2.1 A Background to Cell Structure

1. 2.1 A Background to Cell Structure

2. Cell Theory • 1. All known living things are made up of cells. • 2. The cell is structural & functional unit of all living things. • 3. All cells come from pre-existing cells by division.

3. Modern cell theory adds the following: • Cells contains hereditary information which is passed from cell to cell during cell division • All cells are basically the same in chemical composition. • All energy flow (metabolism & biochemistry) of life occurs within cells.    

4. Cell Theory • The discovery of cells and their structure is linked to the development of the magnifying lenses, particularly the microscope.

5. Robert Hooke • The first description of the cell is generally attributed to Robert Hooke (1635−1702) • He described the microscopic units that made up the structure of a slice of cork and coined the term "cells" to refer to these units.

6. Antoni van Leeuwenhoek (1632−1723). • This Dutch microscopist made over 500 microscopes. • He observed moving particles in his microscopes and described the microorganisms that he saw in great detail. • He is considered the father of microbiology.

7. Rudolf Virchow • In 1855, Rudolf Virchow proposed an important extension of cell theory. • "All living cells arise from pre-existing cells". • This statement has become what is known as the "Biogenic law".

8. How do new cells arise? • Until the 18th century, many scientists believed in spontaneous generation. This was the idea that non-living objects can give rise to living organisms. • It was common “knowledge” that simple organisms like worms, beetles, frogs, amd salamanders could come from dust, mud, etc., and food left out, quickly “swarmed” with life. • Jan Baptista van Helmont’s recipe for mice: • Place a dirty shirt or some rags in an open pot or barrel containing a few grains of wheat or some wheat bran, and in 21 days, mice will appear. There will be adult males and females present, and they will be capable of mating and reproducing more mice.

9. Franscesco Redi • In 1668, he did an experiment with flies and wide-mouth jars containing meat. • This was a true scientific experiment

10. In the control group of jars, flies were seen entering the jars. Later, maggots, then more flies were seen on the meat. • In the gauze-covered jars, no flies were seen in the jars, but were observed around and on the gauze, and later a few maggots were seen on the meat. • In the sealed jars, no maggots or flies were ever seen on the meat.

11. Conclusion(s): Only flies can make more flies. • In the uncovered jars, flies entered and laid eggs on the meat. Maggots hatched from these eggs and grew into more adult flies. • Adult flies laid eggs on the gauze on the gauze-covered jars. These eggs or the maggots from them dropped through the gauze onto the meat. • In the sealed jars, no flies, maggots, nor eggs could enter, thus none were seen in those jars. Maggots arose only where flies were able to lay eggs. This experiment disproved the idea of spontaneous generation for larger organisms

12. Louis Pasteur-1861

13. Pasteur’s conclusion • There is no life force in air, and organisms do not arise by spontaneous generation in this manner. • “Life is a germ, and a germ is Life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment.”

14. Cell Structures Compare prokaryotic cells and eukaryotic cells: How are they similar? How are they different?

15. Cell structure and function ANIMAL CELL

16. Plant Cell

17. Cell membrane Structure: Phospholipid bilayer with embedded proteins

18. Function: • Acts as a barrier between the inside of the cell and the outside environment. • Import and export of substances from the cell • Cell recognition: self vs non-self. • Communications/ connections with other cells

21. Cytoplasm

22. CYTOPLASM • Consists of all the contents between the nucleus and the cell membrane. • Made up of the cytosol and organelles such as mitochondria and ribosomes. • The fluid part of the cytoplasm is the Cytosol. It is clear in color and has a gel-like appearance. It is composed mainly of water and also contains enzymes, salts, and various organic molecules. • Also located within the cytoplasm is the cytoskeleton, a network of fibers that help the cell maintain its shape and give it support. • Function: The cytoplasm helps to move materials around the cell and also dissolves cellular waste.

23. Nucleus • The nucleus is the largest organelle in a cell. It directs all activity in the cell. • It also controls the growth and reproduction of the cell. • It is the location for most of the nucleic acids (DNA and RNA) a cell makes. • The nucleus controls the shape and features of the cell. • Double membrane with pores

25. The nucleolus is an area of the nucleus where ribosomes are constructed. • It is not membrane bound • It is rich is proteins and nucleic acids, so it appears darker. • There may be more than one nucleolus

27. Nuclear pores: allow for passage of materials between cytoplasm and nucleoplasm

28. Cytoplasmic Organelles

29. Mitochondria • Site of cellular respiration: provide the energy a cell needs to carry out its activities • Membrane-bound organelles, and like the nucleus have a double membrane. • They are about the size of bacteria but may have different shapes depending on the cell type.

30. The outer membrane is fairly smooth. • The inner membrane is highly convoluted, forming folds called cristae. • The cristae greatly increase the inner membrane's surface area. • It is on these cristae that food (sugar) is combined with oxygen to produce ATP - the primary energy source for the cell.

31. Endoplasmic Reticulum • Comes in two forms: Rough ER and Smooth ER

32. Rough ER: - sheets of unit membrane with ribosomes on the outside                - forms a tubular network throughout the cell • Function - transports chemicals between cells and within cells                - provides a large surface area for protein synthesis • Smooth ER: functions in the synthesis and transport of lipids (fats)

33. Ribosomes • Ribosomes are molecular machines that make all the proteins found in every living thing on the planet. • They are made in the nucleolus • They are found in the cytoplasm and attached to the ER

34. Golgi Apparatus • AKA Golgi Body, Golgi Complex • The Golgi is principally responsible for directing molecular traffic in the cell • Molecules are modified and packaged into vesicles for transport

36. Vacuoles • Compartments which are filled with water and various molecules in solution. (dissolved salts, minerals, ions, proteins) • They may contain solids which have been engulfed. • In plants: usually one large vacuole • In animals: many small vacuoles (look like vesicles)

38. Centrioles • Found only in animal cells • Paired organelles usually located together near the nucleus • The centrioles are positioned so that they are at right angles to each other • Function: form the spindle fibers in mitosis and meiosis- cell reproduction.

40. Lysosomes • Double membrane sacs that contain chemicals to break down large food particles into smaller ones • Break down old cell parts and release the substances to be used again.   • Keeps the harsh chemicals from escaping and breaking down the rest of the cell

42. Cell wall • Plant cell walls are made of cellulose. It is a polysaccharide that forms long straight chains and can be woven into fibers. • The cell wall is structurally strong, but it is porous.

44. Chloropasts • Found only in plant cells • They are the site of photosynthesis • Carbon dioxide + water glucose + oxygen • 6 CO2 + 6 H2O C6H12O6 + 6 O2 • This is the most important chemical reaction on the planet…it takes the energy from the sun and changes it to chemical energy that can be used by living things.

46. Endosymbiosis Theory