Lecture 1 / - Molecular Biology

Cell Composition and Structure

• The lecturer is Dr. Michelle Kuzma
• Material adapted from Dr. Danuta Mielżyńska-Švach
• The study is about molecular biology 2024/2025
• Focuses on cell composition and structure

Areas of Cell Study

• Cytology
• Cytochemistry
• Cytopathology
• Cytophysiology
• Cytogenetics

The Cell

• Cells are the basic structural and functional units of all organisms.
• Cells are formed by the division of other cells (cell division).
• Cells contain genetic information passed to daughter cells during division.
• All cells are made of the same chemical compounds.
• All metabolic processes essential to life occur within cells.

Types of Cells

• Prokaryotic Cells:
  • Bacterial Cell Anatomy
  • Pilus
  • Capsule
  • Cell Wall
  • Plasma Membrane
  • Nucleoid (DNA)
  • Ribosomes
  • Plasmid
  • Flagella
• Eukaryotic Cells:
  • More complex structure
  • Microtubules
  • Centrosome
  • Pair of centrioles
  • Chromatin (DNA)
  • Nuclear pore
  • Nuclear envelope
  • Nucleolus
  • Extracellular matrix
  • Vesicles
  • Lysosomes
  • Peroxisomes
  • Ribosomes
  • Golgi apparatus
  • Intermediate filaments
  • Endoplasmic reticulum (smooth, rough)
  • Plasma membrane
  • Nucleus
  • Actin filaments
  • Mitochondria
  • Endoplasmic reticulum (smooth, rough)

Types of Cells (Classification)

• Bacteria
• Archaea
• Eukaryota (e.g., animals, plants, fungi, protists)
  • Subdivisions within these groups

Eukaryotic Organisms

• Single-celled: Protozoa, some algae, and some fungi.
• Multi-celled: Plants, fungi, and animals.

Prokaryotic Cell Components

• Cell surface:
  • Cell membrane
  • Cell wall (mucus)
  • Capsule (mucus)
  • Flagella, cilia
  • Pili, fimbriae
• Cell Interior:
  • Cytosol
  • Nucleoid (equivalent of cell nucleus)
  • Ribosomes
  • Plasmids

Eukaryotic Animal Cell

• Cytoplasm (cytoplasmic matrix)
• Cytoskeleton
• Nucleus
• Endoplasmic reticulum (smooth & rough)
• Mitochondria
• Golgi apparatus
• Lysosomes
• Peroxisomes

Cell Components

• All organisms are composed of inorganic and organic chemicals.
• Inorganic compounds primarily make up the non-living parts of nature.
• Organic compounds are mostly found in living organisms or their remains.

Inorganic Components

• Chemical elements
  • Macroelements (at least 0.01% of cell mass, e.g., 0.1 mg/1g)
  • Microelements (between 0.01 - 0.00001% of cell mass, e.g., 0.1 mg/1g to 0.1 µg/g)
  • Trace elements (µg/g range in cells, intake required is on the scale of mg/g)
  • Ultratrace elements (µg/g range, require µg/g of dietary intake)
• Water (~70%)

Chemical Elements

• Macroelements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P), Sulphur (S), Potassium (K), Sodium (Na), Magnesium (Mg)
• Microelements: Iron (Fe), Silicon (Si), Copper (Cu), Manganese (Mn), Fluorine (F), Iodine (I), Boron (B), Molybdenum (Mo), Zinc (Zn)
• Ultraelements: Radium (Ra), Silver (Ag), Gold (Au)

Water

• The main component (~70 - 80%) of living cells.
• Essential for body function.
• Solvent for many chemical compounds.
• Crucial environment for all reactions.
• Substrate and product of many chemical reactions.
• Biological functions depend on its structure & properties.

Water Molecule Structure

• One oxygen atom and two hydrogen atoms.
• Polar due to uneven charge distribution.
• Hydrogen bonds exist between oxygen and hydrogen.

Carbon Atom Structure

• Nucleus contains 6 protons, 6 neutrons.
• Two electron shells (K shell with 2, L shell with 4 electrons).
• Four valence electrons and four vacancies.

