bio 2
Carbohydrates and Macromolecules
Macromolecules covered: carbohydrates, proteins, nucleic acids, and lipids.
Carbohydrates have subcomponents called monosaccharides (e.g., glucose, galactose, fructose, ribose, ribulose, glyceraldehyde).
Rings: sugars with five or six carbons often exist as rings in solution. The ring formation occurs when the functional group (described as a carboxyl group in the transcript) participates in closing the loop; the oxygen becomes part of the ring.
Classification: monosaccharides are classified by the position of functional groups and by the number of carbons; many isomers share the same molecular formula but have different names.
In cells, five- and six-carbon sugars typically exist as rings.
Disaccharides: Sucrose is glucose + fructose. Sucrose is formed through a synthesis process; simply mixing glucose and fructose in water will not produce sucrose.
This synthesis is an uphill reaction with energy input required: \Delta G > 0.
Polysaccharides: polysaccharides have roles in storage and structure.
Storage: humans store glycogen; long chains of glucose that can be rapidly broken down to provide energy.
Plants: polysaccharides contribute to structural integrity (e.g., cellulose).
Cellulose is made of linear glucose polymers; fibers form through hydrogen bonding, creating lattice structures that support plant cell walls; cellulose is exported to form external cell walls.
Hydration: fully hydrated polysaccharides can occupy a lot of space in solution.
Proteins
Proteins are polymers of amino acids; 20 amino acids exist.
Each amino acid has three components: an amino group, a carboxyl group, and a side chain (R group).
Structure examples: space-filling representation (e.g., arginine depicted) shows a typical amino acid scaffold.
Side chains determine properties: some are nonpolar/hydrophobic, others polar/hydrophilic, and some are electrically charged.
Common examples of side chains include glycine, alanine, leucine, methionine, phenylalanine, tryptophan, and proline.
The sequence of amino acids constitutes the primary structure of a protein, with an amino (N) terminus and a carboxyl (C) terminus.
The N-terminus is the amino end and the C-terminus is the carboxyl end.
Amino acid properties influence folding and final structure. For example, combining many bulky or bulky aromatic residues (like tryptophan or phenylalanine) can guide a different fold than many small residues (like glycine).
The single-letter code for amino acids is commonly used in sequence notation; glycine is often represented as "G" and has a three-letter code "Gly". A historical anecdote about the one-letter code: tryptophan has the letter "W" due to a naming story.
Protein folding hierarchy:
Primary structure: the amino acid sequence (N-terminus to C-terminus).
Secondary structure: local folding patterns such as alpha helices and beta sheets (not always discussed in detail here).
Tertiary structure: three-dimensional folding of a single polypeptide chain; often involves subunits.
Quaternary structure: arrangement of multiple polypeptide subunits (e.g., hemoglobin).
Mutations and folding:
Substituting one amino acid can have little or no effect, or drastically alter function depending on impact on folding.
A single amino acid change can cause diseases (e.g., sickle cell anemia in hemoglobin).
Cystic fibrosis is often linked to single amino acid changes in a chloride transporter; folding and function are critical.
Protein design and disease treatment:
Advances in editing and therapy include CRISPR-based approaches to gene editing (e.g., potential editing of the hemoglobin gene).
Protein architecture and interactions:
Hydrophobic core vs. hydrophilic exterior: many proteins fold to bury nonpolar side chains inside and expose polar side chains outside.
Cysteine can form disulfide bonds (covalent cross-links) which stabilize structure.
Peptide bonds and polypeptides:
Amino acids link via peptide bonds formed in condensation reactions between the carboxyl group of one amino acid and the amino group of the next.
A polypeptide has an N-terminus (amino end) and a C-terminus (carboxyl end).
Proteins are dynamic in solution; they constantly form and break noncovalent interactions (hydrogen bonds, hydrophobic interactions, Van der Waals forces).
Structural examples and terminology:
Hemoglobin as a classic example of quaternary structure with two alpha and two beta subunits.
Sickle cell disease caused by a single amino acid change affecting folding and function of hemoglobin.
Protein functions include:
Enzymes: catalysts that lower activation energy and drive biological reactions; bring substrates into close proximity.
Antibodies: part of the immune system; engineered antibodies (monoclonal antibodies) serve as targeted therapies.
Hormones and signaling: insulin as a hormone/protein that regulates metabolism.
Transport and storage: membrane transport proteins (e.g., the sodium-potassium pump) move ions across membranes; various proteins store or transport molecules.
Structural roles: components of the extracellular matrix (e.g., collagen, keratin) and intracellular scaffolding.
Insulin and biotechnology:
Insulin was cloned into bacteria in the 1970s, leading to scalable production; earlier insulin was sourced from animals.
Biotechnological production reduces reliance on animal-derived insulin and enables more consistent supplies.
Production involves removing endotoxins when using bacterial expression systems.
Enzymes in digestion and metabolism:
Digestive enzymes in the liver and elsewhere catalyze the breakdown of biomolecules.
Saliva contains amylase, an enzyme that helps break down starches in bread.
Nucleic Acids and the Central Dogma
Two primary nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
DNA is extremely stable; RNA degrades easily in typical conditions.
RNase enzymes (ribonucleases) break down RNA and are abundant; exposure without proper protection can lead to rapid RNA degradation.
Central dogma (Crick): DNA encodes RNA, and RNA encodes proteins.
