligand replacement reaction occurs and a bond is formed between Pt atom and N atoms in G bases.
Has to be cis isomer in order to have correct orientation for cells
What are the downsides of cisplatin and how is this combatted?
Cisplatin can bond to DNA in healthy cells as well as mutated DNA causing serious side effects such as hair loss. It’s given in small amounts to try to reduce these effects. Its effectiveness long-term means it is used despite short-term negative effects.
