Module 1: Introduction to Cell Biology and The Cell Theory

What is a cell?

A cell is the fundamental/basic unit of life

• All organisms are made of either a single cell or a group of cells

Who made the first observation of cells?

Robert Hooke and Anton van Leeuwenhoek

Robert Hooke (1665)

• Described chambers of cork as “cells”

• Was looking at empty walls, the remains of dead cells

Anton van Leeuwenhoek (1673-1700)

• Early light microscopist → improved magnifying power of microscope lenses

• Saw “animalcules” in pond water 

How do we see cells?

Microscopes

What are the 3 microscopy’s?

1. Light

2. Electron

3. Fluorescence 

Who was the cell theory formulated by?

1. Schleiden → 1839, a German botanist 

2. Schwann → 1839, German zoologist

3. Virchow → 1855, German zoologist 

What did Schleiden (1839) claim? 

all plant tissues composed of cells; plant embryos arise from single cell

What did Schwann (1839) claim? 

same conclusions about animals; plants and animals are similar

What did Virchow (1855) claim? 

cells can arise only from pre-existing cells

What is the cell theory?

1. Cells are made up of one (unicellular) or more (multicelular) cells 

2. Each cell is the structural or functional unit of life

3. Cells can arise only from pre-existing cells

What are the exceptions to the cell theory?

1. Viruses

2. Viroids

3. Prions

Viruses

• Small amounts of nucleic acids with a protein coat

• Outside a living cell → inert

• Host cell is needed for viral reproduction

• Virus is an exception because it doesn’t have a nucleus, it has a capsid

Viroids

• Smallest infectious agents 

• Small circular RNA lacking protein coat

• Need host machinery to replicate 

Prions

• Abnormal infection of proteins

• Proteinaceous infectious particles 

• No nucliec acids

• Fatal 

What are the basic properties of cells?

1. Highly complex, organized and have physical barrier

2. Genetic program

3. Capable of producing themselves

4. Acquire and utilize energy

5. Carry out a variety of chemical reactions 

6. Engage in numerous mechanical activities

7. Able to respond to srimi

Basic Property of Cells: Highly complex, organized and have physical barrier

Cells are highly complex and organized but all are enclosed by a physical barrier called the cell membrane or plasma membrane

• Cytoplasm → all contents found inside the cell membrane; expect nucleus 

• Cytosol → jelly-like internal fluid environment of a cell (cytoplasm minus organelles)

  • Contains water, dissolved ions, and molecules 

Basic Property of Cells: Genetic Program

DNA and the Central Dogma

• The DNA is an information archive 

• Central dogma is the pathway from DNA to RNA to protein

Basic Property of Cells: Capable of producing more of themselves

Duplicate genetic material before division

Basic Property of Cells: Acquire & utilize energy

Acquire & utilize energy → bioenergetics

• e.g. light energy → chemical energy in plants

Basic Property of Cells: Carry out chemical reactions

Carry out a variety of chemical reactions

• E.g. metabolic pathways (cellular metabolism) such as glycolysis & citric acid cycle

• ATP currency: ATP is the chemical energy of the cell

Basic Property of Cells: Engage in mechanical activities

• Cells engange in numerous mechanical activities 

  • e.g. materical transported into/out of/through cell

  • e.g. move muscles (moving or contracting cells)

Basic Property of Cells: Able to respond to stimuli

• Receptors

• If you cut yourself, your cells respond to the wound and heal it

Basic Property of Cells: Capable of self-regulation

• Inability → uncontrolled growth

  • Tumours → cells that lost ability to control cell division

What are the classes of cells?