Carbon Atom Unique Role

• Forms strong covalent bonds with other carbon atoms to form:
  • Chains
  • Branched structures
  • Rings
• Basis of organic compounds

Organic Components

• Cells contain four major families of small organic molecules (containing carbon and hydrogen):
  • Saccharides
  • Fatty acids
  • Amino acids
  • Nucleotides
• These are usually found free in the cytosol.
• Subunits (monomers) form larger macromolecules (polymers).

Organic Component Hierarchy

• Small organic building blocks (sugars, fatty acids, amino acids, nucleotides).
• Larger organic molecules (polysaccharides, fats/membrane lipids, proteins, nucleic acids).

Carbohydrates

• Consist of carbon, hydrogen, and oxygen.
• Categorized by the number of sugar molecules:
  • Monosaccharides (glucose, fructose)
  • Disaccharides (sucrose, lactose, maltose)
  • Oligosaccharides (raffinose)
  • Polysaccharides (cellulose, starch).
• Solubility decreases with increasing carbon chain length.

Carbohydrate Function

• Energy storage/production: Glycogen in animals, starch in plants.
• Structure: Cellulose (plant cell walls), chitin (fungal cell walls), ribose & deoxyribose in DNA & RNA.
• Modifiers of proteins
• Transport: Glucose in animals & humans, sucrose in plants

Fatty Acids

• Usually contain an even number of carbon atoms (14 to 24).
• Carboxyl group (acid) connected to a hydrocarbon chain (fat).
• Shorter chains are more fluid.
• Saturated fatty acids have only single bonds.
• Unsaturated fatty acids have one or more double bonds.

Lipids

• Esters of fatty acids bonded to alcohols.
• Examples include glycerol, sphingosine, and higher monohydric alcohols.
• Insoluble in water due to low polarization.

Types of Lipids

• Simple lipids: Fats and oils (triglycerides), Waxes (esters with non-glycerol alcohols)
• Complex lipids:
  • Phosphoric acid - phospholipids
  • Carbohydrate - glycolipids

Lipid Functions

• Structural: Building blocks of biological membranes, like phospholipid bilayers.
• Energy storage: In animals (subcutaneous tissue, hibernators), and plants (seeds, fruits, roots).
• Signaling: Steroid hormones, vitamins A and D.
• Protection: Protects eyes, kidneys, and abdominal organs in animals, and plants from water loss. Also protects marine mammals from cold.

Cell Composition (Summary)

• Water (~70%)
• Organic molecules (~30%)
  • Proteins (~15%)
  • Polysaccharides (~2%)
  • Other organic molecules (~13%)

Cell Structure

• The internal environment of the cell is separated from the external environment by a cell membrane (plasma membrane), or sometimes an additional cell wall (e.g., in bacteria and plant cells).
• The internal environment is called the cytoplasm.
• Organelles (little organs) are membrane-bound.
• Non-membrane-bound organelles.

Cell Structure: Cell Membrane

• Surrounds all cells and organelles.
• Composed of lipids, proteins, and sugar.
• Functions:
  • Protection
  • Reaction to stimuli (chemical, thermal, mechanical)
  • Enzymatic catalysis (of metabolic reactions)
  • Transport regulation (substances in and out of the cell)
  • Maintaining osmotic pressure balance between inside and outside of the cell

Cell Structure: Cytoplasm

• Colloidal solution filling the cell and giving it shape.
• Environment for suspended organelles.
• Site of metabolic reactions
• Facilitates Movement of organelles and cell substance.
• Has states of semi-liquid and semi-solid.

Cell Structure: Cytoplasm cont.

• Movement of cytoplasm: Rotationally (around usually centrally located vacuole), circulating (between organelle), pulsating (in different directions), fountaining (around 2 vacuoles in opposite directions).

Cell Structure: Cytoskeleton

• System of filaments that allows cells to rearrange internal components during growth/division.
• Three families of protein filaments:
  • Intermediate filaments (8-10 nm diameter)
  • Microtubules (25 nm diameter)
  • Actin filaments (7 nm diameter)

Cell Structure: Cytoskeleton (cont.)

• Intermediate filaments: Provide resistance to mechanical damage, help maintain cell shape, build the nuclear lamina.
• Microtubules: Build centrioles and mitotic spindle, responsible for transport, form cilia and flagella. (in non-dividing cells, group into centrosomes).
• Actin filaments: Provide mechanical support for organelles, involved in cytoplasm movement, allow cell creeping and shape change, participate in muscle contraction.

