Unit 4.7 - Amino acids, peptides and proteins Flashcards
What are amino acids?
Carbon compounds which contain two functional groups:
An amino (amine) group - NH2
A carboxylic acid group - COOH
Two functional groups of an amino acid
-NH2 (amine)
-COOH (carboxylic acid)
Most common group of amino acids
2-amino acids (alpha amino acids)
Describe a 2-amino acid
Both functional groups are attached to the same carbon atom
Why is the 2-amino acid the most common group?
It’s the type of amino acid most commonly found in nature and is the building block from which proteins are made
Type of amino most commonly found in nature and from which proteins are made?
2-amino acids/alpha amino acids
H2NCH2COOH
Aminoethanoic acid (glycine)
Aminoethanoic acid (glycine) formula
H2NCH2COOH
CH3CH(NH2)COOH
2-aminopropanoic acid (alanine)
2-aminopropanoic acid (alanine) formula
CH3CH(NH2)COOH
C6H5CH2CH(NH2)COOH
Phenylalanine
Phenylalaline formula
C6H5CH2CH(NH2)COOH
HOCH2CH(NH2)COOH
Serine
Serine formula
HOCH2CH(NH2)COOH
What may X be in the 2-amino acid structure?
A wide variety of groups, each making a different amino acid
What do all 2-amino acids have except for Aminoethanoic?
A chiral centre on the 2-carbon
Only 2-amino acid without a chiral centre on the 2-carbon atom
Aminoethanoic
Chiral centre
Has 4 different groups or atoms attaches to the carbon atom and forms optical isomers
What type of amino acids all have a chiral centre (except for amino ethanoic)
2-amino acids
Describe the optical isomers of 2-aminopropanoic acid
Have the same structural and molecular formula, but have different spatial arrangement of atoms. Same chemical and physical properties but rotate plane polarised light in opposite directions. The two isomers are known as enantiomers.
What do most naturally occurring materials have?
Chirality
What type of materials do most of them have chirality?
Naturally occurring ones
Amphoteric behaviour
Can react as both an acid and a base
Describe amino acids at room temperature
White crystalline solids
Describe amino acids solubility in water and in non-polar solvents
Readily soluble
Describe the melting point of amino acids compared to alkanes of similar molar mass
Fairly high
What type of compound are the properties of the solubility and melting points of amino acids typical of?
An ionic compound, not a covalent compound
What type of forces predominate in the solid of an amino acid?
Ionic
How do we explain the high melting points and solubility of amino acids?
Talk about the Ionic bonds, they do not form hydrogen bonds
How do amino acids exist?
As internal salts known as zwitterions
What are zwitterions?
Hybrids - how amino acids exist as internal salts
What type of form is the zwitterion form of an amino acid?
Ionic
Where is the ionic form of amino acids found?
Also in aqueous solution
Is an aqueous solution of an amino acid acidic or basic and why?
Neutral since the basic and acidic properties cancel one another out since the amino acid is in its ionic (zwitterion) form
Equilibrium of the amino acid amino ethanoic acid in aqueous solution
NH2CH2COO- —><— NH3+CH2COO- —><— NH3+CH2COOH
What does an aqueous solution of amino acids contain?
Zwitterions
When does the compound of an amino acid exist as the zwitterion itself?
At a certain pH
What does the compound of an amino acid exist as at a certain pH?
The zwitterion
What does the isoelectronic point vary with?
Depending on the amino acid
Isoelectronic point
The pH at which the compounds exist as the zwitterion itself
The pH at which the compounds exist as the zwitterion itself
Isoelectronic point
What is essentially happening to a zwitterion when acid is added?
It becomes protonated
What is essentially happening to a zwitterion when alkali is added?
It’s deprotonated
What happens when acid is added to a zwitterion?
Free acid forms
Describe a free acid
Both protonated
What forms when alkali is added to a zwitterion?
Free amine
Describe a free amine
Neither protonated
What forms when acid is added to a free amine?
Zwitterion
What forms when alkali is added to a free acid?
Zwitterion
What happens when an amino acid is reacted with HCl?
A dipeptide is formed
How is a dipeptide formed?
If an amino acid is reacted with HCl
Dipeptide
2 amino acids bonded together
2 amino acids bonded together
Dipeptide
Peptide link
Forms when the amino group from one amino acid reacts with the carboxylic acid group from another amino acid
Which groups of 2 amino acids react to form a peptide link?
The amino group from one, the carboxylic acid group from the other
What is eliminated during the formation of a peptide link?
Water
What type of reaction is the formation of a peptide link?
Condensation
What is a peptide link essentially?
An amide link
How many dipeptides would be possible if we were to mix 2 amino acids?
4
Explain what proteins are
Complex molecules derived from amino acids in condensation reactions
From what type of reactions do proteins form?
Condensation reactions
What do proteins make up?
A significant amount of living tissue - muscles, skin, hair
Why does the body require a constant supply of protein?
For growth, replacement of old protein and for metabolic reactions in the body
How are proteins formed in the body?
By reactions between 2-amino acids
How are the amino acids needed for growth obtained?
From proteins in the diet
What catalyse the formation of proteins?
Enzymes - protease enzymes
Basic link between amino acids
The peptide (amide) link
Dipeptide
2 amino acids
Tripeptide
3 amino acids
Polypeptide
Many amino acids
What is a protein essentially?
A polypeptide containing between 200 and 60,000 amino acids in a chain
How many polypeptides are proteins made up of?
One or more
Haemoglobin
A globular protein containing 4 polypeptide chains
How many amino acids are there in the body required for the formation of proteins?
20
How do we obtain the proteins needed?
The body produces some of them, others can only be obtained from plant material
How are proteins similar?
Chemically
Even though proteins are chemically similar, what’s different?
