L2 - Organisation and Complexity

Introduction to Human Biology

• The human body is a complex machine.

• The following lectures will focus on cells.

• Basic biological education is assumed; some topics may be covered quickly.

• Goal: Ensure everyone is on the same page.

Cells as Basic Units

• All organisms are made of cells.

• Cells are the basic units of development and life.

• All cells come from preexisting cells.

• The human body originates from a single fertilized egg containing all necessary genetic material.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells: Bacterial cells.

• Eukaryotic cells: Cells in animals, plants, and multicellular organisms.

• Key difference: Presence of a nucleus in eukaryotic cells.

• Nucleus: Contains and replicates DNA; the starting point for cell division.

Size Comparison

• Prokaryotic cells: ~1 micron diameter.

• Eukaryotic cells: 10-100 microns diameter (10 to 100 times larger than bacterial cells).

• Exceptions exist (cells smaller than 10 microns or larger than 100 microns).

Cytoskeleton and Organelles

• Cytoskeleton: Present in eukaryotic cells, supports cell structure.

• Prokaryotic cells lack a cytoskeleton, making them more flexible.

• Organelles: Present in eukaryotic cells, provide specific functions.

• Prokaryotic cells do not have organelles.

DNA Content

• Prokaryotic cells: 1,000,000 to 5,000,000 base pairs of DNA.

• Eukaryotic cells: 15,000,000 to 5,000,000,000 base pairs of DNA.

• Eukaryotic cells are more complex and have more genes.

Chromosomes

• Prokaryotic cells: Single, circular DNA molecule of ~1,000,000 base pairs.

• Eukaryotic cells: Series of linear molecules; human cells have 23 pairs (46 total).

Tissues

• Cells form tissues; complex arrangements of cells.

• Examples of tissues:

  • Epithelial tissue: Lines organs.

  • Connective tissue: Supports structures.

  • Muscle tissue: Forms muscles.

  • Nervous tissue: Central nervous system.

  • Adipose tissue: Fat stores.

• Each tissue consists of multiple cells with a single function.

Organs

• Tissues combine to form organs.

• Organs contain different combinations of tissues.

• Example: Stomach consists of epithelial lining, muscular layer, and nerves.

Organ Systems

• Organs are part of organ systems (e.g., digestive system).

• Digestive system organs: Esophagus, stomach, gallbladder, pancreas, small and large intestines, anus.

• Each organ has specialized cells performing specific functions.

Cell Functions

• Cells provide:

  • Chemicals to regulate processes.

  • Supporting structure.

  • Energy.

  • Scaffolding.

  • Propulsion systems (nerves controlling muscles).

  • Pumps, ventilation, plumbing (filtration).

  • Purification and protection (immune system).

  • Control systems (nervous system).

  • Capacity to create, construct, and repair damage.

• Cells interact to perform these roles.

Cell Numbers and Composition

• Human body: ~37,000,000,000,000 cells.

Cell Distribution by Mass and Number

• Red blood cells:

  • 70% of the number of cells.

  • 5.5% of the total mass (small size).

  • Need to be small to fit through narrow blood vessels.

• Muscle and fat:

  • Muscle: 44% of the total mass.

  • Fat: 28% of the mass.

  • 50 billion fat cells and 17 billion muscle cells.

  • Only 8.7% of cells contribute to nearly 70% of the mass (large, bulky cells).

• Skin cells: 5.5% of the total number of cells; skin is the largest organ (~2 trillion cells).

• Lymph and blood vessels: 6.8% of total; ~2,500,000,000,000 endothelial cells.

• Nervous system: 8.3% of the total cells; 100 billion neurons supported by 3 trillion glial cells.

  • Nervous system uses ~20% of the body's energy.

Body Fluids

• 40-45% of body mass is solid (skeleton, tendons).

• 55-60% of body mass is fluid.

• Two-thirds of fluid is intracellular.

• One-third of fluid is extracellular.

  • 20% of extracellular fluid is in the bloodstream.

• Fluid is essential; concentrations must be tightly controlled.

Importance of Controlled Concentrations

• Blood tests measure molecule concentrations.

• Examples:

  • Glucose: 87 mg/dL (range: 65-125 mg/dL).

  • Sodium ions: 140 mmol/L (range: 136-144 mmol/L).

  • Potassium: 4.6 mmol/L (range: 3.6-5.1 mmol/L).

• Deviations cause diseases (e.g., diabetes, renal disease, cardiovascular disease).

• Potassium over 7 mmol/L is fatal.

pH Regulation

• Arterial blood pH: ~7.4.

• Arterial plasma bicarbonate: ~24 mmol/L.

• Narrow range is critical; fluctuations cause acidosis or alkalosis.

• Intracellular pH is slightly lower (~7.2-7.3).

Surface Area to Volume Ratio

• Large surface area to volume ratio is necessary for efficient exchange.

• Example: Lung alveoli surface area ~ half a tennis court per lung (~200 square meters).

Achieving Large Surface Area

• Gut lining example: Finger-like structures (villi) increase surface area.

• Microvilli on individual cells further increase surface area.

• Similar adaptations in the kidney and respiratory system.

General Cell Features

• Each cell has the genetic information to grow and function.

• Many different cell types exist.

Examples of Cell Functions

• Cardiac myocyte: Contracts and relaxes.

• Breast cancer cells: Move and metastasize.

• Neuron growth cone: Finds connections.

Cell as a Factory

• Analogy to a factory helps understand cell structure.

• Plasma membrane: External surface.

• Cytoplasm: Fluid inside the cell with organelles.

Molecular Level

• Genome: Total DNA, double-stranded.

• Transcriptome: All RNA molecules transcribed from DNA.

• Proteome: All proteins made from RNA.

• Metabolome: Small molecules (amino acids, sugars, lipids) used in the body.

Genome Sequencing

• First human genome: 13 years, $5 billion (Craig Venter and Francis Collins).

• Now: A couple of weeks, ~$1,000.

DNA and Proteins

• DNA controls replication, growth, differentiation.

• ~20,000 genes in the human genome.

• Proteins carry out DNA instructions.

• 60,000-80,000 proteins.

• Alternative splicing generates different proteins from one gene.

Cell Components and Functions

• Nucleus: DNA storage.

  • Nucleolus: RNA transcription and ribosome biogenesis.

• Rough Endoplasmic Reticulum: Extension of nuclear membrane with ribosomes; protein synthesis.

• Smooth Endoplasmic Reticulum: Lipid and steroid hormone production.

• Heterochromatin: Protein and DNA mix.

• Golgi Complex: Sorting and dispatch of proteins and hormones; processes and traffics proteins to destinations.

• Mitochondria: Powerhouse, makes ATP, replicates by fission, contains its own DNA; maternal inheritance.

• Lysosomes: Waste disposal, low pH for digestion.

• Cytoskeleton: Structure and support, filaments and tubules.

Protein Transport

• Proteins are sorted by the Golgi complex and transported via filaments and tubules.