General Biology: Macromolecules, Cells, and Cell Structures Study Guide

Macromolecules: Carbohydrates, Lipids, Proteins, and Nucleic Acids

Carbohydrates

Carbohydrates are essential biomolecules that serve as energy sources and structural components in living organisms.

• Biological Roles: Provide energy (glucose), serve as structural materials (cellulose in plants, chitin in fungi and arthropods), and are involved in cell recognition and signaling.

• Composition: Mainly composed of carbon (C), hydrogen (H), and oxygen (O) atoms, typically in a 1:2:1 ratio.

• Monomers: The building blocks are monosaccharides (simple sugars), such as glucose, fructose, and galactose.

• Classification by Carbon Number:

  • 2 carbons: Diose

  • 3 carbons: Triose

  • 4 carbons: Tetrose

  • 5 carbons: Pentose

  • 6 carbons: Hexose

• Examples of Simple Sugars: Glucose, fructose, galactose, ribose, deoxyribose.

• Oligosaccharides: A few monosaccharides linked together (2-10 units).

• Polysaccharides: Many monosaccharides linked together (hundreds to thousands). Examples: starch (plants), glycogen (animals), cellulose (plants), chitin (fungi and arthropods), peptidoglycan (bacteria).

• Digestibility: Humans cannot digest cellulose due to lack of the enzyme cellulase.

• Recognition in Chemical Structure: Carbohydrates often have multiple hydroxyl (-OH) groups and a carbonyl group (C=O) as either an aldehyde or ketone.

Table: Major Polysaccharides and Their Functions

Name	Location	Function
Glycogen	Animals (liver, muscle)	Short-term energy storage
Starch	Plants	Energy storage
Cellulose	Plant cell walls	Structural support
Chitin	Fungi, arthropods	Structural support
Peptidoglycan	Bacteria	Cell wall structure

Lipids

Lipids are hydrophobic molecules that play roles in energy storage, membrane structure, and signaling.

• Types: Triglycerides (fats/oils), phospholipids, steroids, waxes.

• Elements: Mainly carbon (C), hydrogen (H), and oxygen (O); some contain phosphorus (P) (e.g., phospholipids).

• Monomers: Triglycerides are composed of glycerol and three fatty acids; phospholipids have glycerol, two fatty acids, and a phosphate group.

• Fatty Acids:

  • Saturated: No double bonds; solid at room temperature; found in animal fats (e.g., butter).

  • Unsaturated: One or more double bonds; liquid at room temperature; found in plant oils (e.g., olive oil).

• Simple Fat: Triglyceride (glycerol + 3 fatty acids).

• Bond Linking Fats: Ester bond (formed by dehydration synthesis between glycerol and fatty acids).

• Biological Role: Energy storage, insulation, protection of organs.

• Phospholipids: Amphipathic molecules (hydrophilic head, hydrophobic tails); form bilayers in cell membranes.

• Phospholipid Structure: Glycerol backbone, two fatty acids, phosphate group, and a variable group (e.g., choline).

• Steroids: Four fused carbon rings; examples include cholesterol, testosterone, estrogen.

Proteins

Proteins are polymers of amino acids that perform a vast array of functions in living organisms.

• Biological Roles: Enzymes, structural support, transport, signaling, immune response, movement.

• Monomers: Amino acids (20 standard types in humans).

• Amino Acid Structure: Central carbon (α-carbon), amino group (-NH2), carboxyl group (-COOH), hydrogen atom, and variable R group (side chain).

• Groups of Amino Acids: Nonpolar (hydrophobic), polar (hydrophilic), charged (acidic/basic).

• Oligopeptide: Short chain of amino acids (2-20 residues).

• Protein Structure:

  • Primary: Sequence of amino acids; peptide bonds; linear shape.

  • Secondary: Local folding (α-helix, β-pleated sheet); hydrogen bonds.

  • Tertiary: 3D folding; interactions among R groups; disulfide, ionic, hydrogen, hydrophobic bonds.

  • Quaternary: Multiple polypeptide chains; same interactions as tertiary.

• Denaturation: Loss of structure due to pH, temperature, or chemicals.

Nucleic Acids

Nucleic acids store and transmit genetic information in all living organisms.

• Types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

• Biological Roles: DNA stores genetic information; RNA is involved in protein synthesis and gene regulation.

• Monomers: Nucleotides (composed of a phosphate group, a five-carbon sugar, and a nitrogenous base).

• Sugars: DNA contains deoxyribose; RNA contains ribose.

• Differences between DNA and RNA: DNA is double-stranded, contains thymine, is more stable, and stores genetic information; RNA is single-stranded, contains uracil, is less stable, and functions in protein synthesis.

• Complementary Base Pairing: Adenine pairs with thymine (A-T) in DNA or uracil (A-U) in RNA; cytosine pairs with guanine (C-G).

• DNA Replication: Semi-conservative process where each new DNA molecule has one old and one new strand.

• Transcription: Synthesis of RNA from a DNA template.

• Translation: Synthesis of proteins from mRNA template at the ribosome.

Table: Key Nucleic Acid Terms

Term	Definition
Nucleotide	Monomer of nucleic acids
Oligonucleotide	Short chain of nucleotides
Polynucleotide	Long chain of nucleotides
Genome	Complete set of genetic material
Gene	Segment of DNA coding for a protein

Cells & Microscopes

Cell Theory

The cell theory is a fundamental concept in biology describing the properties of cells.

