Biochemistry Flashcards
What is a non polar bond?
A covalent bond formed between two atoms that have the same electronegativity. The electrons are shared equally between the two atoms.
What is a polar bond?
A covalent bond that is formed between two atoms with different electronegativities. In this bond, the bonding electrons are not shared equally, and more of the negative charge will be found closer to one of the atoms. So the term “polar” means uneven distribution of charge. A dipole is formed.
Why is CO2 a nonpolar molecule but H2O is polar?
The two molecules have different geometries: the CO2 is a linear molecule and thus is not polar, H2O has a tetrahedral geometry and thus has a dipole.
What are the two shapes that amphipathic molecules can form?
Micelle: where the individual units are wedged shaped (head is bigger than tail).
Bilateral: where’d individual units are cylindrical shaped (cross section of head = that of the side chain).
What is an ionic bond?
An ionic bond, or salt bridge, is an electrostatic interaction that occurs between groups of opposite charge.
What is a hydrogen bond?
A hydrogen bond is an electrostatic noncovalent interaction. It is electrostatic in nature because the interaction occurs between an atom (the H) that has a partial positive charge and an atom (the A) that has a partial negative charge.
What are dipole-dipole interactions?
This is another type of electrostatic noncovalent interaction. It is electrostatic in nature because the interaction occurs between an atom that has a partial positive charge and an atom that has a partial negative charge.
Water is essential to biological systems, not only because it is present in large quantities, but because of the following two reasons:
- Biological molecules like proteins assume specific 3-D shapes due to the chemical and physical properties of water. Their specific 3-D shapes are tied directly to their functions.
- Water can ionize to H+ and OH-. Due to this, it can participate as a key reactant
in many reactions that occur in biological systems.
What are London dispersion forces?
London dispersion forces are van der Waals interactions. They are the weakest type of noncovalent interaction. They occur when non-polar atoms are very close together in space. They originate from very, very small induced dipoles generated in atoms by the random movement of negatively-charged electrons around a positively-charged nucleus
What is the hydrophobic effect?
water’s tendency to minimize its contact with hydrophobic molecules by organizing itself around hydrophobic molecules that become clumped together. Hydrophobic molecules clump together so that fewer organized water molecules are necessary. The further organization of the hydrophobic molecules is outweighed by the fact that fewer organized water molecules are present. Overall, this is more favourable and the entropy is higher.
What is a property of strong acids?
Strong acids like HCl become completely deprotonated when placed in water. So, for example, if you place 100 molecules of HCl in water, you would quickly see 100 Cl- and 100 H+. Strong acids do not have a strong affinity for their proton(s).
What is a property of weak acids?
Weak acids do not automatically become completely deprotonated when placed in water. Weak acids have a strong affinity for their proton(s) and don ’t want to release them.
The degree to which a weak acid will become deprotonated is expressed through its dissociation constant Ka.
What is a property of a strong base?
Strong bases like NaOH have a high affinity for protons and will quickly bind to them in solution.
What is a property of a weak base?
Weak bases have a weaker affinity for protons and don’t always bind to them in solution.
What is pH?
pH is a measure of the acidity of a solution. It is the logarithmic value of the free proton concentration ([H+]) in solution. It is calculated using the following equation:
pH = -log[H+]
When [OH-]=[H+], the pH is 7 and the solution is neutral.
What is a buffer?
A buffer is a substance that prevents drastic changes in pH by preventing changes in free [H+] due to the addition of acid or base.
What are the components of a buffer?
A buffer consists of a weak acid (A) and its conjugate base (CB).
What happens when a strong acid is added to an unbuffered solution?
Adding a strong acid like HCl to an unbuffered system like pure water will result in the [H+] rising. When a buffer is present, the conjugate base can prevent changes in pH by binding to the protons that are being added to the system:
A = CB + H+
I
What substances can act as good buffers?
Strong acids cannot be buffers since they completely ionize leaving no A behind. Water cannot be a buffer since it does not ionize sufficiently. Weak acids are best! They sufficiently ionize and allow us to see A and CB.
When do we see 50% acid and 50% conjugate base in solution?
When pH = pka (the inflection point)
At what pH values is each given weak acid/conjugate base pair a good buffer?
The optimal buffer zone is found when the pH = pKa ± 1.
What are the three main ways to make buffers?
- Start with A and add a strong base until you reach a pH that is within pKa ± 1.
- Start with CB and add a strong acid until you reach a pH that is within pKa ± 1.