Prokaryotes and Eukaryotes

Prokaryotes

Prokaryotes translates to before Nucleus → Have no nucleus

• Most abundant organisms on Earth

• Includes organisms in the Domain Bacteria and Archea

  • E.g., TB, Salmonellaosis, Chlorea

Eukaryotes

Eukaryote translates to true nucleus

• Includes organisms in the Domain Eukarya 

  • Animals, plants, fungi

Information Flow: Nucleic Acids - Stores & Transfer Information

• Cells contain a stable blueprint of information in a molecular form as deoxyribonucleic acid → DNA

• The molecular structure and base-pairing of the DNA double-helix ensures fidelity during replication → make more copies of the DNA

Information Flow

• The central dogma → DNA to RNA to Protein

• A gene is the DNA code for the information necessary to produce a functional product 

  • Product is often a protein

• DNA is initially transcribed into a RNA message → change into a similar language of nucleic acids

• The RNA message can then be translated into a protein → change into a different language from nucleic acids to amino acids

What are Prokaryotes?

Prokaryotes are single cell organisms that do not have a nucleus or membrane bound organelles → simple organization

What are the 2 domains of prokaryotes?

Two prokaryotic domains → both have single circular chromosome 

1. Bacteria → many have plasmids, have cell wall surrounding cell membrane

   1. Plasmid: 5-carbon compound lipid, which can replicate independently of the chromosome

2. Archaea → isoprenoid cell membrane, often inhabit extreme environments

What are the features of prokaryotes?

Rely primarily on the cell wall and internal rigid protein framework for support 

What are Eukaryotes and what are the kingdoms within it?

Eukaryotes cells have a membrane bound nucleus

• The main difference is the genome is separated

• Kingdoms:

  • Protists

  • Fungi

  • Plants

  • Animals

  • Cells can get large single diffusion is no longer a factor  

Eukaryotes: What are Protists? 

• A diverse group → mostly single cells but some form colonies 

• Includes:

  • Algae

  • Water molds

  • Slime molds

  • Protozoa

  • Produce 30-50% of worlds O2 

Eukaryotes: What is Fungi? 

Fungi have cell walls made of chitin, which is a modified polysaccharide 

• Includes yeasts, rusts, smuts, mildews, molds, mushrooms 

• They are heterotrophs; they get energy and nutrients from other organisms

  • Dependent on the performed organic molecules for carbon and energy → absorb directly from the environment

Eukaryotes: What are Plants? 

Plants are multicellular and have cell walls made of polysaccharides 

• Have large water-filled vacuoles → contributes to turgor pressure

• Have intercellular connections → plasmodesmata

• Are autotrophs → produce their food

  • Chloroplasts convert the sun’s energy into chemical energy

Eukaryotes: What are Animals? 

They are multiceullar and don’t have cell walls

• Are heterotrophs → gain energy and carbon from preformed organic molecules

• Have a distinct mode of early development

How is a Eukaryote cell organized?

Cells have a membrane bound nucleus (a nucleus stores chromosomes)

• It is organized by

  • Internal protein scaffolding known as the cytoskeleton → can be remodelled quickly 

  • Dynamic membranes → endomembrane system 

Eukaryote Feature: Cytoskeleton

• Provides internal support for cells 

• All eukaryotic cells have 2 cytoskeletal elements

  • microfilaments and microtubles

• Animals have a third cytoskeletal element → intermediate filaments

Eukaryote Feature: Endomembrane System

A network of internal membranes

Includes:

• a nuclear envelope

• Endoplasmic Reticulum → ER 

Nuclear Envelope 

Defines boundary of the nucleus and contains an inner and outer membrane with nuclear pores

Endoplasmic Reticulum

A complex network of interconnected tubules and flattened sacs

• Involved in protein and lipid synthesis

  • Rough ER → have ribosomes for protein synthesis

  • Smooth ER → lacks ribosomes

Golgi Apparatus

Modifies proteins and lipids produced by the ER

• Sorts proteins and lipids to their destination 

• Adds carbohydrates to proteins and lipids

Mitochondria

Produces energy in form of ATP

Lysosomes

Membrane bound sacs containing digestive enzymes

Peroxisomes

oxidation of fatty acids and detoxification of certain toxic compounds (hydrogen peroxide)