Cell Structure

1. Cell Structure Chapter 4

2. Cell theory Cells were 1st discovered in 1665 by Robert Hooke Leeuwenhoek- 1st observed live cells, referred to them as �animalcules�. Early studies of cells were conducted by Schleiden (1838) and Schwann (1839) Together they proposed the cell theory Cell theory 1.) All organisms are composed of cells 2.) Cells are the smallest living things 3.) Cells arise only from pre-existing cells

3. Cell theory Cell size is limited As cell size increases, it takes longer for material to diffuse from the cell membrane to the interior of the cell. Surface area-to-volume ratio: as a cell increases in size, the volume increases 10 times faster than the surface area For example: If the cell radius increases by 10 times, the surface area increases by 100 times, but the volume increases by 1000 times.

4. Surface-area-to-volume ratio

5. Microscopes are required to visualize cells Types of microscopes Light microscopes- compound light microscopes Can resolve structures 200 nm apart Electron microscopes Can resolve structures 0.2 nm apart 2 types SEM (scanning electron microscope) Forms 3-D images by beaming electrons onto the surface of the specimen TEM (transmission electron microscope) Also uses a beam of electrons that are transmitted through an ultra thin specimen, interacting with the specimen as it passes through it The use of stains aids in viewing cell structure

6. All cells exhibit basic structural similarities 1.) The genetic material is located in a centrally located nucleus or nucleoid. 2.) A semi fluid matrix called cytoplasm fills the inside of the cell. 3.) The plasma membrane encloses the cell and separates its contents from its surrounding.

7. Prokaryotic Cells 2 types of Prokaryotes: Eubacteria and Archaea Lack a membrane-bound nucleus Instead genetic material is located in nucleoid Prokaryotic cells possess Cytoplasm Plasma membrane Cell wall Ribosomes However, they lack membrane-bound organelles. Flagella are present in some prokaryotic cells Used for locomotion Rotary motion propels the cell

8. Structure of prokaryotic cell

9. Flagella in prokaryotes

10. Prokaryotic cell walls Function to protect the cell and maintain shape Bacterial cell (Eubacteria) walls consist of peptidoglycan May be gram + or gram � Detected by gram-staining procedure Gram +: thick, single layer peptidoglycan cell wall that retains the crystal violet stain (purple) Gram -: more complex, multilayered cell wall that does not retain the crystal violet stain; stain with counterstain,safarin (pink) Archaea lack peptiodoglycan

11. Eukaryotic cells Possess a membrane-bound nucleus More complex than prokaryotic cells Compartmentalize cellular functions within organelles and endomembrane system Organelles: membrane-bound structures that form compartments Endomembrane system: system of connected membrane compartments Have a cytoskeleton for support and to maintain cellular structure

12. Structure of animal cell

13. Structure of plant cell

14. Nucleus in eukaryotic cells Stores the genetic material of the cell in multiple, linear chromosomes DNA is organized with protein to form chromatin Surrounded by a nuclear envelope Composed of 2 phospholipid bilayers Nuclear pores: opening in the nuclear envelope, allows proteins and nucleic acids in and out of the nucleus Nucleolus (nucleoli): site of rRNA (ribosomal RNA) synthesis

15. The nucleus

16. Ribosomes Site of protein synthesis in the cell Composed of ribosomal RNA (rRNA) and proteins Found within cytosol of the cytoplasm and attached to internal membranes Each ribosome is composed of 2 subunits Large and small subunit Types of RNA rRNA (ribosomal): provide a mechanism for decoding mRNA into amino acids and to interact with the tRNAs during translation mRNA (messenger): carries coding information from DNA tRNA (transfer): carries amino acids

17. Endomembrane system Series of membranes throughout the cytoplasm Divides the cell into compartments where different cellular functions occur Endoplasmic reticulum (ER) SER RER Golgi apparatus Lysosomes

18. Rough endoplasmic reticulum Membranes that create a network of channels throughout the cytoplasm Attachment of ribosomes to the membrane gives a rough appearance Synthesis of proteins to be secreted, sent to lysosomes or plasma membrane

19. Smooth endoplasmic reticulum Relatively few ribosomes attached Functions: Synthesis of membrane lipids Calcium storage Detoxification of foreign materials

20. RER vs. SER

21. Golgi apparatus Flattened stacks (golgi bodies) of interconnected membranes Packaging and distribution of materials to different parts of the cell Synthesis of cell wall components

22. Protein transport through the endomembrane system

23. Lysosomes Membrane bound vesicles containing digestive enzymes to break down macromolecules Destroy cells or foreign matter that the cell has engulfed by phagocytosis

24. Lysosomes

25. Microbodies Membrane bound vesicles Contain enzymes Not part of the endomembrane system Types: Glyoxysomes in plants contain enzymes for converting fats to carbohydrates Peroxisomes contain oxidative enzymes and catalase

26. Vacuoles Membrane-bound structures with various functions depending on the cell type There are different types of vacuoles: Central vacuole in plant cells Contractile vacuole of some protists Storage vacuoles

27. Mitochondria Organelles present in all types of eukaryotic cells Contain oxidative metabolism enzymes for transferring the energy within macromolecules to ATP �Powerhouse� of the cell Surrounded by 2 membranes Smooth outer membrane Folded inner membrane with layers called cristae matrix is within the inner membrane Intermembrane space is located between the two membranes Contain their own DNA

28. Mitochondria

29. Chloroplasts Organelles present in cells of plants and some other eukaryotes Contain chlorophyll for photosynthesis Surrounded by 2 membranes Inner and Outer membrane Thylakoids are membranous sacs within the inner membrane Grana are stacks of thylakoids

30. Chloroplast structure

31. Endosymbiosis Proposal that eukaryotic organelles evolved through a symbiotic relationship One cell engulfed a 2nd cell and a symbiotic relationship developed Mitochondria and chloroplasts are thought to have evolved this way Evidence that supports Mitochondria and chloroplasts: Have 2 membranes Possess DNA and ribosomes Are about the size of a prokaryotic cell Divide by a process similar to bacteria

32. Proposed endosymbiotic origin of eukaryotic cells

33. cytoskeleton Network of protein fibers found in all eukaryotic cells Support the shape of the cell Keep organelles in fixed location Helps in moving materials within the cell Cytoskeleton fibers include Actin filaments: responsible for cellular contractions, crawling, �pinching� Microtubules: provide organization to the cell and move materials within the cell Intermediate filaments: provide structural stability

34. cytoskeleton

35. Cell movement Cell movement takes different forms. Crawling is accomplished via actin filaments and the protein myosin. Flagella: undulate to propel the cell Cilia: can be arranged in rows on the surface of a eukaryotic cell to propel the cell forward Cilia and flagella have similar structure 9-2 structure: 9 pairs of microtubules surrounded by a 2 central microtubules Cilia are usually more numerous than flagella on a cell.

36. Flagella and cilia structure

37. Extracellular structure Includes Cell walls in plants, fungi, some protists Extracellular matrix surrounding animal cells Cell walls present surrounding the cells of plants, fungi, and some protists the carbohydrates present in the cell wall vary depending on the cell type plant and protist cell walls � cellulose fungal cell walls - chitin

38. Extracellular matrix ECM surrounds animal cells composed of glycoproteins and fibrous proteins such as collagen may be connected to the cytoplasm via integrin proteins present in the plasma membrane

39. ECM

40. Which structures are present in what organisms