Cell Organelles (Eukaryotic Animal)

• Mitochondrion
• Peroxisome
• Nuclear envelope
• Golgi apparatus
• Transport vesicle
• Cytosol
• Endoplasmic reticulum
• Plasma membrane

Cellular Components: Organelles

• Double Membrane-Bound Organelles:
  • Nucleus (contains genetic information)
  • Mitochondria (site of cellular respiration)
  • Chloroplasts (a group of organelles in plant cells)
• Single Membrane-Bound Organelles:
  • Golgi apparatus (modifies proteins, secretes substances)
  • Lysosomes (contain digestive enzymes)
  • Peroxisomes (vesicles for breaking down compounds)
  • Endoplasmic reticulum (network of channels & cisternae)
  • Vacuoles (sequester waste products)

Cellular Components: Non-Membrane Bound Organelles

• Cell wall (outer covering of some non-animal cells)
• Cytoskeleton (provides cell structure)
• Ribosomes (location of protein synthesis)
• Centrosome/microtubule organizing center (contain centrioles)
• Centriole (cylindrical organelle required in spindle fiber creation)

Nucleus

• Abundance: Monokaryocytes, bikaryocytes, polykaryocytes (not erythrocytes or stratum corneum).
• Size/shape: Varies based on cell type, age, and function (spherical, ellipsoidal, or fragmented).
• Volume: ~10% of mammalian cell volume.
• Position: Typically in the center but can vary slightly.

Nucleus: States

• Interphase (between cell divisions, preparing for division).
• Mitotic (during cell division).
• Metabolic (resting state, Go phase, directs metabolic & maintenance processes).

Nucleus structure during Interphase

• Nuclear envelope (membrane).
• Nuclear matrix (nucleoplasm).
• Nucleolus
• Chromatin (Condensed/ heterochromatin, Dispersed/euchromatin.)

Nucleolus

• Usually one nucleolus, no membrane.
• Contains fragments of 5 chromosomes (NORs).
• Site of rRNA synthesis and ribosome formation.

Nucleus: Functions

• DNA synthesis (replication before cell division).
• RNA synthesis (transcription).
• Ribosome formation (structure responsible for protein synthesis.

The Endoplasmic Reticulum

• System of single-layer membranes forming cisternae, channels, and vesicles.
• Functions:
  • Increases internal surface area of the cell.
  • Divides cytoplasm into compartments.
  • Regulates transport of organelles, substrates, and products.

The Endoplasmic Reticulum (types)

• Smooth ER: Lacks ribosomes, involved in lipid & steroid synthesis and removal of toxins.
• Rough ER: Contains ribosomes for protein synthesis, modification, and quality control. Connects to outer nuclear membrane and other cell membranes.

Ribosomes

• Made of rRNA and proteins.
• Two main types in eukaryotes:
• Free Ribosomes: produce proteins functioning in the cytosol.
• Bound Ribosomes: (attached to rough ER) produce proteins for export or modification.
• Ribosomes in mitochondria and chloroplasts are smaller, like prokaryotic ribosomes.

Ribosomes (cont.)

• Two subunits (small and large).
• Prokaryotic ribosomes (70s)
• Eukaryotic ribosomes (80s).

Mitochondria

• Number varies based on organism, cell type, and energy demands.
• Size varies (2-8 µm).
• Shape can change quickly (filamentous, granular, branched).
• New mitochondria form via division of existing ones.
• Number of Mitochondria in Various Cells:
  • Epidermal cells: 2 - 6
  • Sperm cells: 20 - 50
  • Liver cells: 1,000 - 2,500
  • Skeletal muscle cells: up to 1,600
  • Skin cells: ~2,000
  • Nerve cells: 10,000
  • Ova: >100,000
• (Existing information is maintained below.)*

Mitochondrial Structure

• Two-layered membrane (outer membrane is smooth and allows many substances to pass through via passive transport, inner membrane allows selected compounds through).
• Intermembrane space between the two membranes.
• Inner membrane has folds called cristae.

Mitochondrial Structure (cont.)

• Mitochondria contain:
  • mtDNA (double-stranded circular mitochondrial DNA)
  • Ribosomes (70s)
  • Enzymes for ATP production.
  • Nucleoids (mtDNA packing complexes)

notes + quiz