- Use the HH equation to calculate how much CB and A you need to add to get a solution at a certain pH.
What are the 2 assumptions that are made in this course for the protonation states of functional groups?
When the pH is 1 unit BELOW the pKa, we will assume that the functional group with an acidic proton is completely protonated. When the pH is 1 unit ABOVE the pKa, we will assume that the functional group with an acidic proton is completely deprotonated.
What does 1 equivalent of base mean?
Adding an amount of base that is equivalent to the amount of acid that we started with.
What is a half equivalence point?
An amount of base that is half the amount of acid we started with (causes pH = pka).
What are the three main buffer systems in the body?
Carbonic acid/bicarbonate buffer (HCO3-)
Phosphate buffer (H2PO4 -/HPO4 2-)
And proteins
When athletes run they breathe in more oxygen which increases the amount of metabolic acids in the blood which in turn lowers pH. How is this buffered?
As carbon dioxide is exhaled and leaves the body, carbonic acid is used up. This shifts the equilibrium to the left. More protons are used up, decreasing [H+] and preventing the pH from decreasing.
ie. H+(up) + HCO3- = H2CO3 = CO2 + H2O (exhaled)
- reaction shifts to the right
Where are D-amino acids occasionally found?
In bacterial and fungal peptides
How are amino acids linked?
through a linkage known as a PEPTIDE BOND or AMIDE LINKAGE (joined covalently)
What catalyzes the formation of peptide bonds?
The ribosome and other enzymes catalyze the formation of peptide bonds to form peptides and proteins.
What type of reactions form peptide bonds?
Condensation reactions.
ie. Produces H2O
What is an important convention when talking about amino acids?
An amino acid covalently attached to others via peptide bonds is called a residue.
What influences of proteins ability to act as a buffer?
A protein’s ability to act as a buffer depends on the number of acidic protons it has. The more acidic protons it has, the better the buffer it will be.
If it ONLY contains diprotic amino acids, the protein will titrate as a diprotic acid (H2A).
If it contains triprotic amino acids, the protein will titrate as a polyprotic acid H3A, H4A, etc.
What is the primary structure of a protein, and what does it tell us?
The primary structure consists of the sequence of amino acid residues in a protein. It is typically reported using amino acid 1-letter codes.
The primary structure tells us the number of each type of amino acid and their order.
Why is the primary structure of a protein important?
The physicochemical properties of proteins depend on their constituent amino acids. Moreover, the primary structure contains all of the information needed for a protein to achieve its tertiary structure.
What are the two main parts of the protein’s primary structure?
- main chain (or backbone): consists of the amino acid skeletons joined together via peptide bonds. The only difference between the backbone of different proteins is the length.
- side chains: The side chains are what give proteins their personalities or physicochemical properties.
What is the secondary structure of a protein?
Regular local conformations of the BACKBONE mainly stabilized by hydrogen bonds between peptide carbonyl oxygen atoms and amide hydrogen atoms – these hydrogen bonds form H-BOND NETWORKS
What are the two types of secondary structure?
- the alpha-helix; and
- beta-strands.
Both types of secondary structure elements are held together via hydrogen bonds between peptide carbonyl oxygen and amide hydrogen groups.
What is a tertiary structure?
Tertiary structure refers to the overall 3-D conformation of an entire polypeptide chain. In the tertiary structure, we keep track of the conformation of both the backbone AND the side chains.
How do tertiary structures form?
To form tertiary structure, the elements of secondary structure pack together. The tertiary structure of proteins is layered, resembling what is seen in a micelle.
What are 2 types of proteins?
Globular proteins and membrane proteins.
What characterizes a globular protein?
They are water-soluble proteins, the inner layer contains the hydrophobic amino acids; this allows these amino acids to minimize contact with the protein’s aqueous environment. The outer layer contains the hydrophilic and charged amino acids, which can interact with the aqueous environment through a variety of non-covalent interactions such as hydrogen bonds and ionic bonds.
What characterizes a membrane protein?
In membrane proteins, their tertiary structure can also resemble a micelle. However, the consistency of the layers is opposite what is seen for globular proteins.
What characterizes a quaternary structure?
Quaternary structure consists of the 3-D arrangement of the polypeptide chains in relation to one another. Only proteins made up of more than 1 polypeptide chain have quaternary structure. These proteins are known as oligomeric proteins.
What is an oligomeric protein?
proteins made up of more than 1 polypeptide chain