Biochemistry 1: Amino Acids and Proteins

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Proteins

• Amino acids are amphoteric molecules, meaning they can exist as cations, anions, or zwitterions depending on the pH.
• Glycine is the only amino acid that is not optically active.
• A peptide bond is a covalent bond formed between the carboxyl group of one amino acid and the amino group of another amino acid.
• The side chain of an amino acid gives it uniqueness.
• Denaturation of proteins can be caused by pH changes, organic solvents, heat, and charge.
• Size-exclusion chromatography separates proteins based on their molecular weight, with smaller proteins eluting first.
• Disulfide bridges can form between two cysteine residues, linking multiple chains together.
• Hemoglobin is a tetramer, composed of four polypeptide chains.

Peptide Bond Formation

• During peptide bond formation, a hydroxyl group is lost from the carboxyl group of one amino acid, and a hydrogen atom is lost from the amino group of another amino acid.
• The resulting peptide bond is planar, rigid, and polar.

Amino Acids

• Alanine and phenylalanine can form dipeptides through a condensation reaction.
• Glutathione is a cellular tripeptide formed by glutamic acid, cysteine, and glycine.
• Oxytocin and vasopressin are synthesized in the hypothalamus and secreted from the posterior pituitary gland.

Insulin

• Insulin is a polypeptide hormone with two chains linked together by disulfide bridges.
• It promotes the uptake of glucose from the blood into tissues.
• Diabetes mellitus is a disease characterized by disturbed insulin secretion.

Protein Structure

• Primary structure refers to the sequence of amino acids in a polypeptide chain.
• Secondary structure is stabilized by hydrogen bonds and includes α-helices and β-pleated sheets.
• Tertiary structure is maintained by different interactions, including covalent, ionic, hydrogen bonds, and van der Waals interactions.
• Quaternary structure refers to the arrangement of multiple polypeptide chains in a protein.

Hemoglobin

• Hemoglobin has four O2 binding sites per molecule.
• It transports CO2 from tissues to lungs in the form of carbamate at the amino termini of chains.

Enzymes

• Heavy metal ions can bind to the -SH groups in the polypeptide chain, changing the conformation of the enzyme and altering the rate of the enzymatic reaction.
• Malonic acid is a competitive inhibitor of succinate dehydrogenase, increasing the Km but not affecting the Vmax.
• Enzymes can be saturated with substrate, and increasing the substrate concentration will not appreciably increase the reaction rate.
• Noncompetitive inhibition decreases the Vmax without affecting the Km.

Carbohydrates

• Glucose and fructose are isomers, differing in their structure.
• Sucrose, lactose, and maltose are the most abundant disaccharides, composed of glucose and fructose, glucose and galactose, and glucose and glucose, respectively.
• Glycogen is a branched polysaccharide stored in the liver and muscles, composed of glucose residues.
• Starch, cellulose, and glycogen are composed of glucose residues, but differ in their structure and function.

Nucleotides and Nucleic Acids

• Purine bases in nucleic acids include adenine and guanine.
• RNA does not contain thymine, but instead contains uracil.
• A nucleotide is composed of a base, sugar, and phosphate group.
• Peptide nucleic acids (PNAs) are not components of RNA.### Nucleic Acids
• A nucleoside consists of a base and a sugar.
• A nucleotide consists of a base, a sugar, and a phosphate.
• The sugar molecule in a nucleotide is a pentose.
• Nucleotides are the building blocks of nucleic acids.
• Adenine pairs with thymine with 2 hydrogen bonds, and guanine pairs with cytosine with 3 hydrogen bonds.
• The ratio A + G / T + C is constant for DNA.
• RNA does not have a double-stranded structure, and thymine is not present in RNA; instead, uracil is present.
• UMP is not present in DNA.

Lipids

• Linolenic acid is an essential fatty acid.
• Bile salts are polar derivatives of cholesterol.
• Fatty acids with a higher degree of saturation have a higher melting point.
• Lipids in tissues that are subjected to cooling are more unsaturated.
• Naturally occurring unsaturated long-chain fatty acids are nearly always in cis-configuration.
• Palmitic acid has 16 carbon atoms.
• Triacyl glycerol is a storage form of lipid.
• Cholesterol is a precursor for vitamin D, sex hormones, and bile salts.

Proteins

• Biuret reagent forms a purple-colored complex with compounds containing at least four peptide bonds.
• The Biuret method is based on the complexation of Cu2+ to functional groups in the protein's peptide bond.
• The intensity of the color is directly proportional to the amount of protein present in the sample.

Carbohydrates

• Dextrins are partial hydrolysis products of starch of intermediate size.
• The final product of starch enzyme hydrolysis is glucose.
• The final product of starch hydrolysis in the presence of hydrochloric acid is glucose.

Enzymes and Biotechnology

• EcorI is a restriction endonuclease.
• Electrophoresis helps to separate DNA segments.
• Polydeoxyribonucleotide synthase is not a restriction enzyme.

Fats and Oils

• The saponification number is the number of milligrams of KOH required to neutralize the free and combined fatty acid in one gram of a given fat.