The structure of cells
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The Structure of Cells. What is a cell?? - The smallest functional unit of life. The Discovery of Cells. Robert Hooke, 1665, observed a slice of cork under a primitive microscope Anton van Leeuwenhoek observed living blood cells, bacteria, and tiny single-cell organisms in a drop of water.

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The Structure of Cells

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The structure of cells

The Structure of Cells

What is a cell??

- The smallest functional unit of life.

The discovery of cells

The Discovery of Cells

  • Robert Hooke, 1665, observed a slice of cork under a primitive microscope

  • Anton van Leeuwenhoek observed living blood cells, bacteria, and tiny single-cell organisms in a drop of water.

  • With the invention of the microscope, scientists were able to observe the cause of some of the world’s worst diseases.

  • Microscopy: the science of using microscopes to view samples or objects.



  • Compound Light/Brightfield Microscope: magnifies the image 2000x.

  • Transmission Electron Microscope: magnifies the image 1 000 000x. A beam of electrons is passed through the specimen. Denser portions of the specimen allow fewer electrons to pass through and appear darker in the image.

More microscopes

More microscopes…

  • Scanning Electron Microscope: magnifies the image 200 000x. The SEM sweeps a beam of electrons over a specimen’s surface, causing other electrons to be emitted from the specimen, producing realistic 3-D images.

How big is a cell?

If 1000 human body cells were lined up, they would be less than 2 cm long – about as wide as your thumb!

Observing cell structure

Observing Cell Structure

  • With the improvement of microscopes, Robert Brown (1820) was the first to discover the structures within cells organelles.

  • In the mid 1800s, the observations of more scientists led to the some important conclusions about the basis of life.

The cell theory

The Cell Theory

  • All living organisms are made of one or more cells.

  • The cell is the basic organizational unit of life.

  • All cells come from pre-existing cells.

Cells at work

Cells at Work

  • Cells must carry out essential tasks to sustain life:

    • Get food & energy

    • Create energy for the use of the cell

    • Maintenance

    • Chemical reactions

    • Get rid of wastes

    • Reproduce

Two basic types of cells

Two Basic Types of Cells

  • Prokaryotes and Eukaryotes

Prokaryotic cells

Prokaryotic Cells

  • Smallest cells

  • Simple organization, primitive cells

  • No membrane (pro = before, karyon= nucleus)

  • One-celled organisms: bacteria

  • Reproduce through binary fission: cells spit into two > exponential growth

Eukaryotic cells

Eukaryotic Cells

  • Larger more complex cells

  • Cells that make up complex organisms, multicellular

  • Have a nucleus (eu=true, karyon= nucleus)

  • Have many specialized organelles

  • Organelles work together to carry out cell processes

  • Protists, fungi, plants, animals

  • Reproduce by mitosis

Eukaryotic cell features

Eukaryotic Cell Features

  • Eukaryotic cells are very diverse

  • Organelles are bound by membranes

  • Chemical reactions occur in different organelles

The cell s main parts

The cell’s main parts

  • The functions/parts of a cell can be divided into several areas each of which have distinct functions.

  • The nucleus

  • Membrane

  • Membrane transport

  • Intracellular Compartments

  • Energy Conversion

  • The Cytoskeleton

The Evolution of Organelles

Cell contents

Cell Contents

  • Animal CellPlant Cell

Cell membrane

Cell Membrane

  • Cell covering that separates the inside of the cell from the external environment; controls the flow of materials into and out of the cell



  • Entire region between the nucleus and the membrane bounding the cell

    • Consists of a semifluid substance called the cytosol in which are suspended specialized organelles

Nucleus control centre

Nucleus: Control Centre

  • Stores genetic information (DNA) in strands called chromatin

  • Within the nucleus, there is nucleolus which is a special section of chromatin that produces the RNA that is a blueprint for making ribosomes.

  • Has a double membrane with pores that regulates the entry and exit of certain large macromolecules and particles.



  • Long uncoiled strands of DNA

  • During replication, chromatins get shorter and thicker to form chromosomes

  • Different organisms have different #s of chromosomes (human-46, mice-70)

The structure of cells


  • Each chromosome is made up of a long strand of chemical material called DNA = deoxyribonucleic acid.

  • Each strand of DNA can be divided into smaller segments called genes.

  • Each gene provides the cell with a different set of instructions for making different kinds of proteins.



  • Direct growth and development of every living thing by means of a chemical code.

  • Determine how the cell functions and what characteristics it has.

  • Made up of long chains of linked subunits called nucleotides.

  • Monomers of nucleic acids are nucleotides.



  • Sugar ( deoxyribose, ribose)

  • Phosphate Group

  • Nitrogen Base : Adenine Thymine

    Cystosine Guanine

The structure of cells


  • Deoxyribonucleic Acid

  • Main component of genes, the hereditary material in all cells.

  • Made up of Adenine, Guanine, Thymine, Cytosine.

  • Two nucleotide chains joins together into a double helix.



  • Made in the nucleus, composed of two subunits

  • Function: produce proteins/enzymes from the information passed on from DNA

  • Ribosomes attached to the endoplasmic reticulum

  • A human liver cell has a few million ribosomes

Endoplasmic reticulum

Endoplasmic reticulum

  • Endoplasmic=within the cytoplasm, reticulum=network

  • Folded membranes that provide a huge surface area for chemical reactions to occur

  • E.g. production of insulin

  • Rough ER: ribosomes attached

  • Smooth ER: no ribosomes, synthesizes phospholipids & steroids (testosterone in the testes), can pinch off to form vesicles to transport macromolecules, makes enzymes that detoxifies drugs and poisons

Golgi apparatus the warehouse

Golgi apparatus: The warehouse

  • Finishes, sorts, and ships cell products

  • Vesicles from SER fuse with the membrane of the Golgi apparatus

  • Completes the processing of macromolecules, packages them

  • Vesicles send molecules out of cell via exocytosis



  • Transforms energy stored in

    macromolecules into a form that can

    be used by the cell: ATP - adenosine triphosphate

  • Composed of two membranes

  • Outer membrane separates it from the cytoplasm

  • Inner membrane folds= cristae, a large surface area for the chemical reactions that produce energy in the form of ATP

  • Region inside the inner membrane = matrix



  • Break down wastes

  • Contain digestive enzymes that break down macromolecules

  • The by-products are used to make new macromolecules



  • Membrane-covered sacs that transport and/or store materials inside the cell and sometimes help these materials cross the cell membrane to enter or exit the cell



  • Gives shape to cell extending from the nucleus to the cell membrane

  • Made up of three components: actin filaments, intermediate filaments and microtubules



  • Assembles and co-ordinates the activity of spindle fibres during cell division

    • Composed of two centrioles

Cilia and flagella cell movement

Cilia and flagella: Cell movement

  • Cilia: short cylindrical projections that move in a wave-like motion

    • Can move food towards the cell

    • Ciia in lungs move particles out of your lungs

  • Flagella: long projections that move in a whip-like motion

Plant cells

Plant Cells

  • Cell wall: made up of cellulose fibres and adds strength and rigidity to the cell

  • Central vacuole: fills with fluid, presses outwards against the cell wall to add support

    • Stores water and other substances

  • Plastids: e.g. chloroplasts



  • Sacs enclosed within a double membrane and perform photosynthesis

  • Store starches, lipids and proteins

  • Chloroplasts are green because they contain chlorophyll

Comparing animal and plant cells

Comparing Animal and Plant Cells

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