Cellular & Molecular Biology MD105

Cellular & Molecular Biology MD105

• Course taught by Dr. Michaeloudes
• Offered by the European University Cyprus School of Medicine

Lecture Objectives

• Understanding cells and their functions
• The major chemical components within cells
• The diverse morphologies and functions of cells
• Differentiating prokaryotic and eukaryotic cells

What is a cell?

• Smallest unit capable of performing life functions
• Membrane-enclosed, filled with concentrated, aqueous solution of chemicals
• Capable of self-replication via growth and division

Cells are the fundamental units of life

• Living organisms (sea urchin, mouse, seaweed) are diverse
• All living things are created from cells

The main functions of a cell

• Generating energy (all cellular activities)
  • Animal cells: energy from food (chemical bonds)
  • Plant cells: energy from sunlight
• Synthesizing proteins (all cellular functions)
  • Cell structure, enzymes, signaling molecules, receptors
• Making more cells (growth and repair)

Cells generate energy by breaking down nutrients

• Cells break down nutrients (glucose/fatty acids) with oxygen to produce energy
• This occurs in mitochondria yielding adenosine triphosphate (ATP)

The instructions for all the cell's functions are stored in the DNA

• DNA stores hereditary information like computers on a hard drive/cloud
• DNA is a long polymer chain made of nucleotides
• Nucleotides contain 4 different nitrogenous bases (adenine, guanine, thymine, cytosine)

The DNA code provides the instructions for making proteins

• DNA sequence guides mRNA synthesis (Transcription)
• mRNA sequence guides protein synthesis (Translation)

Cells make identical copies of themselves

• Cells duplicate DNA and divide into two identical daughter cells
• Used for growth and damage repair

Cells can accurately duplicate DNA

• The two DNA strands are pulled apart as templates for creation of matching strands

The chemical composition of cells

• Cells are composed of water, ions, amino acids, sugars, fatty acids, and nucleotides

Water

• Most cells contain much water (70-85%)
• Water molecules are polar with an uneven distribution of electrons
• Held together by hydrogen bonds
• Water dissolves polar molecules (hydrophilic)

Hydrophilic molecules

• Dissolve easily in water (water-loving)
• Polar or charged molecules that form hydrogen bonds with water
• Examples include: hydroxyl, carbonyl, carboxyl, and amino groups

Hydrophobic molecules

• Don't dissolve in water (water-fearing)
• Non-polar/uncharged molecules
• Examples: hydrocarbon chains, ring structures

Ions

• Atoms with an electrical charge (anions/cations)
• Examples include: calcium, sodium, magnesium, and phosphate
• Necessary for cellular reactions and processes (e.g., nerve impulses)

Sugars

• Simplest forms are monosaccharides (CH2O)n (n=3, 4, 5, or 6)
• Monosaccharides can link via glycosidic bonds to form larger carbohydrates (e.g. disaccharides & polysaccharides)
• Glucose : important energy source that's broken down to release energy
• Glucose is stored in cells as glycogen (energy storage)

Fatty acids

• Organic molecules with a hydrocarbon chain and a carboxyl group
• Hydrophobic hydrocarbon chain and hydrophilic carboxyl group
• Broken down in mitochondria to produce energy
• Linked to form complex lipid molecules (e.g. triglycerides)

Lipids

• Insoluble in water but soluble in non-polar organic solvents
• Important lipid types are phospholipids and cholesterol (form cell membranes) and triglycerides (energy store)

Phospholipids and cholesterol

• Major components of cellular membranes

Triglycerides

• Made of glycerol and three fatty acids
• Major energy storage form

Amino acids

• Small organic molecules with a carboxyl group & an amino group
• The a-carbon bears distinctive side chains
• Essential for protein synthesis

Proteins

• Polymers of amino acids linked by peptide bonds
• Form polypeptide chains, folded into complex 3D structures for various functions (structural/functional proteins)

Structural proteins

• Form filaments (e.g., actin, intermediate, microtubules)
• Create cytoskeletons for cell structure and movement
• Found in connective tissues (tendons, ligaments)

Functional proteins

• Mostly enzymes, functioning as catalysts for specific reactions
• Accelerate the rate of chemical reactions
• Do not undergo permanent change during reactions

Nucleotides

• 5-carbon sugar linked to a nitrogen-containing base & one or more phosphate group
• The sugars are either ribose or deoxyribose
• Bases include: adenine, thymine, uracil, cytosine, guanine
• Building blocks of nucleic acids

Nucleotides are building blocks of nucleic acids

• Nucleic acids (e.g., DNA and RNA) are linked by phosphodiester bonds
• Involved in storage and retrieval of biological information

Adenosine triphosphate (ATP)

• Molecule that carries energy needed for cellular processes (e.g., muscle contraction, nerve impulses)
• Stores energy in high-energy phosphate bonds
• Release of energy from ATP involves cleavage of phosphate bonds

Small organic molecules

• Are building blocks of macromolecules (sugars, fatty acids, amino acids, nucleotides)

The diversity of cells

• Many cell types in the human body (~200 types)
• Different morphologies and functions
• Different lifespans (e.g., white blood cells ~13 days, red blood cells ~120 days, neurons throughout lifespan)

Prokaryotic and eukaryotic cells

• Prokaryotic cells (e.g., bacteria and archaea) lack a nucleus.
• Eukaryotic cells (e.g., animal and plant cells) possess a nucleus.
• Key difference: presence of a nucleus in eukaryotic cells.

Prokaryotic cell structure

• Small size (0.2-2 µm)
• Lack membrane-enclosed organelles
• Have cell walls
• Have circular DNA located in nucleoid

Prokaryotic cells

• Diverse habitats (Human body ,Ocean floor, volcanic muds)
• Survive using organic (sugars, amino, hydrocarbons, methane) and inorganic (CO2, Fe2+) sources, and light
• Bacteria/Archaea

Bacteria

• Traditionally classified by shape (spherical, rod, spiral)
• Gram-positive/Gram-negative
• Exist for ~3.5 billion years
• Some cause disease, others are beneficial
• ~10¹⁴ microbes in the human body

Eukaryotic cell structure

• Larger size (10-100 µm)
• Contain membrane-enclosed organelles
• No cell wall (only membrane)
• DNA enclosed in the nucleus
• Linear DNA with multiple strands
• Animal cells, plant cells, fungi