Biology Chapter 1: Cell Functions and Structures

Cellular and Molecular Biology MD105

• Course taught by Dr. C. Michaeloudes, European University Cyprus, School of Medicine
• Topics covered include cell structure and function, lecture objectives, what is a cell, the main functions of a cell, cells generating energy by breaking down nutrients, instructions for all cell functions stored in DNA, cells making identical copies, chemical composition of cells, chemical constituents of cells, water, hydrophilic molecules, hydrophobic molecules, ions, sugars, fatty acids, lipids, phospholipids and cholesterol, triglycerides, amino acids, proteins, structural proteins, functional proteins, nucleotides, and nucleic acids.

Lecture Objectives

• Understand what a cell is and its basic functions
• Know the main chemical components of cells
• Recognize the diversity of cell morphology and function
• Learn the key differences between prokaryotic and eukaryotic cells

What is a cell?

• Smallest unit capable of performing life functions
• Membrane-enclosed units filled with a concentrated aqueous solution containing numerous chemicals
• Capable of generating copies by growing and dividing in two
• Fundamental units of life in all living organisms

The Main Functions of a Cell

• Generate energy: Essential for all cell activities; animals obtain energy from food molecules, plants from sunlight
• Synthesize proteins: Proteins perform diverse roles in cells (e.g., structural components, enzymes, signaling molecules)
• Make more cells: Crucial for growth and repair.

Cells Generating Energy by Breaking Down Nutrients

• Cells break down nutrients (glucose/fatty acids) using oxygen to produce chemical energy in the form of ATP
• This process occurs in mitochondria

The Instructions for all Cell Functions are Stored in DNA

• The instructions for all cell functions are stored in the DNA
• Cells need to store their hereditary information (like computers store information on a hard drive or cloud)

Cells Making Identical Copies of Themselves

• Cells make copies of themselves that have exactly the same DNA.
• To do this, they duplicate their DNA and then divide in two.
• Daughter cells can further divide, producing more cells

Cells Can Accurately Duplicate Their DNA

• Cells create accurate copies of their DNA through DNA replication.
• During this process, the two strands of the DNA helix are pulled apart, used as templates to synthesize complementary strands.

The Chemical Composition of Cells

• Cells consist of six main components: water, ions, amino acids, sugars, fatty acids, and nucleotides.

Chemical Constituents of Cells

• Although cells vary in morphology and function, they use the same chemicals for chemical reactions.

Water

• Most cells (except fat cells) are 70-85% water; crucial for reactions
• Water molecules are polar due to uneven electron distribution.
• Water molecules are held together by hydrogen bonds.
• Polar and charged molecules dissolve in water via hydrogen bonds.
• Water is the solvent for most reactions in a cell.

Hydrophilic Molecules

• Hydrophilic molecules readily dissolve in water ("water-loving").
• Polar or charged molecules.
• Form hydrogen bonds with water. (Examples include hydroxyl groups, carbonyl groups, carboxyl groups, and amino groups)

Hydrophobic Molecules

• Hydrophobic molecules do not dissolve in water ("water-fearing").
• Non-polar/uncharged.
• Do not form hydrogen bonds with water. (Examples include hydrocarbon chains and ring structures)

Ions

• Ions are atoms with an electric charge (either negative (anion) or positive (cation)).
• Key inorganic chemicals (e.g., potassium, calcium) for chemical reactions.
• Essential for cellular control mechanisms and transmitting electrical signals in nerves and muscles.

Sugars

• Simplest forms are monosaccharides (e.g., glucose)
• Made of carbon, hydrogen, and oxygen (CH₂O)n , n = 3, 4, 5, or 6
• Monosaccharides can link via glycosidic bonds to form larger carbohydrates.
• Disaccharides (two monosaccharides); Polysaccharides (thousands of monosaccharides)
• Glucose is a vital energy source for cells; broken down into smaller molecules via metabolic reactions to release ATP energy; stored as glycogen for later energy use.

Fatty Acids

• Organic molecules containing a hydrocarbon chain (hydrophobic) and a carboxyl group (hydrophilic).
• Broken down in mitochondria to produce energy.
• Fatty acids link to other molecules to form complex lipid molecules, including triglycerides.

