General Biology Study Notes: Biomolecules, Cell Structure, and Organelles

Biomolecules and Macromolecules

Proteins

Proteins are essential macromolecules composed of amino acids, performing a wide variety of functions in living organisms, including catalysis, structure, transport, and regulation.

• Amino Acids: The building blocks of proteins, each containing an amino group, carboxyl group, hydrogen atom, and a unique side chain (R group) attached to a central carbon.

• Peptide Bonds: Covalent bonds formed between the carboxyl group of one amino acid and the amino group of another, releasing water (dehydration synthesis).

• Protein Structure:

  • Primary Structure: Linear sequence of amino acids.

  • Secondary Structure: Local folding into alpha helices and beta sheets, stabilized by hydrogen bonds.

  • Tertiary Structure: Overall 3D shape of a polypeptide, determined by interactions among side chains (hydrophobic interactions, ionic bonds, disulfide bridges).

  • Quaternary Structure: Association of multiple polypeptide chains.

• Functions: Enzymes, structural support, transport, signaling, immune response.

• Example: Hemoglobin is a protein that transports oxygen in the blood.

Nucleic Acids

Nucleic acids are polymers that store and transmit genetic information. The two main types are DNA and RNA.

• Nucleotide: The monomer of nucleic acids, consisting of a phosphate group, a five-carbon sugar (deoxyribose or ribose), and a nitrogenous base.

• DNA (Deoxyribonucleic Acid): Double-stranded helix, stores genetic information.

• RNA (Ribonucleic Acid): Single-stranded, involved in protein synthesis and gene regulation.

• Base Pairing: In DNA, adenine pairs with thymine, and cytosine pairs with guanine.

• Example: mRNA carries genetic instructions from DNA to ribosomes for protein synthesis.

Lipids

Lipids are hydrophobic molecules important for energy storage, membrane structure, and signaling.

• Types: Fats (triglycerides), phospholipids, steroids.

• Phospholipids: Major component of cell membranes, consisting of a hydrophilic head and hydrophobic tails.

• Example: Cholesterol is a steroid that stabilizes cell membranes.

Carbohydrates

Carbohydrates are energy-rich molecules composed of monosaccharides, disaccharides, and polysaccharides.

• Monosaccharides: Simple sugars (e.g., glucose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose).

• Functions: Energy storage, structural support.

• Example: Cellulose provides structural support in plant cell walls.

Cell Structure and Function

Microscopy

Microscopy is essential for studying cell structure and function.

• Light Microscopes: Use visible light to observe living cells.

• Electron Microscopes: Use electron beams for higher resolution; includes transmission (TEM) and scanning (SEM) types.

• Staining: Used to enhance contrast in cell samples.

Cell Types

Cells are classified as prokaryotic or eukaryotic based on their structure.

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles; include bacteria and archaea.

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles; include plants, animals, fungi, and protists.

Cell Membrane

The cell membrane is a selectively permeable barrier that regulates the movement of substances in and out of the cell.

• Structure: Phospholipid bilayer with embedded proteins.

• Functions: Protection, communication, transport.

• Fluid Mosaic Model: Describes the dynamic arrangement of lipids and proteins.

Cell Organelles

Nucleus

The nucleus is the control center of the cell, containing genetic material.

• Structure: Surrounded by a double membrane (nuclear envelope) with pores.

• Function: Stores DNA, coordinates cell activities (growth, metabolism, reproduction).

Endoplasmic Reticulum (ER)

The ER is a network of membranes involved in protein and lipid synthesis.

• Rough ER: Studded with ribosomes; synthesizes proteins.

• Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies chemicals.

Golgi Apparatus

The Golgi apparatus modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Structure: Stacks of flattened membranous sacs.

• Function: Processing and transport of macromolecules.

Lysosomes

Lysosomes are membrane-bound organelles containing digestive enzymes.

• Function: Breakdown of waste materials and cellular debris.

• Example: White blood cells use lysosomes to digest bacteria.

Vacuoles

Vacuoles are storage organelles found in plant and some animal cells.

• Function: Store nutrients, waste products, and help maintain turgor pressure in plant cells.

Mitochondria

Mitochondria are the powerhouses of the cell, generating ATP through cellular respiration.

• Structure: Double membrane, inner membrane folded into cristae.

• Function: Energy production via aerobic respiration.

• Equation: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

Chloroplasts

Chloroplasts are organelles found in plant cells responsible for photosynthesis.

• Structure: Double membrane, contains thylakoids and stroma.

• Function: Convert light energy into chemical energy (glucose).

• Equation: $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

Cytoskeleton

The cytoskeleton provides structural support, shape, and facilitates movement within the cell.

• Components: Microfilaments (actin), intermediate filaments, microtubules.

• Functions: Cell shape, movement, division, transport of organelles.

Summary Table: Major Cell Organelles and Their Functions

Organelle	Structure	Function
Nucleus	Double membrane, nuclear pores	Stores DNA, controls cell activities
Rough ER	Membranous network with ribosomes	Protein synthesis
Smooth ER	Membranous network without ribosomes	Lipid synthesis, detoxification
Golgi Apparatus	Stacked membranous sacs	Modification and transport of proteins/lipids
Lysosome	Membrane-bound vesicle	Digestion of macromolecules
Vacuole	Large membrane-bound sac	Storage, turgor pressure
Mitochondria	Double membrane, cristae	ATP production
Chloroplast	Double membrane, thylakoids	Photosynthesis
Cytoskeleton	Protein filaments	Support, movement

Additional info:

• Some details about protein folding, cell fractionation, and microscopy techniques were inferred for completeness.

• Equations for cellular respiration and photosynthesis were added for academic context.