They show a wide variety of functions, reflecting the immense number of combinations
What reflects the immense number of combinations of amino acids to form proteins?
The wide variety of functions they have
4 main type of protein structure
Primary
Secondary
Tertiary
Quaternary
Primary protein structure
Describes the sequence in which the amino acids are arranged
What does a particular protein have?
A sequence of amino acids unique to itself
What can enzymes do to a polyptide chain?
Can hydrolyse protein at particular peptide links in the chain
How do identify the amino acids in a protein?
Enzymes can hydrolyse proteins at particular peptide links in the chain
The sequence of amino acids in the protein is found
The peptide and subsequently the amino acids in the protein can be identified by chromatography
What type of bonding do proteins have within the structure?
Hydrogen bonding
Where is the hydrogen bond formed in a secondary protein structure?
Between the H atoms bonded to the nitrogen and the O atoms on the carbonyl group
What happen in the secondary protein structure when hydrogen bonds form within the structure?
The chain folds into a spiral
Secondary protein structure
The shape (conformation) of the spiral formed when hydrogen bonding occurs within the structure
2 types of secondary protein structure
Alpha helix
Beta pleated sheet
Alpha helix
The structure coils up into a helical shape. Typically, eighteen amino acids make five coils
Beta pleated sheet
The hydrogen bonds can form predominantly between adjacent protein molecules, resulting in a pleated sheet structure extending over 3-10 amino acids
Describe the secondary structure of a protein
Short-range three-dimensional shape (covering a small number of adjacent amino acids) and is generally either an alpha helix or a beta pleated sheet
How is the tertiary protein structure formed?
Amino acids in some parts of the protein react with the different amino acids in the protein
Describe the tertiary protein structure
The spiral can be folded back on itself in a loop by bonds between sulfur atoms, which are found in some amino acids (e.g - cystine)
Type of amino acids example where bonds occur between sulphur atoms
Cystine
What is the secondary structure of a protein due to?
Hydorgen bonding between adjacent chains
Hydorgen bonding in silk
Between chains
Hydrogen bonding in wool
Within the chain
Quaternary protein structure
The way in which different polypeptide chains come together to form the final protein structure
Final 3D conformation of a protein
Quaternary structure
What do proteins with more than one polypeptide chain have to do?
Undergo additional folding to form the quaternary structure
Explain how the quaternary structure of a protein forms
Various bonds join together the polypeptide chains. Different polypeptide chains coming together to form the final protein are typically bonded together either via hydrogen bonds, covalent bonds or ionic bonds.
Types of bonding in quaternary structure
Hydrogen, covalent, ionic
Diners
Proteins made up of two polypeptide chains
Trimers
Proteins made up of three polypeptide chains
Tetramers
Proteins made up of four polypeptide chains
Proteins made up of four polypeptide chains
Tetramers
Proteins made up of 3 polypeptide chains
Trimers
What are enzymes?
Proteins
What are enzymes composed of?
Polymers that act as natural catalysts to regulate the speed of many chemical reactions involved in the metabolism of living organisms
Categories of enzymes
Hydrolysis
Oxidising
Reducing
What does the classification of an enzyme depend on?
The type of reaction they control
Example of enzymes that control many different reactions + explain
Pepsin and trypsin
Bring about the digestion of meat
Example of enzymes that are specific and only accelerate one reaction + explain
Urease
Breaks down urea
Why are enzymes useful?
They’re very efficient
Minute quantities can accomplish at low temperatures and mild conditions what would require violent reagents and high temperatures by ordinary chemical means
What are enzymes being designed to replace?
Transition metal catalysts
What do the kinetics of enzyme reaction differ from?
Those os simple inorganic reactions
What is each enzyme selectively specific for?
The substance in which it causes a reaction
When are enzymes most effective?
At a temperature particular to them
Why don’t we just increase the temperature of enzyme catalysed reactions?
Although an increase in temperature may accelerate a reaction, enzymes are unstable when heated
What does alcoholic fermentation depend on?
The action of enzymes that are synthesised by the yeasts and bacteria used in the production process
How are the medical uses of enzymes illustrated?
By research into L-asparaginase, which is thought to be a potent weapon for the treatment of leukemia
Types of enzymes used in laundry and their mode of action
Amylases, lipases, proteases
Removing stains from clothes caused by starch, fats and proteins
Types of enzymes used in brewing and their mode of action
Amylases, glucanases, proteases, zymases
Hydrolysing polysaccharides and proteins into smaller molecules
Types of enzymes used in dairy and their mode of action
Rennin
Hydrolysing protein in cheese making
How come amino acids are amphoteric?
They contain a basic NH2 group and an acidic COOH group
What type of catalysts are enzymes?
Biological
Zwitterion
A dipole form of an amino acid where the carbonic group loses a proton, becoming a COO- and the amino group gains a proton to become NH3+
What type of reaction would hydrolysis be to an amino acid?
Decomposition
What happens when acid is added to a zwitterion?
Everything can can be protonated will be
What happens when alkali is added to a zwitterion?
Everything that can be deprotonated will be
What might we have to do to make amino acid questions easier?
Rearrange the amino acid
What does “heated with concentrated sulphuric acid” imply and what does this mean?
Hydrolysis of the protein
Amino acids form
What does a question involving “alcohol in the presence of a small amount of concentrated sulphuric acid mean is happening?
Esterification
Why do amino acids have stronger melting temperatures than other acids?
They exist as zwitterions, so they have a strong ionic character and so stronger forces between the molecules than other acids and thus a higher melting point
When can we only form one dipeptide?
When it’s formed from two molecules of the same acid
When can we not form a zwitterion?
When there’s no acidic hydrogen in the carboxylic acid group
Why do zwitterion forms of molecules have high melting temperatures?
Strong ionic character and strong forces between molecules