Lipids

• Complex molecules insoluble in water but soluble in non-polar solvents.
• Contain long hydrocarbon chains or multiple rings.
• Important lipids include phospholipids and cholesterol (2% of cell mass).
• Phospholipids form cell membranes and intracellular membranes around organelles; Triglycerides are the body’s main energy stores.

Phospholipids and Cholesterol

• Main components of cell membranes
• Phospholipids have a hydrophilic head and hydrophobic tails.
• Cholesterol is also a component of cell membranes.

Triglycerides

• Made of glycerol and three fatty acids.
• Act as energy stores for cells.

Amino Acids

• Small organic molecules with a carboxyl group (-COOH) and an amino group (-NH₂) attached to a central α-carbon.
• The α-carbon also carries a side chain that distinguishes one amino acid from another.

Proteins

• Polymers of amino acids linked by peptide bonds.
• Folded into complex 3D structures for specific functions.
• Structural proteins form the cytoskeleton and extra-cellular components.
• Functional proteins act as enzymes, speeding up chemical reactions within cells.

Structural Proteins

• Long chains of proteins that form filaments (e.g., actin, intermediate filaments, microtubules).
• Form the cytoskeleton, providing structural support and enabling cell movement.
• Present in connective tissues (e.g., tendons, ligaments).

Functional Proteins

• Primarily enzymes that catalyze diverse specific reactions within cells.
• Bind to specific molecules (ligands) to convert them into different products, without changing the enzyme.

Nucleotides

• Consist of a five-carbon sugar (ribose or deoxyribose), a nitrogen-containing base, and one or more phosphate groups.
• Five different bases: adenine, thymine, uracil, cytosine, guanine.
• Building blocks of nucleic acids (DNA and RNA).

Nucleic Acids

• Polymers of nucleotides linked via phosphodiester bonds.
• DNA (deoxyribose) and RNA (ribose)
• Store and retrieve biological information.

Adenosine Triphosphate (ATP)

• A molecule that carries energy within cells.
• Stored in high-energy phosphate bonds; breaking the bonds releases energy for cellular processes (e.g., muscle contraction, nerve firing).

Small Organic Molecules

• Building blocks of larger macromolecules.
• Examples include sugars, fatty acids, amino acids, and nucleotides, which can assemble to form larger molecules such as polysaccharides, lipids, proteins, and nucleic acids.

The Diversity of Cells

• The human body comprises 30 trillion cells, with over 200 cell types, distinct morphologies, and functions.
• Different cell types exhibit varying lifespan.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells (e.g., bacteria, archaea) lack a nucleus; DNA is in the nucleoid.
• Eukaryotic cells (e.g., animal cells, plant cells, fungi) possess a nucleus with linear DNA.
• Major differences in size, and the presence/absence of membrane-bound organelles.

Prokaryotic Cell Structure

• Small size (0.2-2 µm).
• No nucleus, DNA in nucleoid region.
• No membrane-bound organelles.
• Cell wall (protective coat).
• Plasma membrane.
• Circular DNA.
• Divide quickly (e.g., every 20 minutes).
• Live as individual cells or communities.
• Can utilize diverse energy sources

Bacteria

• Traditionally classified by shape (spherical, rod-shaped, spiral).
• Classified as Gram-positive or Gram-negative based on cell wall structure.
• Plays a crucial part of the human microbiome.

Eukaryotic Cell Structure

• Larger size (10-100 µm).
• Contain membrane-bound organelles.
• No cell wall (except in plants).
• DNA enclosed within a nucleus.
• Linear DNA - multiple strands.
• Multicellular organisms (e.g., animals, plants, fungi) are composed of diverse cell types.

Cell Sizes

• Different cells have varying sizes (e.g., viruses, bacteria, eukaryotic cells).
• Different microscopy techniques are used to visualize cells of varying sizes.

Human Cell Diversity

• 30 trillion cells in the human body with diverse morphology and functions.
• Different human cell types have variable life spans.

Test your knowledge on the fundamental concepts of cellular biology with this quiz covering the smallest units of life. Explore key functions, energy sources, and differences between prokaryotic and eukaryotic cells. Perfect for students studying cell biology or preparing for exams.