📖 Biochemistry
Water Acid Bases & Buffers -pKa
BiochemistryAcids and bases can be classified as proton donors and proton acceptors, respectively. This means that the conjugate base of a given acid will carry a net charge that is more negative than the corresponding acid. In biologically relavent compounds various weak acids and bases are encountered, e.g. the acidic and basic amino acids, nucleotides, phospholipids etc.
Weak acids and bases in solution do not fully dissociate and, therefore, there is an equilibrium between the acid and its conjugate base. This equilibrium can be calculated and is termed the equilibrium constant = Ka. This is also referred to as the dissociation constant as it pertains to the dissociation of protons from acids and bases.
In the reaction of a weak acid:
HA <-----> A- + H+
the equlibrium constant can be calculated from the following equation:
Ka = [H+][A-]/[HA]
As in the case of the ion product:
pKa = -logKa
Therefore, in obtaining the -log of both sides of the equation describing the dissociation of a weak acid we arrive at the following equation:
-logKa = -log[H+][A-]/[HA]
Since as indicated above -logKa = pKa and taking into account the laws of logrithms:
pKa = -log[H+] -log[A-]/[HA]
pKa = pH -log[A-]/[HA]
From this equation it can be seen that the smaller the pKa value the stronger is the acid. This is due to the fact that the stronger an acid the more readily it will give up H+ and, therefore, the value of [HA] in the above equation will be relatively small.
Basic characteristics of enzymes
BiochemistryThe basic characteristics of enzymes includes
(i) Almost all the enzymes are proteins and they follow the physical and chemical reactions of proteins (ii) Enzymes are sensitive and labile to heat
(iii) Enzymes are water soluble
(iv) Enzymes could be precipitated by protein precipitating agents such as ammonium sulfate and trichloroacetic acid.
PHOSPHORUS
BiochemistryPHOSPHORUS
Serum level of phosphate is 3-4 mg/dl for adults and 5-6 mg/dl in children. Consumption of calcitriol increases phosphate absorption.
Functions of phosphorus
(a) Plays key role in formation of tooth and bone
(b) Production of high energy phosphate compounds such as ATP, CTP, GTP etc.,
(c) Synthesis of nucleotide co-enzymes such as NAD and NADP
(d) Formation of phosphodiester backbone structure for DNA and RNA synthesis
Hypophosphatemia is the condition which leads to decrease in absorption of phosphorus. it leads to hypercalcamia
Hyperphosphatemia, increase in absorption of phosphate was noticed. Hyperphosphatemia leads to cell lysis, hypocalcemia and thyrotoxicosis.
Protein Structure- Biochemistry
BiochemistryProteins are complex macromolecules composed of amino acids that perform diverse biological functions. Understanding their structure-function relationships is crucial for medical applications and biochemistry.
Levels of Protein Structure
Primary Structure
- Linear sequence of amino acids connected by peptide bonds
- Determines all higher levels of organization
- Coded by DNA sequence
Secondary Structure
- Local folding patterns stabilized by hydrogen bonds
- Alpha helix: Right-handed spiral structure
- Beta sheet: Extended polypeptide chains arranged side by side
- Beta turn: Connects different secondary structural elements
Tertiary Structure
- Three-dimensional folding of entire polypeptide chain
- Stabilized by:
- Hydrogen bonds
- Disulfide bridges
- Van der Waals forces
- Electrostatic interactions
- Hydrophobic interactions
Quaternary Structure
- Assembly of multiple polypeptide subunits
- Present only in proteins with more than one polypeptide chain
- Examples: Hemoglobin (4 subunits), antibodies
Protein Classification
Based on Structure
-
Fibrous Proteins
- Elongated, insoluble
- Structural functions
- Examples: Collagen, keratin, elastin
-
Globular Proteins
- Compact, soluble
- Functional proteins
- Examples: Enzymes, antibodies, hormones
Based on Composition
-
Simple Proteins
- Composed only of amino acids
- Examples: Albumin, globulins
-
Conjugated Proteins
- Contain non-protein prosthetic groups
- Glycoproteins: Contain carbohydrates
- Lipoproteins: Contain lipids
- Nucleoproteins: Contain nucleic acids
- Phosphoproteins: Contain phosphate groups
- Metalloproteins: Contain metal ions