CH30 AA, Proteins and DNA Flashcards
Functional groups of amino acids
NH2 and COOH
How many naturally occurring AA are there in the body
20
What type of AA are found in the body
alpha-AA
NH2 is always on the carbon next to COOH
Why are alpha-AA chiral
One carbon has 4 different substituents
Which enantiomer do alpha-AA exist as in nature
-ve enantiomer
How can amino acids be synthesised industrially
RCHO + NH4CN –> RCH(NH2)CN via nucleophilic addition
RCH(NH2)CN + HCl + 2H2O –> RCH(NH2)COOH + NH4Cl (hydrolysis, dilute HCl)
Need to reflux the reaction mixture
Is the product from AA being synthesised naturally optically active - why
No - racemic mixture formed as CN- can attack from above and below planar C=O bond with equal likelihood
In what form do AA exist as solids
Zwitterions (ionic lattice) - High MP and BP
What colour solids are most zwitterions at RT
White
Do zwitterions dissolve in water - why
Yes - contain polar bonds
Define zwitterion
Ions which have both a permanent positive and negative charge, but are neutral overall
How do zwitterions occur in AA
COOH deprotonated - COO-
NH2 protonated - NH3+
What happens to AA in acidic conditions
Gains proton on NH2 group
What happens to AA in alkaline conditions
Loses a proton from COOH group
What is the peptide linkage
- CONH-
- C-N-
- C=O
- N-H
What is a dipeptide
2 amino acids bonded together
Name given to chains of AA up to 50 AA
Polypeptides
Name given to chains of AA with more than 50
AA
Proteins
What are polypeptides and proteins found in
Enzymes
Wool
Hair
Muscles
Process by which polypeptides and proteins are broken down
Hydrolysis
Conditions needed for hydrolysis
6 mol dm-3 HCl
Reflux for 24 hours
What is primary structure of a protein - how is it bonded
Sequence of AA along the protein chain
Bonded by covalent bonds
How is primary structure represented
Sequence of 3 letter abbreviations of AA
How can primary structure of protein be broken up
Hydrolysis
6M HCl
24 hour reflux
What is secondary structure of a protein
The shape of a protein chain
2 options for secondary structure
alpha-helix
beta-pleated sheets
How is secondary structure held together
H bonding
Between C=O and N-H groups
What is the tertiary shape of a protein
Alpha-helix or beta-pleated sheet folded into a complex 3D shape
How is tertiary structure held together
H bonding
Ionic interactions between R groups
Disulfide bridges
van der Waals forces of attraction
Why is tertiary structure important
The shape of protein molecules vital in their function
How can AA be bond to each other
H bonding
Ionic interactions
Disulfide bridges
What is wool - how is it held together
Protein fibre with secondary alpha-helix structure - H bonds
What does wool’s structure and bonding mean for its properties
Can be stretched - H bonds extend
Release it and return to its original shape
Wash too hot and H bonds permanently break so garment loses its shape
What is TLC plate made of
Plastic sheet coated with silica, SiO2
This is the stationary phase
Describe how to carry out TLC
Spot samples onto pencil line few cm above base of TLC plate
Place this in beaker with solvent level below pensil line - ensure lid on beaker to avoided solvent vapour escaping
Wait until solvent front almost at top of TLC plate, remove and analyse
Why does TLC separate AA
Solvent carries AA up TLC plate. Rate of movement depends on AA affinity for solvent (solubility) and affinity for stationary phase (attraction to silicon)
What do you often have to do to enable AA to be seen on chromatogram
Spray with ninhydrin or shine UV light on them
How to calculate Rf value
Distance moved by substance / Distance moved by solvent front
How can Rf values be used to check AA
Compare experimental values with accepted values
What is 2D TLC
Uses a square TLC plate
Spot AA in 1 corner
Run TLC in first solvent
Flip plate 90 degrees and repeat TLC in a different solvent
Benefits of 2D TLC
Separates spots of AA more
Gives 2 Rf values for each AA
How to find primary structure of protein
Reflux with 6M HCl 24 hours
Carry out TLC
How to find secondary and / or tertiary structure of a protein
X-Ray
Diffraction
What is an enzyme
Protein based catalysts that speed up reactions in the body
How many reactions can 1 enzyme catalyse
1
Structure of enzyme
Globular protein containing an active site
How does its structure help the function of the enzyme
Lock and Key - reactants fit directly into active site
How else do they increase RoR
Reacting molecules form temporary bonds to enzymes - weakens bonds in molecules, promotes electron movement and lowers activation energy
What does stereospecificity of enzymes mean
Active sites are so selective of the shape of the substrates that only reactions involving 1 enantiomer can be catalysed
What does stereospecificity mean for most naturally occurring molecules
Means they can only occur as 1 enantiomer due stereospecific enzymes
How are enzymes denatured
Change in temperature or pH
How does enzyme inhibition work
Molecules with very similar shape and structure binds to enzymes active site
Blocks active site
Substrate cannot adsorb to active site and reaction is not catalysed
Example of drug which works through enzyme inhibition
Penicillin
Benefits of modelling new molecules on computers
Understand factors that affect shapes of complex proteins
What does DNA do
Present in all cells and is a blueprint from which all organisms are made
What structure does DNA take
A polymer with 4 monomers - can be combined differently
What constitutes a nucleotide
Phosphate ion
Sugar
Base
What forms between adjacent nucleotides
Hydrogen bonding
Which bases pair up between nucleotides
A and T
G and C
How does DNA polymerise
OH on phosphate group and OH on number 3 carbon of 2-deoxyribose react to eliminate H2O
What kind of polymer is DNA
Condensation polymer chain –> backbone of phosphate and sugar molecules with bases attached
What defines properties of DNA
Order of bases
Why does DNA have a double helix shape
Exists as 2 strands
H bonding between bases of 2 strands
Why is it important that DNA is exactly copied when cells divide
Because it codes for proteins and makes all cells
How is DNA exactly copied when cells divide
H bonds between base pairs break Covalent bonds in polymer chains remain intact Sequence of bases maintained Separate nucleotide molecules move to H bond with relevant bases They polymerise - DNA replicated exactly
How does the body se information stored in DNA
Template for arranging AA into protein chains
What is cisplatins function
Anti-cancer drug
Bonds to strands of DNA to distort shape and prevent cell replication
Bonds to N on 2 adjacent G bases
N atoms replace Cl- ligands in ligand substitution reaction
Why are Cl- ions able to be replaced by N on the base
N atoms on the G base have lone pairs that co-ordinately bond to Pt ion
N atoms better ligands than Cl-
Drawbacks of cisplatin
Affects healthy cells that are replicating quickly - hair loss
What happens when excess bromomethane is added to AA
CH3BR in excess - every H on N atom and lone pair on N atom replaced by CH3 group
Quaternary ammonium ion