• All living things are composed of one or more cells.

• The cell is the basic unit of structure and function in living organisms.

• All cells arise from pre-existing cells.

Microscopy

• Light Microscopes: Use visible light to magnify specimens; types include brightfield, phase-contrast, fluorescence, and confocal.

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

Cell Structures & Functions

Cell Membrane

The cell membrane, also called the plasma membrane, regulates the movement of substances in and out of the cell and provides structural support.

• Functions: Selective permeability, communication, protection, and compartmentalization.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotes: No nucleus, no membrane-bound organelles, smaller size (e.g., bacteria, archaea).

• Eukaryotes: Nucleus, membrane-bound organelles, larger size (e.g., plants, animals, fungi, protists).

Endosymbiosis Theory

This theory proposes that certain organelles (mitochondria and chloroplasts) originated as free-living bacteria that were engulfed by ancestral eukaryotic cells.

• Evidence: Double membranes, own DNA, ribosomes similar to bacteria.

Animal vs. Plant Cells

• Animal Cells: No cell wall, small or no vacuole, no chloroplasts, centrioles present.

• Plant Cells: Cell wall, large central vacuole, chloroplasts, no centrioles.

Prokaryotic Cell Structures Table

Structure/organelle	Function(s)	Structure	Notes
Capsule	Protection, adherence	Polysaccharide layer	Virulence factor
Cell wall	Shape, protection	Peptidoglycan	Absent in animal cells
Cell membrane	Selective barrier	Phospholipid bilayer	Also called plasma membrane
Cytoplasm	Site of metabolism	Gel-like fluid	Contains ribosomes, DNA
Ribosome	Protein synthesis	RNA and protein	70S in prokaryotes
Nucleoid	DNA location	Region with circular DNA	No membrane
Plasmid	Extra DNA	Small, circular	Antibiotic resistance
Flagellum	Movement	Protein filament	Rotary motion
Fimbriae	Attachment	Short protein filaments	Not for movement
Pili	DNA transfer	Longer protein filaments	Conjugation
Cytoskeleton	Shape, support	Protein filaments	Less complex than eukaryotes

Eukaryotic Cell Structures Table

Structure/organelle	Function(s)	Structure	Notes
Nucleus	Genetic control	Double membrane	Contains DNA
Nucleolus	Ribosome synthesis	Dense region	Inside nucleus
Nuclear membrane	Encloses nucleus	Double lipid bilayer	Has pores
Nuclear pore	Transport	Protein complex	Regulates entry/exit
Chromatin	DNA + protein	Fibrous	Condenses to chromosomes
Endomembrane system	Transport, synthesis	Membranous organelles	Includes ER, Golgi, vesicles
Endoplasmic reticulum (rough)	Protein synthesis	Membrane with ribosomes	Continuous with nuclear envelope
Endoplasmic reticulum (smooth)	Lipid synthesis	Membrane without ribosomes	Detoxification
Golgi apparatus	Modification, sorting	Stacked membranes	Cis, medial, trans regions
Lysosome	Digestion	Membrane vesicle	Contains enzymes
Phagosome	Engulfs particles	Vesicle	Fuses with lysosome
Mitochondrion	ATP production	Double membrane	Cristae, matrix
Chloroplast	Photosynthesis	Double membrane	Thylakoid, stroma
Peroxisome	Breaks down peroxide	Membrane vesicle	Detoxification
Vacuole	Storage	Large vesicle	Prominent in plants
Cytoskeleton	Shape, movement	Microfilaments, microtubules, intermediate filaments	Dynamic
Centrosome	Microtubule organizing	Contains centrioles	Animal cells
Cell wall (plants)	Support	Cellulose	Not in animals
Cell wall (fungus)	Support	Chitin	Not in animals
Flagellum	Movement	Microtubules (9+2)	Eukaryotic structure
Cilium	Movement	Microtubules (9+2)	Shorter than flagella

Cytoskeleton & Cell Junctions

Cytoskeleton

• Types of Filaments: Microfilaments (actin), intermediate filaments, microtubules (tubulin).

• Functions: Cell shape, movement, division, intracellular transport.

• Flagella/Cilia: Movement; internal structure is a 9+2 arrangement of microtubules in eukaryotes.

Cell Junctions

• Animal Cells: Tight junctions (seal cells), desmosomes (anchor cells), gap junctions (communication).

• Plant Cells: Plasmodesmata (channels for communication).

Key Terms

• Actin: Protein forming microfilaments.

• Myosin: Motor protein interacting with actin.

• Tubulin: Protein forming microtubules.

• 9+2: Arrangement of microtubules in cilia/flagella.

• Dynein: Motor protein in cilia/flagella.

• Nexin: Protein linking microtubules in cilia/flagella.

• Motor proteins: Proteins that move along cytoskeletal filaments.

• Centrioles: Organize microtubules in animal cells.

• Collagen: Structural protein in extracellular matrix.

• Proteoglycan: Protein-polysaccharide complex in extracellular matrix.

• Fibronectin: Glycoprotein in extracellular matrix.

• Integrin: Transmembrane receptor connecting extracellular matrix to cytoskeleton.

Additional info: Some explanations and table entries were expanded for clarity and completeness based on standard General Biology content.