The Structure of Cells

1. The Structure of Cells What is a cell?? - The smallest functional unit of life.

2. 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.

3. Microscopes • 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.

4. 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!

5. 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.

6. 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.

7. 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

8. Two Basic Types of Cells • Prokaryotes and Eukaryotes

9. 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

10. 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

11. Eukaryotic Cell Features • Eukaryotic cells are very diverse • Organelles are bound by membranes • Chemical reactions occur in different organelles

12. 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

13. Cell Contents • Animal Cell Plant Cell

14. 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

15. Cytoplasm • 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

16. 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.

17. Chromatin • 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)

18. DNA • 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.

19. Function • 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.

20. Nucleotide • Sugar ( deoxyribose, ribose) • Phosphate Group • Nitrogen Base : Adenine Thymine Cystosine Guanine

21. DNA • 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.

22. Ribosomes • 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

23. 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

25. 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

27. Mitochondria • 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

28. Lysosomes • Break down wastes • Contain digestive enzymes that break down macromolecules • The by-products are used to make new macromolecules

29. Vesicles • 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

30. Cytoskeleton • Gives shape to cell extending from the nucleus to the cell membrane • Made up of three components: actin filaments, intermediate filaments and microtubules

31. Centrosome • Assembles and co-ordinates the activity of spindle fibres during cell division • Composed of two centrioles

32. 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

33. 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

34. Chloroplasts • Sacs enclosed within a double membrane and perform photosynthesis • Store starches, lipids and proteins • Chloroplasts are green because they contain chlorophyll

35. Comparing Animal and Plant Cells