Most cases follow: DNA -> RNA -> protein.
Exceptions exist: some viruses (retroviruses) bypass or modify this flow.
Retroviruses (example: HIV):
HIV is an RNA virus; after infection, its RNA is reverse-transcribed into DNA, which is integrated into the host genome (a lentivirus behavior).
RNA roles and the genome:
DNA serves as the stable genetic library; RNA serves primarily as a messenger and translator to proteins.
There are RNAs with catalytic roles and RNAs involved in regulation beyond the central dogma's simple path (not all details covered here).
Antibodies and proteins:
Antibodies are proteins that recognize specific targets; modern biotechnology engineers antibodies for therapeutic purposes (e.g., in cancer therapy).
An antibody–antigen interaction can recruit macrophages to eliminate the target.
The active-binding portion of an antibody involves roughly about 20 amino acids in the binding region.
Antibodies can be grown in culture, purified, and used as drugs.
The Translation Machinery and mRNA Processing
Gene expression flow (high level): DNA is read by enzymes to produce messenger RNA (mRNA).
mRNA processing in the nucleus:
The 3' end of mRNA often gets a poly-A tail (polyadenylation) to increase stability; the tail length is around of adenine (A) nucleotides, which helps purification and stability.
The poly-A tail allows purification techniques using poly-T capture matrices.
mRNA export and translation:
Processed mRNA is exported to the endoplasmic reticulum (ER) or cytoplasm for translation.
Translation uses transfer RNAs (tRNAs) that carry specific amino acids and recognize mRNA codons via anticodons; the ribosome coordinates this process.
tRNA and codon decoding:
The genetic code consists of codons (three-nucleotide sequences) that specify amino acids.
Example: glycine is encoded by codons such as GGG; a corresponding tRNA would have anticodon CCC to pair with GGG.
Glycine has the one-letter code "G" and the three-letter code "Gly".
The ribosome:
The translation machinery is largely RNA-based (ribosome contains RNA and proteins).
Translation results in a polypeptide that folds into a functional protein.
Practical and Real-World Implications
Medical therapies and biotechnology:
Antibodies as targeted therapies provide powerful cancer treatments; examples include monoclonal antibodies engineered to bind specific targets.
Insulin modern production demonstrates how biotechnology transformed medicine from animal-derived to recombinant protein production.
CRISPR and related gene-editing technologies hold potential for correcting genetic diseases (e.g., targeting the hemoglobin gene in zygotes is mentioned as a hypothetical future direction).
Disease and genetic variation:
Single amino acid changes can lead to diseases such as sickle cell disease and various forms of cystic fibrosis, highlighting the critical link between sequence, structure, and function in proteins.
Historical context:
Stories surrounding codon discovery and amino acid coding reflect the intertwined nature of biology, history, and science.
Biological organization and design principles:
Proteins demonstrate a hierarchy of structure from primary to quaternary; folding is driven by an interplay of covalent (e.g., disulfide) and noncovalent interactions (hydrogen bonds, electrostatics, hydrophobic effects).
The concept of denaturation (e.g., cooking egg white) illustrates how structure and function can be disrupted by environmental changes.
Key Concepts to Review
Monosaccharide ring formation and isomerism; examples of common sugars.
Disaccharides and polysaccharides: energy storage vs structural roles in plants and animals; examples include glycogen and cellulose; understanding why some polysaccharides are not digestible.
Protein structure and function: primary to quaternary, importance of side chains, mutations, denaturation, and diverse roles (enzymes, antibodies, hormones, transport, structural components).
Amino acid properties and codon/anticodon relationships; the significance of the one-letter codes.
Enzyme function and catalysis; examples such as amylase in saliva.
Nucleic acids and the central dogma; exceptions through retroviruses like HIV; differences between DNA stability and RNA lability; the role of RNases.
Translation and mRNA processing: poly-A tail, transcription, tRNA charging, ribosome function, and the genetic code.
Contemporary therapeutic approaches: monoclonal antibodies, insulin production, and potential CRISPR-based therapies.
Real-world implications of molecular biology in medicine, industry, and ethics.
Quick Reference Formulas and Notation
Uphill reaction for sucrose formation: \Delta G > 0
Sodium-potassium pump transport direction (typical simplified representation):
Poly-A tail length in mRNA processing:
Glycine codon/anticodon example:
Protein structure hierarchy: primary → secondary → tertiary → quaternary
Protein basic reaction concept: enzymes reduce activation energy and bring substrates together to facilitate reactions.
Connections to Foundational Principles
Structure–function relationship: amino acid properties strongly influence protein folding and ultimately function.
Emergent properties: higher-level structures (secondary, tertiary, quaternary) govern complex activity beyond the sequence alone.
Evolutionary perspectives: structural motifs and fold stability reflect evolutionary pressures for function, stability, and interaction networks.
Interdisciplinary relevance: biotechnology, medicine, and pharmacology rely on understanding these macromolecules and their interactions.
Note on Context and Ethics
The content includes historical anecdotes and student-focused storytelling about scientists and discoveries.
There are discussions of genetic engineering (CRISPR) and antibody therapies, highlighting ethical, safety, and accessibility considerations in modern biotechnology.
Practical lab considerations are touched on (e.g., endotoxins in bacterial production of insulin), underscoring real-world laboratory constraints and quality control needs.